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Maximizing Decibels, and a Few Other Questions...

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Maximizing Decibels, and a Few Other Questions...

Unread postAuthor: PAV » Wed Jul 06, 2011 3:11 pm

Hi. I apologize in advance for the length, but I want to make sure I provide enough information to answer the questions.

We are in the final chassis design stages of a paintball vehicle loosely-based upon the AML-90 armored car, and we're starting design work for the vehicle's various systems (electrical, armament, etc.). The main gun on the vehicle will fire nerf footballs, the "standard" heavy weapon round in scenario paintball. Scenario regulations restrict velocity to somewhere between 240-300 fps, depending upon the event's insurance.

After some discussion, the team has settled upon a steel pneumatic QDV gun, probably 3- or 4-inches of bore diameter, and 8- to 10-feet in barrel length. The pneumatic QDV will allow us to vary pressures, keeping velocities low for paintball, and allowing pressures up to 250 psi for off-the-field entertainment. We have not yet decided upon the chamber size or configuration.

We have a few questions for the experts:

1 - How can we maximize the report of our gun? We want as big of a gut-shaking boom as we can create - literally, the biggest bang for a given pressure/air volume.

2 - We are thinking the chamber will be a 60# propane cylinder (12"X44", 64.8L before subtracting barrel volume), configured concentrically around the barrel as with technician2002's Marshmallow Gun, or an oxygen cylinder (9"X55", 49L) in an over-under configuration. The over-under configuration will make design of the quick-loading breech mechanism easier, but will the angle-induced turbulence and increased resistance from increased valve-to-projectile distance limit our flow noticeably? (We'd love to see maximum effect on random household items using concrete-filled projectiles and 250 psi!) :lol:
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Unread postAuthor: warhead052 » Wed Jul 06, 2011 5:24 pm

Why not use a piston valve and go with an over under design? The piston valve will make a very loud bang, or at least thats what I have heard.
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Unread postAuthor: jackssmirkingrevenge » Wed Jul 06, 2011 5:33 pm

Given the fact that you'll be using a large bore high flow valve, it's guaranteed to be loud, though a shorter barrel would make it more impressive. Get the performance you want using a stubby barrel and high pressure if you want more noise.

I doubt you'd notice a performance loss using the over-under design.
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Unread postAuthor: saefroch » Wed Jul 06, 2011 6:50 pm

Loudest boom for a given pressure and volume will be from the shortest barrel. Fixed barrel length and volume, maximize the chamber pressure.

So long as you have a good pilot valve, there will be little performance loss using the over-under. However, the T-shirt cannon Tech built for the final Intel Trailblazers competition had a breech-loading mechanism on it, so you may be able to get the best of both options.
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Unread postAuthor: jackssmirkingrevenge » Wed Jul 06, 2011 6:51 pm

saefroch wrote:So long as you have a good pilot valve


With a QDV, does that mean "having a good arm" :D
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Unread postAuthor: Technician1002 » Wed Jul 06, 2011 10:33 pm

You can hear the t shirt launcher at about 35 PSI here. At 100 PSI it is quite loud.
http://www.youtube.com/watch?v=9Klxqav_6NM
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Unread postAuthor: MrCrowley » Wed Jul 06, 2011 10:53 pm

It would be interesting to measure cannon reports, don't think anyone has tried it before. It could even lead the way for a highest cannon report contest; I would definitely enter with the piston hybrid :D
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Unread postAuthor: saefroch » Thu Jul 07, 2011 9:16 am

jackssmirkingrevenge wrote:
saefroch wrote:So long as you have a good pilot valve


With a QDV, does that mean "having a good arm" :D
:roll: I could have sworn the over-under configuration would be a classic piston valve. Fail.
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Unread postAuthor: Labtecpower » Thu Jul 07, 2011 10:26 am

Of course I have to advertise for my own cannon :D

[youtube]http://www.youtube.com/watch?v=yxpdd9s-wAw[/youtube]

Extremely loud when using light projectiles like pingpong balls, or without a barrel.
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Unread postAuthor: warhead052 » Thu Jul 07, 2011 10:34 am

Another thing you can do, use a burst disk cartridge, and simply fire that at the same time as your turret.
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Unread postAuthor: SpudBlaster15 » Thu Jul 07, 2011 11:07 am

For maximum acoustic output, you want to maximize both barrel cross sectional area and muzzle pressure.

Basically, a large diameter barrel and a high C:B ratio will give you the results you're looking for.
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Unread postAuthor: Ragnarok » Thu Jul 07, 2011 11:46 am

MrCrowley wrote:It would be interesting to measure cannon reports, don't think anyone has tried it before.

Actually, I have - and it's a little more complex than "Get dB meter, turn on, fire", unless you've got a very good and rather specialised meter. Most are designed for checking less "sharp" noise levels - concert speakers, extraction fans, etc. Not gunfire.

It could even lead the way for a highest cannon report contest

Without equivalent measuring equipment and precise testing setups, the results would be useless.

The difference between measuring at 1 yard and 1 metre could be more than enough to win such a thing.
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Unread postAuthor: ramses » Thu Jul 07, 2011 12:13 pm

Ragnarok wrote:
MrCrowley wrote:It would be interesting to measure cannon reports, don't think anyone has tried it before.

Actually, I have - and it's a little more complex than "Get dB meter, turn on, fire", unless you've got a very good and rather specialised meter. Most are designed for checking less "sharp" noise levels - concert speakers, extraction fans, etc. Not gunfire.

It could even lead the way for a highest cannon report contest

Without equivalent measuring equipment and precise testing setups, the results would be useless.

The difference between measuring at 1 yard and 1 metre could be more than enough to win such a thing.


Perhaps an acoustic burst disk test setup, then. Move disk supported in a ring along a line perpendicular to the muzzle, such that the axis of the disk is on that line. Whoever can have the disk furthest away and still break wins. Of course, that would require uniform disk support, disk diameter, disk material, disk thickness, etc.
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