The PCB has 8mm tracks for the main output and those tracks are filled with solder. Why? well ESCs could deliver huge amounts of current, over 20A. So with such a thin copper layer, solder was needed so the track won't burn out.
The drivers are duals, meanning each driver could control a pair of transistors. Driver are needed since the Arduino works at 5V and the MOSFETs at a voltage higher than 12V. Also, the design has back voltage diodes since the motor has coils and that could induce voltage spikes. The speed is controlled with a potentiometer. Next version, says EN that will have a PWM control just as any other commercial ESC.
Posted by Andrei