1. I have a school project that requires a device that can launch a projectile, using a non-metallic elastic solid (rubber bands, wood, plastic, etc.) 3. Would an onager be the correct machine to use in this? I'm new to the forum so sorry if I'm not posting correctly! :) I've been researching onagers and they sound as though they would be the right thing, but I've been unable to find any information about where they actually get their power from. I'm familiar with how trebuchets work (done some projects on those). Is the onager the same basic idea, just with an extra piece to stop the arm so as to obtain more force? Thanks!