If you work in manufacturing, automation, or process engineering, you’ve almost certainly worked alongside a servo motor, even if you’ve never stopped to think about exactly what makes it different from a standard electric motor. Understanding what a servo motor is, how it works, and why it fails can make a real difference to uptime, cost, and production efficiency.
The Core Definition
A servo motor is a rotary or linear actuator that allows for precise control of angular or linear position, velocity, and acceleration. Unlike a standard induction motor, which simply spins when power is applied, a servo motor operates as part of a closed-loop control system. This means it continuously receives feedback, typically from an encoder or resolver and adjusts its output to match a target position or speed with high accuracy.
That feedback loop is the defining feature. The motor “knows” where it is at any given moment, corrects errors in real time, and responds almost instantaneously to changes in command signals. This makes servo motors the motor of choice in applications where precision and repeatability are critical.
Where Servo Motors Are Used
Servo motors are found across a wide range of industrial and commercial applications, including:
- CNC machinery — controlling tool paths and cutting heads with micron-level accuracy
- Robotics and automated assembly lines — managing joint movement and pick-and-place operations
- Packaging and labelling equipment — synchronising multiple axes at high speed
- Injection moulding machines — controlling clamping and injection cycles
- Printing presses — maintaining registration and web tension
- Conveyors and material handling — managing precise start/stop positioning
Anywhere that motion needs to be controlled, repeated, and accurately, a servo motor is likely involved.
How A Servo Motor Works
A servo motor system consists of three key components working together:
- A servo motor consists of the motor itself, typically a brushless DC or AC permanent magnet motor and a feedback device, usually an encoder that reports position back to the controller.
- The servo drive (or amplifier) which interprets commands, reads feedback, and adjusts current to the motor accordingly
The drive compares the commanded position or speed against the actual position reported by the encoder. If there’s a discrepancy, known as a position error, the drive adjusts power to the motor to correct it. This all happens in milliseconds, thousands of times per second, allowing for smooth, accurate, and highly dynamic motion.
Servo Motors VS Standard Electric Motors
The distinction matters practically as well as technically:
| Feature | Servo Motor | Standard Induction Motor |
| Control type | Closed-loop (feedback) | Open-loop (no feedback) |
| Precision | Very high | Low to moderate |
| Speed range | Wide, including very low | Limited at low speeds |
| Response time | Milliseconds | Slower |
| Typical use | Automation, robotics, CNC | Pumps, fans, conveyors |
| Complexity | Higher | Lower |
Standard motors are reliable workhorses for continuous, fixed-speed applications. Servo motors excel where motion needs to be dynamic, precise, and repeatable.
Why Servo Motors Fail and Why It Matters
Because servo motors run intermittently, moving a carriage, cutter, or robotic arm to position before stopping, they can be harder to diagnose than continuously running machines. Common failure modes include encoder faults, winding insulation breakdown, bearing wear, overheating, and drive-related issues.
Many failures develop gradually, showing up as positioning errors, increased cycle times, or unexplained stops before a full breakdown occurs. And because servo motors only run for short periods, there isn’t enough operating time to gather meaningful trend data in the way you might with a continuously running pump or fan. That means waiting to see a pattern isn’t a viable strategy, by the time you notice something is wrong, you may already be facing unplanned downtime.
One often-overlooked risk is backup motors. Many facilities keep spare servo motors on the shelf, but have no way of knowing whether those backups are actually in good condition until the moment they’re needed most.
Workshop-Based Testing: The Right Approach
Servo motor diagnostics require a controlled workshop environment and specialist equipment. On multi-axis machines in particular, taking control of a servo axis while the machine is running risks crashing the entire system, so meaningful testing simply can’t be done in-situ. Motors need to come into the workshop, where they can be properly assessed under safe, controlled conditions.
RJW uses Octava Engineering’s latest system “Origin” to carry out health checks on servo motors, including backup units. Unlike basic pass/fail testing, Origin measures encoder and resolver condition levels and produces detailed reports with empirical data and graphs. You get real, measurable evidence of your motor’s condition, not just a best guess.
Get Your First Servo Motor Health Check For Free
Most servo motor failures don’t announce themselves, they build quietly, then strike at the worst possible moment. The only way to stay ahead of them is to know what’s actually going on inside the motor before something goes wrong.
RJW’s specialist team is currently offering the first Origin health check completely free. Send in your Servo motor or that backup unit sitting on the shelf that’s never been properly assessed and we’ll carry out a full diagnostic using the Octava Origin system, measure encoder and resolver condition levels, and produce a detailed report with real, empirical data. Whether your Servo motor passes or fails, you’ll walk away with measured evidence, clear options, and a specialist team ready to act, not an OEM queue stretching weeks or months into the future.
No guesswork. No “fingers crossed it’ll last another year.” Just the facts so you can make informed decisions, plan maintenance on your terms, and stop leaving critical equipment to chance. Click here to book in your FREE Servo Motor Health check now!
