search this string in youtube, please.
the link above is a series of fires with a treb the Cal Lab built in our off-time built for a Subbase New London Morale boosting event.
We had a ton of fun doing it. Especially since we all work in the electronics field and got to wrap our heads around a mechanical, physical problem.
Throwing arm is 8 ft. 105" weight drop of 195 lbs (I think underpowered but out bar was 1/2" blackiron pipe, maxed out). axle is 2.75 feet from weighted end. After tuning (you can see a couple shots go not so well in the first part of vid) sling length was 6 ft., release pin at about a 50 degree angle. Max distance was 67 yards by laser rangefinder and spotter.
So it was the first time we did something like this, and we got outshot by only one of the other trebuchets, who had the full 15 ft throwing arm and 750 lbs of counterweight allowed in the rules, not too bad.
Wanted to share this beast and look for some constructive criticism. enjoy, and fire away.