Servo: what it is, how it works, and why it is so important in automation

In the world of engineering and automation, servomotors are true protagonists. These small yet mighty allies allow machines, robots, and electronic systems to operate with spectacular precision and efficiency. But what exactly is a servo? And why is it so important in fields as varied as robotics, industry, medicine, and even video games?

This article covers it all—from how servos work internally to their types, advantages, applications, and control methods. If you’ve ever wondered how robotic arms move so accurately or how a camera lens stays perfectly stabilized, keep reading to uncover all the secrets of this key technology in our digital age.

What is a servomotor?

A servomotor is an electromechanical device that lets you precisely control the position, speed, and acceleration of a shaft. To achieve such fine control, it relies on a feedback system that compares the desired position to the actual one and automatically adjusts the movement until the target is reached.

Unlike a conventional motor that just spins, a servo “knows” exactly which angle it must reach and does so with great accuracy. This capability makes it indispensable wherever precise control is essential.

Key components of a servo

A servomotor is more than just another motor. Its structure includes several elements working together for its unique functionality:

• Motor (AC or DC): The source of motion—AC for more power, DC for finer control.
• Control circuit: Interprets the input signal and adjusts the motor’s movement accordingly.
• Encoder or potentiometer: Detects the shaft’s true position. Simple versions use a potentiometer; advanced ones use an incremental or absolute encoder.
• Gearbox: Increases torque and enables finer output control.
• Servo drive or amplifier: The intermediary module between motor and controller, regulating delivered power.
• Power supply: Provides electrical energy—from +5 V for small servos to much higher values in industrial setups.
• Cooling system (in some cases): Prevents overheating in demanding environments.

How does a servomotor work?

The basic principle is control through PWM (Pulse-Width Modulation) signals. Generated by a microcontroller or electronic controller, these pulses of varying width tell the servo which position to reach.

A feedback system detects the shaft’s actual position and compares it with the desired one. If there’s a discrepancy, the controller adjusts voltage and rotation direction until the error is corrected. This closed-loop control enables spectacular precision, even under challenging conditions.

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Types of servomotors

Servos can be classified in several ways. Below are the main categories:

By current type:

• AC servos: More powerful, used in heavy industrial machinery. They offer greater durability and better efficiency at high speeds.
• DC servos: Perfect for tasks needing precision and quick response. Found in robotics, cameras, medical devices, and CNC machines.

By brush configuration:

• Brushed servos: Use brushes for contact. Cheaper but require maintenance due to wear.
• Brushless servos: No brushes—longer-lasting, more precise, and more efficient. Common in high-end applications.

By type of movement:

• Positional rotation: Typically rotate up to 180°. Very common in robotics or steering systems.
• Continuous rotation: Can spin indefinitely in either direction. Controlled by speed and direction.
• Linear servos: Convert rotational motion into linear motion—useful in automated systems requiring straight-line movement.

Analog vs. Digital

Servos process control signals in two ways:

Analog servos:

Receive low-frequency PWM signals. They respond only when a signal is active, resulting in slower starts and lower precision. Ideal for simple, budget-friendly tasks.

Digital servos:

Process high-frequency PWM using an internal microprocessor. This enables faster, smoother, and more precise control—even under load. They are the go-to choice today for demanding industrial or advanced robotic environments.

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Advantages of using servomotors

• Extreme precision: They control position, speed, and acceleration with impressive accuracy.
• High energy efficiency: They consume power only when movement is required.
• Compact yet powerful: Deliver high torque in small sizes.
• Fast response: Perfect for systems requiring dynamic, agile movements.
• Low maintenance: Especially true for brushless models.

Real-world applications of servos

Servos appear across countless sectors. Some of the most notable:

• Robotics: Robotic arm movement, actuators, wheels… (Boston Dynamics).
• Aerospace: Control of ailerons, flaps, and rudders.
• Medical: Equipment like MRI machines, automated pediatric beds, or robot-assisted surgery.
• Automotive: Power steering systems, electronic brakes, automated manufacturing.
• Consumer electronics: Cameras with autofocus, drones, smart toys.
• Industry 4.0: 3-D printers, CNC machines, automated production lines.
• Entertainment: Animatronics for movies, theme parks, and video games.

How to control a servomotor

The key to servo control lies in PWM signals. These signals dictate movement based on pulse width:

• Positional servos: The angle depends on pulse width (typically between 1 ms and 2 ms).
• Continuous servos: Direction and speed change according to PWM value.

Two common ways to send these signals:

• Microcontrollers: Such as those from Arduino, Raspberry Pi, or ESP32—ideal for DIY projects.
• Servo drivers: Dedicated controllers that receive commands from the main system and fine-tune motor behavior—typical in industry.

Servomotor maintenance

Proper installation and maintenance can extend a servo’s life beyond 10 years. Essential guidelines include:

• Rigid mounting: Prevents vibration.
• Good ventilation: Especially important for high-power models.
• Gear lubrication: If not enclosed.
• Feedback checks: Encoder or potentiometer calibration is crucial.
• Firmware updates: For programmable controllers.

Common problems and solutions

• Excessive heating: May require lower load, better cooling, or motor replacement.
• Mechanical noise: Often caused by worn gears or poor mounting.
• Loss of precision: Calibrate or replace the encoder.
• No response: Check power supply and PWM signal.

Servo durability and cost

Well-maintained servos can last 5–10 years (10 000–20 000 operating hours). Prices range from around €10 for basic models to over €2 000 for industrial-grade units.

Key factors when choosing a servo

Know your requirements well. Consider:

1. Torque: In Nm—higher loads need higher torque.
2. Rotational speed: Measured in RPM.
3. Power density: Critical in space-constrained applications.
4. Precision: Especially in 3-D printing, CNC, robotic arms, medicine, etc.
5. Feedback system: Encoder, potentiometer, resolver, and so on.

Servomotors are the heart of modern automation. Their ability to deliver precise motion control, coupled with their flexibility, makes them invaluable across nearly every technological field today. Understanding their operation and capabilities is key to improving designs, optimizing systems, and staying on the cutting edge of engineering and electronics.

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