Today I manage to repeat the setup that could command the robot base using the gamepad, via xbee. However the xbee modem is working in API mode. The message payload has three bytes, the first one is used to provide the signal of direction and speed, the second is the direction value and the third is the speed.
The results are much better compared to the older implementation using xbee AT mode. This may be due to the data structure that is now being used.
Now I will post pictures and videos of the completed robot at this point, as it will be unmounted to test the new arduino fio board, with the new 3.7v power supply.
I still want to test the robot behaviour when the coordinator is also sending messages to other modems.