MosFet

A FET, more correctly a MosFet is a 3 terminal device that supplies current to the end user, typically, but not exclusively the motor that turns the propeller.
The terminals are gate, source and drain, the gate switches it on (and off), the source is the battery and the drain goes to the motor. Unlike transistors which have a voltage across them when switched on (.6v for Silicon) a MosFet has a forward resistance measured in mohs (millionths of an ohm). This means that a relatively small device can carry hundreds of amps with ease.

This little guy can hold back 55volts, and allow 100amps through without even breaking into a sweat!

And now Im confused where is all of this I assume its part of the ESC we dont need to worry to much about as it takes care of itself.

Dead right Stephen, it's just that when a question is asked I try to make sure there's some kind of entry in the Technical section. There's no such thing as a silly question, only silly answers!

Oh that bit is clear as mud now I normally thow it away :whistle: :whistle: Now I know why my leccies dont run ,thought it was the little tiny starter motor.