This is a simple catapult model that I designed to shoot Nerf Rivals balls. To assemble it, simply slide the arm in followed by the block, then add the shaft and put the shaft lock on the end of the shaft where it has a notch. The shaft lock does not need to be pressed the whole way, just as far as you can get it. All tolerances are 0.3mm.

There are three options for “blocks” that determine the angle at which the ball is shot. The normal block, or the shortest one, shoots the highest, and the “high block,” or the longest one, shoots the lowest.

This model relies on the flexibility of PLA, so I recommend printing in only PLA. However, ABS would also likely work, but I suspect that PA will be too flexible to work as intended.