How to use servo motors with the Arduino Uno

Servo motors come in many different sizes, shapes, and styles, but the ones found in maker environments are almost always like the one shown in Figure 1.

These types of motors provide accurate positioning, and while some can rotate a full 360º (900-00008-ND), most have a 180º rotation capability (900-00005-ND). Even though these motors can provide accurate position (via a digital input signal or PWM), they use DC brushed motors, which do not have step capabilities. So how can a servo know when it is pointed in the right direction? The answer is closed-loop feedback!

While the motor that drives servos is a DC brushed motor, the motor is connected to a series of gears that step down the rotation (to increase torque), and the “output gear” is also connected to a small potentiometer. As the servo rotates to the desired position, the value of the potentiometer changes, and this value is fed into a small onboard circuit that compares the requested angle with the potentiometer value. From there, the motor can be made to turn either clockwise or counterclockwise to match the rotation of the output shaft with the desired angle. 

Read the full article in the September issue of DPA.