Stepper motor wiring I've never seen before

[t.hoehler]

Hi group, I have a question. I have several of these stepper motors, they
have eight wires, three of the wires are about 20 ga. and the other five are
about 25 ga. there is no continuity among the five small gauge wires, I
suspect they go to a tach circuit, but the three heavy wires have 2.8 ohms
from wire to wire to wire. It steps if I put 10 volts from wire to wire. It
appears to be a delta winding setup, but I have never seen this
configuration in a step motor before. I cannot disassemble the motor without
tearing it up, epoxy sealed. I am sure it is a stepper as you can feel the
magnetic detents as you turn the armature by hand. Can anyone shed light on
this configuration and maybe steer me to a site where drivers for this type
of motor are displayed? I have googled step motor circuits/drivers, and they
all refer to unipolar or bipolar steppers, and this one is not one of
either!
Thanks for any help, I lurk this group, you guys have a broad range of
knowledge.
Regards,
Tom

 

[Isaac Wingfield]

Hi group, I have a question. I have several of these stepper motors, they
have eight wires, three of the wires are about 20 ga. and the other five are
about 25 ga. there is no continuity among the five small gauge wires, I
suspect they go to a tach circuit, but the three heavy wires have 2.8 ohms
from wire to wire to wire.

There is no reason for a stepper to have a tach. I have no idea what the
five wires are for.

Three-wire steppers were used some time ago; perhaps they were the first
steppers? The original Calcomp plotters (ca. 1957) used three-wire
steppers.

You can drive them with three non-overlapping pulses, or you can do a 1,
1&2, 2, 2&3, 3, 3&1 kind of overlap to get twice as many steps.

Isaac

 

[James Sweet]

There is no reason for a stepper to have a tach. I have no idea what the
five wires are for.

A tach no, but optical encoders are common, it's the only way to get
absolute position data from a stepper, otherwise you only know relative
position.