CHAPTER 17 ■ DC MOTORS
Rotor Commutator
At the end of the shaft is a commutator (see Figure 17-5). It contains two or more segments to receive
the electricity for the armature windings. Because the commutator segments are electrical contacts, it’s
important that they do not become soiled or coated in any non-conductive lubricant.
The commutator is necessary because power wires need to be attached to the armature windings.
However, the wires can’t be attached directly because they’d tangle up as the rotor turned. Instead, the
commutator slides between metal brushes (see Figure 17-6) to make an electrical connection between the
power wires coming in from the cap and the wire windings in the armature.
As the commutator rotates around, sometimes a winding is connected to the positive and negative
terminals of the battery, and sometimes a winding is connected in reverse. This feature flips the electrical
flow forwards and backwards. Thus, the magnetic field flips between attract and repel.
A great thing about the commutator mechanism is that the flipping automatically speeds up as the
motor turns faster!
Figure 17-5. Motor commutator
Figure 17-6. Shaft installed in the cap with brushes pressed against the commutator