Overdrive Internals: how does it work?

On a very low level, how does an OD create the gear reduction?

Here's what I've determined so far, please correct me. I've read that the splined/main shaft spins freely in direct drive, and is stationary in overdrive. This shaft has a sun gear (teeth on the forward end) that mate with the planetary/spider gears which in turn drive the bowl gear. The spider hub (the part with splines that mate to the transmission output shaft) holds planetary gears in orbit. I've read that the OD reduction is caused by the planetary gears spinning on their axes. So somehow making the main shaft stationary causes this.

I can't seem to connect how staying the main shaft has an impact. The best idea I have is that the sun gear only turns if the main shaft turns (ie, it doesn't spin freely on its own axis independently of the splines). So in direct drive the free spinning main shaft means that the planets do not spun on their axes (bc the sun gear can rotate at the speed of the spider hub). This means that the bowl is driven at the speed of the planets which matches the speed of the hub which matches the speed of the trans output shaft.

And in OD the stationary sun gear causes the planetary gears to spin slowly against rotation. Which drives the bowl gear slower than the hub, creating the 25% reduction. Is this correct?

 

http://auto.howstuffworks.com/automatic-transmission3.htm

Google is your friend

 

my attempt of enlightenment:
the (go) devil makes the planets orbit the sun, the sun makes the planets spin, you are the person on the surface of the planet. you are now spinning as you orbit,


in direct: the sun rotates as part of the drive train everything acts as one unit; being pulled at the axis of the planet gears

in O/D: the sun gear is stationary to the case, the planets are rolling around the sun still pulled at there axis; by the go devil (and transmission)
the axis of the planets are now traveling as fast as the devil (and transmission) but the the planets are rotating individually around the sun. the transfercase is driven at the speed of the teeth at the outside of the planet gears. so you have the engine speed at the center of each planet gear being multiplied slightly at the outer surface because the planet gears are also spinning themselves

 

Perfect! Thanks.