I saw them testing the one for the discovery channel over in Scotland, during testing and that thing was the real deal.
In my autocad class this semester we're going to have to make an electric model of a trebuchet and make it work.
I cant believe you guys are doing that with the cars parked, but I guess if it only goes in a straightline you wont have a problem.
Are you in highschool physics? My senior year our class had to make a visualization of the "hunter shooting a monkey on a tree, monkey jumps at the same time as the bullet is shot, the monkey is shot midair because gravity pulls them both down at the same speed" theory so we had this killer crossbow setup and then a big piece of pvc pipe that would drop a can and then we'd hit it it in midair. The one time we missed our little ball cracked the PVC pipe. The other groups killer projects missed and made a nice "3" wide .25" deep chip out of a concrete wall.
Kinda OT, but I had to solve for the lagrangian equation for a trebuchet in one of my physics classes this semester. I just saw the title and decided I had to respond. I didn't know what it was until I took the exam. Kinda cool to actually see a working one though.
The lagrangian is similar to newtons laws except they allow you to generalize everything down into two generalized coordinates. I think on this problem we generalized it down to theta(angle with torque arm) and phi(angle with swinging arm).
EDIT: I don't know if that makes any sense or not though or if it is anything that would really be helpful to you. :confused1
Just let me know what you want to know and I will do my best to help.