Landracing Forum
Tech Information => Technical Discussion => Topic started by: Richie on August 06, 2011, 11:42:18 PM
-
Is square tubing legal for use as a roll cage and if so would it if have to be 1 continuous piece ?
(http://i376.photobucket.com/albums/oo206/pedal2themetal/102_1562.jpg)
-
Even if it was legal I doubt anyone who really thought about it would use it..........
When you smack your helmet on something you hope it doesn't have a sharp edge on it.
When you bend tube you want it to have the forces on it spread evenly, I don't reckon that happens with square stuff.
-
"What's the difference between experience and education ?"
The difference is reading, re-reading and asking the correct officials the question.
That said, the rulebook states that tubing, does not specify round or square, of certain properties must be used. Looks like you have proceeded without guidence.
I would change my consultant if I were you.
DW
-
X2, I would run away from your consultant and hide till he/she disappeared. Tony
-
What's more that appears to be aluminum tubing and I can pretty much guarantee that it won't make it past tech for any crash protection purposes and likely not as a main chassis material.
Pete
-
Experience without education is a brutal and imprecise teacher at best.
Education without experience leads to impractical and un-buildable designs.
The experienced person lacking education will do the right thing because others did it before him even though he doesn't know why. At worst, experience without education forces us to repeat past mistakes without learning from them. The educated person will attempt theoretical perfection without regard to practical requirements like available tire and tubing size.
We need both. The first thing I ask anyone who comes up with the latest-greatest idea is "how is everybody else doing that?" If it really is a good idea, they can prove it's worth by comparison. Likewise, anyone who gets into the trap of "we-do-it-this-way-because-we've-always-done-it-this-way" needs to step back from time to time and take a fresh look.
All of that said, roll cages should be made of round tubing for the simple reason that crash forces come from all directions, with multiple impacts that are not oriented to the structure we build.
-
With all of the education and experience advice out of the way. NOPE square tubing won't cut it. The tubing specifications called out by most sanctioning bodies call for X.XX Diameter tubing = round. get a rule book and read,read,read then ask,ask,ask. GL
-
Even if it was legal I doubt anyone who really thought about it would use it.......... / Why ?
When you smack your helmet on something you hope it doesn't have a sharp edge on it. / padding and/or radius tubing might help?
When you bend tube you want it to have the forces on it spread evenly, I don't reckon that happens with square stuff .\ i've bent both with a gas axe and i dont know bout the forces on it ... but it did bend
-
The difference is reading, re-reading and asking the correct officials the question. / I will... though who's to say there a 100% correct
That said, the rulebook states that tubing, does not specify round or square, of certain properties must be used. Looks like you have proceeded without guidence. / true... like i stated in an earlier thread built that to get the shape of the body and to see if i could fit in somin that size.
I would change my consultant if I were you. / na i don't have a consultant... inspiration
DW
(http://i376.photobucket.com/albums/oo206/pedal2themetal/102_1593.jpg)
-
Richie
It looks like you are building a motorcycle streamliner
If you have a rule book , you should look at rule 7.H.4
Roll Cage:
Shall completely surround the rider and shall be fitted in the rider’s compartment. Minimum diameter is 1-1/4 in. with .090 in. nominal wall
thickness, mechanical steel tubing. No galvanized pipe, black water pipe or threaded fittings are permitted. The design of the roll cage shall
incorporate the following features as a minimum: Two (2) roll bars, (one forward and one after the rider’s head), which shall be tied together and
capped with a steel plate .090 in. thick. The cap shall cover the upper 140 deg. of the rider’s head. The roll bar shall be braced with a tube of the
same dimensions on each side. Rider head movement shall be limited to no more than 2 in. to each side, top, or rear, with rider’s head in the
normal position. Roll cage padding meeting SFI specification 45.1 for round tube roll cage padding and SFI specification 45.3 for flat roll cage
padding is required in the vicinity of the driver’s helmet.
Forward movement: All motorcycle streamliners presented for inspection shall have an engineered and tested SFI
spec 38.1 type head and neck restraint system. All motorcycle streamliners shall have an engineered and tested SFI spec 38.1
type head and neck restraint system.
Lateral movement: Shall be constructed such that the helmet can not exit the outer plane of the roll cage,
You will note is states "steel tubing" so aluminum is out
The other thing you should consider is buying the correct roll cage padding and HANS type neck restraint, then working out if you fit in the cage
Also, I'm not keen the way the cross bar is made in sections. It think would be better to make the round section and weld the front to back bars to it.
G
-
HANS type neck restraint / i'm not sure bout that , if u could make the cage and padding to prevent such movement ... why need that device ... and round roll bars would be easier to produce ... and i was sure bout the aluminum structure, just cause the melt issue even if saddled by 1/4" plate ... :cheers:
-
"HANS type neck restraint / i'm not sure bout that , if u could make the cage and padding to prevent such movement ... why need that device ..."
Because the rulebook states that the item is required. There is no provision to not use one.
The officials have literly 100s of years experience combined. If you can disprove that with your design knock yourself out.
Good luck, and I really mean it this time.
DW
-
Before you get any further into the build I'd be very tempted to run your design and material choices past the officials of the organizations where you plan to run. That way you won't have put in all the money and effort and find that you can't run where you want to if at all.
Pete
-
I am always mystified as to why people build space frame type structures with square tubing. Is it because they are unable to visualize the tube joints using round tubing? With todays many types of various tools to cut and miter round tubing at almost any angle and providing perfect tube fits using square tubing seems almost inexcusable.
Rex
-
I think it's because they think it's easier Rex. It may be if they aren't willing to tool up a little.
At the same time there are a few square tube based cars that are very nicely done and the results show it.
Pete
-
Even if it was legal I doubt anyone who really thought about it would use it.......... / Why ?
When you smack your helmet on something you hope it doesn't have a sharp edge on it. / padding and/or radius tubing might help?
When you bend tube you want it to have the forces on it spread evenly, I don't reckon that happens with square stuff .\ i've bent both with a gas axe and i dont know bout the forces on it ... but it did bend
Inspired indeed Richie and brave too, I'm unaware of many people who have got as far into a build without running their design under the nose of someone familiar with one of the LSR racing bodies rules.
The difference is reading, re-reading and asking the correct officials the question. / I will... though who's to say there a 100% correct
I'm not going to nit-pick but if you are going to run it you will need to pass tech, there is a natural hierarchy that establishes itself in these type of organisations and looking at the above statement you're having a little trouble getting your head around it.
There are no shortage of builders who push the envelope and who are always at the edge of what is felt to be legal but they still adhere to accepted basic standards of engineering.
If square was stronger, trees would be square.
Experience without education is a brutal and imprecise teacher at best.
Education without experience leads to impractical and un-buildable designs.
The experienced person lacking education will do the right thing because others did it before him even though he doesn't know why. At worst, experience without education forces us to repeat past mistakes without learning from them. The educated person will attempt theoretical perfection without regard to practical requirements like available tire and tubing size.
We need both. The first thing I ask anyone who comes up with the latest-greatest idea is "how is everybody else doing that?" If it really is a good idea, they can prove it's worth by comparison. Likewise, anyone who gets into the trap of "we-do-it-this-way-because-we've-always-done-it-this-way" needs to step back from time to time and take a fresh look.
All of that said, roll cages should be made of round tubing for the simple reason that crash forces come from all directions, with multiple impacts that are not oriented to the structure we build.
Richie have you looked over many bike-liners before? I get the feeling you have some inspiration for a "radical new approach", you'd be hard pressed to find a more determined bunch of lateral thinkers than the guys who build and race "Special Construction" if you learn up on the history of these vehicles you'll have a comprehensive idea of what has and hasn't been tried. Most of what hasn't been tried has been thought about and a genuine understanding will be based upon knowing why some ideas are used and others aren't.
-
A better look at his project.
FREUD
-
Even though square tubing actually has more metal than a comparable round tube, it may deflect more than round tube.
I just ran a pretty simple test in solidworks. criteria is 1-5/8 x .125 wall tube, square and round.
I modeled a single pc 24" long and placed a 12" pc perpendicular on each end (centered on the 12 dim).
running the simulation on 1020 stl, fixed one end pc and applied 1000# load on top of the other end.
results surprised me, the sq tube deflected 4.34" (45° tube orientation), 4.04" edge aligned with axis of force and 2.99" on the round tube.
-
I am always mystified as to why people build space frame type structures with square tubing. Is it because they are unable to visualize the tube joints using round tubing? With todays many types of various tools to cut and miter round tubing at almost any angle and providing perfect tube fits using square tubing seems almost inexcusable.
Rex
I have asked that question of some who insisted on using square tubing and always get the same response..."Because it is easier to work with."
I try to explain that round is actually easier to work with once over the hump on the learning curve, but it usually falls on deaf ears.
-
Richie
Have a look at these two build diaries
In particular, Ross Brown of the DLRA
http://www.landracing.com/forum/index.php/topic,9113.0.html
http://www.dlra.org.au/forum/viewtopic.php?f=18&t=1314
G
-
"Because it is easier to work with."
That was my first thought when reading this thread.
DW
-
I am always mystified as to why people build space frame type structures with square tubing.
Cause they believe it will work and be more rigid and safer... possibly allowing better hook up
"Because it is easier to work with." really it isn't especially if you wanna bend it
-
author=Dr Goggles link=topic=10147.msg166365#msg166365 date=1312751451]
If square was stronger, trees would be square.
I wonder how strong trees would be without the ground around them.
Richie have you looked over many bike-liners before? many pictures on the internet ... i'm here to learn
(http://i376.photobucket.com/albums/oo206/pedal2themetal/102_1619.jpg)
-
Putting aside the rulebook’s “diameter” implication that only round tubing is suitable for frame construction, it may be instructive to look at the section properties of the two tubing types and orientations. Calculating these and unitizing them based on the round tubing properties, and using the same sections (1.625 dia x .125 wall) as johnneilson did with his model in reply # 17, we get the following:
Area I (in^4) S (in^3) 1/S Sig max Sig/A Deflection
circular tube 1.00 1.00 1.00 1.00 1.00 1.00 1.00
square tube 1.273 1.698 1.698 .589 .589 .463 .589
diamond tube 1.273 1.698 1.200 .833 .833 .654 .589
Which tells us that the square tubing is somewhat heavier (area ratio) than the round per unit length, that the bending moduli of the square and diamond are superior to the round, that the stress levels of the square and diamond are less than the round for the same load (Sig max), that the stress per unit weight is also superior, and the bending deflection under the same load is less than the round. This improved performance is largely due to the fact that a good part of the square and diamond material is outside the diameter of the round, and the sections are in effect larger.
So, maybe, as Blue noted, it would be good to step back from time to time and look at things as they are, not as they have become familiar, before loosing off-the-wall criticism.
As an aside, it is unclear where the results reported by Reply 17 went wrong, but it appears that he has confused the “deflection scale” number with the actual deflection. Clearly, 4” deflections are unrealistic. The deflections of the situation that he modeled are actually more on the order of 0.9” circular and 0.54” square. And that is assuming an elastic solution. In fact, all of these sections under that modeled loading are well beyond their mild steel material yield strength.
-
So then, the seemingly standard method of building a 2X4 rectangular frame and a round tube cage above that is still the way to go then? :-)
-
wow, 2x4... i have been accused of overbuilding once before, but woulda never thought of using 2x4"... seems like tractor building material... and without googling it i have never heard of diamond tube before, unless you mean tilting square tube on it's corner, i have heard of elliptical tubing (streamline) whatever they wanta call it... though i think that only comes in 4130 moly and that can get pricey
-
I followed Sums build until he stopped. It seems everything but the roll cage is square or rectangular tubing. Interesting build but I have to wonder why not round. Any thoughts?
-
IO,
it didn't sound right to me either yesterday.
I ran it a couple different times and still the same result. I will try another simulation tonight once all are sleeping.
I am wondering if it is because of the excess amount of pressure beyond the material yeild point that is issue.
I will try to find some actual chassis (karting) and see what happens to them with excessive force.
John
-
There are a lot of LSR cars with square and rectangular chassis. All have round tube roll cages that I know of. Best thing to do is come to the salt and look at the cars and see how they are build, this goes for bikes as well.
-
I think it's best to consider this a mock-up.
First you'll have to figure something else for front suspension and steering, what I see is not stable for the bumps and ruts. Second, weight is not the enemy on the salt, it is not a drag race or road course. All your hard effort to save weight is wasted since the weight will have to be added back (and more) to get traction. Last bit, aluminum and the small tubing size is much more flexable then you want, at speed you'll be countering frame flex that would make a H1 Kawasaki pilot nervous.
That said, I would complete more of the build (but don't skin it) and maybe think of plunking a stock engine in it if you think the layout is going well. A short run down a dirt road will show you what I mean about the frame and front suspension, expect to crash. Just don't get too angry or frustrated. People who have designed their sixth frame are still finding things to remember to change on the seventh. Going fast is a process. 8-)
-
that's the plan, i have a suzuki 50cc... somebody put regular 30 wieght oil in it, i have since drained and replaced with 2 stroke oil, but i can't seem to keep it running... i'm thinkin a carb rebuild is what's needed, once i get it runnin i can get back on track and begin some test's
-
Once I read a structures book that refered to bent tubing as "pre-buckeled" tubing--- a good point, I think. However, so as not to create a problem in tech, my roll cage is all bent round tubing.
Regards, Neil (Ouray, CO)
-
For equal cross sections and wall thicknesses round is lighter and stronger in torsion while square is heavier and stronger in bending. It would be very difficult to get a satisfactory wrinkle free bend in square tubing for roll cage construction.
Pete
-
author=Anvil* link=topic=10147.msg166489#msg166489 date=1312834954]
I think it's best to consider this a mock-up.
That said, I would complete more of the build (but don't skin it) and maybe think of plunking a stock engine in it if you think the layout is going well.
I most likely will skin it with sum flat plate... atleast the area around the driver , also was thinking bout puttin a training wheel (sidecar)
on it cause, i will be starting of at a slow speed
-
Another reason i was thinkin aluminum was when i seen this pic i thought that was aluminum tubing... after lookin at pics on chevyasylum i realized it was steel, just wonderin what size tubing?
Awesome bikeliner
(http://www.yacoucci.com/albums/album85/aug15_27.sized.jpg)
-
Unfortunately that lying forward style liner has been made illegal, at least for now.
Pete
-
author=Peter Jack link=topic=10147.msg166656#msg166656 date=1312944735]
Unfortunately that lying forward style liner has been made illegal, at least for now.
Pete
makes ya wonder why , seems it has proven to work
-
The original question from richie asked if square tubing could be used to construct a roll cage.
I think DW implied that it could. I don't think it can.
In fact section 3.B.1, in the first sentence requires the use of ".... 1 5/8" O.D. round steel tubing..." for all roll cages class down to the F class. Starting with the G class and below the requirement is "...round steel tubing not less than 1-1/2 in. O.D..."
Look pretty clear to me.
-
Many of the really fast big diesel truck roll cages have been constructed of square tubing. I'm sure they are thicker than .120"; perhaps as thick as 5/16". Many of the faster lakesters and liners also have square tubing under the driver which is considered part of the cage system. My advice would be to prove the strength of what you want to do to the technical committee prior to making the commitment to do it...............Good luck
-
Ref: Reply #32
However strong Pete’s conviction is that round tubulars of the same outside dimension and thickness as a square cross-section have better torsional capacity than the square, it would be remiss not to point out that that point of view is in conflict with established engineering practice.
For a closed, thin-wall tube of any shape, the torsional capacity, to a close approximation, is proportional to the area bounded by the centerline of the wall thickness. So, in the case of the 1-5/8 x .125 wall round vs. square tube, the ratio of the square’s area to the round’s is 4/(pi) or 1.27. Square wins again, but that is not to say it may be the best or allowable choice for a roll bar.
(See “shear flow” in any Strength of Materials textbook.)
-
author=old chevy truck link=topic=10147.msg166662#msg166662 date=1312950480]
The original question from richie asked if square tubing could be used to construct a roll cage.
In fact section 3.B.1, in the first sentence requires the use of ".... 1 5/8" O.D. round steel tubing..." for all roll cages class down to the F class. Starting with the G class and below the requirement is "...round steel tubing not less than 1-1/2 in. O.D..."
Bub rules state , 1 1/4" x .090 does not specify round or sqaure... highlights no aluminumn hardware as part of the belt system,but does state this Builders of any frame other than those constructed of steel shall submit frame structure information to the promoters that document the durability of the structure. When requested, provide test certifications on components and stress examination as required.?
-
Thanks IO. I'll go digging a little deeper. That's one I've had locked in my mind for a long time. I can't remember the source but now I'll go looking further. Don't want to be dispensing inaccurate information. :? :? :x
Pete
-
IO, All,
yes, I goofed reading the results, I miss read the Deformation scale for the displacement.
I really need to wear my glasses more and pay attention.
I am not really sure if the picture attached would have survived better being round tubing or not.
My immediate thought would be to increase the wall thickness and stop sliding into k rails sideways........
FWIW, IO had the numbers pretty spot on for displacement, and correct, overloaded to the point of ridiculous.
J
-
author=johnneilson link=topic=10147.msg166370#msg166370 date=1312753619]
(http://www.landracing.com/forum/index.php?action=dlattach;topic=10147.0;attach=27727;image)
could you perform the test this way?
(http://i376.photobucket.com/albums/oo206/pedal2themetal/183276133_o.jpg)
-
here you go, same model with centered force@ #1000
these plots show the displacement of the center point.
-
author=old chevy truck link=topic=10147.msg166662#msg166662 date=1312950480]
The original question from richie asked if square tubing could be used to construct a roll cage.
In fact section 3.B.1, in the first sentence requires the use of ".... 1 5/8" O.D. round steel tubing..." for all roll cages class down to the F class. Starting with the G class and below the requirement is "...round steel tubing not less than 1-1/2 in. O.D..."
Bub rules state , 1 1/4" x .090 does not specify round or sqaure... highlights no aluminumn hardware as part of the belt system,but does state this Builders of any frame other than those constructed of steel shall submit frame structure information to the promoters that document the durability of the structure. When requested, provide test certifications on components and stress examination as required.?
Section 3.B.1 is addressing a car not a motorcycle. My old rulebook(2009) so it may have changed does mention in 7.H.4 "flat roll cage".
Best to shoot some pictures by the appropriate SCTA or sanctioning body of choice not the interwebby place.
-
Richie, Stop smoken crack. This thread is going to long. GET A RULE BOOK AND LEARN TO READ. Cripes man light weight vehicles are for drag racing. this is not drag racing. you need structural integrity and the aluminum frame that you have posted aint got no back bone man . ie Steel, cheese and rice man.WTFM
-
author=johnneilson link=topic=10147.msg166786#msg166786 date=1313077388]
here you go, same model with centered force@ #1000
these plots show the displacement of the center point.
Thanks for taking time to run them test :cheers:
-
Cap Thunder,
Internet rage?
Get it ALL the time!
-
While I can honestly say that I sometimes don't agree with certain rules, I usually go looking for examples of fully tested units/models. The problem with simulation is that you only get the results from the criteria that you enter into the test. The attached sample picture is from a car that left a race track and landed in a clump of trees.
-
Bystander , Richie, yep internet rage, fabricator rage(mine) no time no money rage, you name it. apologies.
-
i'm misunderstood most of the time ... :cheers: