[rightbyte]

Has any computer been built out of spur-gear differentials? Like maybe some sort of adder circuit, not necessarily a full instruction executing computer. The only uses I could find was what seems to me like the differentials being part of some sort of analogue computer.

[thechao]

Spur gear differentials are naturally adders (with carry!); so, traditionally they've only ever been used for analogue logic. They're overly complicated for digital logic: you need two spur gears to build a single gate (NAND) to perform a single binary operation. If you want any sort of reasonable lash characteristics you're going to need ~60 teeth. At that point, two 60 teeth spur gears give you a 3600-valued adder. That'd take something like 300+ spur gears in binary: it just doesn't make any damn sense.

I think the last time I looked at this, if I used the cast spur gears available I needed a staged approach to "start" the computer and a 1100 hp motor to run it.

[jcgrillo]

A huge steam engine might be the ticket, that'll solve your starting torque problem

[rightbyte]

> a 1100 hp motor to run it

Oh, ye that sounds impractical. A really big truck engine more or less.

[thechao]

Convincing Mrs. thechao that we needed to drop 80000$ on a blown V8 to build a 4b 3 function calculator didn't workout, BTW.

[rightbyte]

Well I want to be on your side but I think one need to keep the dreams not within grasp but at least in sight.