Obviously the Torque and RPM of an electric motor are dependant upon how many turns of wire there are, is it possible to make the number of effective windings (semi)dynamic through the use of MOSFET taps in a layout similar to this? Is there any reason it wouldn't work? Motor Winding Transistors

Where the red circles are the the Drains of the MOSFETs, Sources are commoned together on the motor driver output and Gates are addressed by a controller to switch between.

  • \$\begingroup\$ Apologies for the MS Paint diagram \$\endgroup\$ – Tanenthor Dec 11 '16 at 10:54
  • \$\begingroup\$ Regardless of the tool used, the diagram is meaningless because a MOSFET is a 3-terminal device, not 2. How do you propose that they actually be connected to the windings and how do you propose to control them? \$\endgroup\$ – Dave Tweed Dec 11 '16 at 12:11
  • \$\begingroup\$ Have clarified the diagram, in my head it was clear already, but obviously not to an outsider \$\endgroup\$ – Tanenthor Dec 11 '16 at 13:18
  • \$\begingroup\$ Do you understand that current needs to flow in both directions through each winding? This would require at least a "half-H" (totem-pole) driver at each of your red circuit nodes. In any case, there already are 3-phase motors with dual windings on each pole, intended to be connected either in series or parallel for operation at a particular voltage. You need to be more clear about what aspect of the motor you're trying to optimize with your "variable winding" approach. \$\endgroup\$ – Dave Tweed Dec 11 '16 at 14:41
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    \$\begingroup\$ "The idea is to have a wider range of RPMs while being also able to have a much higher torque at low RPM, effectively negating the requirement of a gearbox." - This already happens when motor speed is controlled with PWM (high voltage/low current -> low voltage/high current). Maximum torque is determined by motor size and design, not number of turns (which only changes the voltage required to get it). \$\endgroup\$ – Bruce Abbott Dec 11 '16 at 18:40

Brushless motors requires electronic control circuits that time the switching of the excitation with the rotor position like a DC motor commutator. Alternatively, the excitation can be timed to simulate a polyphase AC power supply. Anything done to change the number of winding turns that are energized would not seem to simplify or improve the performance of the usual modes of control.

DC motors with commutators including universal motors can be configured for multiple speeds in this manner. AC induction motors can be controlled this way also, but only to a limited extent. This is one way to configure a motor for a multi-speed fan. A more complicated switching arrangement can be used to change the number of poles to make a two-speed or perhaps even a three-speed motor.

This sort of thing has been done with electro-mechanical switches. To do it electronically would seem to add nearly the cost of an electronic speed control to offer only two or three fixed speeds.

  • \$\begingroup\$ Where would the main cost factors of controlling it this way come in? And what would be the advantage of using relays as opposed to mosfets? \$\endgroup\$ – Tanenthor Dec 12 '16 at 4:57
  • \$\begingroup\$ There is no advantage in using relays. There is some advantage in using switches in that switches provide both the manual means of selection and the electrical mechanism of implementation. There is a cost in adding connections to the windings. This comment and more that half of my answer primarily applies to motors other than BLDC. If you are only interested in BLDC, I believe you must concentrate on finding the best motor design and electronic control strategy. I agree with @Bruce Abbott. \$\endgroup\$ – Charles Cowie Dec 12 '16 at 14:48

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