Servos are one of the most commonly used components in tandem with Arduinos. A servo motor is a self-contained electrical device, that rotates parts of a machine with high efficiency and with great precision. The output shaft of this motor can be moved to a particular angle, position, and velocity that a regular motor does not have. Because of this precision and the general small sizes and power needs of servos, they make for perfect companions for FTC when you need an actuator.

Types of Servos

Positional Rotation

Positional Rotation Servos can only rotate from 0° to 180° or 0° to 270°. These are used when the degree of rotation needs to be very precise. 

Continuous Rotation

Continuous Rotation Servos have an infinite degree of rotation. These are used when precision isn't required but rather speed and direction.


Linear Servos are functionally the same as other servos but the rotational movement of the servo output is converted to linear movement. This can be done with a series of specialized gears.

Inside a Servo

All Servos have a motor, set of gears, casing, and control unit. Depending on the type of servo and precision of its rotation, there are two main methods of tracking the position.


A potentiometer is a variable resistor. These use a track of carbon with specific resistance to vary resistance as the shaft spins. When the resistance changes, the control unit will read a voltage drop. Depending on the voltage drop, the servo will be able to tell what position is in. This works in the opposite way as well where you can input a voltage for the potentiometer to meet which will correlate to degrees turned. These are usually found in 180° or 270° servos since potentiometers can only spin about the same distance. 


Encoders work by measuring the distance a disc rotates where each unit will be a degree or less. This disc will sometimes be a fine tooth gear that will count each tooth that passes, or on more precise encoders, a laser that passes through equally spaced slots that is read by a light sensor. The light sensor is attached to a control unit that will output a high pulse square wave each time a light is sensed. This can further be associated and read to be a degree or less at a time. 

Controlling a Servo with PWM

Varying the pulse width between 1ms and 2ms will move the servo shaft through the full 180 degrees of its travel. You can bring it to rest at any angle you desire by adjusting the pulse width accordingly

Controlling a Continuous Servo with PWM

Varying the pulse width between 1ms and 1.5ms will make the motor spin counterclockwise with the shorter pulse widths causing the motor to spin faster.

Varying the pulse width between 1.5ms and 2ms will cause the motor to rotate clockwise with the longer pulses resulting in a faster speed.

Servo Connections

The three connections to the servo motors are as follows: