Hello guys, I got a nice challenge. Myself and some other people at my school are constructing a trebuchet to compete in the Kwantlen College Science Challenge. I've already got ideas for the frame construction, however a few points need to be worked out. Limitations on the device - Must fit in a 75cm box when loaded - No more then a 5Kg counterweight - projectile can be anywhere from 10 - 100 The frame I'm going to try and build out of the heaviest materials I can get. Thus it would sink any kick from the arm and hold transfer more energy to the projectile itself. The trough I'm thinking of just using some curved sheet metal, the metal would be smoothed out as much as possible, then given a coat of Armour All to eliminate as much friction as possible. The trigger I think would work well on the arm, a simple pin release. Reason being that putting the pin on the end of the sling might cause it to veer. Now I come to the two main problems. 1. The sling release. I've taken a good look around and all the designs use a slot of some kind on the end of the arm but I have not been able to locate specific plans. How do these systems work? To more accurately set release angles I was thinking of a string trigger release, where once the sling reaches a certain angle relative to the arm its it's own release by pulling a string which in turn pulls something that releases the connecting band. 2. Connecting arm to the axle. Well this sounds simple, the axle can be made out of whatever. However the arm must be as light as possible while being strong enough to withstand about 5.5Kg of mass on each ends, the other forces while firing, and while having a certain flexibility. Whatever axle we decide to use it will be at least one inch thick, in order to both hold the weight and stand up to the torque. Drilling enough one inch holes into the arm would to allow us to adjust the ratio as needed will compromise the integrity of the arm. I was thinking of using a collar of some sort. One we could loosen, slide the arm, and then re-tighten. This gives us more freedom to adjust the ratio, while not weakening the arm, and having to detach the axle constantly to do so. Any ideas, help, and opinions are welcome.