[Al Skierkiewicz]

Bob and Alex,
In the absence of actual conversion in your code, the speed controllers are capable of "learning" the joystick values from PWM input for full forward and full reverse and will use the center position to set brake/coast mode and zero throttle. Since most resistors in joysticks are +/-20% accurate minimum, if you pass joystick values directly to the controllers, they will not match what was set at the factory. In that case, full throttle may not be achieved, motors will not come to rest when the joystick is centered, etc. Hobby PWM uses values of 0 indicate full throttle in one direction, 254 full throttle in the other direction and 127 for zero throttle.