Lawrence Harris via EV wrote:
I was thinking it might be more interesting if they put the rotor on
a lead screw and allowed the positioning of the magnets w.r.t. the
coils to be adjusted.  Would provide something like field weakening
on a permanent magnet motor.


There is a style of induction motor that does this. A classic single-phase induction motor requires a trade-off in rotor resistance. You can design the rotor for high starting torque, or high running torque; but not both.

So they made one with two rotors. One optimized for high starting torque, the other for high running torque. They are mounted on the same shaft, end-to-end. There is a spring that pushes the high-torque rotor into the stator when the motor is off. When you power the motor, the high-torque rotor provides the torque needed to start the load. But then, the stator's magnetic field acts like a solenoid, to compress the spring and pull the high-efficiency rotor into the stator. This type of motor got used in millions of home appliances.
--
Whether we or our politicians know it or not, Nature is party to all
our deals and decisions, and she has more votes, a longer memory,
and a sterner sense of justice than we do. -- Wendell Berry
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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