Second Test!

First things first, we added some plywood on the outside of the rails, just in case. More importantly, we got a 7:1 hoist to lift the counterweight. However, we later discovered that the hoist significantly limits the height to which we can lift the arm. The baseball diamond was occupied, so we took the trebuchet to the varsity football field, instead. We got three shots off, the first with 4 45lb plates, and the others with 6, for a total of about 300 lbs with the bar. The triggering mechanism is of our own design, and has worked surprisingly well so far. There is a 2x6 spanning the vertical supports in top, to which the hoist is attached. When firing, we pull on a knot with two webbing length going from it. The shorter pulls out the triggering pin. With all the weight taken off of it, the 2x6 can then be pulled to the side by the second line, so that the arm doesn't hit it. A small line keeps the 2x6 from flying off towards the trigger man. After reviewing the video, we have concluded that we will need to make the bridle attaching the arm to the hoist shorter, so we may lift the arm higher. Also, we will make the sling shorter, as sling releases after the arm decelerates.
I tried to take the videos from different angles to make sure everything got captured at least once.