Today I learned: Apparently, automatic transmissions are hydraulic computers. Or at least the ones up until recently; recent ones have more and more electronic control.
@Motodrachen If you don't mind explaining something I'm having trouble understanding, since this seems like your area of expertise: Something I've never understood is how exactly changing gears works in them. Everything I can see just says "it's just using planetary gears" in the same way you might say "it's just using magic"; I don't follow how planetary gears allow you to do anything regular gears don't, except perhaps having concentric input and output shafts.
The Gear Wars
@Rosemary Okay funny you should mention that, Epicyclic assemblies were my Specialty in school.
Okay, so the cool thing about a planetary gearbox is that you can send input power to the Sun gear, and spin the planetary carrier, and get a certain specific reduction. Arrest that and allow the Annulus to spin, and you get a different reduction. And you can link straight thru to give direct output.
On top of that you can stack multiple epicyclic gearsets and shift back and forth by engaging and disengaging shift dogs between the gearsets.
If you wanna see a miniature example, Cordless Drills use planetary reduction. It also spreads the load out across multiple gear teeth, reduces backlash and makes for a compact, coaxial package.
And I can't remember the Exact multiplier but it's something like 1.81* the gear rate between the sun gear and annulus, if you're taking the torque off at the planetary carrier. Oh, and input and output are always the same direction no matter how many reduction steps.
re: The Gear Wars
@Motodrachen This is going over my heads again, I'm afraid.
re: The Gear Wars
@Motodrachen How do you change which gears are engaged to the shaft, though? What I'm getting from this is that you need to have one of the three gears connected to the input shaft, one to the output shaft, and one fixed in place, but how do you rearrange all that with so little room to work, without having far too many moving parts for any semblence of reliability?