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Quadrotor Digital PID Control System and Dynamics Modelling

Posted by James Goppert on March 16, 2011 at 4:30pm

A digital control system model of the pixhawk quadrotor was constructed in scicoslab along with a continuous model of the quadrotor dynamics (the visual model is an arducopter). The user can input the guidance commands to the autopilot through sliders. As the video shows, the yaw response it not optimal, which also happens in the actual system. Using the mavsim Scicoslab toolbox (https://github.com/openmav/mavsim/) , the model can be simulated and then, once the system has been correctly identified, the dynamics can be linearized. The linear model of the system makes the problematic modes clear and aids in designing an improved controller.

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Comments

  • Developer
    James Goppert March 19, 2011 at 5:46pm
    Here is how to install: https://github.com/openmav/mavsim/wiki/Build-from-Source
    Its best to build from source since I haven't included all the quad stuff in the deb package yet. It's easy to build on ubuntu/ debian though.

    Ixx, Iyy, Izz for the pixhawk team since we don't have the 3d cad model yet we just approximated using a solid sphere 8cm radius approx. with parallel axis theorm to offset the cm below the motors. 3d modelling software obviously would be the best way.
  • Hyon Lim March 19, 2011 at 5:36pm

    @James,

    I'd like to install and test. Can you explain the procedures simply?

    I'm familiar with Ubuntu.

    And how did you get the model parameter like Ixx,Iyy,Izz?

     

    @Roy,
    You're welcome. But parameter selection article may be by kostalexis?


    @kostalexis
    What parameter do you mean? Can you send me the papers that you collected
    about the mentioned subject?

  • Developer
    James Goppert March 19, 2011 at 3:41pm

    The mavsim scicoslab toolbox provides communication with the jsbsim flight dynamics, and hardware in the loop via the mavlink protocol. This was written in C++ so you would have to compile those parts on windows. The openscenegraph part is already optional. I just don't have any good windows testers so far. You would have to install cmake and I'd help you through the obstacles.

     

    The current dynamics have been verified by the pixhawk guys and these gains flew on their quadrotor. The force models were based on various papers. You can find all the equations in mavsim/theory.

  • Roy Brewer March 19, 2011 at 3:15pm
    @Hyon Lim, thanks for the Maciejowski reference. I was familiar with his multivariable control book, but not his MPC one.

    I'd also be interested in the optimal parameter selection articles, if you don't mind my asking.

    @UFO-MAN, James,

    I am also interested in using scicoslab on Windows to model and design quadrotor controls. Both scicoslab and FlightGear run on windows. If I can live without the fancy graphics, can I skip the linux?

    @James,
    What did you base the quadrotor model on? Has it been validated against a real world quad?

    Thanks everyone
    Roy
  • UFO-MAN March 19, 2011 at 1:43pm

    Aha ...  then I should be able to get this flying over UDP/IP!

     

    Will report back later.

  • Developer
    James Goppert March 19, 2011 at 1:40pm
    I am using a udp instead of tcp/ip, but yes. The socket communication can talk to any host. If you click on the jsbsimcomm block you can specify hostname:port. So as long as it doesn't have trouble going through the vbox it should work. I run flightgear on other workstations in our network all the time. To setup flightgear for this type of communication you can take a look at the script in mavsim/scripts/fgrunExt.sh. You should be able to setup most of that in your flight gear configuration file.
  • UFO-MAN March 19, 2011 at 1:27pm
    By the way, can the link between Mavsim and Flightgear be run on a TCP/IP socket? Isn't that the way it operates anyway? If it is the idea in the last post should work. I could even run Flightgear on another box here.
  • UFO-MAN March 19, 2011 at 1:26pm

    Yo!

     

    Flightgear seems like it sux a bit in terms of execution speed under Vbox. Even with 3D acceleration enabled.

     

    Perhaps it's better to run Flightgear under native XP so it has direct access to the graphics hw. Then the Mavsim stuff could run on the VM. I may try that.

     

    ufo

  • Developer
    James Goppert March 19, 2011 at 1:19pm
    @ UFO-MAN good luck, make sure you have your graphics card enabled in virtual box. If you get something that works well let me know and I will host a virtual-box for mavsim. Mavsim will work without flightgear and will allow flightgear to run non-realtime via the external fdm protocol (jsbsimcomm block), so the speed shouldn't be critical, but annoying. Worst case you could dual boot :-).
  • UFO-MAN March 19, 2011 at 12:59pm

    Hi James.

     

    I have been installing just that since my posting earlier today :)  I installed Ubuntu on Virtual Box and is in the process of installing Flightgear with Synaptic now. I will have to evaluate the performance, as it looks a bit (ehh. very...) slow. However so far the install procedure looks like its flying.

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