Brushless motor speed (Kv)
Kv is the motor’s gearing in disguise: a 1000 Kv motor on 11.1 V wants to spin at about 11 100 RPM, like a bike that goes a fixed distance per pedal turn.
RPM(no load) = Kv × V
No-load estimate. A loaded motor runs 10–20% slower, and a LiPo sags under load (nominal 3.7 V per cell, 4.2 V full). Match Kv, propeller and voltage so the ESC and motor stay within their current ratings.