On Thu, 15 Feb 2018 23:25:07 +0000, The Natural Philosopher
wrote:

On 15/02/18 21:42, DerbyBorn wrote:
"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.

yes, but thats just torque. Bigger diameters can't rev as much so teh
power generally is no better.

I guess that can depend on the design of the motor.

For example, if you had a PM DC motor and were able to back off the
power of the permanent magnets using a coil (coils), then you could
allow the motor to rev higher once you had made best use of the lower
rev torque.

It certainly seemed to work well from what I saw as it sailed past me
.... stuck at max rpm on my conventional PM motor. ;-(

Cheers, T i m