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Thread: Sway bar attachment methods

  1. #11
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    Don't need to make it a splined end. You can start with stock that is a convenient shape for retaining, and then turn down to the torsion rod.

    Kev

  2. #12
    Kevin,

    HI! What is a "stock" ?

    Claude

  3. #13
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    Stock is 'the part of the gun you make soup from' Claude (old silly definition of 'Stock' in karting).

    Kevin is using the term as used in Australia when describing steel bar, ie, 'round stock', 'square stock', 'flat stock', 'hexagonal stock' etc

    Pat
    The trick is... There is no trick

  4. #14
    Pat, Kevin,

    OK, thank you for te Australian translation.... then what? How do you connect one end of the torsion bar with the suspension (rocker for example) and the other end with the chassis? Because if we are speaking about an hexagon or square section end, I am afraid we could go back to the square one story about play and clearance,

    Claude

  5. #15
    Claude,
    Do you think it's impossible to preload the joint enough to eliminate free slop?
    Penn Electric Racing

  6. #16
    Adam, unless I misunderstand your question: The pre-load in one rotation direction will become a play in the other,
    Claude Rouelle
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  7. #17
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    Claude,
    I don't think there is any play in the MX-1 torsion bar ride-spring installation. I don't have the drawings handy to check, but from memory the square bar is clamped like it might be in a bench vise (or across opposing corners between little "V-blocks"). Plenty of clamping load trying to crush the bar.
    -- Doug

  8. #18
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    Claude,

    Quote Originally Posted by DougMilliken View Post
    ...the square bar is clamped like it might be in a bench vise (or across opposing corners between little "V-blocks").
    Not obvious???
    ~o0o~

    And thinking about the "prior art". What was that funny little car that sold, ooh..., more than 20+ million times...? The, err, ... something... "Beetle"?

    As I recall (it was many decades ago that I last looked, although plenty of them still around...), they have front springing via lateral torsion bars, with said "bars" made from a stack of rectangular leaves, which together make up a roughly ~20 x 20 mm "square bar". Inner leaves of stack about 20 x 4 mm, and outermost leaves ~10 x 4 mm.

    This arrangement of multiple leaves gives a lower rate and more maximum twist angle for a given length of bar, hence more strain-energy capacity (ie. more efficient because less unstressed "dead area" in the centre of the bar/s). And no problems if one leaf breaks, just a slightly sagging suspension...

    These top and bottom, lateral, "square torsion bars" are fixed to the twin-trailing-suspension-arms (at each side of car) with a ... pointed grub screw! The point of the grub-screw comes in "sideways" to the stack, thus wedging apart the inner leaves of the stack, and thus "clamping" the bar-stack inside the squarish hole in the trailing-arm. This then allows the bar to carry the torsional forces without "fretting", and also the wheel's lateral (Fy) forces that try to pull the trailing-arm out of its housing.

    Methinks both students, AND Design Judges (!), should spend more time climbing around car wreckers yards...

    Z

  9. #19
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    Claude,

    First off I am sorry if the word "stock" is not used outside of Australia. I am often caught by surprise how often the Australian use of the English language is just better. I'm fairly sure that in 1000 years or so we will have eliminated most of the syllables from the language and be able to communicate complicated engineering concepts with little more than a grunt.

    I think the play and clearance issue has been dealt with after my post.

    I would add that in practice splines can be more difficult to reduce slop than profiles with defined flat surfaces or angles. This is one of the reasons that some of the very good steering quick releases do not use spline profiles.

    Kev

  10. #20
    Yes we simply machine an external hex on the end of our ARB torsion springs, and an internal hex in the ARB arms with a large slit, and we simply clamp the s*** out of it. I guess this is not what you would normally think of when you consider a preloaded joint, but you can design the clamp arms to undergo a rather large elastic deformation around the hex, resisting rotation in both directions.

    If the slit is not large enough or the internal hex is machined too large then yes it does not work, but this is just an exercise in GD&T.

    I would love to try polygonal splines as a method to reduce stress risers at the clamped locations. Traditional splines are great but difficult to machine in a typical student shop, although we are having good results with our jerry-rigged 4th axis and some clever work in our post processor.
    Penn Electric Racing

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