"Gareth Magennis" wrote in message
...

Well you see the commutator is not round in the conventional sense,
it's flat with three sort of "pie" shaped segments on the back of the
armature. So the brush surfaces are flat. Lenny




I've tried and tried but can't imagine how that actually works.


Gareth.

If the commutator was a cotton reel, I guess he's saying that the contact
segments are where the label would be on the end, not where the cotton would
be as in a conventional motor. Thus there are three segments in a flat 'pie'
configuration, presumably with the motor shaft through the middle, and a
brush either side, parallel to the shaft. I'm sure that I have seen this
somewhere on a motor over here.

As to the arcing at the brush contact surface, I guess some C across the
brushgear would help - much like the 'condenser' across the points in an old
Kettering ignition system. Also, are the gaps between the commutator
segments clean ? When I used to 'service' model motors many years back, I
always used to 'rake out' the gaps with the tip of a dressmaker's pin, and
also smooth the edges of the segments so that they were slightly rounded,
rather than a sharp 90 degree knife edge. If the contact area has been
subjected to emery paper treatment, the segment edges might well be quite
sharp.

Arfa