Protech ZOOM 425 ccpm Specifications download pdf (Page 195)

stator, since the R/C model should not turn with the motor shaft. The magnets or windings may

be part of the stator, depending on the motor type.

The part of the motor which rotates is called the rotor. If the stator has the windings, then the

rotor will have the permanent magnets, and vice versa.

In order for the motor to rotate, the magnet windings must be switched on and off. This pro-

cess of switching the windings on and off is called commutation. The motor can be commut-

ated either mechanically or electrically.

There are many different arrangements of coils and magnets which will make the motor shaft

turn, and therefore many different categories of motors.

The first two categories which we will discuss are: brushed and brushless motors.

30.1.12.1. Brushed motors

For a typical brushed motor, the magnets are attached to the inside of the motor case, and the

motor windings are attached to the motor shaft.

The motor windings are commutated by a mechanical device which makes and breaks the

electrical connection. There are a few (usually three) copper contacts mounted in a circle

around the motor shaft called the commutator. The stator has two brushes which touch thes

copper contacts as the motor rotates.

The are two main types of brushes: carbon (graphite) and precious metal.

Carbon brushes are typically used for larger motors designed for higher current because the

carbon brushes can handle high currents well.

The carbon brushes in smaller motors are attached to a springy metal which presses the car-

bon brushes against the commutator. Imagine a tiny toothbrush where the bristles are replaced

by a small block of carbon, and the handle is replaced by a springy metal.

The carbon brushes in larger motors are a block of graphite (about 4mm x 4mm) which are

pressed against the commutator by a spring. In these types of motors, the brushes can be re-

placed.

Precious metal brushes are typically used for smaller motors because they are easier to manu-

facturer for small motors, and they do not handle high current well.

A precious metal brush is usually a strip of springy metal (usually a beryllium alloy) with the

end cut into thin fingers. These fingers are pressed against the commutator to make and break

the electrical connection.

The are three main reasons for brushed motor failure:

a. Dirty commutator

When the motor is new, the commutator will be shiny. As the motor is used, the commut-

ator will become dirty due to arcing and brush material deposition. When the commutator

becomes dirty, it will not conduct electricity well, and the motor becomes less efficient and

loses power.

b. Brush wear

As the motor spins, it will cause wear on the brushes, and eventually the brushes will fail.

Technical Appendix

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Protech ZOOM 425 ccpm Specifications Page 195