Here's a video of the String Launcher in action. It was inspired by a video I saw by Bruce Yeany. His string launcher is beautiful and I knew I lacked the woodworking skills to replicate it, so I just 3D printed what I would need.

Unfortunately I can't share all the details. I don't know were the motors came from. They were in a box of left over stuff from a physics make and take workshop from 10 years ago or so. However, I made this in Tinkercad and you can easily go in and edit my model to fit what ever motors you happen to find.