Re: [CAD_CAM_EDM_DRO] RE: Re: Mavilor Servos, how to test + Identify

John Harnedy wrote:

> Thanks Jon for the quick reply.
> Did some further examination
> Nameplate says DC servo motor, amazing what one can find out when i open my eyes!!!

Ahh, that helps.

>
> took off the encoder and can see 4 brushes, so am i correct in assuming a DC brushed servo motor
> the brown and white wires go the the brush zone, the purple one appears to be terminated (deadend) inside the motor housing
> the brown, blue and green/yellow group go into the main body of the motor, which carries a "do not dismantle motor" label, + "permanent magnetic DC motor"
> Is there any document like the Stepper motor white paper?

Unfortunately, there are lots of variations. Are the brushes all the same, and in
the same plane? Or, are there brushes on each end, or on two sections of the
motor that are different diameter? (Many DC servo motors have a separate,
or integrated DC tachometer, which is almost identical to a motor, but usually has
smaller wires and a commutator with many tiny segments.)

If it is a plain 4-pole DC motor, then of the 4 brushes, opposite ones will likely be
connected together. (Some arrangements bring the 4 wires out, and connect
together back at the servo amp to reduce circulating currents.)

Many servo motors have temperature sensing devices (thermocouples, thermistors
even thermostats) inside to warn the machine control of overheating. Some really
oddball servos have windings that either boost or buck the permanent magnet
field.

Check the Green/Yellow wire to see if it is a case ground. If so, mystery solved.
Check the resistance on the brown and blue wires, maybe that will indicate
something. Inspect the interior of the motor with a flashlight and see if there is
a cooling fan. Put a voltmeter on the brown and blue wires and turn the motor.
If you get a voltage, it may be a tach winding.

Jon