Couldn't it also be that we added an extension to the frame rail or in this case the subframe connector that is welded into the floor from the subframe to the rear of the passenger main floor? And that Extension is then welded to the floor in a way that no flat plate ever could be? It must weld to the floor in like 10 different planes. Then on top of that on the back side of the base is the rocker and the inner rockers. Plus when we are done we can weld a small kicker from the bottom of the main hoop to the subframe connectors.
Had we have just welded flat plate to the floor I'm not sure where we would find a flat enough section to get anything more then a few square inches of surface area.

I'm not trying to be a much of a smart ass as this sounds, But can you explain how your going to compute how strong that base plate box is? Sure I can go with the fact of just the box welded to the cage. But the fact its welded in 3 planes to the to subframe connector mean your going to have to compute the strength of the subframe connecter that is welded in to the floor by lets say to 12" strips on each side so now you will need to compute the strength of everything bolted in the area of the floor, like the subframe it self and probably the trans crossmember which would be acting in tension with a side impact. Plus the base plate we have is then welded to the the inner quarter, the floor, the inner rocker and the outer rocker would be contributing to the the strength of this piece. I find it very difficult to understand how someone can just to do a quick accurate calculation about this base plate that is not even complete. Because once you find out the fact we plan to add short kickers it will change all calculations.


Thanks

The reason I posted my question is that I ASSumed the box was fabbed from bent sheet...I didn't look close enough to see that the box was welded plates with the beads ground down. :captain: I've only seen plinth boxes where all the weld beads were left on but they look, ahem, rough.

http://i207.photobucket.com/albums/b...n/DSCN3425.jpg

Obviously Ironworks goes the extra mile. Rock on guys!

It's actually cut and formed 4x4" square tube. Thanks

Absolutely badass. Been in love with the rendering since I first saw it.

Its actually very easy, and time consuming, to figure out exactly what the forces are on that system in the event of a collision. The point is that unless you have a plate underneath what is shown, that the size of the plate doesn't really matter, the force would travel along the plate and down to the sheet metal, at which point the shear of the sheet metal becomes the determining factor of the strength of that particular joint.

here are some examples of NASA / FIA approved methods of what you're building:
http://i1107.photobucket.com/albums/...hread/Foot.jpg
NASA requires at least a 3 x 4 x .125 footprint that mounts directly to the body

Rodger - I hope that Krylon is the stuff from Walmart - they have theirs made from a special formula that makes it 3.75x stronger than the Krylon available off the shelf anywhere else LOL.

You guys are all bad-azz just for being able to HAVE these conversations and I apprecate you for being willing to have them in public. I always come away having learned something new.

Looking great guys! Keep it coming.
G

James your drawing looks almost exactly like what we did. Except mine is welded to the subframe connector which is once again much stronger then the floor.

Thanks Gregg - it's coming together.

One of the difficulties that seems to occur from time to time in forum conversations on the interweb is that (a) comments can be made without knowing all of the facts, (b) opinions can be presented as facts with minimal or partial support, and (c) it's difficult to know the tone of the intended commentary and replies. I guess that's why questions and answers always seems more palatable to me. These conversations are great but I always prefer to make sure that some background is given as well - and to that end...

The roll cage in this car is being built following the NASA Rally Sport rule set, which is founded in the FIA Article 253 Safety Equipment rule set. Both the NRS and the FIA rules are fundamentally the same but there are differences beyond the FIA's use of french and somewhat difficult to follow layout - the FIA rules call for CDM tubing only whereas most North American sanctioning bodies allow for (and provide specifications for) DOM. The FIA rules also specify dimensions in cm rather than inches (which don't always convert the same) and there are rules and specifications the FIA have in place that are not included in some other rule sets. Regardless of the differences, most sanctioning bodies pull their specification (and even diagrams) from the FIA rules and most sanctioning bodies will recognize approved roll cage designs from alternative bodies provided they are not fundamentally different. I chose the NRS rules because they are very clearly laid out, they exceed the NASA CCS minimum in most regards, and they are applicable to most of the events that I will be running. I know that I am comfortable using the NRS rules and we're building the cage out of DOM which is acceptable just about everywhere in North America but this means that the car would not be legal per FIA rules. I am, however, still following the FIA rules as a foundation.

These rules may not be the same as the rules that you will need to follow when you construct your car so I suggest that you follow the rule set that you need and, if you have specific questions regarding your cage design, that you consult the applicable sanctioning body directly.

With respect to the plinth box design which Rodger has used there are a couple of applicable rules - NASA RS Rules state:

Which we are adhering to (the approximate area of the plinth, if you were to unfold it, is 95 square inches).

The NASA CCR rules state:

Which we are adhering to.

The FIA Rules state:

The rules go on to say that the use of bolts is a minimum requirement and that mounting plates may be welded

So we are in compliance with this rule set as well.

The three diagrams that James posted above are Figures 253-54, 253-55, and 253-56 in the FIA rules; there are a total of nine figures in that group of examples so there are other acceptable options available as well.

As I said above, however, what really matters is the answer to this question: “Is my roll cage compliant to the specific rule set that I am following for my intended application?” and ultimately that question can only be answered by a tech inspector. And in my case above that question has been answered by the regional scrutineer and tech supervisor – so I am satisfied with the design.

James,

GREAT EXPLANATIONS!



--Eric