[NickE]

Instead of a sprinkler valve, you might be better off with something pressure rated for compressed gases. Sprinkler valves are designed for liquid and if a failure arises, it would likely be catastrophic. For a robot that's going to promote your team in front of people, it's probably better to be safe than sorry.

We're running 6 6" KOP "sticky" wheels on our t-shirt cannon with the center wheel dropped. They work fine on a variety of surfaces.