Robot Joint Module Solutions for Humanoid Robot Arms and Legs

The application of robotic arms is expanding rapidly across a wide range of industries. A robotic upper body can form part of a complete humanoid robot, or it can be combined with a fixed robotic arm and mobile base, or a robotic arm with a dexterous hand, to perform tasks such as picking and placing components, screw fastening, connector insertion and removal, switch operation, box handling, power tool operation, vision-guided picking, warehouse picking, automotive assembly, 3C electronics assembly, laboratory operations, and medical assistance.

At the heart of these applications are robot joint modules, which play a critical role in delivering the required motion, torque, precision, and responsiveness.

Smaller joints generally prioritize low weight and fast response, while larger joints require higher torque density and reliability. A good joint solution is not simply a matter of scaling the same module up or down. Instead, each joint should be precisely matched to its specific load, range of motion, and control requirements.

HONPINE's robot joint modules include four harmonic joint module series — HPJM, TCHL, HAU, and HAG — as well as planetary joint module series HPA and JRM.

In this article, we use the HONPINE HPJM series as an example to present a robot joint module solution for humanoid robot upper and lower limbs.

Humanoid Robot Upper Limb Joint Solution: Torque-Graded Configuration for the Shoulder, Elbow, and Wrist

Wrist and Fingers: 3–10 Nm

The wrist and finger joints are among the smallest joints in a humanoid robot. They require extremely low weight and fast response to achieve agile movements.

The HONPINE HPJM-RE30-40 series provides a peak torque of 3.3–4.8 Nm with a weight of only 0.19 kg, making it well suited for wrists, fingers, and other distal joints.

With a 24–48 V wide voltage range, CAN communication, and a highly integrated design, the module provides a compact solution for lightweight humanoid robot joints.

Elbow: 20–50 Nm

The elbow joint needs to support the load of the forearm and hand while providing sufficient range of motion.

The HONPINE HPJM-RE50-60 series provides up to 34 Nm peak torque with a weight of 0.45 kg. Reduction ratios of 51, 81, and 101 are available, making it a practical choice for humanoid robot elbow joints.

For applications requiring higher torque, the HPJM-RE60-70 series provides up to 66 Nm peak torque, supporting higher payload requirements.

Shoulder: 50–150 Nm

The shoulder is one of the largest joints in the upper limb. It needs to support the weight of the entire arm while providing a wide range of motion.

The HONPINE HPJM-RE70-80 series provides 69–108 Nm peak torque, while the HPJM-RE80-97 series delivers up to 217 Nm peak torque, covering a wide range of shoulder joint requirements from lightweight to higher-load applications.

The dual-encoder version supports both CAN and EtherCAT, enabling more precise synchronization and coordinated control across multiple robot joints.

Lightweight Design for Humanoid Robot Upper Limbs

A common priority across humanoid robot upper-limb joints is weight reduction.

Compared with the standard PRO series in the same size class, the HONPINE HPJM-REPRO-S series is approximately 15%–30% lighter. This can be particularly valuable for humanoid robots where controlling the overall system weight is critical.

Humanoid Robot Lower Limb Joint Solution: Balancing High Load and Lightweight Design

Lower-limb joints face significantly higher load and impact requirements than many upper-limb joints. The key challenge is to balance torque capacity, structural strength, responsiveness, and weight.

Ankle: 30–80 Nm

The ankle joint plays a critical role in maintaining balance and requires fast response combined with adequate torque capacity.

The HONPINE HPJM-RE50-70 and HPJM-RE60-70 series can be used for ankle applications, providing 34–66 Nm peak torque with weights of approximately 0.6–0.8 kg.

This provides a balance between response speed and load capacity for humanoid robot ankle joints.

Knee: 80–200 Nm

The knee joint experiences significant impact loads during walking, squatting, and other dynamic movements. It therefore requires high torque capacity and reliable operation.

The HONPINE HPJM-RE80-97 series provides 121–217 Nm peak torque, while the HPJM-RE80-110 series provides up to 217 Nm peak torque, making these series suitable for a range of humanoid robot knee applications.

The large hollow design, with a 27 mm through-hole, facilitates internal cable routing and the passage of pneumatic or hydraulic lines.

Hip: 150–800 Nm

The hip is one of the largest and most heavily loaded joints in a humanoid robot. It needs to support the robot's overall body weight while enabling multi-axis movement.

The HONPINE HPJM-RE100-120 series provides 267–459 Nm peak torque, while the HPJM-RE110-145 series delivers up to 491–800 Nm peak torque, providing high-torque options for heavy-duty hip joint applications.

The product is rated for more than 10,000 hours of service life while maintaining accuracy under specified continuous torque conditions, supporting long-term operating reliability.

Why Integrated Harmonic Joint Modules Matter for Humanoid Robots?

For humanoid robot lower limbs, one of the key engineering challenges is achieving the right balance between high load capacity and lightweight construction.

The HONPINE HPJM series combines a harmonic reducer with a frameless torque motor, providing high torque density in a compact package. A cross-roller bearing provides high axial and radial load capacity while offering strong resistance to impact loads.

This integrated architecture combines the major components required for a robot joint into a compact module, helping reduce the complexity and overall weight of the joint assembly.

Robot Joint Modules and the Working Envelope of Humanoid Robot Arms

The most basic function of a robot arm is to reach outward. However, the real challenge is whether the arm can cover a sufficiently large workspace, reach targets with the appropriate posture, and coordinate effectively with the robot's vision system, torso, and lower limbs.

The upper limb acts as a distal cantilever and therefore creates a long-lever-arm load. On a humanoid robot, the weight of the arm itself can generate significant overturning moments on the hip, waist, and lower limbs.

An integrated robot joint module can help reduce the weight and complexity of each joint while maintaining the torque, control, and motion performance required for the application. This enables more compact and responsive humanoid robot arms while supporting coordinated full-body motion.

Contact HONPINE to learn more about our robot joint modules and discuss a suitable joint solution for your humanoid robot application.