Floating Arm Trebuchet


After a fairly successful trebuchet I made for a Honors Physics project, I decided I wanted to continue building trebuchets especially different kinds. A trebuchet was originally a siege weapon used during the Middle Ages. It differs from a catapult in that it uses gravity to drive the system instead of tension. Since the one for school ended up lacking structural stability, I decided to plan this one out ahead of time, even modeling it in the 3D rendering program Blender. Over the winter break of 2010, My friends Christian, Ryan, and I built a floating arm trebuchet.


In order to create accurate plans that we could built the machine out of, I used the program Blender to model the trebuchet make blueprints by taking screenshots of its various sides. (Click the picture to view larger)

I decided to create the plan where one block is one square inch. This made it easy to use the plans in the real world. I also included views from the front, side, and top. I also included a close up of the wheels on the track, because that is a specifically confusing area.

After modeling the trebuchet. I used Blender's rigging tools in order to animate it and render it.


After completing the plans, we eagerly set off for supplies. We went to the Home Depot and bought 2x4's and wheels. I cleared up some room in my basement and we began working.

We finished building after a few days and we were very pleased with the result. The weights go on the metal pole on the top.

As the weights fall, the wheels will roll first to the left, then quickly to the right as the arm swings forward. Since the weights fall straight down, there is no wasted energy.

We used a small metal hammer as a safety lock that ensures the trebuchet will not fire while we are loading it or carrying it.

Here we stand next to the completed trebuchet. (Nick on the left, Christian on the right, Ryan couldn't make it for the photo)
Here is a video of me testing out trebuchet with a 10 pound counterweight. There is no sling attached because it is indoors.


After we finished building it and attaching the sling, we carried it up the stairs and onto my driveway for launching. We tried different weights for the counterweight and adjusted the sling release pin at the end of the arm to make sure that the trebuchet is releasing at the optimum 45 degree angle.

In this video, we launched a lacrosse ball using a 30 pound counterweight. So far we have used up to 50 pounds and launched the lacrosse ball up to 100 feet. We hope to tweak it and have it launch to its maximum potential!

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