[What's_nitro?]

The BEMF pulses are what tells the ESC where the rotor is relative to the stator coils. When one pole of the rotor passes under a coil, it sends a pulse back to the ESC. The ESC then "knows" that this particular pole (N or S) is 60 degrees from the next coil, and can determine when it should fire the next coil. Have you ever wondered why sensorless motors "cog" only at low speeds, or very high gearing? It's because the rotor's speed is to low to send accurate pulses to the ESC, and in turn the ESC can't accurately calculate timing.