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Thread: Discrepancies in Tire Test Data Matlab Plots

  1. #1

    Discrepancies in Tire Test Data Matlab Plots

    Hello everyone,

    I am a member of Michigan Tech's FSAE team and am attempting to more effectively integrate tire data into our chassis/suspension design process using TTC data.

    To accomplish this, I have decided to use a Matlab live script, which was made available to students via the MathWorks RacingLounge (https://blogs.mathworks.com/racing-l...ing-tire-data/) as a first step. The intention was that this code would lay the groundwork for a more in depth analysis down the road by allowing a time efficient comparison of key characteristics of different tire models in rounds 6, 7, and 8. I realize that tire analysis is infinitely more complex than Fx vs. SR and Fy vs. SA but it's a starting point.

    The code itself runs, plots the data, returns coefficients for the Pacejka magic formula, and directly takes .mat run files as available in TTC rounds 6 and onwards, however a few key issues came up that I was hoping to get some feedback on:

    1) When I plot lateral tests (both the test files provided with the code, and cornering tests from TTC Round 8 for instance) the plot x-axis label shows SA, however the values themselves range from approximately +/- 0.4. Initially I assumed these to be in radians, however the TTC data specifies that for the given cornering test file that I plotted, SA is only swept from +/- 12 deg.

    2) When plotting lateral tests using the code, the Pacejka approximation deviates quite significantly at the origin (I have attached some lateral runs to illustrate this). The approximation improves for higher SA values.

    3) When using the live script to plot longitudinal runs, this discrepancy at the origin does not appear - however while the matlab code approximations for the test file provided with the tool are quite close, when I use the code to plot longitudinal data taken from DriveBrake files in Round 6 of testing for instance, the approximations deviate quite significantly from the raw data at higher SR's. In addition to this, the TTC documentation specifies that the SR for the DriveBrake test in question only varied +/- 0.2, while the Matlab tool shows data in the ranges of +/- 0.3 - 0.5 for SR's. This is also shown in the longitudinal plots I attached.

    I have been unable to figure out why this is the case, and was hoping someone on this forum might have some input. I have not dealt with Pacejka approximations much, so is there something I might be missing that makes the plots outputted by the code plausible?

    Have others run into similar issues by chance? Is it possible that any of these issues stem from aspects of the tire tests themselves and are not inherently a coding issue?

    Cheers, and thanks for the help!

  2. #2
    Senior Member
    Join Date
    Mar 2008
    Brighton, MI

    Pacejka Lounge

    What happens in the Lounge should stay in the lounge. It is obviously flawed. SNAFU.

    I can and will help you with this, but the conversation must take place in the TTC forum, otherwise Gods of Rubber Duckville will have a shit fit.

    I've left a reply message for you there..

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