How Robot Frameless Torque Motors Power Humanoid Robots

You may have already seen short videos of humanoid robots—doing backflips in labs, carrying parts in car factories, or even having natural conversations with people. Behind these seemingly “human-like” actions lies a core enabler: the joint system. If algorithms are the robot’s brain and sensors are its senses, then the Robot Frameless Torque Motor is its muscle—determining how fast it can run, how heavy it can lift, and how stable it can walk. Today, we will start from several mainstream humanoid robot products to dissect where this “muscle” technology excels and how it supports an industrial transformation.

I. Why Are Humanoid Robots Inseparable from Robot Frameless Torque Motors?

Let’s get to know our protagonist. A frameless torque motor is a unique existence—it has no housing, no shaft, no bearings. By removing all “packaged” peripheral components, it retains only the stator and rotor core, which are directly embedded into the robot’s joint structure. The benefits are straightforward: smaller volume, higher torque. In a humanoid robot, large-torque joints such as the hip, knee, and shoulder demand extremely high power density and compactness; traditional motors often take up too much space, while a frameless torque motor can be integrated inside the joint to achieve a “motor-joint一体化” design, making the overall structure more compact and efficient.

Data also confirms its importance. Take Tesla Optimus as an example: every one of its 28 actuators uses a frameless torque motor, highlighting the core role of this product in joint actuation.

II. Mainstream Product Configuration Analysis: Different Joints, Different “Muscles”

If we compare motors to muscles, the requirements for different body parts vary greatly—large joints like shoulders and hips need explosive power, wrists and dexterous hands need precise control, and knees need to bear load while maintaining stability. Manufacturers, based on product positioning and cost considerations, have adopted different motor combination solutions.

Tesla Optimus: The “Full-Stack Configuration” of a Technical Benchmark

Tesla Optimus currently has the most complete and technically transparent actuator solution in the industry. Its joints are divided into three categories:

· Rotary actuators (14 units): Mainly used in large-angle rotational joints such as shoulders, hips, wrists, and waist. The solution is “frameless torque motor + harmonic reducer + torque sensor + dual encoders”, offering three torque specifications: 20Nm, 110Nm, 180Nm.

· Linear actuators (14 units): Distributed in joints with limited swing angle but requiring high thrust (e.g., elbows, knees, ankles). The solution is “frameless torque motor + planetary roller screw”, with thrust specifications of 500N, 3900N, and 8000N.

· Dexterous hand actuators (12 units / both hands): Uses a combination of hollow cup motor + miniature multi-stage planetary gearbox + worm gear. Each hand has 11 degrees of freedom and can lift a 9kg load.

Overall, Optimus uses the 180Nm high-torque actuator for heavy-load joints like the hip and shoulder, and medium/low torque solutions for moderate-load parts like the elbow and wrist, forming a reasonable “muscle gradient”. From a cost perspective, the frameless torque motor accounts for approximately 14.8% of the total robot cost, making it the second most critical component after the planetary roller screw.

Unitree H1/G1: High Cost-Performance “Self-Developed Faction”

Unitree’s approach is significantly different from Tesla’s—they prefer a quasi-direct drive architecture using high-torque-density motors + low-ratio planetary gears, which ensures power output while reducing cost.

H1 is positioned as an industrial-grade large humanoid robot, equipped with a self-developed M107 motor that can deliver a peak torque of 360N·m (hip joint 220N·m, ankle joint 45N·m), with a claimed power density 1.5 times that of competitors. Joint distribution: 14 lower-limb joints (torque ranging 45–220N·m), 14 upper-limb joints (torque ~75N·m), and 2 torso joints.

G1 targets home consumer scenarios: 1.32m tall, weighing 35kg. The standard version has 23 DOF, while the EDU version offers 23–43 DOF. Its lower leg joint uses a “motor + two-stage planetary reducer + encoder + driver” four-in-one integrated module, with a maximum knee joint torque of 90N·m and a maximum arm load of 2kg. Notably, Unitree has achieved a localization rate of over 90%, with motors, reducers, controllers, encoders, and other core components all self-developed, allowing the base version of the G1 to be priced as low as RMB 85,000.

Xiaomi CyberGear: The Miniaturized Integrated “Actuary”

Xiaomi’s CyberGear takes a completely different route—it packs a servo motor, harmonic reducer, dual encoders, and a driver into a tiny body weighing only 317 grams, achieving “small size, big integration”.

Technical parameters: the CyberGear motor has a maximum torque of only 3N·m but can respond as fast as 20 milliseconds. It is suitable for lightweight scenarios such as desktop robotic arms and small robot joints. The motor uses a black anodized aluminum housing for better heat dissipation, incorporates a self-developed temperature detection system and protection algorithms, and comes standard with an XT30 connector and quick-release design. It is sold on Xiaomi’s online store for only RMB 499, making it the “price gatekeeper” for entry-level robot joint modules.

Although its 3N·m maximum torque is far lower than that of Optimus and Unitree’s large-torque solutions, considering its weight of only 317 grams and its “quick-release + integrated” design, it is more than adequate for consumer scenarios (home small robots, educational robots). It follows a “good enough” strategy—enabling small and medium-sized manufacturers to also play in the robotics space.

Zhiyuan Robotics Expedition Series: Pursuing “Ultimate Burst Power”

The Zhiyuan Expedition series is particularly aggressive in motor performance. The Expedition A2 Max robot delivers a peak joint torque of 450N·m, currently one of the highest publicly available joint torque figures. Its self-developed PowerFlow motor adopts a quasi-direct drive technology route—somewhere between direct drive and traditional motors—delivering a peak torque exceeding 350N·m while weighing only 1.6kg, and it also incorporates a liquid cooling system, balancing force control sensitivity and continuous load capacity. Currently, Zhiyuan has launched an industrial base in Chengdu, and products such as the Expedition A3, A2, and Lingxi X2 have achieved mass production.

For intuitive comparison, the key parameters of the above mainstream models are summarized in the table below:

From the table above, it is clear that robot frameless torque motors have become almost standard in heavy-load scenarios such as the hip, knee, and shoulder joints, while more precise hollow cup motors are used at the end of the hands—the only differences lie in the combination of motor type and performance parameters. The direction is consistent.

III. The “Mapping” Between Motors and Complete Robots

So which upstream motor manufacturers are supporting these well-known humanoid robot products? As mass production ramps up, a number of domestic and international suppliers are deeply binding themselves to complete robot manufacturers, occupying key positions.

· Tesla’s supply chain: Inovance Technology holds a leading position in drive-control integrated joints, and Leadshine’s motion control products have also entered Tesla’s supply chain. In addition, Wolong Electric Drive’s frameless torque motors have successfully entered the supply chains of domestic mainstream robots such as Unitree and Zhiyuan, indirectly tying into Tesla, with a domestic market share of about 25%.

· Unitree is a player with an extremely high localization rate; its motors, drive boards, and motion control algorithms are largely self-developed. From a supply chain perspective, Leaderdrive’s harmonic reducers and Haozhi Electromechanical’s frameless torque motors, among others, supply Unitree.

· Xiaomi’s CyberGear motor does not rely on external motor suppliers, but teardowns reveal that it integrates ams OSRAM’s magnetic encoder and GigaDevice’s main control MCU. Meanwhile, Inovance Technology also supplies Xiaomi.

· Zhiyuan has a number of suppliers deeply tied to it. Wolong Electric Drive has not only entered Zhiyuan’s supply chain through an “industry + capital” dual binding but also indirectly holds shares in Zhiyuan. Other domestic leaders supplying servo systems and frameless torque motors include Inovance Technology, STEP Electric, and Veichi Electric.

Overall, the frameless torque motor field is witnessing an acceleration of localization. In the high-end market, international brands such as Kollmorgen and MOOG still occupy the technological high ground, but in terms of mass production, cost control, and customized services, domestic players like Inovance, Wolong, and STEP are rapidly rising.

IV. Higher-Level “Muscle” Requirements: Encoders and High-Precision Joints

Motors solve the problem of power output, but to achieve sufficiently accurate joint positioning, fine force feedback, and smooth motion control, another key component is required—the encoder.

The encoder acts as the robot’s “nervous system,” responsible for real-time feedback of position, speed, and angle information. In humanoid robots, the dual encoder solution has become mainstream: one encoder is installed on the motor side, the other on the output side, and the angular difference between them is compared to calibrate torque and position. In heavy-load joints (such as the hip and knee), the encoder determines how precisely the robot can control gait and force; in fine hand operations, encoder accuracy is a critical variable measured in millimeters.

V. SDM: An Emerging Star in Domestic Robot Frameless Torque Motors and Magnetic Encoders

Against the backdrop of accelerating localization, a company from Hangzhou—SDM—is gradually stepping into the core of the humanoid robot industry chain with its dual-wheel product matrix of “robot frameless torque motors + magnetic encoders”.

SDM’s differentiated advantages in frameless torque motors are mainly reflected in three aspects:

1. Fully self-developed motor design capability. SDM’s frameless torque motors support high-speed response and real-time torque closed-loop control, using aviation-grade alloy materials and high magnetic energy product magnets, significantly improving torque density and impact resistance. Targeting the differentiated needs of various robot joints (hip/knee/shoulder), SDM has launched multiple motor product lines with peak torque covering 50Nm to over 200Nm, flexibly adapting to applications ranging from light commercial service to industrial heavy load.

2. Core technology in magnetic encoders. SDM’s self-developed multi-turn absolute magnetic encoders and single-turn magnetic encoders match international mainstream solutions in accuracy, stability, and anti-interference capability. Using high-precision magnetoresistive sensors and multi-pole magnetic ring technology, SDM’s magnetic encoders achieve positional resolution better than 18 bits, while significantly optimizing anti-vibration and high/low temperature characteristics. This “motor + encoder” integrated capability allows complete robot manufacturers to achieve one-stop joint drive solution selection, greatly improving development efficiency and system integration.

3. Rooted in the “Hangzhou Six Little Dragons” industrial cluster. SDM is located in Hangzhou and the Yangtze River Delta region, which hosts China’s densest concentration of robot component resources, covering reducers, bearings, sensors, and other key parts. Benefiting from the continuous promotion of Zhejiang Province’s humanoid robot industry development policies, SDM is gradually extending from single-component supply to complete joint module solutions.

As humanoid robots move from the laboratory stage to the “mass production era”, the competition among upstream motor and encoder suppliers is upgrading from “cost-effectiveness” to a dual-track battle of “performance + reliability”. SDM, leveraging the advantages of its local Hangzhou industrial chain and its self-developed motor and magnetic encoder capabilities, is becoming an indispensable force in the “power source” of domestically produced humanoid robots.