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#

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).