Paintball Spin Physics - Getting to the final Answer

[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

[ezrunner]

oops

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.

[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]

Palladin

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" ?
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