Men built the tower of babel to reach the heaven, then it all fell down and everyone started talking different languages and could not co-operate since they could not communicate. Now I am trying to reach some 10m above the ground with the quad-copter and ghosts of babel still haunt me. The arduino speaks PWM to the electronic speed controller, fine I can deal with that. I need to speak to the arduino, can't have 2 serials over radio on-board so I will speak to the arduino from the gumstix via i2c. So now I speak to the gumstix via serial and it can run the flight control and speak to the GPS and IMU over serial as well - it has 3 serial ports (UARTS). After all is said and done we have no more free ports left - how are we going to talk to the system while in flight ?
We will have to sacrifice the hardwired serial console to the gumstix (FFUART) and pass-it through a X-bee or similar. I could also shell out a few hundred and get a wireless chip enabled clipon board, but it will have much shorter range than the Zigbee.