I've been thinking about motor designs and where all the power goes for an electric motor, especially in terms of used/unused power. I noticed that in most motor designs, the neodymium magnets float either on the inside or outside of the motor as the rotor, with the opposite as either the AC or DC electromagnetic poles acting on the magnets.

However doesn't this waste potential force/power since the opposing magnetic fields aren't utilized? For example couldn't you take a U-shaped electromagnet and run a neodymium magnet through it's center so that all 4 poles of both magnets are utilized and potentially generating more force/torque?

Typical motor design with internal rotor: enter image description here

Couldn't you run a flat neodymium magnet through this to utilize all 4 magnetic poles? enter image description here So you'd end up with a configuration like this, roughly speaking. This would be a design for an AC induction motor... Obviously you can add/remove poles/magnets as necessary, again, this is just an example.

The idea here is that by using a U-shaped electromagnet for your stator you condense the magnetic field, thus pushing more torque through the motor when the neodymium magnets on the rotor pass through the electromagnets. enter image description here enter image description here Otherwise with conventional layouts the neodymium magnets on the rotor rotate on the outside edge of the electromagnets and it seems like you lose some of the magnetic force of the opposite that don't come in contact with the electromagnet.


1 Answer 1


Your first diagram is incomplete. Motors with that arrangement of poles tend to include an iron flux return ring round the outside, which is usually used as the motor case.

The very first electrical machines did use a horseshoe magnet arrangement. This is one of Edison's, and it's from here Put 'vintage electrical generator' into your search engine.

enter image description here

  • \$\begingroup\$ The question isn't about the diagram... That just shows a simple conventional configuration. The idea is to utilize many U shaped electromagnets in a circular configuration and run an array of neodymium magnets through the center of the horseshoe and whether that provides anything economically or torque wise? \$\endgroup\$
    – FatalSleep
    Mar 15, 2020 at 5:41
  • \$\begingroup\$ And to clarify DC fan motors are built in that array if I recall. \$\endgroup\$
    – FatalSleep
    Mar 15, 2020 at 5:41
  • \$\begingroup\$ Perhaps you'd indicate how you might use the horseshoe magnets to improve over your first diagram with a flux ring, it's not obvious to me, a diagram of a single magnet doesn't suggest an arrangement. A fan motor is an interesting case, as the fan is physically big, the motor is not significantly size constrained. It doesn't need to produce much power, and is potentially cooled by a ferociously large airflow, so doesn't need much efficiency. Form factor and cost are therefore the driving specifications, and strong magnets in fresh air can produce an economic design. Note I stress economics. \$\endgroup\$
    – Neil_UK
    Mar 15, 2020 at 5:53
  • \$\begingroup\$ I'll mockup a design. \$\endgroup\$
    – FatalSleep
    Mar 15, 2020 at 6:07
  • \$\begingroup\$ +1. In a book from 1897, you can trace the progress from that generator, as the "U" got shorter and fatter year by year, and performance improved, as designers learned how to design better magnetic circuits and shorten the reluctance path. \$\endgroup\$
    – user16324
    Mar 15, 2020 at 12:56

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