GreatScott! has created a great video showing how Brushless DC Motor and Electronic Speed Controllers work. We see lots of these in quadcopters these days. The basic DC motor is popular and simple to control but as more things are using brushless motors it is nice to know how they work.
“Brushless DC electric motor (BLDC motors, BL motors) also known as electronically commutated motors (ECMs, EC motors) are synchronous motors that are powered by a DC electric source via an integrated inverter/switching power supply, which produces an AC electric signal to drive the motor. In this context, AC, alternating current, does not imply a sinusoidal waveform, but rather a bi-directional current with no restriction on waveform. Additional sensors and electronics control the inverter output amplitude and waveform (and therefore percent of DC bus usage/efficiency) and frequency (i.e. rotor speed).”