ESC – Electronic Speed Controller. Is an electronic circuit that is used primarily to vary an electric motor’s speed. ESCs are often used on electric powered RC models and UAVs, with the variety most often used for brushless motors providing an electronically generated three phase electric power to the motor(s).
Most current ESC contain a microcontrollers that control the motor using specialized firmware. Some ESCs can have their firmware changed, or “flashed”. This is done to adapt the ESC to a particular application, such as with SIMONK firmware specific for multirotors.
An ESC may also contain a BEC (battery eliminator circuit). This part of the ESC is designed to deliver electrical power to other components of the aircraft systems without the need for a separate battery, typically 5V DC. ESCs without a built in BEC are often referred to as “OPTO” ESCs (although the terminology is not always used properly as OPTO is meant to refer to optical isolation of the high power from the signal to prevent noise, but the term has become often misused in the industry to mean lack of built in BEC.)