Planetary gears play a critical role in power transmission systems used in aerospace, wind power generation, and other advanced engineering applications, offering broad research potential and practical significance. Traditional studies on planetary gear dynamics have primarily focused on torque-dominated load conditions. To investigate the dynamic behavior and transmission characteristics of planetary gear systems under non-torque loads, this paper proposes a semi-analytical dynamic modeling method based on a rigid-flexible coupled system described in a global coordinate framework by fixing the retainer. The proposed modeling approach includes: constructing a flexible body model for the ring gear;  establishing a lumped parameter submodel for the sun gear, planet carrier, and planetary gears; and  introducing a moving elastic coupling boundary to connect the time-varying meshing interface between the ring gear and planetary gears. Based on this modeling framework, a radial load is applied to the input shaft of the planetary gear system. The effect of non-torque loads on the planetary wheel drive system is investigated by fixing the planetary carrier, calculating the displacement of the sun wheel, the transmission error between the planetary wheel and the tooth ring, the meshing force and the acceleration value of the measuring point on the tooth ring.

global coordinate system, non-torque load, flexible ring, moving elastic coupling