Recently, overseas engineer Grant performed a full teardown of the Unitree G1 knee joint actuator and released extensive internal structure details and measured test data.
Weighing approximately 1 kg, this joint integrates an 18 slot, 16 pole motor, a 22.5:1 two stage planetary gear reducer, dual encoders, cross roller 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 two stage 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, multi strand 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 stripped back 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 fine strand PTFE insulated wire rather than a single thick conductor, allowing the cable to bend without fatiguing the strands. Two conductors are paralleled to increase current carrying 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 motor facing side of the power board shown in the figure reveals: six MOSFETs forming the B6 bridge; two R003 shunt resistors for phase current sensing; two white circles for the magnetic encoder pair (left: output side sensor IC; right: rotor side target magnet holder); an array of ceramic capacitors for DC bus decoupling along the left edge; and two XT30 2+2 connectors at the bottom for daisy chaining.
On the outward facing side of the logic board in the figure, a large QFN packaged MCU sits at the right middle position (markings on the top surface have been laser ablated). Horizontally laid out across the upper half are copper pour areas for phase outputs (gold colored 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 single frame overview of all removed components.
