Originally Posted by
dscheidt
No, rotating magnets in a stator create drag, even when there's no load for the current to run through. Not rotating the magnets is an efficiency improvement. I don't think it's a big enough one to worry about, nor one that outweighs the increase in mechanical complexity.
The mechanical coupler will still need to rotate in order to maintain alignment...which will create drag (and probably more than a well made rotor). No matter where you draw the interface there will never be a perfect decoupling, might as well make it electrical.