T-Shirt Cannon

[Sperkowsky]

Originally Posted by GeeTwo

The recoil will not be nearly this large, unless you're tossing chain mail t-shirts. The 50 psi air will be rushing through a 3/4" or 1" solenoid valve and quickly expanding to push on a half pound projectile over 7 square inches of area. My back-of-the-envelope calculations based on how far a half-pound T-shirt is tossed tells me that the recoil force for our no-sabot system (we roll the shirts into their own sleeves and muzzle load them) is more like 40 pounds than 350 pounds. If you are feeding the shirts in cylinders, you may require more pressure and will generate more recoil.

Speaking of chain mail t-shirts our team is making chain mail armor right now.

[fatmandandan]

Originally Posted by DonShaw

Are you using one tank as the HP side and the other one for the accumulator tank to provide the volume of air at LP to fire the shirt? If so you will not want to use the valve in the LP tank to gain the volume of air flow. You can use 3/4"
steel pipe with NPT threads.

A typical scuba regulator will drop the HP pressure down to about 170psi and I would suggest an additional regulator that is adjustable and will drop the pressure again to 150 psi max.

You can view ours at prhsrobotics.com under outreach. It is built on the same principle that you are using.

Yup, I am using one as a high pressure storage tank, and the other as a firing tank. Thank you for the insight on the regulator and the airflow out of the accumulator tank, I will keep those in mind.

[FrankJ]

We use a 2-1/2" nominal (2.465" ID) copper pipe as our barrel. Tee shirts have to be carefully rolled and are still tight. It takes about 30 PSI to pop them out. Normal demos we shoot at 40-60 psi. We go up to 110 psi on the football field. We are a little unique in that we use a shooting accumulator that discharges completely on every shot rather than feeding the cannon directly off the storage tank.

You want your hose between the barrel and the air accumulator as big and short as possible. That will limit the cannon's range of motion. I would mount the fire valve on the cannon to keep the flow in the hose as high as possible. Tapping pipe threads in a block of steel is doable. Especially with working pressures less than 120 psi. 3/4 pipe is getting on the big side for hand taps though.

[HumblePie]

Here's the result of our offseason project:

We have 4 fixed 3" barrels, all plumbed to a single manifold. The manifold has 3 Clippard tanks plumbed into it, giving approximately 100 cubic inches per shot. Each barrel is plumbed to the manifold through a fairly pricey 1/2" air piloted valve, salvaged from a piece of production equipment slated for disposal at our main sponsor. The manifold is recharged between shots via the compressor and a 2 gallon tank. Manifold refill takes 1.5 to 2 seconds. The ball valves shown are used to precharge the tank and/or manifold with shop air to lessen the load on the compressor (30% duty cycle). Short shots take about 40-50 psi and a full 100 psi charge results in distances of about 90 feet, depending on rolling skill. We use a short section of the barrel material to check the roll, looking for a slight interference fit.

[GeeTwo]

Originally Posted by HumblePie

Here's the result of our offseason project:

We have 4 fixed 3" barrels, all plumbed to a single manifold. The manifold has 3 Clippard tanks plumbed into it, giving approximately 100 cubic inches per shot. Each barrel is plumbed to the manifold through a fairly pricey 1/2" air piloted valve, salvaged from a piece of production equipment slated for disposal at our main sponsor. The manifold is recharged between shots via the compressor and a 2 gallon tank. Manifold refill takes 1.5 to 2 seconds. The ball valves shown are used to precharge the tank and/or manifold with shop air to lessen the load on the compressor (30% duty cycle). Short shots take about 40-50 psi and a full 100 psi charge results in distances of about 90 feet, depending on rolling skill. We use a short section of the barrel material to check the roll, looking for a slight interference fit.

If your Clippard tanks use the usual FRC fitting, those three 1/4" diameter fittings are the limiting factor on getting air to the shirts quickly. If you used a section of galvanized pipe as a tank, with reducers at the end to feed a 3/4" or 1" valve, you could achieve the same launches with much lower pressure and probably less air. 3/4" normally closed valves are available for about $20, and I recall seeing 1" NC valves for less than the 5 port solenoids usually used in FRC.

Edit: This draws more current than the air piloted valve, I am sure. We drive ours through a 12V relay module, though a spike relay could serve the function, if you don't mind driving brads with a 3 pound hammer.

(not that exact module, but a similar one with four ports)

[HumblePie]

[quote=GeeTwo;1514515]If your Clippard tanks use the usual FRC fitting, those three 1/4" diameter fittings are the limiting factor on getting air to the shirts quickly. If you used a section of galvanized pipe as a tank, with reducers at the end to feed a 3/4" or 1" valve, you could achieve the same launches with much lower pressure and probably less air. 3/4" normally closed valves are available for about $20, and I recall seeing 1" NC valves for less than the 5 port solenoids usually used in FRC.

Thanks for the input.

Since this was being built from mostly scavenged parts, and didn't have to be FRC legal, we prototyped a single cannon with the 1/2" valves we had available and a commercially available (small) manifold with 4 Clippard tanks attached. Initial trials were uninspiring. Your point about cross-sectional flow area is well taken, as when we opened up the ports on the Clippard tanks to 3/8"NPT, we were shooting about 90 feet at 100psi. We were even able to maintain that distance with just 3 accumulator tanks, so that's where the design is now. We also replaced some tube fittings between the manifold with a 1/2" close nipple to improve flow. Down the road, we'll see about replacing one of the Clippard tanks with a smaller one and see if we can maintain a similar (or at least acceptable) max distance.

Can't wait for January 9th!