Servo motors are the driving force behind the precision and power of countless machines. If you've ever seen the precise movements of a robotic arm, used autofocus on a camera, or simply walked through an automatic door at your local supermarket, you've seen these motors at work. 

But how does a servo motor work? We’re going to go deep into everything connected to these motors — and recommend a high-quality servo-controlled robot arm for your shop floor. 

We’ll cover:

• What is a servo motor?
• Servo motors vs. regular motors
• Components of a servo motor
• How servo motors work
• Different types of servo motors
• Common applications 
• Advantages and disadvantages

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What are servo motors, and how do they work?

Servo motors, or simply “servos,” are precision instruments in the world of motors. In essence, it's a motor with a built-in ability to rotate accurately. The key feature that sets it apart is its control circuit, which constantly monitors and adjusts the motor's position. This feedback allows servo motors to perform incredibly precise movements.

For example, if you need to rotate an object to a specific angle or distance, you use a servo motor.

A servo motor is, at its core, a basic motor driven by a servomechanism. A servomechanism is a closed-loop system with four parts — a controlled device, a controller, an output sensor, and a feedback system.

Servomechanisms are often used in situations where the exact control of position and speed is essential.

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Types of servo motors

In the industrial world, there are two main types of servos used — DC servo motors (powered by a direct current source) and AC servo motors (running on alternating current).

DC servo motors

A DC servo motor is typically used for smaller projects that prioritize simplicity and cost-effectiveness. They're affordable, efficient, and straightforward. However, DC servo motor construction relies on brushes and a commutator, which can wear down over time, so requires regular maintenance. 

Unfortunately, DC servo motors are prone to electrical noise and offer limited speed control precision, which makes them less ideal for high-performance applications.

AC servo motors

In contrast, AC servo motors dominate in industry. AC servo motors provide the muscle needed for more demanding industrial applications, while also delivering precise control and minimal maintenance needs. Their construction features a stator and rotor assembly, as well as encoders or resolvers that ensure accurate control.

Additionally, most AC servo motor systems incorporate advanced brushless designs for extra durability. 

This design allows AC servo motors to operate continuously in harsh environments, but without the wear and tear associated with DC servo motors. However, major disadvantages for AC servo motors include their complex integration and sophisticated control systems, both of which contribute to AC servo motors’ high cost. 

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Servo motor working principle

Servo motors operate on a unique working principle and come in various types and capabilities. 

To truly understand how a servo motor works, we need to take a look under the hood:

1. The motor is part of a closed-loop system comprising a motor, a gear system, a position sensor, and a control circuit. The motor can be either a DC or AC motor, depending on the power source and specific application needs.
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2. The control signal gives feedback to an electronic control unit, most commonly about the position and the speed of the motor. 
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3. The position sensor (feedback mechanism) is typically a potentiometer but could also be an encoder, a resolver, or another position-sensing device. The control circuit can be either an analog or digital circuit.
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4. The motor is connected to the gear system, which serves to reduce motor speed, increase torque, and provide feedback to the potentiometer. This feedback is then converted into an electrical signal by the potentiometer.
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5. The signal is sent to the control circuit, which decodes it, compares it to the desired position, and adjusts the motor's rotation accordingly. 

Servo motors are among the most efficient motors used across various industries. They allow the precise control of position and speed, making them indispensable for tasks that other motors struggle to perform. For deeper insights into servo motor basics, you can explore: What is servo control, a beginner’s guide. 

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Applications of servo motors

When asking, “What is a servo used for?” you'll find that it's used for operating everything from remote-controlled toy cars to automatic doors in daily life. They also handle more important jobs in manufacturing, robots, pharmaceuticals, and food services. Some of the most common servo motor applications include robotics and robotic vehicles.

• Servo motors are used to power robotic arms and grippers, ensuring the arms and joints move precisely. 
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• In robotic vehicles, servo motors control wheels, providing the necessary torque for movement. 
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• CNC machining also relies on servo motors to accurately control the speed and position of cutting tools. You'll find them offering exact motion control in CNC milling machines as well.
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• Conveyors benefit from servo motors to keep things running smoothly. A servo motor ensures products start and stop exactly when they should, which is crucial for jobs like product labeling, bottling, and packaging.
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• Hobbyists often use servo motors for projects like robots and model airplanes. For more on their uses, check out: Servo motors, what are they used for? 

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Benefits of servo motors

The benefits of servo motors combine exceptional precision and powerful output, enabling accurate movements that quickly and easily adapt to varying specifications. Plus, they’re now more affordable and widely available. There’s a lot to love about servo motors. So, let’s take a look at the main benefits in detail.  

• Accurate and fast: Servo motors excel in precision, making them ideal for applications in industrial automation. Their high accuracy allows for easy adjustments for specific tasks while ensuring precise results.
  
  Servo motors also have strong motor output power to provide quick and precise movements. This means they can easily adjust to changing needs as well.
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• Affordable: While servo motors were once considered expensive, their cost has dropped significantly in recent years. They may still be pricier than some motors, but the price gap is narrowing.
  
  Both industrial automations and hobbyists are turning to servo motors for their affordability. This makes them a practical choice for various projects.

• Readily available: Servo motors are easily accessible, and you can find them from many retailers that specialize in industrial parts. This availability is a big plus for businesses because they won't struggle to find replacement parts.

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How to choose the right servo motor

Choosing the right machine for your application involves a process known as “motor sizing.” This simply means figuring out the size and strength of the servo system you need. You base the sizing process on how fast it should go and how strong it must be. Speed and torque requirements are key factors to consider.

1. You want to match the torque and speed needs of your application to the motor's speed and torque rating. This prevents overheating or stalling issues and ensures accuracy.
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2. Gear ratio is another factor — some servos use gears to boost their torque. The gear ratio tells you how much the motor's power is amplified.
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3. Size and weight should align with the application's needs. Larger, heavier motors suit high-torque applications, whereas smaller, lighter motors are ideal for speed and high-precision tasks.
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4. Accuracy largely depends on its feedback system, which you should match to your application's needs. Environmental factors like ambient temperature, contamination, and vibration can affect performance.
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5. Consider where the motor will work and choose a motor designed for extreme environments if necessary. 

For precision applications, integrating servo positioners for enhanced control can help.

Servo motors in robotics

Servo motors almost always come up when discussing robotics and automation. Thanks to their precision, power, and torque capabilities, servo motors play a crucial role in automation applications. No matter the task at hand, there's a servo motor for it. Servos come in various sizes and strengths, making them versatile for robotics.

• Cost control is incredibly important in industrial processes. Consider robotic arms, a common sight in many applications. 
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• A single robotic arm typically requires at least five servo motors to achieve the desired range of motion. This can be costly, but thankfully, servo motors fit the budget — in all senses.
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• Convenience is another important part of industrial settings. Whether it's building robotic arms or similar systems, a straightforward approach is essential.
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• Servo motors are simple, requiring only a voltage and pulse-width modulation (PWM) for control. They eliminate the need for motor controllers and are rapidly replacing stepper motors in the industry. They can also use digital signaling, especially in more modern systems. 

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Servo motor disadvantages: Troubleshooting common servo motor problems

The main disadvantages of servo motors include vulnerability to contamination, bearing failures, overheating, brake malfunctions, and winding or cable issues — each capable of causing catastrophic downtime if left unchecked.

However, regular maintenance, proper installation, environmental control, high-quality feedback cables, and knowing how to troubleshoot these common issues can ensure you get the best performance from these motors.

Contamination

One leading cause of servo motor failure is contamination. Oil, coolant, and debris can infiltrate servo motors and cause damage to critical components like bearings and windings. You can fend off contamination by checking and cleaning your servo motors regularly.

You could also consider sealing motor windings and using fully enclosed motor systems.

Bearing issues

If you hear growling or shrieking noises when your motor operates at high speeds, it's a sign of bearing failure. This can be brought on by various factors, including typical wear and tear, and improper installation or reinstallation. Regularly inspecting and replacing bearings can prevent these failures. This also helps extend your servo motor's lifespan significantly.

Overheating

Few servo motors escape the issue of overheating. High temperatures can cause damage to the internal components or connected systems, leading to costly downtime.

Motor blockages, high ambient temperatures, and long operating hours are all common causes of overheating. Thankfully, many servo motors feature fail-safes that shut down the motor when things get too hot.

Whenever possible, place your servo motor in a temperature-controlled environment with proper airflow. This minimizes the risk of overheating issues.

Brake failure

Brake failure is often a result of overuse. While motor brakes play a critical role in stabilizing loads when your motor stops or powers down, these brakes are not designed for continuous and frequent use.

To avoid brake failure, always engage the brake when the motor is at rest, allowing it to take a breather. If your application needs frequent stops or dynamic braking, look at brakes designed for that specific purpose.

Bad windings and cable issues

Winding and cable issues are also common problems in servo motors, often due to wear and tear. Contaminants, such as water exposure, or the motor's natural vibrations, can harm the copper coils inside.

As time goes on, power and control cables can wear down and potentially cause motor failure or voltage spikes. To tackle winding problems, regular maintenance tasks like rewinding damaged coils can help.

You should also choose top-notch feedback cables. This ensures reliable operation over time.

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FAQs

What is the difference between DC and AC servo motors?

A major difference is that DC servo motors offer precise control for low-power tasks but need frequent maintenance, whereas AC servo motors excel in high-power, industrial applications with greater efficiency and durability.

Moreover, an AC motor relies on an AC power source, while a DC motor relies on DC power, such as batteries. AC servo motors are considered the better option compared to DC motors, as they have higher torque and efficiency with less radio frequency noise.

Which is better, a servo motor or a stepper motor? 

Servo motors are the ideal choice for high-speed, high-torque applications, whereas stepper motors are best for slower-speed, highly accurate applications. However, both servo motors and stepper motors have the same goal of providing precise speed control and positioning, but they differ in design and performance.

And, with a servo motor’s 3-wire connection to the power supply compared to the six required for stepper motors, servo motors work faster. They offer a straightforward solution.

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Summing up

Servo motors are quite the unsung heroes of technology, quietly powering precision in various applications. They can move and hold positions with pinpoint accuracy. Servo motors control torque and speed in the blink of an eye, which makes them perfect for handling complex tasks, including tricky manufacturing processes.

With many companies using servo motors for their reliability, precision, and efficiency, you'll likely keep seeing these devices in use for years to come. For more insights on how does a servo motor work, explore our resources on servo motor basics and applications.

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Next steps with RO1 by Standard Bots

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