Pirate 4x4 banner

21 - 40 of 74 Posts

·
Registered
Joined
·
758 Posts
Discussion Starter #21
Nobody said:
How do you determine COG?
I got this link from other threads on COG topics:

http://www.jeepaholics.com/tech/cog/

KingOf_Pain: Yep, your right. The verbage should actual read 3" BELOW TC for the Lowers and 4" ABOVE tc for uppers. Whoops. That is a copy/paste gone bad! Thanks.

I'm going to try to model this as a parallel lowers and triangulated uppers today (and post it tonight) to see how that effects the variables. And lastly I will model it as uppers and lowers as parallel. The model will blow up with respect to calculating AS (which as we know is differently calculated from triangulated setups), but it should tell us what we want to know.

In the end I should end up with 4 models/layouts showing how each setup varies from one another while trying to keep everything else constant.

Useful???? Don't know. But might help to explain to people what each setup looks like and how things are calculated.
 

·
Registered
Joined
·
11 Posts
bigbene said:


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:
Right, sprung weight is the deal.

I have a formula at home for figuring the sprung CG if you know the total CG and the weight of axles, tires, etc. (approx.) I'll try to post it tonight.

I think if you use the old "cam shaft" rule of CG location on a rock buggy or big Jeep, you'll get close enough.
 

·
Registered
Joined
·
758 Posts
Discussion Starter #24
bigbene said:
What's the old 'cam shaft' rule?
It is "felt" that the dimension from the ground to the back of the camshaft of your motor is close to the CG location of your rig. Don't know if this is true or not. But that's what they say.
 

·
Registered
Joined
·
2,999 Posts
The only camshaft rule I've seen is 9/10 times people talking about camshaft lift/duration/timing don't know WTF they're talking about!

Seriously though ya gotta look at the distribution of mass. Throwing an external cage on and 44" bogger up top will move the body/frame COG quite a bit. (Regardless of where the camshaft is!)

Ken
 

·
Registered
Joined
·
1,363 Posts
I don't suppose you would be willing to setup a wishbone a arm on top and a triangulated 2 link for the lowers? I'd like to see how one affects the other and if binding does indeed occur.
 

·
Registered
Joined
·
6,382 Posts
all i can say is thanks, i am fixing to do a 4 link here shortly and this sure makes everything easier to figure out. mike
 

·
Registered
Joined
·
758 Posts
Discussion Starter #29
ECF said:
I don't suppose you would be willing to setup a wishbone a arm on top and a triangulated 2 link for the lowers? I'd like to see how one affects the other and if binding does indeed occur.
Sure I can throw that version in and see what comes out. Let me make sure I understand the setup first. Essentially you are talking about a double triangulated setup, except that the upper is an "A" where there is one link at the axle and two at the frame. Right? If so, this is essentially what I modeled already with the file called "4link", except that I have about 4" of seperation for the upper link at the rear axle. From a suspension geometry and action standpoint, it isn't much different from that. Looks like that would be real quick to do. I will do it anyway and post it this evening.

PIG: Thanks. But unfortunately, that's all it is right now is drawings. Time to put paper to steel and prove or disprove the theories.

Gunracer1: Not a problem. That is why I posted it. To help out others and to help explain how all of the variables go togther.

Does anyone have any other setups that they would like to see modeled? Shorter arms? Flatter arm angles?

One of the things I struggle with is to be sure that I am modeling what happens in real life. And the biggest question I have had is by just lifting and lowering the rear tires to induce flex, is this realistic? I've tried lifting just one tire at a time and it creates a lot of rear steer. But after looking at the situations involved in flexing, it seems that one tire up and one tire down is the right way to look at it. Imagine a rig going up a ramp with one front tire. As that tire climbs, the body rolls, but the rear axle stays squarely on the ground. So essentially, you have pushed one rear tire up and pushed one rear tire down. The same would apply if you were doing the ramp in reverse. True? Making sure that I model real life is the hardest, and most important part of this whole thing.
 

·
Registered
Joined
·
11 Posts
Slowzuki said:
The only camshaft rule I've seen is 9/10 times people talking about camshaft lift/duration/timing don't know WTF they're talking about!

Seriously though ya gotta look at the distribution of mass. Throwing an external cage on and 44" bogger up top will move the body/frame COG quite a bit. (Regardless of where the camshaft is!)

Ken
You're right, but eye ball a sideview shot of a rock buggy or Jeep w/cage and it looks to me like the CG is reasonably close to cam shaft height. Besides, how much accuracy do you need?

Get a close estimate of where this point is, extend it to the vertical point above the front tire and draw the force line back down to the rear tire. Once you have that line, keep your rear link IC below it for < 100% anti-squat or above it for > 100%
 

·
Registered
Joined
·
4,166 Posts
four_by_nut said:




One of the things I struggle with is to be sure that I am modeling what happens in real life. And the biggest question I have had is by just lifting and lowering the rear tires to induce flex, is this realistic? I've tried lifting just one tire at a time and it creates a lot of rear steer. But after looking at the situations involved in flexing, it seems that one tire up and one tire down is the right way to look at it. Imagine a rig going up a ramp with one front tire. As that tire climbs, the body rolls, but the rear axle stays squarely on the ground. So essentially, you have pushed one rear tire up and pushed one rear tire down. The same would apply if you were doing the ramp in reverse. True? Making sure that I model real life is the hardest, and most important part of this whole thing.

You are right on for the real life flex. The rig isn’t getting any heavier or lighter so for ever inch of up travel the other wheel should have close to the same down travel. I think
 

·
Registered
Joined
·
195 Posts
MaXJohnson said:


You're right, but eye ball a sideview shot of a rock buggy or Jeep w/cage and it looks to me like the CG is reasonably close to cam shaft height. Besides, how much accuracy do you need?

Get a close estimate of where this point is, extend it to the vertical point above the front tire and draw the force line back down to the rear tire. Once you have that line, keep your rear link IC below it for < 100% anti-squat or above it for > 100%
Sorry guys I'm new to calculating CG and anti-squat . Could you explain further? I have a buggy that works pretty well but you have me second guessing what I've built.:confused:
In real life we're never on level ground so what does all this squat and anti squat do when you're trying to climb #3 at St George? If your links are short and slope up, the tires try to climb under the rig and hops, right? What about the plane from your axle to your IC should'nt it be under your CG ? Help!
And PRO-E?? what ,where and how much?
 

·
Registered
Joined
·
11,078 Posts
Cool post!

I have a good request... :D

How about a 4 link with the lower links converging at the t-case and splayed out to 40-45" wide , but with the upper links parallel to each other about 32"apart. The links mounting distance apart is 6" on the frame and 6" on the axle. The links be 36" long while looking at the side profile.

Ride height would be with the links only at a 7-8 degree down. The suspension will have 8" of uptravel at the splayed outerlink end and about 8" of downtravel.

Not that I would ever build it in a buggy front and back or anything.
 

·
Registered
Joined
·
12,996 Posts
zags said:
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.
Dammit! I should have changed the phrase "movment of the CG" to "weight transfer" but got lazy... and just clicked post.

That's exactly what I mean: weight transferring to the rear of the vehicle will compress the springs, decreasing the angles of all of the links and reducing your effective anti-squat. Part of what makes a hill-climbing link suspension hard to nail down. Any pile of tubes will flex it's ass off in a flat rock garden unles you really fawk it up... :D

Zags's point about the CG staying constant, and the weight transferring, can be summarized in this pic.
 

Attachments

·
Registered
Joined
·
195 Posts
Air Ride said:


It doesn't quit work like that. Anything above a 100 lifts on steep hills.
Under a 100 is definitely the way to go.
Anything above 100 lifts? the rear? Would that add pressure to the front tires? Say if you used a limiting strap to keep your rear from coming up too much and your rear axle from going under your rig like Neils red rig. sorry Neil.
 

·
Registered
Joined
·
758 Posts
Discussion Starter #36 (Edited)
rocraven: I wouldn't second guess for a minute what you have built. If it works, go with it!!! Only think about changing it if it doesn't get you to the top of the hill you are climbing! There is someone on this board (and rockcrawling comps) that uses the converging link setup to GREAT effectiveness. It has a good deal of antisquat which he counteracts with a strap to the diff. Do a search using "4 Link" or "God of Suspension" in the search criteria. You'll get more info than you have time to read! There are some really good discussions and explainations covering the question you are asking about lifting the front, walking underneath, hopping, etc.

EDF: I modeled the setup you mentioned. Go to:

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

And click on the 3link_upper_a.pdf file.

Mieser: I will model that tonight and try to post the "results" tomorrow evening. I have to use a converter to get it into PDF format which is at my office.
 

·
Registered
Joined
·
12,996 Posts
four_by_nut said:
There is someone on this board (and rockcrawling comps) that uses the converging link setup to GREAT effectiveness. It has a good deal of antisquat which he counteracts with a strap to the diff.
Ken Shupe's comes to mind, as do some Avalanche and SNORT setups. :)
 

·
Registered
Joined
·
195 Posts
four_by_nut Thanks for the direction to the G.O.S. thread. I can see now no one can give a ideal example of any link. just plenty of opinions & B.S. But at the risk of starting more. What about front link design. Is there a design that is thought to add pressure to the front tires?
 

·
Registered
Joined
·
11 Posts
If your interested in figuring the unsprung CG height and know the overal CG ( http://www.jeepaholics.com/tech/cog/ ), here's a formula I use:

((Total weight/sprung weight)*CG height) - ((unsprung weight/sprung weight)* hub height)

To get an approximation of the sprung weight, subtract the weight of:

100% of both axles (complete with brakes)
100% of tires and wheels
50% of suspension arms
50% of springs and shocks
50% of drag link
50% of drive shafts
20% of swaybars (100% of links)

from total weight. Remainder is sprung weight.

Example:
5500lbs/3700lbs*38" = 56.49
1800lbs/3700lbs*17" = 8.27

sprung CG height = 48.22"

The force available for anti-squat isn't free. It's a percentage of the torque applied at the rear wheels. When you increase anti-squat, you take away from the power available to climb.
 

·
Registered
Joined
·
758 Posts
Discussion Starter #40
Mieser: I ran your setup last night and will have a PDF this evening to post. I must say..........this is the BEST setup (by the numbers) that I have seen yet. (this is my opinion people, not fact). It has good compromises of all aspects. I set it up with a little longer arms than what you mentioned because I wanted to keep the models all at 100" wheel bases (so as to keep comparing apples to apples so to speak). The rear steer was a little more than the double triangulated setup (7 degrees versus 3 degrees). But AS numbers were lower and the rear axle doesn't want to swing to the side under articulation. I pretty much stays nicely centered. And the links aren't anywhere near touching, even under 40" of total wheel travel (20" up one side, 20" down on the other). Roll axis is a little high, but that can be worked slightly with how the mounts are placed. This setup reminds me of one I saw pictures of on this board. I am sure others have this setup too, but Camo's comes to mind, and I was able to find a pic of it. (see pic). And it appears that Camo's links are much flater than my model, thereby bringing the roll axis to a flatter dimension.

I will post the drawing for this setup tonight for all to see.
 

Attachments

21 - 40 of 74 Posts
Top