INTRODUCTION
Electric motors are so much a part of everyday life that we seldom
give them a second thought. When we switch on an electric drill,
for example, we conWdently expect it to run rapidly up to the correct
speed, and we do not question how it knows what speed to run at, or
how it is that once enough energy has been drawn from the supply to
bring it up to speed, the power drawn falls to a very low level. When we
put the drill to work it draws more power, and when we Wnish the power
drawn from the mains reduces automatically, without intervention on
our part.

The humble motor, consisting of nothing more than an arrangement
of copper coils and steel laminations, is clearly rather a clever energy
converter, which warrants serious consideration. By gaining a basic
understanding of how the motor works, we will be able to appreciate
its potential and its limitations, and (in later chapters) see how its
already remarkable performance can be further enhanced by the addition
of external electronic controls.

This chapter deals with the basic mechanisms of motor operation, so
readers who are already familiar with such matters as magnetic Xux,
magnetic and electric circuits, torque, and motional e.m.f can probably
aVord to skim over much of it. In the course of the discussion, however,
several very important general principles and guidelines emerge. These
apply to all types of motors and are summarised in Section 1.8. Experience
shows that anyone who has a good grasp of these basic principles
will be well equipped to weigh the pros and cons of the diVerent types of
motor, so all readers are urged to absorb them before tackling other
parts of the book.

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