Hardware

Switched Reluctance Motors

Posted 6 Oct 2003 at 17:29 UTC by steve Share This

Switched Reluctance motors can run on AC or DC, can behave like stepper or servo motors, require no permanent magnets and no brushes, achieve efficiencies of 90% and speeds of 100,000 RPM. The rotor has no windings or coils. Shaft position is a function of the control electronics, so sensors and encoders are not needed. Invented in 1838 as an Electromagnetic Engine, Variable Switched Reluctance motors were quickly abandoned because without modern electronic controllers, they're very difficult to use. But now that we can easily control them, they're making a big comeback. According to a NewScientist article, Dyson is about to introduce a new Vacuum cleaner with a 100k RPM SR motor. A Control Engineering article from earlier this year provides a nice overview of the technology. As the prices drop, SR motors may start turning up in robots too.

Eh., posted 6 Oct 2003 at 19:14 UTC by jimbo » (Journeyer)

Actually, the control engineering article seems to say they're no good for position control servo applications.

positioning, posted 6 Oct 2003 at 20:26 UTC by steve » (Master)

Yeah, there seems to be some mixed info out there on some aspects of these things. I guess it's one thing to "behave like a stepper motor" and another to be "useful as a stepper motor". :-) On the other hand, while searching for some of those links, I ran across references to several papers by Japanese robotics researchers on using SR motors for positioning of joints in biped robots so it may depend on type of control circuit being used. The SR motors were controlled by mechanical relays while the motor in Dyson's vacuum cleaner is computer controlled.

We use them, posted 10 Oct 2003 at 08:09 UTC by zw » (Observer)

We are using BLDC motors in our robots for quite some time (Barbora, Dana). How the motor behaves depends completely on the control electronics. The motor can be used as a stepper but with our motor you would get only 18 steps/rotation. When operating without a sensor (encoder) it is also almost impossible to achieve slow speeds (as I was told by the company that made the sensorless motor controllers :)). That's why we are building a new controller with encoder. Is anyone experienced in this area? We could use some help :).

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