what seems to be popular now are what looks like modded paintball guns. They have a similar set up, with an adapted barrel to hold a rolled up t-shirt (most made out or poly carb). If you can find a painball gun with a common thread size (aka not Tippman) then you should just be able to fabricate a barrel and give it a shot! (not sure how much pressure you would need vs. what a stock paintball gun could give you or how far you plan on launching it)
Thanks for all the info an tips.
It’s giving us a good start, and well be sure to follow up on some of the stuff posted here when we start to actually build it. We haven’t actually started our off-season yet, we’ve just been gather ideas and plans.
we did one where it was PVC piping connected to 3 cylinders, you could strap it onto your arm, and it was connected to a battery pack and compressor in a backpack. very dangrous, but very cool. it could launch t-shirts one at a time, but we mainly used it for those little stress balls, ie the NI soccer balls that they had during te deminstration in the pits during championships.
also you might want to look into what diffrent sports teams use, i was at the magic game, and they had one built into a trash can, but it launched t-shirts rolled up into bals, with rubber bands.
Look into McMaster part number 8585K21 for barrel stock.
That’s the pipe I used on my muti-barrel tee shirt launcher. Although it is on the expensive side, I had to guarantee that the tee shirt launcher would be safe to operate around large numbers of people outside, and at temperatures which had a good chance of being below freezing.
There was absolutely no PVC used anywhere on my launcher for safety reasons; everything that held pressure was rated for high pressure gas use and below freezing operation.
I built a t-shirt cannon this fall, and we used it for some robotics promotional stuff. Took it to a basketball pep-rally, that sorta thing… Although PVC might not be the safest thing, you’re probably ok as long you make sure that not only the pipe itself, but also the fittings are all pressure rated. The only thing that isnt pressure rated in my setup was the sprinkler valve. We’ve managed to hook it up to 4 compressors, and load the reservoir all the way up to around 140PSI, and we can shoot t-shirts across our school’s gymnasium (two basketball courts side by side).
We had also planned to hook it up to a promo robot (similar to 1726), but we ran out of time in the fall… Maybe the team will hook the cannon up to a kit chassis with a mechanum drive or something this fall…
PLEASE DO NOT USE PVC FOR AIR CANNONS. PERIOD.
PVC is NOT AT ALL safe for pressurized use, as it is a very brittle material. If there ever is a leak in the material, the result will be a catastrophic explosion of PVC shrapnel. Just because it may have been used without problems does not mean that it is safe.
Please, for the sake of innocent bystanders who may be near the robot if the PVC explodes, don’t do it. Spending a little more money up front on better materials is well worth it if someone is severely injured from PVC shrapnel and decides to sue.
And please make sure its UL certified no matter what you use.
I agree. As I read my previous post, I realized that it could be seen that I was advocating a PVC air cannon. In no way am I doing so. I was simply stating how I built an air cannon. (Just a little disclaimer)
PVC is dangerous folks, and shouldn’t be used for super-atmospheric pressures
Actually, 120 psi is a lot. There is a reason FIRST has us use only 60 psi. If you do make a pvc gun, please, please make sure that you don’t use pvc for the air storage or charging.
Wrapping the tube (barrel) in duct tape a lot and putting a bigger tube around it makes it a little safer.
be safe, Vivek
When originally designing our T-shirt cannon, We looked at the pressure ratings listed in the Engineering toolbox.( http://www.engineeringtoolbox.com/pvc-cpvc-pipes-pressures-d_796.html )
It clearly lists that the maximum allowable operating pressure for 3" schedule 40 (which is what we used) is 158 Psi, and the minimum bursting pressure is 840 psi. Considering that that is 38 psi above what the exhaust valve on the pump we were using is set to, combined with the fact that we had the tank encased in a plexiglass shield and we wouldn’t be operating it in temperatures above 140F (thank God)… I’d say we were perfectly within the confines of what would be considered “safe”.
As for wrapping the barrel and/or tank in Duct tape, and placing it in a larger section of pipe, that would not only make it a little safer, it would virtually eliminate any safety hazard at all. No shrapnel means no major injuries… and the chances of the larger pipe bursting (if it is sealed) are minimal as well, because the largetr pipe would be exposed to a much smaller pressure PSI than the little one was.
As for the reasoning behind FIRST having the teams limited to 60 PSI, I doubt it has to do with the bursting pressures of PVC,but can more likely be attributed to them being overly stringent with their safety regulations… but as there have been no major pneumatic related injuries that I know of thus far in the program, I’d be an idiot to argue with their reasoning.
I’d say that as long as you have the tank well guarded from any shock, and you don’t abuse the thing, you’re safe to use PVC in a 120 PSI system.
I know a team built a tshirt cannon for use at one of our competitions this year that used PVC for air storage. They shot shirts on Thursday and part of Friday I believe before they were asked to stop because of danger.
If you aren’t concerned about your own safety, please be concerned for everyone else’s.
Even though these ratings are printed, for what type of application are they defining? Liquid or Gas?
Liquid does not compress very well, so the chance of PVC exploding with a liquid is very slim. However, gas does compress well, and therefore, the chance of the PVC exploding is much greater. You must also think about the size of the molecules and how they interact with the structural integrity of the PVC pipe. Liquid molecules in general are much larger than gas molecules, so liquid can be contained much easier.
Here is an example of what I’m getting to:
You have 2 balloons, fill one with water and one with gas. Wait a week and look at the size of both balloons. I bet the one with liquid is much larger than the one with gas. Also try popping both balloons. The one with air will be much more violent. This same concept applies to PVC pipe.
We’ve had our own accident with PVC exploding in a kids face, and he could have been killed very easily. He was well in the 120PSI zone (around 40PSI) when a coupling split in two pieces and made the whole tank shoot off like a rocket into the ceiling.
Also, PVC tanks do weaken over time from expanding and contracting. Water lines do the same, but most water lines remain compressed all the time, so the process is much slower. With an air cannon, it goes from 0PSI to xPSI every time it is shot.
There have been many horror stories of PVC exploding and people saying not to do it:
Okay, we finally got around to putting stuff together, and we are looking for tips on how to improve the cannon.
It actually has pretty decent range (shoots t-shirts about 30-40 feet), but it takes about a minute to fully pump up the tank. Now, this is pumping it to 80 PSI, but right now we are working at someone’s house, not the school, so we should be able to lower the PSI and still be able to get shirts into the stands.
Currently, the barrel and tank are both made of 3 inch diameter PVC (please keep reading) and are both about 30 inches long. We are pumping the tank with two of the KOP air compressors. It takes about 1 minute and 40 seconds to pump the tank full with one compressor.
Now, as for the PVC tank- Yes, we are aware it is dangerous. However, we are limited on funds (currently have NO sponsors), and don’t have many other options right now. We will be getting a different tank ASAP, but this is what we have right now. We have taken plenty of safety precautions (we stand around the corner from the tank, so if the tank explodes, it will explode into a wall and the person’s lawn).
Now, if someone could suggest how to get a better pump, a better tank, or another way to do this more efficiently/effectively, we would be much obliged.
EDIT- Just remembered, and thought I would mention- We are currently using a 24v sprinkler valve hooked up to a standard FIRST control system (i.e. a 12v circuit). Would this make the solenoid open slower, and thus give us less bang per shot, or would it really not affect it at all?
take a look at our development of a similar system which has been documented here on C.D. The sprinkler valve you mention has also been discussed on C.D. and even a very nice animated graphic shows how it works. It is a relatively slow opening with a membrane that does flap during exhaust. Does your cannon honk when it shoots? Ours did.
We currently use 1 inch black pipe with npt thread for air storage as it is rated for pressurized air and is available at hardware stores. Stainless pipe is also available. One could even use a 5 gallon Craftsman air tank with only cost $20. On our system, the valve is immediately after the black pipe so that the pvc tubing and barrel do not maintain pressure except during the shot. We got better results when going to the manual ball valve but the best results are with the valve rated for this purpose. The local Parker dealer donated the valve to our team as it lists for $100.
We used ABS and could someone post material that is rated for a 1,000 psi. Ours works successfully, but we want to rebuild it. Also use a sprinkler valve, it works really well.
We use 2 KOP compressors to charge our tank. It still takes a long time to charge from 0PSI to shooting pressure, but we can get 3 shots out of the tank before having to wait again.
We are using an old freon tank used to charge air conditioners that was empty. It’s a bit large for our use, although I can’t think of any other tanks that would work better.
For the sprinkler valve, we connected 3 9V batteries together in series to a relay (not a spike) and connected the relay to a spike. This gives the sprinkler valve 27V of power, which shouldn’t hurt it at all (and hasn’t hurt it over the past 4 years). We put a software limit on the amount of time the shooter can shoot which saves on air and charging time.
The example above me is pretty much the system we use.
I don’t think the size of molecules changes when changing states from liquid to gas.
pressure rated pvc pipe is perfectly fine to us as long as you dont exceed the rating
abs plastic is not pressure rated but when it fractures its like safety glass on a car YOU SHOULD NEVER USE ABS PIPE
steel pipe is the best but most people dont have lots of money for steel pipe
bottom line you can use pressure rated pipe as long as you are smart and dont exceed the rating
Is liquid not thicker than air? Try to move your arm through water, then do it through air. You will notice a big difference. Gas is much more free and energetic than liquid. That’s my point. The actual size of the molecules don’t change from changing states, but the different molecules in the gas form and in the liquid form are much different.
Actually, I believe that the molecules are the same. The difference is the spacing between the molecules.