[math-fun] Non-electronic analogue computers

Anyone know of any good designs for an easy-to-make analogue computer based on springs, masses, and dashpots? That is, we want a supply of easily-interconnectable components that we can combine in ways that correspond to a prescribed differential equation, so that the behavior of the system will be a solution of the equation. As I recall, there’s also a way to get hydraulic analogues of LRC networks (though I forget what the three sorts of components are called); is there a good design for a hydraulic computer? Jim Propp