It all work as expected when I use other motors but it doesn´t with the tamiya gearbox.
Strange it works with other motors. The Tamiya's are toy motors, and such as those usually take higher
PWM duty values before they start turning, but you seem to have that covered with
analogWrite(ENA,255);//start driving motorA
[BTW, you should use the '#' button to wrap your code].
Care to give a link for the h-bridge board.