[Zamiel_Snawley]

Electromagnets for the rotor cause significantly more heating, exactly where it is hardest cool, and where the heat is most likely to seep into the load.

For high torque density applications, heat dissipation is often the limiting factor on duty cycle.

Also, the slip rings capable of passing high current to an electromagnet rotor are expensive and less robust than permanent magnets.

Essentially: it’s possible but I haven’t seen an application where it’s practical.

[pbmonster]

> Also, the slip rings capable of passing high current to an electromagnet rotor are expensive and less robust than permanent magnets.

The new designs are all inductively coupled, i.e. they have a rotating transformer coil built into the shaft. No brushes, no slip rings.

[Workaccount2]

Coupling without using a core (or using an air core) is gonna hit efficiency pretty badly though.

[pbmonster]

Unfortunately, I can only find material from the marketing department on that issue. But if I understand correctly, both coils have a ferrite core (and yoke), but there is a small air gap where the rotating side is separated from the stationary side.