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Comment by moffkalast | Hacker News Reader

> In contrast to the magnet-free concepts of so-called separately excited synchronous motors (SESM) already available today, ZF’s I2SM (In-Rotor Inductive-Excited Synchronous Motor) transmits the energy for the magnetic field via an inductive exciter inside the rotor shaft. This makes the motor uniquely compact with maximum power and torque density.

Permanent-magnet-free would be more accurate, this is sort of like a BLDC motor, except that if I understand this correctly they use some kind of wireless charging to power coils on the rotor? Doesn't wireless charging have only like 70% efficiency?

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https://m.youtube.com/watch?v=43JMIuwVrY4&pp=ygUOSW4gcnVubmV...

A regular BLDC motor is already using induction. See this video.

The 70% number you are referring to is for a flat coil through a much greater distance than would be needed here. For the new design, I imagine another set of coils inside and separated from the rotor, and the magnets on the rotor replaced by a simple ring. The induction coils would need to be offset to produce torque on the ring. Yes, it would be less efficient because you are using power to produce the magnetic field. However, no rare earth metals are required.

There is EM induction happening in the stator coils, but it is not substantial to how the motor effect comes about. This effect is due to magnetic force of the coil poles acting on the permanent magnets, no induction is needed to create this effect (thus it exists even when instantaneously, EM induction in any one coil is zero).

This sounds like it's an induction motor where the inductors are on the spinning part (the rotor - or maybe in both?)

People are downplaying this, but I'm not so sure (yes I know about synchronous motors, etc), but there sure it is covered in marketing fluff (which is not wrong per se - if tesla passes gas people would have been all over it)

Maybe compensated a bit by the lack of friction and the overall lifespan of the device ?

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