This is the clearest diagram I have found so far.
The notes and jpgs tell the difference in the Ford and GM
practices. The fact that the Ford Ring gears and planet
carriers are separate parts make them more suitable for
our purposes. The front and rear planet sets are
obvious. GM parts must be heavily modified to work.
However the up side is they are straight cut gears so
no gear thrust bearing is needed.


http://www.innerauto.com/Automotive_Systems/Automatic_Transmission/Planet_Gear/


"Almost all automatic transmissions use a pair of gear groups
called epicyclic, or planetary gears. Each group consists of; an
outside "ring" gear, a shared "sun" gear in the center, and a
set of "planet gears", which mesh in between the sun and the
ring gear. Planet gears are so named because each one turns on
its own axis as they orbit the sun gear, like planets do. Each
group of planet gears is held in a "planet gear carrier"."

"Single epicyclic gear sets work like this: To increase torque:
When the ring gear is stopped, and the power is applied to the
sun gear, the planet gears are forced to go around the sun gear.
This makes the pinion gears revolve more slowly around the
inside gears, and drive from the carrier will have lower speed
and increased torque."



Paul Lamar