Well I originally had a blog post on this project, but now that I have video I feel like it is time for an official post.
This was built by my group in drafting class. It was decided that I got to take it home since I did most of the design work. The challenge was to build a trebuchet out of 2 12"x24" sheets of wood that would be cut by the laser cutter at school and assembled with glue. Who's ever threw the furthest won; We won. Everyone else in the class had some pretty small trebuchets. I have no idea why they figured to do that. I guess they were not the best at using all the material in an effective manner.
Here are some snapshots of the CAD files. They were not easy to dimension properly:
Here are snapshots of the laser cut layout:
It has dove tails so the parts would interlock and hold together. Some people designed a trebuchet but did not put much thought into how it would fit together. The bottom could not be dove tailed, but I did use some notches to interlock the parts.
The ratio of throwing arm to counter-weight arm is 3:1. The throwing arm is a single piece and the counter-weight is made of 2 pieces. This means it comes together in a 3 piece thick section where the dowel rod runs through the arm.
I am using a Pepsi can filled with pennies as a weight. At school we used something else, but I had to make my own for home. This weight ties onto holes that are in the rear of the arm. A Pepsi can works MUCH better than a Coke can ;)
The sling is made from one of those reusable shopping bags.
Part of the sling is tied onto a hole in the end of the arm and the other half is tied into a loop and put over a paper clip. I convinced my teacher to allow use to use paper clips as the release. He was convince we could do it with just the hole, but I still do not understand how he figured that. Once we all used paper clips, the trebuchets were throwing a lot further and consistently.