Servo or stepper motor: how to choose

Key differences

• Feedback: a servo drive reads an encoder or resolver and corrects the position continuously. A basic stepper runs open loop, so a missed step goes unnoticed.
• Torque and speed: stepper torque falls as speed rises. A servo holds its rated torque across most of its speed range and can briefly deliver several times that torque for acceleration.
• Smoothness: servos run quietly and smoothly at high speed. Steppers can resonate at certain speeds unless microstepping or damping is used.
• Cost and setup: steppers are cheaper and simple to commission. Servos cost more and need tuning of the control loops.

How to decide

1. Calculate the load inertia, the required speed and the move profile (distance and time).
2. Check the torque required at the working speed, including acceleration, with a safety margin.
3. If the torque fits comfortably inside a stepper's speed-torque curve and the load never changes unexpectedly, a stepper is likely enough.
4. If you need high speed, tight settling time, or protection against lost position, select a servo.
5. Consider a closed-loop stepper as a middle option: it adds an encoder to a stepper to detect and correct lost steps.

Match the drive and motor

Always select the drive and motor as a pair from the manufacturer's data: voltage, current, feedback type and communication interface (pulse and direction, analogue, or a fieldbus such as PROFINET or EtherCAT) must all match your controller.

Frequently asked questions