David82:
Also, don't I also have to make sure the pots on the joystick are the same resistance as the pots that were originally on the speed controller?
It's a 100k pot. Looking at the schematics it's not simply connected to V+ and ground. There is a 100k resistor on the high side and a 10k connecting it to ground. So yeah it won't act the same unless the joystick pots are 100k. Or you change the resistors to compensate.