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Thread: Steering Geometry, Fore of Aft Rack position/ Steering arm length

  1. #1

    Steering Geometry, Fore or Aft Rack position/ Steering arm length

    Hello,

    Currently, I'm working on our steering geometry.

    I assumed the turning radius to be 3.5 m ( the min Radius in the autocross) then i calculated turn angle of the wheel on the inside of the turn and then Rack travel.

    Here are the results:

    maximum turn θi 28.99138701 deg
    steering wheel movement 180
    Steering Ratio S.R 6.208740546
    Steering Wheel Radius r 130 mm
    The steering wheel travel for one complete rotation 817.1428571 mm
    Rack travel L 131.6116934 mm

    I Need to know are these results reasonable for a FSAE Racing Car?


    Also, I need to apply 80% Ackerman and i need to know how to measure the steering arm length and also need to know which is better fore or aft rack position?

    Thanks in advance,
    .................................................. ...............
    Last edited by mohamedabolezz; 02-05-2018 at 07:52 AM.
    Mohamed Abolezz
    Helwan University, Egypt
    HFS Racing Team | Team Captain

  2. #2
    Senior Member
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    Steering Committee

    The required steer arm length will depend on the steering gear's effective pinion radius (presuming you will use a R&P gear). The S.R. is (for all practical purposes) the ratio of the steer arm length to the pinion radius. Now go figure.

    As far as leading or trailing tie rods, ask yourself whether it is better to pull on a chain or push on one. (and why this analogy applies).

    Hopefully your Ackermann fraction was determined by taking into consideration the properties of the tire you have selected as well as the minimum turn radius requirement.

  3. #3

    Usefulness Vs precision....

    Mohamed,

    maximum turn θi 28.99138701 deg
    Steering Ratio S.R 6.208740546
    The steering wheel travel for one complete rotation 817.1428571 mm
    Rack travel L 131.6116934 mm

    You just made a classical mistake that irritates design judges. At least it irritates me: do you need that many digits after the "."?

    One more comment: make sure you calculate the steering torque. It is an usual other FS mistake. Try to stay under 5 Nm. On passenger cars the maximum steering torque at the wheel is about 3 Nm.
    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. #4
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    Claude,

    Thank you for that. I wanted to say the same, but have only just stopped banging my head on the wall. How anyone could spend all that time typing in all those numbers, and not see the STUPIDITY of it, is beyond me!
    ~o0o~

    Mohamed,

    Do you realize how expensive it would be to manufacture a rack to 0.1 NANOMETRE PRECISION? Is that even possible???

    So please enter a new post with sensible numbers.

    Also, what do you mean by "turning radius"? Is it from corner-centre to car-CG? Or to inner-wheel? Or to outside of outermost-wheel (= "between curbs")? Or "between walls"?

    And what is your definition of "Ackermann"?

    Z

  5. #5
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    Pie in the Sky

    You ought to know that your value for Pi is low, too. Try 4*atan(1) in your spreadsheet instead of 3.14285714269231 that your pasted values indicate.

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