If you’re stuck inside with a 3D printer and no project that comes to mind, check out this spring powered car as modified by Jason King. King started out with the basic components from a shared project on Thingiverse and used the print as a chance to play with some fun color materials and the always interesting NinjaFlex print material. He ended up with a satisfying and zippy little car and a gripping set of NinjaFlex tires that allowed it to scoot speedily across even a slippery surface. Read more about this fun project: http://3dprint.com/46515/pla-spring-powered-car/
Below is a photo of the finished car project: