Choosing the motor that best meets your application needs is important. When both stepper and servo motors fit 

the needs of a positioning system, you should know the differences. This will help you make the right choice.

This article will explain the difference between stepper and servo systems.

We'll start by comparing the two motor technologies.

Stepper Motors vs. Servo Motors

Pros:                                                                                                                         Pros

Low-speed torque with good performance                                                            High-speed torque

No tuning, no hunting                                                                                             Peak torque available

Compact Motor Size                                                                                                Continuous Duty

Cost-effective                                                                                                           Pack with Functions

Cons:                                                                                                                         Cons

Less high-speed torque                                                                                            Needs Tuning

Limitation of the duty cycle                                                                                      Works only with feedback

No peak torque                                                                                                         Hunting

Open-loop loops are the most common                                                                  The cost of the product

Both servo and stepper motors use permanent magnets for their rotors. To work, they also require drive circuits. 

Their designs differ. The differences in their designs lead to different performance.

Motor Design

The system uses the encoder to guide a stepper motor to the desired position. You will first notice that a servomotor 

requires an encoder. This increases its length.

Second, the difference in the number of poles. People call these poles "magnetic" poles, and they can either be north 

magnetic poles or south magnetic poles. The poles are stable areas where magnetic fluxes from the stator can interact

with the rotating rotor.

We'll have to dig deeper into the motor designs to understand how stepper motors differ from servomotors. Below, 

the left image shows the stepper motor's construction.

Stepper Motor

The stepper design uses a rare-earth permanent magnet sandwiched between two toothed rotor cups. The teeth 

on the rotor cup become magnetized poles by axially magnetizing the permanent. The rotor can be either 100 or 50 teeth.

Both rotors are slightly angled at half the tooth pitch. Each tooth of the rotor cup becomes a pole for a stepper.

Servo Motor

In a servomotor (shown above), engineers use a radially magnetized rotor instead of teeth. This is why servomotors 

are significantly smaller. The system requires encoder feedback to reduce errors caused by the low number of poles.

A typical servo design uses a 3-phase stator (U, V, W) and a rotor that has 28 poles. The rotor of the servo motor has 

segments with permanent magnets. This is different from a stepper motor, which has an axially magnetic rotor.

Stop Accuracy

The motor’s accuracy in stopping is a primary requirement for positioning applications. A stepper motor or a servomotor 

can both stop with accuracy.

The accuracy of a stepper motor relies on its electrical winding and the design of its teeth. A servo's accuracy depends on the 

quality of its construction, the encoder, and the algorithm used. The only friction between the stator and rotor comes from 

the ball bearings. Friction torque or even gravitational loads can affect the actual stopping position.

Stop accuracy depends on several factors. These include the winding properties, the quality of the rotor's construction, and 

the number of poles or teeth on the rotor. Assembly accuracy, encoder resolution, and the operating algorithm determine 

the stop accuracy for a servomotor.

You can think of a stepper as a device designed for mechanical positioning. A servo is made for the same purpose, but in an 

electrical way.

High Speed Performance

The servo motor is known to run at higher speeds. This means that a servo will produce more torque for a given RPM than 

a stepper motor.

The difference between servo and stepper motors comes from their pole counts and inductance. The number of poles can 

affect how many turns the motor's winding needs to make for one full revolution. It may only take 12 "steps" for a motor 

to complete a revolution. For a two-phase motor, however, 200 "steps' are required.

This doesn't matter at low speeds. At high speeds, the driver won't be able to fully energize the coils. Because torque is 

proportional to current, torque will decrease at higher speeds.

High Speed Performance

Servo motors are generally known for running higher speeds than stepper motors. What this really means is that the servo 

motor will output more torque at a specified RPM than a stepper motor. The difference in torque performance comes from 

the pole count and winding inductance in servo and stepper motors.

The number of poles also affects the number of times a motor winding needs to be advanced for a full motor revolution. 

For a servo motor, it may take only 12 "steps" to advance a full revolution. However, it takes 200 "steps" for a 2-phase 

stepper motor.

At low speeds, this doesn't make a significant difference. However, at high speeds, the driver will not be able to fully energize 

the windings. Since current is proportional to torque, the torque decreases at high speeds.  

The performance difference between stepper motors and servo motors can be best shown by their speed-torque curves. 

Stepper motors with a high pole count can start quickly and smoothly run at low speeds. The motors can be positioned 

quickly.

They respond fast and generate holding torque. They do this without needing an encoder. The L/R constants and high 

pole count of winding inductances reduce torque in high-speed regions.

Servomotors have a low pole count and winding inductance. This means they create low starting torque. However, they keep 

this torque better at all speeds.

Closed Loop Feedback

A servomotor must operate in closed-loop mode by definition. Typically, users operate stepper motors with an open-loop 

system. A servomotor uses feedback to control its position, speed, or torque.

You can tell the stepper motor to move in a certain direction without feedback. However, an overload might cause it to lose 

sync.

The driver gets more complex with the feedback system to stay in sync. A servo system has a pulse generator, a phase 

sequencer, and an FET for a stepper motor. It also has an F/V converter, current amplifier, speed amplifier, position amplifier, 

and deviation counter. You need all of these parts to run the motor in a PID loop. The driver checks for errors and adjusts 

the proportional, integral, and derivative gains for corrections in real time. These are the reasons why servomotors cost 

more and require processing time.

Along with closed-loop feedback, the motor's load-to-rotor-inertia-ratio also increases. A stepper motor can manage 

about 10 times its rotor inertia. A servo motor can manage 100 times its rotor inertia. As a comparison, a closed-loop 

stepper motor can handle 30x its rotor inertia.

Stepper motors operate without the need for feedback, so they require fewer components to operate. This is why they're 

more cost-effective. Servo motors require feedback and operate in a PID loop, therefore, more components are necessary.

Efficiency

The stepper motor uses a current-chopper driver, which ensures a constant supply of current regardless of the load. The 

duty cycle of a stepper is limited by the temperature.

The Servo Motor is better at controlling current. It only uses the amount of current it needs. Stepper motors are better at 

generating holding torque when the speed is zero. The holding torque generated by servo motors is higher.

Efficient current control also leads to improved performance, including reduced noise and vibration. Size motors correctly. 

When stepper motors are not properly sized, they tend to vibrate a lot more. If it is not correctly sized and tuned, servo 

motors will "hunt".

The closed-loop control also makes current management more efficient. This helps keep motor temperatures lower and 

extends their life. 

Observe how the temperature increases with duty. It is for this reason that stepper motors need to have a limited duty cycle. 

Temperature affects the life expectancy of bearing grease, which is what determines the service life.

Servo systems can draw only the current they need. This advantage helps increase their lifespan, reduce noise in some cases, 

and lower power use. A stepper must close the loop to provide the same level of current control.