What options do I have for creating a resistance to a mechanical movement apart from simple friction?
Assume I have a lever, which will result in either circular or linear motion. I want to be able to apply a resistance to this motion, so that the user will have to apply extra effort to move the lever in either direction. I could use a spring, which would resist motion in one direction, but this would then result in a restoring force when the initial displacement force was removed. I want the extra force to act in both directions, so that the lever is "heavy" to move, but will stay in its new position when displaced.
I want the force to be able to be calibrated and remain constant, so I don't want to have something like a brake pad, which will wear, or just a nut to do the joint up tight, as this will be too difficult to achieve a calibrated force.
Is there something that could be done with a spring or pneumatic air muscle or by using hydraulics?