one other thing that I might add is that esc's use PWM (pulse width modulation). Basically you have a mosfet, and basically that is an on and off switch that is capable of switching anywhere from 2000 times per second on up. How it works is if you want 70% throtte, it leaves the switch on 70% of the time, and off 30% of the time. So in this way you are getting 100% of the power 70% of the time, which looks like 70% power.