This paper explores the design, performance optimization, and application of coreless geared motors in the dexterous hands of humanoid robots.

Coreless geared motors, with their ultra-small size, high torque density, and rapid dynamic response, have become a core component for joint actuation in the dexterous hands of humanoid robots. This paper systematically analyzes their structural design principles, key performance parameters, and application advantages in medical surgical instruments and intelligent robots. Considering the technical challenges faced by domestic manufacturers in winding technology and planetary gearbox integration, optimization solutions and future development directions are proposed.

1. Introduction

With the rapid development of humanoid robots and minimally invasive medical devices, higher demands are placed on the size, efficiency, and control precision of drive motors. The 12mm coreless geared motor, as a representative of micro-drive systems, eliminates iron loss and reduces rotational inertia through its coreless rotor structure. Combined with a planetary gearbox to amplify torque, it has become an ideal choice for precision actuators such as dexterous hands and scalpels.

2.1 Coreless Geared Motor Structure and Working Principle

2.1 Coreless Rotor Design

The coreless motor adopts a coreless winding structure, with the coil wound in a cup shape and directly connected to the rotor shaft. Compared to traditional brushed motors, its advantages include:

- No cogging effect, resulting in low torque ripple;

- Low moment of inertia, with a mechanical time constant down to 3.86 ms;

- High efficiency, with energy utilization reaching 75%~90%.

2.2 Planetary Gear Integration

To meet the output torque requirements of dexterous hand joints (typically 5~20 mNm), 8mm, 10mm, 12mm, and 13mm coreless motors often integrate miniature planetary gearboxes, with reduction ratios ranging from 5 to 1500 and output speeds from 5 to 2000 rpm. The planetary gear structure features:

- Coaxial output, compact structure;

- High torque density, capable of amplifying output torque by more than 10 times;

- High transmission efficiency (>90%), suitable for frequent start-stop scenarios.

3. Key Performance Parameter Analysis

Taking the 12mm coreless motor from Shenzhen Kegu Technology Co., Ltd. as an example, its typical parameters are as follows:

- Rated Voltage: 12V;

- No-load Speed: 18,000rpm;

- Stall Torque: 11.5mNm;

- Torque Constant: 4.85mNm/A;

- Mechanical Time Constant: 3.86ms;

- Maximum Efficiency: 72%.

This motor can output 11.5mNm of torque at a stall current of 2.4A. With a planetary gearbox with a reduction ratio of 10:1, the output torque can reach 115mNm, sufficient to drive a dexterous hand to perform grasping and pinching actions with a single finger.

4. Application Scenarios and Advantages

4.1 Humanoid Robot Dexterous Hands

- High Degree of Freedom Drive: A single dexterous hand requires 6-12 motors. A 12mm hollow cup motor can be integrated into the finger joints to achieve complex movements such as extension, retraction, and flipping.

- Rapid Response: The mechanical time constant is 10,000 hours, far exceeding the 1,000-3,000 hours of brushed motors.

4.2 Medical Surgical Instruments

- Miniaturized Design: With a diameter of 12mm, it can be embedded in surgical instruments such as scalpels and endoscopes.

- High-Precision Control: With an encoder, it achieves 0.1°-level position control, meeting the needs of minimally invasive surgery.

5. Domestic Technology Challenges and Breakthrough Paths

5.1 Technological Barriers

- Winding Process: Hollow cup coils require high-precision winding. Overseas leaders use one-piece molding technology, while domestic manufacturers mostly rely on manual or winding processes, resulting in low yields.

- Planetary Gear Precision: Miniature planetary gears require μm-level machining precision, and domestic equipment is still struggling to achieve stable mass production. 5.2 Breakthrough Paths

- Automated Winding Equipment Development: Introducing a vision-guided winding system to improve coil consistency;

- Planetary Gear Material Optimization: Utilizing powder metallurgy or ceramic materials to improve wear resistance and transmission efficiency;

- Integrated Design: Integrating the motor, reducer, and encoder into a single package to reduce assembly errors.

6. Conclusions and Outlook

The 12mm coreless geared motor, with its high power density, fast response, and long lifespan, has become a core component in the precision drive field. In the future, with breakthroughs in domestic winding technology and planetary gear processing technology, its cost will decrease significantly, driving its widespread application in consumer electronics, smart homes, and other fields. Simultaneously, combined with AI control algorithms, more intelligent torque and position control can be achieved, further expanding its application boundaries in humanoid robots and medical equipment.