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Thread: Paintball Spin Physics - Getting to the final Answer

  1. #211
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    Originally posted by bjjb99
    ...the spatial separation...with a uniform distribution in azimuth about the paintball's axis...
    Show off!

  2. #212
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    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.


  3. #213
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    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.

  4. #214
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    Thanks, sorry for wasting everybody's time.

  5. #215
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    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.

  6. #216
    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.
    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-
    Last edited by osiris; 05-01-2003 at 12:49 AM.
    Speed is fine. Accuracy is final.

  7. #217
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    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

  8. #218
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    *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......
    To be an AGD supporter, one cannot be an AGD bigot. -Nero

    Truth is a complex thing. One must govern by simplicity. -M. Mercier, special counsel to his Majesty for domestic matters. The Brotherhood of the Wolf

    "You can't outrun Death forever, but you can make the bastard work for it."


  9. #219
    Please check and correct my comments here:

    http://groups.google.com/groups?dq=&...port.paintball

    as necessary.

    -m-

  10. #220
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    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.


    Hey Hitech your starting to sound like me! - AGD
    Hitech is the man.... - Blennidae
    The only Hitech Lubricant

  11. #221
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    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.

  12. #222
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    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.

  13. #223
    Quote Originally Posted by ES13Raven
    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.

  14. #224
    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.

  15. #225
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    Quote Originally Posted by Lurker27
    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.

  16. #226
    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...A_Apr_2002.pdf

    http://project.seas.gwu.edu/~fsagmae...AA-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.

  17. #227
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    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.

  18. #228
    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

  19. #229
    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.

  20. #230
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    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).

    Last edited by hitech; 08-12-2004 at 03:41 PM.

  21. #231
    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.

  22. #232
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    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.

  23. #233
    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.

  24. #234

    Another thought

    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.

  25. #235
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    Quote Originally Posted by 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
    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.

    Quote Originally Posted by Lurker27
    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.

  26. #236
    Why not? one ball per pull, right? Just let them collect in series of 2. Impractical yes, Illegal...no-ish.

  27. #237
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    Quote Originally Posted by 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.

    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

  28. #238
    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

  29. #239
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    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....?

  30. #240
    Quote Originally Posted by 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....?

    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.

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