Identifying a servo motor

Hello folks, Im posting looking for help identifying these motors, they are hooked to a small CNC mill, I have absolutely no reference about them, just my educated intuition. I think these are servos because they have a 4:1 reduction and have encoders on their back.

Here are photos of the units:

Both are NEMA34 mount

One is square, 8 wires coming out of it, 2 sets of the same color

Attachment 179321


the wires go to a connector:

Attachment 179327

4 of the wires are hooked together, if this where a stepper, doing this would prevent the unit from turning, or am I wrong?

The other is round, same US Digital Encoder on the back:

Attachment 179323

This also has 8 wires all different colors, but the connector is connected in the same fashion:


Attachment 179324

These are connected to a small board that looks like some sort of protection (has 4 diodes) since its not wired like a rectifier

Attachment 179325

also attached to this little board is this power resistor that looks like an energy dump:

Attachment 179326

The driver is homemade and its made out of a set of 8 darlingtons BU941ZP and three 74HC00 logic gates.

So my conclusion is these are brushless DC servos (but I may be wrong of course)

I would like to know how to determine the wires and if possible determine their voltage, so I know if I can use them with any known servo drive.

Thanks a lot in advance!


Pablo

My guess is a 8 wire stepper hooked up like the first example here

Stepper Motor Connections - Motion Control Information

Notice 4 wires are hooked together to V+

and that would make sense why there are 8 darlingtons as that would give you bipolar switching..

sam

maybe, but if these are steppers indeed, I wonder why they use a 4:1 reduction, that would be counter productive.

Also, on the square motor, there are two sets of cable of the same color, one set, all the 4 wires are hooked together, wouldn't this prevent the motor of turning due to the induced current?

upon further reading, maybe these are steppers wired unipolar as you told me, unipolar has less initial torque but the torque curve is flatter, maybe this explains the 4:1 reduction

Sam, today I was able to remove the motors from the machine and you were right, these are steppers. The obvious confirmation came when I turned the shaft and felt the steps :)

Already deduced the wiring but I could use some help regarding how to determine their inductance.


Pablo

To be pedantically correct, they are steppers being used as servos (since they have feedback). Sounds like someone did an interesting sort of roll your own CNC...