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Rear Links - And so it begins - finally!

Further playing with the Calculator <bows to Dan and Greg> <bows again just because I appreciate it so much> leads me to the following numbers for adjustment. Spacing is at 2" due to the hole size.

Z Adjust
Upper Frame 34 36
Upper Axle 32 34
Lower Frame 30 32
Lower Axle 20 22 24

These seem to be the only numbers that yield number that make sense to have as options (assuming my numbers on weight/CoG are even close) without majore PIA for the mounts. Thoughts?

All of these mount holes will be angled to follow the link arc and minimize length adjustment necessary to move from hole to hole.
 
Ha always back to Bluetorch, I guess I will just call Dan up and see what he can do for me. He has always treated me awesome so I really have no reason to go anywhere else. Thats where I got all my 3/4s, misalignments for my stuff and for dad's race car, and tubing inserts from.
 
Just updated my web progress page to include some SolidWorks renderings and my 4 Link Calculator with numbers set at my current "best guess values". Gives you a starting point if your inclined to play around and try some of the options.
 
With regard to the bending, denting, or kinking of the lower links there are really only two failure modes. One is to dent it. The other is to Buckle it. If it kinks at a sidewall point load you've failed it both ways at the same time.

Object Lesson: Balance on a Coke (Coors, Bud, 7-up, etc.) can on one foot. Touch or have someone touch the side of the can. That's a buckling failure caused by the near max compressive loading and the point loading. Oh yea, do it fast or suffer squashed fingers.
Pure buckling failure is resisted much better by diameter than by wall thickness, though in this application wall thickness will help resist a point load inspired buckling failure. One way to increase pure bending strength of a tube is to run a piece of all-thread or cable down it's center and tension it. Trying to bend the tube increases the tension in the center part. Steel responds well to tension and not so well to compression.

By my spreadsheet calcs going to a 2.0 x .25wall tube from 1.75 x .375wall is a 23% increase in bending strength and a 15% weight loss, but going to 2.0 x .312wall is a 32.5% increase in bending strength and a 2% increase in weight. The .312wall will be even better than the .250wall at resisting a pointload inspired buckling failure. My spreadsheet isn't set up to do Buckling strength calcs. Yet.
 
ntsqd said:
By my spreadsheet calcs going to a 2.0 x .25wall tube from 1.75 x .375wall is a 23% increase in bending strength and a 15% weight loss, but going to 2.0 x .312wall is a 32.5% increase in bending strength and a 2% increase in weight. The .312wall will be even better than the .250wall at resisting a pointload inspired buckling failure. My spreadsheet isn't set up to do Buckling strength calcs. Yet.
Click to expand...


Looks like someone's holding out on us on what could be a useful "download".....

:shame:



I showed you mine.....now show me yours! (Man I haven't said that since about the 5th grade!):D
 
I hope it wasn't another guy then too.! :whistle:

Thanks for the hard info. I knew that intuitively, but did not have the knowledge or resources to put numbers to it.
 
Greg72 said:
Looks like someone's holding out on us on what could be a useful "download".....

:shame:

I showed you mine.....now show me yours! (Man I haven't said that since about the 5th grade!):D
Click to expand...

It could be, but I'm not comfortable with some of the numbers it's coming up with and I haven't had the time (ok, ok, MADE the time) to dig into the formulas to check for errors. Some of the numbers do not look right. I would've expected that several particular tubes to have less deflection than the calcs show them to have. B/c of this I've not been sharing it.

Basically what I did was look at every wall thickness in every round tube OD (NO pipe!) from 0.5" to 3.0" that was listed in one of my steel catalogs. I also started on square and rectangular tubes. I'm not the Excel wizard that some here are, so it's been a lot of manual data entry. I've been working on it, on and off, since long b4 my first log-on to cK5. It started out to be an aid in choosing a tube for a tie rod or drag link, and morphed into something much more general.

It calc's weight per foot, inches deflection for a 1k lbs load centered on a 12" simply supported beam, and a torsional deflection using a 1k lbs load on a 12" length tube with a 12" lever arm. The idea was to easily be able to compare different tube OD's and wall thickness' to find the most ideal for the application. Some of the numbers are totally idiotic. For instance, a 0.5" x .028" wall tube will deflect 1034" in the bending calc. We all (most?) know what would happen in real life, but the goal was to be able to compare each tube at some common load, not provide numbers for actual applications.
 
BadDog said:
I hope it wasn't another guy then too.! :whistle:

Thanks for the hard info. I knew that intuitively, but did not have the knowledge or resources to put numbers to it.
Click to expand...

Russ,

Hey now! Tortilla Man is strictly hetero.....let's not get the wrong idea here. :D


ntsqd,

I would be happy to collaborate with you on those calcs if you're interested. I know my way around Excel somewhat, and could probably save you some time there....

Now that my move is mostly completed (and the boxes slowly being unpacked and put away) I have more bandwidth for these types of things again. I owe Triaged (Dan) quite a good chunk of time on ExcelCAD to review his latest improvements and revisions....so that's on my To-Do list in the near future also.


.
 
New idea on the cross member. What do you think? It's on the progress page along with description, but here it is for the lazy...

cross3.jpg
 
what about triangulating off of the arch to the top of the framerails to eliminate your worries of upward force in the center?

BGreen's idea for exhaust is interesting to me. I had a similar idea before, namely cutting and reinforcing the frame to pass the exhaust outside the frame rails without going under or over the rail. http://www.pirate4x4.com/forum/showthread.php?t=106709&page=8
 
Brook's pass through also peaked my interest, not sure if I'll use it though. It's basically my backup.

I'm also concerned that triangulation off the top of the arch wouldn't have enough angle to be effective. I think it would behave pretty much like a square. Better then without certainly, but not really ideal and it adds yet more stuff in the way. I think the gusset sort of thing would have more effect, take less time, use less steel, and be less in the way. If the top cross member idea was a clear winner for strength, then it would trump the other benefits, but I don't think that's the case...

Another thing I'm considering is laying that piece of 2 x 3 x 0.188 flat instead of tall. Then using 2 arches instead of one. Puts the tube in a weaker orientation, but it's still overkill, but doubles the tubes, which are the marginal part (I think). Not sure what I'll do yet...
 
If you triangulate of the base of the arch(half on the 2x3 half on the tube) it will have more angle. Just a thought. I like where you are going with this stuff. I'm aiming for stiffer rear setup to try and eliminate the need for that crossmember. That and I'm going with a single triangulated so I have no need for the crossmember mounting point.

My only issue with the through the framerail exhaust is that if I were to do it I would likely go true dual with no crossover point, and thats not what I want to do. I want to stay with large tube y pipe to single muffler to larger tailpipe. Exhaust will be last thing I do but not an after thought. Looking for the best setup I can get to produce good power from the 383 and not kill everyones ear drums on the trail.
 
I agree on the exhaust. I had a y-pipe made with a drop out section and fed into a 3" x 36" glass pack muffler with 3" dump. Nice rumble but not loud, with good low rpm response and sufficient back pressure that the o2 is happy. Headers might help a very small amount, but I hate headers...

Ok, I see what your talking about. Thought about that but it puts the brace right where the only logical place for my exhaust would be. But that exact idea is what lead me to the gusset/brace that only goes part way out. The rectangular tube resistence to bending is WAY high enough that the brace does not need to go to the point. As long as it triangulates into the upper rail at some point, I think it will be all about the same. My only concern is the tortional load on the rail at that point, and I think the arch (or double arch) will be plenty to keep that in an acceptable range. <shrug> I'm getting out of my depth at this point so I could easily be wrong...
 
I'm certainly not the most knowledgeable but the double arch idea seems like a pretty good one. As long as your welds aren't crap it should be quite strong torsionally.
 
A couple of thots;

Why not just move the frame mounts closer to the frame and move the axle mounts out by the same amount? The closer you get to the rail, the less leverage the links will have to tweak the x-member.

Failing that for whatever reason(s), dump the u-bends altogether and make the x-member flat across the top from rail top to rail top. Port it as needed for exhaust plumbing. Notch it as needed for driveshaft clearence. Put a preferably straight small tube across the gap under the drive shaft if at ALL possible.

OR go to a two piece driveshaft and put the carrier bearing in/on the x-member.

Exhaust is easy with mandrel u-bends and a decent arm on the hacksaw or a bandsaw. Took me less than a day to do a whole cat-back on Patch, including matching up to the stock hangers. Not much strength in the web of the frame rail. I'd poke the clearence hole and nail on a thin diamond shaped doubler plate and call that done.

On my Excel file, just a little experience with Excel huh Greg? LOL
The issue is that I have random numbers that don't seem correct. It's been long enough since I looked at it that I don't recall the particulars. I recall thinking I needed to look up the formula's in my ref book (which is at work) and check to see that I'd coded them correctly in Excel. The rectangulars and squares were the worst as I recall.
 
The drive shaft goes through almost dead center in the gap between the 2x3 rubes on each side. Rough estimate is that it can move up no more than 2", and down by no more than 3, depending on where I set the bump/limits. If I run the cross member high, then those lower links are going to be trying to twist it due to leverage with the brackets hanging way down.

No way to put a tube under the drive shaft. To keep it out to the shaft, it would become an anchor. And redoing the shafts with a carrier bearing is more trouble and expense than I want to fool with, already about at my limit on both, and I still expect I will do a buggy down the road, so hopefully this is just a stop-gap anyway. That or I'll stay in this funk long enough I get fed up and sell out.

As for moving the mounts outward, the upper mount is already almost against the frame, and the outside of the lower axle mounts are about 1" inside the backing plates. So I already put them as far outboard as I could.

So you think this latest design won't hold up? Or just suggesting ways that would be better? I do plan to triangulate from the inboard side of the upper mount to the bend at the top of the rail (where it goes vertical to horizontal).
 
Sorry, wasn't clear. Am suggesting that the x-member be full rail height. Am trying to reduce the flex as much as practical. Consider a box structure made up of flat sheets welded together. Would laminate around the "U" opening.

Too bad you can't bridge the bottom, that would elim a lot of flex possibility.

Haven't played with it enough to know, what does moving the frame end of the lower links outwards toward the rails do to other considerations?
 
Primarily it increases roll axis inclination by several (3) degrees of over steer and raises it by 1 inch (to 33"). That was my previous design which does make the brackets and cross member simpler. But I wanted to flatten out the roll axis and it seemed the roll axis was getting a little on the high side. Of course that can be countered in other ways, but that took those points out of bounds or had other detrimental effects. Playing with that sheet with a goal in mind can have adverse affects on your mental health...
 
Took longer than I thot to model this. Dang'd newly learned Pro/E 'skills' (a joke) getting in the way of getting things done with SolidWorks.
Anyway, this is generally what I was thinking of for an x-member.
 
Wow! That's some serious beef! Unless I miss my guess, that cross member would be several times stronger and more rigid than any part of the stock frame, or any other link cross member I've seen for that matter. Most seem to do fine with only triangulated roll bar tubing for the link supports, even on stock frames and trugies where space-frame type triangulation is not possible. I respect your knowledge, but clearly I'm missing something since that seems way overkill.

Of course, over kill is good when it doesn’t cost you anything (or at lest not much) but that design complicates exhaust and other plumbing as well as requiring me to go in search of the materials required since I have nothing close to that size (nor the plate to build it). That's fine if I need it, but I guess I'm just not convinced. I'll readily concede that yours is a better design, but is it necessary and therefore worth the costs?

Probably wouldn't be much heavier than my design though, so maybe worth the other costs just for the beef. It could be pierced like Brook's for the exhaust, and the brakes, fuel line, and electrical could get a half moon notch at the frame rail to feed through. Hmmm... Decisions, decisions... And that cross member is about the last of the pieces to cut/build before I can start putting it back together. Maybe I'll go work on the spring mounts instead, give this more time to simmer in my head…
 
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