DC Motor Armature, Commutator, and Rotor - Page 1
Forum section: electronics / beginners

author: eev_carl
author_rank: Regular Contributor
timestamp: October 24, 2021, 01:30:33 pm
content: 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

author: vu2nan
author_rank: Contributor
timestamp: October 24, 2021, 03:00:00 pm
content: Yes.Nandu.

author: Benta
author_rank: Super Contributor
timestamp: October 24, 2021, 03:52:38 pm
content: Almost. The commutator has a second (static) part, which is the brushes.

author: eev_carl
author_rank: Regular Contributor
timestamp: October 24, 2021, 04:00:20 pm
content: Quote from: Benta on October 24, 2021, 03:52:38 pmDoes that mean the brushes are part of the rotor?

author: Siwastaja
author_rank: Super Contributor
timestamp: October 24, 2021, 04:33:19 pm
content: In basically all designs, brushes are stationary so not part of therotor which is therotating 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.

author: andy3055
author_rank: Super Contributor
timestamp: October 24, 2021, 04:35:02 pm
content: 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.

author: Benta
author_rank: Super Contributor
timestamp: October 24, 2021, 04:42:56 pm
content: Quote from: eev_carl on October 24, 2021, 04:00:20 pmIs the word "static" confusing somehow?

author: TimFox
author_rank: Super Contributor
timestamp: October 24, 2021, 04:50:47 pm
content: The general terminology for rotating equipment divides it into “rotor” and “stator”. The commutator in a DC motor comprises both rotor and stator components.

author: eev_carl
author_rank: Regular Contributor
timestamp: October 25, 2021, 12:41:10 am
content: Quote from: Benta on October 24, 2021, 04:42:56 pmYeah, to me it means "stator" not "rotor"

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 25, 2021, 03:14:06 am
content: 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.

author: james_s
author_rank: Super Contributor
timestamp: October 25, 2021, 04:03:05 am
content: 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.

author: andy3055
author_rank: Super Contributor
timestamp: October 25, 2021, 04:24:54 am
content: 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.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 25, 2021, 07:48:44 am
content: 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, andagainit'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.

author: Jwillis
author_rank: Super Contributor
timestamp: October 25, 2021, 07:51:14 am
content: The Stator is thestationaryor 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 .

author: Siwastaja
author_rank: Super Contributor
timestamp: October 25, 2021, 07:55:27 am
content: 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".

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 25, 2021, 09:50:07 am
content: Quote from: Jwillis on October 25, 2021, 07:51:14 amIf 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.

author: Zero999
author_rank: Super Contributor
timestamp: October 25, 2021, 12:57:44 pm
content: Quote from: Siwastaja on October 25, 2021, 07:48:44 amThat'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.

author: elekorsi
author_rank: Regular Contributor
timestamp: October 25, 2021, 03:10:19 pm
content: Rotor winding - armatureStator winding -field

author: james_s
author_rank: Super Contributor
timestamp: October 25, 2021, 07:28:35 pm
content: Quote from: Siwastaja on October 25, 2021, 07:55:27 amIn a universal motor both the rotor and stator windings carry AC current when the motor is powered by AC.