What Makes an Electric Motor Work?

• The Science and Technology Behind Electric Motors

Introduction

• We’re going to make a small working motor similar to the one pictured at the left… but what makes this or any electric motor work?

Let’s check it out!

Electric Motors - The Magnets

A magnetic field exists between the north and south poles of a permanent magnet.

Electric Motors - The Armature

• An electromagnet (wire coil) is wound on an iron core and the core is placed on a shaft so it can rotate. This assembly is called the armature.

Iron Core

Shaft

Wire Coil

Electric Motors - The Assembly

The armature is placed in the permanent magnet’s magnetic field.

More Details

• The ends of the armature coil are connected to semicircular sections of metal called commutators (A & B). Brushes (X & Y) contact the rotating commutator sections and energize the armature coil from an external power source. (Important - the polarity of the armature’s electromagnet depends on the direction of current flow through the coil.)

• A battery is connected to the brushes. Current flows into brush X to commutator section A, through the coil to section B, and back to the battery through brush Y, completing the circuit. The armature coil is magnetized as indicated in the sketch.

• The north pole of the armature is repelled by the north pole of the field magnet. The south pole of the armature is repelled by the south pole of the field magnet. The armature turns one quarter revolution, or 90 degrees.

• The north pole of the armature is attracted by the south pole of the field magnet. The south pole of the armature is attracted by the north pole of the field. The armature turns another quarter turn. It has now turned one-half revolution.

• As the commutator sections turn with the armature, section B contacts brush A and section A contacts brush B. The current now flows into section B and out section. A. The current has been reversed in the armature due to commutator switching action. This current reversal changes the polarity of the armature, so that unlike poles are next to each other.

• Like poles repel each other and the armature turns another quarter turn.

• Unlike poles attract each other and the armature turns the last quarter turn, completing one revolution. The commutator and brushes are now lined up in their original position which causes the current to reverse in the armature again. The armature continues to rotate by repulsion and attraction. The current is reversed at each one-half revolution by the commutator.