Re: Servo Motor Wiring

daveland@... wrote:

> From: daveland@...
>
> Gents
>
> I bought two Yaskawa servo motors from a Robot. They were
> directly driving short ball screws on the arm and have
> intergral tachs and encoders. The motors have 4 connections
> that are unlabeled and there are 4 brushes on the motor.

This is a 4-pole motor.
Connect the brushes that are diametrically opposite together.
That leaves you with 2 terminals, which should respond just like
any DC brush motor with 2 wires.

> How do I hook them up to test them? Any ideas on how
> to identify the leads? I don't know if they are Permanent
> magnet or have a field winding. How do I tell? Why
> do they have 4 brushes instead of the normal 2? Resolution?

4-pole motors run slower than 2-pole motors. It is not exactly
analogous to a 4-pole induction (AC) motor, but somewhat
similar. If there are just 4 brush terminals, and no other connections,
then they are permanent-magnet motors. If there are still more
wires coming from the interior of the motor, they could have
wound fields, but I doubt it. If you find practically zero resistance
between all 4 wires, they are all brush connections. To identify
which wire goes to which brush (if that is hidden) just take the
brushes out, and ohmmeter to the brush holder. Then tie together
the opposite ones. If you find motor wires that have a resistance
of, maybe 25-100 Ohms, and isolated from other brush terminals,
that could be a field winding, but I doubt it.

Don't take Yaskawa motors apart, the permanent magnets could be
damaged. If necessary, however, you can probably get away with
removing the brush-end cap, to trace the wiring. Note also that
some servo motors have thermocouples or other temperature
sensors inside, to warn the controller of overheating.

The tach should be fairly simple, if a standard DC tach. It will generate
a DC voltage proportional to speed.

The encoder is a bit more complicated to decipher. If you dare, you
might have to take the cover off (very carefully) and trace the wires
inside. Most likely, you'll get clues, like a black wire for ground, and
a red wire for +5 volts. If you find these color wires attached to a
circuit board, with a tantalum or electrolytic capacitor wired across
them, and with a polarity mark on that cap, you can be quite confident
in hooking up +5 volts across those wires. Then, you should be able
to dope out the signals with a voltmeter, and very careful turning of the
shaft.

Jon