BB Rotation

[krap101]

Originally Posted by Styrak

Maybe I'm missing something here, but wouldn't the spin velocity change based on hopup material used and also have no relation to how fast the BB is travelling (at least not a linear relation)?

I made a no slip assumption, so the material doesn't matter. In reality, it does, but this thread was made to find out the theoretical maximum, which is with no slip. It has since morphed into something much different, and much more interesting :P

Originally Posted by ThunderCactus

I thought TK barrels didn't actually provide any lateral spin, but rather the spiral barrel grooves simply allow the air to remain laminar and uniform beside the BB, making it easier to keep the BB centered in the barrel. As opposed to straight grooves where air in one groove could be traveling faster than in other grooves.

Also, it's worth testing short barreled GBB pistols versus short barreled AEG's. I'd like to see if my theory is true as well. We had a big discussion about it in another thread, but for those who didn't catch it, essentially I theorize that gas guns have better range and accuracy not only due to higher air pressure to center the BB down the barrel, but because it leaves the hop rubber at a faster velocity, increasing the spin. And that it would explain why a GBB shooting 300fps with .30s BBs would get a better trajectory than an AEG shooting 300fps with .30s. And that's absolute velocity measured with a .3 on both guns.

Yes, the TK-twist is "air rifling" or "reverse rifling", where the only spin on the bb should be from the bb rolling on the top of the barrel (whether that happens or not isn't very well defined).

I have to disagree with your "faster velocity over hopup" theory, because you "zero" your hopup at level or slightly upward curved flight. At the same muzzle velocity, and same angular velocity, the bb will behave the same regardless of what happened earlier (sure turbulent flow and other factors may come into play, but I believe those two are the big ones)

[R1ghty]

Someone watched mythbusters and is a pro now..

[krap101]

Originally Posted by R1ghty

Someone watched mythbusters and is a pro now..

Please clarify...

[R1ghty]

Was aimed at Dynamo, who gave an overly simplistic 'solution'

[krap101]

Originally Posted by R1ghty

Was aimed at Dynamo, who gave an overly simplistic 'solution'

Okay. I'm still a little bit twitchy from a few arguments I had on ASM, hence the super-ultra-uber-hyper-defensive response.

I feel like on Sunday, when I actually try to record some shots, everything is going to go wrong, so any input is helpful. For my nub, the biggest thing is consistent angular velocity, and muzzle velocity can be easily measured with a chrono. I would like a better way to plot z(elevation) vs time. I want some graphs like from the airsoft trajectory project, but I think he just used a few chrono's in series.

http://mackila.com/airsoft/ATP/index.htm

[Dynamo]

Originally Posted by R1ghty

Was aimed at Dynamo, who gave an overly simplistic 'solution'

oh im sorry, did you want me to also post the math needed to do the conversion?

you can measure both velocity and rotation/sec with a camera. it would give you a much more accurate result than just looking for rotation alone and not worrying about the FPS until later, as different FPS will give you different rates of rotation.

[m102404]

I'm not sure I understand why so much investment into figuring out what the RPM of a BB will be at a given FPS?

The system is going to be so variable (i.e. rubber/bb surface/bore condition/FPS/airseal/etc...) that in practical application the "ideal" nub may be unobtanium.

It may amount (and the massive/vast product landscape out there bears it out) to good enough is generally good enough for everyone.

What is interesting is the impact of various shapes of nubs/hopup systems on the consistency and application of hopup on ranged shots.

I.e. the PTW hopup style vs. "TM" vs. H/whatever other names vs. "ticklers"

I'm a big fan of the PTW style hopup. The consistency delivers awesome accuracy...the effective application of back spin delivers great range to a variety of BB weights at a variety of speeds.

Note...my PTW hopups are modded with different material....and shoot dramatically different from stock setups. While the different material affects the amount of backspin applied...I believe that it's the hopup design and mechanics that facilitate the consistent application of backspin to shot after shot after shot.

So...if the objective is to make a nub that assists in generating the straightest shot and most consistent application of backspin...why the focus on absolute RPM numbers? (bearing in mind that "typical" AEGs vary between 5-10fps per shot...and good AEGs vary 1-3fps) Wouldn't chasing down a nub that provides 0.000000001% variation be a loss leader since the system that it'll be working with is highly variable?

[krap101]

Originally Posted by m102404

I'm not sure I understand why so much investment into figuring out what the RPM of a BB will be at a given FPS?

The system is going to be so variable (i.e. rubber/bb surface/bore condition/FPS/airseal/etc...) that in practical application the "ideal" nub may be unobtanium.

It may amount (and the massive/vast product landscape out there bears it out) to good enough is generally good enough for everyone.

What is interesting is the impact of various shapes of nubs/hopup systems on the consistency and application of hopup on ranged shots.

I.e. the PTW hopup style vs. "TM" vs. H/whatever other names vs. "ticklers"

I'm a big fan of the PTW style hopup. The consistency delivers awesome accuracy...the effective application of back spin delivers great range to a variety of BB weights at a variety of speeds.

Note...my PTW hopups are modded with different material....and shoot dramatically different from stock setups. While the different material affects the amount of backspin applied...I believe that it's the hopup design and mechanics that facilitate the consistent application of backspin to shot after shot after shot.

So...if the objective is to make a nub that assists in generating the straightest shot and most consistent application of backspin...why the focus on absolute RPM numbers? (bearing in mind that "typical" AEGs vary between 5-10fps per shot...and good AEGs vary 1-3fps) Wouldn't chasing down a nub that provides 0.000000001% variation be a loss leader since the system that it'll be working with is highly variable?

I've considered making a roller-hop, but this would require me to redesign the hopup entirely, in order to maintain the seal, and I'm not equipped or have the time to do this, although I have heard stories of how good the ptw hopup is. The rollers on the PTW hopup almost guarantee a no slip condition, which is why I think they perform so well. I'm hoping I can achieve this without having to massively modify the conventional hopup.

I have gotten my vsr-10 (not necessarily applicable, but I can try my nubs in there if I want) down to .1 variation, and one of my friends got 0 for 8 out of 10 shots with his DMR.

The reason I'm focusing on absolute rpm+muzzle velocity, is because this will tell me how consistent the nub is. Imo, the biggest increase in accuracy in current airsoft guns (after airseal and barrel) is the hopup. If you understand bernoulli/magnus, you'll understand how much of an effect a 5% change in rpm can have on the flight path of the bb. The two "output variables" assuming each bb is perfect and alike (big assumption), are muzzle velocity and angular velocity, which determine flight path. Currently there is very little actual rpm data besides that done by RiotSC and soon to be BBBastard.

Here's how I will rank consistency:

Barrel>Compression>BB>hopup... where the first three can be taken care of fairly easily.

[m102404]

Ok...that's admirable.

I just think that it's an impractical thing to isolate. But kudos for trying!

I've been wrong for well over 30 years...but still learning all the time

[krap101]

Originally Posted by m102404

Ok...that's admirable.

I just think that it's an impractical thing to isolate. But kudos for trying!

I've been wrong for well over 30 years...but still learning all the time

Well, it's the next logical step. The one after this one is waayyy down the road when we can have a bb within a hollow shell, where the inner bb gives the round gyroscopic stability, while the outer shell allows for backspin/hopup. Now what's impractical?

[Schlyder]

hahahaha multi layer technology... you are talking golf ball technology now. Golf is way ahead in this kind of testing. How cover materials and core materials react to control spin and trajectory. They have evolved from a leather pouch filled with a top hat full of feathers, to Gutta Percha formed into balls, to a fluid filled ball wrapped in miles of rubber windings covered in a thin shell of Balata, to space age multi layer polymer compounds with extremely thin covers. They also discovered that the nicks on the originally smooth featheries,(golf ball) would stabilize the flight and improve performance, which led to the development of dimple design and configuration
Actually it would be interesting to see if a golf ball launch monitor could pick up a BB?? Probably too small. But it would tell you spin rates, launch angles, initial velocity, deviation from a target line. Some even give you a trajectory profile as well.

[krap101]

Originally Posted by Schlyder

hahahaha multi layer technology... you are talking golf ball technology now.
Actually it would be interesting to see if a golf ball launch monitor could pick up a BB?? Probably too small. But it would tell you spin rates, launch angles, initial velocity, deviation from a target line. Some even give you a trajectory profile as well.

Interesting thought. I think another problem is that our bb's are smooth, as well as I believe spin on a bb is something like 15000rpm or so, which seems to be out of the range of something designed to track a golf ball (quick search said something like <4000 rpm). This is the closest to what I need though, so I might be able to find one somewhere... I'll start the emails

ty

[Schlyder]

Originally Posted by krap101

Interesting thought. I think another problem is that our bb's are smooth, as well as I believe spin on a bb is something like 15000rpm or so, which seems to be out of the range of something designed to track a golf ball (quick search said something like <4000 rpm). This is the closest to what I need though, so I might be able to find one somewhere... I'll start the emails

ty

hahah I added tht in my edit.

[Schlyder]

< 3000 - 4000 RPMs would be with a driver. With a sand wedge RPMs can get in the 15,000 range. Yes the spin rates may be too excessive for BBs to register. But the technology may be able to be tweeked to read a higher spin rate.

[Schlyder]

Yes a smooth BB creates a lot of problems for flight stability. Mini dimples may be a solution, if they work in scale. But smooth creates more drag than dimpled in golf balls.