What is a Frameless Torque Motor? Core Advantages in Robot Joint Design

With the rapid development of artificial intelligence, intelligent manufacturing, and robotics technology, robots are gradually evolving from traditional industrial automation equipment towards more intelligent, flexible, and human-collaborative systems. From industrial manipulators to collaborative robots, and more recently to the rapidly developing humanoid robots, quadruped robots, and intelligent service robots, the performance requirements for robot motion are continuously increasing.

As the core component for robot motion control, the joint system directly determines the robot's flexibility, precision, load capacity, and overall performance. A high-performance robot joint not only requires powerful power output but also needs to meet multiple demands such as miniaturization, lightweight construction, high response speed, and precise control. However, traditional servo motors, due to their complete motor structure, are gradually struggling to meet the demands of advanced robot development in terms of space occupation, integration complexity, and torque density.

Against this backdrop, the Frameless Torque Motor has gradually become a key technological solution in the field of robot joints, owing to its unique structural design and excellent performance. Unlike traditional motors, the frameless torque motor removes non-core components such as the external housing and bearings, retaining only the high-performance stator and rotor assemblies. This allows it to be directly integrated into the robot joint's internal structure, achieving a more compact and efficient power output.

Currently, frameless torque motors are widely used in high-end robotics, precision automation equipment, and intelligent machinery. They not only help robots achieve motion capabilities closer to human joints but also enhance system reliability and control precision, providing key technical support for the development of next-generation intelligent robots.

What is a Frameless Torque Motor?

A frameless torque motor is a high-performance motor that removes the traditional motor housing, bearings, and standard mechanical structure, retaining only the core electromagnetic components.

Simply put, it consists of two main parts:

• Stator: Contains the winding structure used to generate a rotating magnetic field.
• Rotor: Typically uses high-performance permanent magnet materials to output rotational torque through magnetic field interaction.

Unlike standard servo motors, a frameless torque motor is not used as a complete motor product on its own. Instead, it serves as the power core within the robot joint, highly integrated with the reducer, encoder, driver, and mechanical structure.

The term "frameless" refers to:

Removing the traditional external motor frame and embedding the motor's core components directly into the equipment's structure.

This design approach significantly reduces mechanical redundancy, allowing the robot joint to achieve a more compact and lightweight structure.

Working Principle of Frameless Torque Motors

The working principle of a frameless torque motor is similar to that of a standard permanent magnet synchronous motor, operating through electromagnetic conversion to produce rotational motion.

When three-phase AC current is supplied to the stator windings, a rotating magnetic field is generated. This field interacts with the permanent magnets of the rotor, producing electromagnetic torque that causes the rotor to rotate.

The robot control system achieves precise joint motion through:

• Encoders for position detection.
• Drivers for current adjustment.
• Control algorithms for optimizing motion trajectories.

For robotic applications, the motor output is not just about speed, but more importantly:

• Precise position control.
• Stable torque output.
• Fast response capability.

Therefore, frameless torque motors are naturally suited for high-precision motion control scenarios.

Differences Between Frameless Torque Motors and Traditional Servo Motors

To better understand the advantages of frameless torque motors, a comparison with traditional servo motors is helpful.

Comparison Item	Frameless Torque Motor	Traditional Servo Motor
Structure	Core component form	Complete motor structure
Integration	Flexible embedding into equipment	Independent installation
Size	More compact	Relatively larger
Torque Density	High	Average
Customization	Strong	Weaker
Suitable Fields	Robot joints, precision equipment	Automation equipment, machine tools

For robots, the internal space within a joint is limited and needs to accommodate:

• Motor.
• Reducer.
• Encoder.
• Controller.
• Braking mechanism.

Therefore, the smaller size and higher performance of the frameless torque motor make it an ideal choice.

Core Advantages of Frameless Torque Motors in Robot Joint Design

1. High Torque Density, Enabling Robot Lightweighting

Robots, especially humanoid robots, are highly sensitive to weight.

Lighter joints mean:

• Lower energy consumption.
• Higher movement speed.
• Better dynamic performance.
• Longer endurance.

Frameless torque motors use a compact design to deliver high torque in a small form factor.

Compared to traditional motors, the advantages are mainly:

• Reducing the weight of the motor housing.
• Increasing output capability per unit volume.
• Optimizing the overall robot structure.

This allows robots to achieve motion capabilities closer to human joints.

2. High Precision Control, Improving Robot Motion Performance

Robot joints must perform numerous complex actions, such as:

• Precision assembly.
• Dexterous grasping.
• Walking balance.
• Human-robot collaboration.

These applications require the motor to have extremely high position control accuracy.

Frameless torque motors typically feature:

• Low cogging torque.
• Low torque ripple.
• High response speed.

This reduces motion errors, making robot movements:

• Smoother.
• More stable.
• More precise.

3. Highly Integrated Structure, Reducing Robot Joint Complexity

Traditional robot joints often use a multi-stage combined structure like:

Motor + Coupling + Housing + Connectors.

In contrast, the frameless torque motor can be installed directly inside the joint, forming an integrated design with the reduction mechanism.

This approach offers significant advantages:

Reduces the number of components.

Lowers mechanical assembly difficulty.

Improves reliability.

Reduces failure risks from connecting parts.

Saves space.

Makes the joint structure more compact.

Therefore, many high-end robot joints now adopt the combined solution of "Frameless Motor + Precision Reducer + Encoder".

4. Large Hollow Structure, Facilitating Internal Robot Wiring

Robot joints typically require routing for:

• Power cables.
• Signal lines.
• Sensor wiring.

Frameless torque motors can be designed with a hollow structure, allowing cables to pass through the center.

This feature is particularly important for:

• Manipulator joints.
• Collaborative robots.
• Humanoid robots.

It reduces external cable exposure, improving the robot's overall aesthetics and reliability.

5. Fast Response, Enhancing Dynamic Motion Capability

When robots execute actions, they need to quickly complete the process of:

Start → Accelerate → Stop → Adjust.

Frameless torque motors possess:

• Low rotational inertia.
• Fast electromagnetic response.
• High control bandwidth.

This allows them to respond rapidly to control commands.

For high-speed motion robots, such as:

• Robotic arms.
• Quadruped robots.
• Humanoid robots.

Fast response capability directly impacts motion performance.

Typical Applications of Frameless Torque Motors in Robotics

1. Humanoid Robot Joints

In recent years, the rapid development of humanoid robots has placed demands on joints for:

• High burst power.
• High precision.
• Miniaturization.

Frameless torque motors can be installed in:

• Shoulders.
• Elbows.
• Legs.
• Hip joints.

This helps robots achieve human-like motion.

2. Collaborative Robots

Collaborative robots need to work alongside humans, thus placing greater emphasis on:

• Safety.
• Compliant control.
• Precise operation.

Frameless torque motors combined with force control technology enable more natural human-robot interaction.

3. Industrial Manipulators

Industrial manipulators require long-term, stable operation.

Frameless torque motors can provide:

• High repeat positioning accuracy.
• Stable torque output.
• Long operational life.

They are widely used in:

• Precision assembly.
• Semiconductor manufacturing.
• Automated production lines.

4. Medical Robots

Medical robots require extremely high precision, for example:

• Surgical robots.
• Rehabilitation robots.
• Exoskeleton devices.

The miniaturization and high precision of frameless torque motors make them suitable for medical equipment.

Development Trends of Frameless Torque Motors in Robot Joints

As robotics technology continues to advance, the future of frameless torque motors will move towards:

1. Higher Power Density

By optimizing:

• Magnetic circuit design.
• Material properties.
• Heat dissipation structures.

Further enhancing output capability.

2. More Intelligent Control

Future motors will integrate:

• AI algorithms.
• Smart sensing.
• Real-time control systems.

To achieve more precise motion control.

3. Higher Integration

Future robot joints may form highly integrated modules combining:

Motor + Reducer + Encoder + Driver.

This will reduce robot manufacturing difficulty and accelerate the large-scale development of the robotics industry.

 

How to Choose a Frameless Torque Motor for Robot Joints?

 

In practical applications, the following key parameters need to be considered:

1. Rated Torque

Determines the motion capability the robot joint can handle.

2. Peak Torque

Affects the robot's instantaneous burst capability.

3. Motor Dimensions

Must match the robot joint's available space.

4. Torque Ripple

Affects motion smoothness.

5. Thermal Management Capability

Determines long-term operational stability.

6. Encoder Matching

Affects the final control precision.

Different robot types require selecting appropriate specifications based on load, speed, and control requirements.

 

Conclusion

 

As the robotics industry continues to move towards intelligence, precision, and miniaturization, the demands on joint power systems are increasing. While traditional motor solutions are technologically mature, they are gradually failing to meet the needs of next-generation robots in terms of space utilization, structural integration, and dynamic response capability. The frameless torque motor, with its compact structural design, high torque density, and excellent control performance, offers a more advanced power solution for robot joints.

Compared to traditional servo motors, the greatest advantage of the frameless torque motor lies in its ability to integrate the motor's core components directly into the robot joint structure, achieving high integration of the motor, reducer, encoder, and control system. This design not only effectively reduces joint volume and overall weight but also enhances the robot's motion flexibility, response speed, and control precision, enabling robots to perform more complex, precise, and naturally human-like movements.

In practical applications, the frameless torque motor has become a key technological choice for high-end equipment such as humanoid robots, collaborative robots, industrial manipulators, and medical robots. Its features of high-precision control, fast dynamic response, and stable torque output help robots adapt to various scenarios like precision manufacturing, human-robot collaboration, and intelligent assembly. Especially in the current context of rapid humanoid robot development, lightweight, high-performance, and highly reliable joint drive solutions will become a crucial direction for future robotics technology competition.

Looking ahead, with continuous advancements in motor materials, electromagnetic design, intelligent control algorithms, and manufacturing processes, the performance of frameless torque motors will further improve. Motor products with higher power density, lower energy consumption, and stronger integration capabilities will drive robot joints towards modularization, intelligence, and high efficiency, accelerating the transition of robots from R&D experimentation to broader commercial applications.

Overall, the frameless torque motor is not only an advanced motor technology but also a crucial foundation for achieving performance breakthroughs in robot joints. By optimizing power structures, enhancing motion control capabilities, and improving system integration, the frameless torque motor is providing a more reliable, efficient, and precise core driving force for next-generation intelligent robots. As the robotics industry continues to upgrade, the frameless torque motor will play an increasingly important role in future intelligent manufacturing, humanoid robotics, and automation equipment.