I'm working on a project with a Pixhawk on a DJI Phantom. We substituted the proprietary NAZA controller with the Pixhawk because we want to edit the firmware, adding new sensors and changing the way to control it. We need to interface the Pixhawk with an Arduino, because we're trying to automate the landing through ultrasonic sensors and Pixhawk seems to be limited on the number of sensors. So our idea is to read the sensors through the arduino and send data to Pixhawk through the serial port.
At the moment I just found how to hardware interface them ( http://forum.arduino.cc/index.php?topic=188222.5;wap2 ) and what to write on the Arduino to let it send data through serial (TX, RX pins), but I have no idea about what to write on the Pixhawk firmware and, above all, where.
Hope someone can help me, once the landing system will be ready I'll post all the codes and the documentation I can.