DC Motor Armature, Commutator, and Rotor

[eev_carl]

Hi,

I've looked through a bunch of DC motor diagrams and I can't tell if the armature and commutator are part of the rotor.  Is the rotor the entire rotating assembly (armature, commutator, shaft)?

Thanks,
Carl

[vu2nan]

Yes.



Nandu.

[Benta]

Almost. The commutator has a second (static) part, which is the brushes.

[eev_carl]

Almost. The commutator has a second (static) part, which is the brushes.

Does that mean the brushes are part of the rotor?

[Siwastaja]

In basically all designs, brushes are stationary so not part of the rotor which is the rotating part.

Brushes still logically belong to the commutator. But sometimes people refer just to the moving part when talking about "commutator", and talk about "brushes" separately.

This is just a matter of terminology choices and terminology always has some slight variation. It's more important you understand the concepts.

[andy3055]

The armature is considered as the moving component of a motor. The stator is the non moving part. Brushes are there merely to transfer the electrical current over to the armature as it moves or rotates in this case of a motor.
If you consider an electric bell, the armature is the soft iron part that vibrates.

[Benta]

Almost. The commutator has a second (static) part, which is the brushes.

Does that mean the brushes are part of the rotor?

Is the word "static" confusing somehow?

[TimFox]

The general terminology for rotating equipment divides it into “rotor” and “stator”.  The commutator in a DC motor comprises both rotor and stator components.

[eev_carl]

Almost. The commutator has a second (static) part, which is the brushes.

Does that mean the brushes are part of the rotor?

Is the word "static" confusing somehow?

Yeah, to me it means "stator" not "rotor"

[Capernicus]

stator isnt supposed to move terminology wise, and the rotor is moving,  but its completely relative which one is moving and which one isnt,  either can be moving or stationary in your finished machine.

[james_s]

I've always considered the commutator to be the part with the copper segments that is part of the rotating assembly and the brushes are a separate component. Obviously the two go hand in hand, a commutator is not much use without brushes. Either way the rotor comprises the entire rotating part and the stator is stationary. Some motors have the windings on the rotor, some have them on the stator, some use windings for both and no permanent magnets. The terminology still applies.

[andy3055]

The term armature is mostly used on motors with windings on the "rotor" with a comutator whereas, rotor is used to describe the rotating part of an induction motor which is normally called a squirrel cage rotor. It still has a "winding" of copper bars that resemble a squirrel cage, if we ignore the iron core/stampings. Just how I see it.

[Siwastaja]

Rotor is the more generic term, every motor has a rotor, it's the rotating part relative to the mounting of the motor.

Both induction motors and brushed DC motors have "rotors".

As used by some, armature is a specific term that applies to some types of motors only. You can still call it "rotor" as well.

I find little use for the "armature" term because it's just a different name for the same thing that can be used in some cases, pretty confusing. I feel it easier to understand that in the typical brushed DC motor design, rotor just has windings and commutator copper segments. No need to give it a different name.

Wikipedia defines "armature" as: " the armature is the winding (or set of windings) of an electric machine which carries alternating current". This shows the bullcrappiness of the word "armature" - completely different meaning to what some use, and again it's a replicate. For windings, we already have the term: "winding".

So it seems "armature" can mean anything, and it's always just a duplicate name for something that already has a proper name.

[Jwillis]

The Stator is the stationary or static  part of the motor that carries a  magnetic field . This can be a coil winding or a permanent magnet . The Rotor is the part that rotates. The Armature is the winding or windings that carries the alternating current . The armature  can be either on  the stator , or on  the rotor .

[Siwastaja]

After posting, I myself realized that there is a subtle difference between that definition of "armature" vs. "winding". In case of SepEx motors, both rotor and stator have windings, but one set carries DC current only. Just the AC current winding set is called "armature".

[Capernicus]

The Stator is the stationary or static  part of the motor that carries a  magnetic field . This can be a coil winding or a permanent magnet . The Rotor is the part that rotates. The Armature is the winding or windings that carries the alternating current . The armature  can be either on  the stator , or on  the rotor .

If the battery rotates with the motor,  it could be the stator thats moving.  I know thats a bit unusual but its true.
For the case of stall torquing robotic actuators, either part can be grabbed.

Other than that I guess so,  maybe its best to use the stator as the static member of the motor.

[Zero999]

Wikipedia defines "armature" as: " the armature is the winding (or set of windings) of an electric machine which carries alternating current". This shows the bullcrappiness of the word "armature" - completely different meaning to what some use, and again it's a replicate. For windings, we already have the term: "winding".

That's true for both an induction and DC motor. In the case of a DC motor, the commutator acts as a mechanical inverter, which converts the DC to AC, to power the armature/rotor.

[elekorsi]

Rotor winding - armature
Stator winding -field

[james_s]

After posting, I myself realized that there is a subtle difference between that definition of "armature" vs. "winding". In case of SepEx motors, both rotor and stator have windings, but one set carries DC current only. Just the AC current winding set is called "armature".

In a universal motor both the rotor and stator windings carry AC current when the motor is powered by AC.