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Thread: Lapsim by bosch

  1. #1
    Hi,

    i am playing with lapsim since some days and i have seen that it uses a particular tyre model with a short pacejka set of coefficients.

    Some time ago, BillCobb said that it is actually possible to find from tyre data the coefficients to model the tyre in lapsim way.

    Lapsim Vehicle and tyre parameters can be opened with matlab. So if anybody knows how to extrapolate this coefficients we could play around with a free lapsim.

    I have seen, in particulare, that the coefficients the software has inside seem to be not so much sensitive to load. So, for example, you change track lenghts and/or CG height, results doesn't change so much.
    But, the same changes produce a sensible difference in maximum cornering performance estimated with a corner simulation i made in matlab..

    Anybody can help?

    Maybe this is a question for Bill...

  2. #2
    Senior Member
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    I believe I posted the code for the Lapsim tire fitting routine on the TTC site. In fact, it produces coefficients for additional surfaces (some of which Lapsim doesn't use, but are useful for other non-Lapsim modeling, synthesis and analysis projects.

    I'll go see where I stashed it...

  3. #3
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    I put some files out on the TTC forum for you to work with. One is a GUI to show you what the 4 terms do to the tire Fy characteristics.

    The other file uses the 4 term model to compute the 4 term FY, MZ and MX coefficients from TTC data. Lapsim does not use the MZ or MX data, but you SHOULD.

    Note that I've used this tire model to perform some rudimentary vehicle testing on a FSAE sample car in an ISO procedure. This Matlab model is also posted in that forum. The point is that this type of analysis should be guiding your vehicle parameter specifications and tire selection process.

  4. #4
    I know your posts with example of how to work in matlab on tire dta. I found them very useful.

    I actually have done a simple constant radius cornering sim to find maximum grip and the effect on cornering perforamnce of car parameters, considering also Mz (not Mx for now).

    And i have seen that where there is no difference with lapsim, i see differences in maximum lateral acceleration performed by my model.

    Is this something that makes sense to you?
    Do you know how lapsim find cornering performance at the apex? Because it is very fast in finding a lap solution, doesn't seem to iterate till a convergnece point.

  5. #5
    Don't know specifically how Bosch's software works.

    You could always write your own lap time simulation program, won't take more than a couple days.

  6. #6
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    Run your model without including Mz effects. Ruud feels that Mz effects are very small at max lateral g, but that's usually not the case because of the net rigid body aligning moment.

    While tires are usually insensitive to slip angle changes at max lat, weight transfer and camber influences are still strong players. Implementation of these factors would produce a difference.

    BTW: Differences are good. Findings of no difference would make me suspicious of the model. There may be effects caused by the use of the free version vs. the purchased version, too.

  7. #7
    it won't take more than a couple of days if you know how to do it!

    I hae not so much time at the moment, but just now i don't know the logic behind the driving the car around a lap.

    Till now i have only iterated on a corner, but lapsim seems to find cornering sped and accelerations at the apex like if it was something given immediately by a formula..

  8. #8
    Anybody has experience on doing a lap simulation?

    Or anybody can direct me on something about it?

    I guess the first step is to find, as i said, minimum corner speed, and then to elaborate the rest, but what about the way to do it and what, for example, about braking points etc?

  9. #9
    There are corners, and there are straights. Sounds like you have the corner part down.

    In a straight, there's acceleration and there's braking. Make something simple for each, then think about how to splice them together.

    Then figure out how to splice a corner onto either end.

  10. #10
    http: //fsae .com/ eve/forums/a/tpc/f/125607348/m/217101453?r=31620500941#31620500941

    Read this post from the "Reasoning your way through the FSAE design process" thread.
    San Jose State University

    FSAE Chassis and Ergonomics Lead '12-'13
    FSAE Chief Engineer '11-'12
    FSAE Chassis Technical Lead '10-'11
    Formula Hybrid Chassis Grunt '09-'10

    "A designer knows he has achieved perfection not when there is nothing le

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