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Pneumatic Cannon for airsoft.

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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Pneumatic Cannon for airsoft.

Unread postAuthor: Einhander » Mon Aug 16, 2010 9:04 pm

Good afternoon everyone,

I am currently in the design phase for a pneumatic cannon for use in airsoft. Most of what I have been able to read has been "NEED MAOR! SHOOT FASTER!" which is awesome, but not for use on an airsoft field.

Safety is my PRIMARY concern with this build both in use as well as that of the projectile.

What I am looking for is a precision device capable of launch a tennis ball around 250-300 fps (possibly slower, looking into the safety aspect of it) consistently without eyeballing the PSI gauge.

I want to minimize the chance of user error so I want to be able to dail in the PSI being used then lock it in once I have found the desired FPS on the build. My rough plan of attack is to use a large capacity CO2/HPA tank from paintball, divert it into a pressure chamber up to the desired PSI, then quick release it and thus launch the ball to the dialed in velocity.

Any tips/tricks/hardware/resources you might recommend would be helpful.

-Ein
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Unread postAuthor: Technician1002 » Mon Aug 16, 2010 9:25 pm

A primary regulator for an air distribution system is adjustable and can be locked into position with a lock nut. Tools are required to change the adjustment. Set it and from there it is fill and shoot.

One of these with the adjustmet replaced by a bolt;
Image

Another option is a throttle plate that is an insert into the airstream between the valve and barrel. This would limit the flow rate. Drill an orifice and adjust it up to the desired maximum FPS at your system pressure.

Either works.

There are downsides to both. The pressure regulator is slow filling because as the pressure is reached, the flow is reduced.

The throttle plate wastes lots of energy.

A 3rd option is a small pre stage tank that is kept at a regulated pressure and dumped into the chamber like a fuel meter for each shot. This will deliver a fixed volume of air and thus a highly repeatable amount of air.

The best option is to reduce the size of the chamber. This requires less air, is highly effecient and limits the total energy for a launch.
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Last edited by Technician1002 on Mon Aug 16, 2010 9:30 pm, edited 1 time in total.
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Unread postAuthor: Lockednloaded » Mon Aug 16, 2010 9:25 pm

well finding a tennis ball barrel might be hard, but for such low speeds, you could just jam the tennis ball into the end of a 2" coupler.

Many of your questions have been asked before and answered; use the search function to find dozens of tennis ball cannons and guns built for airsoft
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Unread postAuthor: spudtyrrant » Mon Aug 16, 2010 9:30 pm

A qev slide valve combo on a regulator seems like yourbest shot it will give you a quick, consistent, easily adjustable platform that will still get quite a few shots of a tank.
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Unread postAuthor: clemsonguy1125 » Mon Aug 16, 2010 9:31 pm

I think a PVC cannon with a sprinkler valve will be good enough. I think regulated hpa is the best way for you to fill the cannon. A 2 foot 2 inch chamber will be good enough for the low velocities you need and a 3 foot 2.5 inch barrel. I don't have and answer for what pressure you should operate at but once you have built the gun chronolograph it at different pressures until
you find one that's at your required fps. Then I would suggest at a safety popoff at that pressure to stop from over filling
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Last edited by clemsonguy1125 on Tue Aug 17, 2010 1:37 pm, edited 1 time in total.
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Unread postAuthor: Einhander » Tue Aug 17, 2010 1:07 pm

Thank you very much for your help everyone,

I like clemsonguy's suggestion (I do want to keep it simple for a first run), but I was curious about a couple of things:

Are there variable-PSI pop-off valves? If I could tweek the max pressure from there, I could dial in the cannon. I am not exactly the most handy person in the world, but I will have a boilermaker buddy of mine help me out with the build.

Also, does anyone know of a resource for the "Safe" velocity of various objects? I know that it seems a little silly, but 250-400 FPS for a BB vs 250-400 FPS for a tennis ball is quite different in terms of how hard it hits. I have a little leeway (everyone is wearing eye protection, there will be a minimum engagement distance for it, etc) but again safety is key here.

Thanks!
-Brett
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Unread postAuthor: clemsonguy1125 » Tue Aug 17, 2010 1:22 pm

They do make adjustable popoff valves, I have not seen any in stores but you can usually find them on ebay or online.
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Unread postAuthor: BeaverRat » Fri Aug 20, 2010 1:59 am

You can buy adjustable pop off valves from McMaster...
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Unread postAuthor: Mr.Sandman » Fri Aug 20, 2010 2:16 am

Getting hit with a tennis ball going 400 fps would be incredibly painful and could break ribs if shot close enough. You might want to use nerf pocket vortex rockets instead. The soft heads make getting hit much less unpleasant. Another thing, what would you use a tennis ball cannon for in airsoft? Unless you were using "tanks" a tennis ball launcher would be incredibly impractical and dangerous.
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