Motor rotation principle

Regarding electric current, magnetic field, and force

First, to facilitate the subsequent explanation of motor principles, let's review the basic laws/rules concerning electric current, magnetic fields, and force. While it may feel a bit nostalgic, it's easy to forget this knowledge if you don't frequently use magnetic components.

The rotation principle of an electric motor

The following explains the rotation principle of the motor. We will use pictures and formulas to illustrate this— when the conductor frame is rectangular, the force acting on the current must be considered.

The force F acting on sides a and c is

It generates torque with the central axis as its pivot.

For example, when considering the state where the rotation angle is only θ, the force acting at right angles to b and d is sinθ, therefore the torque Ta of part a is expressed by the following formula:

Considering part c in the same way, the torque is doubled, generating the torque calculated by the following formula:

Since the area of the rectangle is S = h·l, substituting it into the above formula yields the following result:

This formula applies not only to rectangles but also to other common shapes such as circles. Motors utilize this principle.

Key points

• The rotation principle of an electric motor follows the laws (rules) related to current, magnetic field, and force.

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