Passive vs Active Rotor
Drexel,
I am glad to see you thinking this through. OK, the motor designs I am suggesting have a passive iron rotor. This allows these motors to operate with No Back EMF and gain in efficiency because they do not create any forces or fields that buck or resist themselves. There is ONLY ONE magnetic field in the system, the field of the stator coils, and they passively attract the rotor while turning on and off.
The moment you introduce a permanent magnet in the rotor, now you have TWO MAGNETIC FIELDS in the system. These two fields can and do interact with each other. These interactions invariably cause cross inductions, leading to the Back EMF problems the passive iron rotor avoids.
The small Lenz Law forces that appear in the stator coils account for the "rise time" and the "collapse time" of the magnetic fields produced by turning the current On and OFF. The movement of the iron rotor changes the inductance of the coil/core and therefore also affects the rise time and collapse time of the magnetic fields. But these changes are small, when compared to the losses produced by Back EMF.
Perhaps you should just run a few experiments on your own so you can see what happens. Thinking about these things can only get you so far. At some point, you must "see for yourself."
Peter
Originally posted by Drexel
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I am glad to see you thinking this through. OK, the motor designs I am suggesting have a passive iron rotor. This allows these motors to operate with No Back EMF and gain in efficiency because they do not create any forces or fields that buck or resist themselves. There is ONLY ONE magnetic field in the system, the field of the stator coils, and they passively attract the rotor while turning on and off.
The moment you introduce a permanent magnet in the rotor, now you have TWO MAGNETIC FIELDS in the system. These two fields can and do interact with each other. These interactions invariably cause cross inductions, leading to the Back EMF problems the passive iron rotor avoids.
The small Lenz Law forces that appear in the stator coils account for the "rise time" and the "collapse time" of the magnetic fields produced by turning the current On and OFF. The movement of the iron rotor changes the inductance of the coil/core and therefore also affects the rise time and collapse time of the magnetic fields. But these changes are small, when compared to the losses produced by Back EMF.
Perhaps you should just run a few experiments on your own so you can see what happens. Thinking about these things can only get you so far. At some point, you must "see for yourself."
Peter
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