Joint Motors: Powering the "Muscle Revolution" of Humanoid Robots

If we compare a humanoid robot to an athlete, joint motors are its powerful and dynamic “muscle system.” While AI algorithms and advanced sensors often get the spotlight, it is the actuators—the joint motors embedded in each limb—that truly bring robots to life with fluid and purposeful movement.

Over the past decade, AI and perception technologies have advanced rapidly. However, without robust, responsive, and flexible actuators, humanoid robots cannot transition from lab demonstrations to real-world applications. Today, breakthroughs in joint motor technology are helping robots cross the final threshold from "mechanical motion" to "biological agility."

Let’s take a look at how key players are designing their robotic “muscles”:

Tesla Optimus: Equipped with 28 joint motors, focusing on industrial-grade stability and cost-efficiency to build a versatile labor force.

Unitree H1: Features 19 lightweight joints, optimized for service and household use, with fast response and high durability.

Xiaomi CyberOne: Focused on mass production and cost control, with ongoing improvements in motor integration and lightweight structure.

Boston Dynamics Atlas: Combines electric and hydraulic drives, delivering exceptional dynamic performance across complex terrains.

These robots reflect different design philosophies—some prioritize strength, others focus on flexibility and cost. At the heart of them all lies the critical role of joint motors.

Frameless Torque Motors: The Hidden Powerhouse

Frameless torque motors eliminate the traditional housing and are directly integrated into the robot's joints.

Advantages: High torque density, rapid response, compact design, and high efficiency

Challenges: Complex heat dissipation, higher manufacturing cost

Applications: Tesla Optimus, Boston Dynamics Atlas

Coreless DC Motors: Ideal for Dexterous Hands

Coreless (or ironless) DC motors are lightweight, compact, and offer fast response times, making them suitable for delicate joints such as robotic fingers and wrists.

Notable Brands: Maxon, Faulhaber, Panasonic

Trend: These motors are gradually being replaced by domestic alternatives in China due to cost and supply chain advantages

Gearbox + Encoder + Controller: The Closed-Loop Trio

Accurate joint control depends on the seamless integration of:

Harmonic Drive Gearboxes (e.g., from Green Harmonic or Double-Ring): Provide high precision and gear reduction

Magnetic Encoders (e.g., Tamagawa, Inovance): Offer precise position feedback

Integrated Motor Controllers (e.g., from UBTECH, Fourier): Combine motion control, power management, and communication interfaces

The future is moving toward standardized “motor kits” that simplify wiring and assembly across robot platforms.

Global Landscape: China's Rapid Rise

The humanoid robot market is seeing intense global competition, with each company taking a unique approach to joint motor systems:

Company

Technical Approach

Tesla    In-house frameless motors with force sensing    General-purpose industrial use    

Boston Dynamics    Electric + hydraulic hybrid drive    High-performance, extreme environments    

Apptronik (Apollo)    Commercial motor modules    Mass production-ready humanoids    

Agility Robotics    Redundant control + energy efficiency    Warehouse logistics    

Xiaomi, Unitree    Domestic sourcing + integrated design    Consumer and service markets    

Although Chinese companies entered the market later, they are rapidly catching up in cost optimization, system integration, and production efficiency. They are also making strides in core component development, such as precision motors and gearboxes.

1. Full-Stack In-House Development

Like Apple's approach to chip design, robot makers are increasingly treating motor development as a strategic core competency. Controlling the actuator stack means controlling the future of the robot ecosystem.

2. Intelligent Motor Control

By embedding AI into motor control systems, next-gen motors will adapt in real time—learning optimal output strategies based on environmental feedback and task demands.

3. Modular and Platform-Based Ecosystems

Joint motors, gearboxes, drivers, and power units will be modularized into standardized "muscle blocks," enabling faster development and easier integration across different robot types.

4. Thermal Management and Power Efficiency

As robots are expected to operate for extended durations, improved thermal management and energy efficiency will be essential to ensuring long-term performance and reliability.

5. The Golden Window for Domestic Substitution

Chinese companies such as Qinchuan Machine Tool, Aochi Motor, Green Harmonic, and Hiconics are accelerating R&D in core parts like motors, gearboxes, and encoders, breaking foreign monopolies and capturing global market share.

Modular Motor Platforms: All-in-one motor modules could become the “chips” of the robot industry, offering scalable platform value.

Domestic Substitution of Core Components: High-precision components like gearboxes and encoders present strong growth potential and high profit margins for local suppliers.

AI + Motion Control Integrators: Companies mastering both software algorithms and hardware systems could become the “Huawei” of the robotics era.

Conclusion: Master the Muscles, Shape the Future

Joint motors are the key to unlocking lifelike movement in humanoid robots. In the coming decade, whoever gains mastery over intelligent actuators will likely lead the next industrial revolution driven by robotics.