You're right I'm thinking of featherweight - at the small end of the scale where costs are small and everything can be built on one desk without needing any special lifting equipment but not too small to be a pain to build!

I'll try and find a build thread for Diotoir. It might help to see what others have done, even if the scale is different.

With regards the re-cocking of the spring, I was thinking a steel cable that can just be released and then wound back up, or perhaps designing it so it could be re-cocked faster using the entire machines drive system, like into a wall or something.