My buddy, his grandfather (doctorate in engineering), and I built a model for a trebuchet this week. It's very cool. I'll get pics up soon, but I'll give you the story. I read here a while back that someone built a treb. Seemed like a great idea, so I suggested it to my friend as something to do over spring break. He told me about his grandfather, and we decided to build a scale model of the real thing, to test the principles. The throwing arm is about 4 feet long, and the counterweight is 20 pounds. We launched golf balls to a distance of 150 feet. It's very accurate. He lives on the lake, so we took it out on his dock and launched it onto the ice too. We thought it would bust the ice, but instead they bounced about 20 feet. Very, very cool. I'll get some pics up tonight.