Hi all dear guys,I' m back after long time spent to work abroad, just to start again with more entusiasm.Ok, the question:- I have implemented succesfully a Kalman filtering for my stabilization IMU so I can get good outputs and results just from accelerometers and gyros.I read lots of material about stabilization, I doewnloaded premerlani 's documents, and ardupilot code (this one is really difficult to understand, to me).Forgetting about navigation, (I ll take care about it in the future) I want that my IMU must stabilize itself once on board of the rc modell.Could you please direct me or give me some useful tips to write code to stabilize the aricraft?I read about the sinecosine matrix, and I suppose that's the key, but, since I don't want to equip my plane with a GPS yet, I cannot get velocity value, so the matrix is really unuseful.Moreover, since I dont want to implement the navigation code, the tranformation from body frame refernce to earth frame refernce is still unuseful.Or, (please tell me if so) I thought...I can get velocity about the frame body of the aricraft simply intergating accelerometers outputs and getting the speed about the three axis.Could be it an idea?I know that acceleromers don t give good results if intergrated over time..Sorry if I missed some informations!thank you all in advanceBye!Dave
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Accelerometer signals contains deterministic and stochastic errors,
kalman filter can estimate these variables.
Integration of Acc emerges large errors and lots of noise,
not practical.
I am working on a similar project to you. It sounds to me like you got some good answers from Paul however the rest of us cant see them :) I was wondering If you could post what he sent you.
:) :) :)
Ok Paul, thank you for youzr answer.
Yes I have implemented a kalman filter on a 6 IMU board.
I read, searched, got crazy on this topic for almost 1 monnths and fnally I got it working (on the Table I mean...) Thanks to many conrtibutions by Tom Bycke, and other person I m proud to have calibrated, rewrote the code on a IMU.
Again, on the table it gives accurate results, but it never flow yet (the reason is: I m looking for a suitable airframe first).
Now you say that kalman filter is much better than DCM, ok. BUT, sorry to say tthat, if you say me "keep kalman", I don`t understand how to develop a PID (or simply a proportional controller) for govering ailerons and elevator.
Ryan gave me a great suggestion and he confirmed me the proportional equation that I should use to develop such controller.
BUT, still it is hard to me to understand HOW to implemente a aileron-elevator coupled action
You spoke about the DCM, ok, but now you are telling me to keep kalman.
Since kalman gives me onla acurate angle (pitch roll and ywa) it doesn`t take in account other effects, such as elevator compensation during a steady turn.
In the firts draft, Bill premerlani spoke about the first UAV board (with dof, the ET312) and at the time he developed simply another proportional controller for correcting picth durign turns. BUT he said also that solution was a bit... "rough".
And now I don`t understand whether should I use DCM for correcting pitch or using kalman outputs and another kind of controller..
That`s all :(
I thank you again for your patience and your explanation.
I never gave importance to DCM before your siggestions :)
Well there a lot of things to you can try but the best is to have a groundstation set up so you can watch the estimated angles as it flys. Most likely you will have missed a negative sign or misplaced some much needed equations. If you don't have a ground station you can try the feedback of control trick but if it departs you don't really know why. Tuning an IMU in flight involves using some common sense but with out any information as to what it is doing its almost impossible.
Replies
kalman filter can estimate these variables.
Integration of Acc emerges large errors and lots of noise,
not practical.
you can have a look to this link
http://www.voidpointer.de/rsimu/index_en.html
the autor deals also with the autopilot code and made same improvements (error correction).
Paul
I am working on a similar project to you. It sounds to me like you got some good answers from Paul however the rest of us cant see them :) I was wondering If you could post what he sent you.
Cheers,
Will
Ok Paul, thank you for youzr answer.
Yes I have implemented a kalman filter on a 6 IMU board.
I read, searched, got crazy on this topic for almost 1 monnths and fnally I got it working (on the Table I mean...) Thanks to many conrtibutions by Tom Bycke, and other person I m proud to have calibrated, rewrote the code on a IMU.
Again, on the table it gives accurate results, but it never flow yet (the reason is: I m looking for a suitable airframe first).
Now you say that kalman filter is much better than DCM, ok. BUT, sorry to say tthat, if you say me "keep kalman", I don`t understand how to develop a PID (or simply a proportional controller) for govering ailerons and elevator.
Ryan gave me a great suggestion and he confirmed me the proportional equation that I should use to develop such controller.
BUT, still it is hard to me to understand HOW to implemente a aileron-elevator coupled action
You spoke about the DCM, ok, but now you are telling me to keep kalman.
Since kalman gives me onla acurate angle (pitch roll and ywa) it doesn`t take in account other effects, such as elevator compensation during a steady turn.
In the firts draft, Bill premerlani spoke about the first UAV board (with dof, the ET312) and at the time he developed simply another proportional controller for correcting picth durign turns. BUT he said also that solution was a bit... "rough".
And now I don`t understand whether should I use DCM for correcting pitch or using kalman outputs and another kind of controller..
That`s all :(
I thank you again for your patience and your explanation.
I never gave importance to DCM before your siggestions :)
Thank you
Dave