Paintball Spin Physics - Getting to the final Answer

[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]

Some noodlings before I get home. :)

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]

hmmmm....

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