We have a spring catapult that is pulled down with Andymark's Shift-to-Neutral Winch
(am-2774). The winch has a ratcheting wrench inside of it to prevent it from backdriving, and a dog gear to disengage. To release the dog gear inside, we have a rotating cam on a window motor that provides all the force we would ever need. We were thinking of using the recommended pneumatics, but our robot doesn't have any pneumatics in the design so the cam made more sense.