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Thread: uNav INS

  1. #701
    Senior Member+ mjs513's Avatar
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    @brtaylor - @Don Kelly

    Looks like its working. Getting a nice steady Yaw most of the time when not moving. I added a option to zero the gyro when I start seeing yaw drifting. Use it once or twice after starting the Filter and yaw stays steady. If moving there doesn't seem to be problem with yaw.

  2. #702
    Senior Member brtaylor's Avatar
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    Quote Originally Posted by mjs513 View Post
    @brtaylor - @Don Kelly

    Looks like its working. Getting a nice steady Yaw most of the time when not moving. I added a option to zero the gyro when I start seeing yaw drifting. Use it once or twice after starting the Filter and yaw stays steady. If moving there doesn't seem to be problem with yaw.
    Great to hear! Yeah, with the platforms I've been testing for, they're always moving some.

  3. #703
    Quote Originally Posted by Don Kelly View Post
    Willie.from.texas,
    Where are you in TX? I'm in SE Houston. Don
    I'm about 30 miles south of Dallas, in a little town called Midlothian.

  4. #704
    How to choose these parameters? Are there any methods and skills
    // Sensor variances (as standard deviation) and models (tau)
    float aNoiseSigma_mps2 = 0.05f; // Std dev of Accelerometer Wide Band Noise (m/s^2)
    float aMarkovSigma_mps2 = 0.01f; // Std dev of Accelerometer Markov Bias
    float aMarkovTau_s = 100.0f; // Correlation time or time constant

    float wNoiseSigma_rps = 0.00175f; // Std dev of rotation rate output noise (rad/s)
    float wMarkovSigma_rps = 0.00025; // Std dev of correlated rotation rate bias
    float wMarkovTau_s = 50.0f; // Correlati1on time or time constant

    float pNoiseSigma_NE_m = 3.0f; // GPS measurement noise std dev (m)
    float pNoiseSigma_D_m = 6.0f; // GPS measurement noise std dev (m)

    float vNoiseSigma_NE_mps = 0.5f; // GPS measurement noise std dev (m/s)
    float vNoiseSigma_D_mps = 1.0f; // GPS measurement noise std dev (m/s)

  5. #705
    Senior Member+ mjs513's Avatar
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    For me i usually do a web search but you will have to get an understanding of noise and standard deviation. Heres a couple of references:


    Those values seem to work fairly well for me with a T4.0, MPU9250 and a Ublox Zed-F9P.

    ALso sometimes what i do is just to tweak the numbers and see what they do.

  6. #706

    thank you

    Quote Originally Posted by mjs513 View Post
    For me i usually do a web search but you will have to get an understanding of noise and standard deviation. Heres a couple of references:


    Those values seem to work fairly well for me with a T4.0, MPU9250 and a Ublox Zed-F9P.

    ALso sometimes what i do is just to tweak the numbers and see what they do.
    thank you for your reply!!

  7. #707
    Senior Member+ mjs513's Avatar
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    Quote Originally Posted by brtaylor View Post
    Attached is a zip of the corrected code. It was being used with some CMake build tools, but should be easy enough to get it working as an Arduino library. Requires Eigen.

    Yaw tracking has been good while moving. Here is a plot of a test I did where I was walking on a north-south aligned street and compared the EKF results with the DJI A3 flight control system, a VN-200 and a VN-300. The EKF was using an MPU-9250 IMU (hence the label) and a F9P GNSS receiver. The weird data dropouts on the VN-300, I think were due to a specific cable - this test was performed in February and in April, I tried to reproduce the data dropouts to debug with VectorNav engineers, but couldn't reproduce the issue, which is why I think it was an intermittent cabling fault between the Teensy and the VN-300. Prior to this test, all of the filters were warmed up by moving the platform in pitch, roll, heading circles and changing position for about 5 - 10 minutes.
    @brtaylor
    Well finally got the whole test bed set up with a simple logger and a button to end logging and close the file.

    Plot is a bit confusing but put a little plot of the lat/long from google maps. Basically started of pointing North (approx) and let it run for a little bit, the did a turn to point to about west, the picked it up and moved to the East - walked backward so still point west then walked forward a couple of time, then turned walked north - then south backwards a couple of time. The pitch down was intentional to act as marker for when I started the walk.

    Test really started about 90s in. Ok walked outside with a compass and the angles are about right.
    Click image for larger version. 

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  8. #708
    Senior Member brtaylor's Avatar
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    Quote Originally Posted by mjs513 View Post
    @brtaylor
    Well finally got the whole test bed set up with a simple logger and a button to end logging and close the file.

    Plot is a bit confusing but put a little plot of the lat/long from google maps. Basically started of pointing North (approx) and let it run for a little bit, the did a turn to point to about west, the picked it up and moved to the East - walked backward so still point west then walked forward a couple of time, then turned walked north - then south backwards a couple of time. The pitch down was intentional to act as marker for when I started the walk.

    Test really started about 90s in. Ok walked outside with a compass and the angles are about right.
    Click image for larger version. 

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ID:	20755
    Thanks for posting! I'm going to have to think through this a bit more.

  9. #709
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    Maybe this will make it a bit clearer, added some notes along the test curve:
    Click image for larger version. 

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  10. #710
    who research on Visual navigation aid GPS/INS, can you provide some reference materials?

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