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Discussion Starter · #1 ·
Triangulated 4 Link - Why DOESN´T it Bind??

I´ve been searching and reading for the past three days, reading everything till I´m blind. I still don´t get it.........:(

WhyTF doesn´t this suspension bind?!?











There was a good discussion about it in this thread:

http://www.pirate4x4.com/forum/showthread.php?threadid=194560

but I just dont get it. It seems to me that as one side droops, the links would go thru an angle and this would result in a pinion angle change which could not be compensated for by the links on the other side.

Obviously, I´ll accept that it works and from what I´ve read, works well. And for my rig, this set-up would be the easiest 4-link to build. But rather than taking a big leap of faith, I´d like to understand WHY it doesn´t bind.....

What am I missing?? TIA.........
 

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If you look into all of it, how each link travels in a different radius, and one is going to pull close when another might stay still or push back, and then consider length is static, it seems to be amazing that it actually works.

Make a small model of that and play around with it. Carbboard models are great to figure out things... (i use them all the time) ;)
 

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And I think its because of this- *Insert picture below right here*

The vertical separation can push the top of the axle back and forth, and the bottom can move separate from the top as well. So the differences in radius arcs (Where a link swings and how) are made up for by moving the top of the axle forward and back...

Making any sense? Im planning on doing this type of link system too, since it seems to be the simplest, and easiest on space.
 

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Try thinking of it in terms of what movement is allowed to happen if you remove one of the links and you will see that if any one of the links is removed then the axle can flop all over the place.

Removing one of the bottom ones is easy - the axle will move sideways (and remain parallel to the origional position and wont "steer"), the two uppers will remain parallel as they move sideways and the lower will rotate the whole diff as it moves.

To visualise removing one of the uppers is a little harder but basically the same thing happens. Because the lower is triangulated this remains as a triangle as the axle is moved sideways (so as you push it sideways the axle "steers") and again the sole upper will rotate the whole diff as it moves.

So you can see that you need all the links to correctly restrain the diff and also you can see that any of the links can be made a bit shorter or longer and the links can still be conected (although the diff would be in the wrong position)

Sam
 

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Unless I am missing something - the hand drawn pictures are not a correct representation of the vehicle itself, in that the drawn pictures show vertical separation at the frame, and the picture sure looks like top and bottom links are on the same vertical plane :confused:
 

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I think instead of binding it pulls the axle from side to side... I'll try to draw some pics to explain it.
 

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Well, here is my lame MSpaint attempt... mabey it will help.

 

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ErikB said:
I think instead of binding it pulls the axle from side to side... I'll try to draw some pics to explain it.
That and up and down. And it rotating (pinion moving up and down)

Basically, each individual link has a limited range of motion. But when separated vertically, they can push and pull the axle around, making it rotate up and down, and side to side.

If they was no vertical separation, it would bind and there would be little movement...
 

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Rudezuk said:
The mounts on the crossmember side are all on the same mounting surface....no verticle seperation
But there SHOULD be some vertical seperation, less so on the frame end then the axle end, correct? :D
 

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Wilson said:


Not always
So when would you want no seperation at the frame? :confused:

I always read that you want some vertical seperation at the axle end and a little bit more on the frame end. :confused:
 

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I haven't studied these enough to tell you when. I learn by building and trial and error. I have seen several setups with the forward link ends on the same plane. A lot of people call them "bastard" setups and say the math just doesn't work but DSI, Avalanche and Roggy (among others) have built setups similar to what was pictured (Which was built by S&N). They run that link setup on a lot of buggies. It tends to give high anti-squat numbers, which is good as of late for comp rigs.

-Mine will be a dual traing setup with a little less seperation at the frame than at the axle. I'm hoping for a fairly neutral setup for my trail rig.
 

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Re: Triangulated 4 Link - Why DOESN´T it Bind??

billj said:
WhyTF doesn´t this suspension bind?!?
Why's a positraction in a plymouth work? it just do!
 

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Discussion Starter · #17 ·
Except for the mullet :rolleyes: , great stuff!!! Thanks for the insight........;)

I´m gonna print this thread out now and take it to my "thinking place" .

I do all my best work there.........:p
 

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Discussion Starter · #18 · (Edited)
Just got back from my "thinking place".........:p :D


I think that ErikB has hit on the key to what´s going on. As the axle tilts, the lower link on the stuffed side goes more horizontal, thus getting longer as viewed from above. The lower link on the other side gets correspondingly shorter, resulting in the axle shifting towards the drooped side. Intuitively, this seems to be a good thing, perhaps creating a subtle "down force" on the drooped tire......

Another thing that seems to be good about this design is that if the two parallel upper links are horizontal at rest and with good spring balance, then there would be very little axle steer.

I´m gonna explore this design in CAD to see what I can come up with. I´ll post up some drawings in a few days......

This round´s on me!!!!

:beer: :beer: :beer: :beer: :beer: :beer: :beer:
 

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Jason R said:


So when would you want no seperation at the frame? :confused:

I always read that you want some vertical seperation at the axle end and a little bit more on the frame end. :confused:
wow that would give you some fawked up crap, with very little movement. :flipoff2:

no seperation at the frame end gives you a constant IC (Instant Center). so the Anti-Squat % remains the same through out the range of motion(sorta). However due to the large amount of seperation we have between the axle and frame this type of suspension leads to a roll center of the axle that creates forward and aft movement of the wheels during articulation.

And as for Billj yes the suspension does bind, we just happen to get a range of motion out of it that is usefull to our purposes.
 

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what it looks like to me is that instead of binding you'd get some steer, because when one side droops, both links on that side get shorter horizontally, pulling the axle closer to the center of the vehicle, horizontally, while the opposite happens on the stuffed side, both upper and lower links get slightly longer horizontally and push that tire away from the vehicle, UNLESS, the angles of the links are perfectly symetrical above and below a center horizontal line while sitting at ride height, then the stuffed tire will move up and toward the center of the vehicle due to the arc of the linkage and the drooped tire will go down and toward the cent of the vehicle. i don't think there is a suspension that doesn't allow for some binding and/or some axle steer, well, i think there is, but it has just as many other problems too (double wishbone, one pointing forward, attached to the rear axle with bushings and the frame will a big ball and socket-type joint and then the exact same, but opposite for the upper, attached to the frame bushings and the top of the diff will a big ball socket joint. only problem is, the links might hit each other).
 
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