force feedback

How is this rod to move ?

Will there be another rod connected to one end that will be controlled ?

Or ......

A little more info about quantities and max cost would help, IOW how much NRE versus materials.

One idea: Stepper motor, little wheel on its shaft, rope around that, other end of rope to rod. Then use a stepper motor controller chip and set the torque. If it has to stop pulling at a previous position you need at least some analog S&H, plus a loop.

Hydraulics would be anotehr option but that requires lots of ME design.

Nitinol will do that. Check out the specs:

OK, the current idea is , I need 12" of travel and have more then enough room for a 24" long rod in the panel.

II The origional idea was to have two gears spaced about 12" apart, linked with plastic chain, one gear has a dc motor attached, either geared down or straight to the gear, the idea being to pWM the motor with a fet as a short to vary the resistance. The rod would be linked to the chain at one point. I have a linear pot with 24" travel and 10K resistance for output and feedback. force needs to be consistant for both directions of travel.

The traditional way to to this is have springs that have a jackscrew attached to vary their compression, but that is ugly and overy complex.

The nitinol wire idea sounds cool, but its gonna need a bunch of wheels and a spring for when you push the rod in, which makes controlling it a intersting proposition. .

Lookup a thing called a torque motor. It is designed to work at stall as well as forward or backward.

That only allows you to vary the apparent damping, i.e. the force vs. velocity. If you want the control to move to some commanded position with no applied force then this won't do the job for you.

I don't see where you need the sample and hold -- you could do this with a purely analog circuit. You may find you need a fancier control loop than mere proportional to account for the dynamic behavior if the user lets go of the thing -- do you want it to slide smoothly to a stop, is it OK if it goes "boing", is it OK if it oscillates?

You may also find that by the time you add sample and hold, multipliers, &c., that "K.I.S.S." means "microprocessor and (easy to change) code".

The name of what you're doing is "haptic feedback" by the way.

Depending on how accurate the force needs to be and the customer's latitude to variation in the feel of the thing moving fast vs. slow you may get by just fine with a motor, but haptic feedback is, by definition, touchy-feely, which means that you're going to be dinking with it -- and dinking with something like this, in a repeatable way that in amenable to field modifications, pretty much demands a microcontroller.