I'd like to thank those people who have written me lately with questions about catapult building. There's no doubt a renaissance in interest in the ancient art of hurling.
Catapults are wonderful, exciting examples of technology. They are simple yet complex; delicate yet brutal. Unlike looking at say your computer or an airliner, you can pretty much look at a trebuchet or ballista and kind of understand what's going on. On the other hand, the physics and kinematics are complex and intricate.
If you're interested in catapult building, I've posted before on this blog about catapult building, and it might be worth your while to check the index and read those posts. If you need plans, get a copy of my book, the Art of the Catapult (see link below).
Tips for building a catapult for school projects:
- Use modern materials. While it might be cool to build a coiled rope torsion spring like the ancient Greeks, you'll probably find it difficult to get enough spring power without torquing down the ropes so much that you'll crush the frame. Better to use bungee cords.
- I find hardwoods and metal frames work better than softwoods.
- If you're making a trebuchet, consider forgoing the pouch on the sling and simply attach a cord to the object you're hurling:. That way, when the projectile flies, then so does the cord. I call that "a sacrificial sling." It's way, way easier.
- Consider your release mechanism carefully. For bigger catapults, consider a pelican hook (it's a peice of hardware that sailors use, and you get them at stores that cater to boating) or possible an archer's arrow release. You get those at sporting goods stores. Their fairly cheap and they work well with smaller machines.
- I've created a post exclusively on obtaining triggers at http://nfttu.blogspot.com/2008/02/catapult-and-trebuchet-triggers.html