T-Shirt Cannon Help

Hi all, my team has been looking to build a t-shirt cannon. I’ve been looking at other team’s cannons and stumbled upon team 135’s launcher. Here is a link to their reveal video. I noticed that their cannons are connected to what looks like PVC tubing. I was wondering if this was the case or if they used something else. Also, what type of valves are they using?
Thanks in advance for the help.

They won’t be using PVC tubing. ABS, maybe. Metal even more likely.

And probably sprinkler valves.

Pro-tip: mentioning “PVC” in any thread on T-shirt cannons is a recipe for a horde of people telling you all about the safety risks.

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Yeah haha, I’ve gone through many threads where I see people saying no to it. If they are using ABS, where would we be able to find the end of the pipe where you connect the tubing? Also, are they storing their air in that back pipe and refilling it every time a cannon is used?

At my college we built a T-shirt Gatling gun and used a lot of FRC parts in the process. The basic operation of it was we stored our air in a large primary tank (we used compressed nitrogen for our use case), from there a valve would open to fill a smaller secondary tank and then close when full. Then another valve would open, releasing all the air in the secondary valve and launch the T-shirt(s). The purpose of the secondary tank was to ensure we didn’t release all of the air in the primary tank when shooting off one round.

I would imagine that 135 is using a similar setup. The large yellow tank seen would be their primary, and while I can’t make it out in the video, I would imagine there is a valve then between the yellow tank and the large black pipe like in ours. Then to shoot, they’ll make sure the valve between the primary and secondary tanks are shut, before proceeding to open the valves that launch their shirts.

Hope that helps a bit.

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This definitely clarifies some questions that we had. Are there any valves that you would recommend for building a cannon? Also what is the part called that can measure the amount of air in a tank and send that value back to be used in code? We have a pressure switch though that only outputs a true/false. We’d want something that could help us determine when to stop the compressor from filling up the tank.
Thanks for the help!

Looking at the video, it looks like this is the valve 135 used: https://www.homedepot.com/p/Rain-Bird-3-4-in-FPT-In-Line-Valve-CP075/202078357

My team (2412) currently uses this valve, and it works fine for our cannon.

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Thanks for that! We’ll definitely be using that valve when we go to build our cannon. I’ve been looking all around for ABS pipes which can sustain any sort of air pressure and can’t seem to find any elbow or fork pieces except for this straight pipe which can sustain air pressure. Do you know of any places that sell air pressure rated ABS piping?

For our cannon, all of our parts were sourced from Home Depot. I’ll give that a check right now to see if I can find the parts we used.

This would be really helpful! Please let me know if you find anything.

Yeah, I can’t find the parts we used but it looks like most ABS size adapters are fine for air pressure. If it’s possible, you could run a pressure rated flexible tube between a straight rigid barrel and air tank to remove the need for angled couplings (for example if you could find a good way to mount it, you could use this:

https://www.homedepot.com/p/Everbilt-1-3-8-in-O-D-x-1-in-I-D-x-24-in-Clear-PVC-Braided-Vinyl-Tubing-HKP002-PVC006/303132513

That’s not a problem. Thanks for the help!

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Valves: the key thing is that it operate quickly (solenoid vs motor), and have a large air cross section, at least 3/4" and preferably 1". As hinted above, avoid any plastic-body valves which are almost certainly rated for water but not air. Air is not more likely to break a part than water, but because air compresses so much more, it causes significantly more damage if the part is likely to fragment (vs tear). Oh, yes - normally closed. You only need the valve open for a few milliseconds at a time! Here’s what looks like a good one:

https://www.google.com/shopping/product/15246637585462115180

Sensor: You’re looking for a pressure transducer. Here’s one I found quickly that will do what you need for a T-shirt cannon inexpensively:

https://smile.amazon.com/AUTEX-Pressure-Transducer-Stainless-Compatible/dp/B00NIK98O8

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No, because ABS piping is not rated for air pressure. The product that you linked to states that it is suitable for non-pressure applications.

Please this technical manual from Charlotte Pipe, which contains this warning and similar throughout:
image

Please take the time to do this right, and only use air pressure rated components.

These are exactly what we were looking for, thanks for that! I was also wondering if you knew of any electric regulators that could be connected to regulate the PSI amount that is released into the barrel.

I may have misunderstood what you mean here, but just in case:

The way pretty much every cannon I have seen works is by regulating the pressure to the air tank that is attached to the valve. Generally pressure regulators also regulate volume of air because of how small the openings are in the attachments. For regulating pressure to the tank, you can just use a standard pressure regulator used on any other FRC pneumatic system.

Edit: I don’t know if that was clear enough. The air tank is usually attached to the barrel with tubes and fittings with 3/4-1in innner diameter for higher flow rate.

Ah I see, that makes sense. I guess what I was trying to ask was if there was a way to regulate the pressure at which the t shirts are shot at remotely, although now that I think about it, I feel as though the easiest solution to this would be to use the FRC regulator to manually set the desired air pressure.

Since it doesn’t need to be FRC legal electronics, you could connect your compressor to a relay or motor controller, and just turn it on whenever the sensor you use drops below a certain value. Then back at the driver control board, you could have a value somewhere for adjusting firing pressure.

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I didn’t even think about using a motor controller, that is something to definitely think about using! I assume then that the valves can also be connected to motor controllers and opened/closed through them?

Yes, they can. That’s how my team has always done it (although when I redid our electronics board this year, we switched to using an old Spike. Same concept though.)

If your air is coming from a compressor/tank with internal compressor cutoff, you can do this even easier - install a small solenoid valve (an FRC-official sized one, for example) between the compressor output and the accumulator tank. Close it when the pressure in your launch accumulation tank reaches/exceeds the desired level. All you’ll need will be a controller with one analog input (pressure), two digital outputs (input solenoid valve, output solenoid valve), a relay for the output solenoid valve, and whatever inputs/outputs you want so the operator can control it.

For small, non-FRC relay needs, I like 12V relay modules similar to this. They are also available in 2-, 4-, 8-, and 16- channel versions:

https://www.amazon.com/HiLetgo-Channel-Isolation-Support-Trigger/dp/B00LW15D1M/