Low Range (Ring Gear Held); Drive Range (Sun Gear Held) - Chevrolet Trailblazer Service Manual

Planetary gears function very similarly to conventional transmission gears. However, their
construction is different in that three elements make up one gear system, and, in that all
three elements are different from one another. The three elements are: an outer gear that
is shaped like a hoop, with teeth cut into the inner surface; a sun gear, mounted on a shaft
and located at the very center of the outer gear; and a set of three planet gears, held by
pins in a ring-like planet carrier, meshing with both the sun gear and the outer gear. Either
the outer gear or the sun gear may be held stationary, providing more than one possible
torque multiplication factor for each set of gears. Also, if all three gears are forced to rotate
at the same speed, the gear set forms, in effect, a solid shaft.

Low range (ring gear held)

Drive range (sun gear held)