[turbofail]

Another permanent-magnet-less motor design is the switched-reluctance motor. Its primary advantage over the induction motor is its dirt-simple rotor construction - it's essentially just a properly shaped chunk of iron, where an induction motor would require a copper squirrel-cage.

Its disadvantage relative to the induction motor is that it requires some cleverness in its controller and/or sensors in order to run at all. I actually wrote some control software for one as a side project - it was a somewhat frustrating experience (though a good portion of the frustration was due to malfunctioning hardware).

http://en.wikipedia.org/wiki/Switched_reluctance_motor

[pjkundert]

Also interesting is their capability to produce their full Torque output at 0 RPM. For applications requiring high torque for "station keeping", this is crucial, and is pretty unique to SRM (Switched Reluctance Machine) motors.

I've been quite interested in repurposing the little Dyson "digital motor", but I suspect that a complete drive system redesign would be necessary to enable full variable RPM control (ie. 0-max, in both directions).

Question for turbofail: did your project happen to use the SRM motor from the Neptune front-load washers, or some other motor?

[turbofail]

It was a custom-made SRM made by someone else. They were intending to use it in an electric vehicle.

[kragen]

Very interesting! WP also says, "Stepper motors are similar to switched reluctance motors (which are very large stepping motors with a reduced pole count, and generally are closed-loop commutated.)" I didn't know!