Designed to fit on an ender 3, i used metal skewers for the pivot pins and axles, ill work out a better trigger design when i can
Supports = Arm only
Arm has a hole in the top for a piece of wire/paperclip etc for the launch pin
Trebuchet in action
I heated the trigger lightly with a lighter and bent it into position with a bit of trial and error
2nd video with trigger
Credits:
BJWilliam