this problem. To adjust the point at which the brushes touch the commutator
segments, the motor end-bell can be rotated relative to the motor body.
“Advanced” timing gives the coils more time to develop a strong magnetic field so
they can pull on the permanent magnets longer and with less magnetic conflict.
Timing of the
Electro-Fusion
motor on the
Corona
helicopter is usually set between
15 and 20 degrees for best results.
Brushless Motors
Brushless motors require no brushes. The copper coils are usually located on the
outer surface of the motor case (instead of on the spinning armature) where they can
be connected directly to a power supply. The permanent magnets are mounted on
and rotate with the output shaft. A small, computerized speed controller turns the
coils on and off at the appropriate time to operate the motor at a particular speed.
Brushless motors are more difficult and expensive to manufacture than brushed
motors, but are more efficient and powerful. With no brushes to burn out, the coils can
carry very high currents. Since the computer operated speed-controller can be
programmed to turn the coils on and off at just the right time, the power loss
associated with conflicting magnetic fields is very low.
O-Brushless eff graph
Efficiencies of good brushless motors approach 90% (that is, 90% of the battery
power going into a brushless motor ends up rotating the output shaft). As shown in
Fig. 3-3, brushless motors also can operate efficiently over a wide speed range. At
such high efficiencies, brushless motors tend to run cooler than brushed motors
because less electric power is wasted as heat.
Op er a tor's Guide
Electric Motors
LITE MA CHINES
3-5
Figure 3-3.
