Roll Cage material ?

[Dr Goggles]

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.

[Freud]

A better look at his project.

FREUD

[johnneilson]

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.

[Gwillard]

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.

[grumm441]

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

[dw230]

"Because it is easier to work with."

That was my first thought when reading this thread.

DW

[Richie]

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

[Richie]

 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

[Interested Observer]

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.

[gearheadeh]

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?

[Richie]

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

[rambler jack]

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?

[johnneilson]

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

[Glen]

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.

[Anvil*]

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.