16864Re: Poor performance (again ;-)
- Oct 1, 2003--- "bill.foote" <bill.foote@v...> wrote:
> There is no question that the current 5-pole motors have visiblyThe problem with the 3-pole motors (I don't think this has been
> superior characteristics compared with the earlier 3-pole motors
mentioned) is called "cogging". The three poles of the armature are
strongly attracted to the two poles of the magnet, giving six stable
positions per revolution. At slow speeds a relatively large torque is
needed to turn the armature between these positions. (You can see and
feel the cogging if you turn the motor with a toothpick!) Most
controllers are not able to give just the right amount of "oomph" to
kick the motor smoothly between the "cogs".
5-pole motors have 10 "cogs" and need less torque to turn from one to
another (try it!), so controllers have an easier job driving the
motor slowly and smoothly.
Cogging is avoided in can (Faulhaber/coreless) motors and by using
skew windings. Cogging can also be overcome by a suitable controller.
I have made a controller that copes with cogging, even in 3-pole
motors, and drives nearly all locos smoothly at very slow speeds, and
gives smooth acceleration and braking. Unfortunately I do not yet
have a design ready for production. I am still working on it!
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