"行星齿轮传动" can be translated into English as "planetary gear transmission" or "epicyclic gearing".
"Planetary gear transmission" is a more straightforward and commonly used term in engineering contexts, directly describing the mechanism where gears rotate around a central (sun) gear, similar to planets orbiting the sun.
"Epicyclic gearing" is another technical term that refers to the same type of gear system, with "epicyclic" meaning "moving around a central point," which aptly describes the motion of the planetary gears.