Catapult

thingiverse

Supports needed briefly for underside of "wheels" to ensure stability during assembly. Assembly is required, but don't worry, it's easy. The upper brace has a chamfer that should be facing up and forward when installed. Additional adhesion like glue or plastic weld may be necessary, depending on your preferred level of rigidity and printer accuracy. A standard office-sized rubber band is used in the photo as an example, but feel free to experiment with other sizes for better results. The entire assembly is included in one .STL file, along with each part on a separate .STL file for easy printing.