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Why Are Frameless Motors Used in Humanoid Robots?

Created on Today, Published on Today
Humanoid robots are becoming an important development direction in robotics.
Unlike conventional industrial robots, humanoid robots are designed to operate in environments built for humans. Their mechanical structures often include multiple joints, compact transmission systems, and complex motion-control requirements.
Every joint needs an appropriate drive solution.
Frameless motors have attracted attention in humanoid robotics because their structural design allows engineers to integrate motor components directly into robotic joints.
But why are frameless motors suitable for these applications?
Let's explore their main characteristics and design considerations.

1. Compact Mechanical Integration

Humanoid robots have limited installation space, especially around their shoulders, elbows, wrists, hips, and knees.
Traditional motors with complete housings may create additional mechanical constraints.
Frameless motors consist of separate stator and rotor assemblies, allowing engineers to integrate these components into their own mechanical structures.
This provides greater flexibility when designing compact robotic joints.

2. High Torque Density Requirements

Robotic joints need to generate sufficient torque while maintaining a compact mechanical structure.
This is particularly important for humanoid robots, where weight and available space influence overall system design.
Torque density is therefore an important consideration when evaluating motor solutions.
Engineers should compare motor torque capabilities with installation dimensions, cooling conditions, and operating requirements.
Actual performance must be verified against the selected motor's technical specifications.

3. Flexible Joint Design

Different joints have different mechanical requirements.
For example:
Robot Joint
Main Design Considerations
Shoulder
Load capacity and motion range
Elbow
Compactness and dynamic response
Wrist
Small installation space and precision
Hip
High torque and structural integration
Knee
Load characteristics and thermal management
A single motor configuration may not be suitable for every joint.
Customized motor dimensions and torque characteristics can help engineers adapt the motor to different mechanical designs.

4. Compatibility with Different Transmission Systems

Frameless motors can be integrated into different mechanical architectures.
Depending on the joint design, engineers may consider:
  • Direct-drive configurations
  • Harmonic drive systems
  • Planetary gearbox systems
  • Other customized transmission structures
The appropriate solution depends on the required torque, speed, precision, backlash, efficiency, and installation space.
The motor and transmission should be evaluated as a complete system.

5. Important Factors When Choosing Motors for Humanoid Robots

Before selecting a frameless motor for a humanoid robot, engineers should evaluate several parameters.
Torque Requirements
Determine continuous torque and peak torque based on the joint's load and motion cycle.
Operating Speed
Consider the required speed range and acceleration characteristics.
Mechanical Dimensions
Evaluate outer diameter, inner diameter, axial length, and mounting structure.
Thermal Management
Assess heat dissipation under the expected operating conditions.
Control Compatibility
Check encoder requirements, servo drive compatibility, and feedback interfaces.
These parameters help establish a practical motor specification.

6. The Importance of Motor Customization

Humanoid robot development often involves continuous mechanical optimization.
Standard motor dimensions may not always match the requirements of a specific robotic joint.
Customization can help address requirements such as:
  • Specific outer and inner diameters
  • Different axial lengths
  • Different torque requirements
  • Customized mechanical integration dimensions
At Frameless Motors (Suzhou), we focus on customized frameless torque motors and high-precision geared motors.
We support flexible customization according to project requirements and accept orders without a minimum order quantity.

Frequently Asked Questions

Q1: Why do humanoid robots use frameless motors?
Frameless motors allow motor components to be integrated directly into robotic structures, providing mechanical design flexibility for compact joints.
Q2: Can one frameless motor be used for all humanoid robot joints?
Not necessarily. Different joints have different torque, speed, size, and operating requirements. Motor configurations should be selected individually.
Q3: Can frameless motors work with harmonic gearboxes?
They can be integrated into joint designs using harmonic transmission systems, provided that the motor and gearbox specifications are compatible.
Q4: What information is needed to customize a robotic joint motor?
Engineers should provide application details, torque, speed, installation dimensions, voltage, thermal conditions, and available mechanical drawings.

Conclusion

Frameless motors offer mechanical integration flexibility that makes them relevant to humanoid robot joint design.
However, successful motor selection requires a complete understanding of torque, speed, dimensions, thermal conditions, transmission systems, and control requirements.
As humanoid robotics continues to develop, customized motor solutions will remain an important consideration for robotic system designers.

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Developing a Humanoid Robot or Robotic Joint?
Looking for a customized frameless torque motor for your next robotics project?
Frameless Motors (Suzhou) provides customized frameless motor solutions with flexible dimensions and torque requirements, without a minimum order quantity.
Contact our team and share your motor drawings or technical specifications. Let's discuss your project requirements.
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