How a Brushed DC Motor Works
Direct
current electrical motors function through the creation of magnetic
fields whose attraction and opposition keeps a central rotor turning. In
a brushed motor, fixed magnets are placed on either side of a rotating
electromagnet, one oriented to a positive pole, the other to a negative
one. The electromagnet is formed by a series of coils (usually three
placed at equidistant points around the rotor) called the commutator.
When electricity is passed through these coils they generate their own
magnetic field that is repelled and attracted to the magnetic fields
generated by the fixed magnets. Current is transferred to the coils of
the commutator by metallic brushes which rotate along with the rotor.
When the motor is switched on, current is passed to the electromagnets
whose magnetic fields are repelled by one fixed magnet and attracted to
another, causing the rotor to turn. As the rotor turns, the metallic
brushes come into and out of contact with each coil in series so the
opposition and attraction between the resulting magnetic fields and the
fields of the static magnets keeps the electromagnet turning.
How a "Brushless" DC Motor Works
In
a brushless DC motor, the positions of the fixed magnets and the
electromagnetized coils are reversed. The fixed magnets are now placed
on the rotor and the coils are placed in the surrounding casing. The
motor functions via current being passed through each surrounding coil
in series, so repulsing and attracting the fields of the fixed magnets
and keeping the rotor they are attached to turning. For a motor of this
kind to work, the coils of the commutator need to be kept synchronized
with the fixed magnets so that the fields are continually in opposition
and the rotor is kept turning. This requires an electronic controller or
microprocessor to coordinate the application of current to each
electromagnetic coil.
Advantages of "Brushless" Motors
The
chief advantage of brushless motors is that the transfer of current to
the commutator is not mechanical. Because brushed motors depend on the
physical contact of the metal brushes with the coils of the commutator
they are subject to a loss of efficiency due to friction with the
contacts and also, like all mechanical parts, wear and tear on the
brushes and the connections after long periods of use. As brushless
motors get less hot (due to the lack of friction) they can work at
greater speeds (because great heat interferes with magnetic fields).
Advantages of "Brushed" DC Motors
The
chief advantage of brushed DC motors is that they are cheaper and
simpler to construct and maintain than brushless motors as the mechanism
is less complicated.