Originally Posted by RONALDO_UK
I didn't want it to get TOO involved!
Looking at the excellent link Ron VS supplied (bedankt) which is like RC For Dummies (just what I wanted!) - it said the ESC is like a very fast switch so voltage changes from either zero to max/ max to zero with throttle inputs, which I suppose is kind of same/different to what you said.
Here are two more links for what's involved in these brushless motors, (and why its far better to buy one, rather than design your own!) Even if a person had the ability to design one of these ESC's and the ability to program the microcontroller for it, building one of them from scratch, or even a few dozen from scratch would far exceed the cost of buying one ready to go. Buying components in very large quanities really reduces the cost of the product.
Microchip ESC Info
The first few pages of this PDF file shows basic information on what is involved to drive a brushless motor. Take a look at page 3 of this file, which explains in very simple terms, what happens to your brushless motor during one revolution of the motor.
This PDF file covers some of the mathematics on what is involved in these brushless ESCs.
As can be seen from these files, there is a lot of stuff going on "under the hood" of these brushless ESC's. Its all being done by the microcontroller that is controlling the power drivers of the ESC. Circuitry wise, compared to a cellphone, these ESC's are pretty simple. But, the computer programming to actually run these ESC's is NOT simple!