pic: Team Fusion's T-Shirt Shooting Robot

[Ronald_raygun]

That's correct. The pneumatic piston is connected to the lever instead of it being hand-operated.

Here's a reasonably detailed explanation of how this works.

There is only one real problem with this repeating crossbow, the drawstring wears faster because of the effort of being pushed up and down. One possible solution to this is if there is some sort of replaceable protection for the drawstring (duct tape, plastic, alum foil, etc.)

And, I'm not sure of you've ever heard one of these in action but if you purposely set the slot on the side of the mazagine so the string always hits the stop. It should make a sufficient enough sound, though I'll admit we all know how cool the "thump" of a pneumatic cannon can be.