This nefarious device can easily launch a U.S. penny across a room when printed at 1:1 scale. It’s one of the primary engines used in a game of Seej.
This is another design inspired by The Art of the Catapult.
The nock on this model is the very tip of the throwing arm from the Zheng3 Penny Catapult, turned on its side and modified a bit so that it fits smoothly into the firing groove.
I repurposed the winding keys from the Zheng3 Penny Catapult to hold the ballista’s rubber bands in place.
Construction is really simple! Needlenose pliers are recommended, but not strictly necessary.
You’ll need two elastic bands to complete this ballista. Tie a single band through the bore on one of the two D-shaped locking keys. Repeat the process with the other locking key.
Feed the end of one band through the rectangular bore on the ballista’s left post. Insert the tenons of the locking key into the square mortises on the post to lock the band in place. You’ll be tempted to repeat the process with the other side, but don’t give in. It will save you precious minutes of frustration.
Unlike the Zheng3 Penny Catapult, these locking keys should be a snug fit. If some settling of the plastic during printing has made the mortises too small, trim the tenons a bit with your blade of choice.
Center the nock on the knot that connects the two rubber bands. Make sure that the penny’s cradle is facing forward.
Feed the end of the band that’s been locked down through the rectangular bore on the nock. Tie the free end of the band to the second band. Now feed the free end of the second band through the outside of the rectangular bore on the right post and loop it through the second locking key.
The nock has a wee nub on its underside. Slide this nub into the ballista’s firing groove; it will improve accuracy.
Load a penny into the nock, pull it back, and fire away. Be safe! Don’t hit the cat.
Flagrant stagecraft alert: There’s a piece of hookup wire holding the nock in firing position for dramatic flair.