Catapult and Trebuchet Triggers

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More in my series of posts on How to Build a Catapult

In this post, I discuss Catapults, Ballistas, Trebuchets and the Triggers, Releases, and Latches that operate them.

I receive quite a few inquiries about making catapults and trebuchets. And among the most frequent questions is: how do I build the trigger? It's an important question.

Catapults are fun and educational to build and operate. They would make a very good entry in a science fair or science contest. For ideas on catapult related science fair projects, check out "The Art of the Catapult" and "Backyard Ballistics," available at book stores everywhere. (Click on the Amazon link to the books above for more info) Believe me, there is plenty of physics and math behind the machine for cerebral types.

When building a catapult, trebuchet, ballista, mangonel, or any of the hundred names by which such hurling machines are known, you'll find out that the mechanism that releases the throwing arm is often the most complicated part of the machine.

You may build your own release, which is tricky because you need to design the latch so that it will release reliably under full load. Actually, you can get pretty creative about triggers.

But considering how cheap and easy it is to buy one, it might make more sense to use one of the commercial solutions below, and spend your time working on the other aspects of the machine.I've spent time researching the best triggers and releases for small catapults. You can follow the links below to obtain high quality, inexpensive catapult release trigger mechanisms that should work well for most small experimental catapults. There are three good, off-the-shelf solutions: The archer's arrow release, the sailor's pelican hook, and the horse trainer's panic snap.

Archer’s Arrow Release:

This is the premier solution. Works dependably, quickly and very smoothly. It costs a bit more, but of all the catapult releases I've tried, I like this one the best.

Sailor's Pelican Hook:


This is another excellent hurling machine trigger. Its normal use is in sailing, where it is used to securely hold and release lines and ropes. Basically a pelican hook is a hinged hook that can be quickly secured or released by a sliding ring. It is quite a bit less expensive than an arrow release, but it holds securely under load. The downside is that they can be awkward to release sometimes.

Horse Trainer’s Panic Snap:

A panic snap is a mechanism often used between a lead and a horse's harness. They are decent catapult triggers because they can be disconnected under load. A panic snap is specially built so that the latching mechanism is separate from the load bearing structure. Just pull back on the latch and the load releases. Very inexpensive, but not as smooth or dependable as the arrow release.