Here’s another grandson and his project. His idea was to build a catapult that could launch walnuts, which we have in abundance in the fall. I’m pleased with the design we came up with. It avoids one of the issues with most catapult designs, that is that the throwing arm normally slams into a hard stop to get the best launch angle. In this design, we used two opposing springs (bunji cords), a strong one to provide the launch power and a lighter one to stop the arm. Even from a full power launch, the stopping cord provides a soft stop, but still has a consistent launch angle. We haven’t tried a walnut yet, but it can easily send a golf ball 50 or more feet.
The catapult is built almost entirely out of thin wall conduit, which is strong, light and cheap. The joints are simply welded together. The cup that holds the projectile is a piece of sheet metal formed into a shallow bowl.
