cheers for the suggestions. The water damper is an interesting choice, made me wonder if I could use a big enough set of pulleys to cycle an old fork damper instead (it’d work out as a ratio of ~10:1 though, which is a bit excessive, but would be fun)
I recon if it’s counterbalanced correctly then damping isn’t too big an issue (as even if it’s moving quickly, the effective force is low). so the current plan is :
l side – chain goes over a pulley to a counter weight on a single pulley (resulting in a 2:1 ratio), hidden in a drainpipe.
r side – chain goes over a pulley then wraps around an old 26″ wheel mounted in a knackered fork lower which is screwed directly to a beam. This gives just enough ‘pull’ on a single rotation (1750mm for a 559mm rim) to pull in all the chain needed for a 1200mm drawbridge (1700mm needed..)
so I then just need to figure out a handle for the old front wheel (something can probably be mounted to the disk mount points, or bolted onto the rim/spokes) and then a way of securing it ‘shut’ (little fabric loop for the aformentioned handle).
Then I need to over-engineer the bridge itself enough to keep it nice and rigid. Simple 🙂
PS: aformentioned child is still only 1, so this *might* be more of a project for me than him for the next couple of years..