DTSFab.com (Desert, Trail and Sand)
Automotive Powered Off Road (AKA: Buggys, Jeeps, Trucks, Etc,Etc. ) => Chassis and Suspension => Topic started by: fabr on June 05, 2012, 08:21:15 PM
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For quite some time I've read about ,watched the use of, and questioned the thickness of the sheet metal many are using for components such as a arms. For smaller ,lighter buggies such as the barra2da I see no issues at all but for a bit larger, midi size , I have serious doubts about the use of 16ga material I see sometimes used especially since I bent both lower a arms on my rorty R16 car made from 1.25 x .120 4130.
Thoughts and opinions?
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Dont know abot the sheet, but my arms are 1.5 .120 CM with 20 " of travel and estimating the final weight at 2200. What are you estimating the weight of your car?
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If you look at the stress plots for the Barra2uda they prove that a properly designed (I hope it's yet to be beat upon) will be significantly stronger than a tube structure. Almost all the big boy off-road trucks run boxed sheet metal arms. They can't all be wrong...........there must be a reason they're not using tubes. Now my driving style might be severe compared to others but the fact remains that they bent. I even attempted to box the tubes on the single seater two different ways and they still bent, I'm now on the third set of tubed arms (at some point I'll probably retro-fit them with the new boxed design). Scooter's wife Dawn's also bent. He went to 4130 tube and additionally boxed them. I don't know how the 4130 ones held up this season. The first set of her's (mild steel) bent just like Samantha's............
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Fabr,
Another thing to think about is that running in the sand is entirely different than running in the desert (you've spoke many times of the desire to run in the desert). In the sand you support the weight of the buggy and it lands in a semi soft medium when it gets air. In the desert it's like landing on asphalt every time you jump. Add in the rocks and sometimes boulders that put themselves in your way and the impacts alone will take out the arms. In my opinion and I'm sure some will disagree but the desert is a factor of 2 or 3 harder and more abusive than the sand is on a vehicle.
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Dont know abot the sheet, but my arms are 1.5 .120 CM with 20 " of travel and estimating the final weight at 2200. What are you estimating the weight of your car?
I'm 1800 with sand tires/wheels and 2000#with dirt tires/wheels.
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Fabr,
Another thing to think about is that running in the sand is entirely different than running in the desert (you've spoke many times of the desire to run in the desert). In the sand you support the weight of the buggy and it lands in a semi soft medium when it gets air. In the desert it's like landing on asphalt every time you jump. Add in the rocks and sometimes boulders that put themselves in your way and the impacts alone will take out the arms. In my opinion and I'm sure some will disagree but the desert is a factor of 2 or 3 harder and more abusive than the sand is on a vehicle.
we're in complete agreement.
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If you look at the stress plots for the Barra2uda they prove that a properly designed (I hope it's yet to be beat upon) will be significantly stronger than a tube structure. Almost all the big boy off-road trucks run boxed sheet metal arms. They can't all be wrong...........there must be a reason they're not using tubes. Now my driving style might be severe compared to others but the fact remains that they bent. I even attempted to box the tubes on the single seater two different ways and they still bent, I'm now on the third set of tubed arms (at some point I'll probably retro-fit them with the new boxed design). Scooter's wife Dawn's also bent. He went to 4130 tube and additionally boxed them. I don't know how the 4130 ones held up this season. The first set of her's (mild steel) bent just like Samantha's............
Again ,we agree . My point was I suspect 16ga mild will not hold up on a car the size/weight of mine. I don't mean to knock anyone's design but ,sorry engineer, I was skeptical when you posted your arms and now I'm really skeptical after bending mine. Engineers car is ,I think ,comparable in size/weight as mine. At any rate we're probably twice your cars weight. As for the big trucks ,I'm betting they use a bit thicker than 16 ga.
I understand box section is stronger. Look at Mosebilt stuff. All his front arms are made from square tube,then boxed. That man builds some innovative stuff that works.
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Not saying 16GA (.063) is the answer for yours. Obviously it would have to be sized appropriately. I first modeled them at .120 sheet. My stress guy told me twice "Go Thinner". Changing the sheet thickness as a result of the stress plots is very easy. They just get heavier the thicker you go :)
I agree the big trucks use thicker material but then they have 600+ horsepower to push them thru the desert.
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My research and little knowlegde lead me to the idea that square material is stronger if the forces come straight in on flat side, if from the 90* corner they're weaker than same sized round. Round is same from all around and thus better for the novice builder. I'm guessing the boxed arms fit in that, but drowning drowning. If modeled and put thru the stress like Lance did (which was pretty damn cool) you could workout most weakness.
I hope to see Engineer's but at this fall ride, ;)
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Please understand that I'm NOT talking about the barea2uda. I AM saying that 16 ga will not hold up to serious or even casual use whether the sand or hardpack on a bigger heavier car . Sheet metal box structures can and are used very successfully on all size cars. There is a huge difference tho in the stresses a light small buggy suspension arm will see and what will be seen by larger heavier cars. In this topic,I'm not in the least considering small buggies. It is only about stuff that will be 1800# or so and larger such as engineers car. Again ,lance ,I am NOT talking about the barra2uda. IMO your design will work quite well and looks very very nice and professional. That said,I stand by my opinion.
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Problem with FEA,as I found out recently while playing aroiund with Alibre FEA is that it is Vvery much a high tech witchcraft tool. Works very well but the saying "garbage in=garbage out" really applies to FEA.
How ,for example, can you determine the load applied to anything when you have no way to measure what that load is?
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I understand. I was only using it as a comaprison, albiet a smaller ligther version of your car or Engineers. It all scales up. The heavier car the more the g-forces are a factor upon impact as a result of more mass hitting a solid unmoveable item. Obviously the sheet thickness needs to be adjusted accordingly to the weight of the vehicle aka the final load it will see.
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Problem with FEA,as I found out recently while playing aroiund with Alibre FEA is that it is Vvery much a high tech witchcraft tool. Works very well but the saying "garbage in=garbage out" really applies to FEA.
How ,for example, can you determine the load applied to anything when you have no way to measure what that load is?
In my case it was easy. I had bent enough arms in real life that I knew where they failed and I knew how much the buggy weighs. I just took the old arms and modeled them and applied the load till they failed like in real life. There I had a real life load and parameters to apply to the "new" arms or certainly a comparitive load. Plus I have a very talented Stress person doing my anaylsis. Shall we say an expert at the witchcraft :)
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I fully agree with what you are saying. Additionally,box structures can be made with thinner materials but that does not necessarily mean lighter total weight.
Example,1.5" round has a circumference of 4.71" vs 1.5" square being 6". A difference of 28% more material. so,material of approx .090 could be used in place of .120 and weigh the same.
I would guess that the .090 square tube supported at both ends and a vertical load applied at the midpoint would support more than the .120 round. With that said I also see advantages to box construction on things such as a arms when considering horizontal loads. I think I will take a page myself from Mosebilt and build a arms and the like from square tube ,plated where needed. Stronger for one thing and also much easier to attach tabs and such. IMO ,a no brainer to go square. Just need to be careful and consider the weight of square vs round when designing. Make sense?
Biggest issue I see with using tube instead of sheet metal is that box construction is "in" and square tube is not. For sales appeal sheet metal is the way to go but from a fab standpoint of building one offs the tube works best I'd think. I have a lot of respect for the out of the box thinking Mosebilt does and his willingness to do what he feels is best regardless of what others are doing.
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Just a quick weight comparison of 1 foot long peices for you.
(https://dtsfab.com/proxy.php?request=http%3A%2F%2Fwww.dtsfab.com%2Findex%2FMGalleryItem.php%3Fid%3D1482&hash=21c1c92f450e72a600bf7d7eaa24742be259e8a4)
(https://dtsfab.com/proxy.php?request=http%3A%2F%2Fwww.dtsfab.com%2Findex%2FMGalleryItem.php%3Fid%3D1483&hash=1ced3a102719a0f98d1937c70675ec0e9d04b4b8)
(https://dtsfab.com/proxy.php?request=http%3A%2F%2Fwww.dtsfab.com%2Findex%2FMGalleryItem.php%3Fid%3D1481&hash=f6a3b0e431132a63ce41f7971ff11f69683d1bd3)
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How bout carve them out of billet. Some of the big boys using them even on dual sports. Its the best looking of the "in" thing.
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How bout carve them out of billet. Some of the big boys using them even on dual sports. Its the best looking of the "in" thing.
Anything billet would be substantially heaver Carl. I think what Lance is doing here is saving weight not adding it.
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The billet stuff,IMO,is just bling and not an improvement. I think lance is doing the right thing for the 2da's. Very hard to billet anything and make it lighter and stronger.
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Just a quick weight comparison of 1 foot long peices for you.
(https://dtsfab.com/proxy.php?request=http%3A%2F%2Fwww.dtsfab.com%2Findex%2FMGalleryItem.php%3Fid%3D1482&hash=21c1c92f450e72a600bf7d7eaa24742be259e8a4)
(https://dtsfab.com/proxy.php?request=http%3A%2F%2Fwww.dtsfab.com%2Findex%2FMGalleryItem.php%3Fid%3D1483&hash=1ced3a102719a0f98d1937c70675ec0e9d04b4b8)
(https://dtsfab.com/proxy.php?request=http%3A%2F%2Fwww.dtsfab.com%2Findex%2FMGalleryItem.php%3Fid%3D1481&hash=f6a3b0e431132a63ce41f7971ff11f69683d1bd3)
Pretty close to my guesstimates.
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for the plate/sheet for the LCA's use 0.120" for the main structure and if you are gonna do any additional bracing in high stress areas (i.e. shock mounting area) then use 0.090" on top of the 0.120". . .that's what the pro's use that you pay mucho dinero for. . . I didn't know if you had the arms built yet but this is what I found for info. Hope it helps!
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Sure does but only to a point. Are they using mild 1018 or 4130?
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FWIW,I'm going to do a boxed round tube construction for the lower control arms front and rear since I somehow have an abundance of 1.75 x .120 laying here and a nice supply of .125 4130 plate. I must have had my head in a dark place where the sun never shines when I added up footage. eyes I'm thinking they should look nice also. That is if I weld them worth a crap. For whatever reason I'm on a roll so far. The welds look fantastic. Hope that holds out till finished. ;D ;D ;D
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Sure does but only to a point. Are they using mild 1018 or 4130?
4130 from what I understand.
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FWIW,I'm going to do a boxed round tube construction for the lower control arms front and rear since I somehow have an abundance of 1.75 x .120 laying here and a nice supply of .125 4130 plate. I must have had my head in a dark place where the sun never shines when I added up footage. eyes I'm thinking they should look nice also. That is if I weld them worth a crap. For whatever reason I'm on a roll so far. The welds look fantastic. Hope that holds out till finished. ;D ;D ;D
Are you mig or tig welding? Those will be extra beefy arms, you should have no troubles!
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TIG. I need beef. I tend to bend things.
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Thanks for the vote of confidence. ;D
My upper arms are 16 ga, but the lowers are 14 ga and considerably heavier. I saw where the 3200 lb 1000hp cars were using 1/8" and decided I didn't need to be nearly that heavy, but I may be wrong.
I calculated the weight of a tubular arm then tried to come up with a sheet metal design at nearly the same weight. As Lance pointed out a square tube is stronger because more of the material is further from the bending point. A sheet metal arm has most of its material at the furthest distance from the bending axis. So if you are the same weight with the material distributed more efficiently then it should be stronger.
Where I am concerned is when you start narrowing down to the outer connection point at the spindle. If the total cross sectional area of the arm gets down to the equivalent of the cross section of your heim shank then you are asking for trouble. I have seen people add doubling plates for the last few inches that spreads the loads back to where the cross sectional area of the arm is much greater.
What I really like about the sheet metal design is the front to back strength. If you lawn dart, tubular arms want to pivot at all the connections and parallelogram, where the sheet metal (if there is enough material to keep it from folding) should have much more resistance to folding back.
The reason I went lighter on the top arm is because my wheel center is about 3" from the lower arm and about 9" from the top arm. When you jump and land, the lower arm is holding all the weight, all the upper arm has to do is control camber. If your lower spindle connection is tucked into the wheel reasonably the camber control load isn't very significant. When you hit a square edge bump pushing the wheel straight back, the 3-9 inch ratio tells you that the lower arm will take 3/4 of the hit and the upper arm will take only 1/4.
That was much of my reasoning for what I did. Remains to be seen if it will work out.
I don't see how you can go wrong boxing the tubular arms either.
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TIG. I need beef. I tend to bend things.
Well if your not bending shit, your not trying hard enough! ;D
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I know johnny greaves truck runs boxed lowers and tube uppers. His truck has to way 4,000lbs according to torc rule book. They seem to hold up pretty good unless he gets hit really hard in the front, the upper control arm tends to break or bend. That's short course off road racing for ya though! His whole truck is chrome moly everything. Here's a link to check out his truck.
http://www.race-dezert.com/home/feature-vehicle-johnny-greaves-pro4-1631.html (http://www.race-dezert.com/home/feature-vehicle-johnny-greaves-pro4-1631.html)
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Well if your not bending shit, your not trying hard enough! ;D
Think I'll beef and try harder yet...................... ;D
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I know johnny greaves truck runs boxed lowers and tube uppers. His truck has to way 4,000lbs according to torc rule book. They seem to hold up pretty good unless he gets hit really hard in the front, the upper control arm tends to break or bend. That's short course off road racing for ya though! His whole truck is chrome moly everything. Here's a link to check out his truck.
http://www.race-dezert.com/home/feature-vehicle-johnny-greaves-pro4-1631.html (http://www.race-dezert.com/home/feature-vehicle-johnny-greaves-pro4-1631.html)
I'm thinking the same thing since,just as engineer pointed out , the uppers get quite a lot less abuse. My car is all 4130 also. Thanks for the link. I'll look at it now. Always good to have something to compare or scale to.
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Love the RDC feature section!I have looked at every vehicle on there,tons of design info.
Sucks that they started puting the ghost RDC on the pics though.
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Think I'll beef and try harder yet...................... ;D
Now your talkin! ;D
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Love the RDC feature section!I have looked at every vehicle on there,tons of design info.
Sucks that they started puting the ghost RDC on the pics though.
My heart is in short course off road racing, I spend countless hours on RDC trying to soak up as much knowledge on truck design that my head wants to explode! :o Yeah the ghost image sucks but what do you do. My bro and I head up to the Mecca of short course racing in Crandon, Wisconsin to watch the races and take in up close knowledge from drivers and mechanics. It's my Graceland. ;D
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Hey Fabr, what deserts you gonna hit when this thing is done? I was in arizona this last christmas and spent the day four wheeling through canyons and wide open desert! One of the best times I've ever had! I'm going back around the same time next year for a week and plan to spend it all in the desert. There's an outfit in the pheonix area that rents out sxs's for the day so I'm gonna hit that up and blast all day. Wifes cousins have four wheelers so we'll hit the canyons and mountains as well. I can't wait!
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Wish I knew. Open to ideas.
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Wish I knew. Open to ideas.
I'll call the wife's cousin in az and get some info for ya. He lives in the pheonix area and thats were we went four wheeling. Nevada is also another place 2 research.
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COOL!!!! Thanks!
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If you have any pics of your arms can you post em? Just curious!?! ;D
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Control arms that is, I don't need to see YOUR arms! ;D
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Some stuff showed up on brown today. I'll have some arm pics soon.
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Ok!
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are you going to box in both front and rear arms? are you going to give the a-arm rear end a try in the rear or the current design? did you keep the bent arm ? if so take them to the dunes with you I would like to see them in person.
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Lowers will be boxed ,front and rear.
A arm rear @28 degrees droop will five 26" rear travel with 3" frame clearance at full bump using approx 28" arms pivot to pivot with only approx 1/4" axle length change.
Yes I have bent arm still. I'll try to remember to bring it/them.