Loss of Synchronism, Missed Steps and Stall: What Is the Difference?

These terms are related, but they are not interchangeable.

A stepper motor moves by following the magnetic field generated by the driver.

When the rotor cannot keep up with the commanded magnetic position, the motor loses synchronism with the driver.

This condition is commonly called loss of synchronism.

In simple terms:

The driver continues sending commands, but the motor can no longer follow them correctly.

Possible symptoms include:

• Position deviation
• Abnormal vibration
• Unstable rotation
• Sudden noise
• Motor stopping during acceleration

Loss of synchronism is the broader technical concept. Missed steps and stall can both be related to it.

Missed steps occur when the driver sends motion commands, but the motor fails to complete some of them.

For example, the controller commands the motor to move 1,000 steps, but the motor physically completes fewer steps.

The driver may still assume that the motor has reached the target position.

This is why missed steps are particularly difficult to detect in an open-loop system.

Common causes include:

• Excessive load
• Insufficient torque margin
• Acceleration set too high
• Operating speed too high
• Driver current set too low
• Sudden load changes
• Mechanical friction or blockage
• Incorrect motor wiring

Missed steps do not always mean that the motor has completely stopped. The motor may continue running, but its actual position has already deviated from the commanded position.

A stall is a more severe operating condition.

The motor is energized, but the rotor cannot continue rotating as required by the command.

Typical symptoms include:

• The motor vibrates but does not rotate
• The motor stops suddenly under load
• The output shaft remains locked in position
• The driver continues sending pulses
• The motor may heat up quickly

A stall may occur when the load torque or mechanical resistance exceeds the available motor torque.

It can also be caused by:

• Excessive acceleration
• Resonance
• Inadequate power supply
• Excessive friction
• Transmission blockage
• Incorrect phase wiring
• Operating outside the motor’s usable speed range

A stall can lead to serious position loss, especially when the system does not have an encoder or other feedback device.

You can understand the three terms this way:

• Loss of synchronism: The motor can no longer follow the driver’s magnetic commands correctly.
• Missed steps: The motor has failed to complete part of the commanded motion.
• Stall: The motor has lost the ability to continue rotating and may stop completely.

The three conditions may occur together, but their severity is different.

Lost steps do not necessarily cause the motor to stop completely, while stall usually results in more obvious position loss.