epicyclic train

noun Machinery.

1. a train of gears or pulleys in which one or more of the axes revolve about a central axis.

noun

1. a cluster of gears consisting of a central gearwheel with external teeth (the sun), a coaxial gearwheel of greater diameter with internal teeth (the annulus), and one or more planetary gears engaging with both of them to provide a large gear ratio in a compact space