Mechanical Systems 351
motor are shown in Figure 14-1. A simple DC motor is constructed in the
same way as a DC generator. Their basic parts are the same. DC generators
were discussed in Chapter 7.
The motor principle is illustrated in Figure 14-2. In Figure 14-2A, no
current is flowing through the conductors because of the position of the
brushes in relation to the commutator. In this state, no motion is produced.
When current flows through the conductor, a circular magnetic field de-
velops around the conductor. The direction of the current flow determines
the direction of the circular magnetic fields, as shown in the cross-section-
al diagram of Figure 14-2C.
When current flows through the conductors within the main mag-
netic field, this secondary field interacts with the main field. The interac-
tion of these two magnetic fields results in the production of motion. The
circular magnetic field around the conductors causes a compression of the
main magnetic flux at points A and B in Figure 14-2B. This compression
causes the magnetic field to produce a reaction in the direction opposite to
that of the compression. Therefore, motion is produced away from points
A and B. In actual motor operation, a rotary motion in a clockwise direc-
tion would be produced. If we wished to change the direction of rotation,
we would merely have to reverse the direction of the current flow through
the conductors.Figure 14-1. Basic parts of a DC motor