1 Humanoid robots usher in a new era

In August 2021, Tesla CEO Musk publicly demonstrated Tesla Bot, a humanoid robot concept machine, at the first “Artificial Intelligence Day”. In February 2022, Tesla successfully launched a humanoid robot prototype in just six months after the concept was proposed, and it was used as a development platform for in-depth research and development. On September 30, 2022, Tesla held its second annual “Artificial Intelligence Day” and released the latest version of the Optimus humanoid robot, which can achieve complex actions such as walking upright, carrying, and watering. According to Musk, the Optimus will reach mass production in three to five years, and eventually the number will reach millions, and the cost will be reduced to about $20,000. On May 16, 2023, Tesla released the latest demonstration video of Optimus humanoid robot at the 2023 shareholder meeting. In the video, Optimus walks more naturally and flexibly, completing a range of complex tasks such as motor torque control, more precise force control, environmental detection and memory. Optimus also demonstrated its ability to categorize objects based on end-to-end AI learning of human behavior. Tesla robots have made all-round progress, and their motion control and AI capabilities continue to improve. Musk said Tesla’s long-term value will come mainly from humanoid robots, and predicted that demand for humanoid robots will reach 10 billion units.

1.1 Optimus Details

Tesla’s humanoid robot currently achieves 28 degrees of freedom, equivalent to about one-tenth of human body function. These 28 degrees of freedom are mainly distributed in the upper and lower body. The upper body includes the shoulders (6 degrees of freedom), elbows (2 degrees of freedom), wrists (6 degrees of freedom), and waist (2 degrees of freedom). The lower body includes the hip joint (6 degrees of freedom), knee joint (2 degrees of freedom), and ankle joint (4 degrees of freedom). Dexterous hand 6 actuators in one hand, 11 degrees of freedom. The dexterous hand uses metal tendons to propel the robot to grasp small, thin objects with precision. In terms of electrical and intelligent systems, based on the mature electric vehicle industry chain, to achieve battery system integration, FSD and other technologies and product reuse, based on experience accumulation, will help humanoid robots speed up industrialization. Tesla designed the humanoid robot structure and joint distribution, and optimized the process through simulation models and practical verification to maximize the performance of each actuator under the goal of low power consumption, low cost and the highest quality. A total of 28 large actuators (excluding finger actuators) containing 14 rotary actuators and 14 linear actuators were reduced by analytical optimization to 6 actual actuators containing 3 series of linear/linear actuators and 3 series of rotary actuators.

Rotary actuators are mainly distributed in the joints requiring large Angle rotation such as shoulders and hips, while linear actuators are distributed in the single-degree of freedom joints such as knees and elbows with small swing angles and the two-degree of freedom but compact joints such as wrists and ankles.

The reducer, servo motor, linear actuator and roller screw are the hardware equipment with large value in the motion control industry chain of humanoid robot. 1) Motor: more quantity, more categories, need to meet the driving needs of the body joints, hands need to use micro motor. 2) Reducer, transmission: the number is more, the rotary actuator continues the demand for RV and harmonic reducer, and the planetary roller screw is needed as a linear transmission device in the linear actuator. 3) Environment perception: Different solutions for industrial robots to recognize external machine vision devices in fixed scenes. Humanoid robot scenes are complex, and solutions such as Lidar and camera are needed to realize environment perception, three-dimensional reconstruction and path planning, which have higher requirements for equipment categories, algorithms and real-time computing power. 4) Motion control: similar to industrial robots, operation control algorithms are self-developed by manufacturers, difficult to develop, is one of the core competitiveness; Tesla Optimus reuses the sensing and computing power of Tesla cars to develop a controller system for humanoid robots based on a fully autonomous FSD chip. The number, category and complexity of actuators of humanoid robots are much higher than those of industrial robots, which requires high real-time computing power and integration of controllers. Considering the current domestic selling price of components, the cost of Tesla Optimus is divided, and the rotary joint (composed of motor + harmonic reducer + lock brake + dual encoder + torque sensor + bearing) accounts for 40%, and the linear/linear joint (composed of motor + planetary roller screw + position encoder + force sensor + bearing) accounts for 30%. The hands accounted for 14 percent and the rest 16 percent.

1.1.1 Rotate the actuator

The rotary actuator consists of a motor + harmonic reducer + lock brake + dual encoder + torque sensor + bearing.

The rotary actuator as a whole is powered by a battery pack and matched with an electric drive servo joint, based on the rotary joint of the motor + harmonic speed reducer. The overall output torque density of the rotary joint is similar to the joint performance of the major humanoid robot manufacturers, highlighting the force output capability. In humanoid robots, the possibility of using RV reducer is relatively low, because the accuracy of RV reducer is lower than that of harmonic reducer and the volume weight is greater than that of harmonic reducer. RV reducer is more suitable for high strength, high torque and large load products. Harmonic reducer is more suitable for small load, small volume and small weight scene.

1.1.2 Linear/linear actuators

The linear actuator consists of a motor + planetary roller screw + position encoder + force sensor + bearing.

Tesla uses a planetary roller screw, which is one of the most powerful, but also one of the most expensive, subcategories of the screw class. The planetary roller screw has the characteristics of high load, high stiffness and long life, or it has become the key transmission device of the linear actuator of humanoid robot. It is the premise of large-scale production to achieve cost reduction by adapting to the needs of humanoid robot. According to the information presented at Tesla AI Day 2022, the Optimus linear actuator solution is a planetary roller lead screw integrated servo electric cylinder. We think that it is more likely to use high-load and high-stiffness planetary roller screw as the transmission device for the servo electric cylinder of the hip, knee, ankle and elbow joints of the upper limb. The structure of the planetary roller screw is complicated, the processing is difficult, and the cost is high. The premise of its large-scale application is to reduce the cost by adjusting the design and process scheme to meet the needs of humanoid robots.