Howstuffworks.com's "Inside a Combination Lock"

Inside an Electric Motor
by Marshall Brain

In this article we will take apart an actual electric motor and see what's inside. The motor being dissected is a simple electric motor that you would typically find in a toy:

You can see that this is a small motor about as big around as a dime. From the outside you can see the steel can that forms the body of the motor, an axle, a nylon end cap and two battery leads. If you hook the battery leads of the motor up to a flashlight battery the axle will spin. If you reverse the leads it will spin in the opposite direction. Here are two other views of the same motor. Note the two slots in the side of the steel can in the second shot - their purpose will become more evident in a moment:

The nylon end cap is held in place by two tabs that are part of the steel can. By bending the tabs back you can free the end cap and remove it. Inside the end cap are the motor's brushes. These brushes transfer power from the battery to the commutator as the motor spins:

The axle holds the armature and the commutator. As descibed in "How Electric Motors Work", the armature is a set of electromagnets, in this case three. The armature in this motor is a set of thin metal plates stacked together, with thin copper wire coiled around each of the three poles of the armature. The two ends of each wire (one wire for each pole) are soldered onto a terminal, and then each of the three terminals is wired to one plate of the commutator. The figures below make it easy to see the armature, terminals and commutator:

The final piece of any DC electric motor is the field magnet. The field magnet in this motor is formed by the can itself plus two curved permanent magnets:

One end of each magnet rests agains a slot cut into the can, and then the retaining clip presses against the other ends of both magnets.

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