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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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  • Developer
    James Goppert March 19, 2011 at 12:28pm
    @ UFO-MAN, a virtual machine running the latest ubuntu or debian release is your best bet right now. We have mac almost working on cmake and mingw version for windows could be possible if we get some more interest.
  • Kostas Alexis March 19, 2011 at 4:38am

    @ Hyon_Lim

    I have experimentally implemented MPC in Quadrotors. You are right about the computational complexity but this is something that can be accomplished using model embedded CPUs. 

     

    @James Goppert

    I'll send you some articles on the topic of optimal parameter selection. Give me one day to collect. 

  • Birdeye March 19, 2011 at 3:36am
    Cool Project.

    http://birdeye.dk
  • Developer
    James Goppert March 18, 2011 at 3:38pm
    Sounds interesting. Any good papers you can point me to?
  • Kostas Alexis March 18, 2011 at 2:44am
    Well you could optimally select the different linearization points and guarantee smooth transition through Linear Matrix Inequality optimization. I have worked on something similar using Model Predictive Control on Quadrotors. I will check your code - thanks James!
  • Matthew Coleman March 17, 2011 at 3:44pm

    Now I am completely out of my depth but I did ask for it..

     

  • Developer
    James Goppert March 17, 2011 at 2:11pm
    Ahh, that's a good point. Since the state is continually evolving you would have to design an lqg control system for a set of dynamic states and then have a hybrid controller that would jump into those modes. Which would lead to transition problems, and good luck with gain scheduling. What I"m currently working on in mavsim is using linear quadratic output feedback optimization as described in lewis and stevens to optimize a given controller structure. This gives the best of both worlds, a simple, optimal design. However, unlike lqg it doesn't have the automatically robust phase margin. If you want to check this out see the linear quadratic script demo in mavsim.
  • Kostas Alexis March 17, 2011 at 1:55pm
    LQG is a linear controller and assumes that all states can be estimated through a LINEAR observer. On the contrary all quadrotors (and MAVs genearally) use Nonlinear Kalman Filters (mainly EKF). So do you think that designing - experimentally verifying an LQG is a straight-forward process?
  • Developer
    James Goppert March 17, 2011 at 10:37am
    The pixhawk guys are using a kalman filter for state estimation so the thought of using an lqg controller definetly crossed my mind. But for now I wanted to help them optimize their existing controller. Also tuning a linear quadratic regulator in the field is not an easy task and if you have any modelling errors they tend to not be as robust as classical designs. If we could integrate an LQR solver into the ground control station it might be more feasible.
  • Matthew Coleman March 17, 2011 at 12:03am

    Great work James.

    Have you thought of applying the aircraft model to a state space controller instead of PID?

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