Checkerheads new project.

[Clint]

. I will be buying these next. I just have to modify the width of my mounting brackets which seems like hard work at the moment

http://www.emfrodends.com/category-s/1942.htm

Greasable. Rebuildable. No nylon or teflon. Bombproof and not much more that good quality teflon lined rod ends

They look good but you're not allowed greaseable suspension joints if you want to get certified & road legal. Designing your setup so you can fit those in later would not be silly though as I doubt any WOF man would notice.

I used some SKF SI25C rod ends on the chassis end of my front arms but they wouldn't do enough angle for a funky 4-link. I've got a spare set of front arms built up with similar but greaseable rod ends for when they wear out.

Cheers
Clint

[Checkerhead]

Spent a bit of time on Andy's (TeamTonka) lathe last night. Need to finish off my Reduction gearbox then I can get the mounting position for the winch sorted.

[Big]

that's looks interesting.. nice and big and fast.. how are you going to apply a braking system to it? what's the diff out of?

[Checkerhead]

Wont be fast. Only about the same as some of the quick PTO's (like Leigh or Mikes).
Brake is going to be on the output of the reduction gearbox, which sits between the PTO and the diff.
Diff is just a Surf one.

[imsohi]

Mines quicker than Mike's

[Checkerhead]

Any idea on theoretical meters per minute for yours?

I'm only looking at about 36 meters/min max (top gear at rev limit, first layer of drum). Realistically only about 20 meters/min most of the time, which is about the same as no load speed for a standard high mount.

Hopefully make up for slowness with usability.

[skidmark]

Just out of curiosity, as it's a surf diff, are you using the ADD as free spool?

[Checkerhead]

Just out of curiosity, as it's a surf diff, are you using the ADD as free spool?

Yep.

[Checkerhead]

Have got the winch tacked in place.
Bump cans tacked in as well.
Proper upper control arms have been assembled. Need full welding and new bushes pressed in.
Purchased material for lower links. Still need to have a good think about how I'm going to mount the shocks and do the bracing on the lower links.
Winch gearbox is complete enough to sit in place and make drive shafts etc.
Picked up a surf rolling body mainly for the passengers door and guard, but it gives me spare bonnet, windscreen, drivers door, wing mirrors, winch diff etc.

Will try to add a few pics to this post in the next day or two. (I took a few but too dark and my camera is too rubbish to deal with that, will get some in the day light).

edit. Pics added.

[Checkerhead]

Okay. Back to lower link design. Think I'm going to run a straight lower link (rather than a bent one which would be self stabilizing by having the shock acting below the center line between the joints at either end).
The Bush at the front of the lower link will have to deal with all these "inverted pendulum" type force that will seek to roll it over. Check out DAMM racing ultra 4 car on facebook. They are doing it this way.

edit. Here's a pic of DAMM racings lower link.


So far as actual link design goes, I'm really not to sure what I'm up to. "A little bit of information can be dangerous" and I'm squarely in that category.

This is my first thought at what the cross section of my link might look like. All made out of standard flat bar sizes from steel and tube. It would have eyes welded into it (through both the angled plate and the vertical plate.
Looking at that DAMM racing one made me feel like it might be overkill though (not that I think my material is the same quality as theirs)


So Then I moved on to a more simple design. Just shock mounts and a little bracing. I'm using 40NB sch80 for the main tube. It's seamless 48.3mm OD and has a 5.07mm wall.


Then the question is, how do I know if it's strong enough? Did some quick calcs to figure out approx spring rate. came up with a combined rate of 250 pounds. That gives me a bit over 1800 kg to compress 16 inches.
This is the part where I really don't know what I'm doing. Tried some FEA analysis in solidworks. Selected the material as 1035 steel. I think the mild steel we use here is 1090 but that wasn't an option in solidworks and the 1035 had the closed yield strength (1035 is about 10% stronger).

I couldn't get my link assembly to work with the FEA test. I redrew a same same but different part out of "one piece" to avoid the problems I was having. This one is missing the rodend and the Safari bush housing off the ends.
It looks bad with all the red in there, but it's just using an auto scale. The dark red stuff is only moving 0.6 mm with 1800kg applied at the forward most shock mount. The Saf bush would go at the front of the link which is the top left corner in this pic.


So... Who wants to tell me what I have done wrong?

[Ralfie]

.

[Checkerhead]

To figure out what kind of load I might expect from my shocks on the lower link I have simply multiplied the spring rate by the travel. 250 pounds per inch x 16 inches give me 4000 pounds or 1818kg. Then I bumped it up a little.

I realize this is only applicable to a static case, and also that fatigue come into this, but that's a little beyond me at the moment.

Anything else I need to consider?

[doddzee]

What is the max stress reached for that loading scenario? its a little hard to read.

The way in which you have fixed your link arm is not that realistic, if you consider a simple beam with both ends fixed (which is similar to how you have fixed it) the beams bending moment is half that of if it was fixed at one end and simply supported at one end i.e. link attached to chassis and the other end at the diff which is free to move as it is on a wheel, therefore simply supported is twice the stress. There are other factors to consider but that's the simple explination for straight bending as per your calculation.

I cant help with the solid works model to much as I haven't ventured into it too deep, I use the old hand calc method.
If you work out your laden static stress and max stress in the loading scenario above I can give you an idea on were you stand.

In regards to fatigue all your section transitions should be as gradual as possible. A big radius in the corners where your red bits are will reduce the stresses in these areas.

[Checkerhead]

Hey Doddzee. Thanks for the reply. You've got me thinking.

First off, I only have a single stress and strain paper under my belt (combined with zero real world practice) so please forgive me if I ask/say anything daft.

Max stress in that pic is 214 MPa. I have tried a few things around that high stress point and in the end I just modeled it with a 75x14x3 strip welded to the top where the stress spikes are. This was the most effective thing I tried that I could actually do (while still fitting the shock in and not completely redesigning the link).

You make a really good point about how I have modeled it with both ends fixed. My initial theory was that in a static situation it would have an equal and opposite moment acting at the shock and the axle end, thus in a static situation I could ignore the second free end.

I have modeled both ends as a "fixed hinge" rather than just "fixed", so it is free to rotate about the bush housings. All this gives me a nice zero net force and means that I should be getting pure bending. You have got me second guessing myself though.

I understand that if I leave the axle end completely free, I will get very different results. If I am sitting my chassis and axle still and press on my shock until the spring (on the shock) is fully compressed, then that should be the same as what I am modeling. Is this overly simplistic?

Given that my link will be attached to the axle, should I not model it as such?

Really appreciate you help/feedback.

Arron.

[doddzee]

You have me thinking as well, I'm a heavy vehicle transport enginner/certifier. This is a little different than what I typically come across and I havent been 4wding for about 5 years so its a good head scratcher in regards the different loading scenarios.

In regards to the material spec 1090 has a yield of 540 MPA, 1035 yield 370 MPA, Typically NZ hollow tube (Steel and Tube catalouge) yield 480 MPA hot rolled, ERW welded tube 240 MPA. I would confirm the material spec before going any further and confirm you can get 3mm plate with a similar yield if your looking at the higher tensile steels. If your looking over 500MPA you need to put a little more thought into the welding too in regards to electrode and interpass temperatures if you need more than one pass.

On page 2 it looks like you are running two springs in one coilover, as long as the coils are identical then I agree with you linear calc to get your 1800kg. What prevents your coil overs from bottoming out? I assume the bump stop is onto the axle housing so the link does not see any greater load than the compressed coil?

Here is what I would base my design on if I was going to throw some numbers at it:
Max load stress no greater than 75% yield, allows for overloading and axial loads
Laden static stress no greater than 75MPA (with regards to fatigue) if you keep the sudden change in section where your red high stress areas are, could increase this if you smooth out the transition.
No weld stresses greater than 50% electrode tensile strength.

None of the above reflects any of the design standards I use as the factors of safety would be overkill, its just what I think would be appropriate.

In saying all this i didnt consider any of this on my last truck, nothing broke so I guess I built it to heavy. My truck didnt do that many ks, was apart alot so was often inspected so I wasnt too worried.

If I am presented with a solid works analysis of a chassis or component I usually do a couple of simplified hand calcs to see if the stresses are close. May pay you to do the same https://www.google.co.nz/search?redir_e ... 3194777343

[Checkerhead]

In regards to the material spec 1090 has a yield of 540 MPA, 1035 yield 370 MPA, Typically NZ hollow tube (Steel and Tube catalouge) yield 480 MPA hot rolled, ERW welded tube 240 MPA.

Shit. I'm using Schedule 80 seamless pipe, grade B. Which is 35000 psi but I had read as 350MPa. However 35000 PSI is only 240 MPa. So that's a bugger.

On page 2 it looks like you are running two springs in one coilover, as long as the coils are identical then I agree with you linear calc to get your 1800kg.

Springs are different, but the combined rate is 250 pounds. However I see your point here. Once the tender spring bottoms and the harder spring is doing all the work, then my spring rate increases (the entire point of dual rate and I didn't include it. Bugger again). So yeah, I need to rethink that loading.

What prevents your coil overs from bottoming out? I assume the bump stop is onto the axle housing so the link does not see any greater load than the compressed coil?

Correct. Bumps are on the chassis. So for my link to see a load greater than the fully compressed spring, my bumps are screwed, chassis is bent, shock is grenading and I'm not to happy either way.

Here is what I would base my design on if I was going to throw some numbers at it:
Max load stress no greater than 75% yield, allows for overloading and axial loads.

Cool, appreciate the experience and will use this as a design parameter.

Laden static stress no greater than 75MPA (with regards to fatigue) if you keep the sudden change in section where your red high stress areas are, could increase this if you smooth out the transition.
No weld stresses greater than 50% electrode tensile strength.

Was planning to MIG it but can TIG if necessary, was going to let my final design dictate this. No idea what my MIG wire tensile strength is, but surely I can find out. Either that or TIG and buy appropriate filler wire. Again, thanks, I will use this as a parameter.

If I am presented with a solid works analysis of a chassis or component I usually do a couple of simplified hand calcs to see if the stresses are close.

Yep. This is my plan as well. The paper I have done was 100% hand calcs. The solidworks is all self learning so was planning to do a few plausibility checks by hand once I had a final(ish) design.

Thanks again for your input. You've helped me find a few flaws in my reasoning. Time for a rethink, remeasure and rebuild.

[Checkerhead]

Also Suzolla if you're still reading, turns out I was wrong and you were spot on re the yield of the A106 Sch80.

I'm sure you knew that. Makes that DOM look even better though.

[doddzee]

Regarding the welding electrode strength look for in in the Specification / Classification of the wire.

e.g. AS/NZS 14341 B-G49, the 49 x10 = the tensile strength in MPA so 490 MPA
If its American it will be something like ER70-6 the 70 means 70,000 PSI Tensile strength

[De-Ranged]

Very interesting.... thank you, not to many threads carry this sort of tech and its where I want to get too lol quite a few units to get through first tho

Just something I have picked up from the desert racing sites they have alot of concern about getting the mount points for the shocks under the center line for the link or they run a stabalizer link off to the side to stop the twist I know your running safari/cruiser bushes but when the axle is articulated what sort of side loads are going to happen just curious since your mounting point for the shocks is the highest stress point when your loading is straight down
I would guess the universal ball end in the shock (assuming your planing on decent coil overs) will equalize the load from the shock but the link rotation will mean your load will be at an angle

[rokhound]

Loving this thread. Cheers guys

[suzolla]

Hi Aaron,
Yes still watching with interest, yes DOM is good stuff, but in saying that not going to get any this time for my ZUK Rock Assault front axle install.
Was just going to use Sch pipe but now thinking about using some Medium Tensile RHS, with a Min Yield of 450 MPa and Min Tensile of 500 MPa, possibly 65 x 35 x 4. see http://www.nzsteel.co.nz/content/media/ ... 50_rhs.pdf
Regarding strength calculation, have never used finite element stress calcs, just do it by hand using simple shapes and approx values. in your case you have a Simply supported beam with 2 load points in the middle from the spring ( static condition ) and the from the 2 shocks ( dynamic condition ),
Agree with Reece that even though front pivot is a rubber bush, would want to try and get shock coilover mounts as close as possible to a line drawn between the pivot points.
What is the leverage ratio of the coilover mount relative to the axle end mount, just curious how you came up with your required spring rates if you do not know the final wet racing weight.

Other comment.
What is your rear overhang going to be behind the rear wheels as the pictures give the impression that it is quite alot.

Keep up the good work
Cheers
Tim

[Checkerhead]

Very interesting.... thank you

Glad you're enjoying it. Nice to be able to repay the favor.

Just something I have picked up from the desert racing sites they have alot of concern about getting the mount points for the shocks under the center line for the link or they run a stabalizer link off to the side to stop the twist I know your running safari/cruiser bushes but when the axle is articulated what sort of side loads are going to happen?

Yep, this is a "more development needed" section. Haven't even looked at it yet. Basically once I have a final link design I can do a simple moment calc and take a bit of a stab at this. But let's do a rough run through now.

Let's assume that my Nolathane Safari bush will only allow 8 degrees of twist either way from the center (this is a random number based on nothing more than DAMM racing saying their bush only allows 8 degrees total, so if I assume 16 total, maybe that's a good assumption?)
Let's also assume that my primary (combined) spring rate is 150 pounds per inch and my main spring rate is 400 (These are both a little higher than my current calculated rates of 145 and 363) and that half my travel is at the primary rate, and the second half is at main rate. So at full compression I'm getting the equivalent of 4400 pounds pressing on my shock mount (8 inches x 150 pounds + 8 inches x 400 pounds), which is 2000kg which is close enough to 20,000 Newtons.
I'll assume that my shock mount center is 55mm above my link center line. This is 24mm for the radius of my Sch80 tube, 25mm for the radius from center of my shock eye to shock edge and 6mm gap between the shock and Sch80 tube. So 55mm or 0.055 meters.
Now a little trig.


So we want the length opposite the angle that we know, and we have the hypotenuse length. So 55mm times Sine (8 degrees) = 55*Sin(8) = 7.65mm or 0.00765 meters.
Then the moment (Torque) is simply 20,000 Newtons times 0.00765 meters gives us 153 Nm. It will actually be slightly higher than this because the top of the shock will no longer be directly above my link (and all my maths just assumed that it was) but 7.65mm side ways over 18 inches of compressed shock length is less than a degree.

Is that a lot for a Nolathane bush? I have no idea. But I guess it's something I can test. Also it should be close to my worst case example. I would have to be at full bump (which includes 4 inches of Hydro bump stop) and under max articulation. If I can lower my shock mount with relation to my link center line or if my bush rotates less, then it gets even less "side load".

Now I was probably telling you how to suck eggs for a few lines there De-Ranged, but someone else might find it useful.

just curious since your mounting point for the shocks is the highest stress point when your loading is straight down

It's actually not. A few of the models have highest stress near the shock mounts, but it depends how I build them.

I would guess the universal ball end in the shock (assuming your planing on decent coil overs) will equalize the load from the shock but the link rotation will mean your load will be at an angle

Yep, think I covered that above. I'm not to worried about it.

If any of that wasn't clear, or somebody can find a maths mistake or conceptual flaw, please do say so.

Loving this thread. Cheers guys

Aw shucks. As I said to De-Ranged, it's nice to return the favor.

[Checkerhead]

Hi Aaron,
Yes still watching with interest, yes DOM is good stuff, but in saying that not going to get any this time for my ZUK Rock Assault front axle install.
Was just going to use Sch pipe but now thinking about using some Medium Tensile RHS, with a Min Yield of 450 MPa and Min Tensile of 500 MPa, possibly 65 x 35 x 4.

Interesting. Will check out that link, Thanks. I'm thinking down a similar line (tonight anyway) and will price up getting a c section of "Strenx" (700MPa) cut and folded by realsteel.co.nz

... in your case you have a Simply supported beam with 2 load points in the middle from the spring ( static condition ) and the from the 2 shocks ( dynamic condition )

Excellent, that's what I thought. It's always nice when clever people agree with you.

Agree with Reece that even though front pivot is a rubber bush, would want to try and get shock coilover mounts as close as possible to a line drawn between the pivot points.

That was my original plan. I think I will aim to reduce the 55mm I stipulated in the above reply. Not sure if I will aim for below the center line or not.

What is the leverage ratio of the coilover mount relative to the axle end mount, just curious how you came up with your required spring rates if you do not know the final wet racing weight.

Yeah. There are some big guesses going on in my math here. I have assumed 2000kg wet weight. 60/40 front rear split. Also assumed a 10 degree forward lean on the shock and that the shock mount is 150mm forward of the axle mount on a 975mm link. All of these are educated guesses that may or may not be wildly inaccurate, but I have to start somewhere.

A link I drew tonight had a max stress of 215MPa with a 20,000 Newton load. So if I can build it all out of something with a 450MPa yield then I have a bit of space for poor assumptions. Can burn through that safety margin pretty damn quick though.

What is your rear overhang going to be behind the rear wheels as the pictures give the impression that it is quite alot.

Yeah, defiantly more of a trophy truck overhang rather than a buggy overhang. Not sure what it is though, will have a measure when I'm out in the garage next.

Thanks Tim. Always appreciate your input.

Arron.

[suzolla]

Hi Aaron,
Don't agree with this

So at full compression I'm getting the equivalent of 4400 pounds pressing on my shock mount (8 inches x 150 pounds + 8 inches x 400 pounds)

With springs in series and they are still both free to move you do not add the forces, you would if they were in parallel ( side by side )
When they are in series and both free to move they both have the same force on them but will move different amounts depending on their rate. The travel amount adds not the force. so in your case they can not both move 8" and still be free to move, if you are assuming they both move 8" then that means the soft one will be coil bound or the slider is against a stop, so the force from the coilover at full compression will be just due to your stiff spring, so force of your stiff spring at 8" travel will be 8" x 400 lbs/" = 3200 lbs or 1450 kgs.
Should write some more but it is late so need to go to bed.
I'm certainly no expert but have a bit of mech eng knowledge, would be easier to discuss on the ph if you wanted to toss a few ideas/ concepts around, pm your no if you want to.
Cheers
Tim

[Checkerhead]

Hi Aaron,
Don't agree with this

So at full compression I'm getting the equivalent of 4400 pounds pressing on my shock mount (8 inches x 150 pounds + 8 inches x 400 pounds)

With springs in series and they are still both free to move you do not add the forces, you would if they were in parallel ( side by side )
When they are in series and both free to move they both have the same force on them but will move different amounts depending on their rate. The travel amount adds not the force. so in your case they can not both move 8" and still be free to move, if you are assuming they both move 8" then that means the soft one will be coil bound or the slider is against a stop, so the force from the coilover at full compression will be just due to your stiff spring, so force of your stiff spring at 8" travel will be 8" x 400 lbs/" = 3200 lbs or 1450 kgs.
Should write some more but it is late so need to go to bed.
I'm certainly no expert but have a bit of mech eng knowledge, would be easier to discuss on the ph if you wanted to toss a few ideas/ concepts around, pm your no if you want to.
Cheers
Tim

I'm inclined to say you are correct but I'm not 100% sure. I know that springs in series work like resistors in parallel. My actual individual spring rates were something like 245 and 364, giving a combined rate of 145ish. Once the assembly has traveled far enough to hit the stop, then I just have the rate of the second spring. So I think I follow you and agree on that bit. But surely I need to count the force that is required to get the assemble to the stop? (or to tender coil bind).

Either way, I am assuming that I can get half my travel at the higher rate. I haven't even looked/measured to see if that's the case yet.

I do certainly agree that it is late. I shall ponder this over night.

[De-Ranged]

With springs in series and they are still both free to move you do not add the forces, you would if they were in parallel ( side by side )

No
Only use combined spring rate if neither spring bottoms or stops
your springs will both travel so you have
rate x unit of travel for both I prefer metrics lol
eg 4" of travel forr the tender spring at 245 = 980
8" travel for main @ 364 = 2912

remember they both take weight to compress doesn't matter if they are parallel or series

Unfortunately my keyboard is almost out of battery lol otherwise I would explain

I'm on my phone so this may I include some predictive laughs

Right there is no difference series or parallel if there is weight on them they share the weight you are looking at the rates not the load
How far each moves depends on rate
Series or parallel if there is more than one spring you use the co.boned calc sorry I can't remember it off hand
If you know your combined rate and where your tender spring stops then
Combined rate x distance to stop then main spring rate x remaining distance

Regardless it should be around twice the rear suspended weight divided by two since you have a two links with springs this will give you full articulation as you lift a wheel
Remember to save travel for your bumps how much they ramp rate and when to have them start is a whole different discussion lol

[Checkerhead]

Yep. So in first 8 inches of travel, neither spring should bind or hit the stop, therefore it is springs in series, therefore it is the combined rate times travel.
For the second 8 inches (203.2mm for De-Ranged ) then the tender spring is stopped/bound so it's just the main rate.

Cool?

[Checkerhead]

Sorry Reece, I agree with most of that, but not this line.

Right there is no difference series or parallel if there is weight on them they share the weight

If they are in parallel then they share the weight, ie the combined rate is simply the sum of the rates. In this case something like 245 + 364 = 609.
If they are in series then they both "see" the weight. For example, if I have a 200kg per meter spring and a 100 kg per meter spring side by side (not attached in any way) and I put 50 kg on both. The first spring will move .25 of a meter and the 100 kg spring will move .05 of a meter.
Now if I stacked these springs on top of each other and placed 50kg on them it's the same as putting 50 kg on each. The first spring compresses .25 meters because it "sees" the 50kg, and the second spring also compresses .5 metes because it too "sees" the same 50kg. As such total displacement (travel) for my 50 kg load is 0.75 meters. This means that the combined spring rate is less than either individual spring rate, in this case the combined spring rate is 66.67 kg per meter. 1/rate total = 1/rate of spring one + 1/rate of spring two. (Which is the co.bonded calc I think you were referring to.)

Combined rate x distance to stop then main spring rate x remaining distance

Agree 100%. But Tim has me thinking about weather I need to count that initial combined rate into my loading calc. I believe I do, same as you said.

Regardless it should be around twice the rear suspended weight divided by two since you have a two links with springs this will give you full articulation as you lift a wheel
Remember to save travel for your bumps how much they ramp rate and when to have them start is a whole different discussion lol

I should have 6" or 7" of up before hitting my 4" bump stop. Luckily the bump stop acts directly on the axle housing so doesn't feature in my link loading calcs.

[De-Ranged]

Yes you are right sorry late night doing maths my brain wasn't clicking
Personally I'd use main spring rate for calc as it will build in some more strength I know it's nice to engineer to the load but 4wding is a rough sport and our environment is so varied
I know you've probably mentioned this but you have adjusted your spring rate up due to the leverage the axle gains from your spring being down the link

[The WEHI]

an idea to stabilize the link having the shock's/coilovers above center.