[EricH]

Is it possible? Yes. You'll want an encoder or a potentiometer--probably the pot--connected to the chain somehow, and you'll possibly want a gearbox as well, which might make for a nice place to put the pot. (The other good spot might be on a tensioner, or a random sprocket in the middle of the chain.

As far as what is optimal, that would depend on what exactly you have available. Window motors are good at holding position, but other motors may also work.


Programming setup (basic): First, figure out what the sensor reads at each desired position. Store that somewhere in the code. Next, figure out the command trigger for each position. Store that as well. When a command trigger comes in, compare the desired position to the current position, and move the motor the right direction to match the current position to the desired position. Stop the motor right before it gets to the desired position (it takes a little bit to get the command through). I'm no programmer, so I don't know how to actually implement this in code, particularly in Labview.