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Thread: Presentations on Suspension Compliance Effects and How it Would Influence FSAE Cars.

  1. #1
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    Presentations on Suspension Compliance Effects and How it Would Influence FSAE Cars.


  2. #2
    Thank you very much Bill! Super interesting!

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    Far out that FSAE car from the K&C measurements is quite a mess.

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    Thank you Bill, this is really great, as always.

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    The REAL Findings:

    The best news from it is that Honda UK has an Anthony Best Dynamics SPMM (K&C) machine which was used to get FSAE car data. So now a strategy could be to beg, borrow, or steal some results from another car and compare it to results from a suspension analysis program (OptimumK, etc.

    Then, remain there until the obvious lash, slip, and sponge parts are 'fixed'. For this I would promise a BIG Honda sponsor decal.

    I still recommend putting a torque wrench and a protractor to work to pick the low hanging fruit for compliance minimization.

    Perhaps you noticed the way that some tires stand out as either superior or inferior for the task. The ability to set up a tire evaluation strategy and work it gets you 90% of the way to the best lap time. Presentation points to the max, too.

    I suspect no-one has contemplated different BRANDS of tires on front and rear axles, but the tire data suggests that would be a huge benefit.

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    Quote Originally Posted by BillCobb View Post
    ...Honda UK has an Anthony Best Dynamics SPMM (K&C) machine...
    Sorry to say, that SPMM was auctioned off last year and is being rebuilt for the new owners in Asia. Perhaps we'll see some K&C data from the updated rig...on a car from that side of the world?

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    Brilliant stuff Bill. Thanks for sharing.

    Ben
    Tyre Analysis Engineer - Caterham F1 Team
    Alumnus of University of Birmingham
    www.ubracing.co.uk and Formula Student Design Judge

  8. #8
    Thanks a lot Bill for your continuous contribution to the FSAE community!

  9. #9
    I've personally run about two dozen FSAE K&C tests for various teams over the years. I'm not sure many teams were ever really able to integrate the data into their designs. Mostly we just pulled out some really low hanging fruit like:

    "you have horrible rear toe compliance."

    and

    "that trick adjustable roll bar you made has no overall impact on your roll stiffness distribution"

    or

    "are your kinematics supposed to be completely asymmetric?"

    anyway, there are at least 4 Anthony Best K&C rigs in North America that dedicated students might be able to get time on. There are other options as well. Pretty much every auto or major tire manufacturer is going to have some facility or vendor for K&C tests.

    The hardest part of this is interpreting the data but there are some tricky bits in getting the vehicle onto the rig. FSAE cars are obviously a lot smaller than even A segment cars so everything gets pushed outside of how these rigs are intended to be used. this is especially true with 10" cars. I can see about getting Bill some slides on the specifics (my employer would need to sign off on this so no promises). Here are the rough challenges. I'm making these public so that if if anybody does get rig time the operators aren't starting from scratch. In general this stuff would still be useful for MTS or other rigs.

    - wheelbase. there are some provisions for removing the normally installed table extenders but unless you have a really long wheelbase car it's not worth bothering to do this. most of the SPMM units are 4 position machines (ie they test all 4 wheels) but you can also run them as 2 position machines (install the car, run your front tests. turn it around. run your rear tests). What we found was easiest was running the test in 4 position mode with an artificially long wheelbase and physically dragging the car back to test the rear position.

    - ride height. you need accurate corner loads and ride height measurements for the car + driver. as a bonus you want your reference points to be something you can easily measure with the front or rear wheels hanging off a cliff. What we'll do for the rig setup is clamp the car at the correct pitch angle and then just jog the car down until we get to the right static loads.

    - vehicle clamping surface. the ABD machines generally clamp to the pinch weld running the length of the rocker panels on unibody cars. For everything else (body on frame, monocoque, etc) you need an adapter. Angle iron running parallel to the vehicle center line works well. ideally you would have minimal intrusion into the ground plane because the more you've increased your ride height to get the car onto the rig the less stroke you'll have left for bounce and roll motions.

    - attaching the wheel adapters for the string encoders (or however else that machine measures wheel orientation. all these rigs are slightly different). ABD machines are designed for car bolt circles. If you're running centerlocks or a very small BCD or very small lugnuts be prepared to have a set of adapters made to convert from your bolt pattern to 3 x 100 mm.

    - immobilizing the steering wheel and locking the brakes.on a full size car I'm going to use a steering robot and an air cylinder for this. you'll have to workout your own solution to this. it doesn't have to be fancy. it could be some 2x4's and ratchet straps.

  10. #10
    It has been a decade or so, but Goodyear offered as a prize for winning the skid pad event of a day on their K&C testrig in Akron. Missouri S&T won time on the testrig around 2008 time frame. I asked about their take-a-ways from the testing. Conclusions were that joint compliance were minimal. The largest compliances were by far from the wheel rim (0.25 to 0.5 deg per G) and bearing/knuckle.
    I suspect teams could get the majority of compliance information useful to improving suspension analysis from well-constructed FEA models of wheel, suspensions components, and frames.

    For example, teams can accumulate joint compliance data from FEA or localized testing and add that compliance data to VI-Grade’s SuspensionGen tool which builds K&C curves for realtime simulation (driver in loop or laptime optimizations).
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