I converted Tom Stanton's larger wooden whipper trebuchet into a smaller 20cm wide one.
I havent printed and tested it out yet as my printer is down so you are welcome to experiment with the settings.
The axles and holes might need some sanding to swing loosely.
The counterweight carriage can be used for coins or anything else that fits in.
To cover up the carriage, use a piece of tape or something.
Requires 2 wood screws at the bottom to keep the beams in place.
Heat up a paper clip and melt it onto the top of the arm for the releasing part. ( you can bend the paper clip to adjust the angle )
Anything else like the sling, how to use the trebuchet etc. you would have to refer to his video