[Codythecreator]

Alright... so I recently purchased an older hurco sm1 cnc mill that has been retrofitted with a centroid plc/servo drive and so on. When I purchased this mill, the control cabinet was on the south side of organized and I didn’t feel it was done properly so I decided to rewire it. Good thing I did because some of the wire had completed disintegrated and if memory serves me right, CNCs prefer insulated wires as compared to no insulated ones lol. Anyways while I was rewiring the limit switches and such I noticed the servo motors had 4 wires instead of the typical 2 (red and black). The other 2 are white and blue. The only time I’ve seen a dc motor with 2 extra wires like that was off of an old treadmill, in which those 2 extra wires connected to a proximity sensor for speed control. So this of course means I have to take apart the servo motor and find out what these wires go to. And come to find out they run to a separate set of brushes that sit on a separate armature and rotor with they’re own permanent magnets. Essentially each motor has 2 rotors, 2 armatures, 2 sets of magnets, etc etc. Although the second rotor is 1/4 the size of the main rotor. So my question is, how would I go about wiring these things? Would I wire both sets in parallel? Do they both even need to be wired ? Do they get wired to the same power supply ? The closest description I can find for them is that they are permanent magnet shunt motors But the diagrams aren’t quite looking right to me. I believe the motors are the original electrocraft servos that came with the mill when it born back in the 70s or 80s So any help from someone wiser than myself would be greatly appreciated thank you

[Al_The_Man]

The very early servo systems were DC with drives that used voltage loops instead of the later DC type that used torque mode (current) loop control.
These motors used a DC tachometer that resembles a small DC motor. Servo-Tek was one popular manuf.
These voltage loop drives have to be tuned, first by the inner loop, tach feedback to drive, and then the outer loop, encoder to controller, which were a pain to tune.
The later torque mode drives to not require any feedback to the drive, all is done by the encoder to control.
This is also why you do not see tachometers on motors anymore. So if converting to later drives, the tach can be left on and the tach brushes removed.