Paintball Spin Physics - Getting to the final Answer

[AGD]

Gentelmen,

I have posted a framework of info in the data thread. This is from an extensive study we did in the early 90's. The data is representative of our findings.

Currently on the table:

Spin is the only major factor accounting for paintball inaccuracy. Promoted by Pbjosh

Closed bolt operation has an effect on overall accuracy. Promoted by Glen Palmer.

The paintball flight is subject to "knuckleball effect".

Spin may or may not be possible because of the liquid in the paintball.

Barrels have something to do with accuracy.

Seams have something to do with accuracy.

Balls distort with the impact of the air blast.
Balls distort when leaving the barrel.

Ok lets have a pointed discussion on the subject. For those of you just reading this, this thread is a continuation of the "closed bolt" thread found here.

original thread (http://www.automags.org/forums/showthread.php?s=&threadid=20862)

AGD

[nippinout]

Tom, could you elaborate on the ball exploding pictures?

Thanks.

Moving on...

So if we do have spin, to have any effect on accuracy it must be on an axis differing from it's path.

Whether or not the seams affect flight is what we're after. However, Glenn found differing velocity due to seams. Seams have different effects before and after barrel?

Good discussion!

[Ostwar]

Is it possible to make a paintball with:

1) No seams or 2) completely filled with paint (no air pocket) or 3) completely round (or as round as possible)

Does the impact of the bolt distort a paintball and therefore accuracy?

Considering the high speed movement of the bolt forcing the paintball into the breach of the barrel at up to 20 times per second (closed or open bolt). Even if the bolt is light (delrin or similar) the momentum would have an effect on impact energy being transferred to the edge of the paintball (also this would be far less than the gas pressure released on the ball during firing).

Would a paintball rotate while it is being loaded by the bolt, thereby changing the position of the axis of the seams and affect accuracy as a result?

My thoughts for the brain pool,

Shaun

P.S. Is AGD really Tom Kaye? I would find it hard to believe he has the time to be on these forums, but if he is, kudos to him for connecting with the players at a more personal level.

[ezrunner]

AGD really is Tom Kaye, and he is one of the few people in the
industry who bothers to back up any of his claims with data.

Tom: I come from a precision shooting background and would
like to add a combinatorial statement to the list. This
comes from the realm of bolt action rifle tuning where we
fit the bolts to the breeches
and the barrels to the stocks.
(ie bedding and free floating)

The mechanical repeatability of the positioning of the components
in and around the breech such that the ball is in the same
relative position on each firing contributes greatly to accuracy.

i.e. The barrel should be tight enough that when the ball seam is turned
such that it is at a 90 degree angle to the bore, so that the
seam is only touching the bore at two points, that there is
minimal gap between the ball and the barrel.

Now that we have a good paint to barrel match, we make sure
the bolt stops in the same position before the shot is
fired. This means that the air is always released at about
the same angle of incident to the projectile so that the forces
acting on each ball are nearly the same.

This will ensure that any spin is rather consistent and that the
paint is consistent down the barrel.

What this buys us is mechanical repeatability. A
closed bolt has a small delay even under rapid fire where the
bolt can come to rest. The higher the rate of fire the
smaller this difference is in comparison to the better electros.

A well fitted bolt to the breech ensures that the bolt
stays in the same place for
each shot.

I think this set of conditions
leads to accuracy in any mechanical
system and projectile systems in general.

I know that GP (aka palladin) had referenced something akin
to this in his post on barrels and chambers.

I would love to hear Tom and GP chime in on this?

How does this align with the designs both of you espouse?

The mag had the chamber built into the barrel and the blazer
and typhoon series had closed bolt operation.

How does each guarantee these circumstances, or are they
considered?

-rob
Clemson #12

[pbjosh]

Thank You AGD,

For starting this thread and dropping the photos.

I think we have to define 'Spin' first. I realize there might have been some confusion.

'Spin' as I have been using it is the perpendicular rotation of the ball to its flight.

Not the horizantal rotation like an object shot from a rifled barrel. In fact, since that is so hard to produce in a paintball I think it wouldn't have even been thought that way.

To find the issues with accuracy we need to look for something that is an affect of firing a ball that still affects the ball after it has fired. There are other things that affect the ball, and we do need to explore all of those also.

I think that a Closed Bolt operation helps in keeping spin to a minimuim. The ball starts from a position in the barrel, and is only affected by the travel through the barrel and the air applied to it. In an open bolt system the ball is physicly pushed forward, travels in the breech, then across a barrels rim, into the barrel, and while still in motion, the ball has air applied to it. In the Open system there is alot of added affects to the action of a ball.

A paintball would only be affected by a "Knuckleball effect" only if it wasn't spinning. If it has some small spin that would cancel out the non-rotating action of a knuckleball.

As for "Spin may or may not be possible because of the liquid in the paintball" I personally think that the Flatline barrel is a good example of spin being possible. Since the spin is still affecting the ball until it has run out of forward momentum, I would hazard a guess that the creamy liquid center of a paintball doesn't affect it too much. It can lower the spin faster than if the ball didn't have a liquid center, but I would think that would add more accuracy, to a point, after a bit.

Barrels have alot to do with accuracy, but again I think the incurred spin from one barrel to the next is an issue. The paint to barrel match is important for several reasons, but I think an barrel that is in-accurate would be one that puts more spin on the ball. A short barrel would put less spin on the ball for the most part. The ball can't spin as much if it has less barrel to rub against.

Seams have something to do with accuracy. They do, but I would think mostly in the preshot arena that causes the ball to spin before it leaves the barrel.

"Balls distort with the impact of the air blast.
Balls distort when leaving the barrel. "

Again, in the preshot arena the distortion, if any (personally I think the distortion would only be about .001"-.002" or so, if it happened) would only have an outside accuracty affect if the ball incurred spin from the distortion. The ball would return to normal after it left the barrel I would think.

Okay-

Tear it all apart!

Josh

[314159]

Originally posted by AGD
Closed bolt operation has an effect on overall accuracy. Promoted by Glen Palmer.AGD

i think that this would be better phraised as the firing system has an impact on the overall accuracy of a paintball. because the same firing system in open or closed bolt configurations will have the same accuracy.

[ezrunner]

Paint to Barrel relations

For a given setup on a marker there will be an optimum
barrel of either design.

For a one piece barrel, the longer the barrel, the more
consistent it will be, and the more surface before venting
can aid in air efficiency. This is offset by the drag down the
barrel when the air is nolonger accelerating the ball. At that
point, the barrel should end or should step out to a second piece.

In a two piece barrel, the section that touches the ball
should be long enough to give adequate use of the air expended,
while not causing drag on the ball. I don't know of a 2 piece
that I think causes drag. A one piece 14" barrel seems to
shoot really well, but the 12" tubes are just as good for my
purposes.

The venting in a 2 piece does matter. We have observed with
freak barrel systems that changing from a 12" to a 14" tip
on an AKA Cocker running at about 180 psi (goes to valve
open time for those who understand cocker tuning)
can jump the velocity 20fps or more. The unvented area of the freak tip apparently allows
for some acceleration to still occur even though the paint is not
being sealed all the way around.

Has anyone here used the bolt from Cooper-T for the autococker?

It puts backspin on the ball like a flatline barrel does.
It works best with a small amount of oversize in the barrel
so that the fit is not as tight, and once you break a ball,
you have a mess.

I am not sold on backspin yet but I will be doing a good deal
of testing on this bolt once our cocker bodies come back from
the CNC shop and we build them out. One marked advantage is
that as you turn the marker, the ball begins to hook around.
On a speedball field this could be a devastating advantage
as you take away your opponent's cover. I'm not sold
yet, but we will be doing testing.

-rob
Clemson #12

[314159]

Originally posted by ezrunner
For a one piece barrel, the longer the barrel, the more
consistent it will be, and the more surface before venting
can aid in air efficiency. This is offset by the drag down the barrel when the air is nolonger accelerating the ball. At that point, the barrel should end or should step out to a second piece.

i have once heard someone say, that shorter barrels are more accurate, because of their short lenght, any imperfections on a paintball will not have as significant of an impact, like they would in a longer barrel. i have not thought this through, and am putting this out on the table.

i think that the main deal in "paint to barrel match" helping out accuracy is getting a barrel small enough, so the ball dosen't wobble, and big enough, so that it does not exploide a paintball. i think that the main benifit here, is not allowing a paintball to wobble in a barrel. i think that you could have a straight riffeled barrel, with about 4 rifilings, that would be about 1/8 in wide each. these would be tight on the paintball (maby .678), and the outer area, could be like .700 in dia. the rifilings would hold the paintball tight, not allowing it to wobble, and the area of the barrel that is not riffled, would alow the paintball some room to expand, when it is squeesed into the rifilings. i think that this would keep the paintball from poping, and keep good "paint to barrel match" accuracy over a wider range of paint sizes (at the cost of a little efficency)

[pbjosh]

I would have typed a bit more total, but my 2yo decided it was a good time to come in and erase everything I had typed already!

Josh

[ShooterJM]

Originally posted by pbjosh
Thank You AGD,

For starting this thread and dropping the photos.

As for "Spin may or may not be possible because of the liquid in the paintball" I personally think that the Flatline barrel is a good example of spin being possible. Since the spin is still affecting the ball until it has run out of forward momentum, I would hazard a guess that the creamy liquid center of a paintball doesn't affect it too much.

Josh

I agree entirly. Both the Tippy Flatline and the Z-Body demonstrate induced spin by the trajectories of the paintballs.

AGD - Thanks for posting the detailed photographs and test results! This will make for great reading!

ShooterJM

[hitech]

I don't see enough data presented to draw any conclusions. Certainly not where spin is concerned. I did not see any indication in any of the tests presented that the paintball was "spinning". While it is very interesting, it doesn't appear to be enough, in my opinion, to draw any conclusions from. Did I miss something?

Edit: Thanks Tom. THAT makes much more sense now. I didn't want to assume that the marks on the ball were anything more than shadows.

[AGD]

Ok this is what you do with the data.

1. look at the marks on the ball and determine how far it rotates between each flash exposure. Use that,the distance between shots and the known FPS to determine what RPM's the ball is rotating at. When your done with this you should be able to answer the following questions:

1. What is the balls RPM?
2. Is there only one spin axis or does it corkscrew on two spin axies?
3. Does the spin maintain, speed up or slow, down range?
4. When the ball spins it has higher surface speed on one side and lower on the other. Using the RPM tell me the difference in surface speed, this figures into the Magnus effect.

Once you do this homework then we will go on to correlating the spin to the X,Y ball position in flight.

Don't post until you have this info, the data is in front of you not on PBN.

AGD

[Havoc_online]

ok, I feel lost because I don't see any pictures to look at. However some thoughts just came to mind.

Quote from Glenn(quoting someone else)-


The ball remains round and is infact forced round by gas pressure.

Not entirely true as it does not take into account the distortion of the ball as it is compressed from front to rear by the g-forces of acceleration.Would it not be reasonable to assume that the distortion of the ball would be greater on a closed bolt marker since it is accelerated instantly, as opposed to an open bolt marker that gives two levels of acceleration(THREE on a level 10 Mag) thus giving the ball more time to accelerate. Actually on a level 10 mag, considering the foamie it may be 4 levels of acceleration. Lacrosse balls fly fast, but consider how they accelerate compared to a baseball. This raises the question if an open bolt marker deforms a paintball any less than a closed bolt marker. Maybe acceleration over a longer period is the key to the accuracy debate between open and closed bolt markers. Even golf balls deform under the same high G-forces. If deformation of the paintball does occur it would flatten the front which would cause spin once it left the barrel. If acceleration over time would deform the paintball any less, it would make the ball spin less giving less counterforce for the fill(see below). However the accuracy debate is too close to believe that any deformation between either type of marker would make a paintball spin above 6000rpm even making a difference.



Spin is the only major factor accounting for paintball inaccuracy. Promoted by Pbjosh

Spin may or may not be possible because of the liquid in the paintball.

Seams have something to do with accuracy.
These statements are all related to what I believe. Since the ball is under so much forward momentum the fill is compressed to the back of the shell giving the ball a somewhat stable flight axis before it leaves the barrel. The seam would not cause enough drag to counter the force of the fill enough to make the paintball spin past the point of 6000rpm. Spin does not make a difference below 6000rpm due to the lack of counterforce on the fill. Spin beyond 6000rpm in the barrel only takes place if there is a unwanted variable such as oil/paint, bad paint/barrel match or intentional force is applied(flatline/zbody)before the fill is completely stable. Spin beyond 6000rpm achieved outside the barrel would be obtained by a ball that is badly deformed or highwind/rain/etc.

Therefore it is my opinion that with the current limitations of the weight of paintballs and the restrictions of velocities, as long as your paint fits your barrel the most consistent marker will be the more accurate marker. Although in the hands of a player, two things matter. Recoil under higher ROF which is a case of a level 10 bolt being lighter thus having less reciprocating mass. Trigger pull would be the other factor. Mags and cockers both have tuff triggers so electro's come into play. It's a good thing AGD makes a stock electro;).

If this makes sense great, if not, forgive me, I'm sick and sleepy:(

[bjjb99]

Don't feel lost in your search for the pictures Tom is referring to; they're in Deep Blue's Official Data Thread. It took me a while to find them. Now I feel kinda silly because I didn't go to the Official Data Thread right away, especially since I now see that Tom mentioned that the data was located there in his original post to this thread. I guess I just missed that sentence the first time through.

Yep, I'm awake... honest... really, I zzzzzzzzz. ;)

BJJB

[pbjosh]

Havoc_online:

There is one flaw in your logic.

The spin I am refering to is axial spin perpendicular to the direction the ball is traveling. The spin you are refering to is spin on the same axis as the ball is traveling.

These have severly different affects when going 200mph through an atmoshpere. Do not confuse the two.

When talking about Magnus affect, which is caused by perpendicular spin, the affects are in-stability and hence, in-accuracy, unlike the affects you are talking about.

We are NOT talking about horizantal spin. Which is what rifleing on a barrel does to a bullet.

Josh

[pbjosh]

I just found this.

http://www.marist.edu/physics/applets/magnusg.html

After playing around with some figures from the Data Pics AGD dropped I will trying running it through.

EDIT:

The parameters don't come close to what we were looking for, sorry.

Josh

[Ostwar]

Pbjosh: Since you are not reffering to rifling spin direction, then is what you are saying refer more to the flatline barrel concept? Do you desire to minimize spin altogether on a paintball, giving it a flat or non-spin affect?

Shaun


BTW: your link to the Magnus force applet, excellent! (although I wish to go below .1 on the Mangus force scale, maybe I did it wrong).

[hitech]

Originally posted by AGD
...look at the marks on the ball and determine how far it rotates between each flash exposure...

I assume that you are guaranteeing that the paintball does not rotate more than 360 degrees between exposures. Correct?

[pbjosh]

Shaun,

The Magnus effect only really affects the ball when it is spinning perpendicular, not horizontal. A non-spinning ball will do the 'knuckleball' like in baseball. A slight spin is best. But for the most part we can't control this spin. A gun that incurrs alot of spin will shoot the ball all over the place IMHO.

Also, after looking into it a bit, what we are trying to do is minimize the spin, or the Magnus Effect related to the spin of a ball. So having a dimpled surface would only help in the Flatline or related systems. If it had a rough or dimpled surface the ball would swerve MORE. In other sports the balls surface is rough to optimize spin and rotation, or the Magnus Effect, so you can do all the curveballs and fun stuff you want to do to it.

As for the pics, to study this better we would really need video footage so we could count the number of rotations over a period of time. Right now we do have great high speed footage, and due to the closeness of the shots we can see the ball tumble quite often. Like hitech mentioned, this is not a perfect way to trace the rotation of the ball though. The pics are great, but not under-minding what Tom did, for this theory to be analyzed best we would need to trace a realtime pattern of the ball, plus induce spin that we can control (like the Z-body) which is a bit out of our reach right now. A camera that could take pics like that is way out of our price range-

Josh

[bjjb99]

Why would we need a high speed camera? A good 35mm camera with a bulb setting, a dark environment, and an accurately timed high speed strobe light should be more than sufficient. The faster the strobe, the more data we have to play with, of course. I think we can safely discount any more than a 180 degree rotation per strobe flash in the AGD tests; see below for details.

Assuming the measurements in test 101 are accurate, the ball travels approximately 6 inches between successive stobe flashes as it leaves the marker at approximately 280 fps. This means the stobe flashes are about 1.8 milliseconds apart. I don't know if it's possible to determine what the "further down range" strobe rate is since we don't know the ball's velocity at that point, so I'm going to look only at the near-barrel portion of the test.

Eyeballing the images (I'm not at home right now and thus lack access to proper image processing software), I'd say the ball in test 101 spins around 15 degrees +/- N*180 degrees per strobe flash, where N is an integer. This accounts for the discrete nature of the strobe and the fact that the ball could additionally make one or more complete 180 degree spins and we might not notice it. The spin axis in test 101 appears to be nearly vertical, judging from the underside view portion of the image. There may be a slight precession of the spin axis, but I cannot identify this well from the posted images; I might do better once I get home.

Let's assume the ball spins 15 degrees per strobe flash to start with. This means that the surface velocity of the ball is around 0.089 inches per strobe flash, or 4.1 feet per second; this yields a differential surface speed of 8.2 fps for opposite sides of the ball. The "against the wind" side of the ball sees a 284.1 fps headwind, while the "with the wind" side of the ball sees a 275.9 fps headwind. I'm not all that familiar with the Magnus effect, so I'll leave it to others to utilize this data (if it's is can be used at all) in determining the lateral forces induced as a result of spin.

Now, let's assume the ball spins 195 degrees per strobe flash (15 + a 180 degree rotation that we cannot discern due to the discrete nature of the strobe). Then we end up with a surface velocity of around 53.5 fps, and a differential velocity of twice that. The "against the wind" side of the ball sees 333.5 fps and the "with the wind" side sees 226.5 fps.

Suppose the ball spins -165 degrees per strobe flash (15 - a 180 degree rotation that we cannot discern). Then we end up with a surface velocity of around 45.1 fps and (again) a differential surface speed of twice that. The "against the wind" and "with the wind" sides of the ball have swapped locations, since the spin vector is pointing in the opposite direction this time.

Personally, I don't think the ball spins more than 195 degrees between strobe flashes... 195 degrees per 1.8 milliseconds is already 301 revolutions per second, or around 18000 rpm. Centripetal acceleration is given by V^2/r, if I remember correctly. The surface velocity at 195 degrees per strobe flash is 53.5 fps (16.3 m/s) and the radius is 8.6 mm... this yields a centripetal acceleration of 31000 m/s^2, or around 3150 g's.

In contrast, during firing the paintball experiences a minimum linear acceleration of around 12000 m/s^2 (1220 g's) to go from rest to 280 fps in a 12 inch barrel. A linear acceleration of 31000 m/s^2 yields an exit velocity of around 450 fps. I have no idea whether paintballs can survive being fired at such velocities, but I suspect they don't more often than do. This leads me to believe that centripetal forces resulting from 18000 rpm spin would result in paintball self-disassembly upon exiting the barrel.

I think we can safely limit ourselves to the +/- 180 degree spin regime, and may well be able to ignore the +/- 180 degree portion altogether. This leaves us with at most three scenarios to plug into the Magnus effect for each spin measurement performed.

Happy Magnus-ing! ;)

BJJB

[Pstan]

Gentlemen,

I dont quite know whether my thoughts on this subject will matter to most here........Certainly Mr. Kaye can move this post or delete it as he sees fit, but I would like to join the general discussion having read this post in it's entirety. I come from a background beginning in firearms that has spanned around 20 years now and have been involved with paintball for around 4 years. I am a tinkerer by nature, as my Grandfather and Father were trained as Watchmakers and Jewelers. I hold a MA in History and Education, but have taken courses in every conceivable field, so all of the mathematical jargon here is not totally foreign language to me. However, dont ask me to calculate anything........if I need that done I'll go a to a friend of mine who was a Professor of Mathematics at Georgia Tech University and is now retired.

What I see here are basically 2 lines of thought. One believes that mathematics can describe the relationship of accuracy in 2 different types of paintball guns that cycle differently conclusively. In other words......numbers dont lie. The other group seems to fall into a category that doesnt quite refute that claim, but has misgivings that calculations on paper disprove what they have seen through experience, observation, and personal knowledge. And, in order not to leave anyone out, there are positions here that represent views from both. However, I think the first 2 groups make up the majority.

There are a few points to consider within both groups. First, Mathematics does not prove, or disprove everything that exhists. Einstein proved mathematically that the universe is finite. Other scholars have proved mathematically that the universe is ever-growing and constantly expanding. Who is correct in that argument? Are the numbers lying in one case and not the other? Second, as I look above me everyday I notice that the Sun is moving around the Earth. At night I notice that the Moon is always following my car everywhere I drive. Are my observations of heavenly motion correct simply because I literally see it that way? Or is that really what is going on? Point being, what is seen isnt always what is true.

Whether all of you realize it or not, most seem to be camped out with your respective group and unwilling to do what seems to me to be the optimum thing. That optimim thing is to do another test and start the argument over in a debate where everybody has the same data. Whether one side wins or not ( ie Closed-Bolt v Open-Bolt ) is a moot point to me, but it would be interesting to see the findings in a joint effort.

What do I propose?
1. 2 markers should be constructed. Basically billet aluminum in a stacked tube config.
2. 1 open bolt........1 closed bolt.
3. 1 barrel to be used on both.
4. Both should drilled and tapped for a mounting braket to be used in the test firing.
5. Both should be tested with the same power source and regulating system at the same pressure.
6. Only ammo that is "perfect" should be used......I seem to remember talk of a paint that constitutes this variable being created at AGD? ie not real paint, but of perfect roundness and constant weight.
7. And lastly, all the dimensions of the 2 markers should be the same.......inside and out. Ball position at moment of firing, length, and so on..... of course the closed will need pnuematics mounted and the open will need a valve that provides the gas to recock. Other than those variances, the guns will be the same.


Might this not lead to a better conclusion?

Hopefully, I've not offended anyone. Certainly that has not been my intent. Is this an area that is an acceptable course for this debate to go?


Respectfully,

Pstan

[Top Secret]

That test could be done by an autococker timed to shoot open bolt, then reconfigured and timed to shoot closed bolt. If I get bored enough to swap my cockers 3-way hoses, I'll recreate WARPIG's test using my gun.

[pbjosh]

The thought on the video camera-

That would remove all doubt that there could have been an other sort of tumbling in the ball, and would give an accurate position of the ball at all angles.

Thoughts on guns to use-

We would want a gun that is currently produced. I know of a person who has a open or closed bolt angel ran by the racegun grip. It would be PREFECT for this test.

Also, thoughts please-

Can anybody give us some other thougths as to issues that can be incurred in the gun, and affect the ball after it has left the barrel, besides Magnus affect? I want to hear it

Josh

[AGD]

BJ,

You can eliminate the possibility of the ball rotating more than 180 deg in my pictures. We spaced the strobes at varying widths to determine the general range of spin RPM's on most balls. From that info we spaced them as you see them in the pics so we could measure the spin without missing a turn. Bravo BJ! You get my respect for actually looking at the images and trying to figure something out.

Josh,

So you are saying that the pics are not good enough data but we should continue to debate what we have experienced? You really think high speed video is required? How about we just go through the motions and see what we get?

AGD

[pbjosh]

AGD-

Sorry for the confusion, but people can look at the pics and say- "hey, it might have turned 180+ degrees between shots" etc. (and they did)

Not in any way or form do I think the film is not good enough, it is quite a treat. When I get time I will do a couple of figures myself.

And I agree, lets run as much out of the pics as we can. High Speed video will be a total pain in the........

As for debating what we have experienced, I think we should be looking for other issues besides spin or velocity that can affect the ball, that someway can be incurred in the gun but affect the ball in flight. Part of getting on this so hard is I REALLY want a better explanation than the old "all guns shoot the same velocity, so they all shoot the same distance" BS that has been floating around like Flat Earth Gospel. There is something else, I think it is spin. It might actually be ZAP elves. But unless we throw it out to the wolves and beat it around, add some science, then we won't know, and the stupid arguement and hype will still float around till somebody makes the 'New Science'and hypes the dickens outta it.

This is the perfect place to get it right. Lets do it.

I will freely take the Devil's Advocate for this one. I DO think it is Magnus Effect. Lets just get our brains in on this and really figure it out.

Josh

[Redkey]

This is interesting.

When were these tests run?

Were the paintballs checked for balance before testing? My thought here is that the heavy spot would tend to rotate downwards... This effect would probably be minor compared to other spin effects this close to the muzzle. But, you never know...

Was the barrel cleaned after each shot? Were any balls shot with paint in the barrel to see if spin was induced that way?

I assume there is alot more data... were the findings consistant from shot to shot? or was there a ton of variability?

Is there really air in paintballs? I thought they were filled in a pressurized system... where the paint forced the flexible gel into the two halves of the mold.

Does anyone here use image analysis software?

[flanders]

paintball seems are a good thing, in some ways

fallowing the 2 pionts on barrel to kepe the ball on target is a good thing the ball is stabalized while letting the right amount of air past not to cause blow back

as for airpoctes they allow a ball to not be so birrtal it pops in teh gun, while not makeing a shell even harder, if a bakl infact has no spin forward or back then the airpocet won't matter if it's facing backwards, or if it's roatating at a constant rate so tat it's never forward back up down etc then it will be ok do to compensation

barrel do ahve something to do with accurac, not lengthj ( i dun know if theres a barrel to big or 2 small) but quality, if they are rifled to much and the ball has spin goes pop, if the barrel has burs pop, if the barrel is to big, bouncy bouncy pop bad accuracy, if the barrel aint supper clean pop, if the barrel has odd porting can cause poor release of air causing spin, to tight air can't get through in the right way or ball gets stuck or shell peels off

the ball can distort with high pressure bursts but it would have a reverse translation (as in all liquid filled objects) impact on oen side creats lump on other side this may or may not be a good thing (depending on spin) if spin occurs left or right ball witll be good havign a bullet effect, if ball spins up or down bad ball is lopided pops or screws it up more

as for spin not hapening with liquid, if there was no air pocets then the ball would be hard like a solid object or atleast it doesn't impact or adjust every thign is filled, ball still spins, if there is an air pocket, and the liquid can still move then yes will cause lopsided pickle ball spin. but if the buble does not move it creats a weighted zone creating a similer odd spin, if spin occurs

General hypothesis

If spin lateral spin (left to right)occurs then one or many of the factros will effect accuracy

If spin longitudanal spin (up and down)occurs then one or many of the factros will effect accuracy

[AGD]

Redkey,

There is a LOT more data, so much that I am not about to put it up. We did this extensive study in the early 90's. The data presented is representative of our findings and if properly analized should point to some pretty strong conclustions.

In fact I already have all the answers to all these questions. I am going through the motions with all of you to see if the general public can, or is willing to, understand the reality of paintball accuracy.

Flanders,

Where are you from?


AGD

[ShooterJM]

Quick question.

In the tiff files named p1010027 and p1010028 (The two pictures of the scatter chart looking targets titled "View looking down flight path of ball"), could you tell us the distance at which the readings were taken and if the paintballs were prescreened for roundness? I'd also be curious to know if there is any weight difference between the nylon test balls uses and an average paintball.

Thank you.

*EDIT*: I count 8 seperate issues from the first post. Is the intent for all to be addressed in this thread?

[Pstan]

Essentially, what I've seen in the last few posts from Mr. Kaye relates what I was saying in my original post above. There is so much bias in this discussion that it renders moving forward an unlikely event.

The original question was whether a closed-bolt marker was more accurate than an open-bolt marker. Why I ask is the debate raging over other variables? From my perspective, it is simply the bias everyone is bringing with them. The original question has not been answered.

I proposed a new set of tests with 2 new shooting platforms that removed as many variables as I could think of in the short time I wrote the article. If others can think of more we need to remove feel free to add them. The new shooting platforms remove the bias that one brand of gun is better. The same air system removes the bias that how the platforms are given power affects the test. And so on......until we come to the only variance in the 2 being the type of actuation.

Run the test at that point. Answer the question at hand. Then post the results. Data will be available at that point. After doing that, the variables can be added back to the test until verifiable proof of what actually effects accuracy can be attained.

Lastly, science does not become accepted science until it is published, poked, prodded, redone, refuted, and/or ultimately proven. The scholarly world works in private, and speaks in public.......until that is done on this issue debate will rage.

Respectfully,

Pstan

[bjjb99]

Woo hoo!

I found a webpage which describes the mathematical foundation for the Magnus effect. It is located at the following URL, and describes the effect for rotating cylinders of infinite length:

http://www.mathpages.com/home/kmath258/kmath258.htm

I think it could be applied to our paintball, at least as a first cut approximation. After staring blearily at the equations, we come up with

L = - (rho) * v0 * (gamma), where

rho is the density of the fluid,
v0 is the velocity of the fluid (relative to the object in question), and
gamma is something called the circulation, defined as the line integral of the flow velocity around a closed loop.

What gamma basically means for us is "take the surface speed of the object and multiply it by the object's circumference". Thus,

(gamma) = vc * 2 * (pi) * r, where

vc is the circumferential (surface) velocity of the object,
pi is 3.14159 or thereabouts, and
r is the object's radius.

Let's plug in some of the data derived from the test 101 picture.

rho = 1.293 kg/m^3 (reasonable value for the density of air)
v0 = 85.34 m/s (280 fps)
vc = 1.25 m/s (4.1 fps surface speed)
r = 0.0086 m (radius of a paintball 0.68 inches in diameter)

So from this we get

L = -1.293 * 85.34 * 1.25 * 2 * 3.14159 * 0.0086
L = -7.45 (units?)

I'm not sure what the units should be. Doing a bit of unit analysis on the equation for L, we have the following:

L-units = (kg/m^3) * (m/s) * (m/s) * (unitless) * (unitless) * (m)
L-units = kg/s^2 ???

That sure isn't a unit of force I'm familiar with. We're missing a distance unit in the numerator somewhere, and darn if I can find it. Any help, anyone? :)


I also have happened across the following webpage, which gives a different equation (of similar form) for the Magnus effect:

http://carini.physics.indiana.edu/E105/spinning-balls.html

Here they describe the effect as follows:

M = cM * (rho) * D^3 * f * v, where

cM is the Magnus force coefficient (1.23 works pretty well, according to the webpage),
rho is the density of the fluid,
D is the diameter of the object,
f is the object's rotational frequency (rotations per second), and
v is the velocity of the fluid (relative to the object).

If the Magnus force coefficient is unitless, then a unit analysis of this equation actually ends up with units of force coming out of it. Let's plug in some numbers derived from test 101:

cM = 1.23 (unitless?)
rho = 1.293 kg/m^3 (reasonable value for the density of air)
D = 0.0173 m (0.68 inch diameter paintball)
f = 23.1 rotations/s (15 degrees per strobe flash, one strobe flash every 1.8 milliseconds)
v = 85.34 m/s (280 fps)

M = 1.23 * 1.293 * 0.0173^3 * 23.1 * 85.34
M = 0.016 N

So for that amount of spin we end up with a Magnus effect force of 0.016 newtons. For a 3 gram paintball, this force results in an acceleration of 5.3 m/s^2, or right around 0.54 g's. Let's assume this equation has given us a correct answer, and see what the picture can tell us based on what we've calculated.

I am going to define the "first" strobe as the first image of the ball after it has exited the barrel, and incrementally name each successive ball image to the right of the first strobe (second, third, etc.).

An acceleration of 5.3 m/s should deflect the ball approximately 8.6 microns between the first and second strobes. This deflection is nearly two orders of magnitude smaller than the spatial sampling in the image (around 0.6 millimeters per pixel for the "bottom view" portion of test image 101). So even if the Magnus effect is at work, we simply can't see it from strobe to strobe. So let's look at the first and last strobes in the (strobes 1 and 5).

In this situation, the time interval is four times as large. Assuming the acceleration resulting from the Magnus effect is constant throughout the measured time, we should expect a deflection 16 times greater than that predicted between strobes 1 and 2, or around 140 microns (0.14 millimeters). This deflection is still smaller than the spatial sampling in the image.

If the ball is spinning at 15 degrees per strobe flash (and based on my other spin calculations and Tom's additional comments, I think we can safely assume the ball is not spinning at 195 or -165 degrees per strobe flash), and if the formula I used above is reasonable and accurate, then the high resolution pictures we have of the test are simply not sufficient to detect the resultant Magnus effect.

I looked at the "bottom view" portion of the test 101 picture to see if I could see any horizontal deviation in the ball's path, and I noticed something interesting... the laser aligned string is not straight. It curves slightly in the image. This leads me to believe we either have a camer/lens perspective effect going on here, or the string is vibrating during firing. The blast of air that escapes the barrel could be moving the string around.

I attempted to correct the slightly curved string by using Photoshop's transformation tools, but had little success. It seems that the transformation I'm looking for just isn't available in my version of Photoshop. Instead of measuring each ball's position from a single reference line, I generated local references corresponding to the string's location at each ball's position. I measured the following offsets:

Strobe 1: -4 pixels (-2.48 mm)
Strobe 2: -2 pixels (-1.24 mm)
Strobe 3: -2 pixels (-1.24 mm)
Strobe 4: -1 pixel (-0.62 mm)
Strobe 5: 0 pixels (0 mm)

These offsets are greater than the Magnus effect alone would suggest, unless the Magnus equation I used was incorrect. They may be the result of the escaping gas buffetting the ball around during the first few milliseconds of flight.

Well, that's about all I've got for now. Time to go do some work that actually fills up a paycheck. :)

BJJB

[Redkey]

Originally posted by flanders

as for airpoctes they allow a ball to not be so birrtal it pops in teh gun, while not makeing a shell even harder, if a bakl infact has no spin forward or back then the airpocet won't matter if it's facing backwards, or if it's roatating at a constant rate so tat it's never forward back up down etc then it will be ok do to compensation


As I struggle to read this and make sense of all your spelling errors / typos my only thoughts are that if you ever wish to be taken seriously you should read your post before submitting it.

Could you please explain how an airpocket in the ball will make the shell more brittle?


Originally posted by flanders

barrel do ahve something to do with accurac, not lengthj ( i dun know if theres a barrel to big or 2 small) but quality, if they are rifled to much and the ball has spin goes pop, if the barrel has burs pop, if the barrel is to big, bouncy bouncy pop bad accuracy, if the barrel aint supper clean pop, if the barrel has odd porting can cause poor release of air causing spin, to tight air can't get through in the right way or ball gets stuck or shell peels off


Here you are making some statements about barrels and accuracy. Were I to make claims like this I would also present some data to support my claims.


Originally posted by flanders

the ball can distort with high pressure bursts but it would have a reverse translation (as in all liquid filled objects) impact on oen side creats lump on other side this may or may not be a good thing (depending on spin) if spin occurs left or right ball witll be good havign a bullet effect, if ball spins up or down bad ball is lopided pops or screws it up more


An impact on one side of the ball will not cause a lump on the opposite side. The balls diameter will swell before a lump is created... unless of course there is a thin spot in the shell... it will be the weakest area and will deform first from the hydrostatic pressure.

If the spin occurs left or right the ball will hook left or right.


Originally posted by flanders

as for spin not hapening with liquid, if there was no air pocets then the ball would be hard like a solid object or atleast it doesn't impact or adjust every thign is filled, ball still spins, if there is an air pocket, and the liquid can still move then yes will cause lopsided pickle ball spin. but if the buble does not move it creats a weighted zone creating a similer odd spin, if spin occurs


huh?


Originally posted by flanders

General hypothesis

If spin lateral spin (left to right)occurs then one or many of the factros will effect accuracy

If spin longitudanal spin (up and down)occurs then one or many of the factros will effect accuracy


You could also say if the ball was blue then one or many of the factors will effect the accuracy.

Anyhow... I don't mean to be a jerk but, please review your posts before submitting them. Make sure they contain useful information that is similar to that being posted by the other people.

Thanks...

[AGD]

Pstan,

This is about getting the facts and involves more than just an open or closed bolt issue. In paintball this is as close as we get to publishing.

BJ,

Nice job, that's the kind of effort I was looking for. The result of your investigation points out that the magnus effect is SMALL. So if the expected deviation from the Magnus effect is 1% and in tracking the paintball we see a deviation of 10% then we can safely say that another force besides Magnus is acting on the ball. We don't have to actually see it to make sense of it.

Do not let the string fool you, it was streached tight between two posts and only looks curved because the mirror was not perfect.

Everyone concentrate on test number 114 because we have the additional data for the flight path on that one.

AGD

[Ostwar]

If Magnus force is dependant on spin, then what is involved to cause a ball to randomly move when little to no spin is applied. I take this from volleyball a sport in which if you serve the ball with a "flat" or minimized spin the ball will (for lack of a better word) "wiffle" in the air which will directly affect its trajectory. Is this a possibility in paintball?

Shaun

[bjjb99]

Originally posted by AGD

The result of your investigation points out that the magnus effect is SMALL.


I am withholding that conclusion until I recieve some validation of the equation I used to calculate the force resulting from the Magnus effect. It could well be that the equation I used applies well to things like baseballs and basketballs, but not necessarily to small, paintball sized spheres.


Originally posted by AGD

Do not let the string fool you, it was streached tight between two posts and only looks curved because the mirror was not perfect.


Ah, a slight sag in the mirror would definitely explain the string curvature I was seeing. Hadn't thought of that.


Originally posted by AGD

Everyone concentrate on test number 114 because we have the additional data for the flight path on that one.


I'll take a look at that one this evening and see what I can come up with.

While you're reading this, Tom, I've got a question I've been meaning to ask you. In the video tour of AGD's facility, you show off a large mirror you were grinding to make a large aperture telescope. Has the mirror been finished, and if so, what kind of figure does it have? I ask because if it still has a spherical figure it would be awesome to use it in some large scale Schlieren photography of the airflow behind the paintball as it exits the barrel. Even if it's got a parabolic figure it could still be used with a correction lens for such imaging. :)

BJJB

[Crimson_Turkey]

Sadly I cannot post the evidence, but the raw egg theory does not applie ot paintballs. Paintballs will spin while in flight regardless of the liquid fill. Once the shell is set in motion it will not stop spinning as it moves through the air. As I stood leaning out of my window with a camcorder i filmed and egg pushed off the 5th story of an apartment building. A slight spin was imparted upon the egg as it fell. Earlier I had drawn a red line around the egg and in slow motion I could clearly see the line rotate. I would post the video if I could but this camcorder will not let me.

Eggs spin in the air. I think this is due to the lack of friction on the egg. When you spin an egg on a table it is grinding againt the table, causing friction. In the air there is a much smaller amount of friction on the egg. In addition, I think that because the shell of a paintball accounts for more of the total mass and volume when compared to the fill than an eggs shell to it's "fill" the paintball would probably spin better.

[flanders]

california why?

*turns around with blunt object in hand*

[hitech]

Here is a site with formulas. It is about the physics of paintball and he explains his formulas. bjjb99, you could see if your magnus effect formulas match his theory. You will find that he claims that the magnus effect must be determined experimentally. He does give a "guess", I believe.

There is also an applet that attempts to predict the trajectory of a spinning paintball.

http://home.attbi.com/~dyrgcmn/pball/pballIntro.html

[bjjb99]

I've read significant portions of the site you mentioned before and have found it interesting if somewhat challenging to wrap one's mind around. I've computed the Reynolds number for a 0.68 inch diameter ball moving at 280 fps through air, and it comes out around 1.03x10^5. Judging from the graphs on the site you mentioned, this results in a positive lift coefficient under all conditions, instead of the reverse Magnus effect the site describes. It ends up following near to the curve fitted to the triangular shaped datapoints. Thus, I don't necessarily agree with the anti-Magnus conclusions the author describes.

Using test 101 data, the value for V/U used on that site would be (1.25/85.34), or 0.015. This puts our data point darn close to the left edge of the graph shown, and thus the lift (read "Magnus") coefficient is very very small to the point that it is difficult to even estimate it from the plot. I'd estimate the coefficient at around 0.02.

The site states that the Magnus effect force is characterized in a similar fashion to that of the drag force, and thus I used the drag equation to determine the Magnus force with a Magnus coefficient of 0.02. It works out to be around 0.04 newtons if I did my math right, which is about 2.5 times larger than the value I calculated using the equation on the carini.physics.indiana.edu site. Given the difficulty in estimating the Magnus coefficient from the plot, I think the result is close enough to say that either treatment is "good enough" for a first cut look at this phenomenon. I think the two methods agree with each other sufficiently to convince me that my original calculations are a reasonable approximation of the amount of displacement to be expected in test 101 (i.e. unmeasureable given the spatial sampling of the pictures taken during testing).

I am curious what this conclusion means in terms of the Flatline barrel system... I mean, I've seen floaters that just go and go and go coming out of that barrel, and I've seen horrendous curve balls when a Flatline gun is held sideways. I suppose the spin induced on Flatline-launched paintballs is much much greater than the mere 23 revs per second that test 101 exhibited, pushing the V/U point to the right and increasing the Magnus coefficient significantly.

BJJB

[Paladin]

Well, I've stared at the pictures until I'm cross-eyed and there seems to be very little that I can reach any value conclusions on that would fit into the ongoing discussion.
I cannot see anything here that addresses either, the issue of closed bolt versus open bolt or what effect internal ballistics has on the flight of the ball. However, I did do a bunch of shooting through powdered barrels as Tom suggested and arrived at the same conclusions that I reached through reading the scuff marks on paintballs shot through an un-powdered barrel. Results do seem to indicate that the ball does in fact distort or compress lineally from the forces of acceleration; causing it to tighten against the bore of the barrel for a period of time when launched.
My tests were done with a Blazer (closed bolt) operating with 400 to 450 psi input to the gun and firing Pro-ball paint at velocities of between 305 fps and 220 fps.
Only balls that demonstrated a consistent, loose fit in the barrel were used and each was blown through the unpowdered barrel with breath alone to relativly ensure consistent fit in the barrels before moving to higher pressures for launch.
In addition, each ball was chambered manually to ensure consistent positioning of the ball in the chamber prior to launch. Positioning of the ball was only made relative to the face of the bolt and did not address the position of the seem in relation to the axis of the bore.
Two barrels used: One with a straight bore of .690 and the other with an eliptically honed barrel, also with .690 base bore size but the center section of the barrel tapers out to .694 at 6" from the chamber and back down to .690 at 10" from the chamber. I did not have any Desenex brand powder on hand but Gold Bond, medicated powder seems close in consistency to Desenex.
The results: Almost every shot fired wiped the powder from the complete perimeter of the bore during the acceleration in the first part of the bore and then showed only a two-point track in the front half of the barrel. The length of time that the ball made full perimeter contact with the bore decreased as velocity was lowered. Also noted that the transition from full perimeter contact to a two-point track was more abrupt in the eliptically shaped barrel.
To further verify my results, the target was a bed sheet setup to catch the paint so I could read the balls as well as the barrel bore. Looking at the balls showed that the powder that was wiped from the bore was built up on the ball well forward of the center line of the ball with a wide "scuff" mark of imbeded powder. Thus indicating a significantly wide contact of the surface of the ball with the surface of the barrel bore.
Also, I did not see anything to indicate that any "spin" was happening inside the bore but I was not looking real close in that regard. My focus was on "data" that would indicate whether or not the ball would upset under acceleration. All indications to me are that the ball does in fact change its shape to a somewhat cylindrical form when pressure is applied and acceleration begins and the amount of distortion is relative to the velocity achieved. Your results may vary with different types of valving that might generate different rates of acceleration or different blast impact characteristics.

Now, to address some of the issues "on the table":

"Spin is the only major factor accounting for paintball inaccuracy. Promoted by Pbjosh"

In essence, a true statement IMHO. In this regard, I can only go by what I've seen which indicates to me that the less spin seen on a ball in flight, the more likely it is to go where it is intended. Less spin = tighter shot groups.

"Closed bolt operation has an effect on overall accuracy. Promoted by Glen Palmer." (two N's for this Glenn please :p

Actually, my contention is that closed bolt firing gives me the best opportunity to tune my gun (the whole gun) to maximize the effectiveness of the shot. Without appropriate setup and tuning, closed bolt firing is not likely to be any more effective than any other mode of operation.

"The paintball flight is subject to "knuckleball effect"."

It certainly is and I'd bet that we have all seen it at one time or another.

"Spin may or may not be possible because of the liquid in the paintball."

Spin is certainly possible but in relation to the effect on the flight of a paintball, is this discussion based on the lateral spin as would be imparted by rifling a barrel or the random spin generated by numerous other factors ??

"Barrels have something to do with accuracy."

This is one of the few points that I can see as being addressed in the "data" posted. The data in both pictures of "shot patterns" indicates that different barrels will achieve different shot groups. In both "shotpattern" jpgs, the Smart Parts barrel shows a tighter shot group than either, the Crown Point or Rail ? barrel. However, the tightest grouping seems to be shown in the lower left of the "shotpatterns2" jpg and I cannot make out what that barrel is.

"Seams have something to do with accuracy."

I believe that the seems themselves have less to do with overall accuracy than the size/condition and position of the seem on the ball which can and does effect the consistency of the flight path.

"Balls distort with the impact of the air blast."

A certain amount of distortion seems to be a fact. However, either as a result of impact of the air blast or the "G" forces of acceleration?

"Balls distort when leaving the barrel."

Lets hope not. Hopefully, the forces that cause distortion are relieved before the ball leaves the barrel. Although, the "smoke" tests seem to indicate a very interesting shape to the ball after it leaves the barrel.

The "smoke" shots also seem to show that there is not a collum of air being forced out ahead of the ball but that there is a small cushion of air around the ball. This brings up a question or three about the barrel and valving used for the smoke shots. Automag valving? Length of barrel? Venting in the barrel ?

The biggest problem that I run into with all of this is that I don't/can't use scientific calculations to prove out what I see and can measure. When you guys start spouting all sorts of scientific jargon and presenting formulas that often seem to me to be lacking in variables and such, you put the conversation well out of reach for me. I learned the old style math where 2+2=4 so I am relagated to believing what I see. When the things that I do can demonstrate consistent velocity readings and a tight shot group, I'm pretty well convinced that I'm doing something right. Then when something is changed and the results change too, it is quite easy to see whether or not the change was an improvement or not. Common sense and K.I.S.S. principle engineering has served me quite well for a long time. Unfortunately those things are just not accepted here.








Originally posted by AGD
Gentelmen,


Currently on the table:

Spin is the only major factor accounting for paintball inaccuracy. Promoted by Pbjosh

Closed bolt operation has an effect on overall accuracy. Promoted by Glen Palmer.

The paintball flight is subject to "knuckleball effect".

Spin may or may not be possible because of the liquid in the paintball.

Barrels have something to do with accuracy.

Seams have something to do with accuracy.

Balls distort with the impact of the air blast.
Balls distort when leaving the barrel.

Ok lets have a pointed discussion on the subject. For those of you just reading this, this thread is a continuation of the "closed bolt" thread found here.

original thread (http://www.automags.org/forums/showthread.php?s=&threadid=20862)

AGD

[bjjb99]

Tom, do you know if anyone other than Tippmann has performed tests to measure the amount of spin imparted to a paintball fired from the Flatline barrel system? It would give us another set of datapoints to work with for a barrel that is supposed to put spin on the ball.

Got sidetracked last night and didn't get a chance to look at test 114. I'll see if I can work on it this evening instead. :)

BJJB

[hitech]

bjjb,
Thanks for doing the math. My college physics class was a LONG time ago, and I have never had any practical application for what I learned (I took the class for fun, I know, I'm strange). I can't even factor equations anymore! As the site I gave you stated, the Magnus effect must be determined experimentally. Maybe we will get enough data to determine what it is.

Based on bjjb calculations (I'm using his) we have the following answers (For test 101):

1. What is the ball's RPM? = 23
2. Is there only one spin axis or does it corkscrew on two spin axis? = One axis
3. Does the spin maintain, speed up or slow, down range? = Maintain*
4. What is difference in surface speed? = 8.2 fps

* = I do not have the equipment to measure the spin rate (I couldn't find anywhere that bjjb did) of the downrange paintballs. I also do not know what the difference is in spacing between the uprange and downrange strobes. Based on my observations, the downrange strobes are approx. twice the distance of the uprange strobes. Based on my observations the spin rate is the same downrange.

[bjjb99]

Originally posted by hitech

3. Does the spin maintain, speed up or slow, down range? = Maintain*

* = I do not have the equipment to measure the spin rate (I couldn't find anywhere that bjjb did) of the downrange paintballs. I also do not know what the difference is in spacing between the uprange and downrange strobes. Based on my observations, the downrange strobes are approx. twice the distance of the uprange strobes. Based on my observations the spin rate is the same downrange.

Exactly the problem I ran into...

The balls are chronoed at around 280 fps and travel around 6 inches between successive strobe flashes for the near-barrel case in test 101. This gave me a strobe rate of one flash every 1.8 milliseconds.

If we use the same strobe rate for the downrange image, we get a ball travel of around 10 inches in the same 1.8 milliseconds, for a ball velocity of 463 fps... which of course makes no sense... no ball is going to miraculously speed up to dangerous velocities during the downrange portion of its flight, no matter how many elves are behind it pushing with all their might. Thus, the strobe rate downrange must be different.

We don't know the ball velocity in the downrange images, as it is likely to have slowed down significantly from the 280 fps chronoed value. All we have is a distance of around 10 inches between strobes. I suppose one could estimate what the speed should be by using air resistance, but I think that's just adding more errors into the mix.

So I've basically ignored the downrange data until I can get a handle on how fast the ball is moving at that point, or else get a value for the strobe rate from someone. Without one of those two values I think wer're just shooting in the dark for the downrange data.

Tom, did the strobe unit have a readout for the strobe rate? I'm assuming it didn't since you didn't put those numbers up here for us to utilize. How did you go about figuring the downrange velocity or strobe rate back when the test was conducted?

BJJB

[AGD]

BJ,

Tippman as far as I know just did empirical testing and never measured anything.

The ball is moving slower down range, I would have to try and find the exact FPS. You can get close by shooting over a crono at 40 ft with a ball that leaves the barrel at 280.

Now that I think about it we most likely spaced the strobes wider apart so we could measure the spin in the same place.

Glenn (sorry about the n),

Intersting that you scraped off most of the powder half way down the barrel. Did you dry fire the excess powder out first? We have never seen that happen in our tests, I might have to repeat them. We have seen the ball on initial launch bang sideways into the bore but most of the time we just got two streaks.

Yes we are departing from the closed bolt issue temporarily. We are trying to come to terms with the influences on the ball so we can sort them out and rank them.

AGD

[ezrunner]

What barrels are you guys ysing and what paint?

I would be interested to see these tests with a tight barrel
to paint match. Try turning the bead so that it is parallel to the
direction of the barrel, ie would leave 2 streaks down the
bore and find a match such that the entire ball was touching
as much as possible around the
circumfrence.

I get my best accuracy when shooting paint with this fit
characteristic. The consistency
is best I think with your fit
method, but mine takes you from
+/- 1/2 fps to +/- 3/4 fps in most of the better guns.

I will dig around and see if I have the equipment to duplicate
any of this testing, but we have a tourney this weekend.

You guys (Glenn and Tom) put a lot of thought and work into
this, thanks.

-rob from clemson

[Crimson_Turkey]

You could (if you have the supplies) use video cameras to video theb all as it moves downrange. Just set them up sideby side. Then afterwards you could just measure the spin in slow motion. Like what I did with the egg.

I am going to try and aqquire 4 stock barrels for my 98c. I have heard of a bad flatline idea that some people ave done. If you polish the barrel and then put a piece of tape along the top of the barrel it will increase range a bit. I was thinking of using tape on the sides and bottom to see how much change there is. Ill give you grouping size and how fart he groupings are from the no tape grouping. Plus ill get 4 stock barrels to play with
:D

[ezrunner]

Hey crimson:
check out the official
data thread in the deep blue
forum

Those pics are posted from
like 1992 :-)

-rob

[Crimson_Turkey]

ehhh, oops.

[bjjb99]

Crimson,

A normal everyday videocamera does not have a high enough frame rate to capture the spinning paintball's behavior. A videocamera captures thirty full frames per second (60 fields per second), or one full frame every 0.033 seconds. A ball moving 280 fps will travel 9 feet in that amount of time... quite possibly clear out of the camera's field of view. The ball in test 101 was spinning at a little over 20 rotations per second. To capture this spin you really want to sample the scene (i.e. take a snapshot or a video frame) at least 10 times as fast, or 200 images per second. The strobe used in test 101 resulted in a capture rate of around 550 images per second, which is enough to see and measure the spin of the ball.

If you want to use video, it's going to have to be high speed video on the order of 500 frames per second. As has been stated earlier in this thread, such videocameras are not cheap; they can cost upwards of tens to hundreds of thousands of dollars depending on the size of your image frame, the amount of collection time you want (they suck up memory like you wouldn't believe), the maximum framerate, and so on.

BJJB

[Crimson_Turkey]

I doubt ill be able to do it but my step father is a director of photography. Next time I'm in LA he might be able to hook me up with something really nice.

[Paladin]

Originally posted by AGD
BJ,

Tippman as far as I know just did empirical testing and never measured anything.

Thanks for "empirical",, I needed that. The definition that I found is: "Based on obsevation or experiment and relying on practical experience rather than theory." Good to have a way to accurately define one's views. Fortunately, it does not preclude the use of measuring devises like a pretty good "calibrated eyeball". ;)



[i]
Intersting that you scraped off most of the powder half way down the barrel. Did you dry fire the excess powder out first? We have never seen that happen in our tests, I might have to repeat them. We have seen the ball on initial launch bang sideways into the bore but most of the time we just got two streaks. [/B]

Actually, I did not dry fire air through the barrels before shooting paint through it but I did blow shop air through them first. I was carefull to minimize the amount of powder in the barrel and maintain a level of consistency by thorough cleaning and re-powdering for each test shot. I even tried smoke coating the inside of the bore with soot from an oil lamp (lamp black) and saw the same basic results.
I kind of figured that you would have seen the only "two streaks" results in your tests and I think I know why. However, there are a couple more things that I want to try/test before I stick my neck out with a plain language, "empirical " definition. :D


[i]
Yes we are departing from the closed bolt issue temporarily. We are trying to come to terms with the influences on the ball so we can sort them out and rank them.
AGD [/B]

Isn't the most dominating influence on the effective accuracy of a paintgun, the nature of paintballs themselves and the fact that they are relatively inconsistent in size, shape and seem position in every batch of balls encountered ? What is actually to be gained by this sorting and ranking the "influences on the ball". Aren't we really looking for a definition of what it takes for a paintgun to make the most of what we have to work with (paintballs and velocity limits) and be forgiving of the inconsistencies that it is fed ?

[ezrunner]

Glenn:

I have been a big fan ever since my faculty advisor here had one
of your typhoons. Then when I got into cockers and used your
components there, I was impressed.

I posted earlier about what I thought about mechanical consistency
and projectile systems. I won't recap much of it here other than
to hit a highlight or two.

If we can put to rest the idea that a paintball gets some magic
spin in most conditions (ie not a flatline barrel/zbody/cooper bolt),
Then I think we should look at the following:

A lot of people don't fit the paint to the barrel in the
best way.

Paintball guns should fire the ball under the most consistent,
repeatable circumstances every time.

If you read my earlier 2 posts in this thread there is a lot
more said on both these issues.

-rob from clemson

[AGD]

Glenn,

There is a good reason to rank them. If you find out that a force acts on the ball ONLY after it leaves the barrel and that the barrel has no influence on this force, this is important.

If that force makes up a large percentage of the inaccuracy of a marker, then whatever you do in the gun could not make a significant improvement.

AGD

[Redkey]

Is there a relationship between the amount and direction of spin and the impact point?

Do the balls that are spinning faster tend to land further from the target? If so is the effect consistant? How about the direction of the spin? Do balls that are spinning to the right consistantly hit to the right of the target?

What about balls with no spin? do they always hit the target?

What about velocity drop off? do spinning balls lose velocity faster or slower than non-spinning balls?

While all this is very interesting and a fun to think about... don't most people just carry an extra pod or two of paint onto the field? Perhaps an accuracy vs rate of fire test would be more enlightening.

Finally... does AGD plan on doing anymore of these tests?

Sorry I cannot contribute more than just questions at this time.

[Thurman]

I havn't got a deep understanding about paintballs, but I know a little about aerodynamics and shooting, particularly round ball (lead) shooting. It seems that the fact that tippman flatline barrels will curve a paintball when held sideways is prima facie evidence of the magus effect at work. The Clairaut theorem for rotating fluids should also come into play, which would mean that a paintball will distort into an ellipsoid if spun fast enough, increasing the surface speed, and the lift produced. If the ball is in solid contact with the (flatline) barrel and not slipping (theoretical here) the maximum imparted spin should be on the order of 1500 rpm. The real number is undoubtedly lower, but that does represent more than an order of magnitude beyond the 26 rpm noted above. Has anyone compared the velocity drop down range between a flatline launched ball and a standard one? The flatlined ball should slow down much faster than a standard one as the lift imparted by the rotation induces extra drag. So, the flatline ball may drop less at say, 45 feet, but it is most likely moving slower when it gets there. The only way I can see that spin would be of real benfit would be if the spin is imparted with the spin axis along the same vector as the flight path, as rifles do. The effect here is to curve the relative wind around the ball, effectivly decreasing the ball's CD. The egg/paintball analogy isn't very good BTW, the egg has a thin fluid (the white) surrounding a thicker fluid (the yoke). The yoke is suspended along the long axis by energy absobing elastic bands, which makes it hard to spin along the long axis. Try laying the egg on it's side and spinning it that way (go ahead and try it, I'll wait). You'll find that not only can you impart spin that way, but it sustains the spin nicely as well.
In regards to ball deformation, that is one thing that I'm afraid I have always taken for granted. The only thing different about paintballs and lead balls is that the paintballs may return to spherical shape once the pressure goes down. I was surprised to see the Angel still keeping positive pressure as the ball leaves the barrel. I can envision all kinds of bad things that this would cause. The Dark Angel's chart is more what I expected.

Thurman
Manned Flight Simulation
Naval Air Warfare Center, Aircraft Division
NAS Patuxent River MD

[bjjb99]

Originally posted by Thurman
If the ball is in solid contact with the (flatline) barrel and not slipping (theoretical here) the maximum imparted spin should be on the order of 1500 rpm. The real number is undoubtedly lower, but that does represent more than an order of magnitude beyond the 26 rpm noted above.


Careful with the units there. I'm sure you mean 1500 and 26 rotations per second, not per minute.


Originally posted by Thurman
The egg/paintball analogy isn't very good BTW, the egg has a thin fluid (the white) surrounding a thicker fluid (the yolk). The yolk is suspended along the long axis by energy absobing elastic bands, which makes it hard to spin along the long axis. Try laying the egg on it's side and spinning it that way (go ahead and try it, I'll wait). You'll find that not only can you impart spin that way, but it sustains the spin nicely as well.

An egg is resistant to transients in rotational force. It is entirely possible to get a raw egg to spin on a table, particuarly if one applies a gradual increase in the force applied. As an interesting note, spin a raw egg and while it's spinning quickly stop it from spinning and then remove your hand immediately; the egg will resume spinning because of the decoupled nature of the white/yolk and the shell.

How does this apply to paintball? Not sure if it does. It is difficult to estimate whether the fill/shell of a paintball will be sufficiently decoupled at the rotational accelerations we're looking at. Going from zero to as much as 1500 rotations per second in only a few milliseconds is one heck of a transient force. In this regime, the shell/fill may well act like a raw egg does at lower transient levels.

I've got a couple of ancient (1980s vintage) paintballs sitting in a shot glass. The fill has completely separated in them and the shells are clear. I can spin them by hand and see that the fill remains coupled to the shell at the low end of the transient force scale; so at least at the low end of things a paintball does not behave like a raw egg.

BJJB

[Paladin]

Originally posted by AGD
Glenn,

There is a good reason to rank them. If you find out that a force acts on the ball ONLY after it leaves the barrel and that the barrel has no influence on this force, this is important.

Well now, if the barrel itself was the only thing responsible for getting the ball moving in the general direction of down range, that could make a little more sense to me. The barrel is just one of the forces to be dealt with. It is not going to change the actions of other forces, but what goes on inside the barrel will always be a factor in the the results of influence of the several forces that act on a paintball in flight. If not, anything or everthing that could move a paintball to desired velocities would show the exact same results in the size and shape of a shot group as long as the external conditions stayed the same. I kind of doubt that many people will buy into that hypotheses, regardless of how it comes out on paper.


Originally posted by AGD
If that force makes up a large percentage of the inaccuracy of a marker, then whatever you do in the gun could not make a significant improvement.

AGD

Now I have to ask; at what point does a "large percentage" become so dominant in the equation, that the balance of the percentage should be overlooked? Also, what is the percentage of improvemnt that must be gained in order for it to be deemed "significant" ? :confused:
For the sake of argument; lets say you come up with a determination that some external force is (let's say) 80% of the total influence on the flight characteristics of a paintball. Now, if changes to the barrel and/or valving then made to a piece of equipment, demonstrated a change in the shot group size of (let's say) 10%; would that be considered as "significant"? How about 5% or even just 1%??To my way of thinking, 10% is extremely significan't and I'm elated when I can get even 1% improvement from something I might do. As an analagy; A professional drag racer might spend thousands or tens of thousands of dollars for as little as .1% improvement in his elapsed time for 1/4 mile. The little things don't just ADD up, they multiply up.

[Thurman]

[QUOTE]Originally posted by bjjb99


Careful with the units there. I'm sure you mean 1500 and 26 rotations per second, not per minute.



Whoa geez... NEVER post before the coffees up! Yes, it's 1500 rotations per second, not minute. And, as a way of confusing the issue still more...

Anyone else ever own an AT-85? Nice, big, fat holed barrel. The kind balls just fall right through. Very accurate. The difference was a neoprene gland in the breach end of the barrel that replaced the earlier screw in sizing plugs. Apparently, a good barrel to paint fit didn't make much difference in that gun.

Thurman
older than dirt

stingray (yup, still got it)
spyder compact
AT-85
just bought a sentinel
thinking about a mag

[yeahthatsme]

if somebody would send me a rifled and straight bore barrel and a way to secure a marker so that it wont move when fired i would be perfectly willing to test the grouping differences between rifled and straight bore. i would use an automag with a max-flo air tank. so if i can get the stuff i will do the test.....

[AGD]

Glenn,

If a barrel did it's job perfectly every time and 100% of the spread was due to external forces then it would be a waste of time to try and improve it.

The problem, as I see it, is that people spend 300 dollars for a barrel not knowing if it will make a 1% or 50% difference.

In general I have to ask you, how much of an increase in accuracy have we really seen in 15 years? Given the fact the barrel prices have increased by 10x and are now honed and sized to perfection, what are we getting for the money?

While you may be willing to spend big dollars on a 1% improvement most will not or at least would like to know what they are getting.

AGD

[Paladin]

Originally posted by AGD
Glenn,

If a barrel did it's job perfectly every time and 100% of the spread was due to external forces then it would be a waste of time to try and improve it.

Tom, I have to agree with that statement but it is based on some pretty large and asumtive "IFs". It seems to assume that the barrel is the only factor besides external forces that can have an effect on the placement of the ball. One could also state that if changing only the barrel on a particular piece, produced a measurably improved shot pattern, it was not a waste of time to try to improve on it. It would also be a safe assumption that the way the ball was presented to the external forces, had a significant influence on the effects of those same external forces. Maybe such a barrel was just better suited to the forces behind the ball or maybe just better suited to the balls themselves. In either case, the result was to present the ball to the external forces in such a manner as to allow better consistency of placement of an inconsistent projectile.


[i]
The problem, as I see it, is that people spend 300 dollars for a barrel not knowing if it will make a 1% or 50% difference. [/B]

I know exactly where you are coming from and I whole heartedly agree. New and/or different is not always better.
Even more of a problem is that those same people will often find a way to justify the expence whether it provided an improvement or not. Style points have become far to important to some. [/B][/QUOTE]


[i]
In general I have to ask you, how much of an increase in accuracy have we really seen in 15 years? Given the fact the barrel prices have increased by 10x and are now honed and sized to perfection, what are we getting for the money? [/B]

That is a tough question to answer with any sort of brevity. In the context of this thread, there has been very little improvment in the overall accuracy potential of a paintgun in relation to barrels. Although, I believe that the typical paintgun of today will show measurably better results than the typical 'gun of times long past. It is much harder these days to produce significant improvments to shot groups by changing the barrel because of the general improvements to barrel production as well as the evolution of valving. Essentially, the guns that I built 15 years ago are every bit as accurate (for any one shot) as what we are producing today but I get better shot groups these days due to the better consistency of the air supply being used.


[i]
While you may be willing to spend big dollars on a 1% improvement most will not or at least would like to know what they are getting.

AGD [/B]

To the contrary; I am neither willing to spend my money in that regard, nor am I willing to take my customers' dollars for something that may not be of any real benefit. I've never been a proponent of having a bag full of barrels for your paintgun. Especially since most of my equipment is produced with non-changable barrels. However, we do offer services to ensure that a 'gun and its barrel are tuned to compliment each other and provide the opportunity to put the ball where you need it. I still believe that the valving of the 'gun is at least equally important as the barrel when in the pursuit of optimum performance.

[Crimson_Turkey]

Originally posted by yeahthatsme
if somebody would send me a rifled and straight bore barrel and a way to secure a marker so that it wont move when fired i would be perfectly willing to test the grouping differences between rifled and straight bore. i would use an automag with a max-flo air tank. so if i can get the stuff i will do the test.....

You would need the barrel to be exactly the same except for the rifling though. Unless you can get armson to make you a non-rifled stealth barrel this might be hard for you. You may also be able to get a hold of two old J&J custom barrels.

[AGD]

All,

Now I just want to point out to everyone that Glenn and I are having a very pointed discussion about the subject at hand. We are both presenting facts, opinions and points of view.

It is refreshing to have such a discussion without it breaking down into name calling and disregarding the others opinions. This is why I love Glenn, he is a no BS guy. Doesn't take it and as importantly doesn't give it.

This type of discussion represents what Deep Blue is suposed to be all about.

Thanks Glenn.

Tom

[AGD]

Ok back to the battle,

Glenn, I am purposely leaving the valving air blast thing out of this becasue it's one of the things on the table to be examined at the end.

You do make a point that todays groups may in fact be closer due to the better propellent, aka compressed air, than a decade ago. I also thought about why you may be getting a full powder scrape off the inside of the barrel. It could be because todays balls are much rounder than 10 years ago. I know they could be off by 20 thou in 92.

I will absoulutely give you the valve tuning issue if it concerns tighter velocity spread out the barrel. If it affects down range flight you would have to explain that to me.

AGD

[than205]

Tom,
Since we are considering that paintball production has evolved to the point where they are much "more round".
I'm curious to persue the "ball distortion" issue. Wouldn't we just want to do the powder test with a "very" large bore barrel to find out whether or not the paintball distorts to fit the barrel? Or does it bounce around? Or what ever....

[Cristobal]

Originally posted by than205
Tom,
Since we are considering that paintball production has evolved to the point where they are much "more round".
I'm curious to persue the "ball distortion" issue. Wouldn't we just want to do the powder test with a "very" large bore barrel to find out whether or not the paintball distorts to fit the barrel? Or does it bounce around? Or what ever....

It would be interesting to do more testing to see if the results Paladin got are consistent across the board. Based on the results described in AGD's tech tip on barrel sizing, I'm betting that the ball will only expand to a point and that in a very large bore barrel the ball would bounce back and forth.



From the tech tip:
If the barrel is too big, the ball ricochets back and forth down the tube. We used to say it looked like Zebra stripes in there. Hence big barrels do NOT create an "air bearing". Barrels that are too small scrape most of the powder off and this creates excessive FRICTION. Tighter barrels that were too long were found to slow the balls down due to this friction. In other words, when you cut these barrels down, velocity went up. Remember the 8-10" acceleration distance, these barrels were 14" long and unported.

[hitech]

Tom,
Did you ever photograph any paintball flights that were fired from a barrel with "paint" in it? I think we have all observed enough evidence to believe that "paint" in the barrel adversely effects accuracy, unless you are trying to curve it around a tree. ;)

[Paladin]

Originally posted by AGD
All,

Now I just want to point out to everyone that Glenn and I are having a very pointed discussion about the subject at hand. We are both presenting facts, opinions and points of view.

It is refreshing to have such a discussion without it breaking down into name calling and disregarding the others opinions. This is why I love Glenn, he is a no BS guy. Doesn't take it and as importantly doesn't give it.

This type of discussion represents what Deep Blue is suposed to be all about.

Thanks Glenn.

Tom

Ditto, what Tom just said!! ^ Thank you too. Always a pleasure !!!

Now, I have a couple more tests that I want to try to duplicate today before I get into the "goggles on" envrinment of Tom's next post. :)

Quik Question: Anyone, that is following this thread, have any experience with or a connection to freefall parachuting, aka Skydiving ??
If so, try following some round and/or not so round objects in feefall sometime. Makes for some very interesting observations regarding the effects of air flow over various objects and their shape orientation to the line of flight. Especially at the transition from acceleration to achieving "terminal velocity" speeds ranging from 150 to 300 FPS. I haven't done any serious jumping in many years and I sure wish I had some video of some of the stuff we did.

[bjjb99]

Analysis of the test #114 image

I am calling the first image of the ball outside the barrel "position 1". "Position 0" is inside the barrel.

Front view spin:
Position 1: 36.3 degrees
Position 2: 24.6 degrees
Position 3: 14.4 degrees
Position 4: Washed out
Average spin: 11.0 degrees per strobe flash, spin vector away from camera, "top-spin" from the shooter's point of view.

Underside view spin:
Position 1: -3.2 degrees
Position 2: -22.1 degrees
Position 3: -36.0 degrees
Position 4: Washed out
Average spin: 16.4 degrees per strobe flash, spin vector down, "left-spin" from the shooter's point of view.

Axial spin is negligible.

Based on the measured spin directions, the Magnus effect should cause the ball to drift downwards and towards the camera. Here are the position measurements from the test #114 image.


Front view position of ball:
Position 0: 29 mm above string (bottom of ball)
Position 1: 30 mm above string (bottom of ball)
Position 2: 31 mm above string (bottom of ball)
Position 3: 32 mm above string (bottom of ball)
Position 4: Washed out

Underside view position of ball, "towards the camera" and "in front of the string" is "down" in this portion of the image because of the mirror used to image the underside:
Position 0: Indeterminate. Ball does not appear to line up with barrel exit.
Position 1: 9 mm in front of string (front surface of ball)
Position 2: 9 mm in front of string (front surface of ball)
Position 3: 7 mm in front of string (front surface of ball)
Position 4: Washed out

The ball actually rises slightly and moves away from the camera. The Magnus effect predicts exactly the opposite of what we observe in test #114. There is an anti-Magnus effect that rears its head for smooth spheres, but its effect is generally weaker than the forces predicted by the Magnus effect. Given that test #101 showed that the Magnus effect resulting from a spin of 15 degrees per strobe flash was resulted in too small a deviation to measure with the scanned images provided, and given that the spin in test #114 is comparable in magnitude to the spin in test #101, it is reasonable to conclude (without having to go through all the math) that the deviation imparted by the Magnus effect in test #114 is also too small to measure in the scanned image provided.

Not only is the deviation imparted by the Magnus effect in test #114 too small to be measured, but the deviation is also predicted to be in the opposite direction of the measured deviation!

The rise of the ball as measured in the front view image appears linear (to within measurement error), which seems to indicate that it is either a result of not quite perfect alignment of the barrel and string, or an initial upwards "kick" that occurred just as the ball exited the barrel.

The motion of the ball away from the camera is not quite as linear, but is still reasonably so to within measurement error. The ball may have acquired a slight "kick" away from the camera as it exited the barrel.

What could cause a ball to be kicked slightly in a direction as it exits the barrel? I suppose slight kick could be imparted to the ball as a result of the differential pressures encountered from a nonuniform air release. I took a look at the smoke*.tif images to see if I could detect any nonuniformity in the way the gas escaped, but I couldn't make any conclusions from those images.

Based on tests 101 and 114, I think that the Magnus effect is not what causes the shot-to-shot inconsistency seen in modern markers; the spin resulting from a barrel not specifically designed to induce spin (i.e. Flatline, etc.) is not sufficient to deflect the ball from its normal course. The inconsistency may be the result of nonuniform release of air behind the ball as it exits the barrel. In normal gameplay, pockets of air turbulence may be a factor.

BJJB

[Kip Walker]

:confused: if acuracy is decided by how the liquid in the ball spins or dosen't spin then to get the fill to spin would be to solve a great problem. Mabey making the paint thicker would help the fill to spin when the shell spins. Then the fill would spin with the shell and we could just start rifling the barrels like actual rifles.;) :rolleyes:

[AGD]

BJ,

NICE JOB!! Good analysis. Ok so NOW we are seeing real data that points in a direction, it just seems that the direction is not what everyone expected. So is the way of science.

So please lets assume for a second that this 114 data generaly represents what's going on with paintballs. (I happen to know it does)

The next claim is that maybe the ball is kicked sideways right out of the barrel. If this were true you would expect to see it deviate in one direction and that direction would be significantly increased in the second camera trap. If you look at the picture called "3D interpretation" you will see the balls position plotted as relative movement from one pic to another. If you look at the first position in the second trap (flash #6) you will see that the ball trended LEFT from the #5 flash postion but it hits WAY RIGHT at the final target backdrop.

So if we interpret the data correctly the ball "S" curved in flight. This is not consistent with a ball knocked off course at launch.

We are getting better lets stick to it.

AGD

[Redkey]

Originally posted by AGD


So please lets assume for a second that this 114 data generaly represents what's going on with paintballs. (I happen to know it does)

AGD

So, the conclusion based on BJJB99s nifty numbers work is that spin does not have an effect on accuracy? And... this conclusion is supported by all the other unseen data?

I don't entirely agree with that statement... but, I cannot disprove it. So I'll assume it's true until it can be proved otherwise.

So... where does that leave us? Why don't balls fly straight? Obivously there is something happening during the balls flight to cause it to wander. They had the same problem a few hundred years ago with muskets... everyone knows how they solved that problem.

Have the same accuracy tests been tried with nylon balls? Assuming the solid ball is homogeneous... that should remove any inconsistancies associated with the paintball. From my playing around with shooting nylon balls I found they hooked like crazy. I might have been shooting a bit hot which could contribute to the inaccuracy. Have you seen similar results with nylon balls?

Why is a paintball shot from a barrel coated with paint from a broken ball so inaccurate? Is there spin? Does the paint coating the ball cause it to hook?

What was the flash *duration* on the strobes used for your photographs?

again... more questions than answers. Sorry.

[bjjb99]

Originally posted by Redkey

So, the conclusion based on BJJB99s nifty numbers work is that spin does not have an effect on accuracy? And... this conclusion is supported by all the other unseen data?


I think the conclusion is more along the lines of "the levels of spin seen in the test 101 and test 114 data are not sufficient in and of themselves to affect accuracy to the magnitude seen in those tests." This is not to say that spin has no effect on accuracy; the Flatline barrel turned on its side clearly shows that spin does affect accuracy. But then the level of spin induced by a Flatline barrel is (I assume) significantly greater than what tests 101 and 114 show.


Originally posted by Redkey

Why is a paintball shot from a barrel coated with paint from a broken ball so inaccurate? Is there spin? Does the paint coating the ball cause it to hook?


I think it may be a combination of spin and a nonuniform coating of fill on the outside of the ball which causes the horrible accuracy one sees when firing a shot from a paint-filled barrel. The spin would likely be greater than that seen in tests 101 and 114 so we'd be closer to the Flatline barrel regime in terms of shot curvature. The nonuniform coating of paint on the ouside of the paintball might result in an effect similar to golf ball dimples, increasing the turbulent flow and thus magnifying the effects of spin even more. Of course, this is all guesswork on my part.


Originally posted by Redkey

What was the flash *duration* on the strobes used for your photographs?


The ball from test 101 appears very round in flight, perhaps only a pixel or two "longer" in the direction of flight. Assuming this is from the flash duration, it amounts to about 1 mm of travel during the flash exposure. At 280 fps, we get 1 mm of travel in about ten microseconds. Thus I'm betting that the strobes are around 10 microseconds in duration (or possibly a bit faster if some of the ball elongation resulted from a failure to recover from possible deformations during firing).

BJJB

[bjjb99]

Originally posted by AGD

The next claim is that maybe the ball is kicked sideways right out of the barrel. If this were true you would expect to see it deviate in one direction and that direction would be significantly increased in the second camera trap. If you look at the picture called "3D interpretation" you will see the balls position plotted as relative movement from one pic to another. If you look at the first position in the second trap (flash #6) you will see that the ball trended LEFT from the #5 flash postion but it hits WAY RIGHT at the final target backdrop.

So if we interpret the data correctly the ball "S" curved in flight. This is not consistent with a ball knocked off course at launch.


What is the vertical and horizontal scale (preferably in inches per pixel) used in the file labeled 114axis.TIF? If my measurements from the in-flight shots of test 114 are reasonably correct, and if I'm applying them correctly to 114axis.TIF, then the "WAY RIGHT" you're talking about amounts to about 2.25 inches of deviation from the point of aim at the final target backdrop.

A total horixontal in-flight deviation of less than 2.5 inches might be explained away by unstable air, either in the form of density gradients or residual air currents from people having moved through the test area prior to testing.

BJJB

[Paladin]

Originally posted by AGD
BJ,

So if we interpret the data correctly the ball "S" curved in flight. This is not consistent with a ball knocked off course at launch.

We are getting better lets stick to it.

AGD

Since the ball seems to have a rotation to the right, it makes sense that it would have "S" curved in flight even if it had gotten a little "kick" to the left as it exited the barrel. Based on the orientation of the seem of the ball to the line of flight, as seen in test #1:01 any muzzle blast could easily move it to the left a bit and then allow the rotation to move it back to the right.

[AGD]

BJ,

YES!! You correctly state that spin is a continuum. At the level we see in 114 it has no substantial effect but with the Flatline or wet barrel the magnus effect overcomes whatever the mysterious force "X" is.

So lets talk about spin for a minute. Spin is a FORCE or magnus effect or whatever you want to call it. This force has the characteristic that at high spin rates (flatline) it always pushes the ball off the centerline of the barrel. So I am going to make the broad statement here and say that spin has a force vector randomly perpendicular to the line of flight. I think this is reasonable but I am open to debate.

If your ball spun every shot (again flatline rpm) but the barrel did not induce the spin in one direction like the flatline just in random orientation, you would end up with a target grouping that looks like a doughnut. This is because the spin wants to pull it off the centerline. Ok hold this thought.

We now know some things about the mysterious force "X". We know it has a magnitude because it can overcome the force of low rpm spin. We also know its magnitude is lower than flatline rpm spin. Now remember the doughnut pattern from spin? We get that because the spin force is not completely random, it’s always pointing away from the centerline. When we look at standard shot groups only affected by “X” (clean barrel, low rpm spin) they are randomly distributed, this leads me to interpret this force X as random, meaning it might not affect the ball at all on one shot but throw it off the next. This I think we agree is completely consistent with what the paintball world sees. So if you agree with what I say here, we are looking for force X to have a magnatude that varies randomly from zero to something less than flatline rpm on every shot.

Importantly we see it overcoming the slower spin WHILE THE BALL IS IN FLIGHT. This is the next point of debate so I will start. If the X force happened in the barrel or say a foot from it, then the spin no matter how small should affect the flight path in a direction consistent with the axis of rotation as it flies down range. To state it another way, if the ball in flight was not being affected by X then spin should be the major factor causing deviation. From another point of view, the force X has to be happening while the ball is in flight because in 114 it pushes the ball in two different directions while its going down range. So in order to argue against this you have to explain how something in the gun or barrel can affect the ball down range as we see in 114. The one thing the barrel can do is impart spin to the ball and that affects it down range but since we have that under control you have to come up with something else. Fire away.

Redkey,
Yes we are basing this on unseen data, if when we get to the end, someone wants to see more I will gladly post it. I am quite confident that the brains on this forum, once they comprehend all the factors, will be satisfied with the answers. Like you said they had this same problem with the musket balls its not new stuff

Yes we did test nylon balls, the shot group is #5 in the 8 box shot group pic. The scale of the in flight positions is proportional to the diameter of the ball. So if the diameter of the ball is .680. It deviates to the left less than one ball width in the 114 flight path.

I see that I forgot to post the tiff files for you to download hi res versions. I will try and do that asap.

Glen,

You have to explain the muzzle blast effect in context of the smoke pictures. It is not apparent to me that there is a pressure jet exiting the barrel right when the ball leaves.

Damn this is good stuff....


AGD

[AGD]

I appologize, I thought I had posted the tifs when I first put up the pics but I must have forgotten. Please download the tif and look at the pics, they are much clearer than the lousy jpg's in the thread. Sorry about that, you cant get good data from lousy pics. Here is the link and its in the data thread.

AGD


spin data (http://www.automags.org/~TomAGD/spindata )

[Pstan]

Might I propose someone take a look into the varying ballistic coefficients of paintballs as the mysterious "X" force.


Considering what Mr. Kaye posted above on Force "X", let's look at paintballs. Paintballs have a terrible BC. Might we also say that the BC of every paintball fired is different from the next because of their inconsistant nature. So far, unless handloaded, we cant control the orientation of every round that enters and exits the gun. Might not the Force "X" be the minute diffences in the BC of each and every ball fired? And might not the fact that even Nylon paint has bad accuracy be a result of the poor BC of paintballs in general? If you have a really good Paint/Barrel match flyers still occur. Possibly due to the fact that the tip/width/tail of every projectile fired is minutely different from the last or the next? The Flatline would override this as it imparts the hard spin along a verticle line that overcomes the BC and changes trajectory? Fill on the ball would do so also as it induced a spin?

A few sites on BC that might make more sense....

http://www.chuckhawks.com/bc.htm

From Mr. Hawks...
"Ballistic Coefficient (BC) is basically a measure of how streamlined a bullet is; that is, how well it cuts through the air. Mathematically, it is the ratio of a bullet's sectional density to its coefficient of form. Ballistic Coefficient is essentially a measure of air drag. The higher the number the less drag, and the more efficiently the bullet cuts through the air. So for purposes of flying through the air efficiently, the bigger the BC number the better.

BC is what determines trajectory and wind drift, other factors (velocity among them) being equal. BC changes with the shape of the bullet and the speed at which the bullet is traveling, while sectional density does not. Spitzer, which means pointed, is a more efficient shape than a round nose or a flat point. At the other end of the bullet, a boat tail (or tapered heel) reduces drag compared to a flat base. Both increase the BC of a bullet."



http://www.aeroballisticsonline.com/ballistics/bc1.html


http://www.uslink.net/~tom1/calcbc/calcbc.htm



This may be completely off the wall and entirely wrong, but it's the best a feeble mind like mine can come up with. And, I do realize that paintballs and bullets may be an "Apples and Oranges" comparison, but BC is what describes the change in the shape of projectiles over the years in firearms. I think someone did mention that the firearms world solved this problem long ago, or something to that effect.


Respecfully,

Pstan

[AGD]

Pstan,

Good comeback! Yes BC can affect things in flight. Problem is that all spheres have the same drag coefficient with is something like .7 or .8. The nylon balls being perfectly round to better than 1000th of and inch and missing the seam should fly straight and true but they don't. In fact the shot group for nylon balls is hard to differentiate from regular paint.

This would seem to sugest that the seams, drag coefficient differences and small size variations are not a substantial portion of our X force.

AGD

[BlackVCG]

I could sit here and rattle off all of my Fluid Mechanics knowledge, but this explains things pretty well.

http://www.princeton.edu/~asmits/Bicycle_web/blunt.html

Pstan- The difference between the bullet and the paintball is that one is a streamlined body and the other is considered a bluff body, respectively.

Tom- Not for all spheres. Take a look at the graph. It's a function of the Nr (Reynolds Number), but for all paintballs shooting through air you can consider it the same.

I haven't been reading this thread, but when I find the time I'll look it over and see if I can add some input. It seems like an entertaining conversation thus far.

[AGD]

Black,

Yes of course you are right about the DC being different at different R. You all should look at the site Black pointed out. Very informative especially figure #3....


AGD

The trip wire thing is cool too, I will have to look at that more.

[[5x5]]

Larry De La Brandais turned me towards this very interesting discussion thread, and I thank him for it. You may not. Although I haven't done much on the paintball physics subject for awhile, I still remember some of the stuff I put together, and certainly still have an interest in it. (As a reminder: http://home.attbi.com/~dyrgcmn/pball/pballphys1.html) After seriously wading through the many very interesting arguments and points raised on this thread, I thought I might as well join the confusion. The variety of expertise and depth of thought on dynamics issues is great to see. Warning, I am coming in very late in the discussion and I am trying to summarize a whole lot of stuff, so this will be long.

On spin: The Magnus effect or force is small. Gravity and drag are the two big forces driving any ball dynamics. The problem is that even if the Magnus force is secondary it is sufficient to shift a trajectory enough so that you miss your intended target even when you are aiming with the utmost determination. The Magnus effect should not be considered along just any one particular axis. The effect is general and is based on the dynamics of air moving over a spinning object or ball in our case. Mathematically, it is defined by whatis known as the vector cross product between the spin and the motion of the fluid around the ball. In our case the ball rather than the fluid is moving, but that is simply a frame of reference difference. What it does mean is that any deflection from a true non spinning trajectory depends on the spin direction, the spin velocity (rpm), the ball velocity, the ball direction, and the relationship between the spin axis and the ball direction. The latter relationship dictates that the best we can do is talk about accuracy and spin in terms of a two dimensional splat pattern that will result around a central point unless we can absolutely control the spin axis direction. As I see it, the problem is not whether spin creates deflection, that is a given based on the scientific and practical literature. The real problem is determining how much spin will create how much deflection. (Note that I am not saying here that spin is the only cause of deflection.) On my physics page, I used some of the available literature to try and get some idea of what spin velocities are needed. Of course, none of the data available was for paintballs or for objects as small as a paintball. As someone who for most of his career was an experimentalist, I have a healthy skepticism for theory, especially when it has to stand alone – as in my own calculations. I certainly have to agree with pstan's arguments along these lines. Actually seeing and being able to digest some of Tom Kaye's data is great, and I thank him for sharing it.

Still on spin: Keep in mind that the relationship between spin velocity and ball directional speed is non linear. This is embodied in the lift coefficient curves. Take a look at the data on my site. The lift coefficient which is necessary to calculate the effect of spin, is not a constant. That means the force will not be a constant. Assuming that it is a constant will likely produce very misleading answers to understanding a true spin related trajectory, and definitely will not produce some of the weirder paintball trajectories (those that dip and rise). Several people have already discussed the lift coefficient data that I used in my calculations, where the lift coefficient is plotted as a function of V/U (rotational velocity/directional velocity). The importance of the V/U ratio seems to have been somewhat overlooked in this discussion. If you look at the lift coefficient curves I used, at low V/U there is not much affect (force) on the ball. The reason is that when the ball leaves the barrel, the linear ball velocity is very high relative to the spin velocity. But the inevitable drag force does a great job of rapidly slowing the paintball. Assuming the spin rate does not change (not necessarily true), as the ball proceeds downrange, the forward velocity drops and so the V/U ratio increases. According to the lift coefficient data, the ball would first experience a small negative force and then as it continues to slow a much larger increasingly positive "lift" force. The result is that we will see deflections from a non spinning ball trajectory that are going to be nonlinear, and definitely increase at a faster rate as the ball gets further and further and slower and slower downrange. When I was first doing my calculations, I had a lot of problems understanding this large deflection near the far end of the trajectory until I actually dumped the V/U data in my calculations as a function of distance and watched it rise.

On non spinning effects that affect trajectories: Real paintballs almost always have seams. If you look into the literature of sports ball dynamics and even wind tunnel tests you find that seams or dimples play a very important role in ball trajectories, whether the ball is spinning or NOT. Any asymmetrical imperfection, whether it is a seam or a dimple, can create a differential pressure/airflow around the ball; this will affect its trajectory from an ideal absolutely smooth sphere. If I remember correctly, the magnitude of this effect can be on the same order as the Magnus force for a spinning ball. Although I mentioned this problem on my physics page, I stayed away from trying to deal with it because of its nightmarish complexity and the fear that I was already running the risk of losing readers at a high rate. But the upshot is that inaccuracy in a paintball can occur without spin. As mentioned by at least one other contributor here, there will also be a change in drag with respect to the seam, since the 2D face presented to the direction of motion will be larger. However, using nylon balls with smooth surfaces should minimize this "slider" type effect.

Liquid and air bubble motion in the ball issues: I did deal with this issue on my site, but I would not say it is thorough. This issue is particularly important from several standpoints. The fill may help slow a spinning ball down due to internal frictional forces. That would actually reduce the Magnus effect. Second, if the fill is not uniform from ball to ball that will affect the paintball accuracy even if the pressure driving the ball is spot on for every shot.

Now for my take on some of the generous data offered by AGD, and discussion by others:

I am having a problem understanding the 114 data particularly the 114side image. Tom indicates that the distance was 60 ft for the data shown, but based on the distances shown and the distances between strobe shots mentioned in another photo, the distances come out closer to 88 inches. What am I missing?

Bjjb99's data analysis is great. Thanks for helping us all byspending the time doing it. Bjjb99's analyses of the 114 photos prompted me to look a lot closer at them, because I found the pictures confusing. I think (hope) I understand now. The ball consists of three stripes. Two run parallel to each other around the ball; a third is at right angles to these and runs through one hemisphere only. Looking very closely at the photos and grapping a Christmas ornament from the convenient Christmas tree as a prop, I think I now see what is going on in 114. The axis of spin is very approximately 30 degrees from the horizontal plane and 30 degrees from the vertical plane extending along the direction of motion. Looking at the front view and drawing the spin axis through the ball it would be extending back into the page from the upper right side of the ball at about 30 deg from the plane of the page, and would be coming out of the page extending to the bottom right of the ball. If this is true, then the bulk of the Magnus effect would indeed be manifested in a vertical direction from the true trajectory with only a lower deflection in the lateral or horizontal deflection. The problem is the ball will also be changing position due to gravity.

I also looked at the positions of the balls for the set closest to the muzzle, but only in the view from the under side. I measured the distance from the "laser line" to the bottom of the ball. At the high magnifications I was using to measure the tif images, I could see each pixel. This created a problem because I was not always sure which pixel to measure to. For the three positions I found 4.50 mm, 4.21 mm and 4.15 mm respectively. But the problem is that each pixel was approximately 0.35 mm wide. Hence the middle ball position also was measured as 4.56 mm. Since it appears the error in measurement is just about the same as the differences I see, it is not reasonable to say there is any change. To be quite honest, I am not sure there should be any:

Bjjb99 figured about 20 revs/s or about 1200 rpm. That sounds good to me. When I looked at the data a little less critically then him, I reasoned the spin was between 1000 and 2000 rpm. Now how about the magnitude of the deflection expected form the Magnus effect. All I have to rely on is my handy dandy trajectory calculator (but correct?). What I find when I use: 1200 rpm spin, 280 ft/s linear velocity, 0 gun angle, 90 deg spin axis (90 degrees to ball direction – vertical to maximize side deflection), is a predicted deflection of 0.000301 feet or 0.0036 inches at 3.0 feet downrange. Now why choose the side deflection of the Magnus effect when I have already agreed with Bj that the major deflection due to spin will be in the vertical direction? Because the effect of gravity on the ball's position produces a 0.0020 drop in the vertical position of the ball at the same distance, roughly an order of magnitude greater than the Magnus effect. The reason for this is as I have already said the Magnus force is particularly ineffective when the downrange velocity is high (low V/U), especially this close to the muzzle. Just for comparison, the same calculation shows that when the ball hits the ground about 116 ft from the muzzle, the side deflection is approximately 6". This is the long winded explanation that basically comes to the same conclusion as Bjjb99. You can't see any change due to spin. But the reason is because of the regime the measurements are being made.

One other thing I find curious about Bj's data is the change in the angle between successive points downrange. At first glance, it appears that the spin rate is decreasing rapidly. However, it is clear that in the later strobe shots the ball is still spinning. One possible answer to this dilemma may be parallax between the camera and ball, or it may be due to camera lens distortion or both. Another is that since the spin axis is at a strange angle relative to the camera, that there it is simply a problem of representing a 3D operation in a 2D image.

Could the deflection data that is plotted in the 114axis image be predicted from the known information? Well first I am having trouble understanding the scales in the figures. Second, it could not be predicted by me. To describe completely the direction of a spin axis in 3 dimensions, two angles are necessary. My calculator only considers one angle. This effectively means that one spin axis angle is locked such that I can only determine the maximum possible deflection envelope. This cannot be easily changed without rewriting a fair portion of the programs.

So where does all this discussion put us, or rather, just me:
First, the effect of spin should not be looked for close to the muzzle of the gun. Get downrange to really see the effects – remember CL versus V/U. However, you do need the spin velocity near the muzzle to find what the initial spin velocity is.

The data from Tom says several important things to me, and generates several questions:

Paintballs do spin. Did all shots show the balls spinning or were there a large fraction that did not spin at all? I guess I would expect that all balls would have some spin but with a low average spin velocity.under 5K.

Some or all of the spin on the ball is preserved in the first two and a half feet from the muzzle and is not damped out. The ball holds a spin even further downrange (depending on where the last three strobe shots were taken.)

For me, the shot pattern of the nylon spheres is one of the most interesting sets of data. Even the most perfect balls show a shot pattern, but we still don't know why. It could be spin effects, but that is not at all certain. It should not be due to seam or dimple effects since from the discussion the balls are nearly perfectly round. Several questions come up as I contemplate the data; please don't take them as a harangue. Are air currents possible? Were there any attempts to look for trends in shot pattern versus shot number? What was the distance of the target from the muzzle and was the target center perfectly collinear with the barrel axis? Also what is the scaling? Are the circles accurate shadow representations of a paintball diameter? The reason I ask the latter three questions is because this gives me a way to possibly cross check the accuracy of my trajectory calculator under definitely controlled conditions.

Odds and ends

Someone remarked they don't understand why the last point does not end up at ground elevation in my trajectory calculator, but is usually slightly higher. The reason is that the calculation is stopped when the next point produces a negative elevation. I considered it too much work to have the calculator find the exact zero point, especially when I have no idea how really close the calculations approximate reality

Thurman indicated that the speed of the paintball from a flatline barrel should be no more than 1500 rpm. I find this low considering the speed of the ball. On my site, I calculated that assuming a ball "rolled" down a barrel at 280 fps, it would end up with a spin of over 94K rpm.

Enough for now. Thanks.

[cledford]

Somewhere along the line (in this thread) I thought I saw it mentioned that just about every ball fired through a paintgun experiences the magnus effect to some varying degree. I think it was further stated that the problem is that there isn't anyway to control which direction the effect causes the ball to travel and is essentially random. A description stated that due to this occurrence that the shot pattern of paintguns would look like a donut - or, if a straight line was run through the exact center of the bore to the impact point, the Magnus effect would cause the ball impacts to hit at varying distances from the desired point in a complete ring around that actual point of aim.

So if this is the effect of uncontrolled Magnus, why not try to control it? The flatline does (in an unintended fashion - they aren't trying to "control" anything - just to induce the effect to utilize the result) but is not "adjustable" and is severe. The Z-Body for the 'mag was designed to produce a similar effect as the flatline - but differs in how it accomplishes this. The Zbody uses a "friction plate" that is adjustable from zero to maximum (I guess where it would crush a ball) and I think most people turn it up to a high degree attempting to reproduce the Tippmann result.

What if a similar system was used to put just the slightest amount on magnus on every ball fired from a gun? Instead of going to far and putting a "major" amount on - why not just apply enough to be certain that effect was always consistent? That should theoretically reduce the group size which is another way of saying "increase accuracy."

This might not be the holy grail - but I'm wondering if the line of thought is reasonable. I guess my thought is, "if paintball guns are inherently inaccurate due to variances (inconsistencies) in the shape/size/form of the projectile, and those variances in the projectile are unchangeable and must be accepted - why not try to control how the projectiles behave by forcing their behavior to be more consistent?" This is based on the huge assumption that the varying magnus I described above is caused by the imperfections in the balls themselves.

-Calvin

[ezrunner]

When fired by a human, all shot groups are a donut. The shooter
with the smallest donut wins.

Observationally, paint behaves the same, this is due to the
natural mechanics of the body.

Question: AGD/Tom.. or Glenn,

"Does a paintball marker, when held in a fixed mechanism, exhibit
this same tendency, or is there a pattern grouping that is somewhat
uniform over a reasonably large sample set?"

-rob

[[5x5]]

I believe that the Magnus effect would only produce a well defined donut target pattern if the spin velocities were locked into a small non zero range. I also suspect at least one of the angles defining the spin axis would have to be constant as well. If we set up a coordinate system centered on the ball with x axis being the direction of ball motion, y being in and out of the plane of the page, and z being the vertical axis, then the angle that must be locked is that in the xz plane.

With respect to improving the accuracy by placing a small controlled spin on the ball,I am not sure. You still need only a little friction, or a little asymmetric leakage of gas around the ball to alter its spin axis. If the alteration happened to be along the same axis as the controlled spin the result would be to either speed up the spin, or reduce it. This still leads to dispersion in the trajectory, and a broader shot pattern. Despite this, the controlled spin has momentum, and I think a ball with a controlled spin might therefore resist a change in its spin axis to some extent. On the other hand, many times I have read complaints from people that the accuracy of a flatline barrel is worse than a good straight barrel. At face value, this field observation would tend to negate the hypothesis. However, the preception of inaccuracy could be related to not holding the gun perfectly vertical as has been discussed here. Another possibility is that people can just notice a wayward spin much easier because of the extra distance.

[Redkey]

I stumbled across your website a couple months ago... was meaning to shoot you an email to say hi and comment on your page.. never got around to it though.

so...

Hi

I like your web page. I had a good laugh at your paintball weight studies... I wonder how many people know the difference between mean and median, not to mention the 95% (three sigma?) confidence level. Any plans for future testing?

Later
Geo

[bryan]

I dont know much about the magnus effect, but i do know that a knuckleball goes crazy in flight. Assuming that a nylon ball was not spinning at all, would it not act in the same way as a knuckleball? How much did the nylon ball spin while in flight compared to a regular paintball. If the spin is comparable then i may be way off but i would think that a nylon ball with no seam would not have as much spin as a paintball with dimples/flatspots/seams.

[[5x5]]

Redkey,
I needed the data on paintball dimensions and weights for my calculations. Once I started measuring and really saw how non round a paintball could be, I realized that a portion of our problems with accuracy must be tied to those odd shapes and seams. It was also one of the few times we had more than one type of paintball around. You obviously can image how boring it was sitting there with a micrometer trying to measure the diameters. Another reason for actually putting the study on the web was that I realized that not a lot of people have balances with 10 microgram accuracy available to them. No plans to do any more studies.

[Redkey]

Here are some measurements I made. Min of 20 balls were weighed for each paint type. Yes, I know, 0.1 mg resolution is overkill. I also have some seam and pole crush load data around here somewhere.

<img src = "http://www.cnw.com/~pavlov/ballweights.jpg" >

[hitech]

Welcome [5x5]. Glad to see you are still interested in things like this. Interesting discussion, isn't it? Hopefully Tom will release more data and you can contribute more. Thanks for checking us out.

Larry (Hitech) De La Briandais

[Paladin]

Originally posted by ezrunner
When fired by a human, all shot groups are a donut. The shooter
with the smallest donut wins.

Observationally, paint behaves the same, this is due to the
natural mechanics of the body.

Question: AGD/Tom.. or Glenn,

"Does a paintball marker, when held in a fixed mechanism, exhibit
this same tendency, or is there a pattern grouping that is somewhat
uniform over a reasonably large sample set?"

-rob

Yes, shooting from a firm and fixed hold on the barrel generates doughnut shaped shot patterns. The less spin the ball has when it enters the air stream, the smaller the doughnut.
If the balls leave the barrel with the seem either directly in line with or directly across the line of flight, the shot pattern tends to be more lineal in nature.

[hitech]

Originally posted by ezrunner
When fired by a human, all shot groups are a donut..."Does a paintball marker, when held in a fixed mechanism, exhibit this same tendency, or is there a pattern grouping that is somewhat
uniform over a reasonably large sample set?"


Here are some shot patterns that Tom posted:

http://www.automags.org/~TomAGD/spindata/shotpaterns2_lg.jpg
http://www.automags.org/~TomAGD/spindata/shotpaterns_lg.jpg

[ezrunner]

hitech:

Those pics are just the ticket. It seems that there is a central grouping in each of the pictures, just below a donut of sorts.

Now, to me it suggests that the paint is grouping in a certain area as those balls left the barrel in the same manner (it seam/etc).

The others seem to be fliers from various mechanical factors.

I do not think that paint "spins" or that there is some magic force.

I am very likely wrong, but I think we are best off with a good,
double regulated air source, and a consistent paint with a tight barrel to paint match.

After exams I plan to do some rudimentary testing with several markers (electros mags and cockers).

We may even toss in a spyder or two.

-rob

[AGD]

Originally posted by bryan
I dont know much about the magnus effect, but i do know that a knuckleball goes crazy in flight.

Bryan,

Ah, I see you have brought up the point about a force we have not discussed in detail yet!! Bravo!! Let's see, mysterious force "X" affects the paintball randomy in flight, knuckleball effect happens randomly in flight....

Could there be ANY connection? I'm just not sure....I have to wait and see how the forum examines this.

AGD

[Crimson_Turkey]

*Edit*Why post when under the influence?*Edit*

Ok, I'll shut up now.

[madgoat33]

I was reading the original post and i completly oppose the statement the ball distorts as it is coming out of the barrel. Not only have tests been performed that show this but it just makes more sense to me that the ball stays round. The main one being the fact in order for a round object to get flat on one side it must increase in size somewhere. So it would in turn be like a basket ball with diameter of 14 inchs gets flat on one side and then the diameter of it one way will be >14. Obviously if this happened the ball would become too big for the bore of the barrel so in reality u wouldn't want a perfect paint to bore match you would want a paint too small and it has been proven that that is simply not the case. This has been tested by me. I used paint that was too small in my barrel and chopped every 20-25 balls then when i got paint the correct size I chopped 1 in half a case.

[hitech]

[5x5] asked some questions in his long post. I wanted to make sure they were not "lost" and was hoping they would be answered. So, here goes:

1. I am having a problem understanding the 114 data particularly the 114side image. Tom indicates that the distance was 60 ft for the data shown, but based on the distances shown and the distances between strobe shots mentioned in another photo, the distances come out closer to 88 inches. What am I missing?

AGD: I have not looked up the actual dimensions. The actual layout of the test range was changes several times and it would take a lot of looking to figure it out right now. It isnt 88 inches its more like 60 feet with the first strobes at the barrel and the second set 2/3rds down range.

2. Did all shots show the balls spinning or were there a large fraction that did not spin at all? I guess I would expect that all balls would have some spin but with a low average spin velocity, under 5K.

AGD: most were under 5k and a small percentage had no spin.

Several questions come up as I contemplate the data; please don't take them as a harangue.

3. Are air currents possible?
AGD: NO, the tests were in a temp controlled room inside a bigger building.

4. Were there any attempts to look for trends in shot pattern versus shot number?
AGD: No, each shot was a single shot, not part of a string.

5. What was the distance of the target from the muzzle and was the target center perfectly collinear with the barrel axis?
AGD: about 60 feet and the barrel was laser aligned to the string and the target.

6. Also what is the scaling?
AGD: The ball circles represent the actual ball size.

7. Are the circles accurate shadow representations of a paintball diameter? The reason I ask the latter three questions is because this gives me a way to possibly cross check the accuracy of my trajectory calculator under definitely controlled conditions.
AGD: Yes.

[Aegis]

Pardon me for butting in, I'm a paintball newbie. I am also a tinkerer and reloader for varmint rifles. One thing that struck me in this thread was this comment from AGD:

"Yes BC can affect things in flight. Problem is that all spheres have the same drag coefficient with is something like .7 or .8. The nylon balls being perfectly round to better than 1000th of and inch and missing the seam should fly straight and true but they don't. In fact the shot group for nylon balls is hard to differentiate from regular paint."

If a concentric nylon ball doesn't shoot better than a paintball, and you can't reliably spin paintballs, should we look elsewhere for accuracy?

One thing that I have yet to see in ANY discussion on any forum is reference to the crown of the barrel. I shoot for accuracy with anything from a .17 hornet to a 6BR and I can state without a doubt that the condition of my barrel crown is vital to accuracy, due to the effect that the expanding gases can have on the departing bullet. If that is true for a bullet leaving the muzzle at >4000FPS, I would think that a paintball at <300 FPS would be affected greatly.

Think about it - the gases are expanding much faster than the paintball once the ball exits the barrel. In a rifle, the burning powder is expanding at 15KFPS, while the bullet is moving at around 1/5 of that velocity. I don't know the velocity of expanding HPA or CO2, but it HAS to be faster than 300FPS. That means that the paintball is exposed to a very volatile airstream at the most important moment - when it leaves the muzzle.

I guess my point is that there are a lot of factors in markers that can be addressed to improve accuracy before ball spin. We "sweet-spot" triggers, who has actually tested their gun to determine where the VELOCITY sweet spot is? In a rifle, the difference of .1 grain of powder can reduce a group by 50%.

Or, I could be talking out of my hat, in which case I apologize for my intrusion on Deep Blue. I just bought a used Automag classic - does that get me in the club?

[Rust]

aegis has several very good points that many people over look. but, then again, thats also why most barrels these days have some sort of porting. another factor is that the muzzle of most paintball barrels is very thin walled, where as your .17 is probably sporting a barrel .750+" and has a much larger surface to use for gas deflection. i've thought about trying an 11 or 90 degree target crown, but never bothered too as i simply dont have the means for performing an accurate/deffinative test. i'll try it on my blazer next time i've got a chance to chop up some barrels, and see if i cant rig up some sort of vise to shoot out of, or get a good rest together.
as for velocity sweet spotting it probably varies so greatly with paint changes that it would be really hard to work with. a markers valving should be able to release a pretty consistant volume of air if you have a good set up, which, just like powder charge will affect how a projectile is launched, but the variance in ball size and weight would force you to reset your pressure and velocity for every batch of paint. or you could get really hard core and sit around the house before you play weighing and sizing each ball to make sure they will all fly the same. also, you may find that your sweet spot is either to fast for same play, or slow to the point that what you gain in accuracy you loose in range. the 6br is a good example of that, very very accurate, but traveling at a slow speed compared to more popular varmint rounds. sorry to throw a book at you guys, but he's right, a consistant projectile launch is usually much more important than what said projectile is doing down range. (at least for the distances we work with, its hard to keyhole a paintball)

[Paladin]

For starters; I think that the reason that my powdered barrel tests showed different results than what seems to be expected is that I was doing the tests using CO2 and not compressed air. The higher density CO2 has much different propulsion characteristics. When I did the same tests using compressed air and with the same regulator settings, the velocity went down about 10% and the streaks in the powder did not indicate a full perimeter wipe. What it did demonstrate was that there was less upset to the ball and the width of the marks narrowed back down to thin lines quicker than when using CO2. Lost a few points in velocity consistency as well.
Now, it has been said here that compressed air is a "better" propellent for paintballs but I'm going to need someone to prove that to me.

Also:
"Originally posted by AGD

If a barrel did it's job perfectly every time and 100% of the spread was due to external forces then it would be a waste of time to try and improve it. "

I seem to recall that this was predicated on the consideration of barrels that are "sized and honed to perfection" but I cannot see that "perfection" has yet been defined in the context of this thread. Are we assuming that a straight bore of any given size, with an absolute mirror finish is perfect for launching paintballs ? What if something else apears to yeild better results? Certainly, there are several other factors besides bore size, finish and length involved in giving a paintball its best opportunity to go where it is aimed.

Again from AGD
"Importantly we see it overcoming the slower spin WHILE THE BALL IS IN FLIGHT. This is the next point of debate so I will start. If the X force happened in the barrel or say a foot from it, then the spin no matter how small should affect the flight path in a direction consistent with the axis of rotation as it flies down range. To state it another way, if the ball in flight was not being affected by X then spin should be the major factor causing deviation. From another point of view, the force X has to be happening while the ball is in flight because in 114 it pushes the ball in two different directions while its going down range. So in order to argue against this you have to explain how something in the gun or barrel can affect the ball down range as we see in 114. The one thing the barrel can do is impart spin to the ball and that affects it down range but since we have that under control you have to come up with something else. Fire away. "

There is nothing at all mysterious about the forces that act on a paintball in flight. (even though I don't know how to explain it in scientific terms) It is all a matter of how the ball is presented to the airstream and the results of air flow around a not perfectly round object. The only "random" element in the equation is the projectile itself and the speed and direction of the rotation that it is given or allowed to have when in-flight forces take over. A perfectly round ball would be some improvement but makining them heavier to increase on the ballistic coefficient would show greater improvement. "BC" is a calculated description of a projectile's ability to sustain its energy and resist deflection from external forces. A calculation for the BC of a projectile is based on size, shape, weight and velocity. With the factors being established as "multipliers", the variables don't just add up, they multiply up to significant differences in the outcome of the shot. Aero-dynamics is only part of a BC #.(I've got some heavy teflon balls that will litterally drive tacks at 300 fps and higher, when a lighter weight nylon or delrin ball shows very eratic flight patterns at similar velocities.) I've also seen instances where a gun will shoot paintballs very straight at up to -lets say- 280 fps and the size of the shot group will consistently get larger as velocity increases and then at some point in excess of 400 fps the shot pattern decreases sharply again. I think I know what is going on but I haven't the slightest clue of how to write a formula to demonstrate or prove it.

In short, what goes on down range is greatly influenced by what happens inside the barrel as well as shortly after the ball leaves the barrel. A ball spinning slowly while in flight seems to be subject to a planing effect as the seem and size differential is presented to the air stream at different angles.
Boundry layer and other aero-dynamics stuff applies. At higher rpm's centrifugal forces have to be factored in.

[ES13Raven]

Originally posted by AGD
Ok back to the battle,
Glenn, I am purposely leaving the valving air blast thing out of this becasue it's one of the things on the table to be examined at the end.Time to examine this yet?

[AGD]

Originally posted by Paladin
There is nothing at all mysterious about the forces that act on a paintball in flight. (even though I don't know how to explain it in scientific terms)

Glen,

The discussion so far has lead to the knowledge that spin does not correlate to where the ball hits down range. The fact that the ball changes direction in mid flight indicates that something, "X", is affecting the ball in flight. If you want to say that the barrel is causing this you have to make a reasonable argument on what it is. We all know the barrel can induce spin but this has been discounted in this case study.

Your claim of seam problems is discounted because shooting round nylon balls of the same weight shows no improvement in accuracy.

We were proceeding down a path that was getting somewhere but we seemed to have stalled as we got closer to the truth.

AGD

[Vegeta]

has anyone thought about turbulence caused by air resistance on certain surfaced of the ball? What if those abnormal flight paths were caused by some spots of the paintball being more oily/dry than others? The air would flow over the smooth oily surfaces batter than the dry surfaces, which could, mixed with a slight offset spin from that knuckle ball throw, put the ball off course. THe nylon balls should ot have this effect though since htey are not oilly in any way.. so could it be the barrel? Maybe parts of the barrel have an oily residue where others do not.

All I'm saying is that maybe we are not looking at every variable here.

What about hte surface of hte ball AFTEr it leaves the barrel? maybe rubing against the barrel in certain spots while exiting caused the ball to have a slight dry spot from friction or in the case of geletain balls.. a slight flat spot.. causeing that spot to effect the flight path.


Just ideas.

[bryan]

I would tend to say that the oilyness/condition of the surface of the paintball, except in extreme cases, has little to do with the issue since nylon balls, which hopefully were not greasy, did not show any improvement over a normal, oily paintball. However, making a nylon ball that had one half of it rough, and the other a mirror finish could prove interesting. I think that oily spots in the barrel could definitely have an affect on accuracy. My best analogy is bowling. When you bowl the first half of the lane is slick, and oiled, but when it reaches the other half of the lane, the ball curves in whatever direction you spun it. Thats how the pro bowlers get those cool looking hooks on their balls. Testing for that in a barrel should be easy since you could simply wash a barrel really well, or blow some oil through it after oiling a gun.

[jinxed]

I don't know if I have much to add, but I have used backspin bolts for the last 10 years. I bought a bolt for the Cocker and VM the second they came out in 92 so I have some experience.

First, when they both have the same barrels, paintball and air, they seemed to shoot exactly the same. Granted, any spin added by the open-bolt design was probobly negated by the fast backspin.

When using a .700 barrel, they would shoot flat for a 150 feet or so, then usually curve left/up/right/down in some random way. I don't know if this meant the spin was destabilizing? Because of this, I don't think backspin bolts/barrels increase effective range, only maximum range.

Also, if using a standard .688-.694 barrel, the ball would curve randomly up/down/left/right as soon as it left the barrel. Obviously friction was effecting the spin somehow. You could still use a .692 barrel if it was cut down to 2-3".
In fact, I had barrels of various length that I could effectively control the backspin and FPS. (Which is important if I play at a field with a lower FPS limit).

Most people tell me they find backspin bolts/barrels useless for indoor/speedball/etc paintball, and only use them for long range woods ball...
In my experience, I've found the reverse is true. They don't get you any more effective range, only a flat shot, so I would just use mine for indoor/village/speedball style paintball where I could shoot through a series of windows/bunkers without having to 'curve' it in.

As to the knuckle ball effect- That refers to the ability of a 'rough spinning object' to greatly reduce its drag. That is why the seams and dimples on base/golf balls can fly faster if they are spinning, but only if they are moving at a specific speed. I thought the magic number for a seamless paintball is 600-800fps? Adding seams and dimples lowers that number, but how is that measurable? I suppose if we gradually inceased the fps on a paintball, we would probobly find a speed in which the range suddenly jumped, but the backspin would have to be kept at a constant to keep it from curving upward...

Nick

[s.centralpirate]

The fact that the ball changes direction in mid flight indicates that something, "X", is affecting the ball in flight.

Well, i usally don't tend to get involved in these types of discussions, but since this thread was mentioned on another forum and i am sitting here w/ nothing to do but read today i though i would flex my brain on this topic.

COULD force "X" be caused by a shift in the center of gravity within the paintball itself? since paintballs are liquid filled and the contents prone to separation / settlment over a undetermined period of time.

SINCE every other varible seems to have been accounted for. Inconstencies of the PBs in question i.e. seams, dimples,ectera. ball spin, atmospheric conditions, air sources co2 or hpa, barrel movement, and so on.....

It would be reasonable to assume after elimating all of these EXTERNAL forces that what else would be left to be accounted for....the internal forces of the fill being " stirred" while in flight due to ball spin. Since each ball being fired have its own unique properties( size, weight, shape,fill constency, and "x-factor")....

Anyway thats my best guess

:confused:

[ph0b]

Originally posted by s.centralpirate
... COULD force "X" be caused by a shift in the center of gravity within the paintball itself? since paintballs are liquid filled and the contents prone to separation / settlment over a undetermined period of time. ...
No, because:

Originally posted by AGD
... In fact the shot group for nylon balls is hard to differentiate from regular paint. ...

[hitech]

The mysterious "X" force appears to be the von Karman Vortex Street phenomenon. This phenomenon causes an oscillating turbulent wake behind a cylinder (or sphere). An oscillating wake would most certainly cause a knuckle ball effect. I have not been able to find a good explanation of why this occurs, but it appears to be a well-known phenomenon, at least among fluid dynamics guys. ;) Here are a couple of links that demonstrate this phenomenon:

http://www.csa.ru/~ignatiev/examples_2d_1.html
http://kuwahara.isas.ac.jp/KARMAN/KR1.HTM

Added: Another example of this phenomenon is the vibration of a taut wire as air flows past it. If/when the oscillation frequency of the wake matches the resonant frequency of the wire (the frequency the wire vibrates at) the wire vibrates. We have all seen (heard) this before.

Okay, it appears that I can't find an explanation of why this occurs because no one is sure. Here are some theories:

http://www.pcnet.com/~jdutka/thesis/thesis1.html

[Paladin]

Originally posted by Paladin
There is nothing at all mysterious about the forces that act on a paintball in flight. (even though I don't know how to explain it in scientific terms)
--------------------------------------------------------------------------------
OK, now HiTech has labeled it for us but I tend to think of it as an effect rather than a "force". The actual force involed is air pressure and the way it varies around the projectile as the current flow behind the ball "oscilates".



Originally posted by AGD


Glen,

The discussion so far has lead to the knowledge that spin does not correlate to where the ball hits down range.


Well, you have not yet convince me of that. So far, all that I have seen in that regard is an agreement that a high speed spin (like what is generated by the Flatline barrel) will overcome or diminish the effect of "X". There is a large gap between the high speed rotation and no rotation at all that seems to have been overlooked; or in this case, "discounted". I'm quite convinced that the rate of rotation that the ball has when it leaves the barrel does in fact have an effect on the ball in flight but I can only argue my personal observations. In short, the less rotation, the tighter the shot group.


Originally posted by AGD


The fact that the ball changes direction in mid flight indicates that something, "X", is affecting the ball in flight. If you want to say that the barrel is causing this you have to make a reasonable argument on what it is. We all know the barrel can induce spin but this has been discounted in this case study.


I've not said that I think the barrel causes "X"; just that "X" is not the only factor involved in the flight of the ball.
Certainly "X" affects a ball in flight but the properties of the ball and its movement after the gun is done with it have an influence on the magnitude of the force created by "X". That is what I was eluding to when I mentioned having followed various objects in freefall and had the opportunity to witness first hand and close up, the variable effects of air flow over an object.



Originally posted by AGD
Your claim of seam problems is discounted because shooting round nylon balls of the same weight shows no improvement in accuracy.



The seam itself is far less of an influence than the not -round shape that influences the shape and frequency of the wake behind the ball. Pressure builds and falls in varying degrees relative to the shape of the object and the speed of its rotation. In freefall, "X" apears to have more influence on the line of flight of a true sphere than on something like a paintball and rigid objects are affected differently than flexible ones are.



Originally posted by AGD

We were proceeding down a path that was getting somewhere but we seemed to have stalled as we got closer to the truth.

AGD

Actually, I'm still not sure just where it is we are going with this.
What is it that the truth is going to conclude ?

[hitech]

Glenn,
are you aware of the phenomenon know as vortex shedding or the von Karman Vortex Street? I believe this is the major problem with paintball accuracy. It causes an oscillating wake behind a cylinder (or sphere). Here is an example of that wake:

[ES13Raven]

That definitely looks like it would cause the ball to "S" curve....

[Paladin]

Originally posted by hitech
Glenn,
are you aware of the phenomenon know as vortex shedding or the von Karman Vortex Street? I believe this is the major problem with paintball accuracy. It causes an oscillating wake behind a cylinder (or sphere). Here is an example of that wake:

Yes, in fact I am aware of and somewhat familiar with the phenomenon. I just didn't know the name for it or even how to describe what I do know about it. I learned much about objects in flight about 30 years ago, while trying to follow or catch things in freefall at velocities very similar to firing paintballs. Alas, I have only emperical obsevations to work with.

[Paladin]

Originally posted by hitech
Glenn,
are you aware of the phenomenon know as vortex shedding or the von Karman Vortex Street? I believe this is the major problem with paintball accuracy. It causes an oscillating wake behind a cylinder (or sphere). Here is an example of that wake:

Yes, in fact I am aware of and somewhat familiar with the phenomenon. I just didn't know the name for it or even how to describe what I do know about it. I learned much about objects in flight about 30 years ago, while trying to follow or catch things in freefall at velocities very similar to firing paintballs. Alas, I have only emperical obsevations to work with but I believe that the more stable the object is when flight begins, the less drastic the results of the oscillating wake/vortex.

[Paladin]

Originally posted by hitech
Glenn,
are you aware of the phenomenon know as vortex shedding or the von Karman Vortex Street? I believe this is the major problem with paintball accuracy. It causes an oscillating wake behind a cylinder (or sphere). Here is an example of that wake:

In the attached images, what does the "R=xx" reference indicate ??

[hitech]

Originally posted by Paladin
Yes, in fact I am aware of and somewhat familiar with the phenomenon...Alas, I have only empirical observations to work with but I believe that the more stable the object is when flight begins, the less drastic the results of the oscillating wake/vortex.

From what I have been able to read it has to do with the reynolds number (in our case, the fps). I even found an equation that predicted the effect. All the testing I have found was for stable objects. There are even pictures of the effect occurring in the wind wake of an island. Based on all the flow patterns I have looked at (the internet is great for find this kind of thing, search for "Karman Vortex") it would appear that this phenomenon whould have a large effect on a paintballs trajectory.

Just for fun, here is a picture of the vortex shedding around an island (the bottom is a 3d view, use a red lens over your left eye).

[ezrunner]

does the positioning and posible
movement of the seam of the ball
affect these patterns of airflow?

In hull designs (boats) there is
much attention paid to these small
details, are we seeing the same
thing?

i.e., if the ball is in flight
and turbulence is being induced
as air flows over the seam, and
that turbulence changes as the
ball is rotated in response to
the turbulence.


-rob

[hitech]

Originally posted by Paladin
In the attached images, what does the "R=xx" reference indicate ??

That is the reynolds number. I don't know how to calculate it. However someone here said at 280 fps it is ~ 10^5. It is a function of speed, so as the paintball slowed the number would decrease. I think the effect would be more apparent "down range" as the paintball slowed.

[AGD]

Hitech....those pictures (falling to knees).....ARE BEAUTIFULL!.....(tears come to eyes)..we have arrived at the altar...

AGD

[manike]

How's about an animation of this effect :D

http://www.iihr.uiowa.edu/projects/low_reynolds/xyxz.gif

Apparently...


This animation shows the shedding vortical structures at Re = 300 computed using Jeong and Hussain's lambda-2 method. Along with the hairpin vortices revealed by the numerical streaklines, oppositely-oriented induced hairpins can be observed shedding from the sphere.

You can imagine how the effect of this would cause the ball to follow that 's' shaped path.

manike

[bjjb99]

I've been reading up a bit about how the Reynolds number is calculated, and I figured I'd toss in a basic formula [ref. 1]:

Re = r * d * v / u, where

r is the radius of the sphere in question (could be diameter... there's some dispute over this)
d is the density of air
v is the velocity of the sphere relative to the air, and
u is the viscosity of air

For our paintball case,

r = 0.34 inches = 8.64x10-3 meters
v = 280 fps = 85.3 m/s
d = 1.229 kg/m^3 (air density at sea level, according to a NASA website [ref. 2])
u = 1.73x10-5 N-s/m^2 (air viscosity at sea level, from same NASA site as air density value)

Plugging in our paintball-related values gives us a Reynolds number of right around 52000 (or twice that if the paintball's diameter is supposed to be used instead of its radius). The highest Reynolds number in the photograph presented was Re = 161, and the animated model presented used a Reynolds number of Re = 300.

I am leery about extrapolating behavior seen at these Reynolds number values up into the regime occupied by a paintball moving at 280 fps. If my constants and Reynolds number forumla are reasonably accurate, then an Re = 300 paintball would be moving at around 1.6 fps. That's two full orders of magnitude we're extrapolating over here, and it makes me nervous. :)

If we can get our hands on some Re = 25000 or higher pictures, I'd be more inclined to believe that Karman vortices were a major contributor to the paintball's behavior in flight. As it stands now, I remain at least somewhat skeptical.

BJJB

References:
[1] - http://www.aero.ufl.edu/~uhk/STOKES2.pdf
[2] - http://www.grc.nasa.gov/WWW/K-12/airplane/airprop.html

[s.centralpirate]

Well... I'm no scientist, but i would have to agree with bjjb99 to some extent about the Reynolds number in relation to the aerodyamics of the PB in question.

It was my impression that the discussion was relating to the Paintball that, out of a series of shots would, for no explainable reason change directions in mid flight. Now I ask is did this same change of direction occur with the nylon balls as well as the paintballs in the test firing?
If so then the answer would point towards a issue of aerodynamics to a sphere in flight. If that were so I would rest my case.

It is only my obervations on the paintball field that lead me to this conclusion. that all paintballs are not created equal, no ball is without its own characteristics as I said earlier...To what final conclusion this thread takes toward the determation of "x" a person must discount all other factors...THEN account for the varible characterists of each ball fired.

But then thats what we call science...

Play on....

[ezrunner]

any reynolds affect would be more pronounced on a paintball
than say a black powder ball. This is because of the surface
area/weight ratio, or desity.

That makes things interesting, I know that for distance shooting
we load boat tail bullets which have the back edge of the bullet
tapered to decrease turbulence behind the projectile.

......<get's calculator>.......
well, I thought I would have free time this week, guess not.

-rob

[hitech]

Originally posted by bjjb99
I am leery about extrapolating behavior seen at these Reynolds number values up into the regime occupied by a paintball moving at 280 fps. If my constants and Reynolds number forumla are reasonably accurate, then an Re = 300 paintball would be moving at around 1.6 fps. That's two full orders of magnitude we're extrapolating over here, and it makes me nervous. :)


I read that the effect continued well past those numbers. I think it's just easier to photograph at the slower speeds. I'll try to find the information and post it (with links).

Okay, I found it. Everything I have posted has been about flows past a cylinder. Here is what they say about spheres. It appears that the cross over point from minor to major influence is at approximately the reynolds numbers paintballs fly at.

Flow Past a Sphere

Wakes behind spheres are observed to be steady for Reynolds numbers below 300-400. Above this limit (which also depends on the surface finish) vortices break off and are periodically released to form vortex loops that are connected like in a chain.

At Re above 6000 the vortex shedding is very periodic, with Strouhal number ranging from 0.125 to 0.20, the largest figure being a limit at high Reynolds numbers (Achenbach, 1974). Similar wakes can be observed behind particles falling in water. Effects of the surface geometry have been studied for the evaluation of the aerodynamic performances of sports balls (Metha, 1985)

Here is the link that includes the above text:

http://www.aerodyn.org/Unsteady/unsteady.html

[bjjb99]

*chuckle* In the time between my reading your initial statement about finding and posting the link and your actually posting the link, I happened across the very same link! :)

I'll agree that the Karman vortex effect does occur at high Reynolds numbers. As part of the link I found while you were posting it, they mention something called the Strouhal number. I dug into this a bit, and it seems that the vortex shedding frequency can be determined from this number, the object's diameter, and the object's velocity. Here's only one of several links I found. This one in particular has Strouhal numbers in the Re ~ 10^5 range, so it worked out nicely with our paintball studies.

http://www.enseeiht.fr/hmf/travaux/CD0102/travaux/optmfn/gpfmho/01-02/grp6/pages/strouhal.htm

For a 68 caliber paintball moving at 280 fps, I get a vortex shedding frequency of about 940 hertz. I don't know if that means one vortex every 1/940th of a second, or one vortex pair per 1/940th of a second. This would mean that we have a vortex (or vortex pair) every 4 inches or so as the ball heads downrange. Given that the vortex shedding is "very periodic" at high Reynolds numbers, wouldn't this result in a purely oscillatory motion instead of what Tom is seeing, namely a strong divergence in one direction near the end of a ball's travel? Even near the end of its flight, a paintball that has enough energy to break on a target still has a pretty darn high Reynolds number.

On another note ;)

Since vortex shedding alters the pressure distribution of the air surrounding it, do you think this shedding would be audible? Do you think that might be the characteristic "whoosh" sound you hear when a paintball flys past your head? On a lark, I played a 940 hertz pure tone using Mathematica, and it sounds fairly similar to the fundamental tone you hear when a paintball goes by... something to think about, I suppose. :)

BJJB

[hitech]

Originally posted by bjjb99
Given that the vortex shedding is "very periodic" at high Reynolds numbers, wouldn't this result in a purely oscillatory motion instead of what Tom is seeing, namely a strong divergence in one direction near the end of a ball's travel? Even near the end of its flight, a paintball that has enough energy to break on a target still has a pretty darn high Reynolds number.

I'm thinking that very periodic could easily mean significantly more vortices are shed from one area of the sphere that the other. It would follow that the sphere would then change course. This would alter the angle of attack and maybe that could further alter things. As you have probably guessed, I don't know. ;) However, it sure seems feasible to me.


Originally posted by bjjb99
For a 68 caliber paintball moving at 280 fps, I get a vortex shedding frequency of about 940 hertz...This would mean that we have a vortex (or vortex pair) every 4 inches or so as the ball heads downrange. Since vortex shedding alters the pressure distribution of the air surrounding it, do you think this shedding would be audible?...On a lark, I played a 940 hertz pure tone using Mathematica, and it sounds fairly similar to the fundamental tone you hear when a paintball goes by your head...

Very interesting. Something has to be causing the vibrations that cause that noise. :D

[AGD]

YES!!!!! YESSSS!!!! I LOVE YOU GUYS!!!!

We have arrived!! I didn't think it would ever happen that players would take the time to investigate the science behind paintball flight to its logical conclusion but the magic of AO comes through.

YES vortex shedding happens in the R numbers we are talking about.

YES we can verify this because paintballs make a buzzing sound when they go by.

YES this happens with perfectly round nylon balls too.

Now for the last step. BJ mentioned that well maybe its just oscillating so it really doesnt have an effect on accuracy. Here is the last thing to look up. Its called "The drunken mans walk". Its a statistical model that fits what we are talking about here to a tee. Go get it!!

A very excited,

AGD

[joeyjoe367]

Wow, I just read this thread, from page 3 (yeah, I skimmed a bit) and this is just incredible. Only on AO could you see this kind of thing. Absolutly amazing.

It's awesome that we've found out (apparantly TK's always known) about this "reynolds number" but more importantly (to me anyway ;) ) how do we combat this? or Can we?

Is the future of paintball going to see differantly shaped paintballs?

[bjjb99]

Originally posted by AGD
YES!!!!! YESSSS!!!! I LOVE YOU GUYS!!!!


Awwww... shucks. ;)


Originally posted by AGD


YES vortex shedding happens in the R numbers we are talking about.

YES we can verify this because paintballs make a buzzing sound when they go by.

YES this happens with perfectly round nylon balls too.

Now for the last step. BJ mentioned that well maybe its just oscillating so it really doesnt have an effect on accuracy. Here is the last thing to look up. Its called "The drunken mans walk". Its a statistical model that fits what we are talking about here to a tee. Go get it!!


I'm already familiar with random walks of many sorts, and I would agree that a series of random "kicks" perpendicular to the ball's trajectory would result in a random walk sort of behavior.

In a normal random walk, if the steps are of uniform length but each in a random direction, then the average distance between the start and end location is directly related to the square root of the number of steps taken. I cannot remember off the top of my head what happens if the steps are of both a random length and a random direction... gonna have to think on that one a bit.

For a paintball, the steps change the ball's velocity perpendicular to its trajectory... more along the lines of a random walk with random stepsize and direction.

However, to conclude that vortex shedding and a random walk are reasonable culprits for the observed inaccuracies of paintballs, we need to establish two things first:

1. The vortex shedding must be random in nature. The references I've seen so far seem to indicate that the shedding is periodic (i.e. repetitive and thus nonrandom, at least the way I interpret the term "periodic") at high Reynolds numbers.

2. The shed vortices must impart enough momentum to the ball in a direction perpendicular to the ball's trajectory to affect its flight by the amount observed at the end of the ball's travel.

Once we establish these two and can do a bit of modeling, I think we might have a nearly complete explanation of what's happening with respect to paintball accuracy. :)

Incidentally, if vortex shedding is the cause, then the shed vortices can only impart so much momentum to the ball during its flight. If the paintball is more massive (thicker/denser fills, anyone?), then that momentum would not change the ball's lateral velocity as much. Similarly, heavier balls are less sensitive air resistance and would tend to travel farther (I think... it's early and I'm operating on about 8 hours sleep for two days).

Tom, have you witnessed lighter balls having a statistically larger shot grouping than heavier balls fired at the same initial velocity?

BJJB

[confedman75]

whats the hypothesis, and conclusion? I am realy not in the mood to read 7 pages of posts.

[hitech]

Here is the definition of a random walk (I'm assuming that the "Drunken Man's Walk" is a random walk):

A random process consisting of a sequence of discrete steps of fixed length. The random thermal perturbations in a liquid are responsible for a random walk phenomenon known as Brownian motion, and the collisions of molecules in a gas are a random walk responsible for diffusion. Random walks have interesting mathematical properties that vary greatly depending on the dimension in which the walk occurs and whether it is confined to a lattice.

Here is a link that elaborates on this more:

http://mathworld.wolfram.com/RandomWalk2-Dimensional.html

It seems like a very simple concept to me. Each vortex shed would "pull" the paintball in the opposite direction that it was shed in. If they shed in random directions then the paintballs flight should follow a random walk. Tom, you never managed to photograph evidence of the vortices shedding from the paintballs, did you?

[Vegeta]

Confedman-

what this means is.. we have been looking for what this "X" force is that is making hte balls go all walkabout on us.

We find that when the Reynolds number in in this certain range or higher, vortexes are shed off of parts of the ball in that neat little chain loop fashion seen in the pics. Each one of these sheddings would pull the ball in on the opposite side. The sheddings pullign the ball here and there make for that nice unpredictable movement we all see.

Now we just must define it better.

Unfortunately I don't see any real world fix for this. It is a natural occouring thing.

I think I got all that right. That was sorta a recap for me.

[confedman75]

hmm does the walk about worst or better with thicker fill?(im guessing better). we should try like a powder ball, but not too fine since some people would have a horrible time breathing if they got hit in the mouth(throught the mask). how about a fill thats like a damp flour? muddy but not dusty.

[joeyjoe367]

I don't think it has anything to do with the fill of the paintball. It's simply a naturally occuring phenomenon that happens when you've got a non-spinning object that's traveling though the air at high speeds/reynolds numbers.

[AGD]

Ok look at these applets. They demonstrate where the ball will end up (usually off center) at the end of the random walk.

http://math.furman.edu/~dcs/java/rw.html

Lets imagine that the applet above allows you to "fire" a ball down range. If we are shooting a ball 80 feet, and we assume that the vortex gets shed and takes a "Step" every 4 inches (as proposed above) then we would get about 250 steps. This is too few to see anything in the applet but lets input 500 steps and then run and clear the program a bunch of times to see the effect.

Now notice that if you didn’t know any better (and couldn't see the small movements) the balls would look like they were CURVING away from center. Also notice that some go right down the middle. Every once and a while you get a real "flier" that curves way off. Does this look familiar??

Here is another applet that records were each ball "hits" at the end of the walk. Every hit gets recorded as a red bar that builds vertically. The red bars are distributed to the left and right of center. This is only one dimensional but you should be able to get the idea. Hit start and let it run for a while.

http://stp.clarku.edu/simulations/one-dimensional-walk.html

Once you get enough "hits" your graph will look like a bell curve. This means that MOST of your shots will be pretty close to center and you will get fewer and fewer hits the farther you get from center.

Stack up enough hits and use the gaussian button on the right to see how well your shot pattern fits the bell curve. Fits pretty good after a bunch of trials right?

Now here is the leap. The fact that it fits a bell curve means that the results are RANDOM!! The gaussian fit is a test for RANDOMNESS. Why is this so important?? After all its what you were expecting right? It’s important because if it’s random, then NOTHING IS AFFECTING IT!!! If it were the bolt, or the barrel or anything else that could improve accuracy it would not make a bell curve. Well actually the turbulence is affecting it but in a completely random way.

So lets think about it, the ball gets pushed around by the bolt, the air blast, the barrel and whatever else is in the way until it leaves the barrel. Now its alone by itself in the free air and instead of clear sailing to the target it gets viciously attacked by the “X” factor Shredding Vortices. Hundreds of times it a couple of seconds it gets pummeled mercilessly back and forth through the air. After a thorough beating it ends up on target randomly distant from the center.

Now I ask you, after this thrashing, this pinball machine of air flow, this twisting vortex tail of tormented accuracy, how does the barrel, bolt or air blast make your paintball more accurate??

AGD

[ES13Raven]

The barrel can make your shot more accurate by keeping the velocity more consistant with the proper paint/barrel match.....

[joeyjoe367]

Right, keeping velocities consisitant is the only thing that we paintballers can do in order to make our guns more accurate.

the graph that's on applet one shows where the ball would land, assuming that velocity is consistant, and that nothing else is effecting the ball's flight.

now having inconsisitant velocities is alltogether pointing the ball in a differant direction, wheter it be higher (higher velocity) or lower (lower velocities). It's like moving the graph itself around, and then re-drawing your random points.

[FooTemps]

My opinion is that the gun can't effect the paintball's accuracy besides consistency. Like joey said, the higher and lower velocities would move the target graph of the landing point. So that means it would take more steps or less steps in the random walk applet providing that it still gets pummeled by airflow at the same rate. That means the longer it flies the more chance of random movement and the shorter it flies the less chance of movement. The only problem with the shorter distance is... well... shorter distance.

[bjjb99]

Originally posted by joeyjoe367
I don't think it has anything to do with the fill of the paintball. It's simply a naturally occuring phenomenon that happens when you've got a non-spinning object that's traveling though the air at high speeds/reynolds numbers.

I think you're missing the intent of my statement. It's not that the fill somehow changes the way the air travels around the ball, it's that a denser fill (and thus a heavier ball) is more resistant to the forces resulting from the way air travels around it. Since I don't know how much brand-to-brand (or batch-to-batch) variance there is in paintball fill density, I can't conclude that this is a signficant contributor to accuracy.

BJJB

[joeyjoe367]

Ah, I see. a denser fill/heavier ball would be less effected by the vortex shredding since it carries more momentum than a lighter ball.

I believe that there are regulations concerning the weight of a paintball. A heavier ball packs a bigger punch at 300 fps than a *EDIT*lighter*EDIT* ball, so safety concerns are there.

Unless you lower the speed at which you fire the ball. You might actually not lose any range since the heavier ball loses velocity slower than a lighter ball.

Hmm... How about a weighted 10 gram nylon ball? That could test our theory... I would be more than willing to bet that it would be more accurate.

[manike]

Last time I checked (years and years ago now...) paintballs averaged between 50 and 54 grains. I tend to use 52 grains as my average when doing calculations. They may weigh differently now?...

manike

[ES13Raven]

I think the average is about 3.2 grams.....

Some paintballs weigh A LOT less. RPS Lightning weighs 2.5 grams :eek:

Here are some weights I have found so far:

Inferno--3.27g
JT--3.19g
Flash--3.23g
Direct Hit--3.26g
PMI--3.21g
Marbalizer--3.25g
Lightning--2.56g (Now RPS Mercury)
Big Ball--3.18g
All Star--3.23g
All Star Yellow--3.14g
Evil Marbs--3.22g
Great American Premium--3.17g

[bjjb99]

Originally posted by AGD
Ok look at these applets. They demonstrate where the ball will end up (usually off center) at the end of the random walk.

http://math.furman.edu/~dcs/java/rw.html


I could not get this one to work through the various firewalls and such... all I got was a page with some text on it but no java applet, so I wrote my own random walk using Matlab. It takes a series of one unit steps in random directions and computes the endpoint of the travel.


Originally posted by AGD
Here is another applet that records were each ball "hits" at the end of the walk. Every hit gets recorded as a red bar that builds vertically. The red bars are distributed to the left and right of center. This is only one dimensional but you should be able to get the idea. Hit start and let it run for a while.

http://stp.clarku.edu/simulations/one-dimensional-walk.html


You can't use this applet to describe the distribution of paintball hits. The behavior of a fixed stepsize position-based random walk in one dimension is not the same as a fixed stepsize position-based random walk with random direction in two dimensions. The "distance from center" distributions are nowhere near identical.

In the one dimensional case, the mean distance from center at the end of travel is equal to zero, and the standard deviation is equal to the square root of the number of steps taken. The distribution of distances from multiple trials fits a gaussian nicely.

In the two dimensional case things are quite different. Now the mean distance from center at the end of travel is equal to the square root of the number of steps taken. The standard deviation is darn near half the mean value. The distribution's shape is by no means gaussian anymore, and actually more resembles a Poisson distribution.

Additionally, a two dimensional position-based random walk is not identical to what's happening during a paintball's flight. At best it is a mapping of the ball's lateral velocity components during flight. This mapping must then be converted to the actual ball's position, which is a cumulative process.

After a bit of number crunching, it looks like the Poisson-like distribution is retained through the conversion of random walk based velocities into actual distances from the origin, but the magnitudes of the distances are much greater than for a plain positional random walk. Instead of the mean distance being around the square root of 250 (around 15.8 times the step size), the mean distance is now upwards of 1000 times the step size. In addition, the relationship between the mean distance and the number of steps taken now seems to be more quadratic in nature instead of the familiar "square root of number of steps taken".

So you're right in saying that a random series of "kicks" to the paintball during its flight will result in a randomization of the shot pattern. However the shot pattern you get from the effects of these "kicks" is not gaussian in nature, assuming the kicks are all of equal magnitude. Instead, it should be more Poisson-like than gaussian. This has the interesting effect of making the probability of hitting close to your intended point of aim very small, and giving the shot grouping a donut shape (if the Poisson distribution is sharp enough).

With respect to whether the "kicks" are randomly oriented, I still have reservations. I've yet to see a reference that explains why shed vortices would be periodic in time but random in orientation when they come off the back of the paintball. All I've seen so far is that at high Reynolds numbers the vortex shedding is periodic, and I still interpret that to mean "cyclic with respect to time and space".

BJJB

Incidentally, I created a short-lived Von Karman vortex street in my bathtub a couple of nights ago, using nothing more than my arm. Fascinating stuff... ;)

[Paladin]

Certainly, the pressure variables from a random shedding vortex is one element of the actual flight of a paintball but I think that to conclude that it is the only element involved in the size of the shot pattern on target, is really a stretch. If the hardware played no role in the event, it must then follow that any device or combination of hardware fired at the same velocities with the same batch of paint should show essentially identical shot groupings (in terms of the size of the shot group), but that is not the type of results that I've seen.
It seems to me that the calculations of the results of a single effect on a rigid sphere should not be held as the last word in predicting the flight path of a flexible and not so round projectile like a paintball. Since a paintball in flight can present both round and elliptical shapes to the airstream and at varying "angles of attack", it apears that the pressure variables in the vortex become much less random. The hardware can affect the status of the ball (relative to shape and rotation) when it enters the air stream; which in turn will influence the results or magnitude of other forces that act on the ball in flight.

[hitech]

Originally posted by bjjb99
I've yet to see a reference that explains why shed vortices would be periodic in time but random in orientation when they come off the back of the paintball. All I've seen so far is that at high Reynolds numbers the vortex shedding is periodic, and I still interpret that to mean "cyclic with respect to time and space".

I have been looking for the same evidence/explanation. However, it seems more likely that the shedding frequency is periodic and the orientation is random, at least random with respect to the previous vortex's orientation. After all, what would the orientation be? It seems that any slight difference in the air flow around the sphere would influence the shed orientation, especially with our not quite round spheres. It may not be truly random, but it doesn't seem that there is any way to predict it (the orientation).

I haven't played around with any of the applets, but I may. Or, I might write my own. The code for the walk is extremely simple, I just need to come up with a simple way to represent the results.

Man this is fun stuff. Now I know why I took physics in college just for fun. :D

[ben_JD]

If my posting this here is inappropriate, please erase.

My question may seem trite, but are the vortices shed by a paintball strong enough to influence a second paintball following along a similar path?

i.e. do vortices shed by prior paintballs further disrupt subsequent paintballs in a long string of shots (indepedent of the subsequent paintball's own vortex shedding issues)?

[bjjb99]

Originally posted by ben_JD
If my posting this here is inappropriate, please erase.

My question may seem trite, but are the vortices shed by a paintball strong enough to influence a second paintball following along a similar path?

i.e. do vortices shed by prior paintballs further disrupt subsequent paintballs in a long string of shots (indepedent of the subsequent paintball's own vortex shedding issues)?

Good question. I do know that vortices can hang around for a surprisingly long time. And I do know that wing tip vortices from aircraft can disrupt the airflow over a subsequent aircraft's wing. So I suppose it is at least possible for a paintball's vortices to affect subsequent shots.

For now, however, I think I'm going to concern myself with how the vortices affect the paintball that's doing the shedding. Can anyone point me towards a reference describing the magnitude of momentum change imparted by a shed vortex? Preferably one with big writing and lots of pretty pictures... ;)

BJJB

[bjjb99]

Originally posted by hitech


I have been looking for the same evidence/explanation. However, it seems more likely that the shedding frequency is periodic and the orientation is random, at least random with respect to the previous vortex's orientation. After all, what would the orientation be? It seems that any slight difference in the air flow around the sphere would influence the shed orientation, especially with our not quite round spheres. It may not be truly random, but it doesn't seem that there is any way to predict it (the orientation).



How about "two consecutive orientations are radially symmetric about the paintball's trajectory"? I'm not saying that we should be able to predict where the shedding occurs; rather, I'm suggesting that the shedding oscillates between a couple of distinct locations on the ball. Once the oscillation is started, it may well be tough to kick it out of such a back-and-forth mode... sort of a metastable oscillation state, if you will.



Originally posted by hitech


I haven't played around with any of the applets, but I may. Or, I might write my own. The code for the walk is extremely simple, I just need to come up with a simple way to represent the results.



What exactly are you trying to represent? A good scatter plot from multiple random walk trials is a decent way of showing where each path ends up. A histogram of "final distance from origin" data will show the distribution reasonably well. And of course there's the good old mean and standard deviation results to look at too.

Do you have access to Matlab? If so I've got random walk code already written, along with a transformation from acceleration/velocity to positional data. You can plot pretty much any variable against any other as long as the vectors/arrays are the same size.


Originally posted by hitech

Man this is fun stuff. Now I know why I took physics in college just for fun. :D

Heh. Guess I have fun for a living then. ;)

BJJB

[Vegeta]

At 300 fps, firing 10 balls per second, the paintballs are going to be 30 feet apart in the air.

What we need to do is figure out if/how the vortices in the air will spinoff and possibly cause our next shot to vary off course. The thing is, at 10 balls per second at 300 fps, yes they may be 30 feet apart which seems like alot but they are travelling at that same speed so the balls will be 0.1 seconds behind each other. Will the air turbulence from the vortices shedding hang around for 0.1 seconds? because if so, that ball behind the first is going to come through that are where the first ball shed the vortice and hit that turbulence exactly 0.1 seconds later going 300fps, and possibly shedding vertices of it's own.

I might have to make some 3d animation of this process in real-time if i have a chance... that would really convince people.

[hitech]

BJJB,
Now I see what you are getting at. Yes, it would be nice to find something that states the vortices shed randomly. I could see them oscillating and the orientation spinning, possibly back and forth.

Not I do not have Matlab, I don't even know what it is. I was thinking of writing a simple VB program. Having the program walk is easy, showing it on the screen is what I have to figure out. Simply listing the ending point with direction and distance requires math formulas I don't know. :( I may have taken physics in college, but I've never used it since. ;)

I'm sure it's not as much fun when it's work. ;)

Here is a link on the force generated. Is it any good?

http://www.eas.asu.edu/~squires/sphere_summary.html

[bjjb99]

Hitech,
Matlab is a data processing and visualization programming language. It was designed to allow rapid scripting of processing algorithms. The scripts are processed interpretively instead of being compiled, like the old interpretive BASIC programs of yesteryear. Matlab operates on matrices very quickly, allowing the user to skip having to write a bunch of nested loops.

Distance from origin is simply the Pythagorean theorem:

distance_from_origin = sqrt(X_endpoint^2 + Y_endpoint^2)

Direction would be a trigonometric exercise if you want angles instead of a vector. I used a pre-canned function called atan2... it's a four-quadrant arctangent function, covering the full 360 degrees of a circle instead of just a portion of it.

The link you listed had a nice plot of force coefficient versus some formula that I couldn't identify. I think the greatest contribution I obtained from that link was a new suite of search terms to plug into search engines. :)

BJJB

[hitech]

BJJB,

Thanks. I was thinking of using angles, but I'll rethink that. I found another site that had many formulas that were over my head. ;) I think I used the yahoo search engine, advanced search for all the words: vortex shedding sphere force. I'll see if I can find it again.

[ben_JD]

Originally posted by ben_JD
i.e. do vortices shed by prior paintballs further disrupt subsequent paintballs in a long string of shots (indepedent of the subsequent paintball's own vortex shedding issues)? This is an exaggerated model, due to the objects only being 7 diameters apart, but it is a reference point.

Animation (http://www.city.ac.uk/hydraulics/CFD/ANIMS/2c7d.html)

[hitech]

Okay, it appears that a sphere does NOT perform like a cylinder. We have been basing out arguments on cylinder experimentation, which is inaccurate. The problem is that good experimental data for sphere does not appear to exist. Here is what I found:


Based on these studies it is known that vortex shedding in the sphere wake occurs for Reynolds numbers greater than about300. As the Reynolds number is increased beyond this value the vortex shedding process goes through a series of bifurcations which successively increase its complexity.

One characteristic feature of vortex shedding from cylinders is that every shedding cycle involves the formation of two counter-rotating vortices. As a result of this, the lift oscillates at the shedding frequency whereas the drag oscillates at twice the shedding frequency. Thus the cylinder wake exhibits a strong superharmonic component. In contrast vortex shedding from a sphere at low Reynolds numbers involves the formation of one vortex loop per shedding cycle and thus a significant superharmonic component does not exist. This difference between the two wakes is expected to result in a markedly different response to flow perturbations.

All of this was taken from the following link. BJJB, you might want to check out that link, there is much more there including some formulas.

http://project.seas.gwu.edu/~fsagmae/AIAA-99-3806.pdf

[hitech]

Originally posted by ben_JD
This is an exaggerated model, due to the objects only being 7 diameters apart, but it is a reference point.


Pretty interesting. It seems reasonable that at high rates of fire the turbulent wake of the previous paintball has a damping effect on the wake of the following paintball.

[joeyjoe367]

..so the faster you shoot, the more accuracy you will have?

[ben_JD]

Attempting to post a spreadsheet for you guys with Reynolds calculations.....nevermind, cannot post a .xls file. Look at this:

Reynolds Number = 92,634.533 (Re = U*(D/v))

U = Velocity (m/s) 91.44
D = Diameter (m) 0.017526
v = Viscosity 1.73E-05 (http://www.grc.nasa.gov/WWW/K-12/airplane/airprop508.html)


Check my work, please...but it looks like a paintball (.69 inches in diameter) traveling through air at sea level at 300fps will have a Reynolds number of 92,634? Seems high to me, but I am not sure. Most of the articles and theses have been focused on <800 Re.

Also, there are 3.28084 feet in every meter for those of you who (like me) often forget to convert to metric before calculating.

[edited to insert URL for viscosity]

[joeyjoe367]

Take a Screenshot, if possible of the spreadsheet and post it up. If you don't know how to do that, PM me.

[AGD]

There is some historical, anecdotal evidence for fast firing rates to produce tighter groups. In the early 90's Paintball Consumer Reports International clamped a minimag in a vise with an auto response trigger and fired full speed at a target.

The results stated that the configuration was the most accurate they had ever tested. This is just a commentary without any verification but I thought it was interesting.

I personally think there might be a chance that a drafting paintball might stay in line better. (thats why I always shoot fast :))

Lots of good stuff here guys, this is really facinating!!

AGD

[bjjb99]

Originally posted by ben_JD

Check my work, please...but it looks like a paintball (.69 inches in diameter) traveling through air at sea level at 300fps will have a Reynolds number of 92,634? Seems high to me, but I am not sure. Most of the articles and theses have been focused on <800 Re.


Yep, that's a reasonable value. The formula I used includes fluid density in the numerator (air is around 1.23 kg/m^3), so my numbers will be a bit higher than yours.

A lot of the articles deal with slow moving objects (and thus low Re values) because they are much, much eaiser to collect data from.

For those following the entire thread, I did finally conclude that the variable corresponding to the paintball's dimensions was supposed to be its diameter, not its radius. Thus my 50,000 or therabouts Reynolds number value should actually be 100,000 or therabouts. ;)

BJJB

[bjjb99]

Originally posted by hitech
Okay, it appears that a sphere does NOT perform like a cylinder. We have been basing out arguments on cylinder experimentation, which is inaccurate. The problem is that good experimental data for sphere does not appear to exist. Here is what I found:

[Snip of quoted material]

All of this was taken from the following link. BJJB, you might want to check out that link, there is much more there including some formulas.

http://project.seas.gwu.edu/~fsagmae/AIAA-99-3806.pdf

That's some good stuff there, though it is a bit beyond my understanding in places. I never did learn much about fluid dynamics. However, the 3-d plots at the end of the document were worth a zillion words towards convincing me that at high Re values the vortex shedding around a sphere becomes chaotic. It actually makes sense on a less technical level if you think of it in terms of "where on the surface can vortices be shed?"

On a cylindrical surface, you basically have two choices... a vortex can shed from the top or the bottom semicircle. If the first one sheds off the top, then it is likely that the next one will be off the bottom due to the imbalances created in the airflow. Thus, you end up with a periodic top-bottom-top-bottom... behavior. Slight vortex asymmetries along the axis parallel to the cylinder's axis still result in the vortex shedding from the same side of that cylinder. There's no way for chaotic behavior to build up.

With a spherical surface, you have a whole mess of choices as to where the vortex will shed. When one vortex sheds, any asymmetry in the way it comes off the sphere will influence where the next vortex will shed. A slight shift one side and you're no longer symmetric about the axis of flight, and the next vortex will come off at some goofy angle, and so on, leading to increasingly chaotic behavior. I see it as a physical manifestation of the "butterfly wingbeats ultimately causing a hurricane halfway around the world" concept often tossed about in studies of chaos.

I'll buy that the orientations of vortices shed from spheres at high Re values are chaotic in nature.

Now let's find a good reference for the force imparted by one of these vortices. The last one, while interesting, didn't really help me much since I don't know what I need to multiply their lateral force coefficients by to get a usable force (read "something with Newtons as its unit").

Nice work, Hitech.

BJJB

[AGD]

If you can't find a good factor to calc the lateral force due to asymetric flow then it might be possible to ball park it. If you take a snap shot of the shedding vortex as it's pealing away you will see that it has somewhat of a wing shape.

There should be laminar flow around the outside of this turbulent area causing the area encompased by the ball and vortex to flow air like a wing. In other words, the air flowing around one side of the ball travels farther than air flowing around the other side. This is how a wing creates lift.

If you can find a wing lift program that we can plug the shape into then it should give us some idea of the lifting force. If you can find a real calculation then forget this.

AGD

[Crimson_Turkey]

I'm not sure if this is still relevant but a few pages ago it was asked what the spin imparted on a ball shot from a flatline was. After haggling tippmann tech on the tippmann forums and searching every nook and crannie of the web for this I have found the answer. I belive that the flatline spins balls at around 10,000 rpms.

[confedman75]

Well if you really want to get rid of the walk you could give it a fin(pic), but it would load very well. You would have to use a clip.

Not very practical either but I haven't said anything in awhile.


Realistically it isn't that hard to fix, you can even do a test. Fill a paintball with a liquid as thin as water and fill another one with power or thick thick paint and you will see the accuracy suffers with the thin one. Whats the name of that one paint that is extremely thick? Isn't it like nelson anarchy?

[MrShield]

I have been playing paintball for a few years now, and while I haven’t shot every paintball gun out there with every barrel available, I would like to draw some conclusions from my education in physics and mathematics pertaining specifically to Newtonian mechanics. I am not an expert I am just working for my BS right now; however I will state this: isn’t a paintball moving 300fps, going to be moving the same 300fps out of an automag, a cocker, an angel, etc? The answer is a quite simple yes it is the same thing. So working off of that as a base lets look at the issue of accuracy, I believe this is a some what overstated area you all have delved into. Yes we want a paintball gun to be accurate, but is a colonial smooth bore musket accurate? Simple answer no, the ball is round hence very poor aerodynamics combined with a vacuum effect sucking on the “back” of the musket ball. I believe what we need to speak of is squeezing distance out of a paintball. I mean where does Tippman say their flatline barrel is more accurate able to snipe on people? Honestly I have never seen anywhere a statement by Tippman stating such, they do promise adding distance to a paintball by putting induced back spin upon the paintball, which we have pretty much all seen, but in reality what does this mean? Simple you may get 10ft-20ft out of a shot from a tippman flatline depending on the induced back spin, BUT think about this, when were all in High School we all took pens apart and shot them with our thumbs causing a back spin and the pen casing seemingly floated/flew a distance, but it always pitched sharply if the pen was slightly unbalanced or pushed just slightly off center. Meaning with the backspin put on by a flatline, your looking at a paintballs center axis almost always getting thrown off a dead on accurate center trajectory needed for this alleged accuracy, what we all want is range and accuracy. The above was with a solid spherical body, which a paintball is NOT, a paintball is a liquid filled nearly spherical gelatin shelled concoction. The problem is the discrepancies from paintball to paintball whether or not they were completely filled, whether the shell is more rigid than others, and the actual thickness and weight of shells and fills, not to mention size. We could easily go into material tensor dynamics of shells alone, I mean a shell being hard would be better in the fact it wouldn’t deform on air impact if it in fact does, plus any problems with being misshapen do to any other problems such as barrel flaws, gun flaws, and pressure differentials.

Alright first liquid dynamics, paint fills vary from very runny to quite viscous (hence thick fills), The more viscous filled paintballs would hold a spin better but would resist having a spin initially put on it, which would mean less spin, but a higher fill momentum, this certainly applies to completely filled paintballs with no air. Air or empty space within the paintball would cause horrendous changes within the paintball, primarily dealing with throwing off the center of gravity of the paintball hence causing them to fly over a very broad pattern. The lighter thinner fills would accept a spin more readily but would slow down rapidly, and again the empty space would cause center of mass problems. One simple solution for range and accuracy would be buy viscous fill paintballs, and weigh paintballs, find the heaviest densest brands, this will certainly help. Simple physics on that one, something with a heavier mass moving at one speed compared to a lighter object moving at an equal speed, the object with heavier mass will go farther, because it has a greater momentum. P=m*v

Gelatin shells, well what are you going to do on that one? Most players want brittle shells, which will pop on anything, the problem is this causes problems with it deforming and frankly not making it out of the barrel, we all know about that. The solution is settle for something in between. While we are on the topic, what is better for a shell? Something like RPS makes with a non sticky shell, or the generic familiar shell with the semi sticky outside? Well for one it would be more efficient to have a low coefficient of friction as far as gas savings, but would it be so significant that it would make one superior to another? Probably not, but hey it couldn’t hurt right? Lower coefficient of friction means less rubbing, meaning less chances of breaking a ball, and imparting unwanted spin hence more accuracy and possible range. Also the question of seams and this is just from experience and brands, large seams are not good, however they seem to be necessary (no pun intended) for accuracy and efficiency, they act very similar to grooving of a musket ball just in reverse. I don’t believe they cause spin directly, simple friction causes this regardless of seams or not. Truthfully everything I have ever played with has seams, some are just hidden better by another coating of some material, and however it does leave a bulging along the “equator”, which might as well be a seam. I truthfully don’t have any conclusive answers on that one, but I have never seen any difference with the many various brands and grades of paint I have shot, other than big seams in my opinion seem to cause inaccuracy.

Bolt systems, which is superior? Frankly the most simplistic, lightest weight, efficient designed system one can get on their marker. Personally I feel AGD is superior with theirs simply because it allows excellent BPS, accuracy, and efficiency. Does this negate people who own cockers, or have blow backs or the various other styles? Of course not truly what I said before is what goes 300fps out of a cocker, automag, angel, tippman, etc, is still 300FPS bottom line, is the paint and barrel going to make some of the deciding factor on range and accuracy yes, but simply if velocity is held constant and the mass of the paintball is the same then the momentum will be the same so holding the guns at the same angle in a perfectly controlled environment they will go roughly the same distance simple damned physics. Hence I am tired of everyone telling me how damned much range they have on their autococker, try this on: if you played towards the front as opposed to hiding in the back, then possibly out of the 4 hoppers of paint you have been shooting at me, maybe one would break on me for a change eh? (yes slanted personal opinion, but who else is getting tied of it?) I mean going back to momentum, certain paintballs needs more momentum then others to break and by the time your paint has allegedly gone half or all the way down the field the kinetic energy and momentum that were imparted on the ball to begin with have greatly decreased from what they were, simply meaning there is a significant chance the paintball will not break on the desired person not to mention it isn’t brute forcing the air out of it’s way towards the end of it’s trajectory. I mean we have all played on a windy day, it’s the 2nd half of the trajectory that gets greatly affected depending on how high the wind is, this is simply because the momentum has greatly decreased than in the beginning of it’s flight. This is really Newtonian Mechanics pure and simple, a force or forces is imparted upon the paintball it travels with a decent amount of friction down a tube and exits with various pressure differentials upon it and of course we aren’t talking about a rigid body here, but much closer to a semi-rigid object which literally changes with every new paintball in the barrel consistency is something one just can’t expect from paintball, just a close median.

I hope the grammar and spelling in this document aren’t too bad, I proof read 4 times and used spell checker, but no promises friends.

PS
I am not sure if anyone else has stumbled upon this, but you can make your E-mag almost into an electric RT by setting your hall sensor back as opposed to forward, and then by simply switching to "hybrid mode" you gently depress your trigger and rid the firing stud that manual mode would normally push, but infact it gently taps your finger and gives you an RT electric. Quite alot of fun to play with, very very wicked on the competition and easily maxes out the Emag rate of fire.

[hitech]

It appears that the side drag coefficients for a sphere are only an order smaller magnitude than the "forward" drag coefficient. While I will have to determine what that really means, I believe THAT IS A HUGE FORCE. If that is true it is amazing that a paintball ever hit anywhere near where it is aimed.

Added on edit: If I am reading correctly the side coefficient is 0.1.

Here is what I found:

The force on the sphere is decomposed into three components: the drag force Fd , which acts in the streamwise (x-) direction, and the two components of the side force (Fy and Fz ), which act perpendicular to the drag force. The magnitude of the side force can be computed as Fs?(Fy^2 + Fz^2). Figure 1 shows the variation of the drag Cd and side force Cs coefficients with time. The mean values of the drag coefficient for Re = 500, 650, and 1000 are computed to be 0.56, 0.52, and 0.47, respectively, and these are in very good agreement with experiments. The side-force coefficients show a complex behavior with magnitudes that are roughly an order smaller than those of the drag coefficient.

Read the full text at:
http://www.alumni.seas.gwu.edu/~fsagmae/AIAA_Apr_2002.pdf

This is over my head, but bjjb you might want to check this out. There are lots of formulas and I believe some deal with side forces. :D

http://www.eas.asu.edu/~squires/publications/aiaa04.pdf

[bjjb99]

I hereby nominate Hitech for the "most diligent information gatherer of the year" award. How in the world did you find those two .pdf reports? I gave up a couple of weeks ago after no luck in finding anything concerning lateral forces on spheres. I am impressed! :)


Originally posted by hitech
It appears that the side drag coefficients for a sphere are only an order smaller magnitude than the "forward" drag coefficient. While I will have to determine what that really means, I believe THAT IS A HUGE FORCE. If that is true it is amazing that a paintball ever hit anywhere near where it is aimed.

Added on edit: If I am reading correctly the side coefficient is 0.1.


I would give the coefficient (Cs) an average value of around 0.06, judging from figure 1 in the file AIAA_Apr_2002.pdf.

To determine what this means, you need to plug that coefficient into a drag-like force equation; here ya go:

Fs = 0.5 * rho * V^2 * Cs * A, where

Fs is the side force experienced by the paintball,
rho is the density of the air (around 1.239 kg/m^3),
V is the velocity of the air relative to the paintball (around 85.3 m/s for a 280 fps shot),
Cs is the side force coefficient (around 0.06), and
A is the cross sectional area of the paintball (around 0.000234 m^2).

Plug in the numbers, stir gently, and you get a side force of around 0.063 newtons.

What does this mean? Well, let's see what we get for a lateral acceleration resulting from this side force. F = m * a is all we need. The mass of a paintball is around 0.003 kg.

a = F/m
a = 0.063 / 0.003 = 21.1 m/s^2

21 meters per second squared for a lateral acceleration... that's over 2 g's of sideways acceleration this thing is experiencing, and that's for only one shed vortex. There are a couple/few hundred shed vortices during the flight of a paintball. About the only thing that helps us get some level of accuracy out of a paintball is that those vortices seem to be shed in random orientations.

If I get a chance this weekend, I'll see what I can do about generating a random walk using this type of data. The walk will be a random direction walk using random step sizes. We can then plug the results of that walk into a motion model to see where the paintball should fall. Rinse/repeat several times and you end up with a distribution function describing where a paintball will likely strike relative to its aim point.

BJJB

[hitech]

Originally posted by bjjb99
I hereby nominate Hitech for the "most diligent information gatherer of the year" award. How in the world did you find those two .pdf reports?

Thanks. Actually, I'm just good at skimming. You are doing all the real work. Thanks, I really wanted to know the answer to how much lateral force there is. Thanks again.

BTW, has this changed your mind on paintball barrels?

[bjjb99]

It's been so long since the beginning of this thread (and the thread that spawned this one) that I don't remember what my original thoughts re. barrels actually were. ;)

Something popped into my head while writing the above sentence...

We have determined that spin itself does not significantly affect the paintball's trajectory at the spin rates seen coming out of a normal barrel (i.e. not a barrel specifically designed to induce spin). We used something akin to Bernoulli's equations to determine the effects of spin on a paintball's trajectory. The calculated trajectory effects were significantly less than the deviations found in AGD's tests.

So a low spin rate Bernoulli-type differential airflow was not enough to screw up a paintball's flight. However, could that small amount of spin actually induce a preference in the way vortices are shed from the paintball? With no spin, vortex shedding is essentially random in orientation for spheres at these high Reynolds numbers; perhaps spin adds a bit of a bias in the vortex shedding orientation. We see that the vortices result in approximately 2 g's worth of acceleration each time one is shed, so a slight spin-induced preference in vortex orientation may cause a decrease in accuracy as compared to the no spin, pure random walk case.

Something to think about, I suppose...

BJJB

[AGD]

And here I thought this thread was dead! Hitech, man I have to hand it to you, you truely are the KING of internet searches! You should go out on the net and look for a pot of gold!

Its just incredible that we have some kind of number for the side force on the ball. This thread has gone so much farther than we took the research that I am incredibly impressed. Then again when we did the tests we didn't have the net :)

So if Bjj can come up with a random walk program we will actually have a mathematical formula that characterizes paintball accuracy! (and it doesn't include a barrel).

I posted this thread up on the main forum in hopes that the general paintball populace would read it. Again if I had any marketing sense I would have known that they really don't care. So it remains to the few to delve into the unknown in search of knowledge.........

AGD

[luke]

Again if I had any marketing sense I would have known that they really don't care.:) I don’t think that’s a fair statement. I think it’s more that the technical jargon is TOO far over everyone’s head. I am interested in the final answer though. ;)

[hitech]

Originally posted by luke
:) I don't think that's a fair statement. I think it's more that the technical jargon is TOO far over everyone's head. I am interested in the final answer though. ;)

I think it is quite fair. The only "training" I have is a Junior College Physics class. Otherwise I write computer programs for a living.

In simple terms what makes paintballs so inaccurate is 2Gs worth of laterial (side) force from what is called vortex shedding. There isn't anything a barrel CAN do to affect it. The only difference a barrel can have is more consistant velocity. That makes a small difference. That's it.

[luke]

:) hitech, That's probably more physics than 95 percent of us on AO.

When I said "I don't think that's a fair statement" I was referring to Tom's statement "they really don't care." I was implying the debate was over most of our heads, not that we didn't care. In fact, most of us do care in the FINAL ANSWER ;), we just prefer it in laymen terms.

(look at the hits on the thread, to me that implies people are reading it)

[hitech]

I guess my reasoning for it being a fair statement is that almost every day some asks what barrel is better than another. Read the answers. Everyone thinks that paint to barrel match is king. Why? Does anyone know why? Some believe that it give better velocity consistancy. Anyone ever tested this? My simple observation is that it does NOT. Freaks and other barrel kits are very popular and very expensive. And yet NO ONE knows if they even work. I'll bet they don't make even 0.5% difference. My huge bore stock emag barrel often gives the EXACT same reading over the chrono for two shots. How much more consistant can you get?

BTW, I paid $25 shipped for it. Why, probably because it was ONLY a stock barrel.

Added: 3317 views. That is a lot. At least someone is reading this. ;)

[[5x5]]

I just realized I posted a long discussion that tried to summarize some of the major views on this thread on the wrong forum. My discussion also considered an alternate mechanism for the 114 data.
The discussion is quite long, so I hate to repost it here. Please take a look at the last page of the Paintball Talk forum, Paintball Spin Physics thread. I would certainly like to hear this Group's views.

[AGD]

Luke,

Your right it probably was not fair. I just go for the summary when info in not in my hot list.

SO does everyone like Hitech's summary? 2g's lateral force randomly walking around the ball going down range?

AGD

[hitmanng]

Warning:
This is not strictly about the title of Spin physics since I think that has been solved,but it does relate to the original question of open and closed bolt and accuracy, and I think it is appropriate to discuss at this point.

Hi All,
I haven't talked about any of this since Deep blue was the fight club,we discussed reynolds factors and turbulence even back then.
I think there is a big part of the equation that is being missed. You have analysed until you are deep blue in the face what happens durring 99.5% of the paintball flight. That once you have a sphere traveling at 280fps, with the current wt of a paintball, you are going to have a certain level of randomness imparted by the turbulence behind the ball. I for one stand up and say bravo. You have explicitly defined something that we cannot change unless we play in a vaccum (deadly), or fundimentally change the paintball (not likely).
You have also effectively eliminated the need for people to worry about spin/rifleing unless the paintball gets heavier, changes shape, or we shoot it a lot faster.

I think Glenn's problem with all of this (not speaking for him of course), and mine, is that we are in an amazing way ignoring that first 12 inches of the balls travel. At this time we are not looking at the simple fluid dynamics of a ball. I am talking about what happens in the marker and in the barrel before it exits and the effect this has on the tragectory of the ball within the barrel and upon its immeadiate exit from the barrel.
This leads us away from much of Tom's data as he used the same gun and barrel for every shot and it was locked in a vise. This means he removed all of the parameters that we can effect and change to improve accuracy. All that was left was the randomness of air currents (Sorry Tom, not meaning to burst this scientific bubble, but I am the Slayer of scared cows, even yours).

So what matters the first 12 inches? Look at what we have.
1. We have a wall of force (air) accelerating the ball into the atmospheric air(no trailing currents there folks) and in some way disipating. Ok, that is why Tom created the Crown point barrel (he must have thought it mattered) and others created the ported barrel. If the barrel is ported and long enough the issues of the initial push may be eliminated (maybe longer barrels are more accurate).
2. We have the barrel. The ball is traveling through the barrel with forces places upon it. One is the force excellerating it, another is the force of the barrel pushing on a larger ball, or the force of the air passing the ball for a smaller ball.
3. We have a moving marker. I know you may think that doesn't matter but we know that a ball can ricochet around in the barrel from Tom's barrel tips and the talc test. The barel might not be perfectly straight or aligned or you may be moving it.
And doing the math:

The diameter of the paintball is 0.68 approx I am not sure of the bore of a 2 step barrel but let us assume 0.7. If the ball is going down the exact center (which I highly doubt considering manufacturing tolerences) that leaves 0.01 inch that the barrel would have to move. The ball is only in the barrel for about 0.006 seconds.
Thats 0.01 inch divided by 0.006 seconds = 1.66 inches per second. All it takes is moving your barrel 0.01 inches at a rate faster than 1.6in/sec. That is while shooting 6 bps of perfect balls out of a perfect barrel to have a hit. I think maybe it hits more than you think.

Extrapolated From: http://www.automags.org/ubb/Forum4/HTML/000019.html

So what who cares?.... Well you do. These are all elements you can change. They effect what direction the paintball is heading then it leaves the barrel.
So lets say our shot vector is one degree off straight when it leaves the barrel. At 5 feet it is 1 inch off mark, at 50 feet it is 10 inches off mark. Let us say our shot vector is at an angle of 0.5 degrees off center when it exits the barrel. That's 0.5 inch at 5 ft, and 5 inches at 50 ft, and 10 inches off mark at 100ft.

Maybe I am full of it maybe all paintballs leave all barrels and all guns at exactly the same angle. And maybe we always shoot with our gun in exactly the same position, and maybe we never move even 0.01 inch at a rate of 1.6in/sec while taking a shot.

I enjoyed the read on this post it was incredible. Keep up the good work. Now lets look at the other 0.5% of the game and maybe that will make all the difference.
Respectfully,
Your Friend
Hitmanng

[hitech]

Originally posted by AGD
Your right it probably was not fair.

I still think it was fair. Look at the results of this poll:


http://www.automags.org/forums/poll.php?s=&action=showresults&pollid=1143

[pbjosh]

Sorry for dropping out, but life an family have taken me out of this for a little bit. I want to drop a VERY quick couple of comments here-

I am completely in awe of the great numbers everybody has come up with, but I did want to reconnect with some thoughts I posted in the beginning.

There is a difference in accuracy, even on bench mounted guns, between different barrels, different markers, and different paint. If we are to acknoweldge the findings from PCRI for accuracy, we need to also acknowledge that all the guns shot different patterns, with some guns being more accurate than others. We have figured out what the ball does after is leaves the barrel, but we are still neglecting that there is something inherent in the action of a specific marker, even bench mounted, that leads to differences in accuracy. Even a clean to dirty barrel will affect the accuracy, and that IS NOT included in any of the numbers brought up yet.

The fore-ball air colume might be a culprit, but also I think we dismissed the balls rotation too quick. If I am allowed to reverse the Tippmann Flatline #'s (if they are correct) here is a quick thought.

10,000 rpm is 166 rotations per second, and at 280 fps, that is 14 ft traveled per second. 168 inches a second. Or about one revolution a inch. How does that affect the air column?

Can anybody figure out the sideload boundy affect knowing the amount the ball is held up and the amount the the ball is rotaing per second? I will clarify after some thought n my own.

Josh

[bjjb99]

Okay. I originally attempted to perform a full-blown simulation incorporating drag force to slow down the paintball, recalculation or the reynolds number at each time step, and a whole mess of other bells-n-whistles. It was a royal pain in the butt trying to keep track of all the variables, and generated results that just didn't make any sense. I had clearly made some errors in my coding somewhere along the way, and I just couldn't seem to track it down.

So, I decided to simplify things... a lot.

The parameters for the simulation are as follows:

1. The ball's axial velocity (U) is a constant 300 fps (91.44 m/s).
2. The Strouhal number (St) used was 0.2.
3. The paintball's diameter was 0.68 inches (0.017272 m).
4. The vortex shedding frequency (St * U / D) was approximately 1000 Hz.
5. The vortex shedding period was approximately 0.001 seconds.
6. The full distance travelled by the ball was 150 feet (45.72 m).
7. The time of flight from barrel exit to target was 0.5 seconds.
8. The number of vortices shed during flight was approximately 500.
9. The air density used was 1.239 kg/m^3.
10. The air viscosity used was 1.73x10^-5.
11. The Reynolds number used was approximately 113000.
12. The dimensionless lateral force coefficient was approximately 0.05.

This gives us a lateral force magnitude of approximately 0.06 Newtons, using the following formula:

f_lateral = (1/2) * air_density * velocity^2 * paintball_area * lateral_force_coefficient

13. The paintball's mass was 0.003 kilograms.
14. The lateral acceleration was approximately 20 m/sec^2.

The procedure:
Every time a vortex was shed (every 0.001 seconds according to items 3 and 4 above), a randomly oriented acceleration of 20 m/sec^2 was applied to the paintball. I interpolated between these acceleration "spikes" to generate a random-walk-like pattern.

I converted the acceleration random walk into a velocity walk, and then into a position walk.

I noted the endpoint of this position walk, and then repeated the whole process ten thousand times.


The results:
The following links point to plots of the results...cut-n-paste the URLs if necessary...

http://www.geocities.com/jeremiahswinson/random_walk/sim_force_plot.gif <--Plot of forces on the ball as it flies downrange for a single simulation run. Divide these values by the paintball mass to get an acceleration plot.

http://www.geocities.com/jeremiahswinson/random_walk/sim_velocity_plot.gif <--Plot of lateral ball velocity as it flies downrange for a single simulation run.

http://www.geocities.com/jeremiahswinson/random_walk/sim_position_plot.gif <--Plot of lateral ball position as it flies downrange for a single simulation run.

http://www.geocities.com/jeremiahswinson/random_walk/sim_scatter_plot.gif <--Scatter plot of the endpoint positions for 10000 simulation runs.

http://www.geocities.com/jeremiahswinson/random_walk/sim_histogram.gif <--Histogram of the final endpoint distances from the aim point, showing the distance of greates paintball concentration.

http://www.geocities.com/jeremiahswinson/random_walk/index.html <--compilation of all 5 plots

Conclusion:

From the results of the simulation, I cannot conclude that a series of randomly oriented 2-G "kicks" is sufficient to knock the ball off course to the magnitude seen in AGD's tests. The greatest concentrations of simulated paintball strikes falls around 0.15 millimeters from the aim point... a distance much smaller than that observed in AGD's real data.

I suspect that there is still something else at work here, and I believe that it may lie in the possibility that a slight spin on a paintball would induce a preferential orientation for vortex shedding. This may cause the ball to be repeatedly "kicked" in the same direction and would thus end up with a greater deviation than a purely random "kick" orientation would generate. If the shot-to-shot orientation of slight paintball spin is not constant (and I suspect it's not), this greater deviation would be randomly oriented with respect to the aim point, as opposed to a simple off-center grouping.

It would be interesting to measure the spin orientation for many successive paintball shots to see if the orientation is reasonably constant or reasonably random. Tom, perhaps you could provide a bunch more test photos for measurement?

Why do I think we've just come full circle? ;)

BJJB

{edited to add plot compilation link}

[hitech]

I originally attempted to perform a full-blown simulation incorporating drag force to slow down the paintball, recalculation or the reynolds number at each time step...

I hadn't thought of that before. However, I don't think you can get meaningful numbers without having the ball slow. Maybe not recalculate at every step, but at least use some predefined changes. Say five or ten different velocities at various points. I don't think we can use a simulation at only 300fps. The paintball has much more momentum at 300fps. Any idea how fast a paintball is traveling after 80 feet?


From the results of the simulation, I cannot conclude that a series of randomly oriented 2-G "kicks" is sufficient to knock the ball off course to the magnitude seen in AGD's tests. The greatest concentrations of simulated paintball strikes falls around 0.15 millimeters from the aim point... a distance much smaller than that observed in AGD's real data.

Am I missing something? As I read your plots and graphs I see more like 2 meters. What am I missing? Also, the problem is quite probably with using the numbers from only 300fps. The real world just isn't neat enough for that. ;)

[bjjb99]

While I agree that the paintball has more forward (read "along the flight path") momentum at 300 fps, its lateral momentum is very small. Given that the lateral forces are proportional to velocity squared, higher velocities will result in stronger sideways "kicks" to the paintball each time a vortex is shed.

Additionally, the 300 fps constant velocity results in a greater shedding frequency (though quite possibly an equal shedding spacing) than lesser velocities. So if you use a decelerating model, you end up with around the same number of vortes sheddings, each of which is smaller in magnitude than a shedding at 300 fps.

Then again, you have more time between sheddings, so those weaker "kicks" act over a longer period...

I think this could go either way, or could well end up coming out exactly equal in terms of paintball shot distribution. <--- and if that ain't a catch-all sentence, I don't know what is. ;)

As for the 2 meters versus 0.2 millimeters... you're missing the units on the graphs. Matlab just loves to put powers of ten in the corners of plots. For example, the histogram has at the bottom right corner of the plot "x10^-4", meaning all the x-axis numbers should be divided by 10000. So you end up with 2/10000 meters, or 0.2 millimeters.

I plan to try to increase the complexity of the flight model to incorporate deceleration, but it truly was a nasty piece of code to work with during my first attempt. I'm thinking it may take a couple of weeks of off-and-on work to hammer the thing out properly. Working on my home computer leaves much to be desired, too... for some reason the software I'm using wants to poll all my hard drives each time I move between coding and execution windows... bizarre. Eventually I'll upgrade to something with a bit more sanity to it. ;)

On a side note, I've also begun to take a look at what effects a slight bias of the shedding orientation would have on the paintball's flight characteristics by changing from a uniform orientation distribution to something more gaussian in nature. The effects can be quite profound (and sometimes bordering on the absurd) for certain gaussian standard deviation parameters. If a (relatively) slowly spinning paintball can induce such a shedding bias perpendicular to its axis of rotation, then this could well explain the deviations we're seeing.

Someday I'm gonna write all this up in a dissertation and get my Doctorate. ;)

BJJB

[hitech]

Originally posted by bjjb99
Someday I'm gonna write all this up in a dissertation and get my Doctorate. ;)


Actually, that is not all that farfetched. There appears to be very little information on the behavior of spheres. What you will have produced coupled with some of Tom's data would make a very interesting paper. :D

Just thinking about the forces for a minute. If the vortex shedding produces a 2G force in the exact same direction every time (possible if it is truly random) the paintball should be able to rise against gravity by the same amount it would otherwise fall with each vortex shed. Any idea how long of duration the force is present for? If it were applied for say 25% of the shedding frequency it would be able to rise 25% of the distance it would normally far if no forces other than gravity acted upon it. In general, that seems reasonable.

I would really like to see results with more complex calcs. I know, easy for me to say. ;)

[Cristobal]

bjjb99: could you post, or otherwise make available the MATLAB code you used? I'd like to take a look at and try running it.

[bjjb99]

Originally posted by hitech

Any idea how long of duration the force is present for? If it were applied for say 25% of the shedding frequency it would be able to rise 25% of the distance it would normally far if no forces other than gravity acted upon it. In general, that seems reasonable.


What I did was the following:
Each time a vortex was scheduled to be shed (based on the velocity, diameter, and Strouhal number), I would randomly select an orientation for the vortex and used a fixed magnitude for the force exerted in the direction of that orientation. The magnitude was always equal to the lateral force for a paintball moving at 300 fps since we were doing a constant velocity simulation.

After I had a series of "kicks" at specific points in time, I could draw a smooth curve from "kick" to "kick" (spline interpolation) so that at any tick of my time clock (1/10000th of a second per tick) I could see what the forces were. I then applied those forces to the motion model to come up with an X-Y position plot as a function of time.

What this means is that the forces are continually shifting in magnitude and direction as we head from "kick" number N to "kick" number N+1. I believe this continuous method more reasonably describes reality than having a "kick" acting at full strength for some fraction of the shedding interval.


Originally posted by hitech

I would really like to see results with more complex calcs. I know, easy for me to say. ;)

Yeah, easy for you to say. ;)

I have been fiddling with the code here at home and I think I may have found an error. If I correct what I think is the error, I end up with a few orders of magnitude greater positional deviations... so no we're in the 0.1 meter range instead of the 0.0001 meter range. This more accurately represents what folks see in real life, but I do not yet know whether what I'm doing is both physically accurate and correct. :P

I have also been playing with a complete, from-scratch recoding of the deceleration model. I think I've actually written much cleaner code this time around, and it seems to also give results in the 0.1 meter range.

In neither case am I quite ready to conclude that my previous results are wrong and the new results I'm getting are correct... a bit more time will tell. After all, it takes on the order of 90 minutes for a single, 10000-shot test. I'd run fewer trials, but I want the statistical validity afforded me by such a large number of shots.

BJJB

[bjjb99]

Originally posted by Cristobal
bjjb99: could you post, or otherwise make available the MATLAB code you used? I'd like to take a look at and try running it.

Not a problem. Here's a hopefully functional link to the Matlab file. You'll have to remove the .txt extension so that Matlab will recognize the .m extension... Geocities didn't like my attempt to upload a .m file. If worse comes to worse, you could just copy/paste the text into Matlab, I suppose.

http://www.geocities.com/jeremiahswinson/random_walk/prandwalk3.m.txt

I just hope Geocities doens't screw up the formatting too badly.

BJJB

[bjjb99]

Well, I woke up this morning only to find yet more snow falling and traffic accidents everywhere. So I called in to work and told 'em that I'd be late if I was lucky or I'd not show at all, and then I proceeded to sit down and take a good look at the deceleration-based code that I posted last night. It looks physically reasonable to me, and the results look promising.

I've made a new set of plots and posted them on Geocities. Here's a link to all 5 of 'em.

http://www.geocities.com/jeremiahswinson/random_walk/index3.html

Note that now we're talking fractions of a meter instead of fractions of a millimeter. I think these results are probably pretty close to what one would expect. I get an average distance from the aim point of around 8.8 centimeters (about 3.5 inches) at 150 feet; standard deviation is around 4.6 centimeters. The average distance seems to be a bit on the low side, but I think that could be corrected by inducing a slight bias in the otherwise randomly oriented "kicks".

I really don't have much experience regarding shot groupings at this sort of range, so maybe a 7 inch grouping is reasonable after all... I know I'd love to shoot a 7 inch grouping at 150 feet, given my more likely 7 _meter_ shot grouping at that distance. ;)

As for the first set of results with 0.1 millimeter deviations...
um... oops? ;)

The deceleration code I posted yesterday also has a line near the beginning (commented out) which allows one to ignore the drag-induced deceleration and operate at a constant 300 fps. I've not run the trials for that scenario yet, but I'd imagine that the results will be comparable to the deceleration model now that all/most of the bugs are (hopefully) squashed.

BJJB

[pbjosh]

bjjb99

GREAT WORK!

And thank you. I was wondering though.......

If you could show a side ways flight path, maybe with a "shot from this high, went this far" type of programing. Just curious. Please realize I know very little about the programing capabilities on your end, and if you can't I won't protest.

Also you posted this a while back:


On a side note, I've also begun to take a look at what effects a slight bias of the shedding orientation would have on the paintball's flight characteristics by changing from a uniform orientation distribution to something more gaussian in nature. The effects can be quite profound (and sometimes bordering on the absurd) for certain gaussian standard deviation parameters. If a (relatively) slowly spinning paintball can induce such a shedding bias perpendicular to its axis of rotation, then this could well explain the deviations we're seeing.

Have you had any results? Or any even intuative thoughts from what you have seen.

And Back to the biginning again, we have checked the 'Ball in Flight' stuff, but started this whole issue on great ground with alot of questions to ask. Here is the beginning:


Gentelmen,

I have posted a framework of info in the data thread. This is from an extensive study we did in the early 90's. The data is representative of our findings.

Currently on the table:

Spin is the only major factor accounting for paintball inaccuracy. Promoted by Pbjosh

Closed bolt operation has an effect on overall accuracy. Promoted by Glen Palmer.

The paintball flight is subject to "knuckleball effect".

Spin may or may not be possible because of the liquid in the paintball.

Barrels have something to do with accuracy.

Seams have something to do with accuracy.

Balls distort with the impact of the air blast.
Balls distort when leaving the barrel.


What have we really answered in all of this? I must say the flight of a ball after it has left the barrel has been worked over grandly by some really great talent, but I still think we have missed something. Why?

Because not all guns shoot the same. Alot are close, but they all shoot different. To find what we were still searching for we need to explore more.

Josh

[AGD]

DO all guns shoot different? In what way?

AGD

[bjjb99]

Originally posted by pbjosh

If you could show a side ways flight path, maybe with a "shot from this high, went this far" type of programing. Just curious. Please realize I know very little about the programing capabilities on your end, and if you can't I won't protest.


I'll see what I can do about getting you a side view plot, though I am not certain that the code I wrote retained anything but the most recent time interval's position information in order to conserve memory. In other words, I think the data for position N+1 just overwrites the data for position N.


Originally posted by pbjosh

Also you posted this a while back:

{My text about vortex shedding bias snipped...}

Have you had any results? Or any even intuative thoughts from what you have seen.


Basically my conclusion was that I could, by introducing a specific amount of bias, cause a significant deviation of the paintball's flight path. For example, if I took the extreme case of forcing all vortices to be shed in the same direction, then you end up with roughly 2 G's of constant acceleration in a not-necessarily-downward direction and you have a paintball flying off into the wild blue yonder. By varying the azimuthal distribution of the shed vortices, I could essentially dial in any off-center bias I wanted to. I did not look into how the shape of the paintball impact distribution varied with vortex bias, as that would have taken far too long on my poor old home computer. Donations to bjjb's computer fund are not tax-deductible, in case anyone wants to send some dough. ;)

BJJB

[LTLGRMLN]

Originally posted by AGD
Spin may or may not be possible because of the liquid in the paintball.

I think that if you find some possible way that you can put some sort of "seperator" in the middle of the paintball then the liquid might not spin. So what im saying is that you could make the paintball to where it has a seperator shaped like an x in the middle of the paintball, thus prohibiting the paintball from spinning. What the "x" would be doing would be sectioning the paintball into four different compartments, and since the liquid in the paintball was not spinning before, now the paint in the middle will spin with the ball.

What you also said before about paintballs distorting with an air blast also got me thinking. If the air blast "distorts" the paintball it seems as though the paintball would "seal" to the lining of the barrel, which would in turn kind of take away the imperfections in roundness of the paintball, but the more the paintball is like a perfect sphere, the less "effort" the paintball has to go through to destroy the imperfections.

[jtoothman25]

I'm a senior in Mechanical Engineering at OIT, and I've taken classes on fluid mechanics. The Reynolds number has nothing to do with a body moving through air, but it has to do with Air flowing through a body(pipe). The length dimension is the diameter of the pipe the air is flowing through. It doesnt make sense to why the other numbers in the equation have to do with air, and the measurement for diameter or the radius is for a paintball. This just doesnt compute. A reynolds number is there to find if air(fluid) is turbulent or laminar. If an Re(reynolds number) is found to be above 2000-3000, then its turbulent flow, and below that is to be laminar. The reason that a HUGE number was gotten was the fact that if a pipe had air going through it at 280 FPS, and the pipe was the diameter of a paintball, it would surely be turbulent flow.

PS: This discussion part is from a couple pages ago, but I needed to clarify this for this point was thought to be done.

[bjjb99]

Originally posted by jtoothman25
I'm a senior in Mechanical Engineering at OIT, and I've taken classes on fluid mechanics. The Reynolds number has nothing to do with a body moving through air, but it has to do with Air flowing through a body(pipe).


...which perfectly explains why Reynolds number has been used for years and years as a tool for examining the aerodynamic performance of airplane wings...

The Reynolds number is simply a dimensionless value used to represent the ratio of a flowing medium's inertial force and viscous force. Its application is not limited to fluid flow in pipes.

BJJB

[jtoothman25]

ok, i was wrong. I was looking at the wrong internet page, I didnt have my fluid book with me. Lesson learned "dont trust the internet" I just looked in my fluids book, and the equation it gives is 2xAirDensity x Diameter of sphere all divided by air viscosity. This is almost what was stated earlier, but instead of the radius used, its supposed to be the Diameter.
In my internet searches, i found a fun site for paintball.

http://home.attbi.com/~dyrgcmn/pball/pballCalc.html

It has more detail than i've seen on most sites, and its directly related to paintball.

[hitech]

Originally posted by jtoothman25
In my internet searches, i found a fun site for paintball.

http://home.attbi.com/~dyrgcmn/pball/pballCalc.html

It has more detail than i've seen on most sites, and its directly related to paintball.

Yes. The author has posted in this thread as [5x5]. :D

[[5x5]]

originally posted by bjjb99


10. The air viscosity used was 1.73x10^-5.

bj would you please check your viscosity value. At 25 C and 760 mm I believe the viscosity is 0.000185 poises. I doubt that there would be much change in the value if the ambient conditions varied a bit from the stated T and pres. However, even if the viscosity is off by a factor of 10, it probably will not affect your calculations much. Although I don't understand Matlab code, if I make a guess as to what I see, the viscosity is only used to find the Reynolds number, which in turn is used in two arrays to interpolate the Strouhal number and the drag coefficients. Since the numbers don't change much in the region of interest, there probably will not be a big difference in the end result.

[jtoothman25]

since its off by 10, it'd make the final answer off by a factor of 10. Thus, instead of over 100,000 being the final answer, it'd be 10,000. And like you said, it hardly matters, and doesnt change the fact that its HIGHLY turbulent. We need this number to get down around 2000-3000 for laminar flow, which would make the balls shoot more straight (in theory). Since in the equation, we have speed, this shows us that lowering our Velocity on our marker, that we can get closer to laminar flow.. but to get there, we'd have to cut 300 down to 100 aparently, and that'd get us nowhere. I guess with my Emag, i dont care about spin, i just shoot enough paint that it covers anything, "over there". Also, what matter is it at what temperature we shoot at? what if you go out on a cold day, versus a warm day? I played in the rain recently, and it didnt seem to effect the flight of the ball as much as I anticipated.

[bjjb99]

Originally posted by [5x5]

bj would you please check your viscosity value. At 25 C and 760 mm I believe the viscosity is 0.000185 poises.

If you check back around page 4 or 5 of this thread you will see that the units I'm using are N-s/m^2 (i.e. Pascal-seconds) not poises. A poise is 0.1 Pascal-second, so it's perfectly consistent for you to see a factor of ten difference between your value and mine... it's all in the units. Here is the URL from which I obtained my viscosity value:

http://www.grc.nasa.gov/WWW/K-12/airplane/airprop.html

BJJB - "Nothing to see here... move along. ;)"

[bjjb99]

Originally posted by jtoothman25
We need this number to get down around 2000-3000 for laminar flow, which would make the balls shoot more straight (in theory).

That would be true if we were talking about flow through pipes. Flow around spheres may or may not follow the same behavioral relationships as a function of reynolds number. For example, the vortex shedding from a sphere goes from periodic to chaotic at reynolds numbers between 350 and 375... far lower than the 2000-3000 range for laminar flow in pipes. Here's a URL for reference, courtesy of Hitech:

http://www.alumni.seas.gwu.edu/~fsagmae/AIAA_Apr_2002.pdf


Originally posted by jtoothman25
Also, what matter is it at what temperature we shoot at? what if you go out on a cold day, versus a warm day? I played in the rain recently, and it didnt seem to effect the flight of the ball as much as I anticipated.

Temperature can affect air density, though the effect may not be significant when compared to other factors.

BJJB

[jtoothman25]

I think this article might be of significance to us. Its of an extremely large object, but http://naca.larc.nasa.gov/reports/1958/naca-tn-4350/index.cgi?page0003.gif might be fun. I know 60 inches isnt what we are playing with here, but, its hardly a huge part of the equation if you exchange .34 where the 60 was.

[mquinn96]

Simple Question:
Would spinning the paintball along its axis of travel (like a riffled shot) effect the vortex shedding? If not, why were civil war era cannons riffled when they too were shooting solid round balls. Also, the spin of the fluid inside should be discounted for this question since it only involves surface effects.
-Mike Quinn

[FatMan]

Originally posted by AGD
DO all guns shoot different? In what way?

AGD

I liked the idea that bjjb came up with back a bit - about low rates of spin affecting the pattern of vortex shedding.

I have always felt that two balls leaving a gun under the same conditions will travel the same except for variations due to flight dynamics ... which appears to have been shown to be significant enough to account for observed variance in shot to shot placement.

It has always been less clear how much the gun affects the initial flight conditions. I've seen the data posted in the data thread, but that doesn't include a study of paint-to-breech fit, or show how often balls spin at various rates, from different setups, or if muzzle blast is an issue.

For example - will I get the same performance with a 4" smooth-bore barrel as a 12" ported step-bore barrel?

My gut reaction is that MOST of that is not important - maybe some of it to efficiency or loudness, but the only thing that has seemed to have much impact on my shooting (and I've shot both Typhoons and Mags quite a lot) is the consistency of the paint to bore match, and then it seems to primarly result in consistent muzzel velocity.


I'd love to see data that proves or disproves that!

FatMan

[pbjosh]

Man, I need to get in here more often...........

I realize I wasn't concise. When I said "all guns shoot different" I was talking about shot groupings. We are talking about the shot groupings of one Paintball gun compared to another.

AGD, I ask in responce, Do all paintball guns shoot (have consistant shot groupings) the same?

No.

There is still something that makes a Stingray NOT very accurate. I might be into Glen Palmers' "Imperical" datagathering here, but some guns are NOT accurate. If you wanted to quote the PCRI accuracy tests of a bench mounted gun, then it should be apparent that all guns, even bench mounted, do not have the same accuracy. Same with all paint. Remember all the 'Best paint of the Year' tests?

And why? As much as we have looked at the ball in flight to a really decent level, there still is something that makes some guns NOT dead-on-hit-the-target-every-time. WHY?

Remember when the Angel came out? It was fast, but the 'Cocker was more accurate. Did people say that because they could see verticie shedding? If we are to believe that the ONLY issue that affects the gun is what happens AFTER the ball is shot, I could make a crappy barrel, out of tolerance components and a bunch of other bad design specs, and "bench mounted", the gun would shoot EXACTLY the same as any other gun out there, if I used the same paint. In reality though, it wouldn't shoot well. WHY?

Barrel and tolerance are issues, but something else is really at work here. Something is happening to that ball BEFORE it leaves the barrel. Something that makes a 'Cocker and another marker with 'Cocker threads shoot differently even if you used the Same barrel and paint. WHY?

If you have just the tiniest amount of paint in the barrel it can traumendously affect the accuracy. Why is THAT? There would be no affect as it goes throught the air because the small amount of paint on the ball wouldn't affect it. So what is different? Is there NO difference?

I think there is.

Not all Paintball guns shoot the same, even with the same barrel and paint. Unless you have played with only 1 gun in so long you have forgotten, they all shoot a bit different. WHY?

Josh

[hitech]

Tom, I'm slowly begining to see what you meant. Now I understand why you never released the information in the first place. :rolleyes:

[spantol]

Before I wade in here, I just want to state that I'm way, way out of my element here, and that I'm extremely impressed with where you folks have taken this so far.

That said, I don't think Tom's received the answer he was looking for with his last question just yet. I'm starting from a rather ignorant position, so I need to respond to that question with another question.

Let's say you have a Cocker, a Matrix, and an X-Mag, each identical barrels and air systems. Clearly, each of these markers "shoots differently" in that the firing process differs in each case. That said, once the ball has accelerated to 300 fps and left the barrel, how could the firing process possibly make any difference on where that ball ends up? I would be exceedingly grateful to anyone who could explain this to me (preferably using small words :) )

Further, the claim that any one firing system is inherently and quantitatively superior to another is a rather bold one. Carl Sagan said it best--"Extraordinary claims require extraordinary evidence."

[hitech]

Originally posted by spantol
...That said, once the ball has accelerated to 300 fps and left the barrel, how could the firing process possibly make any difference on where that ball ends up?...(preferably using small words :) )


Sure.

It cannot.

Actually, the only thing it could affect is the spin imparted on the paintball. None of the firing systems are different enough in that respect to make any difference.

[nerobro]

Wow, i'm late joining this conversation.....


Originally posted by AGD Let's see, mysterious force "X" affects the paintball randomy in flight, knuckleball effect happens randomly in flight....


has anyone considdered looking at fluid analysis programs? We could examine a circle in 2d. The turbulant wake of a boat, ball, whatever will tug at the ball a little bit. this tug is random. Like the turbulance behind a semi truck. Given that this is random, it should even out in the end. And a few pages later we see comments on the "drunken walk" sounds like a fine scientific term ;-)

*looks at hiteks post on 1/6/03* That's exactly what I'm describing. but the vortex shedding is happening in 3d.. and just a few pages later our friends show us 3d vortex shedding. Really pretty if you ask me ;-)


I personally think there might be a chance that a drafting paintball might stay in line better. (thats why I always shoot fast )
Well, you can be sure that a shed vortex would provide a turbulant "ball" of air that the paintball will happily fall into. I would imagine the wake of a paintball would be like having a ball sit under a water faucet. If you've done the experiement where you fill a pot with water and put a ball under the flow from the faucet, the ball will stay under the faucet instead of being pushed over the edge of the pan.

As posted by Spantol
Further, the claim that any one firing system is inherently and quantitatively superior to another is a rather bold one. Carl Sagan said it best--"Extraordinary claims require extraordinary evidence."

Given that the balls landing pattern is "perfectly" random. I don't forsee how we can alter this pattern. Not without changing the velocity of the ball to change the way the ball is flying. As Glenn noted that at certian velocitys balls are just more accurate. appearantly 300fps is a poor choice of velocity from an accuracy point of view. *makes a funny face* Now how could we alter the paintballs to change the the range of velocitys where they are more accurate.......

What about changing the size of the ball? Course we have seen that heavier balls are more accurate, but that's just becuase they resist the forces that are developed by the peeling off of vorticies. Though i'm not equipped to do the math, would changing the paint size to say.. .70 or .72 make a signifigant difference?

I"m still a little bothered by Glenn's statement that the ball swept the powder out near the base of the barrel. methinks I'll be doing some testing on my own.

[bjjb99]

Originally posted by nerobro
Wow, i'm late joining this conversation.....

Hey there! Better late than never, though. :)



Originally posted by nerobro
has anyone considdered looking at fluid analysis programs? We could examine a circle in 2d. The turbulant wake of a boat, ball, whatever will tug at the ball a little bit. this tug is random. Like the turbulance behind a semi truck. Given that this is random, it should even out in the end. And a few pages later we see comments on the "drunken walk" sounds like a fine scientific term ;-)

It's pretty much been established that we cannot use a 2 dimensional case to examine what's happening to a spherical paintball. The results from these two cases just don't converge. A 2-D case (infinitely long cylinder moving through a fluid) results in a periodic vortex shedding, while the 3-D case results in a chaotic vortex shedding. The former results in a sinusoidal force profile acting on the object, while the latter results in a random-walk force profile.



Originally posted by nerobro
Well, you can be sure that a shed vortex would provide a turbulant "ball" of air that the paintball will happily fall into. I would imagine the wake of a paintball would be like having a ball sit under a water faucet. If you've done the experiement where you fill a pot with water and put a ball under the flow from the faucet, the ball will stay under the faucet instead of being pushed over the edge of the pan.

Similarly, a ping pong ball will remain in a vertical column of air ejected from a vacuum cleaner running in reverse.

However, this is a finite column of moving air, and the ball has to contend with boundary layer effects as it reaches the edges of the moving air column. In the case of a paintball flying through air, the boundary layer effects you'd see in the ping pong ball case are so far away from the paintball as to have zero contribution. You know that the ball under water (or ping pong ball in an air column) dances about, but remains in the stream of moving fluid. What if the moving fluid column was ten feet in diameter? That's more along the lines of what a paintball is "seeing".

Just some random comments from a local madman. ;)

BJJB

[nerobro]

Going by the simulations I've been seeing, and the 3d modeling... the wake created by the leading ball is fairly tight. Say on the order of 1.5-2x the diameter of the ball. I think it would be interesting to see flight data from rapidly fired paintballs. And then again, i'ts now 8:20 am, i've been up all night so I may be talking out of my rear ;-) I'll take a better look a bit later.

And one more thought, dont' the voteicies still peel off at regular intervals, just they peel off in random directions?

[hitech]

Originally posted by nerobro
And one more thought, dont' the voteicies still peel off at regular intervals, just they peel off in random directions?

First off, welcome to the discussion. :D Second, yes, I believe that is true.

[bjjb99]

The frequency of vortex shedding is related to the Strouhal number, which (working from memory here) is related to the Reynolds number. A fast-moving paintball will shed vortices more frequently than a slow-moving one. However, I believe the spatial separation between successive vortices is actually very close to equal for the two cases.

As for the orientation of the vortices, their orientations relative to the axis of travel is probably best described as chaotic. For all intents and purposes we can assume they are random with a uniform distribution in azimuth about the paintball's axis of travel.

BJJB

[hitech]

Originally posted by bjjb99
...the spatial separation...with a uniform distribution in azimuth about the paintball's axis...

Show off! ;)

[m-98]

I haven't read all the posts here, I read the first. The paintball's liquid fill may not spin when a ball is shot, so if you could get the fill to spin with the shell wouldn't that help improve accuracy? Couldn't you make a paintball with a shell inside that is connected to each end of the paintball so that when the ball started spinning it would force the fill to move also. I really can't explain it well so look at the picture. I don't know if this would work and I know that it has flaws but it's just a general idea.

http://www.geocities.com/clan8300/paintball.jpg

[hitech]

Originally posted by m-98
...so if you could get the fill to spin with the shell wouldn't that help improve accuracy?

Nope. Why do you think it would improve accuracy?

BTW, Tom did try it and it did not improve the accuracy.

[m-98]

Thanks, sorry for wasting everybody's time.

[hitech]

Originally posted by m-98
Thanks, sorry for wasting everybody's time.

No problem. BTW, your not wasting anyones time. ;) Posting is what it's all about. :D

[osiris]

Originally posted by hitech


I'm thinking that very periodic could easily mean significantly more vortices are shed from one area of the sphere that the other. It would follow that the sphere would then change course. This would alter the angle of attack and maybe that could further alter things. As you have probably guessed, I don't know. ;) However, it sure seems feasible to me.

Very interesting. Something has to be causing the vibrations that cause that noise. :D

I chopped a bunch of my original post from here...

Onward...

It would seem the single most significant thing which could be changed about this problem is the turbulance behind the ball, and there appear to me no easy outs on that one. It seems the problem to attack is how to minimize that "cavitation".

Teardrop shaped paint balls? Whose done it already and what did they discover? Diabolo shaped paint balls? Surely there are links?

I am sorry. I see I should have read the references elsewhere in that thread ... I ripped this from one of the white papers:

1.2.2 Wake Control
As demonstrated by the collapse of the Tacoma Narrows bridge [1], developing methods of wake control is of particular importance. Bishop & Hassan [25] have shown that for a circular cylinder, with lock-on, there is a substantial increase in not only the oscillatory lift force, but also in the mean drag force. The resultant large amplitude oscillations caused by these forces can lead to the failure of bluff structures. By suppressing this vortex shedding, the coupling between the wake and cylinder can be reduced or eliminated, leading to lower oscillation amplitudes.
Research [4] has shown that the Kármán vortex street can be suppressed by bleeding fluid from the base region of the bluff body. Further, Strykowski [26] suggests that the placement of a smaller cylinder in the larger cylinder's near wake also suppresses vortex shedding for certain Reynolds numbers and the application of suction or splitter plates accomplishes the same task.

For rotational oscillations, very high oscillation frequencies and amplitudes can nearly eliminate vortex shedding and can result in significant reductions in drag, by as much as a factor of six [15, 16].

Application of a sound field producing induced velocities greater than the turbulence velocities has been found to supress free stream turbulence levels, and "substantially increases the coherence of the vortex shedding along the span of the cylinder as is usually found when a cylinder is oscillated" [12, 17].

Periodic freestream flow as in the present study is another possible mechanism for wake control. Inplications of the present work for wake control will be discussed in section 4.

... and ever onward ...

I always wondered why a diabolo shape was more inherently accurate in a smooth bore than a round ball. There were indoor air rifle parlors in most major cities at the turn of the last century and around that time in order to improve accuracy without incurring the expense of boring rifled barrels (buttons weren't in use I guess) diabolo pellets were used. Now I understand we are talking lead vice paint here BUT the sectional density of a small spheres is *MUCH* less than for large spheres.

Whomever is turning those nylon balls, have you turned some wasp waisted pellet shapes? I believe one might be able to construct a better performing projectile than a ball and remain within the safety constraints of the game. Say perhaps a nice long .50 flat nosed, wasp waisted, diabolo shape that weighs 3 grams and has a larger impact area than a sphere. Put it in a rifled barrel as we might as well use that great long bearing area afforded by the cup on the back end of the paint. Make the cup flexible enough to conform to the barrel under the pressure while your at it. It means substantial modifications to the embedded technology but if you make them and they shoot, they will also sell.

Damn, last time I thought out loud like this it was in a letter to Doug Kitridge when he was at PSE and ... aw well ... they built it and sold it ... ;)

You may rest comfortable with the assurance I won't be troubling you folks again till I've got some measurements of wind drift as I promised someone on rec.sport.paintball.

Thanks guys.

-m-

[bjjb99]

Greetings, Osiris, and welcome to Deep Blue. If you're who I think you are, then you're speaking of me when you talk about the someone over at rec.sport.paintball. I look forward to your contributions to this forum. :)

BJJB

[nerobro]

*blinks a few times* Rec.Sport\.Paintball has something OTHER than iditos screaming the praise of smart part? My god. If you are from R.S.P. Welcome. :-) I have a whole bunch of interstesting stuff on RSP from the late 90's if you're intersted.. just search for Nerobro on groups,google.com

People have tried oblong, and finned paintballs. the real issue with them is feeding them. AGD makes a series of VERY VERY VERY VERY accurate paintballs with a skirt on them and riffling on the skirt. The balls (shells more like it) spin up after the leave the barrel and have 90% hit on a human target at 100 yards. Though I may be off on my numbers. And this is also with a paintball that weighs 3x what a normal ball weighs.

Now, how could we get wasp waisted paintballs to feed? AGD's solution was a rotary clip. seems reasonable.... but 10-12 shots at a time... you better hit what you're aiming at.


For rotational oscillations, very high oscillation frequencies and amplitudes can nearly eliminate vortex shedding and can result in significant reductions in drag, by as much as a factor of six [15, 16].

Application of a sound field producing induced velocities greater than the turbulence velocities has been found to supress free stream turbulence levels, and "substantially increases the coherence of the vortex shedding along the span of the cylinder as is usually found when a cylinder is oscillated" [12, 17].


this in particular interests me... if we could MAKE the ball shake faster would it be more accurate? maybe that's the benifit that comes from flying in the wake of the previous ball. it might shake more......

[osiris]

Please check and correct my comments here:

http://groups.google.com/groups?dq=&hl=en&lr=&ie=UTF-8&threadm=3EB3DD4C.4BD2%40nowhere.antispam.com&prev=/groups%3Fhl%3Den%26lr%3D%26ie%3DUTF-8%26group%3Drec.sport.paintball

as necessary.

-m-

[hitech]

I’m not sure which one was your post. So, guessing that it was the one talking about the only way to improve accuracy is to change the shape, then yes, you are correct. The other problem with paintballs is that they are VERY light. The problem is that increasing their weight also increases the energy imparted. The current safety standards are for the amount of energy at the current weight and 300fps. Increase the weight and you have to decrease the velocity. It’s a catch 22.

However, there is some increase in accuracy to be had from changing to a none blunt shape. :D

[Bloencustoms]

I am very impressed by all of this, and want to thank everyone who has contributed to this discussion. It's the most fascinating thing I have read in a very, very long time. The math is completely beyond me, but I think I have at least a superficial grasp of the forces acting on a paintball in flight now. This has changed the way I look at paintball, and the way I listen to them fly over my head as well.

I also thought that if the barrel was imparting some kind of effect on the accuracy of paint (or nylon) balls, why not test them using some other means of acceleration? At first, I though that some kind of sled could be devised to launch them, gradually accelerating them over a long distance to reduce the deformation that rapid acceleration would cause. Still, with nylon balls exhibiting similar inaccuracy, deformation wouldn't be that big a factor. So, why not test them using a sabot of some kind that would be pulled away from the ball by wind resistance similar to a shotgun wad? It still could impart some kind of friction. Then you're right back to using a barrel.

So, I'm not sure where this thread is going from here. It hasn't seen much activity. But I am sure that people want a way to increase the accuracy of their markers. So, what can be done to counteract the vortex shedding? If that's the most significant factor affecting a sphere in flight (beyond gravity), then why not devise a way to negate it?

I worked as a car stereo installer for a few years, and observed the effect that occurs when two subwoofers are played out of phase. They cancel each other out, and the volume is greatly reduced. (Again, I'm no rocket scientist. I can't claim to know to what degree the cancellation has any effect.) But there are some real world applications for this effect. Some military helicopters use out of phase sound to cancel the noise from the rotors, making them much quieter. I have even heard of this technology being used experimentally to quiet the exhaust from automobiles.

After two hours of reading, and one hour of tense nail biting, I find myself somewhat disappointed. Almost a year ago, Osiris mentioned something I had been thinking about for a good part of the read. I was wondering if anyone had recorded the sound made by a paintball in flight, then played it back out of phase during a subsequent shot to see if it had any effect. What if it was that simple? Force the paintball, or the air surrounding it, to oscillate at the same frequency (which decreases with velocity if I read this correctly) only out of phase.

Obviously, it would be impossible to expect people to play paintball with 900-1000 khz tones playing in the background. Still, it might be something to look into.

AGD mentioned a few pages back that players might not care about this discussion. A few of us do. Thanks again gentlemen, this thread is a jewel to be treasured.

[hitech]

Playing a sound 180* out of phase with the sound created by the shedding vortices would indeed cancel it out. The "it", however, is the sound. Trying to pulse air, in the correct direction and at the correct time to "cancel" the shedding of a vortex seems like a monumental task, if not impossible with today's technology.

[Rowdie]

The barrel can make your shot more accurate by keeping the velocity more consistant with the proper paint/barrel match.....


As far as I can tell that's not correct.

Everyone's familure with the blow test? The proper ball to barrel fit means the ball won't roll out but you can blow it out. Well near as I can tell barrels that are too tight according to the blow test actually have the most consistant speed. However, barrels that are of the correct fit, while varying more widely speed wise end up being more accurate.

....

This thread is incredible! I've been reading/studying/contemplating it for two days now. :cool:

[Lurker27]

Guess I'll throw my hat in.

I believe that this thread is part of the search for the most accurate shot. Accuracy, of course, means going where you shoot it. Consistency is also important, and not only with regard to velocity

Lets review a few things I believe about paintballs.

They vary in size.

Seam position varies from shot to shot and is effectively random.

Seams are a constant and vary in size.

They expand around .001-.002 due to acceleration (Palmer found similar results)

At least a significant portion of their fill (boundary layer adhering to the shell, perhaps) spins when spin is imparted via the shell.

The only thing that the gun has yet to control with regard to paintball accuracy is spin.

The problem with accuracy comes in the last one.in general the tight barrel match eliminates spin, which only gets us to a certain level of accuracy. A non spinning imperfect sphere...this sounds familiar...it's a knuckle ball. The seams will create vortices behind the m, which will pull the ball in random directions (the original orientation of the spin was random)

So, it's fair to say that paintballs have a built in inaccuracy as long as we use this kind of barrel.

The solution wold seem to be rifling, but a rifled barrel reall should only be able to effectively shoot balls in the range of expansion, .001-.002 within the spec of the barrel.


Rifling would een out all of the vortices, would it not? IIRC the English Baker rifle used spherical bullets in a rifle.

[hitech]

Rifling would even out all of the vortices, would it not?

No, I do not think that it would. The vortices are not due to the seams, but due to the shape of the paintball (sphere). Because of the huge affect the shedding vortices have everything else is not statistically significant. Since this is all based on velocity, the one exception is consistency. The more consistent the more "accurate". However, small variations in velocity are overshadowed by vortex shedding. It boils down to paintball markers are about as accurate they are going to get, given the current projectile and speed limits.

[Lurker27]

I misspoke, what I meant was that the seams induce random spins, which in turn generate small, uncertain magnus forces.

The vortex shedding itself has an oscillatory nature, and so, on average, cancels itself out. I mentioned the Baker rifle before, and I feel that the comparison still holds...spherical ammunition beig improved by rifling.

http://project.seas.gwu.edu/~fsagmae/papers/AIAA_Apr_2002.pdf

http://project.seas.gwu.edu/~fsagmae/papers/AIAA-99-3806.pdf

Two excellent papers relevant to our discussion...The most important thing to note is the assertio that the mean force from vortex shedding will always be nonzero, but in general approaches zero.

I personally dont believe us to be at the very threshold of paintball accuracy yet.

[hitech]

I haven't had a chance to read all of both those articles, but I will try. The first one looks very interesting. I did read a little and this jumped out at me:


The variability in the orientation of the vortex loops is also found to increase with Reynolds number. Thus, as the Reynolds number increases the preference toward any particular azimuthal orientation diminishes, and the wake is expected to slowly approach a statistically axisymmetric state.

If I read correctly, the top R number they tested was 1000. The R number for a paintball at 300 fps is closer to 10,000 IIRC. That would suggest that at paintball speeds the vortex shedding is almost completely random. Tom's testing of paintball trajectories support this.

[aut911]

I have noticed that some paintballs have a smooth shell while others (more expensive) have a rough shell to them. Would the rough shell infact reduce drag? I know that goldballs rely on the same thing but I am wondering if the rough shells would make a difference on such a "non dense" projectile. the only problem with adding fins or blunt noses is the market.
A customer would have to buy a whole new gun, buy more expensive paintballs and more then likely have to reload more often. I built some "finned" paintballs to see if they would in fact work better than a regular paintball and they do. It would be funt to have a sniper that has a longer range than anyone else on the team. could make war games more fun. I have seen another type of paintball fin(not AGD) that makes a paintball look like a very blunt dart. It is used in law enforcement I believe. I would like to find out where to get a few thousand of those for an experiment, and mabye later, converting a pump gun into a real sniper.

aut

[Lurker27]

Hitech: random perhaps, but the key phrase is "approaching statistically axisymmetric". Isn't he saying that as the reynolds number increases, the wake becomes more symmetrical about the path of the paintball, ie, LESS buffetting about in random directions.


I'm reding some studies of cylinders as bluff bodies too, its very interesting stuff, but I am still not fully convinced of the built-in inaccuracy that we "see" currently.

I really have to shoot a hammerhead.

[hitech]

To me the key phrase is


The variability in the orientation of the vortex loops is also found to increase with Reynolds number.

That is more random, not less. I'm also working backward from Tom's testing. His VERY extensive testing showed the flight pattern to be random. His testing also showed that spinning a paintball about it horizontal axis did not improve the "accuracy". He built a machine that would spin the breech and barrel. It was capable of high RPMs (at leas 10k) and it did not make a difference. I believe that random vortex shedding is the reason.

BTW, I have read that for a specific R number range (can't remember the exact numbers, but it's higher than a paintball at 300 fps) the vortex shedding appears to stop. It is a small range and no one seems to know why.

I still haven't had a chance to read (and digest) those articles. I will try to as they are interesting. There seems to be very little testing with spheres, and that's what we are dealing with. ;)

Cylinder vortex shedding is much easier to study. However, it tends to create predictable loops (alternating between sides).

:cheers:

[Lurker27]

Random will tend to congregate near zero net force, though. Perhaps if we could shed vortices at a higher rate, our groupings would be tighter.

Interesting stuff. Foudn this regarding Reynolds numbers:

Wakes behind spheres are observed to be steady for Reynolds numbers below 300-400. Above this limit (which also depends on the surface finish) vortices break off and are periodically released to form vortex loops that are connected like in a chain.

At Re above 6000 the vortex shedding is very periodic, with Strouhal number ranging from 0.125 to 0.20, the largest figure being a limit at high Reynolds numbers (Achenbach, 1974). Similar wakes can be observed behind particles falling in water. Effects of the surface geometry have been studied for the evaluation of the aerodynamic performances of sports balls (Metha, 1985).

Looking at Figure 3 in the first link I posted, force diagrams for spheres at different reynolds numbers. The distribution shows the least pull away form the origin as as the reynolds number increases.

Even with all this, I still think that non-spin barrel systems are providing less than optimal accuracy, if only via analogy to a knuckleball.

[hitech]

I think the problem here is that the articles you found (sorry, still haven't read all of them) deal with Reynolds numbers MUCH smaller than those for a paintball. The Reynolds numbers for a paintball at 300 fps is ~113000. Back on page six (I think) "we" concluded that at Reynolds numbers that high the vortex shedding orientation is "chaotic", or random.

I do want to read the articles you posted. New information on this subject is always interesting and appreciated. :clap:

[Lurker27]

I'm no arguing the random nature of those vortices, but the tests involved suggest, to me, that the pull along any azimuthal axis will be pretty minimal.

Minimal enough to not explain ALL of the inaccuracy in the bathbeads we're shooting.

[Lurker27]

I'm not sure if we have looked into the effects of rifling on the vortex shedding yet...so...

http://www.ias.ac.in/currsci/apr102004/1033.pdf

Another idea is to create a mareker with an elongated breech and a detent sytem which allowed 2 balls to be fired at the same time, creating a projectile more similar to a cylinder.

Tournament legality could be preserved for one shot, one pull, by storing hte pulls and only firing in clusters of 2.

[hitech]

I'm not sure if we have looked into the effects of rifling on the vortex shedding yet...so...

http://www.ias.ac.in/currsci/apr102004/1033.pdf



Spinning a sphere with the axis perpendicular to the flow will produce significant lift at high enough RPMS (i.e. flatline barrel). Spinning a sphere with the axis parallel (as in rifling) does not produce the same results. Any research on cylinders is useless as it is always with the axis perpendicular. I've never seen any research on the effects of axis parallel spin on vortex shedding. And certainly not at the Re numbers for paintball flight. Other than Tom's experiments. And they did not capture any data on vortex shedding anyway. ;)


Another idea is to create a marker with an elongated breech and a detent system which allowed 2 balls to be fired at the same time, creating a projectile more similar to a cylinder.

Tournament legality could be preserved for one shot, one pull, by storing the pulls and only firing in clusters of 2.

I'd love to see test results for that. It's quite possible that closely "drafting" paintball will avoid the vortex shedding problem. Basically it changes the shape of the object.

It would never be tournament legal. :shooting:

[Lurker27]

Why not? one ball per pull, right? Just let them collect in series of 2. Impractical yes, Illegal...no-ish.

[bjjb99]

I'm no arguing the random nature of those vortices, but the tests involved suggest, to me, that the pull along any azimuthal axis will be pretty minimal.

Minimal enough to not explain ALL of the inaccuracy in the bathbeads we're shooting.


The plots in the first paper you listed indicate that at high Re values the time-averaged lateral force on the test sphere is nearly zero. I would expect this as the orientations of the shed vortices approaches a purely random distribution. This does not necessarily mean that said lateral forces have not significantly deflected the flight path of the sphere during the time-averaged period.

Example: I get in my car, accelerate to 60 miles per hour (positive force), travel at a constant velocity for a while (zero force), decelerate to zero (negative force), and then exit the car. My time-averaged force is zero from the point when I get in the car to when I exit.

Am I anywhere near my starting point?

Zero net force does not equal zero net displacement.

The plots you're seeing in the first paper show essentially a random-walk in force as a function of time. If you took sample points from those plots, inserted them as forces into a model to calculate position as a function of time, and ran the numbers, you'd see that the final X,Y displacement is far from zero, even though the net force is near-zero.

BJJB

[eric1337]

i think the key to range is putting as much fill in the paintball as possible so that the fill does not fly to the back of the ball and make it decelerate so terefore less fill travel inside of the sphereequals more range and less deceleration i think from playing ping pong that when the ball starts spinning faster then the ball is moving forward then the spin takes over and grips the atmosphere also if u had a deadball wind would affect it with horizontal spin affecting the trajectorie the trajectorie is more likely to be strait in windy conditions a bit of topspin would likely provefor the most accuracy ping pong balls show u how spin affects trajectorie very well i recommend if agd does spin testing they use orange ping pong balls because there medium wait and have exposed seems

half of this is prbly spelled wrong i have a grade eight education lol

[Rokudon]

uuhhhh, i have very limited knowlege, and doubt i should be posting on deep blue, but in the beginning, it was talk about the seams creating a minor magnus effect (and btw, any terms i mite use r from wat i read) that was previously believed to have an effect on accuracy... well, now there's talk about the vortex shredding, and then about oscillation cancelling out the effect. so.. i was wondering if it were possible to add intentional seams along the ball to create oscillation, or create more turbulence (to minimize the vorticies)? and to keep it in the right orientation, create a weight bias to the back of the ball so it would revert itself to the right direction while inflight? feel free to flame me, i'm just bored with a ton of grd 10 ecology hwk... and btw eric1337, u mite b in grd 8, but the use of periods was probably introduced aliitle earlier in ur education....?

[captainsarcastic]

uuhhhh, i have very limited knowlege, and doubt i should be posting on deep blue, but in the beginning, it was talk about the seams creating a minor magnus effect (and btw, any terms i mite use r from wat i read) that was previously believed to have an effect on accuracy... well, now there's talk about the vortex shredding, and then about oscillation cancelling out the effect. so.. i was wondering if it were possible to add intentional seams along the ball to create oscillation, or create more turbulence (to minimize the vorticies)? and to keep it in the right orientation, create a weight bias to the back of the ball so it would revert itself to the right direction while inflight? feel free to flame me, i'm just bored with a ton of grd 10 ecology hwk... and btw eric1337, u mite b in grd 8, but the use of periods was probably introduced aliitle earlier in ur education....?


This has been tried in several variations. First, look at tippmans flatline system. These never were very successful in breaking into the open market. Flatline cockers were as close as it got and I have never seen one at a field. Imperial also tried to promote consistent spin with the Undertow bolts. I have owned two bolts and have had good success with both. Whether or not it is superior to a traditional venturi bolt however is another matter. It is also hard to compare to say a NDZ bolt (for impulses) owning to what I perceive as a lesser manufacturing standard of IPB bolts from their high degree of hand craftsmanship.

[Rokudon]

yes i know about the flatlines, what i meant was i have limited physics knowlege, i know enough about paintball (i've been researching and such for 2 years....mostly on low ends and pumpers tho) to know what products do what. the things you mention are used to create spin, and due to the spin, it would create lift and keep the ball along a straight trajectory. what i''m saying is create seams on the ball and have the back of the ball heavier than the front. conventional loaders and equipment would still work, the seams would disrupt SOME of the vortex shedding effect, and the weight bias will keep the seams facing the right direction.

[bjjb99]

what i''m saying is create seams on the ball and have the back of the ball heavier than the front. conventional loaders and equipment would still work, the seams would disrupt SOME of the vortex shedding effect, and the weight bias will keep the seams facing the right direction.

I think you've got your weight distribution backwards. In your configuration, the paintball is unstable and will want to rotate until the weight is biased toward the front. Do a search for "stability", "center of gravity", and "center of pressure". For a stable projectile, you want its center of pressure to be aft of its center of gravity. Your configuration has the positions of the two centers reversed.

BJJB

[edit... I couldn't type "positions" properly the first time through... doh!]

[Rokudon]

lol right, i just remembered that when i thought of the M16 bullet... ya you're right, front heavy makes better stability.. but would the powder mix with the liquid...? wait isnt this suposed ot be spin physics...

[Robotech]

First, let me say that Hitech is the guy that directed me over to this thread...and I'm glad he did. I'm a History major so all this math stuff is making my head hurt (we're just not built for this) but lucky for me I was always good at science and have a natural drive to figure out how things work (hence how I learned computers and programming...go figure).

Anyway, and perhaps I have this all wrong, but if I'm reading this right the ONLY way the marker, bolt system, and barrel affect a paintball's accuracy is by how consistant of a velocity the marker will fire the ball out of the barrel. After that it is up to these vortexes that look like something out of a piccaso painting that determine where the end result winds up. (other than where I'm pointing it of course)

So the next question is with current paintball technology what makes some balls work better than others when fired out of a marker? Why did I have such poor shots with say marbs when comparied to chronic? (And a bore size of .691) I mean, I've seen the difference. Does it have to do with a mis-shapped ball will produce more of these vortexes on one side than another and thus push the shot further off the mark?

As for combating this effect...I wait to see what you guys come up with. I have my own ideas...but I'm not paintball scientist. :)

[Rokudon]

(welcome to AO? 1 post and joined in november...)
- yes, thats what it basically says. after the gun, nothing impacts it except vortecies. also, ithe gun matters in terms of consistent pressure shot to shot.
- to my understanding (i'm a grade 10 student with barely any phisics knowlege) a dimple will cause turbulence, reducing the vortecies on that side? someone please correct me if i'm wrong.
- to the ball patterns, did you test that with one batch, or with multiple batches? you have to remmeber that form batch to batch, the balls are different. also include shelf life, and machining tolerances.
-to combat this, scroll up abit, u'l see an earlier post of mine :D

[Robotech]

Correct. First time poster here and new to this forum. It was a reference to this thread on another forum that brought me here.

As for my wild paint chase...I've tried each brand at different times and, when possible, bought from different stores. I have seen Chronic to be larger in general than the Marblizers. All I can get from this though...when comparing against this data, is that the Chronic allows for more consistant velocity shot to shot than the Marbs did with the barrel I use. After all, according to this study it seems this is the only area which can affect accuracy within the firing process itself.

I understand that many of those who started this thread may or may not still be around...after all it was started some time ago, but I want to say thanks. Some of us out here in the paintball world just want to know the facts even if we cannot arrive upon them ourselves. I would never have gotten this information had it not been for you guys and this is the kind of stuff I have been looking for. I don't understand any but very basic physics but this stuff...when you look at it...makes sense even to me. I don't think that the players themselves don't care to know the truth, but rather that they just go by what is readily available in the knowledge pool. Most, myself included, understand that paintballs are not accurate because they are round but what I, and I'm sure others, didn't understand was just to what degree this condition played in the overall scheme of accuracy.

After reading all this...it is apparent to me that outside the ability of the marker to provide consistant velocity...through a combination of a regulated air source, room for liquid to gas expansion (with CO2), and a quality paint that varies little in size from round to round...that the actual shape of the ball itself and the way it acts in flight is the largest enemy we have when it comes to accuracy. Really it seems that this, above all ELSE, is the cause for inaccuracy. Having an inconsistant marker just serves to agrivate it. :) Thus, while everyone is looking for the best marker/barrel/firing system to increase accuracy the real place everyone should be focussing their efforts would be on redesigning the paintball.

[justjoshin590]

were the tests you did with the same barrel? if so that is the reason for the cronics being more consistant than marbs, different sized paint needs different sized barels to properly hold it, as for redesigning the paintball, look at the fn 303, fin stabilized front heavy projectiles, although the front is very heavy, i think the same results could be achieved as long as the front is heavier than the back

[Rokudon]

ya wat joshin said, but redesigning the ball in terms for aerodynamics would defeat the point of calling it paintBALL. might as well call it mini paintfootball instead... to keep with the acctual name of our beloved sport true, i'd say weight distribution MIGHT be the next way to go for better accuracy. noe for the people that this has happened to, when the fill settles (only heard of, have never seen) does the ball fly funny? as in inconsistent flight paths? if so, then the weight idea might have to be scrapped, as t may cause more inaccurate shots for just ONE accurate shot

[justjoshin590]

well the idea i had was making tails like on the fn303 rounds out of a material significantly lighter than the paitnball, then attach the two with glue or something, and im not to sure about the fill settling, i guess it never happened to me

[Rokudon]

yes but the problem would be if you add a tail to it, the function of a hopper is defeated, becase it provides storage an loading of randomly oriented balls (which is the same in any orientation...) add a tail, the hopper cannot be used and conversion to clip based systems is needed. thats why i said manipulating the seams and messing with weight distribution. keeps it in a ball form, so no major changes are needed to paintball equipment.