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Discussion Starter · #1 ·
I want peoples opinions on my roll cage design.
The cage is going into my 92 Eagle Talon for the Canadian P4 class.

Here are a couple pictures of my [link:photos.yahoo.com/bc/darrylmalone/lst?.dir=/talon+roll+cage&.src=ph&.order=&.view=t&.done=http%3a//photos.yahoo.com/bc/darrylmalone/lst%3f%26.dir=/talon%2broll%2bcage%26.src=ph%26.view=t|cage].
 

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CR>R5 into L3- 100 Finish
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Looks a lot like FIA spec. Good luck getting it in. Those damn cars don't have enough room.
Whiplash RallyeSport
 

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Don't know about FIA spec, but the SCCA rules say the main hoop has to be a continuous tube with bends. FIA cages are legal and preferred, but I don't know their rules about the main hoop and bends and stuff. If I can build a cage without bends, I'll start tomorrow. Your cage looks awesome...nice CAD work. Is that done with SolidWorks?

CP
Desert Storm Rally
A2 Jetta #305
 

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Discussion Starter · #4 ·
RE: Roll Cage opinions

Opps I spelt opinion incorrectly.

The cage was done in Ideas.
The main hoop is continuous one tube, as is the tube that goes from the front floor to the top of the main hoop. The reason the bends are not shown is because the FEA cad software creates it this way.

The cage may be a bit excessive but it's a lot more stiff than a cage with less tubing.
 

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don't cut
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Looks good, a bit overkill, but good. Two points:

1. The rear strut tower cross bar (connects the top of the strut towers). Bend this bar so that it ties down to the floor. There is a major structural unibody reinforcement there that is nice to tie into. Also, it will allow you to fit a spare tire more or less flat in the back! Look at the pics I sent you and you should get the idea, otherwise lemme know and I'll sketch it out.

2. You have a lot of bracing in the main hoop and behind the hoop to the strut towers. While more bracing is always better than less, you may have a bit more then necessary. That area of the car is extremely tight, and fitting and welding those tubes is gonna be a #$^&#$$. Plus, access to anything there will be nearly impossible. Where are gonna put the helmets during transits? How bout coats for winter, other spare stuff, etc....? Point is, the car is very small, and you will need access to that space, so think carefully.

No doubt your FEA has told you that your car will withstand a jump off the Brooklyn Bridge. A few selected deletions should not comprimise strength or safety. I couldn't find my FEA stuff, but if you gimme a call I can probably walk you through my loading scenarios, restraints, etc...


Dennis Martin
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920-432-4845
 

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1) I would agree with the opinion that the x-bracing in the rear is over done. I would delete the lower rear x brace from the bottom of the main hoop to the rear struts; the purpose of the rear bracing is to prevent the main hoop from collapsing forward or aft, and the main hoop tie in to the floor and side bars prevents any real movement there so these braces are not needed.

2) I would also consider removing or modifying the x-brace across the main hoop itself; this does add some extra resistance to distortion for the main hoop, but the upper rear x brace working with the rear braces to the struts serves most of that function. If you retain this, I would suggest that you make it a shallow U shape to the rear; otherwise you may not have the room to get the seats back far enough for proper positioning. (I have made this mistake!)

3) Make the braces beside your helmets from the main hoop to the a-pillar bars short; I see more and more of these, and they do a good job of tieing this point together, but I'm concerned about helmet contact with these braces in hard side impacts. Make sure to pad these well.

4) One of the really weak points in any Talon cage is along the tops of the A pillars. The windshield angle is really flat, and the angle of the bend at the top of the A pillar is very shallow. Any flip and impact down on the top of the A pillar (not even a hard one) can cause collapse of the A pillar and the cage bend is so shallow it can't stop this. I would very strongly encourage you to modify this with a near vertical support (less than 30 degrees from vertical) from near this bend at the top of the A pillar to the floor below. You should also modify the side x-bar for access if you do this. It may be a good idea to actually figure this part out by trial fitment of this vertical bar and the side bars after the main hoop and A pillar hoops are in place, with the seats temporarily installed.

5) You might want to think more about the diagonal across the top of the cage. It does a good job of prevent distortion of the top rectangle, but it goes right over the co-driver's helmet; this opens some possibility of helmet impact and spinal compression right in the neck area with a hard flip and vertical impact down on the roof. If you keep it as shown, make sure the co-driver's position is very low on the floor, which is a bit hard to do on these cars.

Keep in mind that quality of joint fitment and welding is as least as critical as design.

Good start!

Mark Bowers
 

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Discussion Starter · #8 ·
I used FEA to drive the design.

Dennis,
1. I do like your idea to tie the rear cross bar to the floor. I was thinking that maybe if I weld a panel from the horizontal cross bar to the floor may produce the same effect and at the same time keep a direct connection between the strut loads.
2. Unfortunately CARS regulations state that there must be 2 diagonal braces in the main hoop. Having the 2 cross in the middle gave the best results over any other scenario I could come up with.
Thanks again for the pics, they were a big help.

Mark,
1.The lower rear x bracing improves cage stiffness by 3.6 times over bracing from the strut tower straight down to the lower main hoop, and 7.6 times greater than a cage with no lower rear bracing. A stiffer cage will help reduce stress on the unibody but adds weight.
2. See above. I didn't think about the seat placement much. Maybe a good idea to mount the seats in position first to see where they end up.
3. Lots of padding! :)
4. A very good point and FEA results show a huge improvement in stiffness with a tube running from the top of the A-pillar to the bottom of the A-pillar. But the entrance area into the car looks like it would be very tight. I'll have to fit a tube up once I get to that point. I would really like more support in that area.
5. I'll have to relook at this area.
Thanks

The CARS rulebook asks for required rollcage reinforcement but I'm not 100% sure what they are looking for.
Anyone have a CARS rule book that can clarify this for me?
 

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>1.The lower rear x bracing improves cage stiffness by 3.6
>times over bracing from the strut tower straight down to the
>lower main hoop, and 7.6 times greater than a cage with no
>lower rear bracing. A stiffer cage will help reduce stress
>on the unibody but adds weight.

I presume this analysis makes certain assumptions on the strength, meterials thickness, etc., of the lower floor pan?? I only question this because I spent 15 years as a design engineer and several times went down the road of designing for sheer numbers, only to find it was not necessary, and solved no actual field problem!

>4. A very good point and FEA results show a huge improvement
>in stiffness with a tube running from the top of the
>A-pillar to the bottom of the A-pillar. But the entrance
>area into the car looks like it would be very tight. I'll
>have to fit a tube up once I get to that point. I would
>really like more support in that area.

Yeah access will be a pain to make good with this support, but this really is the worst point in cages for these particular cars. (If I were asked what is the next step to add to the rules to maximize safety return for the investment, this is where I would put it.) Toyota Celicas are the same way. I would put the lower point of this support maybe 12-15" forward of the point of where it joins the A-pillar for improved access. Alternately, you may realize most of the gain by welding the upper point to the A pillar 6-8 inches forward of where the downward bend starts; but one needs to look at the bending of the A-pillar bar to make sure it doesn't split; I think this would be a hard analysis. I also wonder if this bar could become a danger in a hard impact down and inward on the top of the a pillar; it might be best to do this in concert with more bracing in the top rectangle to prevent this folding down on the occupants .....ooops..... see, I told you I was a design engineer! I'll be lying in bed at 2 AM rolling this over in my brain!!

Mark ;-)
 

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Discussion Starter · #10 ·
RE: Roll Cage opinions

I did all analysis of the cage independently of the unibody structure. This was done under the assumption that if the cage is stiff enough to sustain a 2g load on it's own then it can only improve once installed in the chassis. I'm also thinking that if the cage is tightly tied to the suspension attachment points most of the loads will transfer directly into the cage thus reducing stresses on the unibody structure.

I am concerned also about the A-pillar area, I've been racking my brain trying to figure out a way to stiffen this area without breaking CARS regulations or getting in the driver?s way.

More thinking required.
 
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