Abstract: The epicyclic gear train for the sprinkler includes a sun gear coupled to an impeller for rotation about a central axis. A planetary gear has a single set of teeth meshing with the teeth of the sun gear for revolving about the central axis while pivoting about a revolving planetary gear axis. A first ring gear is fixed relative to the sprinkler housing and has teeth meshing with the teeth of the planetary gear. Second and third ring gears are adjacent to the first ring gear and rotate about the central axis. The respective teeth of the second and third ring gears mesh with the planetary gear teeth. There is one less tooth on the second ring gear than on the first ring gear, and one more tooth on the third ring gear than on the first ring gear. As a result, the second and third ring gears rotate in opposite directions relative to the first ring gear. The second and third ring gears each have an outer surface with a plurality of protrusions spaced around the circumference.