Kv = rpm/v or rpm = Kv * v
Kv is the factor to multiply the voltage to get rpm
So motor has a range of voltage that it will run on
At half volts the machine should hover
What is the power behind the motor in grammes it will lift per Kv
http://www.dronetrest.com/t/brushless-motors-how-they-work-and-what-the-numbers-mean/564