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Thread: Plotting Cn-Cy and Cn-Ay Graphs.

  1. #61
    Quote Originally Posted by Claude Rouelle View Post
    At OptimumG we always take r into account
    Yeah, r is taken into account. But I guess the point of my input was to highlight that r (chassis rotational velocity) does not equal ay/V, or even an/V. Omega (the rotational velocity of the velocity tangent direction) does is equal to an/V, and to find r from omega you need to remove the body slip velocity. So yeah, you can take r into account, but you need to ensure you have the right value of r.

    Also, while small angle approximations might make sense if calculating the slip angles once or twice, I would hazard to suggest that if you are going to determine a Cn-Ay or Az-An diagram it may be worth the extra computational expense to make use of proper cosines et al.

  2. #62
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    Yes and Yes

    Steady State: Beta-dot ~ zero. Race tires: Mu max ~ 3-4 degrees slip. Cosine / Sine inclusion should not be costing you that much extra computational overhead.

    If you use Matlab, ask the PROFILE and PROFILE VIEWER functions to show you where all the cycles are being spent. Then 'fix' the heavy hitters.

    For example, I use Watcom Fortran modules to do the heavy lifting in Matlab, driven by a pre- and post- processing GUI foundation.

  3. #63

    Why a slip angle sensor could be useful

    Yes many students (and engineers) mix yaw velocity and slip angle velocity (Beta dot)
    Yaw velocity r = V/R is correct because the slip angle speed (beta dot) is = 0 because in steady state Beta is constant
    The gyro captures everything: the total of V/R AND Beta dot but doesn't tell you what part if yaw velocity due to V
    /R and what part is from Beta dot. To do that you need a slip angle sensor.
    Claude Rouelle
    OptimumG president
    Vehicle Dynamics & Race Car Engineering
    Training / Consulting / Simulation Software
    FS & FSAE design judge USA / Canada / UK / Germany / Spain / Italy / China / Brazil / Australia
    [url]www.optimumg.com[/u

  4. #64

    Slip angle sensors

    In the last FSG Electrical design final I judged half of the cars did have slip angle sensors.
    Claude Rouelle
    OptimumG president
    Vehicle Dynamics & Race Car Engineering
    Training / Consulting / Simulation Software
    FS & FSAE design judge USA / Canada / UK / Germany / Spain / Italy / China / Brazil / Australia
    [url]www.optimumg.com[/u

  5. #65
    Bill,

    Answering your question that was posted in the wrong thread (Mumbai seminar)

    Most of the teams used the slip angle sensor either to validate their vehicle simulation and/or use its signal in the control loop of their 4WD torque vectoring / traction control / launch control .
    In one hour of judging I could not go in the details of each team use of theit slip angle sensor.
    I would say that for one third of them the slip angle sensor was used as a BS smoke bomb, just a kind of show off with no substance (but I bet they will be much better this year - you always need a first time), one third was REALLY good - the guys know what they are doing - and the rest was in between.
    I know that is a generic answer but for more we would need more than a FSAE thread: a seminar, a webinar or a complete PDF report - which most FS teams are not good at.

    Claude

  6. #66
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    Hanging on by a thread

    I posted my question on the Mumbai thread so as to not bump your seminar announcement.

    Since as you say, there are some teams with a sideslip sensor, there should be a subset of them who can also sense yaw velocity and forward speed: all the elements of a perfect storm of test data suitable for evaluating their handling models on a professional level. Maybe even steering shaft angle.

    Add a few slides on how and where to mount these devices, sample rates, power needs and an example test procedure. THEN the seeds you plant now will flourish and be ripe and ready for picking next year, too. It's long overdue. I can see why some teams would not want to publish their results, but all it takes is ONE and the gates will open up.

    (Maybe you already have this in the Program, but it sure would be nice to have a Forum thread with some meat in it for once instead of just bones and half baked bread).

  7. #67
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    Claude and Rory,

    Both TOO SLOPPY!!!

    NO DEFINITIONS!!! Why such negligence?

    Too much alphabet-soup, with too much of the extra-strong Cottage-Industry flavouring, and negligible attempt to give even the vaguest hint of what the little noodles represent. (Rory, should the noodles spell "BSAV", or "BVAS", or "BodySlipVelocity" as in the graph-headers???)

    No wonder the students struggle with this.

    Quite obvious that the students should struggle, given that both descriptions (C's and R's) are conflating Point-Mass-(or Particle)-Mechanics with Planar-Rigid-Body-Mechanics, with nary any attempt to explain which noodles apply to what Mechanics.

    For example, it should be abundantly clear that a point-mass CANNOT HAVE A YAW-VELOCITY (as was suggested in C's RCE1 article), let alone a Yaw-Angle or Yaw-Acceleration. (Read Euclid's "Elements", Book 1, Page 1, Definition 1, to find out why.)

    So why mix the noodles from the two different fields of Mechanics into the same equation, and then pretend that this is in any way helpful to understanding? Oh yes, I know. It is because stirring the noodles in the alphabet-soup is FUN, and you can keep doing it forever, without going anywhere...

    Moving on, from Claude in an earlier post:

    The gyro captures everything: the total of V/R AND Beta-dot, but doesn't tell you what part is yaw velocity due to V/R and what part is from Beta dot. To do that you need a slip angle sensor.
    (My added punctuation and spelling correction.)

    Geez, I explained this to you 15+ years ago! YOU DO NOT NEED A GYRO, OR A SLIP-ANGLE SENSOR, to track the full 3-D motion of the car-body, WRT "the fixed stars", or wrt an approximate "ground reference frame", or "the track", or possibly Rory's "X,Y frame", but I can only guess at that last one because it was never DEFINED.

    I have to wonder if Claude has shares in the company that sells those EXPEN$IVE $en$or$. It can all be done much more cheaply, more easily...

    Z

  8. #68

    Cheap Z

    If you can do a cheap and accurate slip angle sensor then just do it, Z!

    And no I do not have any ownership in any slip angle sensor companies.


    What I can tell you is that no one of these teams in FSG E did pay for their slip angle sensor: they make a technical partnership and a knowledge exchange. Companies that manufacture such sensor do like to have students telling them what they do not understand and they like out-of-the-box most of the time very useful observations.

    I just know the benefit of using it. Just think as an example about traction control and the exact measurement of slip ratio.

    I also know that most OZ teams even if they had one free of charge won't know what to do with it.
    Most of them have much bigger and simpler challenge like reliability just to name one.
    The top OZ teams could use it if they had the sense of the level of competition of excellence that is now required in the international world of FS competitions

    On that perspective: on one hand you help - very well- students getting back to the more than necessary basics but on the other hand with your ideal ultra simplistic car, your lack of international experience, your lack of proven records on the race car engineering international scene, you discourage them to be a touch more sophisticated and competitive on the knowledge and on the tracks outside Australia.

    OZ FS team have lost the competitive advantage they had 10 years ago and I have to wonder what part you played in that loss.
    Claude Rouelle
    OptimumG president
    Vehicle Dynamics & Race Car Engineering
    Training / Consulting / Simulation Software
    FS & FSAE design judge USA / Canada / UK / Germany / Spain / Italy / China / Brazil / Australia
    [url]www.optimumg.com[/u

  9. #69
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    That was kind of an unfortunate response, Claude. Insulting OZ student teams with the hope of blaming Z for their perceived lack of success does not speak well of you. You could have just as easily engaged Z in a more positive manner, and those following this thread
    would benefit from the resulting discussion.

  10. #70
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    Slipping by...

    experientia magistra est difficile.

    And from 1999: 00426903.jpg

    we are looking at sideslip angles on the order of 1.5 to 2.5 degrees per g, read at this mounting location between 0 and 2 g. Things are a better now, but this Datron was state of the art 20 years ago.

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