The Role of Motors in Humanoid Robots: Key Technologies and Applications

Coreless DC Motors

Coreless DC motors feature an ironless rotor design, providing high efficiency, high speed, long lifespan, and low friction. By eliminating eddy current and hysteresis losses, these motors in robotics operate more smoothly and offer superior heat dissipation.

Key Features:

Ironless Rotor: Utilizes a cup-shaped winding structure, eliminating eddy current and hysteresis losses, achieving over 80% efficiency.

High Speed and Low Inertia: Capable of speeds exceeding 10,000 rpm, responding 3-5 times faster than traditional motors.

High Power Density: Compact size (as small as 6mm in diameter) and lightweight design make them ideal for space-constrained applications.

Applications:

Dexterous Hands: Tesla's Optimus humanoid robot uses coreless motors used in humanoid robots in each finger joint, enabling precise grasping through coordinated multi-motor control. The thumb employs dual-motor drive for both bending and lateral movement, while the other four fingers each have an individual motor, allowing delicate handling of fragile objects like eggs.

Frameless Torque Motors

Frameless torque motors are compact, lightweight, and have low inertia, making them ideal for applications requiring high torque in constrained spaces. The rotor is directly mounted onto the robot's mechanical shaft, and the stator is integrated into the robot’s structure.

Key Features:

Compact Structure: Frameless design reduces motor volume by 40% and weight by 30%.

High Torque Output: Peak torque can reach up to 3,500 N·m, with harmonic reducers achieving reduction ratios over 1:1000.

High-Temperature Resistance: Uses high-temperature insulation materials, supporting continuous operation at temperatures up to 180°C.

Applications:

Rotary Actuators: Tesla's Optimus robot employs 14 frameless torque motors in its shoulders and wrists, paired with harmonic reducers to withstand extreme torques of 30 kg·m.

Servo Motors

Servo motors provide high-precision motion control, making them ideal for dynamic joints such as shoulders and elbows.

Applications:

Boston Dynamics Atlas: Utilizes 28 servo motors in conjunction with a hydraulic system, enabling complex maneuvers like backflips.

UBTECH Walker X: Features a hip humanoid robot servo motor with 80 N·m torque, enabling stable walking on uneven terrain.

Stepper Motors

Stepper motors are commonly used in low-load, low-dynamic applications.

Applications:

Head Rotation: Lightweight humanoid robots, such as the Pepper robot, use stepper motors for smooth horizontal head rotation.

Vision Module Adjustment: Employed in experimental camera gimbals for precise micro-adjustments.

BLDC motors offer high speed (10,000-20,000 rpm) and low maintenance requirements but have limited torque density (30-50 N·m/kg) and low-speed control precision.

Applications:

Wheeled Robots: Xiaomi CyberDog employs BLDC motors for wheel hub drives.

Auxiliary Power: Some humanoid robots use BLDC motors for waist rotation and arm swinging.

Linear Motors

Linear motors provide high-speed, high-acceleration motion capabilities but require precise guiding mechanisms and are costly.

Applications:

MIT Cheetah: Uses linear motors in its hind legs to achieve speeds of 30 km/h, with acceleration reaching 2.5 m/s² and a response delay of less than 1ms.

Axial flux motors feature a flux path parallel to the rotor axis, reducing rotor inertia by 50% while achieving a power density of up to 150 kW/kg.

Applications:

ETH Zurich: Developed biomimetic legs powered by axial flux motors with a torque density of 200 N·m/kg.

Agility Robotics Cassie: Uses axial flux motors for dynamic walking.

With the increasing demand for humanoid robots, domestic manufacturers are advancing humanoid robot motor technology to compete with global leaders.

Green Harmonic: Supplies harmonic reducers for Tesla’s Optimus, achieving 1 arc-minute precision and over 20,000 hours of lifespan.

Moons' Electric: Mass-produces 16mm coreless motors with torque density comparable to Maxon’s, widely adopted in medical robots.

Leadshine Technology: Developed third-generation frameless torque motors with encapsulation technology, achieving IP67-rated dust and water resistance.

Motor technology is a critical factor in the development of humanoid robots, directly influencing their agility, precision, and functionality. From high-speed coreless motors to high-torque frameless torque motors, each type serves a specialized role in achieving human-like motion. As technological advancements continue, domestic manufacturers are closing the gap with global competitors, pushing the boundaries of humanoid robotics further.