Help with T-Shirt Cannon

[adciv]

How do you open/close the air from the accumulator to the barrel?

Actually, could you post a general diagram of the existing system?

[ASD20]

Originally Posted by adciv

How do you open/close the air from the accumulator to the barrel?

Actually, could you post a general diagram of the existing system?

That is where you would put the solenoid.

[GeeTwo]

Our findings agree with the general consensus that diameter of flow is at least as important as pressure. The key diameter is the smallest orifice between the accumulator tank and the input to the barrel. Ours is 3/4" at the solenoid valve, and with 60 psi of air in the accumulator (a cast iron tank of about 3 to 4 gallons capacity), we can toss a t-shirt from the running track over our stadium's press box - WAY over a 50 foot lateral toss.

In addition to using pressure to adjust the range, we also regulate the "valve time". Our current system opens for 40 or 50 ms; much longer will use a lot more air with little (if any) additional range. Shorter bursts can be used to dynamically shoot shorter range shirts or lighter objects.

It takes a lot of battery to make the amount of compressed air you'll need to fire t-shirts. I'd suggest either having an A/C compressor to fill a storage tank to a higher pressure than your accumulator, or use a scuba tank. Stock scuba regulators bring the pressure down from about 3000 psi to where the regular FRC regulators can fine tune to the 40-60 psi we use in our accumulator (between 100 and 120 psi IIRC).

Finally, let me repeat the warning about PVC (or any other "brittle" material) being used to hold or switch pressurized air. Remember how I said how much energy is needed to compress air? Well, most of that energy is sitting in the tank. If that tank or a solenoid valve should shatter, there's plenty of energy to accelerate shards to hazardous speeds. Work done by or to a fluid on expansion/compression is ∫PdV or (for constant pressure) PΔV. Water at 60 psi is about 200 parts per million smaller than at ambient; Air at 60 psi is about 800,000 parts per million smaller than at ambient. Because air changes volume so much more than water, compressed air has several thousand times as much energy as a similar volume of compressed water at the same pressure. NO SPRINKLER VALVES!

[ThePoopieBandit]

I worked on my team's cannon a lot and our website has a lot of good information that you can use for ideas. https://www.team254.com/shockwave/

The distance the shirt will be fired can be changed dramatically by how you roll up the shirt and if you add rubber bands not. For short shots we roll them up loosely so they open up almost immediately after leaving the barrel, another is to roll it up and add a single rubber band at the back of the shirt to hold it together in flight but after firing the front of the shirt will mushroom out to slow it down and for long shots we add two rubber bands on the shirt, one on the front and one at the back. Another way to adjust distance is to change the amount of time that you leave the valve open.

[chapman1]

Thank you, GeeTwo, for the first factual response I have seen to the "Why not a PVC T-shirt cannon?" question. At last, I am convinced.

[Mattb706]

Originally Posted by Why_A_Username?

Hey CD,

My team has been working on a couple of modules for our outreach robot. Another student and I requested to be in charge of the T-shirt cannon. At first we thought this was fine but now we're a little but stuck (He's in charge of CADD and i do Drive Train and PR). Niether of us has taken physics yet and so we arent entirely sure how to do the calculations for pressure required. We did them on our own, and got some results that didn't seem right, so we where wondering if CD could give us a hand. Below is the poster on which we wrote our answers:



Thanks CD!

We have one, trying to find some video for you......