The C-30 ESC I got from Great Planes had a diode and 3 capacitors with it. The diode was a SK-506, so noted on the diode. I checked google and came up with it being a 5 amp schottky barrier rectifier. The purpose is to quiet the motor noise and make the ESC "slightly more efficent" and "reduce the ESC's operating temperature". Needs to be installed across the motor terminals with the "Bar" (anode) soldered to the + (positive) terminal, other end to the - (negative). As I recall it prevents back EMF to the ESC. You might do a search elsewhere on the web. I could tell you where to look but if I did the moderator said he would have to shoot me. Been there, did that. OOPs, had a reference to a zener diode, my mistake, removed it so there is no confusion.