How does it work

[GriffinRU]

Originally posted by Serum
And for the startup the esc works on a lower frequency. (sensorless)

At a certain point, the possition of the magnet can be determined by the speedo and at this point the controller steps up in frequency.

I think that is the reason that the elder type of controllers are not as smooth as the new ones. i think (I'm not sure about this, but it sounds very logical to me) that the elder controller just worked on a fixed switching frequency.

I am confused with your comment here...
What rotor position have to do with frequency? At start up to find out position ESC firing each phase in sequence (with reduced power by PWM), and acquiring EMF feedback to match later.

The goal here is to make as less switching as possible, but to run motor smooth you need to control voltage in very fine increments (higher freq., more switching)
And depends on your overall usage (most time 50% or 25% or 100% load) you can choose better frequency for particular motor and your needs.

Old ESC's had fixed low frequency due to the fact of available microchips and flexibility in programming(PIC's). Now you can get better (New gen PIC's and new FET's with better Rise and Fall time) components which can operate at rates capable to control motors in fine steps (512-2048) up to +150000 RPM with 2 poles. And yes you can adjust switching frequency on-fly but I haven't seen one yet with such capabilities.

Artur