Summary

This is my version of a penny catapult for use in the game SEEJ. It has a ratchet to allow for easy tightening of the rubber band. I have included an STL file that shows how to assemble the catapult. The assembly file contains ASSY in the name. The files are publicly available on tinkerCAD.com.

Instructions

Step 1: Print all the parts

I print with 1 skin and 10% fill. I do not recommend printing this with acceleration turned on if you are using a Replicator.
If you are going to print all the parts at once I recommend using a raft.
You have some choices to make here. I have included a file that has all the parts. If you are good at printing large files then you can turn this on to print at night and wake up to all your parts in the morning. Otherwise, you can print the parts you want in groups by selecting the individual files.
Decide if you want to use a 1 penny or 3 penny arm. When I play SEEJ my kids and I like to play with the following rule. At the start of each round you count how many flags you have. You get one shot for each flag you have standing. You can decide if you want to load more than one penny at a time or if you want to shoot 3 at a time (a 3 penny shot costs 3 flags). Both arms allow the user to shoot the penny in two orientations â€“ flat or on edge.

Step 2: Assemble the Catapult

Using the ASSY file as a guide, assemble the catapult. I use a little supper-glue to hold the supports in place on the frames.

Step 3: Rubber Bands

Using an elastic band of some sort, create a loop between the left and right frames. Do this by pulling the elastic through the hole in the center of the ratchet/frame assembly, loop it around one of the two shortest supports from the â€œsupportsâ€ file, back through the hole and do the same thing on the other side.
When choosing a rubber band I have had better luck using rubber bands that are wide and that are already fairly tight before you turn the ratchets. If you use a rubber band that is too narrow you will have a hard time getting enough power out of your catapult. If you use a rubber band that is too long you will have a hard time keeping your arm straight.

Step 4: Power Up

Turn the ratchet so that the rubber band twists. Be sure to tighten both sides equally.
As you twist the ratchet it is a good idea to twist one side one full turn (360Â°) and then twist the other side one full turn (360Â°). This will help keep the catapult arm straight.
Be sure to check the arm to make sure it is not twisting.

Step 5: Play

The catapult is easy to use but there is one feature that might not be obvious. If you printed the â€œstopsâ€ they can be used to choose the angle at which your catapult shoots. Slide both of the stops out of the way to get a low straight shot. Slide the biggest stop to the center for a high shot. Slide the medium stop to the middle for a medium level shot.

Step 6: Enjoy!

SEEJ Deluxe Penny Catapult