Armature of motor that's unchanged after turning (5)

I believe the answer is:

rotor

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'armature' is the definition.
(I know that rotor is a type of armature)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for rotor that I've seen before include "It goes around" , "Chopper blade" , "Palindromic revolving part of machine" , "Revolving part of machinery" , "Revolving part of a machine, a palindrome" .)

I've seen this clue in The Independent.

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