The Optimus robot utilizes 28 motion joints throughout its body,categorized into two main types of actuators: Rotary and Linear. Each category
includes three variations of actuators.
14 Rotary Actuators: Composed of a Motor + Harmonic Drive + TorqueSensor + Position Sensor + Cross-Roller Bearing + Angular Contact Ball Bearing.
14 Linear Actuators: Composed of a Motor +Planetary/Leadscrew/Ball Screw + Torque Sensor + Position Sensor.
■ Function and Classification of Screw Shaft
A screw is the most commonly used transmission element in machinetools and precision machinery. Its primary function is to convert rotary motion into linear motion (or convert torque into axial repetitive force). It is characterized by high precision, reversibility, and high efficiency.
Based on spiral transmission principles, thereare three main types:
- Leadscrews (Trapezoidal Screws)
- Ball Screws
- Planetary Roller Screws
■ Ball Screws vs. Planetary Roller Screws
- Ball Screws
Utilizing the principle of linear rolling bearings, ballscrews convert motor rotation into the axial linear motion of a nut.
Components: Screw, Nut, Balls, and a Return System.
Mechanism: The screw acts as the rotatingcomponent with semi-circular threaded grooves (raceways) for the balls to
circulate within. - PlanetaryRoller Screws
This is anew type of linear transmission mechanism based on a compound motion of thread engagement and gear engagement.
Components: Screw, Rollers, Nut, and Planetary Carrier (Housings).
Mechanism: The planetary carrier supports 6 to12 small rollers evenly distributed between the screw and the nut. During transmission, the rollers perform planetary motion around the screw.
■ Key Advantages of Planetary Roller Screws
The planetary roller screw offers several superior characteristics:
- High Load Capacity: Due to the"line contact" (as opposed to the "point contact" of ball
screws) and a high number of contact points, it can withstand significantly
higher loads and impacts. - Compact Size & Precision:It maintains high transmission accuracy within a smaller structural footprint.
- Durability: Under dynamic loadconditions, the multiple rollers disperse the impact along the threaded contact
lines, providing better rigidity and shock resistance. - Efficiency: Despite thecomplexity, it utilizes rolling friction, maintaining a transmission efficiency comparable to that of ball screws.
■ Down streamApplications and Trends
- In Humanoid Robots: Planetaryroller screws are primarily used for linear joints. They offer high load-bearing capacity, fast response, compact volume, low noise, and high precision.
- In CNC Machine Tools: They are used for precisemotion control across various axes. In this sector, the transmission system (including the screw) accounts for approximately 20% of the machine tool's total value.
■ Usage Forecast (Per Robot):
It isestimated that a single humanoid robot may carry 14 linear actuators, requiring: 4 Leadscrews (Trapezoidal), 10 Planetary Roller Screws. As production scales up and the demand for cost reduction increases, the usage per unit may decrease. For instance, in the arm area (specifically the elbows where load and precision requirements are lower), manufacturers may replace expensive roller screws with 2 leadscrews to further reduce costs.
■ Value Distribution (Case Study: Tesla Optimus) According to data from Tesla Optimus, the value distribution of core components is shifting:
- 2023: The top three components by value were Frameless TorqueMotors, Reducers (Gearboxes), and Force Sensors.
- 2030 (Estimated): The value share of framelesstorque motors is expected to decline. Conversely, the shares for Force Sensors and Reducers will rise. Force sensors are projected to overtake reducers to rank second in value. Together, these three components will still account for over 50% of the total value.