Desktop trebuchet from bicycle frame

Step 3 Trim frame and build base

After the throwing arm I built the base for the trebuchet. The base keeps the chain and seat stays from moving, provides a launching strip for the sling and fastenings for the trigger. Before I could build the base I had to trim the chain and seat stays to correct length.

Since the trebuchet I was going to compete against had 30cm axle height, I was going for 30cm too. I don't think I mentioned that this trebuchet is intended for inter-office warfare, did I? This trebuchet will increase my range of fire and give me an upper hand against my boss' trebuchet.

I set up my frame like in the picture, using the axle without the throwing arm. This is not optimal, since it is very difficult to get the drop outs aligned parallel to each other. I measured 35cm from the center of the axle along the outer side of each stay and cut the stays diagonally. It was not very accurate, since the other drop out is bent, but it worked Ok.

After trimming I drilled holes for the base, fastened the crosswise struts and glued the launch strip for the sling. You could use for example a metal sheet bent to low U-shape for the launch strip, but I think this approach is a bit more rigid.