"Jon Elson" wrote in message
news
JB wrote:



And you say four brushes. Typically, two are heavy duty ones (or
have heavy duty wires running to them) and the other two (at right
angles to the first two) are lighter. They are where the tach feedback
pickoff brushes, and probably should not get much current to allow for
clean pickoff of the tach feedback signals.
No, generally, these are 4-pole motors, they use all 4 brushes for the
power armature. Electrocraft made their "motomatic" that had a tach
winding
with a separate commutator on the other end of the armature, but the power
and tach windings were in the same slots.

But, I've never seen a motomatic on a servo-driven machine tool. I think
you will find the brushes exactly opposite each other are connected
together, and the other pair also connected.

I've never seen anything with tach and power brushes on the same
commutator.

Agreed. Looking at the conductor diameters, these are _not_ tacho wires.
I'll post some photos next week.
cheers,
JB