Servo Motor – Types, Construction, Working, and Applications

What Is a Servo Motor ? . A servo motor is a special kind of electric motor designed to enable precise and accurate movement. It is commonly used in applications such as robots or machines. A servo is like a smart motor because it can control its position, speed, and power. This motor works with a sensor that tells it where it is, and a controller makes sure it moves the way we want it to. People use these motors a lot in big machines, especially in places like factories where we need things to move very accurately and smoothly. This article discusses servo , and their importance in various fields such as robotics and manufacturing, explaining how they work, how they’re built, and where they are commonly used.

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Servo motors are like powerful little engines with a high torque-to-inertia ratio, meaning they can generate a lot of twisting force relative to their size and weight. This makes them perfect for tasks that need quick acceleration, deceleration, and precise movements. They come in various sizes and power levels to suit different jobs and can be powered by either AC or DC voltage. What’s good is that we can control their speed and force using special signals called pulse width modulation (PWM). Some servo motors have extra features like built-in controllers and communication interfaces, which makes them adaptable and easy to integrate into complex systems.

What is a Servo Motor?

A servo motor is a type of motor that can rotate with great precision. Normally this type of motor consists of a control circuit that provides feedback on the current position of the motor shaft, this feedback allows the servo motors to rotate with great precision. If you want to rotate an object at some specific angles or distance, then you use a servo . It is just made up of a simple motor which runs through a servo mechanism. If motor is powered by a DC power supply then it is called DC servo , and if it is AC-powered motor then it is called AC servo . For this tutorial, we will be discussing only about the DC servo motor working. Apart from these major classifications, there are many other types of servo motors based on the type of gear arrangement and operating characteristics. A servo usually comes with a gear arrangement that allows us to get a very high torque servo in small and lightweight packages. Due to these features, they are being used in many applications like toy car, RC helicopters and planes, Robotics, etc.

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Servo motors are rated in kg/cm (kilogram per centimeter) most hobby servo motors are rated at 3kg/cm or 6kg/cm or 12kg/cm. This kg/cm tells you how much weight your servo can lift at a particular distance. For example: A 6kg/cm Servo should be able to lift 6kg if the load is suspended 1cm away from the motors shaft, the greater the distance the lesser the weight carrying capacity.  The position of a servo motor is decided by electrical pulse and its circuitry is placed beside the motor.

Construction

The Servo motor is DC motor which has 5 following parts:-

1. Stator Winding: This type of winding wound on the stationary part of the motor. It is also known as field winding of the motor.
2. Rotor Winding: This type of winding wound on the rotating part of the motor. It is also known as an armature winding of the motor.
3. Bearing: These are of two types, i.e., font bearing and back bearing which are used for the movement of the shaft.
4. Shaft: The armature winding is coupled on the iron rod is known as the shaft of the motor.
5. Encoder: It has the approximate sensor which determines the rotational speed of motor and revolution per minute of the motor.

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Mechanism of Servo Motor

It consists of three basic types:

1. Controlling Device
2. Output Sensor
3. Feedback system

The servo works on the phenomenon of the automatic closed-loop system. The controller is required for this closed-loop system. This controller is composed of a comparator and a feedback path. It has one output and two inputs. In this, for producing an output signal, the comparator is used to compare the required reference signal and this output signal is sensed by the sensor.

The input signal for the motor is termed as a feedback signal. On the basis of the feedback signal, the motor starts working. Comparator signal is called a logic signal of the motor. The motor would be ON for the desired time when the logical difference is higher and the motor would be OFF for the desired time when the logical difference is lower.

Basically, a comparator is used to decide that motor would be ON or OFF. Proper functioning of the motor can be done with the help of a good controller.

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Controlling

The servo motors can be controlled by the method PWM i.e., Pulse Width Modulation. These send electric signals of inconsistent width to the motor. The width pulse is varied in the range of 1 millisecond to 2 milliseconds and transfer this to the servo motors with repeating 50 times in a second.

The width of the pulse controls the angular position of the rotating shaft. In this, three terms are used which shows the controlling of the servomotor i.e., a maximum pulse, minimum pulse and repetition rate.

For Example, The servo moves with the pulse of 1 millisecond to turn motor towards 0˚ whereas a pulse of 2 milliseconds to turn motor towards 180˚ Between the angular positions, the pulse width interchange by itself. Therefore, the servo turns to the 90˚ with the pulse of width 1.5 milliseconds.

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There are three wires or leads in every servo motors. The two wires used from positive supply and ground supply whereas the third wire is used to control the signal.

Working of Servo Motors

The servo has a position sensor, a DC motor, a gear system, a control circuit. The DC motor run at high speed and low torque when getting power from a battery. This speed is lower and torque will be higher than gear and shaft assembly connected to DC motors.

The position of shaft senses by position sensor from its definite position and supply information to the control circuit. The signal is decoded by the control circuit from the position sensor and handles the direction of rotation to get the correct position. It needs a DC supply of 4.8 V to 6 V.

The reduction gearbox is connected to a shaft which decreases the RPM of the motor. The output shaft of the reduction gearbox is the same as of motor which is connected with encoder or potentiometer. The output of the encoder is then connected to the control circuit.

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The wires of the servomotor are also connected to the control circuit. The motor is controlled through a microcontroller by sending signals in the form of PWM, which the control circuit decodes to rotate the motor to the required angle. The control circuit moves the motor in a clockwise or anticlockwise direction, and the shaft also rotates in the desired direction. The encoder sends feedback signals to the control circuit.

When the motor reaches to required angle, the control circuit stops motor accordingly with the received signals from an encoder.

For Example., if the motor is at 30˚and microcontroller gives angle 60˚ to the motor then control circuit rotates the motor in a clockwise direction. When the motor reaches 60˚, the encoder sends a signal to the control circuit to stop the motor.

Servo Motor Types

Servo motors come in different types, each suited for specific applications. Let’s explore the main types

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1. AC Servo Motors

AC servo run on alternating current (AC). They are highly reliable and offer smooth performance in applications requiring precise control over high speeds and heavy loads. AC servo  are often used in industrial machinery like conveyor belts, CNC machines, and robotics because of their durability and efficiency.

2. DC Servo Motors

DC servo motors operate on direct current (DC). They are simpler in design and easier to control than AC servo . Due to their quick response and affordability, they are commonly found in low-power applications such as toys, small robotics, and home automation systems.

3. Positional Rotation Servo Motors

This type is the most common and is used for controlling angular movements. They rotate to a specific angle based on input signals, making them ideal for applications like robotic arms, antenna positioning, and camera gimbals.

4. Continuous Rotation Servo Motors

Unlike positional servos, continuous rotation servos rotate freely in either direction without stopping at a fixed angle. They are perfect for creating wheels and conveyor mechanisms in robots.

5. Linear Servo Motors

Linear servo convert rotational motion into linear motion and are used in applications requiring straight-line movements, such as in actuators for industrial machinery and precision equipment.

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6. Brushless Servo Motors

A brushless servo is a type of electric motor that uses permanent magnets and operates without brushes, which reduces wear and tear. It provides higher efficiency, faster speeds, and longer lifespan compared to brushed motors. They are controlled using electronic commutation, offering smooth and efficient motion.

Applications

Servo motors are versatile devices used to precisely control motion in various applications. Their ability to deliver accurate movements and maintain positions makes them indispensable in many industries.

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1. Robotics

Servo are widely used in robotics for controlling movements like robotic arms, grippers, and leg joints. Their precision and responsiveness allow robots to perform tasks such as assembling parts, picking up objects, and even walking.

2. CNC Machinery

In computer numerical control (CNC) machines, servo drive cutting tools or machine beds with exceptional accuracy. This ensures the production of high-quality parts in industries like automotive, aerospace, and manufacturing.

3. Camera Gimbals and Stabilizers

Servo motors help stabilize cameras in gimbals, allowing smooth and steady shots, even in motion. This technology is used in drones, filmmaking, and broadcasting.

4. Conveyor Systems

Servo motors are used in conveyor belts for precise speed control and positioning in industries like packaging, food processing, and logistics. They ensure smooth material handling and sorting operations.

5. Medical Equipment

In the medical field, servo are used in devices like surgical robots, prosthetics, and imaging systems for precise movements and adjustments. For instance, they enable robotic arms to perform delicate surgical tasks.

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6. Home Automation

Servo are used in automated doors, smart curtains, and remote-controlled devices. Their reliability and smooth operation enhance the functionality of modern homes.

7. Toys and Hobby Projects

Servo motors power RC cars, planes, and robots in toys and DIY projects. Their ease of use and compact size make them a favorite for hobbyists and students learning about automation and mechanics.

Advantages and Disadvantages of Servo Motor

Here, we discuss the advantages and disadvantages of servo , helping you understand their capabilities and limitations:

Advantages of Servo Motor

A servo motor is a highly efficient and versatile motor that offers several advantages. Here are some of the key benefits:

• Precision Control: Servo provide precise control over position, speed, and torque, making them ideal for applications that require high accuracy and repeatability.
• High Torque: Servo can deliver high torque even at low speeds, making them suitable for tasks that require high force and power.
• Fast Response: Servo have a quick response time, allowing them to quickly adjust to changes in load or speed.
• Wide Speed Range: Servo can operate at a wide range of speeds, from very low to very high, making them versatile for various applications.
• Energy Efficiency: Servo are designed to be energy efficient, consuming less power when not in use and reducing overall energy costs.

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Disadvantages of Servo Motor

While servo motors offer numerous advantages, there are also some disadvantages to consider:

• Complex Control: Servo require complex control systems and feedback mechanisms, such as Bode Plots in Control Systems, which can increase the overall complexity and cost of the system.
• Higher Cost: Compared to other types of motors, servo motors tend to be more expensive due to their advanced features and precision control.
• Size and Weight: Servo motors are generally larger and heavier than other types of motors, which may limit their use in certain applications with space constraints.
• Heat Generation: Servo can generate significant heat during operation, requiring additional cooling measures to prevent overheating.
• Noise: Depending on the design and quality of the servo motor, it may produce some noise during operation, which can be a concern in noise-sensitive environments.

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FAQs about Servo Motors

What is the difference between servo and stepper motor?

Servo motors and stepper motors both provide precise motion control but have important differences. Servo motors use closed-loop systems with feedback for high precision and speed. Stepper motors, in contrast, operate in an open-loop system, moving in fixed steps without feedback, stepper motors are also less complex and cost-effective compared to servo motors. Servo motors are commonly used in robotics and industrial applications, while stepper motors are used in 3D printers, CNC machines and other positioning tasks. The accuracy and precision of both the motors depend on the model and hence cannot be compared in generic.

Who are the popular Servo Motor manufacturers?

The popular servo motor manufacturers are Siemens, Mitsubishi Electric, Yaskawa Electric, Omron, Fanuc, and Panasonic. The motors from these manufactures can be commonly found in applications such as industrial automation, robotics, and CNC machinery.

How to choose a servo motor?

Choosing the right servo motor depends the torque, speed, and precision required for your application. The most important metric in selecting the servo is the torque needed to move the load. Next, consider the speed requirements and ensure the motor’s rated speed aligns with your needs. Feedback type is also important, if high precision is required, a motor with an encoder or other feedback systems is ideal. Additionally, factor in size, voltage, and power requirements to ensure compatibility with your system.

How to Control Speed of a Servo Motor?

The speed of a servo motor can be controlled by adjusting the input signal’s frequency or pulse width. In a PWM (Pulse Width Modulation) control system, the motor’s speed is determined by the duty cycle of the PWM signal—higher duty cycles correspond to faster speeds. To control speed:

1. Increase the PWM frequency: A higher frequency will increase the motor’s response time.

2. Adjust the pulse width: The duration of the pulse affects the motor’s position, and by controlling how quickly the servo reaches that position, you can influence the speed.

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