Quick question about electric motors

by "BaconSandwich is tasty." (baconsandwich)
Published 01/30/2017 at 19:41

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I don’t know a whole lot about them, but I do have a question about them.

Is there any advantage to having an unequal number of coils to magnets?

Any electric motors that I’ve seen have had generally an even number of magnets on the outside and an even number of coils on the rotor. What would happen if these weren’t equal, but we had a decent controller and a rotation/position sensor on the motor shaft? What would happen to the holding torque? What would happen to the acceleration?

Again, this isn’t something I really know a whole lot about, but I do think it’d be interesting to learn more about it.

I’m not sure if any of you have seen these: http://www.yasamotors.com/ but they seem to have some seriously powerful motors for their size. It’s a shame they seem crazy expensive for what they are. I’d eventually like to build an electric Locost (Caterham style kit car), and stuff something like one of those YASA motors into it. Crazy torque for the size and weight.

Replies (6)

"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
01/30/2017 at 20:10, STARS: 1

I don’t know much about electric motors either, but I think it has something to do with making it easier to start or something.

"MM54" (mm54mk2)
01/30/2017 at 20:11, STARS: 1

If I understand your question right - without them matching up you’d always have some pole misaligned, which would be detrimental to the motor’s performance.

"jimz" (jimz)
01/30/2017 at 20:33, STARS: 1

not all electric motors are the same. I don’t know what ones you’re looking at, but simple DC motors like ones for slot cars and model locomotives are unequal. typically there are two magnets and the rotor has three poles. having the two be odd/even minimizes the chance you’ll power the motor in a situation where the rotor could be “trapped” and sit there in a static magnetic field doing nothing but uselessly drawing current.

Series DC motors like the starters on cars are different still; there are two field poles (wound electromagnets taking the place of permanent magnets) and the rotor has dozens of windings.

AC motors have no magnets at all.

"Tekamul" (tekamulburner)
01/30/2017 at 20:35, STARS: 1

If you mismatch the number of poles and rotors, you’re going to have fighting poles. Phase control won’t help with that.

"BaconSandwich is tasty." (baconsandwich)
01/30/2017 at 23:54, STARS: 0

I was thinking of a DC motor. Now that you mention it, I remember having an electric racing set that had motors with three coils but two magnets.

AC motors still amaze me.

"BaconSandwich is tasty." (baconsandwich)
01/30/2017 at 23:56, STARS: 1

When in motion, isn’t that what you more or less want - some misalignment? You always want the rotor to be attracted to (or repelled from) the next part of the stator.

Anyway, more or less just thinking out loud here. I definitely need to learn more about this kind of stuff.