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Stepper vs Servo Motors



The following will attempt to justly compare stepper vs servo motors assuming the following:

-The motors are of equal rated power
-Both motors we are comparing are of same quality
-Servo is equipped with an encoder
-Stepper is not equipped with an encoder
-The driver is assumed to provide the same features excluding feedback options
-The Servo motors are of DC Brushed type


Keep in mind that this is a comparison only and not a determination on which motor is “better”. Both motors should be viewed as separate technologies, both of which are capable motors given the correct setup and use.




Stepper Vs. Servo Motors
Characteristics Servo Motor (DC Brushed Stepper (Hybrid)
Cost The cost for a servo motor and servo motor system is higher than that of a stepper motor system with equal power rating. This feature would have to go to stepper motors. Steppers are generally cheaper than servo motors that have the same power rating.
Versatility Servo motors are very versatile in their use for automation and CNC applications. Stepper motors are also very versatile in their use for automation and CNC applications. Because of their simplicity stepper motors may be found on anything from printers to clocks.
Reliability This is a toss up because it depends on the environment and how well the motor is protected. The stepper takes this category only because it does not require an encoder which may fail.
Frame Sizes Servo motors are availible in a wide variety of frame sizes, from small to large motors capable of running huge machines. Many of the motors come in NEMA standard sized. Stepper motors do not have as many size selections as servo motors in the large sizes. However stepper motors may still be found in a variety of NEMA frame sizes.
Setup Complexity Servo motors require tuning of the (PID) closed loop variable circuit to obtain correct motor function. Stepper motors are almost plug-and-play. They require only the motor wires to be wired to the stepper motor driver.
Motor Life The brushes on servo motors must be replaced every 2000 hours of operation. Also encoders may need replacing. The bearing on stepper motors are the only wearing parts. That gives stepper motors a slight edge on life.
Low Speed High Torque Servo motors will do fine with low speed applications given low friction and the correct gear ratio Stepper motors provide most torque at low speed (RPM).
High speed High Torque Servo motors maintain their rated torque to about 90% of their no load RPM. Stepper motors lose up to 80% of their maximum torque at 90% of their maximum RPM.
Repeatability Servo motors can have very good repeatability if setup correctly. The encoder quality can also play into repeatability. Because of the way stepper motors are constructed and operate they have very good repeatability with little or no tuning required.
Overload Safety Servo motors may malfunction if overloaded mechanically. Stepper motors are unlikely to be damages by mechanical overload.
Power to Weight/Size ratio Servo motors have an excellent power to weight ratio given their efficiency. Stepper motors are less efficient than servo motors which usually means a smaller power to weight/size ratio.
Efficiency Servo motors are very efficient. Yielding 80-90% efficiency given light loads. Stepper motors consume a lot of power given their output, much of which is converted to heat. Stepper motors are usually about 70% efficient but this has some to do with the stepper driver.
Flexibility in motor resolution Since the encoder on a servo motor determines the motor resolution servos have a wide range of resolutions available. Stepper motors usually have 1.8 or 0.9 degree resolution. However thanks to micro-stepping steppers can obtain higher resolutions. This is up to the driver and not the motor.
Torque to Inertia Ratio Servo motors are very capable of accelerating loads. Stepper motors are also capable of accelerating loads but not as well as servo motors. Stepper motors may stall and skip steps if the motor is not powerful enough.
Least Heat production Since the current draw of a servo motor is proportional to the load applied, heat production is very low. Stepper motors draw excess current regardless of load. The excess power is dissipated as heat.
Reserve Power and Torque A servo motor can supply about 200% of the continuous power for short periods. Stepper motors do not have reserve power. However stepper motors can brake very well.
Noise Servo motors produce very little noise. Stepper motors produce a slight hum due to the control process. However a high quality driver will decrease the noise level.
Resonance and Vibration Servo motors do not vibrate or have resonance issues. Stepper motors vibrate slightly and have some resonance issues because of how the stepper motor operates.
Availability Servo motors are not as readily available to the masses as are stepper motors. Stepper motors are far easier to find than quality servo motors.
Motor Simplicity Servo motors are more mechanically complex due to their internal parts and the external encoders. Stepper motors are very simple in design with no designed consumable parts.
Direct Drive Capability Servo motors usually require more gearing ratios due to their high RPM. It is very rare to see a direct drive servo motor setup. Stepper motors will work fine in direct drive mode. Many people simple use a motor couple and attach the motor shaft directly to the leadscrew or ballscrew.
Power Range Because servo motors are available in DC and AC servo motors have a very wide power availability range. The power availability range for stepper motors is not that of servo motors.

The green selections in the Stepper vs Servo comparison chart above are the selected category winner as designated by CNCRoutersource.com. Of course, its always up for debate depending on the motor and usage of the motor.

The stepper vs. servo motor debate is a hot topic among some CNC manufacturer. You may be able to see many website describing why the motor they use on their product is better. My personal feeling is that either motor is a capable choice given the right setup. Some say that servo = means closed loop system. However, I have seen many closed loop stepper systems as well. I think the “debate” of stepper vs servo motors is pointless. Use the information above to help guide your decision. Most will be swayed by cost alone. If you feel any of this information is in error, please let us know.


Return to the Motors section from Stepper vs Servo Motors section. Least simplicity




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