Demystifying the Relationship Between Servo Motors and PWM: Do They Truly Need It?

Unveiling the mystery: Do servo motors need PWM?

When diving into the world of robotics, automation, or even DIY electronics projects, servo motors are often front and center. They are celebrated for their precision, responsive control, and versatility, making them the preferred choice in everything from RC cars to industrial machinery. But a recurring question on enthusiasts' and engineers' minds alike is: Do servo motors need PWM signals to operate effectively?

At first glance, this question seems simple, but the answer reveals layers of complexity once you peel back the technical skin. To truly understand whether PWM is a necessity, we must first understand what servo motors are and how they work.

What is a servo motor?

A servo motor is a type of rotary actuator that allows for precise control of angular position, velocity, and acceleration. Unlike simple motors that run continuously or are turned on/off with a switch, servo motors are designed to hold a specific position, change position smoothly, or follow a control signal accurately. Their internal anatomy typically includes a DC motor, a gear train, and a feedback device—generally a potentiometer or optical encoder—that reads the current shaft position.

The core of a servo’s functionality lies in its control system: it compares the feedback from the motor to a desired target (or command signal) and then adjusts its output to match that target with high accuracy.

The role of signals in servo operation

The way we communicate with servo motors is through control signals. These signals tell the servo what position or speed to achieve. In remote control (RC) cars, airplanes, or industrial automation, these signals are often pulses — short bursts of electrical energy sent at specific intervals, scaled according to the desired position.

Introducing PWM: Pulse-Width Modulation

Pulse-Width Modulation (PWM) is a method used to encode a value (like a position or speed) into the duration of a pulse within a regular time frame. Think of it as a series of on/off signals where the proportion of the "on" time to the total period—the duty cycle—determines the output.

For example, in typical RC servo control, a PWM signal cycles every 20 milliseconds, with the pulse width varying between about 1 ms and 2 ms. A 1 ms pulse might correspond to the servo being at 0 degrees, and a 2 ms pulse at 180 degrees, with intermediate pulses mapping to intermediate angles.

Do all servos use PWM? Or do they need it?

The term “servo motor” is broad, and not all servos operate on the same principles or require PWM signals. To clarify, we need to distinguish between different types of servos:

Digital Servo Motors: These often accept PWM signals, interpreting the pulse width to determine position commands.

Analog Servo Motors: These also typically respond to PWM signals but might have less sophisticated internal electronics.

Continuous Rotation Servos: These are designed to turn at various speeds rather than hold a position and often interpret PWM signals differently.

Most common hobby servos—those used in remote-controlled vehicles and robotics—are designed explicitly to be controlled via PWM signals. Their internal circuitry is optimized to read these pulses and convert them into motion commands.

Are there servos that do not need PWM?

Yes. Some servos and servo-like actuators operate on entirely different principles and may not require traditional PWM signals at all. For instance:

Stepper motors: These are a different type of actuator often controlled via step/direction signals rather than PWM.

Linear actuators: They may operate based on voltage or other control inputs.

Brushless DC motors with electronic commutation: These require dedicated drivers but do not necessarily depend on PWM signals for basic control.

However, in the specific realm of standard rotary servo motors, PWM is almost ubiquitous because of its simplicity, efficiency, and precision.

Why is PWM so widely used in servo control?

PWM's popularity stems from its effectiveness in controlling power and transmitting position commands with minimal complexity. It offers several advantages:

Energy efficiency: PWM allows the motor to be driven with full voltage but for a specific proportion of time, reducing power consumption during holding positions.

Smooth control: Varying the duty cycle of the pulse grants fine control over the position or speed.

Ease of implementation: Most microcontrollers and servo controllers can generate PWM signals easily, making it accessible for hobbyists and professionals alike.

Summary so far

In essence, for many common servo motors, especially those used in RC and hobbyist projects, PWM signals are the standard and recommended control method. They are not necessarily a mandatory requirement in all motor types but are fundamental for controlling standard hobby servos.

In the next segment, we'll explore more technical insights into how PWM signals influence servo operation, alternative control signals, and whether you can operate a servo motor without PWM. We’ll also delve into how different control methods affect performance and what to consider if you’re designing or tinkering with servo systems.

Part 2 will continue from here, exploring alternative control methods, specific applications, and advanced considerations around servo control without PWM.

Leveraging innovations in modular drive technology, Kpower integrates high-performance motors, precision reducers, and multi-protocol control systems to provide efficient and customized smart drive system solutions.