4-Link 101?

[shimey]

So after finding a ba-gagillion pages with hits on everything "4-link," I've learned alot, but still have some basic questions...

What are some rules concerning 4 link systems? Specifically I'm talking about:
- lengths (upper longer or shorter than lower....benefits of either)
- angles (rise and spread)
- placement on axle (upper vs. lower)
- shock placement (that one I suppose is completely dependent upon shocks/springs/oil....)

Is there a thread someone can point me to? Or give me a good search string? I'm doing a ground up, and I'm all good on the fabrication but there seem to be lots o' ways of setting up 4 link.

I guess I just need to know the absolute no-no's...things that'll absolutely NOT work. I'd like to hit the ground with a running start and the links are the only area that I'm alittle unsure of myself...I wanna save some time, ya know?

THANKS ALL- KILLER BOARD HERE


edit: guess I should include that I'm doing emaxx tranny and axles...I VERY much like the UTRCRC and RCrockgear chassis' but I'm gonna try something billet.....TXT meets....whatever...lol

[willyrocket]

What axles are you planning on using, and what wheelbase are you looking for?

[shimey]

Hmmm. I thought I edited and included that I'm cannibalizing my Tmaxx for the axles and I've got a beefed-up E tranny....

Wheelbase- 15-17...I think.

[shimey]

bump.

Anyone? Or is this just a dumb question?

[Ace]

Just triangulate the uppers (in at the axle) and mnt the bottoms out on the frame... parallel is okay, but be sure they'll clear the tires when turning. Try to keep the links parallel to each other viewed from the side with a fair amount of vertical seperation. If you want to win a comp, keep them horizontal to the ground at rest.

Try to keep the ball links vertical (bolt horizontal) soas not to limit artic from ball joint bind.

Also, mount your bottom links so the bottom of the frame is smooth so you can drag your junk over the rocks w/o getting hung up.

I used to sweat squat/anti squat but 4-link design other than the basics above affects the rig's performance less than low cg, good tires, good gearing/motor, right wheelbase and right width, etc. In other words don't kill yourself on the 4-links, It's important but not everything.

[Reflection]

If you mount the links at the same point on the chassis it will help driveshaft angles quite a bit. If you can't use the same point,the closer you can get to that point the less angle change there will be on your diff yoke. This is not a have to thing,just something that some(including me)do. Here in this pic you can see what I mean. Verticle separation at the axle is roughly 1",verticle separation at the chassis is 1/4". I have VERY little change in the angle of the yoke on the axle throughout all the wheeltravel.



Here you can see that at full droop of one side the yoke is still pointing at the tranny,just as it does at rest.

[rckjeep]

Ok, four link suspensions are pretty complicated. To proparly do a four link you have look at COG, tire size, wheelbase, and what you want to get out of it. But with RC some of the rules are not as important. Ace has the answers. Triangulate both upper and lower links. Looking from the bottom of the truck none of the links should be running parrellel. It will keep your axle centered under the vehicle left to right. You should have your links running parrellel looking from the side though. Although having the lower & upper links mount to the frame through the same hole, though wrong (according four-link design)does seem to work in RC.

[SR5Dave]

Triangulate uppers and lowers.
A)This will stop the axle from moving side to side.
B) You don't HAVE to triangulate the lowers, but it will help get the links out of the way of your tires.

Try to make your uppers and lowers the same length if you can.
A) Only one spare
B)Your pinion won't try to shove itself into the dirt on droop
C) For clod guys, you will keep your motor up higher for better clearance

Try to mount your lowers near the centerline of the axle
This puts less stress on everything, the further your lowers are from the centerline, the more force they will get (A lot more force)

Try to keep the links flat
A) This will stop the axle from moving to the left or right on articulating (different from the movement involved with a lack of triangulation)
B) By doing this, you will probably keep the rig lower than you normally would, which is excellent for overall performance.

You should have a half-inch to an inch or so less vertical separation at the frame end of your links than the axle end. Picture your rig from the side. On the axle, your uppers and lowers will probably have around 2" between them vertically. On the frame end, they should have 1-1.5" of vertical separation.
This will cause the rear end to squat on acceleration, which gives good traction on climbs. Too much, and it will roll over backwards. More separation at the frame means more squat.

Having your Links parrallel is also very good
This gives you great suspension characteristics, good squat, but not too much.

Now for some opinion....

I wouldn't mount the links on one spot at the frame, I would simply run LONGER uppers, that way when it droops, the pinion goes up. So you can keep your angles, and also have good suspension characteristics. That being said I've never driven a shafty. This is what I would do with my 1:1 rig though.

Links should be made from a minimum of 3/16 aluminum. Steel slides over obstacles better, I made mine from steel.

4-40 rod in the links is NOT suitable for crawling, 6-32 is far better. I use 8-32.

If I think of more I'll post up. Ask for clarification anywhere it is needed.

Dave

[Slowpony]

Originally Posted by SR5Dave

You should have a half-inch to an inch or so less vertical separation at the frame end of your links than the axle end. Picture your rig from the side. On the axle, your uppers and lowers will probably have around 2" between them vertically. On the frame end, they should have 1-1.5" of vertical separation.
This will cause the rear end to squat on acceleration, which gives good traction on climbs. Too much, and it will roll over backwards. More separation at the frame means more squat.


Dave

I've got a little different take on the need for squat in your suspension design. If I were driving a dragster I'd want all of the weight I could get on my rear tires for traction, but in a crawler I find I need more traction on the front tires when climbing. Too much traction on the rear will simply flip your rig over backwards.

You can set your rig up for anti-squat so that when you hit the power the rig forces the front tires into the ground. The effect is much less obvious than squat, which is obvious because you can see the rear suspension load up, but the weight will stay forward and your rig will have much less tendency to topple over backwards and will climb much better.

If anyone is suffering from sleep deprivation get a copy of Herb Adam’s Chassis Engineering, it’ll put you to sleep in no time. If you want quick and dirty basics to four link setup 4wheel and offroad did an article in July or August of 2003 that described how to setup a 4-link, but not a lot of the whys.

Scott

[SR5Dave]

But you will also induce wheel hop, which is extremely bad for climbing. (less common in RCs but still notable)

[Slowpony]

Originally Posted by SR5Dave

But you will also induce wheel hop, which is extremely bad for climbing. (less common in RCs but still notable)

Your right, too much squat and you flop, too much anit-squat and you can get wheel hop. It's a balancing act.
There are a lot of things you can do to the suspension to get a desired performance. Suspension geometry is not simple, it's pretty complicated. Link ratio's, placement and COG will all have an effect on how well it all works in the end.
The artical I mentioned is really a pretty good start on understanding how it will effect your rig.... for those who feel they would like to understand it better.

[SR5Dave]

Originally Posted by Slowpony

Your right, too much squat and you flop, too much anit-squat and you can get wheel hop. It's a balancing act.

Very true!!! best way is to make it close to what I suggested, then play with it, depends on where you wheel, how you wheel and what you wheel ;)

Enough info for ya Shimey? ;)

[shimey]

Killer, guys....Lots to digest, THANKS!!!

[BlueMonster]

Does anyone have this article they could photocopy, or is it possibly online anywhere?

[Reflection]

Originally Posted by BlueMonster

Does anyone have this article they could photocopy, or is it possibly online anywhere?

I've got a copy I could scan,but,it would probly be faster and easier to read if you go to their web site. Search for Peterson 4wheel & offroad and go there. I've been to their site in the past and they had archives you can search through for past articles. I'd say their 4 link 101 article,I think thats what they called it,is probly there

[BlueMonster]

Okay, cool. I'll look for that. Thanks! If I find it, I'll post a link to it.

[Natedog]

Originally Posted by BlueMonster

Okay, cool. I'll look for that. Thanks! If I find it, I'll post a link to it.

Here you go:

Tech Articles: Suspension & Brakes
Four-Link Tech - Part 2
The Nitty Gritty Confusion of Four-link Suspensions


http://4wheeloffroad.com/techarticle...131_0307_link/

[Merrixs]

I just got done looking at the 4-Link tech articles on the Petersen site and I have a concern. I learned a lot about the operation of the rear suspension, but I am sure the front suspension requires a different setup to make it function at its best. The front pulls when the rear pushes so I would think you would need two designs. Any input on this?

[76kcfdeng]

Here are my thoughts on it.

links

[Natedog]

Originally Posted by 76kcfdeng

Here are my thoughts on it.

links

You should be able to get a setup that works with all those holes...lol. Good to have adjustability built in.