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Thread: Testing, Testing 1,2 ...

  1. #51
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    Exclamation

    When I hired in to GMPG, they had a machine in addition to the Chevy VHF in Warren) loaded by pumping water in and out of tanks to alter loads. I also remember a Lotus rig that Jack Turner (r.i.p.) ordered for the Chevy P.G. garage. We really needed Mz compliance steer. AND, the machine came unequipped to do it. What a farce.

    Turns out we gave the machine away because no one wanted it. Used for vehicle storage and wheel alignment. As in: Lotus never considered ENF as a player in handling. WTF... From the statistics of their car measurements, they still don't !

  2. #52
    Bill,

    Thanks for the presentation. My original question was, what is the difference between the three different tests (in terms of what it tells us, not how its measured) 1. Lateral toe compliance 0mm offset 2. Lateral toe compliance Xmm offset 3. Mz Compliance.

    And more specifically, why would we want to look at the 'pure Mz' or 'pure lateral force' graphs as opposed to 'lateral force offset', which would induce a force + moment simultaneously.

    I attached some real KnC data from our previous car for the above tests (in-phase). I'm trying to figure out how to utilize it, and more importantly, understand it.

    fy_toe_0mm_trail_fl.JPG
    fy_toe_0mm_trail_fr.JPG
    fy_toe_15mm_trail_fl.JPG
    fy_toe_15mm_trail_fr.JPG
    mz_toe_fl.JPG

  3. #53
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    Quote Originally Posted by Crop View Post
    ...what is the difference between the three different tests...
    You may need to go back to the rig operator to really understand what was tested? Based on experience, I think I can guess, but that isn't good enough. K&C measurements depend on precise definitions of force/moment application and measurement locations. Best to witness a test and discuss details with the operator.

    What I take from your plots: it looks like this car has nearly +/- 0.2 degrees of free-play (slop) at the front wheels, which is way too much. Time for some mechanical detective work to find out what is loose! And fix it. Don't feel bad, I've judged a number of cars at Competition with a similar problem.

  4. #54
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    K & C Testing Issues

    The Fy input at "Zero Offset" I presume to mean that the force is applied at the wheel plate directly below the spindle center point at "the Ground"

    The measurements pick out the separate steer and camber effects from this applied force (same on both ground patches of the axle). This gives you EYF, GYF, EYR, and GYR. The you apply the Mz moments on the wheel plates and record ENF, GNF, ENR and GNR traces.

    The next bridge you must cross is the assumption that superposition of all of these rotations and displacements is valid and in realistic load ranges. In some cases it is not, but there are ways to map the actual functional relationship for a MIMO mechanism.

    I have no clue as to why you would use a presumed offset of 115 mm. That's a lot off mm (certainly not any kind of 'pneumatic trail' effect).

    On another page, Where are these measurements being done and who is processing the data ? Not any facility I'm used to seeing. Is that Excel output? What's up with the sign convention Fy to the right should be positive, not negative. Also, it looks to me like the steer channel is of the wheel plate [Earth] and not the wheel based on the hysteresis signature.

    Plus the FY steer traces are not typical, as in soggy wheel bearings, etc. Sut wit dat ?

    If you have the actual raw data available to you, it's time to produce more relevant, zoomed data fitted to data models.

    I can help with this if you need a jump start.

    Then all you need to do is add up the compliances form each mechanical path (CAF + EYF + GYF + ENF + GNF + EPF + NF) into Front Cornering Compliance and then (CAR + EYR + GYR + ENR + GNR + EPR + NR) into Rear Cornering Compliance and do the integration. . There will need to be a little iteration loop defined to solve for the common slip angle that balances the forces and moments at each slip angle, but, as in Nature, all this works out
    Some geeks go with a matrix inversion process to solve this dilemma, but I recommend an analog solution done with a small delta time step. I don't believe Mother Nature utilizes a matrix inversion process in the nonlinear physics of a Newtonian Universe.

  5. #55
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    Morse Code

    Yep, I thought I recognized Morse Measurements results...aligning_torque.jpg
    Last edited by BillCobb; 03-08-2020 at 09:19 PM. Reason: add the iamge

  6. #56
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    MM or ABM

    Quote Originally Posted by BillCobb View Post
    Yep, I thought I recognized Morse Measurements results...Attachment 1369
    Or is this an Anthony Best result ???20200310_204032.jpg

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