How Do Servos Work?

Pulse Width Modulation (PWM)

• Servos are controlled by sending them a pulse of variable width. The control wire is used to send this pulse.

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• The parameters for this pulse are that it has a minimum pulse, a maximum pulse, and a repetition rate.

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• The angle is determined by the duration of a pulse that is applied to the control wire. This is called Pulse width Modulation. The servo expects to see a pulse every 20 ms. The length of the pulse will determine how far the motor turns. For example, a 1.5 ms pulse will make the motor turn to the 90 degree position (neutral position).�

Pulse Width Modulation (PWM)

• When a pulse is sent to a servo that is less than 1.5 ms the servo rotates to a position and holds its output shaft some number of degrees counterclockwise from the neutral point.

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• When the pulse is wider than 1.5 ms the opposite occurs.

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• The minimal width and the maximum width of pulse that will command the servo to turn to a valid position are functions of each servo. Different brands, and even different servos of the same brand, will have different maximum and minimums. Generally the minimum pulse will be about 1 ms wide and the maximum pulse will be 2 ms wide.