Whipper trebuchet notes:

-print with support to buildplate
-parts should be press fit, main arm should fit very loosely on axle. weight bucket needs to be able to swing free.
-print sling from soft TPU. if not possible, improvise. (I was firing nuts(as opposed to bolts) by threading string through them. Use cotton thread for lines, could use piece of fabric for sling.)
-weight bucket fits 18x2p coins. Approx 40g. works with less, haven't tested more.
-1 small bolt required for connection, feedback: Do I need to put an STL together for this piece so it's more accessible?
-this can fire backwards so look after your eyes!
-don't fire it at people or other animals

Enjoy!