why brushless motors were invented

[Brett Dikeman]

Good guesses included:
-no EMF
-no sparks(for explosive environments)
-no consumables (ie, brushes don't wear.)

The winner is Jim Green, who came the closest with that last guess.

Early on, the US Air Force discovered that they had massive
electrical motor and generator failures on their very high altitude
flights; the reason might not be what you first think.

A certain amount of moisture is CRITICAL to brush systems working
properly; I don't remember all of the physics behind the contact of
the two surfaces(all this was covered while I was touring colleges,
and sat in on a materials engineering course at Swarthmore, which I
loved, though I annoyed the near-grad-level students by following
along and actually contributing to the class discussion :)...but
basically, brushes rely on forming a small layer of the brush
material on the commutator initially(first few turns); once that
happens, you get very, very little wear.  That layer absolutely
REQUIRES some moisture to form; no moisture, the stuff doesn't stick.

   At high altitude(like, really high altitude), there's not much
moisture to be had.  The brush material constantly falls off the
commutator with no moisture to hold it there; the brushes wear down,
and rather quickly you have a plane with no brushes on any of its
motors.  That could be a minor bummer when you're at 100,000 feet, eh?

Failures included gyros, generators/alternators, etc...

B
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