Specifications

For carbon brushes, the brush will become so short that it will no longer touch the com-
mutator. For precious metal brushes, the ends of the metal fingers will wear away and the
brushes will no longer touch the commutator.
c. Overheating
If the magnets of the motor are overheated, they will lose magnetization. This is a vicious
cycle - when the magnets are weakened, the motor will run even hotter, which will weaken
the magnets further, etc.
The commutator and the brushes are the only parts of a brushed motor which wear signific-
antly, so these are the primary limiting factors for brushed motor life.
There are six main methods of extending brushed motor life:
a. Proper motor break-in
Motor break-in is covered in Chapter 10, Helicopter Construction
b. Proper motor timing.
Most motors which are used for R/C helicopters are originally designed for R/C car or R/C
airplane use. R/C car motors are usually manufactured for counterclockwise rotation, and
R/C airplane motors are usually manufactured for neutral timing so it rotates equally well
(equally badly) for both clockwise and counterclockwise rotation.
(The CW/CCW rotation of a motor is the direction of motor shaft rotation when viewing the
FRONT of the motor.)
Most R/C helicopters use a CW rotating rotor with the main shaft driven by a main gear/
pinion configuration, and the motor faces downwards. This motor arrangement requires
the motor to rotate in a CW direction. The few exceptions to this generalization are: Hor-
net, Zoom 400, T-rex, and Viper 70/90 which all use upwards-facing motor.
When a motor which is designed for CCW or neutral rotation is used for CW rotation, then
the motor runs very inefficiently because the motor windings are switched on and off at the
wrong times. This causes sparking which increases brush wear, dirties the commutator,
generates heat and creates RF interference.
There are some brushed motors which are properly timed for CW rotation, such as the
GWS 300H motor and the QRP Hyper S400 (red label).
On some motors, the timing can be changed. Most Speed 540 brushed motors have an
endbell (back face of the motor) which can be loosened by loosening two screws. After the
endbell is loosened, it can be rotated to the desired position.
Some other motors have an endbell which is secured by two tabs of metal which are bent
over the endbell. These can be bent out to loosen and rotate the endbell.
c. Regular motor maintenance
Regular motor maintenance will maintain the efficiency of the motor and decrease aver-
age motor temperature and extend the motor life.
The commutator should be checked every few flights to ensure it is clean and shiny. If the
commutator starts to look dirty, it should be cleaned.
Technical Appendix
183