DerbyBorn wrote in
2.236:

"Brian Gaff" wrote in
news
Well it all depends on what sort of motor it is. All use magnetism in
the end and how the poles that repel and attract are arranged makes
many shapes possible. Some direct drive motors operate via locally
generated dc or different frequency ac.
Thos generally are used when speed differences are required, unless
the
device has more than on motor, or has switch windings to make it
change speed and torque.
Brian


I was thinking of the "leverage" effect of the magnetic field being
greater at a bigger radius - or more of it if the armature was longer.

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Thanks all - very enlightening stuff