The release mechanism for the ballista will be the most complicated part of the whole to build. There are two sleds; one for holding the projectile and one for pulling back and releasing the first. The second will be connected to a rope at the back of the slide, which will pull it back when cranked. (1) In this drawing, it releases the other sled with a fork, which has a stopper under the back of it. (2) The other sled, now finally free, rockets away and (hopefully) hits what it’s supposed to.