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    Re: Yerf ninja build
    #21
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    Leander, TX
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    I finished the second lower a-arm. It's pretty close to mirror image of the first. I plan to add 1/8 to 1/4 in of extra space between the mounting tabs so I can use washers to shim the sides to match perfectly. I just hope these splatter-welds hold.

    [IMG][/IMG]
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    Re: Yerf ninja build
    #22
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    Aug 2016
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    Leander, TX
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    [IMG][/IMG]Here's a shot of both LCAs mounted to the frame. They are about 25 inches from center of bushing to center of heim joint. Should be 60in from outside of tires so hopefully fits in a pickup. You can see my metal is quickly starting to rust. The humidity is ridiculous in central Tx.
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    Re: Yerf ninja build
    #23
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    [IMG][/IMG]I've cut the plates for the upper control arm mounting tabs, and the tubes to build the subframe. I've made the top wider than the bottom by 2in. Why 2in? Why not?? I couldnt find any quick tutorial on the web for best design angle or any rule of thumb. I have noticed that most double wishbone suspensions have the top mounting points a bit wider than the bottom. The height between the upper and lower will be about 6.5 in, which is just about 1/2 in more than center to center on the upper and lower heim joints. I can shim the heims at the spindles if necessary - top, bottom, both, neither - whatever it takes. I've heard stories of poor handling on some homebuilt karts so I'm adding in some adjustability. Hopefully it's enough.
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    Re: Yerf ninja build
    #24
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    Here's why I'm babbling about....

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    Re: Yerf ninja build
    #25
    Vendor - Rorty Crisco's Avatar
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    Aug 2013
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    Sunshine Coast, Australia
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    Cool build. Keep an eye on your double a-arm geometry. You want the top arm to pulling a tighter arc than the bottom one so you get increased negative camber in bump. Helps with corner handling (body roll) but not super critical with many off-road tyres which aren't that sensitive to camber changes.
    You can do it in a number of ways -
    - top a-arm shorter than the bottom
    - top a-arm angled up from the horizontal at ride height and the lower one horizontal (approx) or lower. Then in bump the upper arm will have a greater horizontal movement component (toward the chassis centre line) than the bottom and thus increase -'ve camber.

    I mentioned it as the second way usually means having the chassis mounting points closer together (measured from top to bottom sets) than the ones on the upright (where the hiems are) which reads opposite to what you have. If your top arm is shorter it will work.

    Bit hard to explain in words but I didn't have a diagram to hand . Carroll Smith's books have good explanations.
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    Re: Yerf ninja build
    #26
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    hey, thanks for input! I get what you're saying. My upper a-arms will be a couple inches shorter than bottom - 1in per side due to mounting point spread, and the rest due to kingpin angle. I'm just not sure how much is best. Regarding the angle of the top vs the bottom a-arm, I will be able to add a spacer between the top of the spindle and the upper a-arm in order to change the angle you mentioned if needed. Hopefully I'll have enough adjustment to get this thing to steer. The other big piece of proper handling is the steering rack length and angles, but I'll burn that bridge when I get to it.
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    Re: Yerf ninja build
    #27
    Vendor - Rorty Crisco's Avatar
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    You can model it the old fashioned way with paddle pop sticks and pins to see what sort of camber change you get - there's so many variables that rules of thumb don't work so well. My opinion is that many off-road tyres - especially the UTV/ATV style ones are not that sensitive to camber change, which is sort of good and by design as the track surfaces change so much you don't want to be darting all over the shop. Bump steer and toe control are probably more important with soft long travel suspension.
    Sounds like you've got a handle on it. The front's always harder than the back.
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    Re: Yerf ninja build
    #28
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    Yeah, agree. The tires are rounded quite a bit so I am less worried about camber change than toe control. As I understand I need the joint of the rack and pinion to be in the same plane as the a-arms. With my upper a-arms only 6in apart I need a pretty narrow rack mounted a few inches above the upper arms. I found an 8in rack on desertkarts.com, but I'm not sure they're a real business. Can't seem to find another source. I'll probably just order a Yerf dog rack cause it's cheap, and just make it work. Would love to get some good suggestions for that!
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    Re: Yerf ninja build
    #29
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    Ok, welded the upper control arm mounts to the lowers. Right now the whole assembly is just attached to the frame at the bottom 2 points, but I'll be ordering some more tube and building supports to attach to the frame at 4 more points. Meanwhile it's time to start building the upper a-arms. I will separate the mounting tabs by a couple extra inches so I can use spacers to change the caster. My buddy has a hydraulic tube bender so I'll be trying that out.

    [IMG][/IMG]
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    Re: Yerf ninja build
    #30
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    Btw, I know I need to box the assembly for lateral strength, just havent decided best way yet.
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