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Thread: cause the judges don't like (rod ends in bending)

  1. #31
    Originally posted by M. Nader:
    <BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by atm92484:
    Except none of those rod-ends are in bending...

    It wouldn't surprise me if there was more to the story than the picture is telling.
    How can you tell from the picture they weren't in bending? maybe you can make a case for the lower one where i would guess too little thread was attached, but the rocker one i had no doubt it carried bending load. </div></BLOCKQUOTE>

    From the picture it looks like the rod end which failed at the bellcrank is a pushrod, which should only be in compression (2 pin connections). The lower one looks like it would be a tie-rod, which is also a tension/compression member.

    My guess would be that the "awkward geometry" caused some kind of binding to occur, putting those rod ends into unexpected bending. Nevertheless, this is a good example of how rod ends will fail, however strange the situation.
    Owen Thomas
    University of Calgary FSAE, Schulich Racing

  2. #32
    How can you tell from the picture they weren't in bending?
    I have eyes and a pencil and am able to draw free body diagrams.

    Assuming the rod-ends were the bump stops, FSAE calls that poor design - not rod-ends in bending.

  3. #33
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    I see a couple of blown fuses. Solution: Replace fuses and continue...

    If they used bigger rod-ends, and mounted them with bolts in single-shear, then the fuses would be even cheaper to replace (ie. just the bolts).

    And, BTW, all rod-ends, even at the ends of a two-point pushrod or tie-rod, operate "in bending". This bending comes from the gravitational or inertial loads on the link itself. So suggesting "No REIB" is really saying "No REs at all!!!". So how long before you all have to abandon your easy-adjustable, rod-ended toe-links and start building shim-adjustable, clevis-mounted, staked-in-BJs at the ends of your toe-links?

    Z

    (PS. Eilonoz, As I mentioned earlier, your design looks OK to me. Perhaps make the mounting bases at chassis and upright a bit wider, and use adequately sized REs.)

  4. #34
    Originally posted by atm92484:
    <BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">How can you tell from the picture they weren't in bending?
    I have eyes and a pencil and am able to draw free body diagrams.

    Assuming the rod-ends were the bump stops, FSAE calls that poor design - not rod-ends in bending. </div></BLOCKQUOTE>

    I am not doubting that.

    How do you know how the attachment looked like in the fist place? you only see a broken piece it could very well have had a strange initial angle which caused that! i have seen it before that is why when i first saw the pic i asked about the attachment angles. Perspective that is all
    Cairo University Racing Team Technical Director 2011-2012
    Tyres and Vehicle dynamics
    Suspension team head 2010

  5. #35
    That picture is interesting.
    Two different rod ends appear to have broken at the exact same time.

    That suggests to me either accident damage, or some extremely unusual massive one time overload, like becoming very airborne.

    Now we don't know what actually happened, but if you lose control and hit something really hard, things are going to break.

    And you can only blame the designer if the part failing CAUSED the accident, not if the accident caused the part to fail.
    Cheers, Tony

  6. #36
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    M. Nader,

    Thanks for posting the pic.
    Do you perhaps have more of the car? Both before and after failure?

    Thanks,
    William

  7. #37
    William,

    I initially hadn't looked for it as i came across the pic somewhere and just asked the poster to clarify my guesses a bit and went on. after some looking though here is a pic of how it originally looked.

    Cairo University Racing Team Technical Director 2011-2012
    Tyres and Vehicle dynamics
    Suspension team head 2010

  8. #38
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    M. Nader,

    Thanks for the new pic.
    I followed the link and found this:


    Looking at it I would say that the push rods and dampers look pretty planer.
    But those bell cranks may be narrow enough for the rod ends to bind and fail.

    Can't tell much more from the pics...

    -William

  9. #39
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    With the clue being "big banking" I'm going to go with a failure of the spring and damper mount.
    Can't really see the mount, but it doesn't look too substantial and the spring looks fairly close to coil bind considering the motion ratio. A bound spring as a travel stop + a less than massive bracket would fail pretty easy on some "big banking" leading to unrestrained suspension travel and bound and broken (correctly utilised)rod ends/brackets all over the place. The direction of the bending failure of the push rod rod end would support over rotation of the rocker. Nothing at all to do with REIB IMO.

    Of interest, is that a REIB on the out board upper ball joint? The one that didn't break? Kind of funny given the topic and reason for posting the pic.

    Pete

  10. #40
    Yes it is Pete that outboard rodend, but it is really minimal in comparison to what we sometimes see in FSAE (The rod end would be a bit more extended). still in bending nonetheless, funny how it didn't fail and the correctly utilized ones did.

    Seeing the before pics yesterday i too realized this was not a REIB case, what would load both the pushrod and the Rear upper a Arm mount? with the keyword "massive banking". i will have to give it more thought, but it is safe to say that the loading was not really expected which means that it was during an extreme situation, Jumping of a curb? i think this is a track car but i am not so sure it wasn't used elsewhere
    Cairo University Racing Team Technical Director 2011-2012
    Tyres and Vehicle dynamics
    Suspension team head 2010

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