What is the difference between a servo motor and a stepper motor?

A servo is closed-loop with a feedback sensor — more precise, quieter, lower temperature rise, but costlier and more complex; a stepper is open-loop, cheaper and simpler, but noisy at low speed and prone to step loss. Choose by precision and cost needs.

What types of servo motors are there?

By power source: DC servo and AC servo. By application: positional rotation, continuous rotation and linear servo. DC servo is easy to control, AC servo is brushless and durable; positional types serve toys and robots, linear types serve laser cutting and semiconductors.

When high precision is not needed, should I choose a servo or an induction motor?

If the application only needs steady running at fixed or two speeds (fans, pumps, conveyors), an ordinary AC induction motor is usually more economical and reliable; a pole-changing motor suits two fixed speeds, and an induction motor plus VFD suits continuous control. A servo is only needed for precise positioning and path control.

Servo Motors Explained: Types, Structure and Applications

Q: What is a servo motor?

A servo motor precisely executes actions on command, comprising a motor, controller and sensing device. An encoder returns position signals to form a closed loop, letting the controller correct operation in real time for precise position and speed control.

September 29,2023

The invention of the motor underpins modern civilization. Without motors, productivity would drop sharply, industry would stall and daily life would be far less convenient. Do you know the types of motors? This article introduces the servo motor — its operating principle, control method, and a comparison of servo types.

What is a servo motor?

A servo motor is one that executes actions on command. Broadly, any setup with a motor, a controller and a sensing device that controls the motor based on feedback is a servo. When the controller sends a signal and the motor acts, the sensor returns a signal showing whether the motor ran correctly; if not, the controller issues a corrective signal. This closed-loop, real-time feedback is the core feature of a servo motor.

What does "servo" mean?

"Servo" comes from the Latin for "slave," describing a master-slave relationship between motor and controller: the master (controller) directs the slave (motor), continuously monitors whether it follows commands, and issues new commands in real time for correct action.

Structure of a servo motor

A servo motor is mostly similar to other motors; the key difference is an added encoder that sends position signals for sensing and feedback, forming a closed loop. It has three main parts:

Part	Function
Command device	Issues the motion command
Control device	Generates power to start the motor per the command
Drive / sensing device	Measures whether the displacement is correct and reports back

Types of servo motors

Servo motors can be classified by power source (DC/AC) or by application; each differs slightly in principle and use.

By power source: DC / AC servo

Type	Principle	Characteristics
DC servo	Uses a DC motor; the energized winding is on the central rotor, traditionally with brushes to switch current direction	Speed is linear with voltage, easy to control, widely used, but not suited to high-temperature or flammable environments
AC servo	Uses an AC motor; the winding is on the outer stator, driving the rotor with a rotating field; brushless	No brush wear, easy maintenance, high power capability, suits harsh environments, but speed control needs a VFD to change frequency

By application: positional / continuous / linear

Type	Characteristics	Common use
Positional rotation servo	Most common; often has a physical stop to halt at a set position and avoid large error	Toy cars, robots
Continuous rotation servo	Rotates any direction without a fixed stop; can change direction and speed; highly flexible	Mobile, direction-changing machines
Linear servo (tubular linear motor)	Moves linearly instead of rotating; high precision, quiet, simple structure	Laser cutting, semiconductor industry

Advantages and common applications

A servo motor is controlled by sensing position or speed. For example, a logistics conveyor sorts parcels by the position and speed of a turntable; the motor must reach the right position at the precise moment after receiving the control signal. Its strength is precise position control with little step loss, making it a top choice for many machines and appliances. Common applications include:

Large machines: printing-head control, fine textile weaving, metalworking lathe cutting.
Robotics: robot-pet walking, remote-control toy movement.
Robotic arms: handling and articulated arms.
Conveyors: moving items precisely to the next-step position.
Cameras: servo-driven focus for smooth aperture adjustment.

Servo motor vs stepper motor

Automation is the trend in modern industry, and both servo and stepper motors provide motor control, so they are often compared. A stepper lacks the servo's feedback sensor; it is cheaper but less precise. Choose by application.

Type	Servo motor	Stepper motor
Principle	Closed loop	Open loop
Price	Higher	Lower
Structure	More complex	Simpler
Noise	Quieter	Noise and vibration at low speed
Accuracy	More precise	Prone to step loss
Temperature	Lower temperature rise in continuous run	Higher temperature rise in continuous run

Servo vs ordinary induction motor: how to choose?

Not every machine needs a servo motor. The servo's strength is precise position and speed control, but it is costly and complex. If your application only needs steady running at one or two fixed speeds, an ordinary AC induction motor is often more economical and reliable.

Requirement	Better suited
Precise positioning, frequent start-stop, path control	Servo motor
Steady running at fixed or two speeds (fans, pumps, conveying)	AC induction motor (low cost, reliable)
Two fixed speeds without a VFD	Pole-changing (two-speed) induction motor
Continuous speed control without precise positioning	Induction motor + VFD

Many applications do not need the servo's high precision; switching to an AC induction motor can greatly cut cost and improve reliability. Assess by your actual control-precision needs to avoid over-specifying.

KUO SHUAY Motors

Kuo Shuay is a professional Taiwanese motor manufacturer focused on AC induction motors, with the Asia-Pacific region's first motor UL certification laboratory, a rich product range and multiple international certifications. We produce 0.01kW–15kW AC motors, with strict SOP control from components to whole-motor development and manufacturing, giving our motors competitive characteristics.

If your application does not need the servo's high-precision positioning but rather a reliable AC induction motor, a pole-changing two-speed motor or a custom solution, Kuo Shuay can recommend the best option for your needs with full after-sales support. Contact us.

<Further reading> What is an induction motor? A complete guide
<Further reading> What is a pole-changing motor? Speed control without a VFD
<Product> Kuo Shuay custom motors

What is a Pole-Changing Motor? Speed Control Without a VFD What is an Induction Motor? A Complete Guide

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