5236 Piston Catapult

[Hoffer5236]

This catpult is in the early stages, as we are an inexperienced rookie team, so we are looking for any suggestions you may be able to provide.
We are currently working on making it shorter, as it does not currently fit size requirements, but the viedo is helpful in showing our progression.
The cylinders we are using are 1.5in bore, but I'm not sure on the stroke.
Only the last shot is using the selenoids, all the others use the straight air compressor. All previous shots with the air compressor were at 60psi.

http://www.youtube.com/watch?v=r-9v9loC2As