FIRST air cannon robots PVC??

[Dan Richardson]

I Believe the rating is posted on the side of the pvc? I remember that it was deffinately on the side of the pvc glue bottle for the joint strength. The pvc is usually not the concern however it is the joints. Improper usage of pvc glue can end up in caps flying off in a spectacular like fashion. Another common problem with pvc is under sunlight it can become brittle greatly reducing the strength of the pvc. If put under pressure you can have a failure to occur, and thats no good.

Regardless its still a cheap and effective option. For a freshman engineering project I used pvc to build a marsh mellow launcher. I have considered modifying it for t-shirts as it would work effectively but It would be a one shot deal and we'd like to get multiple shirts fired before pressurizing.

In my marsh mellow launcher I only had one failure and it was due to improperly gluing. In this case I actually did not let the resin settle before I tried it he he. But after regluing I was able to consistently hold about 100 lbs of pressure in a 2 ft long by 2" diameter pvc pipe. Its fun to shoot a marsh mellow at ~ 280 fps. It is however not fun to get hit by one :-)

I've seen shirt launchers being launched at approximately ~40 psi successfully and sometimes almost too far.

Without testing however fatigue could be a concern, it may be something you'd want to consider rebuilding every so often.

[Cody Carey]

We have had our air tank pressurized to 80psi and run the end cap into a wall at about half speed of our robot (6-7mph)... It was an accident, and as soon as it happened I was sure that the tank would explode, but nothing seems to have come of it. The tank also tends to be manhandled when it is taken off of the robot, and that has never had an ill effect. We test the safety of the tank by isolating it from people and pumping it up to 110psi, which is 30psi higher than we use to actually shoot the t-shirts and footballs.

The main thing that I would say be careful about is what glue you use. Someone in a physics class at our school tried to emulate our cannon, and used glue that wasn't rated for pressure... he broke a window out of one of the doors.


Sched 40 pvc holds up fine for our uses, and we have never had a problem.

[artdutra04]

The smaller the diameter of PVC, the more pressure it can stand. In this table, you can see the maximum operating pressure and the minimum burst pressures for various grade and diameters of PVC and CPVC pipe. A 2" Sch 40 PVC pipe has a maximum operating pressure of 166 PSI. If need arieses, instead of using a larger diameter pipe to store more air, I'd just use multiple 2" diameter accumulators clustered together. Also, try to use Schedule 80 whenever possible; the extra wall thickness will certainly help lessen the danger of the accumulator rupturing.

Also to note: PVC loses a lot of strength as the temperature rises. If you ever plan on using your air cannon in 100^oF weather, PVC's maximum operating pressure drops to only 60% of it's original strength. (A 2" PVC accumulator would only have a maximum operating pressure of 99.6 PSI. In hot climates, this may become a major issue.)