Servo motors are built for precision, whether it’s holding a position, helping to trace a toolpath, or maintaining a set speed under load. 

But even the most reliable systems have their limits. Push those too far, skip routine checks, or operate in less-than-ideal conditions, and you’ll start seeing servo motor faults creep in, sometimes gradually, sometimes with a (literal) bang.

This article explores the most common servo motor faults, how they develop, and what you can do to catch them before they cause serious damage.

What Are the Common Symptoms of a Bad Servo Motor?

Servo motors don’t usually fail without warning, but when they do, it’s rarely subtle. Spotting issues early can save you from unexpected downtime and avoid more expensive repairs down the line. Here’s what to look out for, and why these servo motor faults crop up:

• Strange Noises: Grinding, buzzing, or clicking sounds can mean anything from worn bearings to electrical glitches or internal mechanical wear.
• Vibration: Excessive or sudden vibration usually hints at misalignment, a rotor issue, or something coming loose inside the housing.
• Overheating: If the motor runs hotter than expected, you could be dealing with excessive load, poor airflow, or deeper electrical problems.
• Erratic Operation: Random speed changes, stuttering, or sync loss often point to encoder faults, bad wiring, or miscommunication with the control system.
• Loss of Accuracy and Efficiency: Struggling to hold position or burning more power than usual? That’s often a feedback loop issue, mechanical drag, or encoder wear.
• Control System Errors: If the control system throws faults it’s likely flagging load issues, overheating, or broken feedback links.

Common Servo Motor Faults

This section covers the usual suspects when servo motors go sideways.

For each fault, we’ll break down what causes it, how to spot it early, and what you can do to prevent (or at least contain) the damage before it takes down your whole system.

Overheating

Overheating is one of the more damaging servo motor faults. Excessive heat can fry windings, break down insulation, and tank overall performance if left unchecked.

Why This Problem Occurs

• High Ambient Temperatures: Running motors in hot environments pushes them past safe thermal limits.
• Blocked Cooling Paths: Dust, debris, or buildup around the motor housing can choke airflow and trap heat.
• Long Duty Cycles: Continuous operation without enough rest gives heat no time to dissipate.
• Poor Ventilation: Tight spaces with restricted airflow don’t give the motor room to breathe.
• Worn Internals: Aging parts generate more friction, which means more heat.

Symptoms and Signs

• Excess Heat: Noticeable heat buildup during or after operation indicates potential overheating.
• Discoloration: Discolored components may suggest excessive temperature exposure.
• Burnt Smell: A burnt odor often indicates insulation damage or excessive heating of components.

Detection Methods

• Temperature Sensors: Real-time monitoring of the motor’s heat levels.
• Thermal Imaging: Detects heat hotspots and uneven distribution.
• Manual Inspection: Identify signs of overheating through physical inspection.

Prevention and Maintenance Tips

• Proper Ventilation: Ensure motors are operated in well-ventilated environments.
• Climate-Controlled Environments: Operate motors in controlled temperature and humidity settings where feasible.
• Regular Maintenance: Clean cooling systems and replace worn parts to ensure consistent performance.
• Cooling Fans: Install additional fans to improve airflow.
• Failsafe Mechanisms: Use systems that trigger shutoffs when safe temperature limits are exceeded.

Bearing Failure

Bearing failure is one of the more common servo motor faults. When bearings go, friction goes up, noise kicks in, and before long, the motor starts struggling. Since bearings keep the shaft turning smoothly, any trouble here can throw off efficiency and cause bigger performance issues down the line.

Why This Problem Occurs

• Normal Wear and Tear: Bearings degrade over time due to continuous operation and load cycles.
• Improper Installation or Reinstallation: Misalignment from incorrect installation accelerates bearing wear and causes inefficiency.
• Contamination: Dirt, dust, and other particles can infiltrate the bearing system, leading to abrasive wear and failure.
• Overloading: Excessive loads beyond design limits cause stress and early bearing degradation.
• Poor Lubrication: Insufficient or degraded lubrication increases friction, resulting in faster wear.

Symptoms and Signs

• Abnormal Sounds: Growling, squeaking, or screeching noises during operation indicate bearing distress.
• Increased Vibration: Excessive vibrations often point to bearing misalignment or wear.
• Heat Generation: Overheated bearings suggest friction and potential damage.

Detection Methods

• Vibration Sensors: Monitor and detect early signs of abnormal movement patterns in the motor.
• Manual Inspection: Regular checks for noises, heat, or wear signs.
• Temperature Monitoring: Continuously track heat levels to identify overheating.

Prevention and Maintenance Tips

• Routine Checking and Replacing Bearings: Schedule inspections and replace bearings as needed.
• Use Vibration Sensors: Early detection can prolong motor lifespan.
• Proper Installation Techniques: Ensure alignment during bearing installation.
• Keep Bearings Clean: Minimize contamination by regularly cleaning motor components.
• Lubrication: Apply proper lubrication to reduce wear and friction.

Brake Failure

Brake failure in servo motors can lead to positioning errors and unexpected downtime. Since the brake’s job is to hold position, it’s prone to wear, especially if it’s used too often, or forced to handle frequent or emergency stops.

Why This Problem Occurs

• Repetitive Stopping and E-Stops: Servo brakes are not typically designed for frequent stops or repeated emergency stops, leading to accelerated wear.
• Contamination: Dust, oil, and other contaminants can impair brake function and lead to performance degradation.
• Enclosed Design: Many servo motors with high protection ratings, like IP65, house brakes internally, complicating inspections and replacements.

Symptoms and Signs

• Unusual Noises: Grinding or squeaking noises during motor operation may indicate brake problems.
• Erratic Operation: Irregular motor movement or control issues often point to brake malfunctions.
• Heat Generation: Excessive heat around the brake area suggests impending brake failure.

Detection Methods

• Visual Inspection: Routine checks to detect signs of wear, contamination, or damage.
• Performance Testing: Evaluating brake performance under load conditions to identify inconsistencies.
• Thermal Imaging: Thermal cameras help detect unusual heat distribution around the brake system.

Prevention and Maintenance Tips

• Engage Brakes Correctly: Only engage brakes when the motor is at a standstill to minimize dynamic wear.
• Use Specialized Brakes for Frequent Stops: For applications requiring repeated stops, use brakes designed for dynamic stopping, such as spring-set or double C-face brakes.
• Regular Inspection: Schedule routine inspections to monitor for wear and contamination.
• Maintain Clean Environments: Keep the operating area free from contaminants like dust and oil.
• Proper Installation: Follow correct installation procedures to ensure brake function and longevity.

Servo Motor Fails to Turn

If a servo motor won’t turn, you’ve got a showstopper on your hands. Whether it’s the motor, the drive, or the controller, something in the signal chain is broken. The result is downtime, plain and simple.

Why This Problem Occurs

• Controller Issues:
  • DAC Output Problems: If the Digital-Analog Converter (DAC) output is incorrect, the motor may not turn.
  • Outdated Software: Using incorrect or outdated software can disrupt motor function.
• Drive Issues:
  • Drive Efficiency: Inefficient drive operation can impair motor performance.
  • Drive Failure: A failing drive can prevent the motor from turning.

Symptoms and Signs

• Motor Inactivity: The motor fails to move as expected.
• Control System Errors: Error messages or faults appear in the control system.
• Lack of Response: The motor does not react to control inputs.

Detection Methods

• Control System Diagnostics: Check the controller and drive for faults using diagnostic tools.
• Manual Testing: Test motor response to direct control inputs.
• Software Analysis: Examine control software for errors or outdated code.

Prevention and Maintenance Tips

• Regular Software Updates:
  • Keep Software Current: Regularly update control software to avoid compatibility issues.
• Drive Maintenance:
  • Routine Self-Tests: Periodically perform self-tests on the drive.
  • Timely Repairs: Address drive issues promptly.
• Controller Maintenance:
  • Verify Settings: Regularly check settings in the controller’s software/hardware.
  • Check Parameters: Ensure gain, velocity, and acceleration profiles are correct.

Servo Motor Shuts Off At High Speeds

If a servo motor cuts out at high or full speed, it usually means something’s off with the overload protection, cooling, or electrical system. Either way, you’re headed for downtime if it’s not addressed.

Why This Problem Occurs

• Defective Overload Protection System: A malfunctioning overload protection system may prematurely shut down the motor when it’s under excessive load.
• Rapid Overheating: Operating at high speeds without sufficient cooling leads to internal component damage and shutdown.
• Inadequate Bearings: Poorly maintained or improperly installed bearings contribute to overheating and motor failure.
• Blown Fuses or Old Fuses: Outdated or blown fuses disrupt the electrical flow, causing shutdowns.
• Bad Capacitors: Faulty capacitors interfere with the motor’s electrical functions, leading to shutdowns.
• RPM Meter Malfunction: Inaccurate RPM readings can cause incorrect adjustments and force the motor to shut off.
• Voltage Drops or Poor Wiring: Electrical instability or faulty wiring can cause erratic motor operation.

Symptoms and Signs

• Motor Shuts Off Unexpectedly: The motor stops after reaching high speeds.
• Overheating: The motor becomes unusually hot.
• Unusual Noises: Grinding or whining noises from the motor.
• Inconsistent Performance: Fluctuating motor speed or unexpected shutdowns at high speeds.

Detection Methods

• Thermal Imaging: Detect overheating hotspots in the motor.
• Performance Monitoring: Track motor performance for signs of overloading or overheating.
• Visual Inspection: Look for signs of physical damage or overheating.
• Electrical Testing: Use a multimeter to check for issues like blown fuses or damaged capacitors.

Prevention and Maintenance Tips

• Regular Maintenance: Conduct routine checks to ensure proper operation of all components.
• Cooling Solutions: Install additional cooling devices like fans or heat sinks to prevent overheating.
• Electrical Inspections: Regularly inspect wiring, fuses, and capacitors for wear or damage.
• RPM Meter Calibration: Calibrate the RPM meter periodically to maintain accurate speed readings.

Broken Motor Shaft

A broken shaft is about as bad as it gets—it stops the motor cold and can take down anything it’s connected to. It usually comes from mechanical stress, misalignment, or overload, and if it’s not caught early, the damage spreads fast.

Why This Problem Occurs

• Inadequate Mechanical Design: When the shaft is not designed to handle excessive radial loading forces, it can break under stress, leading to motor failure.
• Stuck Load or Severe Overload: If the motor faces a momentary overload or a stuck load, the shaft experiences an abrupt increase in force, which can cause it to fail.
• Misalignment During Assembly: Improper alignment between the motor and connected components creates uneven stress on the shaft, eventually leading to fractures.

Symptoms and Signs

• Loss of Motor Torque: A broken or damaged shaft results in the loss of motor power, causing the motor to fail to transmit torque effectively.
• Grinding or Abnormal Noise During Motor Operation: Unusual sounds, such as grinding, can indicate a mechanical issue with the shaft.
• Unresponsive Motor Even When Powered: The motor may fail to operate at all, even though electrical power is supplied, due to a broken shaft.

Detection Methods

• Visual Inspection of the Motor Shaft and Connected Components: Inspect the shaft for any visible cracks, deformation, or misalignment.
• Torque Monitoring During Operation: Monitor the motor’s torque output to identify any sudden drops that could indicate a shaft failure.
• Vibration Analysis to Detect Imbalances or Misalignments: Vibration sensors can help identify abnormal patterns that suggest shaft issues, such as imbalance or misalignment.

Prevention and Maintenance Tips

• Design Motors to Handle Expected Load Forces: Ensure the motor and shaft are designed to accommodate the maximum expected load to prevent overloading.
• Monitor Load Side Operations for Excessive Stress: Regularly check the load side of the motor to ensure it is not experiencing forces beyond its designed capacity.
• Ensure Precision Alignment During Assembly: Use precise alignment methods during installation to prevent misalignment that could lead to shaft failure.

Lubrication Issues

When lubrication breaks down, friction ramps up, heat builds, and performance takes a hit. Keep the moving parts properly greased, or you’re asking for wear, inefficiency, and eventually, motor failure.

Why This Problem Occurs

• Inadequate Lubrication: Increases friction, causing wear and overheating.
• Contamination: Dirt and debris degrade lubricant quality, raising friction and wear.
• Improper Lubricant: Using incompatible types can reduce effectiveness and damage components.

Symptoms and Signs

• Unusual Noise or Vibration During Operation: Insufficient or degraded lubrication leads to increased friction, which often manifests as grinding or unusual noises and vibrations.
• Overheating Due to Friction: Without proper lubrication, friction increases, causing the motor to overheat, which can further damage the components.
• Decreased Motor Performance: Increased friction and heat result in reduced efficiency, causing the motor to operate sluggishly or erratically.

Detection Methods

• Visual Inspection for Signs of Wear or Noise: Inspect the motor and surrounding components for visible wear, unusual noise, or signs of lubricant leakage.
• Monitor Motor Temperature for Overheating: Continuously monitor the motor’s temperature to detect abnormal rises that could indicate insufficient lubrication or excessive friction.
• Performance Analysis to Spot Inefficiencies: Regularly assess the motor’s performance and efficiency to identify signs of friction-related inefficiencies, such as decreased output or increased energy consumption.

Prevention and Maintenance Tips

• Implement a Routine Lubrication Schedule: Set a regular schedule to lubricate moving parts, ensuring they remain adequately lubricated and free of contaminants.
• Use the Appropriate Lubricant for the Motor: Always choose the right lubricant for your specific motor model and operating conditions to ensure optimal performance and protection.
• Seal the Motor to Prevent Contamination: Use seals and protective covers to prevent contaminants from entering the motor and affecting the lubricant’s quality and function.

Servo Motor Faults Ranked by Severity

As implied in the intro, not all faults are equal. Some faults can be catastrophic, resulting in immediate system failure, while others have a more gradual negative effect on system performance. In any case, an ounce of prevention is worth more than a pound of cure, so if you notice anything amiss with your servo motor hardware, then don’t delay – get it fixed, ASAP.

Severity Rating Explanation:

• 5: Catastrophic failure with immediate downtime
• 4: Severe impact, significant damage risk, urgent corrective action required
• 3: Moderate impact, progressive damage, noticeable performance degradation
• 2: Mild impact, gradual degradation over extended periods
• 1: Negligible impact, easily manageable

Should You Repair or Replace a Failed Servo Motor?

The decision comes down to cost, downtime, motor age, parts availability, and upgrade plans.

Replacement is usually better if repair costs hit 50–70% of a new motor’s price, or if downtime hurts productivity. It’s also the smarter choice for older motors with frequent issues, hard-to-find parts, or poor post-repair performance.

Warranty coverage can tip the balance by reducing costs and making the choice clearer.

How Long Should a Servo Motor Last?

Servo motors typically have a lifespan ranging between 20,000 and 30,000 operating hours under standard conditions. This estimate depends on factors such as usage patterns, maintenance quality, and environmental conditions. 

For more detailed insights on servo motor longevity and best practices to ensure optimal lifespan, see the information from Advanced Motion Controls.

Conclusion

Servo motors deliver precision, speed, and reliability, but issues like overheating, mechanical faults, and environmental factors can compromise performance.

Installing the hardware properly in the first place, in a clean environment is a good way to start a servo’s operational life.

Consistent monitoring, smart diagnostics, and a clean, stable environment are key to keeping servo systems running smoothly once operational.

Early detection of faults with tools such as temperature sensors and vibration analyzers can also help prevent damage and downtime once the system is up and running. 

As the saying goes, early action beats late regret, so deal with servo motor issues before they turn serious. Because when a servo fails mid-cycle, the only thing moving fast will be your stress levels.