机械类翻译成英文(不要直接百度的,要专业的！！！)

2 planetary gear train
The basic set of motion Introduction
Planetary gear train basically includes a sun gear, a ring gear, planet wheels and the planet bracket. A planetary gear mechanism generally has a compact structure, small size, light weight, transmission ratio range, high transmission efficiency and smooth running, low noise, etc., but there are also relatively complex structure, high precision parts manufacturing, internal gear machining more difficult, poor self-cooling conditions, the structure is not easy to have a smaller gear ratio, and the planetary gears at high speed centrifugal force will rapidly increase, not easy to choose the appropriate bearings and other shortcomings.