When you look at servo motor types by their motion, you will find three main categories:
- Positional rotation
- Continuous rotation
- Linear
Many people also group servo motors by their electrical supply, such as AC, DC, or brushless DC. This article focuses on how each type of movement occurs. Understanding the differences between these types helps you select the appropriate motor for your project. Retek Motion offers expert guidance and a range of options for all servo motor types.
Key Takeaways
- Positional rotation servo motors move to specific angles with high accuracy, making them ideal for robotic arms and precise control tasks.
- Continuous rotation servo motors spin endlessly with speed and direction control, making them ideal for wheels, conveyors, and achieving smooth, continuous motion.
- Linear servo motors convert rotary motion into straight-line movement, offering excellent precision and reliability for manufacturing and automation.
- Choose the right servo motor type by matching the motion needed, performance requirements, application, maintenance, and cost.
- Proper selection and installation of servo motors improve performance and lifespan; expert help can guide you to the best choice for your project.
Positional Rotation
Operation
You control a positional rotation servo motor by sending it a specific signal that tells it to move to a certain angle. Most of these motors can turn their output shaft up to 180 degrees. Inside, a potentiometer measures the shaft’s position and sends feedback to the control system. This feedback loop helps the motor reach and hold the exact angle you want. You often use Pulse Width Modulation (PWM) signals from a microcontroller to set the position. The motor compares the actual position to your command and corrects any difference right away. This closed-loop system gives you precise control over movement.
Tip: The physical stops inside the servo prevent the shaft from turning too far, which protects the internal sensor.
Features
Positional rotation servo motors stand out from other servo motor types because of their unique characteristics:
- Limited rotation range, usually 180°
- Built-in potentiometer for accurate position feedback
- Physical stops to prevent over-rotation
- Closed-loop control for precise angular positioning
- Easy to use with microcontrollers and PWM signals
These features make them different from continuous rotation servos, which spin endlessly, and from linear servos, which move back and forth in a straight line.
Applications
You will find positional rotation servo motors in many projects that need precise angle control. Some common uses include:
- Robotic arms for moving joints and end-effectors
- Humanoid robots for balance and movement
- Steering mechanisms in mobile robots and vehicles
- Remote-controlled cars, planes, and toys
- Medical robots for delicate surgical tasks
- Exploration robots for underwater, space, or rescue missions
- Collaborative robots (cobots) that work safely with humans
Hobbyists and professionals both rely on these servo motor types for their accuracy and reliability.
Continuous Rotation
Operation
You control a continuous rotation servo motor by sending it a signal that sets both speed and direction. Unlike positional rotation types, which move to a specific angle, continuous rotation servos spin freely in either direction. You can make the shaft rotate 360 degrees over and over, just like a regular DC motor. The speed and direction depend on the width of the PWM signal you send. If you want the servo to stop, you send a neutral signal. These servo motor types do not have internal position feedback. The potentiometer inside is usually disconnected or replaced with a fixed resistor, so the motor cannot sense its exact position. If you need feedback for precise control, you must add an external sensor, such as an optical encoder.
Note: Continuous rotation servos use an open-loop system. They cannot automatically adjust for changes in load or speed without extra sensors.
Features
Continuous rotation servo motors offer several features that make them useful for many projects:
- Full 360° rotation in both directions
- Speed and direction are controlled by simple PWM signals
- Only one signal wire is needed for control
- No internal position feedback, so you get speed control instead of angle control
- Compact size and easy integration with microcontrollers
You can find these servo motor types with typical voltage ratings from 4.8 to 6 volts DC. Most draw about 120 to 250 mA during movement, but stall current can reach up to 800 mA. Here is a quick look at common electrical ratings:
| Parameter | Value Range | Typical Value |
|---|---|---|
| Operating Voltage | 4.8 – 6 V DC | 5 V |
| Idle Current | N/A | 10 mA |
| Current During Movement | 120 – 250 mA | N/A |
| Stall Current | Up to 800 mA | N/A |
Applications
You will see continuous rotation servo motors in many industries and devices. They power wheels and steering systems in mobile robots, giving you control over speed and direction. Conveyor belts use them to keep products moving at a steady pace. In factories, these motors help feed materials like filaments or sheets at precise rates. You also find them in textile machines, CNC equipment, and even medical devices such as centrifuges and scanners. Other uses include:
- Material handling systems
- Processing equipment like mixers and pumps
- Grinding and polishing machines for surface finishing
- Laser systems for moving mirrors and lenses
These servo motor types are ideal for any task that needs smooth, continuous motion and reliable speed control.
Linear
Operation
You use linear servo motors when you need straight-line movement instead of rotation. These motors start with rotational motion from the motor shaft. The system then converts this rotation into linear motion using different mechanisms. The most common method uses a screw drive. Here’s how it works:
- The servo motor spins a threaded shaft called a lead screw.
- A nut sits on the lead screw and cannot rotate, so it moves along the threads as the screw turns.
- This movement pushes or pulls a connected part in a straight line.
- Some systems use a belt and pulley or gear drive to achieve the same effect.
- For vertical movement, a scissor linkage can change horizontal motion into up-and-down motion.
A controller and encoder provide feedback, so you can control position, speed, and force with high accuracy. This closed-loop system makes linear servo motors very precise.
Tip: Linear actuators often include guides or rails to keep the movement smooth and prevent wobbling.
Features
Linear servo motors stand out from other servo motor types because they create direct linear motion. They use extra gears or a rack and pinion mechanism to turn rotation into straight movement. You get several unique benefits:
| Feature | Details |
|---|---|
| Motion Type | Linear (forward and backward) |
| Mechanism | Lead screw, ball screw, belt drive, or rack and pinion |
| Feedback | Encoder for real-time position and speed control |
| Accuracy | Positioning accuracy up to ±5 micrometers over long distances |
| Load Capacity | Supports light to heavy loads, depending on design |
| Travel Distance | Can reach from under 1 meter to over 50 meters |
| Maintenance | Fewer wearing parts, so less maintenance needed |
You also get zero backlash, high rigidity, and fast acceleration. These features make linear servo motors ideal for tasks that need smooth, repeatable, and accurate movement.
Applications
You will find linear servo motors in many industries. They help automate material handling, move robotic arms, and control conveyor belts. In manufacturing, you see them in CNC machines, metal cutting, and forming equipment. They also power automatic doors, window openers, and solar panel trackers. Here are some common uses:
- Material handling systems for moving products safely and efficiently
- Robotics for the precise movement of arms and clamps
- Food and beverage processing and packaging
- Cutting and forming machines for metal and plastic
- Valve operation in industrial plants
- Solar tracking systems follow the sun
- Printing presses for accurate paper and print head movement
- Agricultural machinery for controlling sprayers and hatches
Linear servo motors offer high speed, accuracy, and reliability. You can use them in cleanrooms, medical devices, and aerospace systems where precision matters most.
Servo Motor Types Comparison
Key Differences
You can compare the three main servo motor types by looking at their motion, control, and best uses. The table below gives you a quick overview:
| Feature | Positional Rotation | Continuous Rotation | Linear |
|---|---|---|---|
| Motion | Rotates to set angles | Rotates endlessly | Moves in a straight line |
| Control | Precise angle control | Speed and direction control | Precise linear positioning |
| Feedback | Built-in position sensor | No position feedback | Encoder for position/speed |
| Typical Use | Robotic arms, steering | Wheels, conveyors, pumps | CNC machines, automation |
| Maintenance | Compact, low maintenance | Simple, less feedback | Fewer parts, low wear |
| Cost | Cost-effective | Varies | Higher, but less upkeep |
- Positional rotation servo motors give you accurate angular control, making them perfect for tasks like moving robot joints.
- Continuous rotation servo motors work best when you need ongoing spinning, such as driving wheels or conveyor belts.
- Linear servo motors turn rotary motion into straight-line movement, which is ideal for precise tasks in manufacturing or medical devices.
Note: You may also see servo motors grouped by their electrical supply: AC, DC, or brushless DC. AC servo motors often last longer and need less maintenance, while brushless DC types offer high efficiency and low wear. This article focuses on motion types, but knowing about these other categories can help you make a better choice.
Choosing the Right Type
When you pick a servo motor, you should match the type to your project’s needs. Here are some steps to help you decide:
- Define the Motion Needed: Decide if your project needs precise angle control, endless rotation, or straight-line movement.
- Check Performance Needs: Think about how much torque, speed, and accuracy you need. For heavy loads or high precision, linear servo motors may work best.
- Consider the Application: Look at where you will use the motor. For example, choose positional rotation for robotic arms, continuous rotation for wheels, and linear for CNC machines.
- Review Maintenance and Cost: Linear servo motors often need less upkeep because they have fewer moving parts. Positional rotation types are usually more affordable and compact.
- Think About the Environment: Make sure the motor can handle your operating conditions, such as temperature or dust.
If you feel unsure, Retek Motion can help you select the best servo motor types for your project. Their experts know how to match the right motor to your needs, whether you need precision, speed, or durability.
You have learned about positional rotation, continuous rotation, and linear servo motors. Each type offers unique motion and control features. When you select a servo motor, consider factors like inertia, speed, torque, and environmental conditions to ensure reliable performance. Proper installation and matching the motor to your application help prevent issues and extend the lifespan. For expert guidance and custom solutions, Retek Motion’s team can help you achieve the best results for your project.
FAQ
What is the main difference between positional and continuous rotation servo motors?
You control positional rotation servos by setting a specific angle. Continuous rotation servos let you control speed and direction for endless spinning. Choose positional for precise angles. Pick continuous for wheels or conveyors.
Can you use a linear servo motor for robotic arms?
Yes, you can use linear servo motors in robotic arms. They provide straight-line movement for tasks like lifting or pushing. This helps you achieve accurate and repeatable positioning in automation and manufacturing.
How do you control a servo motor with a microcontroller?
- Connect the servo’s signal wire to a PWM-capable pin.
- Send PWM signals to set position or speed.
- Use libraries like Arduino’s Servo library for easy programming.
Tip: Always check voltage and current ratings before connecting.
Which servo motor type is best for high-precision tasks?
You should choose a linear servo motor for high-precision tasks. Linear types offer excellent accuracy and repeatability. They work well in CNC machines, medical devices, and laboratory equipment.
Do servo motors need regular maintenance?
Most servo motors need little maintenance. You should keep them clean and check for loose connections. Linear servo motors often require even less upkeep because they have fewer moving parts.
