A Good Day for a Trebuchet, Part II: The Siege of the Sandpit

The Siege of the Sandpit

By Danièle Cybulskie

Sometimes, when crazy people get together, magic happens. This weekend, I visited my in-laws, and a few of us got it into our heads that we should build a bigger, more powerful trebuchet than my little model, using materials we found in my father-in-law’s woodworking shop. We did, and it was awesome.

The 5 Minute MedievalistWe built our trebuchet about four feet tall, with a throwing arm that was initially about seven feet long. Our counterweight was a plastic wine pail that we guessed could hold around fifty pounds of weight (sand), but we discovered that fifty pounds wasn’t nearly enough to get a good swing. As a result, we lost some length in the throwing arm, leaving it at around five-and-a-half feet long. All the structural pieces of the trebuchet were made of scrap wood, save for a steel pipe we used for an axle, and a metal gate latch we used to lock the throwing arm in place while we got out of the way.


Although we did most of the building together, I ended up being responsible for the sling. (No pressure.) Because we were using found materials, I used part of a non-slip rubber mat, held into a curved shape by cable ties, and attached to the trebuchet with nylon rope. The sling attached to the throwing arm via a metal eye underneath, and a wooden dowel (drilled in at about a 45-degree angle) at the end.

As it turns out, the wooden dowel at the end is one of the most critical pieces of the trebuchet. Because we tried using a screw at first, we discovered that even the tiny slope at the head of the screw cost us distance, since the trebuchet launched the projectile too early. The end that holds the part of the sling that releases has to be absolutely smooth for the rope to slip off effortlessly.

We weren’t successful at first, and tried lots of troubleshooting in rope length, weight of the projectile, counterweight, and the wrap of the sling. Because of the slope of the hill, we elevated it a little bit at one end. With a little tweaking, we started to see some success. Real success.


Our little, homemade trebuchet shot a two-and-a-half pound stone more than seventy feet into the sandpit at the bottom of the hill. This would mean it could hit a wall at around fifty feet. Different weights gave us different distances but always in a straight, straight line. If we used the same stone, we could hit the same mark. Seriously. Check out the videos of us hitting a small cardboard box at seventy feet. (That’s me clapping in the background.)

The fact that you can build a trebuchet out of found materials and still have it manage to function consistently and accurately speaks to the genius of the original design. There are lots of places in which we could improve our model, and the ideas are already percolating in our heads. Who knows? Maybe our Thanksgiving visit will yield a full-sized trebuchet, since (as so many of you pointed out after my post last month) it’s always a good day for a trebuchet.

A Good Day for a Trebuchet

(Just as a quick note: Please remember, as we did, that a trebuchet is a weapon, and it’s very dangerous at every stage – especially when it’s loaded. Everyone in our experiment kept well out of range, and we shot into an empty sandpit. If you do try to besiege a sandpit, please keep yourselves safe.)


Check out Daniele's new book!
Check out Daniele’s new book!

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