Trebuchet
What is a trebuchet? Well, it's like a catapult but there's no bending parts or springs or stuff. It works by a counterweight. The thing is like a see-saw with one side significantly shorter than the other. The counterweight is attached to the shorter side, and as it falls, the other side is pulled up very quickly. The end of that side is attached to a string or rope which is attached to a sling that holds the projectile, which begins underneath the machine, is pulled out and over, and then released.
On this page I will describe the fun Charles and I had building this monster of a thing. Actually, it's really small. "Awww what a cute little trebuchet!!" Don't worry, it can still break windows.
Image quality here is sacrificed for loading time. A larger image can be obtained from me if you really care enough. I'll think you're weird, though.
Descriptions are under or next to the pictures.
This is a side view. The counterweight is the big ball on the right, and the projectile to be fired is the little ball attached to the string at the bottom. There's actually supposed to be a sling to hold the projectile, but that's omitted in this picture. The string is pulled up by the main arm, it swings around, and a hook at the end of the arm lets go of it once it swings to a certain point.
Here's the base that we built to start with.
The big bar is the main swinging arm, and on the right end of it is the anvil counterweight. A face mask (the things you use when you mow the lawn to avoid inhaling grass) was the first attempt at a sling to hold the projectile. The small rod and the two little cylinders were the axle around which the arm rotated.
It's assembled. The swinging arm is almost vertical in this picture. It's positioned so that the projectile will fly to the left.
Right now the arm is being held down and the device is ready to fire. In the "sling" is a lighter. The anvil is hanging above, and when it falls, the lighter will be dragged towards the left, then lifted up, and swung over and launched.
The mask does not work well as a sling. We decided we needed a triangular piece of cloth, which sounds somewhat familiar. After many tries at getting underwear from various girls and failing each time, an old shirt was cut up. The outline of the new sling is drawn at the bottom of the shirt.
The old base (first picture) had its supports way too close together. We failed to consider the width of the counterweight (the anvil is only for testing) and if the posts are too close together, the counterweight will smash into them, possibly destroying the structure. So we found another, wider board to make this thing out of. The vertical beams are the same ones as before, but the 45o supports are now augmented by small triangular blocks near the sides. The entire thing is spray-painted gold.
At this point, my basement looks like this. It's quite messy. Yes, I know the arm has turned into a zigzag of pixels, but that's what happens when you you turn a thin line into a small picture with lossy JPEG compression.
Work is still being done on this trebuchet. It's not done yet. To come: the new sling, which does not resemble a thong, and that's about it for now.
The range of this machine with a 1lb counterweight and a tennis ball is approximately 15 feet. 5lb counterweight and tennis ball gets about 25 feet. This is still very far from the 20m (66 feet) that we're aiming for.
Last updated January 30, 2004.
880 hits since March 24, 2006.
