RioBotz Comb t Tutorial
Summarized: Brushless
DC Motors
● Original Text by Professor Marco Antonio Meggiolaro; Summarized by Kevin M. Berry
Editor’s Note: Professor Marco
Antonio Meggiolaro, of the
Pontifical Catholic University of Rio
de Janeiro, Brazil, has translated his
popular book — the RioBotz Combot
Tutorial — into English. In January’s
issue, we summarized part of
Chapter 5, dealing with brushed DC
motors. Continuing the topic, this
month we present in its entirety
Marco’s write-up on brushless DC
motors. Marco’s book is available
free for download at: www.rio
botz.com.br/en/tutorial.html,
and for hard copy purchase (at no
profit to Marco) on Amazon,
published by CreateSpace. All
information here is provided
courtesy of Professor Meggiolaro
and RioBotz.
Brushless DC Motors
A brushless DC motor is a
synchronous electric motor powered
by DC current, with an electronically
controlled commutation system
instead of a mechanical one based
on brushes. Similarly to brushed DC
motors, current and torque are
linearly related, as well as voltage
and speed.
In a brushless DC motor, the
permanent magnets rotate while the
armature windings remain static.
With a static armature, there is no
need for brushes. The commutation
is similar to the one in brushed DC
motors, but it is performed by an
electronic controller using a solid-state circuit rather than a
commutator/brush system.
Compared with brushed DC
motors, brushless motors have
higher efficiency and reliability,
reduced noise, longer lifetime due to
the absence of brushes, elimination
of ionizing sparks from the
commutator, and reduction of
electromagnetic interference. The
stationary windings do not suffer
with centrifugal forces. The
maximum power that can be applied
to a brushless DC motor is very high,
limited almost exclusively by heat
which can damage the permanent
magnets. Their main disadvantage is
higher cost which has been
decreasing due to their mass
production, as the number of
applications involving them
increases.
shows a brushless inrunner of the
KB45 series, used to power the
spinning drum of our featherweight
Touro Feather.
In the outrunner configuration,
the windings are also stationary, but
they form the core of the motor (as
can be seen in the Turnigy motor in
Figure 2) while the permanent
magnets spin on an overhanging
rotor (the “spinning can”) which
surrounds the core. Outrunners
typically have more poles set up in
triplets to maintain the three groups
of windings, resulting in a higher
torque and lower kV than inrunners.
Outrunners usually allow direct drive
without a gearbox because of their
lower speed and higher torque. Due
to their relatively large diameter,
they’re not a good option to be
horizontally mounted inside very low
profile robots.
Remember to leave a generous
FIGURE 1.
FIGURE 2.
SERVO 03.2011 31
