Application Overview
Robotics is the fastest-growing segment of NdFeB demand outside automotive. A single humanoid robot contains 10–40 joint actuators, each built around a PMSM that depends on precision sintered NdFeB magnet rings for its torque density and smoothness. Collaborative robots, surgical robots, and industrial arms share the same fundamental requirements: maximum torque in minimum package, with smoothness demanded by direct human interaction. The magnet is the single most performance-critical passive component in every one of these motors.
Why NdFeB for Robotics
Robotics motors push torque density harder than almost any other commercial application. Only sintered NdFeB in SH-grade and above can deliver the required flux at the temperatures these motors reach under sustained load. Alternative materials cannot match the energy density, and their thermal behavior is incompatible with tight motor packaging.
Key Design Requirements
Torque smoothness
Cogging torque directly translates into joint control instability and vibration. Radial multi-pole sintered rings deliver 2–5% torque ripple versus 8–15% for segmented assemblies.
Temperature stability
Joint motor internal temperatures reach 100–130°C under sustained load. Minimum grade: N42SH; preferred for humanoid joints: N45SH or N48SH.
Dimensional precision
ID tolerance ±0.02mm; concentricity ≤0.02mm. Air-gap sensitivity is extreme.
Batch-to-batch consistency
Each robot contains many identical joint motors — surface flux variance across production must stay under 1% for controller predictability.
Coating durability
NiCuNi is standard; epoxy-over-NiCuNi for humidity-exposed designs; parylene for medical and surgical robotics.
Recommended NdFeB Grades for Robotics
Grade selection depends on the specific duty cycle, operating temperature, and torque requirements of your design. Below are the most common specifications used for robotics.
N42SH
150°C · Super High Temperature (SH)Workhorse SH-grade NdFeB for 150°C traction motors, robotics actuators, and high-duty servo drives.
N45SH
150°C · Super High Temperature (SH)High-flux SH-grade NdFeB for compact, high-torque motors operating continuously up to 150°C.
N48SH
150°C · Super High Temperature (SH)Premium SH-grade NdFeB — the gold-standard magnet for high-performance EV and robotics motor rotors.
N45UH
180°C · Ultra High Temperature (UH)Top-tier UH-grade NdFeB — rare production, reserved for the highest-performance traction and aerospace motors.
Typical Magnet Configurations
- •Radial multi-pole sintered rings — the standard for humanoid robot joint actuators
- •Coreless (hollow-cup) motor magnets for finger and wrist actuators
- •Laminated motor-magnet assemblies for high-RPM applications requiring eddy-current suppression
- •Segmented arc assemblies where manufacturability favors modular pole count
Typical dimensions: Radial multi-pole rings 30–150mm OD, 4–14 poles. Thin wall thickness 2–6mm is common. Concentricity better than 0.02mm.
Design & Procurement Considerations
- 01Specify radial multi-pole rings for any joint where torque smoothness affects control — do not default to cheaper segmented assemblies.
- 02Request 100% flux mapping with serial-number traceability, not batch-sampled data.
- 03GBD-processed SH grades are the correct answer for nearly every humanoid joint motor — the cost premium is typically offset by material savings.
- 04For surgical and medical robotics, parylene coating or full biocompatibility qualification may be required.
Further Reading
Related Article
From Spring Festival Gala to Factory Floor: Humanoid Robot Magnets
Frequently Asked Questions
What type of magnet is used in humanoid robot joint motors?
+
Humanoid robot joint motors overwhelmingly use radial multi-pole sintered NdFeB rings in N42SH to N48SH grades. The radial multi-pole architecture delivers a sinusoidal surface flux distribution that produces smooth, low-cogging torque — essential for the fluid motion required in human-interactive robotics. Leading platforms (Unitree, UBtech, Fourier, AgiBot) all use variations of this architecture.
What temperature rating do robotics motor magnets need?
+
Minimum 120°C (H grade), with 150°C (SH grade) recommended for any motor running under continuous load. Humanoid robot joints are particularly demanding — sustained walking, carrying, or balancing loads drives internal motor temperatures to 100–130°C. Specifying N42SH or higher provides the thermal margin needed for production reliability.
How tight should the tolerances be on robot motor magnet rings?
+
For humanoid robot and high-performance servo applications: ID tolerance ±0.02mm, OD tolerance ±0.05mm, concentricity ≤0.02mm, perpendicularity ≤0.03mm. Air-gap sensitivity means a 0.1mm variation in effective air gap can cause 5–10% torque output variation. 100% dimensional inspection on incoming batches is worthwhile for servo-grade assemblies.
Request a Quote for Robotics
Share your application, target dimensions, operating temperature, and annual volume. Our UK-based engineering team responds within 1 business day with grade recommendation, followed by pricing and lead time typically within 2 business days.