The previous lesson introduced the simple linear motor. Linear motors have some practical applications, but rotating DC motors are much more prolific. The principles which explain the operation of linear motors are the same as
those which explain the operation of practical DC motors. The fundamental difference between linear motors and
practical DC motors is that DC motors rotate rather than move in a straight line. The same forces that cause a linear motor to move “right or left” in a straight line cause the DC motor to rotate. This chapter will examine how the linear motor principles can be used to make a practical DC motor spin.

The next step in our consideration of DC motors is to develop an equivalent circuit which can be used to better understand motor operation. The armatures in real motors usually consist of many windings of relatively thin wire. Recall that thin wires have larger resistance than thick wires. The equivalent circuit then must include a resistor a R which accounts for the total resistance of the armature winding.

The purpose of this supplement is to present the basic material needed to understand the operation of simple DC motors. This is intended to be used as the reference material for
the linear and DC motors lectures in EE301, as this material is not covered in the text.