I built a small pneumatic motor in my Manufacturing class. There is a hole in the main plate that puts air into the cylinder block, pushing the piston out. Just below the air hole is an exhaust hole which bleeds the air out and cycles the system.
Here is the video
http://youtu.be/j8ucVcNfovk
A couple problems:
The system is really dirty and needs constant oil, and constant maintenance
It doesn't have much torque, at all...
Wobbles a lot, which is why it is nicknamed the Wobbler. Its not too stable
Some good things:
Goes really fast, about 3000 RPM at 30 psi
It just sips air, as far as I can tell it really doesn't use up that much air
This is just an example of a motor, not powered by electric motors, that can be theoretically run on an FRC bot. No solenoids, no electronics, just some air and a really fast and weak motor. It is all made of 6061, besides the crank disk which is brass (Ran out of aluminum stock), and can be made by hand with no CNC, although some was used to make my life easier
.