CONTROLLED COUPLING HYDRA-MATIC FUNDAMENTALS
(pg 87)

3. A planetary gear unit offers these advantages:
	a. It is sturdy, because loads are distributed over more gears, and less tooth load is transmitted, because more teeth are in contact at all times.
	b. Planetary gears are always meshed. Thus, there is no tooth damage due to gear clash or partial engagement.
	c. The common axis for all members of the planetary train affords compactness, and provides positive coupling when any two of the members are locked together.
			4. A planetary unit provides reduction and torque-increase in forward in two ways:

In describing the operation of the planetary unit, we refer to pinion "walking" and "idling".
When pinions walk they are moving in or around a member which is held stationary. Thus,
planet pinions walk in the internal gear in the direction opposite their rotation, and walk
around the sun gear in the same direction they are rotating. The pinions idle whenever the
planet carrier is held stationary and power is applied to the internal gear or the sun gear.

To page 88