The STEMFIE Desktop Catapult is perfect for shooting ping-pong balls or crumpled paper. The ball-holding beam moves using the energy stored by two rotor springs. To arm this catapult, you rotate the beam until it locks into place held by the trigger.  

You can shoot ping-pong balls into cups or hit and flip the STEMFIE shooting target, which is included in this project.

Assembly instructions: stemfie.org/sps-000003

Assembly video: youtu.be/8AIVcwuRmV4