Too much "hanger flying". The OP needs to clearly restate the goals of the project and clearly describe the mechanical requirements of his gizmo.
Sorry guys for being late to the discussion. I was thinking the same thing, clearly stating requirements just as for any project.
Problem description: Capacitor shaft turns 70 times between lowest and highest capacitance. It is coupled to a copper pipe loop for use as a transmitting antenna. Voltages/current developed are as high as 4kV and 32A and antenna is extremely sensitive to ohmic losses. Cap shaft has a hard stop at one end and pushing beyond the limit at the other end may knock the shaft lose from internal plate couplings. Also, the capacitor is expensive - USD 200-300 - so tolerance to cap damage is very low. Capacitor range is from 7.5 to 350 pF - roughly 4.9pF per rotation. The antenna is sensitive to 1pF changes in capacitance.
1. Remotely rotate the capacitor shaft.
2. Stop the capacitor from hitting ends on either side to prevent capacitor damage. If #3 is accurate/reliable enough, we may rely on the operator (yours truly) to not turn the shaft beyond predetermined turn numbers.
3. Remote visual tracking of shaft absolute position - both - the turn number and angle (0-360) to allow the operator to figure out which direction to turn the shaft in for matching to a certain frequency.
4. Turn the shaft to allow for 1pF capacitance changes, that is, assuming ~5pF / rotation, comes to a minimum of 72 degree stepping. For safety, lets say 60 degrees.
5. Weather-proof the components since the antenna is to be placed outdoors.
6. No computer (as in a laptop/desktop) control since the antenna is expected to be portable.
7. Cap shaft control mechanism should not connect to the antenna/capacitor electrically in anyway to avoid changing antenna characteristics.
Did I miss anything? Hope not. I suggestion I got was connect identical motors to the same driver. Couple the cap shaft to one via appropriate gear to allow for 1pF stepping and couple the other motor with the exact same gear to a mechanical counter. Identify the lowest and highest counter readings for cap shaft's 70 turns. Is it practical?
Thanks! Really appreciate all the responses to the thread.