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  •   mainlinemick commented on this post about 2 years ago
    Got springs today. $25 for a pair. I hope to use them as front quarter-ellipticals. Each leaf is 45mm wide and 6mm thick.

    I ground off the retainers and pulled the 3 leaves apart ... and figured I'd used a ~400mm long section of the middle leaf.

    So I set up a test rig, clamped one spring to the bench and carefully measured the deflection at the point where my axle will be, for a given load at that point. One spring sagged exactly 6mm for 5kg load.

    So with 2 springs it will sag half of that: or 3mm for 5kg. If my Kart weighs, say, 240kg all up (excluding the unsprung front wheels and axle) and if say 1/3 of this carried by the front axle, that's 80kg on the front axle or 16 x 5kg, so the springs (and body) will drop 16 x 3mm or ~48mm from its unweighted position when at rest, and drop a further 48 mm from a 1G "bump". Putting it another way - if someone about 80kg leant down hard on the front of the kart, they'd lower the front by about two inches.

    So I think I'll run with that and not chop the leaves in half lengthways. It seems to me that, using a spring as a cantilevered quarter-elliptical effectively halves its effective stiffness, compared to using it as a full semi-elliptical, supported at both ends. Makes sense because only half the spring is present and working.
    Comments (4)
    • Good score. Sound like they should work pretty good.

      The calcs that I used included the length as part of the equation, so I think that you areGood score. Sound like they should work pretty good.

      The calcs that I used included the length as part of the equation, so I think that you are correct.
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    • Just looking at the pictures, might be good to put a panhard rod on the front axle to stop it walking. We used to fit them to the rear diffs on rallyJust looking at the pictures, might be good to put a panhard rod on the front axle to stop it walking. We used to fit them to the rear diffs on rally cars, made a huge difference to handling and stability. If you want fancy try a watts linkage. Looks great!  More ...
      Reported
    • fisher42 Thanks, I'll look into that. My first task will be understand what a panhard rod is, and does. It sounds good though. A watts linkage -fisher42 Thanks, I'll look into that. My first task will be understand what a panhard rod is, and does. It sounds good though. A watts linkage - looks even more complex. Damn, I was going for KISS, too!   More ...
      Reported
    • Panhard rod reduces the side to side movement of the axle. Pivoted from the body on one end and on the diff housing at the other. A watts link isPanhard rod reduces the side to side movement of the axle. Pivoted from the body on one end and on the diff housing at the other. A watts link is slightly different but probably a bit better. Pop in to you local library and look at the Ford (watts link) & Holden (panhard rod) manuals from the 1990's pre independent rear end.  More ...
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