Planetary Gear Operation: Notes

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The planetary gear works as a transmission when the sun gear and the internal gear are engaged.
The sun gear, installed inside of the pinion gears, and the internal gear, installed outside of the pinion gears, are engaged with their respective gears. The sun gear and the internal gear rotate on the center of the planetary gear.

Fig 1: Identifying Planetary Gear Components
Courtesy of MAZDA MOTORS CORP.
The pinion gears turn in the following two ways:
- On their own centers ("rotation")
- On the center of the planetary gear ("revolution")

Fig 2: Pinion Gears Turning In Two Ways

Courtesy of MAZDA MOTORS CORP.