Electronic Speed Controllers (ESC's) use a logic level signal to control motor speed.
BEC's are Battery Eliminator Circuits, and are essentially low voltage cutoffs. They “Eliminate” the need for Hotel Load Battery because they cut power to motors when battery voltage dips below a preset level. This allows the pilot to continue flying under reduced or eliminated power. BEC's are used in ICE vehicles to eliminate the battery by filtering alternator output. These BEC's are fundamentally different.
Input Signal: 3.3V or 5V PWM. Pulse width 1.0ms to 2.0ms. Standard 50Hz, but some can operate at higher PWM frequencies as they just average the signal.
Output: 3 Phase AC at whatever the input voltage is.
These are standard DC motors. They are rated by number of turns. Lower turns mean high speed and low torque. High turns mean low speed and high torque.
These are 3 Phase Induction Motors. They are also know as Aysynchronous Motors. An ESC/BEC is required to convert DC voltage into the 3 Phase AC required to run the motor.
They are rated using KV. This number is the RPM per Volt applied. So, a 1400KV motor will turn at 1400 RPM if you apply 1 Volt.
High KV means high speed, low torque. Low KV means low speed, high torque.