I was thinking of building a Trebuchet as part of a joint project between Mark Stephenson and myself. The project is to produce three or more kits of varying complexity. Starting with mechanical and leading up to micro-controllers and interaction.
A small trebuchet or even a series of them might be something to explore.
A trebuchet seems to be a catapult device that uses gravity rather than elasticity to hurl objects. I would expect that a difficulty with devices that use elasticity would be consistency and maintenance. Below is a da Vinci one I came across. It seems most of these use a cross-bow like system or a wind-up system. The cross-bow ones were eventually cut in half to be more like a catapult and reduce the parts count.
The gravity driven ones would also offer some portability since the ballast could be sourced locally. You could move the machine anywhere and then fill up the ballast compartment with stones.
It seems these things are pretty popular among DIY types. They all look sort of like this one which I found.
A couple years ago when a friend told me about this design I was pretty amazed as it had never dawned on my to use gravity rather than elasticity.
I realize these things are more historical and are used mainly by hobbyists as engineering challenges but the design is so functional that they have been in use recently. For example this example from Egypt.
The only moving parts these things have is the main lever with two points of contact with supports and the trigger mechanism. There are piles of them out there in the hobby space. Stuff like this miniature one (below) and many more such as the list at this woodworking site.
Some of the larger ones have hamster wheel style winches. I’m sure this is to allow it to be installed in smaller spaces.
I think making one of these is interesting but there is also a newer design called a Floating Arm Trebuchet (FAT). They are apparently more efficient. They are also commercially available and also popular with the maker community.
A bit more moving parts. Linear rails, bearings and stuff make it a little harder to make. Also a little harder to see how it works. I made a video from pictures I found at this diy site.
There is a commercial version made of laser cut parts. I like how they
There is an interesting version called the Merlin which uses it’s own weight as a ballast.