Ballista

This is recreation of a Roman ballista. Its small (obviously), and isn't an exact replica (Romans didn't work in plastic). Its about the right size to fire a pencil.

It should be fairly obvious how it works, but I have some instructions below, and a short movie.

P.S. I am aware of the Thingiverse policy not to publish "weapons". I see this as a toy -- it can fire a pencil about two feet with considerably less force than I can throw it. However, please be careful as points can always put ou