Editing VNH5019 Library code to control three motors

I am a beginner who wants to control three DC motors using a dual VNH5019 motor driver shield and a single VNH5019 motor driver with UNO R3.
I wanted to edit the Arduino library for third motor and assigned pin numbers for it. Unfortunately, it did not work. As I do not know much about the MCU, I guessed that the following part might be changed:

#if defined(__AVR_ATmega168__)|| defined(__AVR_ATmega328P__) || defined(__AVR_ATmega32U4__) OCR1B = speed; #else

I looked at data sheet of ATmega328, but I did not understand about how OCR1A and OCR1B related to controlling the speed. :confused: I hope anyone can help me to get through this… thanks in advance!
P.S I’m not a native english speaker, excuse my grammar!


It would probably be easier to just control the third driver with PWM and digital pins from the Arduino rather than modify the library. You can use analogWrite() to generate the PWM signal you want.