It's technically not a brush but a slip-ring. The design of these motors is very similar to automotive alternators, just scaled up 100x (in terms of power).

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genter 7 hours ago | parent | next [-]

I've probably taken apart 10 automotive alternators. Every single one had brushes.

	▲	hnav 6 hours ago \| parent [-]
		yeah I misspoke, I meant to say that it's a brush riding on a slip-ring (continuous contact, no arcing, lasts long) rather than a bunch of contacts in a cylinder (commutator, arcing, wears out).

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dheera 7 hours ago | parent | prev [-]

Slip rings have brushes.

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raverbashing 7 hours ago | parent [-]

Yes but they wear less than DC brushed motors exactly because it's a slip ring and not a commutator

	▲	ahartmetz 6 hours ago \| parent [-]
		Because it's the discontinuities in the commutator where the sparks fly (with much help from self-induction of the motor's coils) and erode the ring and brushes.