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 motor. 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 motor, and if it is AC-powered motor then it is called AC servo motor. 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 motor usually comes with a gear arrangement that allows us to get a very high torque servo motor 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.
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 motor can lift at a particular distance. For example: A 6kg/cm Servo motor 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.
Servo Motor Working Mechanism
It consists of three parts:
Controlled device
Output sensor
Feedback system
It is a closed-loop system where it uses a positive feedback system to control motion and the final position of the shaft. Here the device is controlled by a feedback signal generated by comparing output signal and reference input signal.
Here reference input signal is compared to the reference output signal and the third signal is produced by the feedback system. And this third signal acts as an input signal to the control the device. This signal is present as long as the feedback signal is generated or there is a difference between the reference input signal and reference output signal. So the main task of servomechanism is to maintain the output of a system at the desired value at presence of noises.
Servo Motor Working Principle
A servo consists of a Motor (DC or AC), a potentiometer, gear assembly, and a controlling circuit. First of all, we use gear assembly to reduce RPM and to increase torque of the motor. Say at initial position of servo motor shaft, the position of the potentiometer knob is such that there is no electrical signal generated at the output port of the potentiometer. Now an electrical signal is given to another input terminal of the error detector amplifier. Now the difference between these two signals, one comes from the potentiometer and another comes from other sources, will be processed in a feedback mechanism and output will be provided in terms of error signal. This error signal acts as the input for motor and motor starts rotating. Now motor shaft is connected with the potentiometer and as the motor rotates so the potentiometer and it will generate a signal. So as the potentiometer’s angular position changes, its output feedback signal changes. After sometime the position of potentiometer reaches at a position that the output of potentiometer is same as external signal provided. At this condition, there will be no output signal from the amplifier to the motor input as there is no difference between external applied signal and the signal generated at potentiometer, and in this situation motor stops rotating.
Interfacing Servo Motors with Microcontrollers:
Interfacing hobby Servo motors like s90 servo motor with MCU is very easy. Servos have three wires coming out of them. Out of which two will be used for Supply (positive and negative) and one will be used for the signal that is to be sent from the MCU. An MG995 Metal Gear Servo Motor which is most commonly used for RC cars humanoid bots etc. The picture of MG995 is shown below:
The color coding of your servo motor might differ hence check for your respective datasheet.
All servo motors work directly with your +5V supply rails but we have to be careful on the amount of current the motor would consume if you are planning to use more than two servo motors a proper servo shield should be designed.
Controlling Servo Motor:
All motors have three wires coming out of them. Out of which two will be used for Supply (positive and negative) and one will be used for the signal that is to be sent from the MCU.
Servo motor is controlled by PWM (Pulse with Modulation) which is provided by the control wires. There is a minimum pulse, a maximum pulse and a repetition rate. Servo motor can turn 90 degree from either direction form its neutral position. The servo motor expects to see a pulse every 20 milliseconds (ms) and the length of the pulse will determine how far the motor turns. For example, a 1.5ms pulse will make the motor turn to the 90° position, such as if pulse is shorter than 1.5ms shaft moves to 0° and if it is longer than 1.5ms than it will turn the servo to 180°.
Servo motor works on PWM (Pulse width modulation) principle, means its angle of rotation is controlled by the duration of applied pulse to its Control PIN. Basically servo motor is made up of DC motor which is controlled by a variable resistor (potentiometer) and some gears. High speed force of DC motor is converted into torque by Gears. We know that WORK= FORCE X DISTANCE, in DC motor Force is less and distance (speed) is high and in Servo, force is High and distance is less. The potentiometer is connected to the output shaft of the Servo, to calculate the angle and stop the DC motor on the required angle.
Servo motor can be rotated from 0 to 180 degrees, but it can go up to 210 degrees, depending on the manufacturing. This degree of rotation can be controlled by applying the Electrical Pulse of proper width, to its Control pin. Servo checks the pulse in every 20 milliseconds. The pulse of 1 ms (1 millisecond) width can rotate the servo to 0 degrees, 1.5ms can rotate to 90 degrees (neutral position) and 2 ms pulse can rotate it to 180 degree.
All servo motors work directly with your +5V supply rails but we have to be careful about the amount of current the motor would consume if you are planning to use more than two servo motors a proper servo shield should be designed.
Servo Motor Types:
Servo motors come in different types, each suited for specific applications. Let’s explore the main types:
1. AC Servo Motors
AC servo motors 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 motors 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 motors. 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 motors 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.
6. Brushless Servo Motors
A brushless servo motor 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.
Servo Motor Motor 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.
Here’s a look at some common applications where servo motors play a crucial role:
1. Robotics
Servo motors 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 motors 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 motors 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.
6. Home Automation
Servo motors 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.
To learn more about servo motor working principle and practical uses, please check below applications where controlling of servo motor is explained with the examples:
Commonly Asked Questions 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 motors 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 do Servo Motor Torque Calculation?
To calculate the torque of a servo motor, you need to know the force applied and the distance from the pivot point (lever arm). The basic formula for torque is:
Torque (T) = Force (F) × Distance (d)
Where:
Force (F) is the load or resistance the motor needs to move, usually measured in Newtons (N).
Distance (d) is the distance from the pivot point to the point where the force is applied, measured in meters (m).
For more accurate calculations, consider factors like motor efficiency, gear ratios, and any additional mechanical resistance in the 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:
Increase the PWM frequency: A higher frequency will increase the motor's response time.
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.
Using a motor driver or controller, the PWM signal can be modified to vary the motor speed as needed.
Arduino Servo Motor Projects
Now that you have learnt the basics of servo motor, let's take a look at some of the Arduino Servo Motor projects that we have built here at circuidigest. All these projects are available with code and Circuit Diagram for you to easily learn and build something similar on your own. If you have any questions you can leave them in the comment section or use our forums to get answers to your questions
Smart Dustbin using Arduino and Ultrasonic Sensor
Smart Dustbin as its name represents it works smartly or we can say that it is an automatic dustbin. Smart Dustbin is a very good project that we can build using the Arduino board. The project uses a sensor and a servo motor to automatically open and close the dustbin when it should be used.
Arduino Based Color Sorter Machine
As the name suggests, color sorting is simply to sort the things according to their color. It can be easily done by seeing it but when there are too many things to be sorted and it is a repetitive task then automatic color sorting machines are very useful. This project shows how to use servo motors to sort marbles or any colored objects and place them in respectful bins.
IoT based Smart Parking System
With the growing popularity of Smart Cities, there is always a demand for smart solutions for every domain. The IoT has enabled the possibility of Smart Cities with it’s over-the-internet control feature. This project shows how to use a servo motor to build an automatic tool gate that opens and closes to allow cars based on parking availability.
How to build a Simple Arduino Robotic Arm
In this tutorial, we are going to design an Arduino Uno based Robotic Arm from some cardboard and servo motors. The entire process of construction has been explained and it is a very fun to build project. It uses multiple servo motors to build a miniature robotic arm that can pick and place things.
Sun Tracking Solar Panel using an Arduino
The biggest crisis we are heading into is the climate change due to the excessive use of fossil fuels and to overcome these issues, we have only one solution which is utilizing Renewable Energy. This project uses a servo motor to change the direction of the solar panel based on the light availability to increase the efficiency of solar panels.
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hi,
thank you so much for your support
I'm in the industry, working with servo motors I needed to learn their
operation and controls
Request for Servo Motor PDF
Hello Sir,
I request for Servo motor PDF if you have any, I am learning about them.
Thanks
Help me to understand more about servo am in certain industry..
Thanks for your services
Electrical technology
The production of rotating magnetic field and working principal of 3-phase induction motor
It depends on the servo motor
It depends on the servo motor, if it a small torque motor then with some force you should be able to rotate it when not powered. But for metal gear high torque motors the gear ratio will be very high so it get s a bit more hard to rotate the motor.
It is a different story when the motor is powered, even a small torque motor when powered and positioned in a degree (say 90*) then we will not be able to rotate it because the motor is constantly trying to keep the motor in that position 90* so when you rotate the motor by hand it will push it back to the previous position
Also it is not recommended to rotate the motors by hand because it will damage the gears inside
servo tensioners
I need to how servo motor works for wire tensioners ?
Principal & working