Gearing for 9xl 18-20 cells

[captain harlock]

Sorry for keeping you waiting like that. Allow me to give you this suggestion: start form the smallest pinion and go up from there untill you find the most effecient ratio( one that gives you both speed and torque while keeping your system (whether brushless or brushed) at a moderate temp). For a Mod1 51 spur, use a pinion of the same module that has 10-11 teeth and start from there.