{"id":4458,"date":"2026-10-20T19:00:00","date_gmt":"2026-10-20T16:00:00","guid":{"rendered":"https:\/\/kahrobot.com\/?p=4458"},"modified":"2026-10-21T00:08:33","modified_gmt":"2026-10-20T21:08:33","slug":"servo-motor","status":"publish","type":"post","link":"https:\/\/kahrobot.com\/en\/servo-motor\/","title":{"rendered":"Servo Motor: How It Works, from the SG90 on Arduino to the Industrial Servo"},"content":{"rendered":"
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Short answer:<\/strong> A servo motor is a motor you give an angle or a position, and it moves there and holds it, because inside it there is a sensor that measures its position and a circuit that keeps correcting the error. In Arduino projects we use a small servo such as the SG90, which usually turns 180 degrees, and we set its angle with an electrical pulse that repeats every 20 ms. In factories, a servo is a complete system: a brushless motor, a precise encoder and a drive that controls position, speed and torque.<\/p>\n<\/div>\n

If you search for \u201cservo motor\u201d, you'll find a small plastic part that costs a few riyals and an industrial motor with a drive that costs thousands of riyals, under the same name. The reason is that the idea is the same: a motor that knows where it is and corrects its own position. In this guide we explain how a servo motor works, then the Arduino servo, then the industrial servo, compare them in a table, and explain the difference between a servo and a stepper motor.<\/p>\n

How does a servo motor work? The closed-loop idea<\/h2>\n

Every servo motor, small or industrial, has four parts: a motor that produces the motion, gears or a coupling that transmit it, a sensor that measures the current position, and a control circuit. The circuit receives the target position and compares it with the sensor reading, then drives the motor in the direction that reduces the difference, repeating this tens or thousands of times per second. This method is called closed-loop control.<\/p>\n

Imagine filling a glass with water: your eye watches the level (the sensor), your brain compares it with the level you want (the comparison), and your hand slows the pour as you get close (the motor). That's why a servo holds the requested angle even if you push it by hand; it resists to get back there. An ordinary DC motor, on the other hand, keeps turning as long as it has power and doesn't know where it stopped.<\/p>\n

The Arduino servo motor: SG90 and MG996R<\/h2>\n

The most popular servo in Arduino projects is the SG90: it weighs about 9 g and its torque is about 1.8 kg\u00b7cm at 4.8 V. Its position sensor is a potentiometer connected to the output shaft. If you need more strength, there's the MG996R, with metal gears and a torque of about 10 kg\u00b7cm.<\/p>\n\n\n\n\n\n\n\n\n\n
Specification<\/th>\nSG90<\/th>\nMG996R<\/th>\n<\/tr>\n<\/thead>\n
Weight<\/td>\nAbout 9 g<\/td>\nAbout 55 g<\/td>\n<\/tr>\n
Torque<\/td>\nAbout 1.8 kg\u00b7cm at 4.8 V<\/td>\n9.4 to 11 kg\u00b7cm (4.8 to 6 V)<\/td>\n<\/tr>\n
Gears<\/td>\nPlastic<\/td>\nMetal<\/td>\n<\/tr>\n
voltage<\/td>\nAbout 5 V<\/td>\n4.8 to 7.2 V<\/td>\n<\/tr>\n
Suits<\/td>\nSmall locks, pointers and light arms<\/td>\nArms and wheels that carry weight<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

A small servo has three wires: brown for ground (GND), red for power (5V) and orange for the signal. The signal is a pulse that repeats every 20 ms (50 times per second), and the pulse width sets the angle: about 1 ms for one end, 1.5 for the middle and 2 for the other end. But you don't need to calculate this yourself; the Servo library in the Arduino IDE does it for you: attach to set the pin, and write(90) to go to 90 degrees. You'll find the details in Arduino's official Servo library reference<\/a>.<\/p>\n

Warning: a servo draws a lot of current the moment it moves, especially under load. A single SG90 with no load may run from the Arduino's 5V pin for testing, but with more than one servo or with an MG996R, use an external 5 to 6 V supply and connect its ground to the Arduino's ground. So if the servo jitters or the Arduino suddenly restarts, start by checking the power supply.<\/p>\n

There is also a type called the 360-degree (continuous rotation) servo: it turns without stopping, and its signal sets the speed and direction rather than the angle, so it suits wheels, not arms. If you want ideas to start with, see Arduino projects for beginners<\/a> for a servo door lock project and a door that opens with an RFID card.<\/p>\n

The industrial servo: motor, drive and encoder<\/h2>\n

In a factory you don't buy a servo as a single part but as a system of three parts. The first is a brushless permanent-magnet AC motor, designed to accelerate and stop very quickly. The second is an encoder mounted on the shaft that measures the position with very high resolution; a 24-bit encoder, for example, divides one revolution into more than 16 million points. The third is the servo drive, which is the brain and the power at once: it receives the command, runs three nested control loops for position, then speed, then current (torque), and feeds the motor the right power moment by moment.<\/p>\n

Where does the command come from? Usually from a PLC or a motion controller, either as pulses (Pulse\/Direction) or over an industrial network such as EtherCAT, PROFINET or EtherNet\/IP. Most modern drives also come with auto-tuning for the load and a safety function that cuts the torque (STO), and the motor may come with a brake that holds vertical axes when the power goes off.<\/p>\n

That's why you find industrial servos in machines that need fast, precise motion, such as filling and packaging machines, CNC machines, robots, and gluing and cut-to-length machines. Well-known systems include Siemens SINAMICS, Yaskawa Sigma-7, Mitsubishi MELSERVO, Delta ASDA and Panasonic MINAS.<\/p>\n

Comparison table: hobby servo motor vs industrial servo<\/h2>\n\n\n\n\n\n\n\n\n\n\n\n
Item<\/th>\nArduino servo (such as the SG90)<\/th>\nIndustrial servo<\/th>\n<\/tr>\n<\/thead>\n
Motor<\/td>\nA small brushed DC motor<\/td>\nA brushless permanent-magnet AC motor<\/td>\n<\/tr>\n
Position sensor<\/td>\nPotentiometer<\/td>\nA high-resolution digital encoder<\/td>\n<\/tr>\n
Control circuit<\/td>\nSmall, inside the servo body<\/td>\nA separate drive that controls position, speed and torque<\/td>\n<\/tr>\n
Motion<\/td>\nLimited angle, usually 180 degrees<\/td>\nUnlimited full rotation with precise position control<\/td>\n<\/tr>\n
Command<\/td>\nA pulse that repeats every 20 ms<\/td>\nPulses or an industrial network from a PLC or motion controller<\/td>\n<\/tr>\n
Torque<\/td>\nFrom 0.2 to about 1 N\u00b7m<\/td>\nFrom under 1 to tens of N\u00b7m and more<\/td>\n<\/tr>\n
Approximate price<\/td>\nFrom a few riyals to a few tens<\/td>\nThousands of riyals for the motor and drive<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

What's the difference between a servo motor and a stepper motor?<\/h2>\n

A stepper motor moves in fixed steps, most commonly 1.8 degrees, which is 200 steps per revolution. It usually works without a position sensor (open loop): the controller sends a number of steps and assumes the motor carried them out. That makes it simple and cheap, it holds its position well at standstill, and it's widely used in 3D printers and small CNC machines. But if the load increases, it may \u201close steps\u201d without knowing it, and its torque drops as its speed rises.<\/p>\n

A servo motor, on the other hand, always measures its position and corrects any error, and it keeps higher torque at high speeds, but it costs more and needs tuning. An ordinary DC motor is the simplest of the three: it turns, you control its speed with the voltage or a PWM signal, and it doesn't know its position unless you add an encoder.<\/p>\n

Note: the lines have blurred; today there are closed-loop steppers with an encoder that detects lost steps. But the general rule stands: the stepper for simple, cheap motion with known loads, and the servo for speed, precision and changing loads.<\/p>\n

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An engineer's view<\/strong><\/p>\n

In factories, most servo problems that get blamed on the motor are really caused by the selection or the tuning: a small motor on a heavy load, or a drive that wasn't tuned to the real load, so the machine vibrates or overshoots its position. So calculate the load before you buy: its mass and how it accelerates, then choose the motor and drive together. The same rule applies to Arduino in a simpler form: don't load an SG90 beyond its capacity, and give it its own power supply.<\/p>\n<\/div>\n

Where do you start?<\/h2>\n

Start with an SG90 servo and an Arduino: you'll understand the closed-loop idea and control the angle within minutes, and you'll learn an important lesson about external power and a common ground. After that, move on to projects that combine a sensor, a decision and motion, such as a door that opens with a card. If your goal is factories, the industrial servo comes after you've mastered the PLC, because it's programmed and managed through it; you'll find the full order in the roadmap for learning industrial automation from scratch<\/a>.<\/p>\n

Frequently asked questions<\/h2>\n

How many degrees does an SG90 servo motor turn?<\/h3>\n

About 180 degrees on most units, a little less on some. There are 360-degree versions that turn without stopping, but their signal controls the speed and direction, not the angle.<\/p>\n

Why does a servo jitter or shake?<\/h3>\n

The most common causes: a weak power supply that can't keep up when the servo moves, a ground not shared between the Arduino and the servo supply, a load greater than its torque, or damaged gears. So always start by checking the power supply.<\/p>\n

Do I need an external power supply for a servo?<\/h3>\n

For a single small servo with no load, the Arduino's 5V pin is usually enough for testing. For more than one servo, or for a big servo such as the MG996R, use an external 5 to 6 V supply with enough current, and connect its ground to the Arduino's ground.<\/p>\n

Does an industrial servo need a PLC?<\/h3>\n

Not always; many drives can run motions stored inside them from simple signals. But in most machines the command comes from a PLC or a motion controller, because it coordinates the servo's motion with the rest of the machine.<\/p>\n

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Build your first servo project with Kahrobot<\/strong><\/p>\n

In Level 2 of the Kahrobot path you build a servo door lock model, then open it with an RFID card. Start today with Level 1 to master the foundation, and the first two lessons are free.<\/p>\n

Watch the first two lessons free<\/a>Course details<\/a><\/div>\n<\/div>\n
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Further reading<\/strong><\/p>\n