Real time communication of quad with MATLAB

Posted by Nisal Hemadasa on March 3, 2015 at 6:25am

Hi all,

I'm using a 3DRobotics teletry kit and I'm trying to make my 3DR qaudcopter to communicate realtime with
MATLAB. Since the telemetry kit has a UART interface, I tried creating a serial object with baudrate 57600 in MATLAB.(I tried using fread, and fgets functions to read data in MATLAB) But the data 
that I receive in MATLAB is like if they were encyrted (refer the attachment). And ofcourse 3DR radio uses MAVLink protocol where packet encryption is done.

I don't know to decide whether the reason or for this is;
    - encryption of MAVLink data packets, or
    - mismatch of the format between the actual data received by the ground station and the serial object properties such as bit order, stop bit, parity bit,..etc ,

    -or something else.

I would be truly grateful for some advice and ideas to come out of this dead end.

Cheers

fread.JPG

fread_armed.JPG

gets_armed.JPG

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Replies

  • Bryan Galusha March 3, 2015 at 12:15pm

    The data is not encrypted it is just binary.  The MAVLink is a binary messaging protocol, and Matlab is expecting null terminated ASCII.  So to do what you propose you would need to bring in MAVLink parsing helper functions most likely into a realtime MEX function, and then pass readable data to Matlab.  It is doable, but definitely a significant amount of work.
    If you look in our code here:
    https://github.com/fightingwalrus/iGCS/blob/master/iGCS/Comm/Interf...

    The function consumeData: will be something similar to what you need.  It basically goes through byte by byte and uses mavlink_parse_char helper function to reconstruct the MAVLink message before it is passed on to the rest of the system using the handlePacket function.

    fightingwalrus/iGCS
    iOS Ground Control Station for drones. Contribute to fightingwalrus/iGCS development by creating an account on GitHub.
    • Nisal Hemadasa > Bryan Galusha March 5, 2015 at 12:32am

      Thanks a lot Bryan;

      " So to do what you propose you would need to bring in MAVLink parsing helper functions most likely into a realtime MEX function, and then pass readable data to Matlab."

      I've never tried something like this before. I would be truly grateful if you could give me some basic idea or an example of how to implement this, specially parsing MAVLink helper functions to Matlab.

    • Bryan Galusha > Nisal Hemadasa March 6, 2015 at 5:30pm

      Mathworks has some tutorials on how create mex files run through one and create some "hello world" type example:
      http://www.mathworks.com/help/matlab/write-cc-mex-files.html

      I would start with decoding the heartbeat as defined here:

      https://pixhawk.ethz.ch/mavlink/#HEARTBEAT

      I don't have a matlab license so I can't help too much beyond that,

      Bryan

This reply was deleted.