Finding servo motor voltage without specs.

How does one go about determining the voltage and amperage of a servo
motor with no specs available? The motors are unused but ten years
old nippon pulse told me they made these for a customer and could not
release any specs even if they had them. the motor part has 4 brushes
and I assume the middle part is an electric brake with two brushes
and finally an encoder. Any instructions would be appreciated. I
have 3 of them. I need to find out how to control these things. I'm
attempting to create a cnc router.
Thanks, Tom