Electronic Speed Controller (ESC)
An Electronic Speed Control or Electronic Speed Controller (ESC) is an electronic circuit that has two primary functions. First, the ESC regulates the battery source down to the voltage needed by servos and the RC receiver. Second, the ESC converts the signals from the RC receiver to a brushless motor control output. The regulation is used by your receiver and but is not used by the HoverflyPro™. In fact there is no circuit connection between this regulated voltage and the main processing electronics on the HoverflyPro™. This is why a separate connection from the battery to the Power input on the HoverflyPro™ is required (more on this in following sections).
The input signals to the ESC produced by the RC receiver are what are called Pulse-Width-Modulated (PWM) waveforms. The voltage levels of this signal vary in time between the common voltage, thought of as 0 volts, and the RC receiver voltage typically 5 or 6 volts. The PWM signal consists of square pulses separated in time where the width of the pulse corresponds to the commanded position of a servo. A short pulse would drive a servo to its minimum range and a long pulse to the maximum range. When the PWM signal is fed into an ESC the short pulses would signify low throttle (or no throttle) and long pulse to high throttle. The use of throttle here is related to the original use of a servo to literally close and open an air fuel mixture carburetor on a gas engine. For brushless motors, we use low throttle to mean low RPMs and high throttle for high RPMs.
All ESCs operate functionally the same but there are preferred brands that change over time. This information can be found on a forum such as RCgroups.com. However, the size of an ESC refers to the amount of current that it can handle. Each ESC will have an associated current rating and you must carefully design your motor drive system with this in mind. As a general rule, you should always use an ESC with twice the maximum current that you believe will be utilized by the motors. You can match the maximum current to the ESC current rating assuming that the manufacturer also used a safety buffer in the rating. However, we strongly recommend that you over specify your ESCs. If one fails, the aircraft may become unstable if you do not have redundancy built into the system (such as with an X8 configuration).