Just to reiterate, coarse control of piston length has been around for a while. Here is a post about the setup on 1108's 2003 robot with picture and diagram.
http://www.chiefdelphi.com/forums/sh...2&postcount=11
The two solenoid system work for this. I've always thought that the center stop solenoid would be a more elegant solution but never got my hands on one and the rules have changed around some as far as outside part go (I don't know what is allowed this year).
The interesting challenge would be to do fine controls, especially under load, which I haven't done much exploring in.