90° helical planetary gearbox a precision planetary gear train structure with input and output shafts laid out at right angles to each other to achieve high torque density in a compact design. The straight tooth transmission system is carburised and quenched in a controlled atmosphere, with a tooth surface hardness of HRC58-62, combined with a ductile iron case to ensure wear and impact resistance. The single-stage transmission efficiency is ≥97%, and the multi-stage configuration (1-3 stages) can provide a transmission ratio range of 3 to 250, while maintaining a low return clearance of ≤25 arc minutes to meet the demand for high-precision positioning.