3d print catapult
Wheels are attached with #8 or #6 machine screws, partially threaded.
The rest is printed on a 3d FFF printer.
The body comes in two halves so you do not need supports.
Print the launcher on its side with support under the arm. This puts the filaments as hoops to increase strength.
Loop a rubber band over the top bar and around the arm for firing.
I treated the whole thing in an acetone vapor bath.