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Discussion Starter #1 (Edited)
OK........I've been watching and reading all of the posts (past and present) on people designing their 4 link suspensions. And I decided it was time for me to give it my best shot. We're not talking some ho-hum Autocad setup. We're talking full blown 3d modeling.

I and a buddy used ProE and threw every bell and whistle we could think of when putting it together. An output of our design and layout for my CJ7 can be found at:

EDIT (fixed link - thanks to Lance):
http://www.pirate4x4.com/d1/tech/4link/4link.pdf

I appologize up front if we exceed the site's daily bandwidth limit. I just don't have the $$ to pop for a web site. This is a free one. If anyone has a suggestion on where I can post it that it won't get limited on bandwidth, please let me know.

Look it over, both the design and the dimensions, and see if anything seems like it is missing or should be changed.

We worked pretty hard on it to include all we could think of. But my skin is pretty thick......so fire away. It currently does not have a front suspension modeled. That is to come.

One last thing........I have never built a rear 4 link suspension nor have I helped with one. I one of those kind of people that has to analyze the hell out of it before I build it. I plan to start building the final design in the next year.

EDIT: Damned link doesn't work!! Give me some time to fix it! Arrrgggghhh.
 

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Looks almost exactly like my link plans. Of course, mine are on graph paper.
My uppers are 41, and the lowers are 43. I was advised to shorten the uppers, to increase antisquat on compression, and decrease antisquat on extension.

Looks like you have 7" of seperation, in the side view, between the uppers/lowers at the axle, but I couldn't figure out the seperation at the chassis. 6" I'm beting?

Nice work, and tell us what you guys are working on for the front.
 

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AntiSquat (here we go.... :rolleyes:...) is 89.8%, huh? So your suspension will SQUAT slightly under acceleration...

Personally, I've come to believe that a bit of anti squat is good (greater than 100%, but not waaaaay up there). Here's my thoughts:

1. As you accelerate, weight shifting to the rear of the vehicle will cause the rear suspension to squat, reducing the angle of your links. Now you have even more squat...

2. On hillclimbs, where it's most important that the suspension does it's job for me, the CG of the vehicle shifts to the rear considerably. Again, this effectively reduces the amount of anti-squat produced by the rear suspension, or increases the amount of squat produced, if the # is below 100% to start with.

Thoughts? :confused:
 

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RightPedal said:
AntiSquat (here we go.... :rolleyes:...) is 89.8%, huh? So your suspension will SQUAT slightly under acceleration...

Personally, I've come to believe that a bit of anti squat is good (greater than 100%, but not waaaaay up there). Here's my thoughts:

1. As you accelerate, weight shifting to the rear of the vehicle will cause the rear suspension to squat, reducing the angle of your links. Now you have even more squat...

2. On hillclimbs, where it's most important that the suspension does it's job for me, the CG of the vehicle shifts to the rear considerably. Again, this effectively reduces the amount of anti-squat produced by the rear suspension, or increases the amount of squat produced, if the # is below 100% to start with.

Thoughts? :confused:
The C/G changes if you are carrying bowling balls maybe! Just bustin your chops, man:flipoff2: It is a common misconception. In truth is that the C/G stays constant. The effective load transfers to the rear suspension though, giving the effect of more weight in the rear.
Other than compressing the springs further and changing the link angles, it does not effect how the instant center of the rear suspension interacts with the C/G of the vehicle. It is, however, a consideration in how much anti-squat you want to put in it if you want to tune the suspension for hilll climbing.
 

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all I have to say is WOW!

Those drawings also will help people really understand s/as and roll axis. Conveniently, your dimensions are about dead nutz to my rigs specs...my CG is a bit more forward....hmmm...you may have made my decision to go 4link in the rear a bit easier. I really dig those drawings!

Special thanks to your employer for the copy of Pro-E!
 

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Discussion Starter #11 (Edited)
Lance said:


I've placed a copy of the pdf on our server.

http://www.pirate4x4.com/d1/tech/4link/4link.pdf

:cool2:
Lance.........your the man!!! Thanks.

AlumCJ......yes, thanks to my employer for the ProE. :cool: As for CG location, I still need to actually MEASURE it the proper way. I intend to before it is all said and done.

The whole drawing/modeling is driven by those tables on the drawing sheets as well as a few dimensions on specific items. I thought it was really slick how it all went together. Now............It's time to put paper to reality.

One thing I did notice, you still get about 3 degrees of rear steer even with the double triangulated setup. Is this because my roll axis is at a slight angle upwards? I think it is, but just wanted to double check.
 

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Discussion Starter #12
KingOf_Pain said:
Looks like you have 7" of seperation, in the side view, between the uppers/lowers at the axle, but I couldn't figure out the seperation at the chassis. 6" I'm beting?
Actually, the seperation at the axle is about 10" (see sheet 2) and at the chassis it's about 7" (sheet 3, 4" above tcase for uppers and 3" below tcase for lowers = 7" total about)
 

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Discussion Starter #13 (Edited)
Well.......not quite as much discussion as I had hoped on this, but what are you gonna do? I guess everyone is getting burned out on the 4link stuff.

So...........I decided to model it as a converging link setup today. Changed a couple of numbers quickly and got the following. Click on the "converging_link.pdf" for that setup.

http://www.pirate4x4.com/d1/tech/4link/

I tried to keep the links as close to the same as the double triangulated. AS is about 200% (versus 89%) and rear steer is twice the double triangulated version. Also the roll axis is much steeper. Comment???

Please understand, I am not judging any setup here. I have yet to actually build one myself. I'm only noting what the model is showing and what I think we already knew anyway.

The model is extremely easy to change and shows you quickly what effects specific changes will make.

AlumCJ: I just figured out what you meant by "Special thanks to your employer for the copy of Pro-E". RSE, llc is my business that I and a buddy started on the side. Pro-E license is ours. Sorry......I didn't quite understand what you were getting at the first time. But the designs are for all to use if they wish.
 

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four_by_nut said:


Is this because my roll axis is at a slight angle upwards? I think it is, but just wanted to double check.
Yes
 

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RightPedal said:
AntiSquat (here we go.... :rolleyes:...) is 89.8%, huh? So your suspension will SQUAT slightly under acceleration...

Personally, I've come to believe that a bit of anti squat is good (greater than 100%, but not waaaaay up there). Here's my thoughts:

1. As you accelerate, weight shifting to the rear of the vehicle will cause the rear suspension to squat, reducing the angle of your links. Now you have even more squat...

2. On hillclimbs, where it's most important that the suspension does it's job for me, the CG of the vehicle shifts to the rear considerably. Again, this effectively reduces the amount of anti-squat produced by the rear suspension, or increases the amount of squat produced, if the # is below 100% to start with.

Thoughts? :confused:
It doesn't quit work like that. Anything above a 100 lifts on steep hills.
Under a 100 is definitely the way to go.
 

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"(sheet 3, 4" above tcase for uppers and 3" below tcase for lowers = 7" total about)"

Actually the sheet 3 says ABOVE for both links. I knew 1" couldn't be correct.
 

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Looks great to me. I would move the lower shock mounts outward. I've noticed that most of the successful comp rigs are mounting them as close to wheel as possible for better stability.
 

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As for CG location, I still need to actually MEASURE it the proper way. I intend to before it is all said and done.
Every method of figuring the CG that I've seen posted or referred to around here calculates the TOTAL vehicle CG. For purposes of anti-squat, anti-lift or anti-dive, you should use the unsprung CG. On most buggy's, this seems to be at least a foot higher than the overall CG. With this is mind, your quoted anti-squat % is probably on the high side.

HTH
 

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MaXJohnson said:


Every method of figuring the CG that I've seen posted or referred to around here calculates the TOTAL vehicle CG. For purposes of anti-squat, anti-lift or anti-dive, you should use the unsprung CG. On most buggy's, this seems to be at least a foot higher than the overall CG. With this is mind, your quoted anti-squat % is probably on the high side.

HTH
Ok, couple of questions... First, don't you mean you need to use the sprung CG to figure anti-squat?

Second, how do you find the sprung CG? Weigh the front and rear of the vehicle and subtract the weight of the front and rear axles from each number respectivly, then subtract the sum of the axles from the total vehicle weight? Using the final numbers for the CG formula?

Or just add 12" to the verticle position of the total CG?
:flipoff2:
 
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