Deep Dismantling of Unitree G1 Knee Joint Actuator: Full Analysis of 120 N·m Torque, Two Stage Planetary Reduction and Dual Encoders

Recently, overseas engineer Grant performed a full teardown of the Unitree G1 knee joint actuator and released extensive internalstructure details and measured test data.

Weighing approximately 1 kg, this joint integrates an 18slot, 16pole motor, a 22.5:1 twostage planetary gear reducer, dual encoders, crossroller bearings and a complete drive circuit.

Based on this teardown, this article walks you through the internal design philosophy of the Unitree G1 knee joint actuator.

 

Assembly and Cabling

Central Hollow Shaft

A hollow aluminum tube fitted with a PTFE liner runs straight through the entire joint. It passes through the rotor bore, the twostage gear train and the output hub, and is restrained by a needle roller bearing at the motor end. Wiring harnesses for downstream joints are routed through this tube to prevent wire fatigue. Note that the connectors must be crimped after the harness has been threaded through.

Power / Data Connector: XT30 2+2

The XT30 2+2 connector exposed in the figure. The two large bullet pins are used for the DC bus (brown, multistrand wires in parallel), while the two smaller pins carry the differential data pair (white jacket). The black molded material at the cable exit provides strain relief.

 

The image shows the cable entry at the actuator. The parallel conductors and data pair are wrapped in a braided fabric sleeve. At the strippedback jacket, tinned wire strands are visible — this is one of the two parallel DC bus conductors.

Strain relief is applied at every layer. The conductors use finestrand PTFEinsulated wire rather than a single thick conductor, allowing the cable to bend without fatiguing the strands. Two conductors are paralleled to increase currentcarrying capacity (brown and silver conductors for the DC bus), the data pair is differential, and the braided fabric layer over the entire bundle provides abrasion resistance. The harness is routed through the PTFE tube inside the central shaft.

 

The motorfacing side of the power board shown in the figure reveals: six MOSFETs forming the B6 bridge; two R003 shunt resistors for phasecurrent sensing; two white circles for the magnetic encoder pair (left: outputside sensor IC; right: rotorside target magnet holder); an array of ceramic capacitors for DCbus decoupling along the left edge; and two XT30 2+2 connectors at the bottom for daisychaining.

 

On the outwardfacing side of the logic board in the figure, a large QFNpackaged MCU sits at the rightmiddle position (markings on the top surface have been laserablated). Horizontally laid out across the upper half are copper pour areas for phase outputs (goldcolored arcs). A signal interlayer board extends out from the bottom.

 

Overall Module Overview

The two photographs below display the complete actuator laid flat after disassembly, offering the most comprehensive singleframe overview of all removed components.

Third row: XT30 2+2 wiring harness, PCB (logic side), rear PCB plate, PCB housing. Fourth row: metric fasteners.

With all components flipped over, arranged from left to right. First row: 1stage gearbox assembly, rotor (sungear side), stator inside the main housing, top retaining plate. Second row: hollow shaft tube with PTFE liner, external circlip, output top plate, 2stage gearbox assembly. Third row: XT30 2+2 wiring harness, PCB (power side), rear PCB plate (thermal pad side), PCB housing. Fourth row: metric fasteners.

 

The picture displays the inner side of the diecast aluminum rear cover. The blue silicone thermal pad covers approximately half of the disc, and its contour matches the copper pour areas on the PCB in the figure below.

 

Communication Interface

The two XT30 2+2 connectors on both sides of the interlayer board form a straightthrough daisychain path. Power and data enter from the upstream joint and then exit toward the downstream joint. Consequently, the leg adopts chainstyle wiring instead of startype wiring. Pads on the interlayer board are marked A / B / SIG. A and B are common designations for a differential bus. Unitree actuators have used CAN and RS485 in different revisions, so the protocol implemented in this specific unit cannot be confirmed. The approximately 3 kHz command frequency listed in the summary table originates from SDK documentation for the Unitree A1 and GOM8010 series and was not measured experimentally on this joint.

AMASS High current connector widely used in the internal battery, motor, and electrical control connections of embodied robot.