So I managed to resolve any issues with the motor power supply by applying a 12V wall power to the shield. After rewiring the motor connection to the shield according to the correct rotation direction, the movement commands were being sent successfully from the Pi, received on the Mega and the motors were running properly. I also managed to interface the opto-interruptor encoder for the BO Motors, which sucks like hell as I can only keep track of 10 degrees for every count for this encoder. So I will just add this to just keep track of the rotations and not use it any major way. So finally I will just add the encoder code for the 4 motors and close the project there. Next log should be the last. I have also updated the Github with the code and will be putting the final update to it too. Also 12V battery will be added and a final video will be posted.