38D

If the factory does it, then it probably has merit.

Mike S.

John...the diagonal, on the main hoop for example, substantially stiffens the cage in the plane of the hoop. So if you barrel roll, the hoop (rectangular frame) doesn't resemble a parallelogram. The diagonal gets you (stiff) triangles, which are one of a structural engineers best friends. I can go into much further detail if you wish, an I'm one of those inguneers who is involved in structural analysis.

I'll try inserting a very simplified figure below...wish me luck.

Mike

kurt M

it were not for the attributes of the triangle the world would fall down in a pile. The sphere and its derivatives the cylinder and arch are no slouches but the triangle is king!

Unless required by rules X bracing does not need to be of the same size tubing as the main hoop to gain much strength. The shape is key as without the triangle the structure is only as strong as its joints as the force is being concentrated there rather than with good form being spread around and shared so to speak.

RedlineMan

Hey Gents;

Even as a non-engineer, I feel I am quite understanding of the joys and virtues of the triangle. I would certainly welcome the advanced discussion, Mike, as it would be enlightening to someone who never had the native study skills to do so.

However, my question was more along the lines of whether the cost/benefit ratio might be skewed toward benefit? This is a question that all cage designers have to ask, for it is all too easy to keep adding tubes to counter perceived forces, and end up with a Sherman Tank! Or... as I always say, there are many ways to accomplish something, some of them even work, but only a scant few are truly inspired. In most designs, that means accomplishing the most with the least!

This is perhaps something that is impossible to state with any accuracy without a computer model of the forces/vectors involved, but an educated guess would likely suffice.

I have a design in mind that is not only visually interesting, but increases strength while keeping the rear view open. It might even work! I'll post it when I get home Monday.

Reporting Live from Brockville, Ont.

Mike S.

John...will respond with more info, but for now, how about this concept. Mike

RedlineMan

Mike;

That triangulation would only be strong if there were a reinforced central point to tie it into at the bottom. There is not. Further, the idea of rear Xs is to counter suspension induced movement in the unibody. This sort of means tying in AT the suspension points, dig?

Here's a little sketch I did over the weekend of what I am thinking. Not only does it look cool, but it would not fill the rear view, and would not add significant weight. Maybe even an optional short tube at the red lines?



Whadaya think?

Geo

Not sure if you're just asking Mike or the entire monkey cage here, but....

Those tubes with the bends are just weakened. Why do it? Doesn't make any sense to me. The strongest tubes in a cage are those w/o bends, so why bend them if you don't have to?

RedlineMan

Any Monkey can Play, G;

The original idea was to keep the rear view uncluttered. I hate cars where you have to take extra time to really focus on the rear view. I'm a sight-line fanatic!

Of course you are right that a bent tube is not as strong as a straight one. However, that is only if the bent tube is not otherwise supported. In this case, it clearly is. A regular X brace between two rear braces gives you 3 triangles (or 4 if you cross between the bottom points) with relatively long lengths of unsupported tubing. With this I have not only created a 5th triangle, but decreased the size of each. The smaller the triangles, the stronger they are. Or, the shorter the length of unsupported tube, the stronger it is.

This layout might stand to spread forces over a much wider area than a simple straight line to an opposite point, and be very strong. I'm betting it is. Further, it might be so much stronger that it could be made from smaller tubing. Tipo 60/61 "Birdcage" Maserati. More stiffness, less weight? Quite possibly. I'm sure someone a lot smarter than I could do the math given material and dimensional specs.

I think it looks cool too!

Geo

I'm betting is is not as strong. Instead of a triangle in the back you have a huge pentagon.

Also, the support tubes go to the middle of other tubes w/o being supported themselves.

keith

john, you may have something there, minus the short red tubes...

however - I don't know how "uncluttered" it would be with the necessary diagonal in the main hoop... (you were drawing the rear legs there, right?)

or is this purely non-rules, non-series based conceptual design?

in any event, it reminds me of the halo in rally cages (which makes a polyhedron of sorts)

RedlineMan

Hey Keith;

I was hoping you might chime in. Your work is quite sanitary.

Yes, it DOES have the race diagonal, so I am EXTRA interested in not fouling the rear view further. Since I am the rolling chicane in the Red group with my raging 147hp, rear vision is important to my SURVIVAL!

It seems to me that every tube in there will become a stressed member, dividing any loads between far more points than any simple X brace would. I would not be surprised if compression loads never even got up to the main hoop, but were absorbed by the beam effect of the lower members. I'm also curious just how small a tube I could use in this layout to equal the strength of a normal X-brace? Oh well, I can only bend 1.5 & 1.75.

Anyway, I have it laid out with masking tape right now. It will be a substantial vision improvement over the X. I'll snap a pic of the real thing and post it at noon.

Mike S.

John...Given your design criteria is to have a "window" to the rear, there is no question that your rear leg frame is a fundementally sound design. My suggestion would be to push the frame in the direction to make the window as small as you can accept and the rigidity of the structure will be increased.

But I'm more concerned about your safety vs. stiffening the supension tie in points, although the latter can serve the former and visa versa. There is no question that your rear leg spaceframe will assist in stiffening the main hoop, especially given the more upright than typical angle of the rear legs.
Generally, the main hoop is the primary structure that keeps the driver space whole in a roll. and the diagonal there is the most direct solution.

As Keith mentioned, "I don't know how "uncluttered" it would be with the necessary diagonal in the main hoop"....are you planning to omit this main hoop diagonal?

Monkey Mike

P.S. Your rear leg frame, inverted, is a fundementally a vaulted ceiling truss design.

RedlineMan

Thanks Mike;

I love you too, man. I felt in my gut - which is all the training I have - that it was a decent design. Of course, decreasing the bend will increase the strength. I like it where it is, as it was at my chosen compromise point already. Given a choice between structural integrity and esthetics, I'll defer to the former. If possible, I'll always look for points of visual interest within that framework, and after that fact. I think I've struck a good balance.



The cross point of the tape is actually directly behind the belt bar, providing a excellent opportunity for a little 0.75" tie tube between them. If you factor in that this is looking from above, the red lines of a possible X would be substantially in view.

As an aside, here is a finished view of the hoop and diagonal reinforcements. I will be smoothing the weld areas with filler for a seamless finish.

Mike S.

John...I feel the love

I started my last response before Keith sent his. I see you'll be putting in a diagonal on the main hoop...not seeing it in your sketch left me wanting to ask. Dam engineers, dot the i's, cross the t's.

I like it. Clean, effective, simple. And nice visual (tape & red lines) which demonstrates the improved (rear) visual.

Re the RED members, the decision to include these most typically occurs when a long tension member can buckle or if the long member will be have a load along its length, perpendicular to the member, and in the plane of the frame/truss. If this were my cage, I would not add them. Besides moving into the diminishing (structural) returns territory, you'll be opening the door to visual clutter, something I know you're wanting to avoid.

Thanks for sharing all this with us spectators.

Mike

RedlineMan

Hey All;

Here's the latest pics. Fussy stuff for the last few days to a large degree. I am boxing in, filling, and otherwise integrating portions of the tubing into the unibody for a seamless, semi-hidden, custom look. That means lots of welding, grinding, filling, and sanding. Tedious, but the end result will be slick.



Here is my signature sill tube that I start all my cages on. Like the foundation of a building, everything is built on it. I build a chassis within a chassis, in essence. It is nested on top of the frame rail from where you see it here to just past the rear shock mounts. I first weld it directly to the sill at stress points, and then you can see the first piece of sheetmetal tacked in place at the front that will integrate it into the chassis.



Blurry pic notwithstanding, here you can see the rest of the pieces fabricated and the continuous welding about half completed. The last step is the extremely tedious grinding of the entire thing!



The outside of the sill tube is nested right against the rocker pinch weld (the flanges where the inner & outer rocker are spot welded together), then welded down its entire length, then finally ground smooth. Again, fully integrating it into the chassis. Geez... where did all my tools go?!



Here is the final step; the filler having been applied and sanded smooth. Next, a coat of fill primer, wet sanding, and then paint. Although I do not plan to do a door bar at this time, the end result will look something like this...



Maybe I will do those door bars after all? More to come. Stay tuned. I love this stuff!!