automatic transmissions

[KnifeEdge_2K1]

ok i know that an automatic transmission needs a torque converter and a planetary gearset type tranny

i understand the need for a torque converter which allows the engine speed and transmission speed to differ at idle speed but match up when they speed up

what i dont understand is why they use planetary gearsets?

why not use the same type of transmission as a manual just replace the clutch with a torque converter. a computer uses sensor data to change gears with hydraulics in an auto so why not do the same with control rods in a manual type transmission? ive read some info on the subject but i still dont understand. can neone help?

[Matra et Alpine]

ok i know that an automatic transmission needs a torque converter and a planetary gearset type tranny

i understand the need for a torque converter which allows the engine speed and transmission speed to differ at idle speed but match up when they speed up

what i dont understand is why they use planetary gearsets?

why not use the same type of transmission as a manual just replace the clutch with a torque converter. a computer uses sensor data to change gears with hydraulics in an auto so why not do the same with control rods in a manual type transmission? ive read some info on the subject but i still dont understand. can neone help?
as with every other gear question asked so far, check out www.howstuffworks.com it really IS the best place to start as it will explain how planetray works.

WHY it's chosen is that planetary shifts are made by braking gears. This is simple technology to automate with some simple hydralics versus the complicated action os movign gear synnchros in a manual.

I also think that you can create stronger gears in planetary for the same volume as they fit inside each other so a box needs only to as long as the widest gear you want to chose. A 'manual' box however has all the gears seperate so getting more metal onto the gears means a LOT more space.