the engine does not start

[casari42]

Hello everyone, first of all I apologize for the bad English, but was translated by google translator. . My problem is that when I start the simulator arduino turns on the 2 red lights that signal that it is receiving data from the serial port, but the engine does not start . If I open the serial monitor and send commands such as R00 or L00 engines running etc. until the pot is not perfectly in the middle (this applies to both engines.) What can be the problem? thank you in advance for your answers. FYI.