bandit controller retrofit

langdons wrote:

I know they are 6-wire, but perhaps they are 8-wire internally.

They always are 8 wire inside, they all have 4 windings inside, they all have 50 magnetic de-tents inside, making it 200 steps per revolution. There are same types with 400 steps per revolution, meaning 0.9 degree per step instead of the usual 1.8 degree per step.
There are also 3 phase and 5 phase stepper motors, Vexta had some nice videos explaining all the types and versions on youtube.

Do NOT use the COM motor wires on new drives!!!
Do NOT use 5 wire stepper motors with new drives!!!
New drives are always "bipolar" meaning each winding has it's own H-bridge.
Old drives were "unipolar" meaning each winding was driven by a single transistor/MOSFET to ground, while all 4 pins from one side of all 4 windings was wired to + (positive) of the power supply.
Use a DVM in OHM or BEEP mode to find out what wires belong to the same winding, and based on resistance you can also figure out the middle wire, see bellow:
-if you want max torque but lower rotation speed, use the two wires with most resistance, in your case use A1/A2 and B1/B2 and leave ACOM/BCOM unconnected. Do isolate them so they do not touch.
-if you want more speed at lower torque, use the middle wire and 1 of the remaining 2 wires, it does not matter which one, just one.

The 3 bottom wires on the drive boards, what do they have written ?
Do you have an old PC with parallel port?
If those wires are step/dir and GND, fire up the PC, wire some wires from parallel port to those 3 wires, move the machine!

To the left of the ribbon cable, are those optocouplers?
If yes, see what wires go to those optos inputs, those should be step, dir, and maybe enable, one is ground, and for testing you only need 1, the step pin, and if used the enable, but if the drives lock when powered on, then skip enable as they are enabled, so use a signal generator or parallel port, or a small crappy transformer that outputs 3 to 6V AC, should be enough to check if they work, and if they do, leave them on.
Be aware that some older drives use two inputs as step and have no dir at all, so steps on one pin turn the motor one direction, while steps on other pin move motor the other direction.
There are also "quadrature inputs" using steps on both pins, but 90 degrees between them, also no dir.
And as the last type, the 4 input ones, so when testing if the motor does not turn but just vibrates in place, check other pins, there should be 4 that cause the motor to vibrate.
All of those can be controlled by LinuxCNC, even through a parallel port, hence my hesitation to change the drives.
But if you think the time is more valuable, do change them.
And if the motors turn out to be 5 wire ones, they can be changed to bipolar, just require a bit of time and a soldering iron.
BTW, never ever remove the rotor from the stator on stepper motors, that will render them useless as they will de-magnetize.