counterweights
anything based on springs/elastic is going to provide the least force when there
is more slack chain, which is when the most force is needed.
a weight based system provides a constant amount of force, which can be changed
easily.
I would suggest using 2L soda bottles or similar for the weights so that we can
adjust the weight by changing how much water is in them (and they, or milk
cartons, or similar containers should be essentially free for everyone.
The lines between the chain and the weight need to be guided around the top
beam.
Can this be done with eyelets? or do we actually need the lower friction of a
pully?