Paintball

[John Satclaire]

I wonder if a golf-ball textured paint shell was ever tried...

[drg]

Originally Posted by brycelarson

the last graph is the one that seems to apply most specifically to this discussion. What he's saying is that the lower spin rates actually REDUCE range. So, in order for the backspin bolt to increase range it would have to impart 25k + rpm... which seem unlikely.

Why unlikely? Sure 25k seems like a large number but remember this is just a rate ... it amounts to about 6 revolutions on the way out of a flatline barrel, which doesn't seem so far fetched at all.

[brycelarson]

Originally Posted by Railgun

There's just no way to calculate the effects of the forces or lack of them that are at work through the various portions of the ball's travel within the barrel and present any sort of number with a straight face.

the second link is to his calc for predicting trajectory.

The stuff happening inside the barrel is how the spin is created - but the spin outside the barrel is what effects the flight path.

From what I get he did the math then worked backwards from what his math told him the spin rate had to be to get trajectories like we see from the flatline.

Someone with better math skills than me will have to check his math - but he does post the formulas he used to get the results.

[brycelarson]

Originally Posted by drg

Why unlikely? Sure 25k seems like a large number but remember this is just a rate ... it amounts to about 6 revolutions on the way out of a flatline barrel, which doesn't seem so far fetched at all.

I have no doubt that the flatline gets that kind of rotational speed - I'm saying that I have a hard time picturing a puff of air on the bottom of a ball getting it up to 31,000 rpm.

[agentSmith]

The only way to tell for sure would be firing a number of balls that use one side colored differently from the other and film them with a super high speed camera and then study the slow mo' results of the ball coming out the end of the barrel to actually measure the spin RPM

I thought this was done in Tom Kayes experiments with white/black perfect circle paintballs(Agd made these).

The reason I feel the distance fired to be the same for backspun vs nonspun balls, even though their trajectories are different has to do with the fact that the spin is not a constant any more than the velocity is.
As the spin decreases it loses the ability to counteract vortices pushing it downward and because by this point it's momentum has dropped very low, it is rapidly forced to the ground, causing a steep end to it's arc that cuts it's flight short.

Please remember that TK's experiments showed that an anchored paintgun would fire a pattern like a DONUT due to vortex shedding. Not a U, a DONUT. Therefore vortices ARE pushing balls upward in the air, it isn't the magnus lift that's causing these bolts to work and trying to force a magnus positive result will not work in a way that could be made into a paintgun. Good old vortex shedding seems to fit more facts.

Rob

[drg]

Originally Posted by brycelarson

I have no doubt that the flatline gets that kind of rotational speed - I'm saying that I have a hard time picturing a puff of air on the bottom of a ball getting it up to 31,000 rpm.

Why not? Haven't we established that it would most likely be not the air but the flatline-type effect of the ball contacting the top of the barrel on the way out that causes the spin? The question is whether that can actually happen from the bolt design, but the "puff of air" being no different from that in a flatline, there's no inherent reason to think it cannot get a ball rotating at that rate.

[brycelarson]

Originally Posted by HP_Lovecraft

I took an alternate approach. I found a good .694 barrel that was overbore, but not enough. Instead of a flat trajectory, it was making corkscrews. Clearly the added friction was effecting the spin axis.
http://montneel.selfip.com/paintball/cvm03.jpg

So I started cutting it shorter, and shorter. At a certain point, the corkscrews stopped, and the trajectory flattened out:
http://montneel.selfip.com/paintball/cvm04.jpg

Like drg pointed out, with the CooperT bolts, barrels have the opposite effect as the Flatline. The Flatline barrel increases the spin, while the barrel used with the CooperT bolt slows it down. Thus, needs to be way overbored, or extremely short. Neither method was popular with people who liked there overpriced barrels.

this doesn't look like the ball is getting spin from rolling along the top of the barrel... he actually says that a shorter barrel got it working right - and that any longer barrel was changing the angle of rotation - which implies that the bolt itself was creating the rotation.

[drg]

Originally Posted by brycelarson

this doesn't look like the ball is getting spin from rolling along the top of the barrel... he actually says that a shorter barrel got it working right - and that any longer barrel was changing the angle of rotation - which implies that the bolt itself was creating the rotation.

Well you are right that HP's discussions don't seem to consider the flatline phenomenon as the source of the spin, but it's plausible, given the requirements HP found to make the setup work, that it IS the effect being created, as I described in post #28.

And in this case, it is not terribly far-fetched that the ball could gain significant backspin with a normal "puff of air".

[wycked54]

I'm coming in on the tale end of this thread and have noticed that some things might not have been addressed.

1. The paint. I have never seen two paintballs from the same bag with the exact same weight, size, shape, shell density or fill thickness. These are the infinite variables that CP is talking about.

2. A flatline works off of friction. If you feel the inside of a Flatline barrel you will notice that it feels like emery cloth. The paintball drags along the top of the barrel thereby causing the ball to roll along the top of the barrel. If you take a flatline that has erratic patterns and boil it the gelatin that gathers in the grooves will be removed and the pattern will become more standard. It is never perfect because of the paint(see above).

If im not mistaken it appears that the cooper t bolt would force the ball upwards when the air hits the ball causing the ball to roll against the top of the barrel. Since the barrel is almost smooth than there would be only small groves and rough patches along the way in various direction there by causing corkscrews due to the randomness of the friction.

I have seen a cooper t bolt and I do believe that it causes backspin. I just dont have one to test.

To CP and Bryce remember the words of Edison "I found 101 ways to not make a lightbulb." People will always doubt but it is through trial and error that the truth is uncovered.

[pump]

everybody, guess what i got