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Overkillz Dune Truggy Build
- Thread starter Deuling
- Start date
You're basically making a square...but not. Each A arm mounts to the top and bottom of the frame or something like that...and then goes to the top and bottom of the knuckle. Sort of like a not square square...I'm sure there's a geometric term for a goofy 4 sided shape that isn't "square". The top and bottom of the knuckle usually aren't the same distance apart as the A arms on the frame either.
The length of the arms are set for ride height in a road vehicle. Suspension travel in a dune truck. Hence the way the tires don't sit straight up and down on most dune/sand trucks.
As your suspension moves up and down the A arms are fixed to the frame and pivot from their mounting points. The knuckle end is fixed as well. So the different lengths of the arm means the knuckle sorta pivots as the suspension moves around. The top will want to push out and the bottom pull in as the suspension droops and the opposite as it goes up.
You'd have to find a way to have the knuckle some how move around on the control arms and always maintain a vertical alignment to do what you want. No clue how that would work.
It's geometry. Hopefully that explains it or at least doesn't muddy it up too much.
The length of the arms are set for ride height in a road vehicle. Suspension travel in a dune truck. Hence the way the tires don't sit straight up and down on most dune/sand trucks.
As your suspension moves up and down the A arms are fixed to the frame and pivot from their mounting points. The knuckle end is fixed as well. So the different lengths of the arm means the knuckle sorta pivots as the suspension moves around. The top will want to push out and the bottom pull in as the suspension droops and the opposite as it goes up.
You'd have to find a way to have the knuckle some how move around on the control arms and always maintain a vertical alignment to do what you want. No clue how that would work.
It's geometry. Hopefully that explains it or at least doesn't muddy it up too much.
I understand how it works. I dont understand the pount of why its designed that way. If the "knuckles" were designed to have ball joints at the same spot vertically, and then equal length control arms shooting off the frame from the same vertical plane and the same diatance apart as the top and bottom of the "knuckle" it would create a perfect square when the control arms are perpendicular to the frame and keep the tire completely vertical throughout the suspension cycle. It would just push the tire in and out a few inches with suspension movement. I dont see why that wouldnt work great on sand that has alot of give. Sorry no paragraphs on phone.
No, even with it setup as you said the tire would "pivot" as I described it. You'd have to either have one of the control arm mounts slide as the suspension moved or the knuckle somehow slide to keep the perpendicular orientation to the ground.
Idk AJ. To me the compass and ruler dont lie 
And yes I measured with thin lines and just sharpied over to show better.
Bushings on the right side hook ups, ball joints on the left. Sure if it doesnt angle out its pushing harder against the ball joints and bearings, BUT..... its sand so it gives easily...
And yes I measured with thin lines and just sharpied over to show better.
Bushings on the right side hook ups, ball joints on the left. Sure if it doesnt angle out its pushing harder against the ball joints and bearings, BUT..... its sand so it gives easily...
Come on aj! Hit me!
I mean come on. This $hit dont lie
Now to figure out how to make a custom "KNUCKLE" tow mount a spindle and ball joints to 
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I mean im not trying to sound like a stupid kid.. But if 2 circles have the same radius and the center points are on the same vertical plane, every point on the circumfrence of each circle on the same vertical plane is going to have the exact same distance from one another creating a perfect vertical angle.... Im a cad major so i use this stuff every day in class 
The sand rail I am building with my dad has equal length a arms front and rear. They don't mount in equal locations, but the camber does not change under suspension cycle either.
Yah im gonna get some measurements and make some drawings and give kert a call and send him some designs as far as mounting brackets. I think it may work. And if my calculations are correct, 12" of travel with 36" control arms spaced 12" apart would move the wheel horizontally 1.5". And 18" of travel would move it 2.25" roughly from horizontal. To me thats a very small amount.
And if my calculations are correct, 12" of travel with 36" control arms spaced 12" apart would move the wheel horizontally 1.5". And 18" of travel would move it 2.25" roughly from horizontal. To me thats a very small amount.
best advice i can give you is mock it up.
get your measurements and go buy a couple $2 peices of conduit and make a scale model and watch it work and tweak it.
get your measurements and go buy a couple $2 peices of conduit and make a scale model and watch it work and tweak it.
I got an unlimited supply of pipe so mockup will be no prob
make some big ole tall hoops and mount some coil overs or coils to the top and to the point of the top control arm. Tie the driver and pass hoops together over the motor. Make a cross member and test it out. Im gettin pretty stoked over the idea
As far as wheels not staying vertical. I thought it was intentional design for handling. My brother built a stock car for dirt track racing and the arms angled the tire in by design, and more at flex, too keep more tire on the ground when banking in the corners. This is my theory on these race trucks.
I can kick the bottom contol arm out like an inch from the top but keep them same length. This would kick the bottom of the tire out an inch from the top and keep that angle the whole time. Sure in a road driven vehicle this idea wouldnt work. Would be too hard on ball joints and bearings etc... But since this will be trailerd to the dunes and only driven in forgiving sand.... I think it will work great. Hell its worth a try.
BINGO!!!! Negative camber (tire tilts inward at the top) adds stability at speed and for cornering at speed. But, you don't do this on a street driven truck because pavement will eat the inside edge of the tire. Sand wont. You would benefit most from negative camber and a tall thin tire up front.
The problem you will see from building all custom lengths or really wide into the front arms is that the ball joints are only designed to work within certain operating angles. Exceeding those angles could possibly pull the ball right out of the socket, you don't want that happening at speed.
If I had this truggy to F around with, I'd start by cutting the stock control arms and adding 4-6" of length to them using tube/bracing/fishplate/whatever (maybe just extend the mounting points of the arms) and see how they work. It's called R and D. Try it out, beat on it, break it. Find out what worked, what didn't, build new.
Well there must be higher angle ball joints, because people do build long travel stuff...
Im goimg to get all my measurements and build a 3d cad drawing that will move up and down and show how it would work. If i post it up and you guys can give me a logical reason why it WOULD NOT work in the SAND (not dirt track, not trails, not road, not rocks, not mud) then i will not build it. But the cad assembly wont lie because if it parts have contact they will not move.
I know what your saying. Im not gonna hop on this right now. But for my last cad project to finish my degree we have to design a pretty complicated assembly of our choice. This is going ro be mine. We will wheel it in stock form fro a while.
