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Humanoid robots, also known as anthropomorphic robots, possess human-like perception, decision-making, behavior, and interaction capabilities. They have human-like appearances, sensory systems, intelligent thinking methods, control systems, and decision-making abilities, ultimately exhibiting "human-like behavior."

• Humanoid robots involve engineering and control science, integrating research achievements from fields such as electronics, mechanics, automation control, and computer science. They cannot simply achieve humanoid functions by purchasing and assembling components.
• Humanoid robots are classified by height into large humanoid robots and medium-small humanoid robots.

Research on humanoid robots began in Japan and has now entered a high dynamic motion development stage. Reviewing the development history of humanoid robots, there are three significant milestones:

• First stage: The early development stage represented by the humanoid robots from Waseda University.
• Second stage: The system integration development stage represented by Honda's humanoid robots.
• Third stage: The high dynamic motion development stage represented by Boston Dynamics' humanoid robots.

Japan was the first to initiate research on humanoid robots, achieving bipedal walking.

• In 1971, Professor Kato from Waseda University introduced the hydraulic system-based bipedal robots WL-3 and WL-5, achieving a walking stride of 15 cm and a cycle of 45 seconds for static walking.
• The subsequently designed motor-driven WL-9R and WL-10DR achieved dynamic walking through ankle joint torque control, shortening the single-step cycle to 1.3 seconds.
• In 2006, Ichiro Kato's student, Professor Takashi Nishikawa, introduced the humanoid robot WABIAN-2R (with 41 degrees of freedom), achieving a walking speed of 1.8 km/h and adapting to various ground surfaces.

HONDA's Asimo represented the most advanced technology level at the time.

• In 1996, Japan's HONDA developed the first humanoid robot P1, followed by P2, which could walk on ordinary surfaces, and subsequently P3.
• On November 12, 2000, the most representative motor-controlled bipedal robot Asimo was released, standing 120 cm tall, weighing 52 kg, and walking at speeds of 0 to 1.6 km/h.
• The third-generation ASIMO robot was released in 2011, with a walking speed of up to 9 km/h, capable of climbing stairs, kicking a soccer ball with one leg, and jumping on one leg, with a walking stride that can be continuously adjusted, achieving 57 degrees of freedom, making it suitable for fixed environment service robot applications.

Cassie embodies a new drive design, enriching the drive technology route.

• In 1997, researchers including Grizzle from the University of Michigan developed the underactuated bipedal robot RABBIT, which can achieve dynamic walking without feet.
• Based on RABBIT, a series of underactuated walking robots, including MEBAL, MARLO, and ATRIAS, were developed, achieving three-dimensional underactuated walking.
• In 2017, the robot Cassie was released, priced at about $70,000, with its drive motors positioned high, incorporating springs in the legs to achieve efficient gait while being able to stand still.
• In 2022, Digit was launched based on Cassie, featuring robust walking and running gaits, capable of climbing stairs and autonomous navigation, suitable for package handling.

Sources: CNKI, Zhejiang University, 1997, Grizzle et al. from the University of Michigan developed the underactuated bipedal robot RABBIT.

The HRP series robots can achieve stable walking and collaborate with humans.

• In 1998, the National Institute of Advanced Industrial Science and Technology in Japan began leading the HRP series project, aimed at developing a humanoid robot system that can coordinate and coexist with humans in work and living environments, capable of completing complex tasks.
• HRP-2 and HRP-3 can walk stably and perform various dexterous movements (such as Japanese dance), collaborate with humans to lift objects, overcome obstacles, pick up objects from the ground, protect themselves when falling, and stand up again.

Sources: Company website, Zhejiang University, CITIC Construction Investment, Japan's National Institute of Advanced Industrial Science and Technology launched the HRP system bipedal robot.
Atlas uses a self-designed hydraulic drive system, with the world's leading motion capabilities.

• Boston Dynamics developed the hydraulic-driven quadrupedal robot BigDog under the funding of the Defense Advanced Research Projects Agency (DARPA).
• In October 2009, Boston Dynamics released PETMAN, a military device designed for U.S. experimental protective clothing, featuring strong self-balancing capabilities and motion performance, able to adjust its gait in response to external environmental disturbances and maintain balance.
• Since its release in 2013, Atlas has undergone three major iterations, with its all-terrain adaptability representing the highest level currently available.

IIT launched WALK-MAN, influential in Europe.

• IIT launched the WALK-MAN firefighting robot, incorporating force control to form torque-controlled hand joints, but sacrificing some rigidity of the robot.
• In 2008, IIT manufactured the open-source humanoid robot iCub for research on perceptual learning and human-robot interaction, featuring excellent human-robot interaction capabilities. It is designed to resemble a three-and-a-half-year-old child, standing 1 meter tall, with 53 degrees of freedom, capable of walking and balancing on one leg.
• In 2012, the bipedal robot COMAN was developed, with all joints in the forward plane using SEA drives.

Swiss research institutions utilize passive flexibility to further enhance jumping and terrain adaptability.

• In 2011, the Robotics and Intelligent Systems Laboratory at ETH Zurich developed the single-leg robot ScarlETH based on SEA joints, utilizing the robot's passive flexibility to achieve high-energy-efficient jumping and terrain adaptability.
• Based on this, a motor-driven quadrupedal robot StarlETH and ANYmal were developed.

HUBO won first place in the DRC competition, promoting research and development in Asia.

• The bipedal robot HUBO from the Korea Advanced Institute of Science and Technology (KAIST) won first place in the 2015 DRC competition with its hybrid movement method of wheels and feet.
• With the help of Rainbow Robotics, HUBO2 became the world's first commercial humanoid robot platform. It was purchased by leading research institutions worldwide (such as MIT and Google) as a research platform.
• The "HUBO2" robot can walk at a speed of 1.4 km/h with straight knees and run at a speed of 3.6 km/h.

HUBO won first place in the DRC competition in 2015 with its hybrid movement method of wheels and feet.

The University of Tokyo launched a new version of Schaft, reducing costs and energy consumption.

• In 2013, the humanoid robot team Schaft, acquired by Google, won the championship at DRC 2013, standing 1480 mm tall and weighing 95 kg, with functions such as walking and climbing stairs.
• In 2016, a new low-cost, low-energy humanoid robot was released, capable of carrying 66 kg.
  The development of small humanoid robots is in full swing, enriching and expanding application scenarios.
• France's Aldebaran Robotics launched the NAO typical robot, with sales exceeding 10,000 units. The company has consistently pursued a commercialization path, significantly differing from Boston Dynamics and Asimo, and was later acquired by Japan's SoftBank. Subsequently, Pepper and Romeo robots were launched.
• Among small bipedal robots under 50 cm in height, the Darwin-OP robot from South Korea's Robotis company is quite famous for its stable walking and color recognition capabilities.
• South Korea's Hitec company launched Robonova-1, and the domestic company Leju (Shenzhen) Robotics launched the "Aleos" robot.

Domestic research on humanoid robots started relatively late, mainly led by universities and research institutions.

• Tsinghua University, Zhejiang University, Shanghai Jiao Tong University, Beijing Institute of Technology, and the Chinese Academy of Sciences have successively conducted research on humanoid robots.
• The National University of Defense Technology started early, developing the "Pioneer" in 2000 and the Blackman in 2003, standing 1.55 m tall, weighing 63.5 kg, with 36 degrees of freedom, achieving a maximum walking speed of 1 km/h, with in-depth research on robot turning and walking on uneven surfaces.
• In 2002, Tsinghua developed the THBIP-I robot, standing 1.7 m tall and weighing 130 kg, capable of stable walking and climbing stairs.
• In 2022, Beijing Institute of Technology launched the "BHR-1," achieving independent walking without external cables for the first time; in 2005, BHR-2 broke through technologies for stable walking and complex motion planning.

Domestic humanoid robot research started relatively late, focusing on universities and military research.

An average adult typically has 206 bones and nearly 230 joints, constituting 244 degrees of freedom controlled by 630 muscles.

• If accurately modeling the human body, the work would be extremely complex. Hanavan proposed simplifying the human model, usually dividing it into 15 parts corresponding to the head, chest, upper arms, forearms, hands, thighs, calves, and feet.
• Humanoid robots are highly flexible, strong nonlinear dynamic systems, typically analyzed using a combination of multi-rigid-body dynamics systems and numerical simulations.
• Robot motion analysis includes dynamic analysis and kinematic analysis, where kinematics is divided into forward kinematics and inverse kinematics.

Humanoid robots not only possess some human-like features, such as upper limbs and heads, but should also have human-like lower limb structures and bipedal walking capabilities.

• In the design process of bionic mechanisms, the degrees of freedom are determined based on target specifications, deciding on the types and numbers of joints, typically composed of multiple single-degree-of-freedom rotational joints.
• Sensors are typically used to simulate human perception of the environment, such as machine vision, pressure sensors, touch sensors, directional microphones, and sonar rangefinders.
• The NAO robot has 25 drive motors, 2 cameras, 9 touch sensors, 4 directional microphones, 8 pressure sensors, 2 sets of infrared receivers and generators, and sonar rangefinders.

Joint drive route one: Hydraulic drive has high force and strong explosiveness.

• Advantages: High output power, no need for a reducer, strong force, high explosiveness, and strong ability to withstand mechanical shocks and damage.
• Disadvantages: Hydraulic systems are prone to oil leaks, large in size, noisy, and have high power consumption, requiring hydraulic sources.

Joint drive route two: Motor drive is the most traditional, with a simple structure and wide application.

• Advantages: Simple structure, precise position servo.
• Disadvantages: Poor torque servo, high transmission loss, and less explosive power than hydraulic drives.

Joint drive route three: Motor drive + flexible software enhances energy storage and cycling capabilities.

• Advantages: High torque precision, passive flexibility, and energy storage cycling capabilities.
• Disadvantages: Poor position servo and limited response bandwidth.

Joint drive route four: Direct motor drive achieves high position accuracy and fast response.

• Advantages: High torque precision, high position accuracy, and fast response.
• Disadvantages: Motors need to be custom-made, and motor size is large.

Joint drive route five: Pneumatic drive is lightweight and low-cost, but control precision is not high.

• Advantages: Pneumatic artificial muscles are lightweight, low-cost, easy to maintain, and have a larger power-to-volume ratio and power-to-weight ratio compared to cylinders.
• Disadvantages: Control precision is not high, work efficiency is relatively low, and work speed stability is poor.

Each of the three drive methods has its characteristics; motor drive is the most traditional, while hydraulic drive is the most expensive.

• Hydraulic, motor, and pneumatic drive methods each have their characteristics, with motor drive being the most traditional, rapidly advancing in technology, and widely applied globally; hydraulic drive is challenging, with high difficulty in hydraulic valves, making system costs very expensive, but offering the best robot motion performance; pneumatic drive performance is between hydraulic and motor drives, currently applied relatively less.

Balance control directly affects walking performance, and companies usually develop core control algorithms independently.

• The core issues of robot state estimation include: sensor selection and layout, sensor data calibration, modeling of the robot body, and multi-sensor data fusion.
• In the design selection of controllers, control strategies are usually chosen based on the robot's state and model, followed by executing control commands. The design of the controller is the most critical part of robot design.

To achieve good human-robot interaction performance, algorithms, AI technology, and sensors are essential.

• In motion planning and interaction design based on environmental perception, a good understanding and cognition of the environment are required, calculating feasible areas, reasonably selecting contact points (such as bipedal, dual-hand, or using hands and feet), as well as choosing step lengths and optimizing models.
  
  Humanoid robot batteries: Estimating the basic parameters of battery packs from limited performance indicators.
• Boston Dynamics' Atlas robot has a maximum power of 5 kW and a total weight of 80 kg. The mounted 48V lithium-ion battery pack weighs 5-10 kg, with a mass energy density of 200-250 Wh/kg and a volume energy density of 500 Wh/L estimated. The discharge rate of this battery pack is 2C-5C, with a volume of 2-5 L and a mass power density of 0.5-1 kW/kg, and a volume power density of 1-2.5 kW/L.
• Based on the performance ranges of mass energy density and mass power density, we estimate that the battery pack used by Atlas is similar to high-performance power battery packs.
  
  Recent developments in power batteries: CTP3.0 "Qilin Battery" is on the horizon.
• According to CATL's official website, the CTP3.0 technology "Qilin Battery" can achieve a mass energy density of 255 Wh/kg (ternary) or 160 Wh/kg (iron-lithium), a volume utilization rate of 72%, 4C fast charging, 5-minute hot start, and safety without thermal diffusion.
  
  Looking ahead: What are the material demand directions for humanoid robot batteries?
• It can be seen that humanoid robots do not have high requirements for discharge rates and cycle life, but have high requirements for mass and volume energy density, with potential requirements for fast charging capabilities.
• Therefore, batteries and battery materials with high energy density, preferably also considering fast charging capabilities, are the demand direction for humanoid robot batteries.
• High nickel/mid-nickel high-voltage ternary cathodes belonging to layered oxide positives are currently the preferred choice, and in the future, lithium-rich manganese-based positives may also have a place.
  
  Looking ahead: What are the material demand directions for humanoid robot batteries?
• Supplementing lithium in lithium battery material systems involves introducing high lithium content substances into the battery material system, allowing these high lithium content substances to effectively release lithium ions and electrons to compensate for active lithium loss.
• Regardless of whether the anode or cathode is pre-lithified, although lithium consumption still exists, the capacity of active material vacancies in the battery no longer exists, thus improving the actual energy density of the battery.
  
  If solid electrolytes can achieve lightweight, thin, strong, and high stability, it will significantly enhance battery energy density.
• Humanoid robot batteries have relatively low requirements for cycle life but may have high safety requirements, making them a potential high-quality application scenario for high-energy-density solid-state batteries.

Components and Materials Exclusive to Humanoid Robots#

High-explosive motors, high-performance chips, precision reducers, high-precision sensors, long-lasting batteries, and other core components will build a more stable and high-performance humanoid robot hardware system.

Artificial intelligence empowers humanoid robot design.
AI for Design of Humanoid Robots

Based on artificial intelligence technologies such as neural networks, graph grammar, and evolutionary algorithms, humanoid robot modules such as legs, arms, and trunks can be automatically constructed according to scene and task requirements, achieving collaborative optimization of form and control.

Motion Intelligence of Humanoid Robots
Complex terrain walking: Expected to adapt to complex terrains and narrow environments built for humans, such as slopes, steps, and thresholds, achieving stable, adaptive, and anti-interference walking.
Cooperative Operation of Dual-arm: In the case of unstable lower body, humanoid robots are expected to complete high-performance operation tasks with collaborative dual arms using human tools and equipment.
Compensation for Hardware with Software: When the hardware performance of humanoid robots is subpar and the sensory information is lacking, this technology systematically seeks and fully utilizes environmental and information constraints to compensate for the performance of hardware, achieving high-level task execution.

Multimodal Large Model for Humanoid Robots
By integrating multimodal information such as voice, images, text, sensory signals, and 3D point clouds, humanoid robots will have stronger multimodal understanding, generation, and association capabilities, enhancing their generalization ability in complex scene tasks.

Large-Scale Dataset for Humanoid Robots
Based on simulation synthesis or data collected from physical robots, a large-scale, standardized humanoid robot dataset is constructed, which is beneficial for improving the design, simulation training, and algorithm transfer capabilities of humanoid robots.

Embodied Intelligence for Humanoid Robots
Embodied intelligence is a high-quality, high-performance intelligent system capable of making rapid and precise responses under high variability; it is neither a simple computer simulation in a virtual environment nor a purely physical electromechanical system, but is closely related to humanoid robot systems.

Humanoid Robots Inspired by Human Anatomy and Neural Mechanisms#

Unlike most existing humanoid robot research methods that simulate human functions from the outside in, this approach simulates the human musculoskeletal system and neural mechanisms from the inside out, exploring the essential mechanisms by which humans achieve high dexterity, high compliance, and high intelligent behavior. As a new avenue for humanoid robot research, it is expected to build a more efficient and stable system closer to humans.

Open Source Community for Humanoid Robots
This community will gather experts and scholars in the field of humanoid robots worldwide, promoting technical discussions, information exchange, and multi-party cooperation, facilitating deep integration and collaborative development of the industrial chain.

‘Manufactory’ of Humanoid Robots
In a software environment, it will connect the design-control-intelligent algorithm development of humanoid robots based on analytical technologies and large models, rapidly and custom-designed high-quality, intelligent humanoid robot systems according to performance requirements, achieving hardware system verification through software-hardware consistency and the development of new components.

Applications of Humanoid Robots#

Humanoid robots possess versatility and intelligence, seamlessly using human tools, which will ensure their application scenarios continue to expand and deepen, profoundly transforming human production and lifestyle, leading society into a new stage of intelligent development, and bringing disruptive changes to various industries.
In the industrial sector, they will widely participate in dangerous production operations, greatly improving production efficiency and safety; in specialized fields, they will become an important force in executing scientific exploration, disaster relief, security inspections, and other tasks in extreme environments; in the livelihood sector, they will fully integrate into people's lives, from providing housekeeping services to participating in medical assistance, becoming an indispensable presence.

The development history of humanoid robots: When dreams come true, commercialization is imminent.

Multimodal large models endow robots with generalization capabilities, and the dawn of embodied intelligence is emerging.

• General large models bring revolutionary potential to embodied intelligence. The hardware of humanoid robots determines the flexibility of movement, with components mostly migrated from applications in other industries, and cost pain points can be addressed through large-scale production in the industrial chain; while software algorithms act as the "brain" of the robot, determining the upper limits of robot applications and being the main bottleneck for the commercialization of robots. Previously, robots relied on inherent program settings to perform tasks, making it difficult to have universally applicable algorithms across various scenarios, limiting the practical applications of robots. In recent years, the development of general large models such as LLM, VLM, and VNM has endowed humanoid robots with powerful generalization capabilities, allowing them to be applicable in more complex scenarios without requiring programming by non-professionals, accelerating the commercialization process of humanoid robots. "Embodied intelligent" robots are no longer mechanically completing single tasks but are new entities capable of autonomous planning, decision-making, action, and execution based on perceived tasks and environments, incorporating language interaction, intelligent decision-making, autonomous learning, and multimodal perception.

1.3 Tesla leads the way, and tech giants accelerate entry to drive industrial innovation.

• Tech giants are accelerating their entry to drive industrial innovation. 1) Tesla: On September 30, 2022, Tesla launched the humanoid robot Optimus prototype, and in 2023, Musk stated that Tesla's long-term value will come from AI and robotics; 2) OpenAI: In March 2023, OpenAI invested in Norwegian humanoid robot company 1X Technologies; in May 2024, OpenAI announced it had restarted its robotics team two months prior; 3) Samsung: In January 2023, Samsung invested 59 billion KRW in South Korean robot manufacturer Rainbow Robotics; 4) NVIDIA: In May 2023, Huang Renxun stated that the next wave of AI will be embodied intelligence; in February 2024, NVIDIA established a research department for general embodied intelligent agents; in March 2024, NVIDIA released the humanoid robot large model Project GR00T; in June 2024, Huang Renxun emphasized that "the next wave of AI is physical AI, and the era of robots has arrived"; 5) Figure AI: Founded in 2022, it received a total of $675 million in investments from tech companies including NVIDIA, Microsoft, OpenAI, and Intel in February 2024.

1.3 Tesla Optimus's progress exceeds expectations, and the industry has entered a new round of "arms race."

• Tesla Optimus is rapidly iterating, leading a new wave of technological revolution. Musk proposed the humanoid robot concept Tesla Bot at the 2021 AI DAY, and then began rapid development and iteration. In February 2022, the development platform was completed, and in October 2022, the prototype Optimus was officially launched at AI DAY, capable of simple actions such as walking, carrying, and watering. In December 2023, Optimus-Gen2 was launched, significantly evolving compared to the first generation, with noticeable improvements in perception, brain, and control capabilities. Tesla's humanoid robot can form a complete industrial closed loop, and the commercialization landing is worth looking forward to: Optimus reuses technologies related to autonomous driving, rapidly achieving evolution from concept to intelligent flexible robots. The production and sales of Tesla cars also provide preliminary scenarios for the commercialization of humanoid robots, and the advantages of the industrial chain offer possibilities for cost reduction, with a long-term mass production price target of $20,000 per unit.

Humanoid robots will first land in factories and will be applied in commercial services and family companionship in the future.

• Humanoid robots will gradually move from factories to homes, transitioning from B2B to B2C. From the strategic planning of mainstream robot manufacturers, humanoid robots will first be applied in the industrial manufacturing sector, and after accumulating maturity, will expand to commercial services, family companionship, and other scenarios. This is mainly because factory manufacturing scenarios are relatively simple, and the demand for robots to replace humans is more urgent, while commercial and family scenarios are complex, requiring high software and hardware standards for humanoid robots.
• The "Guiding Opinions on the Innovative Development of Humanoid Robots" outlines three major demonstration scenarios: special services, manufacturing, and people's livelihood, envisioning deep integration with the real economy by 2027. The application of humanoid robots in China will proceed in two steps: the first phase aims for application in special services, manufacturing, and people's livelihood sectors by 2025; the second phase aims for accelerated large-scale development of the industry by 2027, with richer application scenarios and related products deeply integrated into the real economy, becoming an important new engine for economic growth, with promising prospects for humanoid robots in daily life.

Tesla Humanoid Robot Disassembly: 14 Rotational Joints + 14 Linear Joints + 12 Hand Joints#

Tesla humanoid robot disassembly: disassembly of rotational joints, linear joints, and hand joints.

• Rotational joints: Mainly composed of "actuator + torque sensor + encoder + frameless torque motor + harmonic reducer + bearing + mechanical clutch," similar to collaborative robot joint modules, transmitting data to the actuator through input sensors, controlling the motor, and amplifying the output torque through the harmonic reducer, with output sensors providing position feedback for optimization algorithms.
• Linear joints: Mainly composed of "actuator + torque sensor + encoder + frameless torque motor + screw + bearing," where the actuator drives the frameless torque motor to rotate, converting rotational motion into linear motion through the screw.
• Hand joints: Mainly composed of "actuator + encoder + sensor + hollow cup motor + planetary gearbox + worm gear," featuring adaptive and non-reversible drive capabilities, capable of bearing 20 pounds, using tools, and precisely grasping parts.

Estimated Costs of Humanoid Robot Components and Potential Suppliers (Taking Tesla Bot and Related Domestic Parts as Examples)#

Estimated Cost Proportions of Various Links/Components of Tesla Humanoid Robot (Based on Domestic Parts Prices)#

Frameless torque motors: High efficiency, compact structure, easy maintenance, used in humanoid robot linear and rotational joints.

• Frameless torque motors are a special type of permanent magnet brushless synchronous motor, lacking shafts, bearings, housings, feedback, or end caps, consisting only of stator and rotor components, with the rotor made of a rotating steel ring assembly with permanent magnets, directly mounted on the machine shaft; the stator is the external component, with gear teeth surrounding steel sheets and copper windings to generate electromagnetic force tightly adhering to the machine casing.
• Frameless torque motors have advantages of high efficiency, compact structure, and easy maintenance. 1) High efficiency: Directly integrating the motor into the rotating shaft component reduces the overall system inertia, thereby reducing the torque required for motor acceleration and deceleration, allowing better control of motor motion and stability time, increasing system bandwidth, and improving machine efficiency; 2) Compact structure: Increasing torque density reduces footprint and weight; 3) Easy maintenance: Fewer mechanical components, with no easily worn or maintenance-required components.

Precision reducers include RV reducers, harmonic reducers, and planetary reducers. Reducers are transmission components composed of multiple gears, utilizing gear meshing to change motor speed, torque, and load capacity, and can also achieve precise control. There are many types and models of reducers, which can be divided into general transmission reducers and precision reducers based on control precision. General transmission precision reducers have low control precision and can meet the basic power transmission needs of mechanical equipment. Precision reducers have small backlash, high precision, long service life, and are more reliable and stable, applied in high-end fields such as robots and CNC machine tools, specifically including RV reducers, harmonic reducers, and planetary reducers.

• Humanoid robot rotational joints will use harmonic reducers, while hand joints or some low-precision body joints may use planetary reducers. RV reducers are larger in size and have limited applications in humanoid robots. Harmonic reducers are small, have a large reduction ratio, and high precision, and will be used for humanoid robot body rotational joints; planetary reducers are small, lightweight, have high transmission efficiency, long lifespan, but lower precision than harmonic reducers, and will be used for humanoid robot hand joints or body joints with lower precision requirements.

Tesla humanoid robots include three categories of 14 linear actuators distributed in the arms and legs. Tesla Optimus has 14 linear actuators, specifically including three types, with output/weight ratios of 500N/0.36kg, 3900N/0.93kg, and 8000N/2.20kg; the distribution locations are in the upper arms (21), forearms (22), thighs (22), and calves (22).

• Currently, the cost of screws is relatively high, with potential for future reductions. Linear actuators are composed of "actuator + frameless torque motor + screw + torque sensor + encoder + bearing," where the screw is an important component. According to our estimates, the current cost of screws accounts for about 23.4% of the Tesla humanoid robot's cost, with an expected final cost proportion of 13.9%. In terms of types, screws used in humanoid robots are divided into trapezoidal screws and rolling screws, with trapezoidal screws used for forearms and rolling screws used for higher load-bearing requirements in upper arms, thighs, and calves.

Compared to ball screws, rolling screws have higher load capacity, longer lifespan, greater speed and acceleration, and smaller lead, making them more suitable for humanoid robots. Screws are transmission accessories that convert rotational motion into linear motion, classified based on friction characteristics into sliding screws, rolling screws, and hydrostatic screws, with rolling screws further divided into ball screws and planetary rolling screws. The distinction lies in that the load transfer unit of planetary rolling screws is a threaded rolling column, which is a typical line contact; while the load transfer unit of ball screws is balls, which are point contacts. Compared to ball screws, planetary rolling screws have more contact points, allowing them to withstand higher static and dynamic loads, with static loads three times that of ball screws and lifespans fifteen times that of ball screws; they also have stronger stiffness and impact resistance, allowing for greater speed and acceleration; and a wider range of pitch design, with smaller lead designs possible.

Screws: Standard rolling screws are suitable for high load and high-speed scenarios, widely applied.#

Planetary rolling screws can be classified into five categories based on their structural composition and the relative motion relationships of components: standard, reverse, circulating, bearing ring, and differential types. Standard rolling screws are suitable for harsh environments, high loads, and high speeds, mainly applied in precision machine tools, robots, and military equipment, and are currently the main application type.

Screws: High precision in manufacturing through cutting processes, including turning, milling, grinding, and other core processes.#

The core components of rolling screws—screw, rolling column, and nut—are all precision threaded parts with small pitches, and the processing steps are basically the same. Traditional processing methods can be divided into two main categories: cutting and rolling:
✓ Cutting: Using the center holes at both ends as the processing benchmark, completed through 10-20 processing steps such as heat treatment, turning, and grinding, achieving manufacturing precision up to P1 level, enabling positioning and transmission functions.
✓ Rolling: A processing method that uses forming rolling molds to cause plastic deformation of the workpiece to obtain threads, with high automation in the mold opening process, low costs, and high efficiency in mass production, but lower manufacturing precision, generally around P7 level, only achieving transmission functions.

The rough processing steps of rolling screws have diverse technical routes, while precision processing still requires grinding machines. The cutting process of rolling screws can be roughly divided into steps: rough blanking, preparatory heat treatment (annealing), rough processing, final heat treatment (quenching), precision processing, and assembly inspection. Rough processing includes turning, milling, and grinding three process routes (which can be used individually or in combination), while precision processing is grinding. New processing techniques such as "turning instead of grinding" and "swirling milling" could theoretically replace grinding and improve processing efficiency, but the technology is still maturing, and precision processing still requires grinding technology and grinding machines.