Our 2009 Lunacy robot is ready to go as a t-shirt launcher with no modifications. Just need to bundle the shirts to fit in the catapult.
http://www.chiefdelphi.com/forums/at...9&d=1239427199
Shoots about 35 ft., good enough for basketball games.
If you are having trouble with air flow capacity through your valve, try parelleling 2 or 3 valves together, so they share a source, and merge their output together. We actually did this on this robot to get the cylinder speed we needed.