A brushed-DC motor comprises external permanent magnets and
electromagnets wound on a rotating core. Brushes manufactured
from graphite and other materials switch, or commutate,
electricity to the coils as they rotate to sustain motion. A
brushless-DC (BLDC) motor turns this construction inside out and
places permanent magnets on the shaft and electromagnets around
it. Electronic commutation external to the motor shifts current
from coil to coil to cause the shaft to rotate. Why would a BLDC
motor appeal to designers? Paul McGrath, an electrical engineer
and east-coast sales manager for Maxon Precision Motors, noted
the primary reason: reliability. "By taking the brushes and
mechanical commutation out of the motor you have fewer ways for
a motor to fail. Often mechanical bearings determine the
lifetime of a BLDC motor. Second, a BLDC motor will operate at
higher speeds than a brushed motor, and third, the operating
environment might dictate a need to eliminate brushes that could
cause contamination or arcing.