Project Trebuchet

The goal of this project was to construct a medieval-style trebuchet capable of launching objects over a distance and looking really cool.
The result? Success on both counts.



Going on a targeted budget of under $100, we set out to home depot. All we had were some basic plans in mind and the work of The Geek Group to go by. Our plan was to build a (slightly) scaled down version of their machine. We bought mostly 2x4s (around 11), some 2x6s, some plywood, a 2' long 1" pipe, a rubbermaid bin to put concrete blocks in, rope to hold them up, and 12 20 lb. concrete blocks. The cost of all this was around $85, and could have been lower if we knew what we now know.
The next day, we began construction. During the day, we had to buy a longer 1" pipe, otherwise the bin would not have fit between the sides. By the end of that day, we had what you see below.



At this point, we began to do load tests. We dry-fired it with 120 lbs. of weight in the bin, no problems. We then tried it with 180 lbs, and it did not go as smoothly. The weights shifted significantly while firing, and we soon found out that it was because the 1" steel pipe had bent quite significantly. This was bad news - it meant we would have to buy a larger pipe and drill 2" holes all over the place. However, the next day we went out and bought the larger pipe and the boring bit, and fixed it up. The 2" version was now ready to go.



The next step was constructing a sling pouch. If you want to know why/how, you can go here. This went smoothly, and we went to test the whole thing. The first few live-fire tests were done with an old 630-MB hard drive. After a few tests, the hard drive kept hitting the crossbar and the back of the trebuchet on its way up. This caused the sling pouch to break, so we were forced to make a new one and shorten it significantly. After that, and some slight modifications to the pin release, all was going smoothly. We were testing it from fairly uneven ground, so we used about 8" of wood to prop it up. However, we didn't expect it to slide off quite suddenly, and did not have the time to save it from completely tipping over with 160 lbs. loaded. Luckily, we did make it significantly durable and were up and running again on more level ground in about 30 minutes. By late afternoon on the second day of construction, it was launching consistently, releasing at the same angle each time. At that point, we were using a 1L soda bottle filled with water. Despite all the force, however, it would only go 10-15 yards, a fairly disappointing range. We have many ideas about how to fix this - we believe the primary one involves changing the lever ratio and lengthening the sling pouch (with an addition of a track, it shouldn't hit the back any more). Given some more money and some more time, the trebuchet stands to improve a good deal. We firmly believe that the potential is there for launches upwards of 50 yards, we just need to fine-tune it.

Movie 1 (2.5 MB)
Movie 2 (5.3 MB)



(Built by Tamas Szalay and Mike Scarito)