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Servo Motors and Pulse Width Modulation (PWM)

A servo motor (or servo) is a rotary actuator (or linear actuator) that allows for precise control of angular (or linear) position, velocity, and acceleration.

Inside Servo

AC Servo motors can handle higher current surges and are thus more commonly found in heavy industrial machinery. 

DC Servo Motors are best suited for smaller applications and have excellent control-ability and feedback. Servo motors are among the most efficient motors used in robotics today. The PWM signal is generated by a microcontroller or a dedicated PWM generator.

Servo Circuit

A servo motor is a part of a closed-loop system consisting of a motor, a gear system, a position sensor (usually a potentiometer), and a control circuit. The motor is connected to the gear system, which reduces the motor speed, increases torque, and provides feedback to the potentiometer. This potentiometer (variable resistor) controls current going into the control circuit. The control circuit then controls the motor’s rotation precisely to achieve the desired position.

Controlling Servo Motors with PWM

Servo PWM

The control of servo motors is achieved using the pulse width modulation (PWM) technique, which involves varying the width of the pulse applied to the motor for a fixed amount of time. The pulse width (or the period for which the switch is closed) determines the angular position of the motor. 

Stepper Motors

Stepper Motor

A stepper motor, also known as step motor or stepping motor, is a brushless DC electric motor that divides a full rotation into a number of equal steps.  The stepper motor is known for its property of converting a train of input pulses (typically square waves) into a precisely defined increment in the shaft’s rotational position. Each pulse rotates the shaft through a fixed angle. 

PWM can be used to control the speed of a stepper motor, although it is not the most common method. Stepper motors are typically controlled using a technique called "chopper drive," which regulates the current flowing through the motor windings.

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