title_body: Drone with SDR for HF antenna field strength measurements, I need a Raspberry Pi based drone kit that I can just buy
upvoted_answer: You might check out this video on using a Pixhawk and a rPi with Python.  The video just walks you through the serial connection and some Python code for basic control.  The Pixhawk is doing all the real time control (Linux isn't good for that part) and the rPi is talking to it over a serial port.
  You might also look at the MicroHawk reference in:  Do drones with inflight API access for control inputs exist? (although the link seems to be broken at the moment).