So I built a trebuchet. If you don't know, a trebuchet is a medieval siege machine. I've always had a fascination with medieval warfare, and I considered it a nice challenge. I've seen people build these huge machines on TV/Internet to throw pumpkins as far as possible.
Two of my coworkers and I decided it would be fun to have a little competition of who could build a machine to throw a 3-5 pound pumpkin the farthest. The rules were simply that it had to be mechanical where it could release stored energy into hurling the pumpkin.
I went to Home Depot one Saturday with a drawing of my design with measurements. It was just like the commercial, a guy confronted me right away and then became very interested in helping me. I guess they don't get to build siege machines very often. I got back home with a bunch of two by fours of various lengths. I had originally planned an axle height of five feet, but with the few extra two by fours, I figured out a way to optimize what I had so that I could make the axle height be six feet. That way I could have a ten or twelve foot throwing arm instead of a eight foot arm.
My axle consisted of a three foot steel bar that fit very nicely inside of a copper fitting which I wedged into the throwing arm. The steel bar had fitting groves on each end so I figured I'd cap them and screw the cap into both support arms. This looked great and even though it was difficult, allowed me to unscrew the axle for transport. The groves were unfortunately too weak for the pressure and snapped when I was turning the whole trebuchet on its side.
I instead had to secure the axle to the arm supports by drilling a hole in each support and tying the axle to each with rope. This was not as secure as I had hoped but proved to be no problem when throwing.
My release trigger was an "L" shaped hook that slipped inside of a loop on the throwing arm and hooked to the base of the trebuchet. It didn't take much to pull this hook out and to trigger the throw and worked very nicely. To be safe I always attached a thick chain to the arm until I was ready to launch.
My counterweight consisted of two huge painters buckets filled with concrete, sand, rock salt, and bricks. They totaled about 130 pounds together. The first time I tried a dry throw (no projectile) with both buckets attached, the S hook bent open and both buckets fell to the ground with the arm swinging wildly. So I got much thicker S hooks and chain links. I would have gone bigger in the weight but I would have needed to turn to slabs of metal to keep the overall dimensions of the counter weight from getting too big.
Luckily I was able to borrow my friend Ashleigh's pickup truck, otherwise I never would have been able to transport my trebuchet to work for the competition. When I build 'em, I build 'em big :)
I had tested numerous times with tennis balls, but my first real throw occurred in my work parking lot. We threw towards the Hudson River one at a time. It was more for fun then it was for a competition. A bunch of people had come from the office to watch and cheer.
Kevin also built a trebuchet. It was smaller yet had more efficiency than mine. He had a much lower angle throw, whereas mine would be extremely high. My throws had a considerable hang time. He built the support arms using hinges so that he could easily transport the machine in the trunk of his car. I barely threw farther than his, and his fit in a trunk, heh.
Ameet built a type of Mangonel out of PVC piping. Using a little pulley system for mechanical advantage, he was able to get a great snap out of those pipes. The problem was that he needed to secure the machine to the ground and it was very light. So he used one of our bosses as a weight to hold down the machine.
I'm now looking for a convenient way of transporting my trebuchet so that when the weather gets a little nicer I can test it on weekends. I imagine a small two wheeled boat trailer would do the trick. I would securely attach the trebuchet to the trailer to give it more support as well. It's currently outside gathering snow and taking up space.
This is my favorite picture. You can see the pumpkin coming back down from its high trajectory.
- 10 foot arm with 2 feet for the short side and 8 for the long
- 12 x 3 foot long base
- 6 foot high axle
- 130 pound counterweight
- 6 foot sling