I've got an old plasma CNC I am trying to get set up with new servo drivers and I am stuck on the loop gain adjustment step. When I increase the resistance I never come to a point where the motor will oscillate on its own. If i manually turn the shaft of the motor it will become unstable. At a low setting on the pot it will have large slow oscillations and at a high setting on the pot it will have quick small oscillations but it will never stabilize in either case.

The servo drive has additional dip switches for changing the resistance or capacitance of the loop, but I have no idea where to start. Any tips or guides for figuring this out?

Equipment:

AMC AB15A100 servo driver
1000 PPR encoder, attached to motor shaft
Burny Phantom CNC
Torque System/CMC 3515 brushed DC servo motor