RE: Electric Jackscrew
I've considered modifying a regular servo to drive a lead screw (screw jack). I want to make an in-flight CG adjustment device.
It should be possible to simply disconnect the internal potentiomenter (mechanically and electrically), and use an external linear potentiometer for feedback.
I haven't found a supplier of an inexpensive, light, and long linear pots. That may have to be a home brewed affair.
The modifications described by kronosrobotics are applicable. Except they only disconnect the pot mechanically. If it is also disconnected electrically, and an external pot used to feedback the position. Then it can drive a lead screw proportionally.
Sorry... I haven't gone beyond thinking about it.