What's wrong with ordinary electric motors?

An ordinary electric motor is based on a simple bit of magnet science we all learn at school: unlike poles attract, like poles repel. Here's how a basic motor works. You take a ring-shaped magnet, put a coil of wire inside it, and feed electricity through the wire. The wire becomes a temporary magnet powered by electricity—an electromagnet, in other words—and the magnetic field it creates repels the field from the permanent magnet that surrounds it.

A large electric motor from an electric lawn mower
Photo: The powerful electric motor from an old lawn mower. The slots at the front are part of the commutator, which is an ingenious device that reverses the electric current and keeps the rotor (the rotating, central part of the motor) spinning in the same direction.



We can also make motors that work using AC (alternating current) instead of DC. Although they're engineered in a radically different way, they're still based on "like poles repel, unlike poles attract": the electricity that powers the motor creates magnetic attraction and repulsion, and a force that makes the motor spin. You'll find more about AC motors—which are also called induction motors—in our article on AC induction motors.

Whether they're powered by DC or AC, ordinary motors are the hidden electric muscles that power modern life: you'll find them in all kinds of gadgets and gizmos in the world around you, from food blenders and refrigerators to vacuum cleaners and electric trains. But in all these machines, the rotors of their motors spin continuously. When you vacuum a carpet or commute to work by subway, the motors that are working for you turn around an arbitrary number of times: there's no precise control over how many times they rotate and what angle they spin through—and it really doesn't matter.

Basic Stepper Motor Operation principles