Another interesting design is the brushless DC (BLDC) motor. The stator and rotor effectively swap over, with multiple iron coils static at the center and the permanent magnet rotating around them, and the commutator and brushes are replaced by an electronic circuit. You can read more in our main article on hub motors. Stepper motors, which turn around through precisely controlled angles, are a variation of brushless DC motors.
It is important to keep this struggle between performance and cost in mind when you talk to customers about energy-efficient motor-driven equipment. Yes, efficiency is probably more important to homeowners now than ever, but that efficient operation comes at a price. And motor manufacturers will keep working to strike that balance between motor performance, efficiency, and cost.
Without getting into a lengthy physics lecture, this process of reversing polarity produces heat (or wasted energy). This is known as hysteresis loss. And that helps explain why increasing the voltage into the motor will not necessarily increase the output. Instead, it can fight the resistance of magnetic materials to reverse polarity--and simply heat iron.
Magnetically soft materials, however, tend to be more expensive. The motor manufacturer must find that proper blend of just enough magnetically soft material to do the work required without putting too big a dent in the customer wallet.