On Thursday, 15 February 2018 12:46:29 UTC, DerbyBorn wrote:
Most motors seem to have the same proportions of length to diameter so
there must be some theoretical principal there.
However, I once operated a milling machine that had what was called a
Pancake motor that drove the feeds. It was large diameter and only about 2
inches deep. Then there is the direct drive washing machine.

Any website I should read to clear this in my mind.

Most elecric induction motors run at near synchronous speed or half or one third.
The speed they run at is determined by the number of (pairs of) poles.
Either 1, 2 or 3,
Low speeds are obtained by use of pulleys or gearboxes with these motors.

However"pancake" motors have many more poles and hence run much slower.
It's become feasible to have slow speed motors with many permanent magnets/poles when neodymium magnets were developed.
This can do away with the neccesity for gearboxes.
They started off very small but now there are bigger ones.
https://en.wikipedia.org/wiki/Electr...al_rotor_motor