Motor braking
Disclaimer - I have never been inside a hobby brushless speed controller and looked at what the software and hardware are arranged to do.
But I do design and make braking resistors and systems (up to about 20MW motors)
Any motor can be stopped by shorting the windings - try it if you are brave and confident!
The currents flowing are huge and the torque released will break mountings and certainly any gears attached.
Much kinder and more controllable is to connect a braking resistor across the windings - so a DC motor needs only one, but ideally an AC motor (brushless) needs one per phase - usually 3 in our world. (you can connect a brake resistor to just one (or two) phases but its a bit uneven and brutal)
How much is right? - well it depends on what you want. My mental rule-of-thumb is that a resistor about equal to the resistance winding (in Ohms) gives a fairly "sharp" stop. For aircraft brakes the resistor is usually set at this value approx (1 to 2 ohms), as usually it's required to fold the propellor.
The "sharp" stop (maybe 1/10 sec) won't do gearboxes any good at all - so a much higher resistance is used - its best to start high and work down (if you ever have to do this use a length of hair-dryer wire, or car light-bulbs to find out what works and is safe)
So - the brushless ESCs may be switching in three resistors (one per phase) for the braking function, but these resistors would be quite large and visible, and would only be used for this function.
So I suspect that the designers use FETS as synthetic resistors (perhaps the same FETS used for the drive). Although FETs have a VERY small resistance when they are fully "on" (and an infinite resistance when off) they can be driven so as to have any resistance, and would almost certainly be pulsed so that the braking can be adjusted.
So in summary:
- You can brake any motor by shorting it - its brutal, please don't
switching in a resistor will give a kinder and controllable brake
ESC manufacturers (probably) do exactly that, but use cunning electronics to create the resistor
Useful/interesting/shut up! andrew?