Working Catapult or Onager

This is a small but fully functional catapult that works the same way real historical catapults did — by twisting rope or string, not by using springs or rubber bands.

When you pull the arm back, the rope twists and stores energy. Let it go, and that stored energy snaps the arm forward and launches the projectile. It’s simple, clever, and very satisfying to watch. You can actually see the physics happening, which makes it a great hands-on way to understand how ancient siege engines worked.

It’s designed to be fun first, but it also quietly teaches a lot: how torsion works, how energy is stored and released, and why this design was used for centuries. Whether you’re testing different strings, adjusting the twist, or just seeing how far you can launch, experimenting is part of the fun.

This model is perfect as a desk toy, an educational project, or a build-and-play model for anyone who enjoys history, mechanics, or just launching tiny things across the room. It’s not just a model to look at — it’s one you’ll actually want to use.

Build: 

-This is a model that needs assembly. It's designed this way so the forces get spread well over the frame. And printing layers are actually used in the same way as wood grain is, to reinforce the build. 

Material needed: 

-String/thread

-CA super glue

The assembly guide is a PDF documentation (download at the bottom)

Additional challenge:

There are 2 more print profiles (These will print faster, but they will be much harder to assemble)

80% scale 

60% scale 

Ultra challenge. Go as small as you can. Objective: The model still works

I have also printed projectiles: 

Donate Filament?

If you'd like to support my 3D printing projects beyond Maker World points, donations are welcome but entirely optional! Your downloads, prints, boosts, and kind words mean the world to me. Feel free to DM or comment (especially if you donate) so I can thank you—it really keeps me motivated!