Thread: ST3 Build 2021

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    Re: ST3 Build 2021
    #31
    Keeper of the Asylum K-fab's Avatar
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    Lower arms can be done with just bolts and pivots running on plastic bushings. Up on top, I'd do heims - gives you adjustment ability.
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    Yellow Dog Racing
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    Re: ST3 Build 2021
    #32
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    Thanks, that makes sense, is the adjustment on the top to ensure that the pivot points are coplanar? both a arms will have a adjustable heim at the end that connects to spindle, what would the adjustment at a arm/body connection be for?

    If you are aware of a build thread on this that still has pictures let me know. i have a hard time searching and dont really know what i am doing wrong.

    Thanks for your help!
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    Re: ST3 Build 2021
    #33
    Keeper of the Asylum K-fab's Avatar
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    Start here: The Mini-Raptor, K-fab Style

    Solidly mounted lowers, adjustable uppers. With the two heims I can make all the adjustments needed.
    Lowers are Delrin inserts with a steel sleeve and a 1/2” bolt thru each pivot.

    Actually you don’t want them to be coplanar, at least looking from the side of the car in, point of view. The front pivots need to be farther apart than the rear so you induce caster changes (2ish degrees) during cycling. Keeps things more stable.

    Don’t know if I sent you here yet but read the whole thread: How to design and build A-Arm suspension
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    Re: ST3 Build 2021
    #34
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    Couple questions for the group. 1) front suspension block, the plans called for the pivot points on the upper a arms to be wider than the lower, based on the suspension post i assume this is to help with scrub angle, i made the pivot points for upper and lower indentical and made upper and lower a arms identical (by accident) is this a problem? i could make upper a arm pivot brackets longer to correct for this but seems like they would be weaker.

    I purchased 4 fresh takeoff mule pro fxt wheels and tires (4x156 bolt spacing) and atv free wheeling hubs, i purchased a trailer stub axle that will need to be turned down to fit inside hub bearings. this seems fine, but i think i have a few options 1) buy trailer hub 4 on 4, and buy new wheels 2) replace bearings on hub that will accept 1" stub axle/spindle 3) have trailer axle turned down to fit with hub.

    Seems like using the mule wheels and tires will be easiest especially for rear, as i can buy rxr/mule internally splined hubs and use rzr/mule axles.

    Let me know your thoughts, really appreciate all the comments. IMG_2820.jpgIMG_2823.jpg
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    Re: ST3 Build 2021
    #35
    Senior Member darwinpayne2000's Avatar
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    Finding bearings to fit might be tricky, but it's probably the easiest option. I suspect that you'll need to have the axle turned down to make it fit.
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    ST3 Build 2021
    #36
    Senior Member Linden318's Avatar
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    Nice work on the chassis so far!

    The reason they have the upper, inner mounts spaced out farther than the lower mounts is to allow your front tires to travel proper suspension geometry. The proper geometry is when the tire comes up to full bump (bottom out suspension) the bottom of the tire will push out and the tire will gain negative camber. Same thing happens as the tire drops to full droop as a result of the different a arm pivot point locations. But, to make this work properly, the top a arm must be shorter than the upper a arm (shorter upper a arm creates a smaller radius when it cycles and thus pulls the top of the tire in when it goes up and down).

    Having your suspension all parallel (same top and bottom mounts and same a arm length) will result in larger amounts of scrub like you mention. It could make the front end feel ‘washy’ since the tire needs to push sideways as the suspension compresses so the tire is no longer rolling only, but also sliding sideways. Also, when you turn a corner, since the chassis will “roll”, called body roll, the tire will angle outward into positive camber (not desireable) and cause the tire to ride on the outside edge of the tire only and not on the flat contact patch of the tire. If you have negative camber gain like mentioned in the above paragraph, the tire angles the opposite way and helps maintain a flat contact patch with the ground (tire tries to stay perpendicular to the ground).

    All of this being said, the buggy will still work good and you shouldn’t have major issues driving it, but a proper suspension geometry will make it more enjoyable and a smoother ride.

    As for your hubs, I would keep the RZR/Mule hub you have in the photo and turn down the axle to fit the existing bearings. I think that sounds like the easiest solution. That way you can run your original tires and just weld the stub shaft into your spindle to accommodate the rzr hub.


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