DC motor rotor arrangements

I know of two ways to arrange a three-phase DC motor armature with respect to the magnets: one is the normal one seen in toy motors, where there are three armature poles for every two magnets; the other is fairly common in RC brushless "outrunner" motors (and possibly in DC brushless motors in general), here there are three armature poles for every four magnets.

Does anyone know if these arrangements have NAMES in academic or commercial circles? Meaning, if I asked a motor designer what they were, what names would I get back?

TIA

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Tim Wescott 
Wescott Design Services 
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Tim Wescott
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Den torsdag den 5. januar 2017 kl. 19.02.47 UTC+1 skrev Tim Wescott:

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Reply to
Lasse Langwadt Christensen

What's wrong with "Bill" and "Paulina?"

;)

Michael

Reply to
mrdarrett

Well, first, there is no such thing as a 3-phase DC permanent magnet motor. The toy motors you mention would be a 2-pole permanent magnet motor with 3 armature poles. These are simple PM DC commutator motors.

Now, when you get to brushless, the only motors that can be called "DC brushless" have electronic commutation circuits built inside the motor. Motors that use external commutation are AC synchronous PM motors, and are now used a LOT in all sorts of machinery. Hopefully, all this AC brushless vs. DC brushless nomenclature has finally settled out, as there used to be a lot of confusion over this.

So, brushless motors with external commutation should be called PM synchronous motors. Further classification is to whether the windings are optimized for trapezoidal or sinusoidal commutation.

I think most motor manufacturers have now come around to these designations, after about 20 years of conflicting naming.

Jon

Reply to
Jon Elson

** DC motors using permanent magnets and brushes are named after the number of armature poles in the rotor ( or segments on the commutator ) with 3 be ing the minimum rising by steps of two. The more "poles" the greater to DC voltage that can be safety handled - generally 2.5V per pole is the limit f or a reasonable life. More than this leads to unacceptable arcing between c ommutator segments.

So called "brushless DC" motors are actually AC synchronous motors with per manent magnets forming the rotor. They operate with variable frequency, mul tiphase drive voltages and may have odd or even numbers of poles on the sta tor. As already mentioned, the multiphase drive system may be internal or e xternal to the motor.

The only thing you can be sure of when you see the name is there are no bru shes or commutators.

.... Phil

Reply to
Phil Allison

There is a qualitative difference between a "brushless DC" motor without drive electronics, and a "brushless AC" motor, ditto.

The "brushless AC" motor will have its magnetic circuits arranged so that the phase voltages are roughly sinusoidal, while the "brushless DC" motor will have phase voltages that are roughly trapezoidal. The drive electronics then need to be different to best take advantage of this, with the "brushless DC" motor being the easier one to drive (because you don't have to mess with sine waves).

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Tim Wescott 
Wescott Design Services 
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Tim Wescott

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