Planetary gear transmission mechanism for speed reducer

The utility model discloses a planetary gear transmission mechanism for a speed reducer, which comprises a first sun gear and first planet gears, the outer sides of the first sun gear are rotatably connected with two first planet gears in a meshed manner, the outer sides of the two first planet gears are connected with a second gear ring in a meshed manner, and a central shaft is embedded in the central position of the first sun gear. According to the utility model, the first sun gear drives the first planet gear to rotate; the diameter of the first planet wheel is smaller than that of the first sun wheel; the linear speed of the first sun gear is equal to that of the first planet gear; therefore, the angular speed of the first planet gear during rotation is smaller than that of the firstsun gear; through the same principle as the first-stage planet gear and the second-stage speed reduction, the original first-stage speed reduction is expanded into two stages, and the torsional forceis dispersed to a certain