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Servo Motor#

A Servo Motor is a cheap rotary actuator used for radio control and small-scale robotics.

Colored Wires#

A servo motor is normally connected using just 3 wires.

Color Purpose
Yellow PWM Signal
Red VDD
Black GND

Control#

image/svg+xml 0° 90° 180° Top View t [ms] 5.0 0 Vout [V] 0 5.0 20.0 10.0 1.0 2.0 5.0 t [ms]
Working principle of a servo motor.

The angle of the servo is determined by the width of the PWM signal that is applied to the control wire. Most servos expect to see a pulse every 20 ms. The angle is calculated as the fraction of the pulse width

\[pw = \SI{1.0}{ms} + \SI{1.0}{ms} \cdot \left( \frac{\alpha}{\alpha_{\text{max}}}\right)\]

with the pulsewidth \(pw\), the current angle \(\alpha\) .

For most RC servos the exact refresh rate is irrelevant as long as it is in a range of 40 Hz to 200 Hz.

Example#

A pulsewidth of \(pw = \SI{1.5}{ms}\) will turn a servo with a maximum angle \(\alpha_{\max} = \SI{180}{\degree}\) to \(\alpha = 90\)° (neutral position).

References#