Cage Design

[heavy85]

Thanks for the info on 8" recommended max. Guess I need to add some more bars in there for the harness. I was pointed out on another forum that effective 2010 there is a requirement for a horizontal bar in the main hoop for SCCA:

"Main Roll Hoop:
1. Main roll hoop (behind the driver) shall extend the full width
of the driver/passenger compartment and shall be as near the
roof as possible. It shall incorporate a diagonal lateral brace
to prevent lateral distortion of the hoop (See figure 16). Any
number of additional tubes/braces are permitted within the
structure of the cage. It is required that the horizontal brace
behind the driver’s seat (described in Section 9.4.2.J.) continue
from the diagonal to the passenger side main hoop upright or
that a second diagonal be installed in the main hoop.

9.4.2.J. In order to provide a secure seat back support a section of tubing
equal to the roll bar shall be installed horizontally from the main
hoop upright to the diagonal brace. This tube shall be no higher
than shoulder height."

I couldn't find anything in NASA though. It doesn't mention if that tube can be bent or has to be straight? A straight bar would interfere with my seat. I assume this means I can't add bars from the b-post back to the strut bar like posted before then run a horizontal off that? Wouldn't attach to the main hoop directly but would avoid having to add bends in the harness bar. The optional diagonal does not make sense if as stated it's suppose to be a harness bar?

Cameron

[SoundGuyDave]

The NASA CCR doesn't specify that the harness bar HAS to be in the plane of the hoop, however it is implied on page 66 of the 2010 GCR, as all the diagrams illustrate the harness bar interrupts or is interrupted by the diagonal. That said, the Autopower bolt-in cage kit for at least one chassis uses a harness bar that bends back behind the main hoop diagonal, and that passes tech, so, ymmv. Best bet would be to contact the Chief Scrutineer for your region and discuss it with them...

[rstoff]

The second diagonal is not for harness mounting. It's required if one chooses not to continue the harness bar all the way across to the opposite side of the main hoop, i.e. stopping at the diagonal. The harness bar must then be a min. 50% of the width of the main hoop. I would surmise that the harness bar can be bent from the drivers side main hoop to the diagonal and then continue straight to the pass. side main hoop (or meet the intersection of the X diagonals).

[Bossbill]

Originally Posted by SoundGuyDave

Best bet would be to contact the Chief Scrutineer for your region and discuss it with them...

Will the Scrutineer talk to me if I'm not an SCCA member? We use their rules, but we are not SCCA affiliates.

[gmorrell]

Need some suggestions for this ChumpCar cage for a Plymouth Laser. We're planning to run ChumpCar at PMI in Pueblo CO in March.

The car should be pretty light, we're thinking a bit over 2000 pounds plus driver. The cage is 1.5" DOM, it has a lot of slip-joints, but the main hoop and hoop diagonal are solid and straight. The feet for the main hoop and front legs are quite good sized and land in fairly sturdy looking places in the chassis.

The side impact protection sucks, and something tells me ChumpCar is a venue where we're going to put a high value on side impact protection. The doors are going to be gutted, so my thoughts for the driver's side is parallel bars into the door with vertical braces, and perhaps a X configuration on the passenger side. I'm also thinking the A-pillar bars could use some mid-span support, and the halo could use some diagonal braces. Obviously, better padding will be used.

Any other suggestions for improving this thing, up to an including cutting it up for scrap, are greatly appreciated.

[Bossbill]

.
0.120 wall?

SCCA specs this car at 2500 in ITA -- sure you can make 2000?

[SoundGuyDave]

Originally Posted by Bossbill

Will the Scrutineer talk to me if I'm not an SCCA member? We use their rules, but we are not SCCA affiliates.

Sorry, I was referencing NASA, not SCCA... My experience is that, yes, they will talk to you, at least in the NASA camp.

[Bossbill]

I agree about NASA.
In order to build my car to NASA specs I had many email conversations with their head tech guy, and he actually helped me build my car to his rule set. Every major deviation from stock I cleared through him before I touched MIG to metal.
Very helpful, even though I was not a member.

[fair]

Originally Posted by gmorrell

Need some suggestions for this ChumpCar cage for a Plymouth Laser. ...The car should be pretty light, we're thinking a bit over 2000 pounds plus driver. The cage is 1.5" DOM, it has a lot of slip-joints, but the main hoop and hoop diagonal are solid and straight. The feet for the main hoop and front legs are quite good sized and land in fairly sturdy looking places in the chassis.

The side impact protection sucks, and something tells me ChumpCar is a venue where we're going to put a high value on side impact protection. The doors are going to be gutted, so my thoughts for the driver's side is parallel bars into the door with vertical braces, and perhaps a X configuration on the passenger side. I'm also thinking the A-pillar bars could use some mid-span support, and the halo could use some diagonal braces. Obviously, better padding will be used.

Any other suggestions for improving this thing, up to an including cutting it up for scrap, are greatly appreciated.

That looks like a good starting point as any, especially for ChumpCar (cool series, BTW - seems to have a lot less funny hat gh3yness than LeMons). I assume its 1.5" x .120 tubing, right? Here's what I might add to it for that car/class, in order of importance:

• Add an X or extended NASCAR style door bars to the driver's side
• Add an X to the passenger side door opening, or at least one horizontal or diagonal
• Some B-pillar corner supports (if your seat has side/head protection - otherwise leave these out)
• Add a dash bar for good measure
• One roof diagonal
• Throw a horizontal bar from the harness bar to the opposite B-pillar upright

Here's my crude mark-ups:



Some of this may be overkill for ChumpCar, and I hate it when people get crazy and over-analyze a cage, usually throwing WAY too many tubes (and too much weight) into the mix. I'm a minimalist when it comes to cages, but your starting cage could use a little more meat to it, yea...

Cheers,

[gt1guy]

I've run into a spot where I need some CC style help. Project is a tube chassis for my 72 Camaro. Track day, ORR ,once in a blue moon street car. When I did the suspension mounts on the chassis, I made multiple bolt holes (3) so I could set different ride heights. Well, the short version is that the rear LCA's (3 link) want to be in the same place as the bottom of the main hoop X when the lowest ride height is used. I did the main hoop X long before I made the suspension mounts. I hadn't thought about adding the extra mounting holes for ride height until I had actually started on the mounts themselves. I knew then there was going to be a interference problem, I decided to address it later. Well, now is later.

Luckily, I ran a solid harness bar, so all I'm dealing with is the bottom of the X.

Here's my dilemma. At the lowest ride height, at full compression (flat bottom of the chassis touching the ground) the LAC is right at 6" above where the main hoop meets the 2x3 frame rail (in side view). At the highest ride height, at 4" droop (wheels off the ground) the LCA is just below where the main hoop meets the frame rail (in side view).

Now to my small brain, having the bottom of the X connecting to the main hoop 6" above where the main hoop connects to the frame isn't good. I initially had it coming in a couple inches above the main hoop to frame connection. I was ok with that. Many cages seem to be that way.

Here's some pictures to show what I have. I placed 1" square tubes to show where the 3 links are and a piece of pvc for the drive shaft. I already removed the bottom of the X today.

Drivers side looking rear. Lowest ride height setting, full bump. The blue tape showing about where the bottom of the X would land.




Highest ride height setting, full droop. The LCA is below where the main hoop ties into the frame.




Kind of a birds eye view of the deal.




Side view. UCA mount obviously hasn't been made yet, but it does sit forward of the plane of the main hoop. The UCA mount will tie into the trans tunnel/center backbone (not built yet) and the lower X.



To me, where the blue tape bottom of the X is hitting the main hoop, is way too high and basically is putting everything above it on stilts. Am I correct in my thinking? Or will this not have the negative effect I think it will?

Possible option. Running the bottom of the X under the LCA. It wouldn't tie into the main hoop, but would land on the side of the 2x3 frame. Actually at the angle it would be coming into frame, and as low as it would have to be, it wouldn't completely sit on the frame. About a 1/2" would want to hang below the frame, therefore I'd have to build some kind of porch for it to sit on.

Would leaving the blue tape X where it is and bracing the outboard side of the main hoop, from the connection point of the X down to the connection at the frame work? That idea doesn't give me a warm fuzzy feeling.

What do you guys think?


Kevin

[Preston]

I swear I posted to this last night Gt1 guy, don't know what happened.
I'll check it tonight it should still be cached. I had a few thoughts.

[gt1guy]

Thanks Preston

Kevin

[Preston]

well crap I 'll just repost now

I was thinking leave the x-bar coming in "high" as you have shown it, and then bring another bar from that node down to the primary x-member on the bottom. Maybe even bring these at a very shallow angle so they meet close to the driveshaft tunnel or somehow suppor the 3 link structure. Downside is you may have to bring the bar you are worried about up even a little higher to still clear the LCA. THis seems like it would be perfectly adequate.

Another approach would be to do something like the picture below, where you are bring the X down inside of the LCA down tot he rpimary x-member. If you're worried about this you could always tie them together with a short horizontal above the LCA interference point. IN my case my x-member is a big 2*3 so I felt like it was plenty strong, and also my "harness bar" is actually a 2nd higher x-member at the midpint of the main hoop, so I didn't feel any further reinforcement was necessary. (and then small ancillary harness bars are put up higher).

Also can you show us your front LCA mount ? I'm having a hard time figuring out where you will have room for the seats and that LCA mount. I tried to do that once and it wasn't good for the seat height position (or sealing the cabin !). I really like the idea of multiple mounting so the car can be lowered. I thought many times about doing that but there was a lot of problems with making it work and of course it adds a lot of weight in extra structure and other design problems. It doesn't seem hard at first but the problems started adding up.

[blainefab]

Originally Posted by gt1guy

I've run into a spot where I need some CC style help. Project is a tube chassis for my 72 Camaro. Track day, ORR ,once in a blue moon street car.
What do you guys think?
Kevin

NASA wants the low end of the diagonal attached "to the main hoop as close to the mounting plate as practically possible", the thought being that a big push on the diagonal loads the pad/chassis in compression rather than a bending load on the main hoop.

I agree that ending them 6" up from the frame isn't good, but if that is "as close to the mounting plate as practically possible", then so be it. To mitigate the bending load, I'd:
- Add a straight transverse tying the base junctions of the diagonals together, to oppose the bending load.
- Extend the plating from the main hoop to the sail panel all the way down to the sill, filling in the gap on the other side of the bending load (I believe that would be termed a shear stress plate, but I'm not a ME and Google got me a bunch of calculus).

[gt1guy]

Thanks Preston, Alan


What do you think of this layout? This keeps everything in the same plane as the main hoop. The additional center diagonals lend themselves well for fabricating the UCA mounting for the 3 link. And, they are in the right spot to run the trans tunnel/backbone into. I think some additional bracing to tie it in to the main rear cross member would be needed.



Here's one with the additional diagonals going to the rear frame cross member. The rear cross member isn't on the same plane as the main hoop. But I'm not so sure that this is a totally bad thing. Would this re route some of the forces running through the other lower diagonals? Essentially cutting down on what the main hoop will see?
Still works for the 3 link mounts, not as good for the backbone.



Side view of the above picture.



Showing the out of plane between the main hoop and the rear cross member.

Extend the plating from the main hoop to the sail panel all the way down to the sill, filling in the gap on the other side of the bending load (I believe that would be termed a shear stress plate, but I'm not a ME and Google got me a bunch of calculus).

I understand what your saying Alan. The plates you see in the pictures are only to hold the chassis to the body at the moment. I have four of the plates holding the chassis, 2 by the main hoop and 2 on the backside of where the doors bolt on. The body is held up off the table by 4 2x2 posts at the same locations, but outboard. I will have to take the chassis in and out at least a couple times before this thing is done. Actually, while I have the chassis tied to the body, I need to make the 4 posts about 6" taller because.......I ...sort... of ....can't get the chassis out from under it at the moment.

More to your point. The reason I'm not automatically planing on tieing in the main hoop to the sill, is that depending on what this pig of a chassis weighs when I'm finished with it, I may make a mold of the body and do it all in composites. I told myself when I started this, that I wasn't going to totally sweat the weight of the chassis, I could loose weight in other areas. So shear plates might be out, short of the sill bolting to the main hoop if I go composite. If I use the metal body, yes I will definitely do the shear plates.

Now with that said, would some kind of taco'ish gusset on the outboard side of the main hoop work? Maybe something like this?

Also can you show us your front LCA mount ? I'm having a hard time figuring out where you will have room for the seats and that LCA mount. I tried to do that once and it wasn't good for the seat height position (or sealing the cabin !).

Preston,

Your right, the front LCA mount for the 3 link was a tight fit with the seat mount. Actually it was a pain in the ass to work out. The LCA's are 50" long. My solution was to combine the two. The LCA mount is also the side of the seat mount.



Due to how far the driver has been set back, my head was where the roof line was starting to come down, so I had to lean the seat back a additional 6*. It's a 20* to begin with. That put the front of the seat higher than normal. The LCA mount lends structure to the height of the seat mount. And there is definitely room for the belts not to touch the LCA itself. I did wrap the seat mount around the back of the seat. I may add two bolts bolts in the lower back of the seat, but I doubt it's needed.

All the mounts run down to the bottom of the chassis. So everything is welded in two planes. The outboard part of the LCA mount is also a 12" long doubler, plug welded to the side of the 2x3 frame rail.

As far as sealing the cockpit. I thinking of a couple shifter boots where the LCA's/UCA will go through the bulkhead behind the main hoop. One facing in the cockpit and the other on the backside of the bulkhead facing to the rear. The rear one, I plan to use nomex boots from one of the used NASCAR parts folks.







Inboard side seat mount. The backbone/trans tunnel will tie into this.



Overall view of the whole mess. If you look at the top of the LCA mount, you see 2 plug welds. Right there is flat bar running straight down, tieing both sides together and turning the front of the mount into one triangle.

I really like the idea of multiple mounting so the car can be lowered. I thought many times about doing that but there was a lot of problems with making it work and of course it adds a lot of weight in extra structure and other design problems. It doesn't seem hard at first but the problems started adding up.

Boy do they. All the mounts end up being taller. In my case, at least 3" taller. On the front suspension where I could have gotten away with two small tabs (with single bolt holes) welded to a single tube, I ended up having to add tubes and box the mounts. The front UCA mount ended up the tallest because I also added two more holes under the "normal" ride height hole, so I could take out the anti-dive I built into it. All the AD is built into the UCA's, The lowers are level. I designed 40% AD into the suspension, the other two holes represent 22% and 4% AD. So that mount ended up with 5 holes.

Here is the front. Ya, there is at least 20# of extra weight. Even without the ride height bolt holes I would have still had the lower three to kill AD.



The front UCA mount. Doubles as a trunk.



The rear UCA mount. The only one that wasn't much of a pain to add the extra holes.



I've already found myself saying,"On the next chassis.........." It's your fault Preston.

So, ideas? Comments? Advice? Tar & Feathers?


Kevin

[blainefab]

Originally Posted by gt1guy

Thanks Preston, Alan

What do you think of this layout? This keeps everything in the same plane as the main hoop. The additional center diagonals lend themselves well for fabricating the UCA mounting for the 3 link. And, they are in the right spot to run the trans tunnel/backbone into. I think some additional bracing to tie it in to the main rear cross member would be needed.

The transverse looks good - but the inside tall diagonals look extra, the small box section tubing they land on is not main structure. Definitely keep the outer lower diagonals on plane and lined up with the uppers, as you have blue taped.

Here's one with the additional diagonals going to the rear frame cross member. The rear cross member isn't on the same plane as the main hoop. But I'm not so sure that this is a totally bad thing. Would this re route some of the forces running through the other lower diagonals? Essentially cutting down on what the main hoop will see?
Still works for the 3 link mounts, not as good for the backbone.

I like the rear diagonals - directs loads out to the main structure of the frame rails.

I understand what your saying Alan. The plates you see in the pictures are only to hold the chassis to the body at the moment. So shear plates might be out, short of the sill bolting to the main hoop if I go composite. If I use the metal body, yes I will definitely do the shear plates.
Kevin

That makes sense - it's odd looking at a steel body on a tube frame. If you do go with the composite body you'll need an extension off the frame to hang it on - maybe do a gusset outboard on the hanger. If I recall correctly, the COT has a double 2x3 box section in this area.

[StanIROCZ]

Originally Posted by gt1guy

Crazy overkill, IMO. What about just running the 'X' as low as possible onto the 2x3 frame rails? It looks like if you put it at the bottom of the 2x3" you'll clear the LCA at full droop and highest ride height. If not, maybe cheat a little bit and let the tube fall off the bottom of the box, then close it off with a plate and maybe some additional, local, reinforcement.

[gregslowsvo]

I am about to start building a cage for the new Sport Touring class (http://www.race-st.com) through irdc and I would like some feed back of what I had in mind ( shell is a 86 svo)
I know the mock is missing a few bars and the fia bar needs to be at the front bend on the halo bar and there is going to be 2 more bars from center point of the dash bar to the bottom of the a pillar bar as well as a cross brace for the main halo but this just to give/get an idea and yes I am moving the drivers seat that far back

[blainefab]

Originally Posted by StanIROCZ

Crazy overkill, IMO. What about just running the 'X' as low as possible onto the 2x3 frame rails? It looks like if you put it at the bottom of the 2x3" you'll clear the LCA at full droop and highest ride height. If not, maybe cheat a little bit and let the tube fall off the bottom of the box, then close it off with a plate and maybe some additional, local, reinforcement.

My viewpoint is biased towards NASA legality, and the NASA CCR is clear about lining up the sections of a 2pc diagonal, even though your suggestion is probably as sturdy, and lighter. If Kevin sticks to No Problem Raceway he could probably get by with it, from what I hear.

[blainefab]

Originally Posted by gregslowsvo

I am about to start building a cage for the new Sport Touring class (http://www.race-st.com) through irdc and I would like some feed back of what I had in mind ( shell is a 86 svo)
I know the mock is missing a few bars and the fia bar needs to be at the front bend on the halo bar and there is going to be 2 more bars from center point of the dash bar to the bottom of the a pillar bar as well as a cross brace for the main halo but this just to give/get an idea and yes I am moving the drivers seat that far back

Good start! I wonder if the transverse between the rear shock towers is necessary - seems to me that the full X in the backstay plane would take care of any force trying to move the shock towers relative to each other. I'd consider putting that steel in lower backstays or a low transverse across the bottom of the main hoop.

Are you planning to tie the front V into the cowl? Lots of section depth and stiffness there compared to the dash bar.

Are you going to leave the door bars flat, or poke them out (at least on drivers side) into the door cavity?

[gregslowsvo]

Originally Posted by blainefab

Good start! I wonder if the transverse between the rear shock towers is necessary - seems to me that the full X in the backstay plane would take care of any force trying to move the shock towers relative to each other. I'd consider putting that steel in lower backstays or a low transverse across the bottom of the main hoop.

Are you planning to tie the front V into the cowl? Lots of section depth and stiffness there compared to the dash bar.

Are you going to leave the door bars flat, or poke them out (at least on drivers side) into the door cavity?

yeah I will be using the KBP IRS AGS suspension with Hard Mount so Ill look in to moving that bar to the base of the main hoop

for the door bars yes they are going to poke out in to the door cavity.

for the cowl here is a few more pics of what I had in mind they will be going through the cowl straight to the front shock towers

[gt1guy]

Crazy overkill, IMO. What about just running the 'X' as low as possible onto the 2x3 frame rails?

I did spend a bit of time investigating this avenue. I can butt a 1.75" tube against the side of the 2x3, horizontally, as if it was a cross member. Everything clears. It's not until I start to angle it up toward the center of the harness bar, that I run into problems. The link is 1.375"od., it has about 1/2" gap between the frame rail, add another 1/2" min for clearance between the link and the X diagonal. That all adds up, and leaves me at either too shallow of an angle, or I have to lower the connection point to the frame rail to the point where it's hanging down below it. The only way to work around that is to fab a porch for it to sit on, and double cope the tube. Now to me, the only strength I'll get from that setup is from the part butting up to the frame rail. The rest is sitting on a lever arm, that I can't gusset up the side of the rail for the same reason that I had to lower the tube in the first place.

The links in my first pictures were just 1" square tube I spray bombed white for contrast. That might have helped to make things look better than they really are.

If Kevin sticks to No Problem Raceway he could probably get by with it, from what I hear.

Ouch. Thanks Allen, let me move a little to left, you only smashed one of my balls when you kicked me that time.

Actually, I would like to drag this car around the country and drive the famous tracks. Luckily, my job gives me the kind of time to do it. I'm not locked into just having the weekends off.

My viewpoint is biased towards NASA legality, and the NASA CCR is clear about lining up the sections of a 2pc diagonal, even though your suggestion is probably as sturdy, and lighter.

I want this thing to be able to pass whatever tech I may encounter at any track day or ORR event. If a solution ends up being overkill, but follows the rules, so be it. I'm out to have fun, nothing more.

The transverse looks good - but the inside tall diagonals look extra, the small box section tubing they land on is not main structure. Definitely keep the outer lower diagonals on plane and lined up with the uppers, as you have blue taped.

Understood.

like the rear diagonals - directs loads out to the main structure of the frame rails.

In addition to the others? Something is going to have to get done to that area anyway. Right now it's just a big open box where the underslung rails land on the rear cross member.

Thanks,

Kevin

[Jason M]

Just looking at the door area, and front of the cage, this is how I would do it. More in line with FIA style cages.

[StanIROCZ]

Looks very similar to mine:



Greg, I don’t care for the shock tower to dash bar ‘v’ that you have there.

Originally Posted by gregslowsvo

The tubes are landed on the center of the dash bar and it will be loaded purely in bending and contribute little to torsional stiffness. Another concern of mine would be a hard hit in the front of the car would push those tubes rearward towards the passengers.

Your a-pillar support bar is structurally good, but IMO is too obstructive for getting in and out of the car.


Our cages are very similar, otherwise (I even have the exact same seat). This is a pic of mine right before I put the roof back on the car but before I had the dash and FIA a-pillar support bars.


Most recent pic, for the most part the cage is completed:

[Ambrosio]

Hey all,

In regards to gregslowsvo cage,
My name is Mario, I am a friend of Greg's and am helping him design this cage. First off Greg and I would like to thank all of you for your help and replies, they are greatly appreciated. We have referenced this thread like a text book in the design process.

Are you planning to tie the front V into the cowl? Lots of section depth and stiffness there compared to the dash bar.

The tubes are landed on the center of the dash bar and it will be loaded purely in bending and contribute little to torsional stiffness.

The lateral constraint of the shock towers has been a great topic of discussion for us. Being constrained by a short distance between the shock towers and the dash bar, I landed at the current design to provide adequate room for the engine and its service/removal. A large taco gusset and lots of ties to the cowl are going to be implemented but are not depicted in the "string mock-up". These gussets are the reason I stuck with this design, as I thought that they would create a structure strong enough to take any loads imposed lateral tire forces. By the way the car will have 295 wide DOT R-compound (Hoosier, Victors, etc) all around and wet weight is scheduled to be 2900#. These bars are purely a stiffening component and have no safety implementations. So my question is with the taco gussets and cowl support attachments are these bars worth it? Or should we add a bar from the middle of the dash to...say the pass. B-pillar base to react these loads?

Another concern of mine would be a hard hit in the front of the car would push those tubes rearward towards the passengers.

I thought exactly the same thing as well, but when I looked at the car physically, we mounted his seat so far back I do not feel a failure here would come close to the driver. HOWEVER the steering column is attached to the dash bar so that could be an issue?

Your a-pillar support bar is structurally good, but IMO is too obstructive for getting in and out of the car.

Just looking at the door area, and front of the cage, this is how I would do it. More in line with FIA style cages.

Another point of intense conversation between us and others. I have reviewed this entire thread looking for any input on this and forgive me if I missed it. What are the differences between what we have laid out and what Jason M has laid out? We came to this design to try and make the "FIA bar" as vertical as possible to minimize the compression force for a given downward force on the roof. This comes at a price that StanIROCZ mention of driver egress. Other thoughts? Any other input is greatly appreciated.

Thanks,
Mario

p.s. All required bars will be 1.75-.095 and all non-reqrd. bars 1.75-.065

[Jason M]

Originally Posted by Ambrosio

What are the differences between what we have laid out and what Jason M has laid out? We came to this design to try and make the "FIA bar" as vertical as possible to minimize the compression force for a given downward force on the roof. This comes at a price that StanIROCZ mention of driver egress. Other thoughts? Any other input is greatly appreciated.

The FIA bar should go from near the top of the windshield to the pad at the bottom of the A-pillar-bar. It should be straight and does not necessarily need to be tied into the door X-bars. The door X-bars should be two bent bars with gussets, not one full bar and one split bar. I'd move the pad for the A-pillar-bar as far forward as possible.

The egress issue mentioned is huge.

[Jack Hidley]

Mario,

I would not underestimate the need to get out of the car fast when there is a fire. I think the chances of a car fire are about 10x that of having a complete flip that runs the risk of buckling the A-pillar tubes. For that reason I would bias the design of the complete A-pillar structure towards fast egress. Once you get a window net in there, a Hans device on, etc. I think your current design will significantly slow this down.

I would keep the short tubes that go from the center of the door X to the midpoint of the rocker panel for side intrusion protection.

Since you already have a shock mount to shock mount tube, I would lose the second diagonal (bottom left to top right) in the rear supports and add one diagonal to the roof instead. This will give you more overall torsional stiffness and improve rearward visibility.

Given the driver's seating position, try to get the main hoop as far forward as possible. This will allow you tie the hoop into the B-pillar more and make the side halo tubes shorter.

Lose the V section between the strut towers and dash bar and replace it with an X in the plan view that goes between the strut towers and the A-pillar tubes where they meet the dash bar. Much stiffer design.

[StanIROCZ]

Originally Posted by Jason M

Originally Posted by Jason M

I'd move the pad for the A-pillar-bar as far forward as possible.

As manufacturing engineer I know so eloquently put it, "you can draw an asshole on paper but it doesn't mean that I can shit through it". The problem with pushing the a-pillar all the way forward to the dash is that it gets very difficult to weld 360 deg around the tubes mating to the a-pillar bar. If they are just rearward of the door opening and above the rocker, they aren't too bad. I had to use some trickery (welding outside the car) for the parts of mine that are below the rocker, but couldn't do the connections at the dash that way. Mario & Greg, think through your "assembly process". Think about what gets put in first, second, third etc. What you can tack in place and remove from the car to finish weld. Make sure that the welding that needs to be done in the car can be done in the car.

[MarkMc26]

I got off my arse long enough today to get this project underway once again. I only had enough time to lay out one of the rear kicker bars (this one on the passenger's side). A Sunday shortage of steel tubing and the lack of desire to create metal shrapnel led me to make a test piece out of PVC. At the hoop, it intersects at the same height where the overhead halo will attach. At the floorpan, it will attach just above the rear subframe. Additionally, it will be welded and gusseted to the rear shock tower as shown. Per TT rules, I can weld a roll cage tube to the chassis no more than 6" from its termination at a plate without being assessed extra points, and as you can see here, the tube would be welded to the shock tower approximately 5.5" from the furthest end of the tube. Part of the back seat mounting bracket has been removed for clearance. I have a floor plate template made out of cardboard (not shown here), but it needs to be extended rearward a bit before welding starts.

Mark

View from driver's side:


View from passenger's side, looking straight back:


View at connection to floorpan (green lines approximate rear subframe location below):


View at connection to floorpan (green lines approximate rear subframe location below):

[blainefab]

Originally Posted by MarkMc26

as you can see here, the tube would be welded to the shock tower approximately 5.5" from the furthest end of the tube. Part of the back seat mounting bracket has been removed for clearance
Mark

Extend your backstay pad up onto the shock tower, keep the total pad area under 100 square in, less than 12" long, and you'll be CMC legal. Gusseting tube to pad is OK, but tube to chassis is not.

[slow M]

Digging through my files, I found an interesting PDF document which I though some of you would enjoy reading.
http://www.mscsoftware.com/support/l...6/07b_brow.pdf
Its a study conducted on a TVR Cerbera chassis by Mark Roots, Jason Brown, Neill Anderson, Thomas W-a-n-k-e and Marco Gadola of Cranfield University, Cranfield, BEDS., U.K.

The study investigates the effects of adding safety structure to a Cerbera chassis frame on its torsional rigidity. While some of the numbers are only produced by modeling, others are both, modeling and test data. It has some great comparative analysis regarding addition of various elements singly and in combination.

Best,
B.

[MarkMc26]

Originally Posted by blainefab

Extend your backstay pad up onto the shock tower, keep the total pad area under 100 square in, less than 12" long, and you'll be CMC legal. Gusseting tube to pad is OK, but tube to chassis is not.

Good catch on that one, Alan. I was considering "getting lazy" and skipping this part if a drill test of the shock tower showed that it was at least 11 gauge thickness, but the CCR says otherwise, now that I re-read it.

Mark

[MarkMc26]

I'm getting back to working on my roll cage, now that I have some time on weekends. This car (2004 Mustang) is intended for NASA TT and CMC/CMC-2 use, where cages are limited by the NASA CCR, and additional attachment points are not allowed.

I'm trying to find a way to brace the lower 6" of the rear kicker bars to the shock towers, while they will primarily attach to the floor pan just above the rear subframe (approximated by the green lines). I first looked at using steel plates to form a box, but there were too many multi-planar, twisted shapes involved to prevent the assembly from being complicated to fabricate and looking stupid. Note that I am still running stock-location springs in this Mustang, but I want to attach the cage to the rear shock towers in the event that I switch to coil-overs (and because there is a significant shock load, as I have been educated).

Here is my latest thought, although it may not be NASA CCR-friendly:



The red lines represent the part of the mount plate that would turn up the shock tower. The green lines approximate the rear subframe under the trunk floor. The black Sharpie line around the white tube represents the 6" limit for attaching a tube to the chassis or a plate (per NASA Time Trial rules). A short piece of 1.75" tube would be used as a brace from the kicker bar to the plate at the shock tower, as shown with a piece of scrap steel. As shown, the steel plate on the trunk floor is at 49 sq in, so I have plenty of room to play before I hit the 100 sq in limit.

However, I'm reading certain items in the CCR, and the arrangement in the photo above might not be legal:

Originally Posted by NASA 2010 CCR

15.6.14.B Tube / Mounting Plate Specifications
Any number of tubes may attach to a plate so long as they are touching each other at the plate. There may be a small gap between tubes to allow welding 360 degrees around each tube. If there is no gap between the tubes, they must be welded around the base as much as possible to form a single figure-eight weld, AND the tubes must be welded to each other two (2) inches up from the base plate.

I certainly have a "gap" where the tubes would attach to the plate, although "small gap" is a subjective term. However, this may all be moot if attaching the rear kickers to the subframe, adjacent to the shock towers, means that additional gusseting is not needed.

Alan and others, what do you think?

Mark

EDIT 1: I found a way to simplify this junction and meet the rules. Dumbass me...overthink and stare at something long enough, and a simpler solution will show up. After moving the kicker bar attachment point forward a few inches, I noticed that the outboard side of the bar is nearly parallel to the inboard face of the shock tower, and they could be made exactly parallel by slightly shaping the vertical portion of the mounting plate. I would only be able to weld approximately 80% of the way around the base of the bar (as it would be tangent to the shock tower), but I could weld the side of the bar to the shock tower with 2 beads (front and rear, approximately 1/2" to 3/4" apart and parallel) and still be within the 6" limit from the end.

EDIT 2: Here's a photo of what I described in Edit 1 above. The vertical shock tower plate would be bent to follow the shock tower contour at the top. The green lines represent the rear subframe. The red lines represent where the rear kicker bar would be welded to the horizontal and vertical portions of the plate, while staying within 6" of the end of the bar. This should eliminate any concerns about the "small gap" between 2 tubes at the same plate, while tying the shock tower to the cage structure.



Comments of all flavors, as always, are welcome.

[Don Hann]

No tech but just be careful out there...

I just watched my car owner destroy our race car on Thursday (I was driver 2) during testing for this years Mint 400. Our cage looked to be well built and did its job well. The first landing was on the top of the co-driver's "A" pillar. It sunk about 4" but nothing broke.

One pirouette on the nose, came down on the "A" pillar, and over the top to the tail, one pirouette on the tail end of the car, then came down sideways and 1.5 rolls till she stopped, laying on the drivers door.

Driver has two broken knee caps, but walked away anyway.

It was a good crash.


Just double check everything aright .

[JohnK]

Originally Posted by Don Hann

..One pirouette on the nose, came down on the "A" pillar, and over the top to the tail, one pirouette on the tail end of the car, then came down sideways and 1.5 rolls till she stopped, laying on the drivers door..

Please tell us you have pictures that demonstrate the end result?

[JPope]

Glad he walked away. Did his knee's impact a bar or something else in the vehicle?

[Don Hann]

I can probably get a few pics. I'll have to talk to the car owner about it but I can't imagine that he'd mind.

Yes... his knees hit the "Lower dash bar". That's the best thing I can come up with to label it. It's a full tube frame car. We had a piece of square stock (with only three sides... I don't know the technical term for it) running across the car below the dash that we had switches mounted to. Fuel pump, ign, lights, parker pumper, etc. I don't know how many times I looked at that and got a little nervous about it. I should have been more adamant in my requests for padding on that bar .

Here are a couple pics pre-dance...

http://www.photoreflect.com/pr3/Orde...&po=347&pc=508
http://www.photoreflect.com/pr3/Orde...&po=425&pc=508

The first one is with the car owner driving and me co-driving, the second with me driving and my co-driver... well, co-driving .


We had just put a set of sway-away triple bi-pass dampers on the back (that I would have voted against) and we were out tuning them. I would have voted against them due to the fact that the car was working "very" well in the race those pics came from. I set the second fastest lap of the race in our class by 16 seconds over 40 miles. That was against a car that wasn't built to the same rules as ours (different sanctioning bodies). It was a sand rail type car with more wheel base and about 800 less pounds. The rules we had that day put all the cars with 1.6l VW engines and less than ~12" of travel in the same class. It's all good though... We absolutely destroyed all the cars that would have been in our class in SCORE.

[blainefab]

Originally Posted by MarkMc26

EDIT 2: Here's a photo of what I described in Edit 1 above. The vertical shock tower plate would be bent to follow the shock tower contour at the top. The green lines represent the rear subframe. The red lines represent where the rear kicker bar would be welded to the horizontal and vertical portions of the plate, while staying within 6" of the end of the bar. This should eliminate any concerns about the "small gap" between 2 tubes at the same plate, while tying the shock tower to the cage structure.

Comments of all flavors, as always, are welcome.

Edit 2 looks good - feel free to bevel the side of the tube to fit up tight to the pad, and weld all round the base, up and over the sides. 360deg weld on multiple planes is good.

[MarkMc26]

Thank you for the input, Alan. The option of beveling the tube absolutely eluded me.

I like the way the 3-piece footwell tube assembly in your photo is, well, 3 pieces. Many people just use 1 or 2 of the ones that you have on the left, which isn't the best way to stop an intruding wheel; the 3rd tube is more nearly aligned with the direction of the force. Where is the other end attached? Also, were these pedals relocated rearward to clear those tubes?

Mark

[blainefab]

Originally Posted by MarkMc26

Thank you for the input, Alan. The option of beveling the tube absolutely eluded me.

I like the way the 3-piece footwell tube assembly in your photo is, well, 3 pieces. Many people just use 1 or 2 of the ones that you have on the left, which isn't the best way to stop an intruding wheel; the 3rd tube is more nearly aligned with the direction of the force. Where is the other end attached? Also, were these pedals relocated rearward to clear those tubes?

Mark

This is the black car from Pages 10-11, starting its 2nd season (time flies, huh?) Seat is set back about 10", pedals about 5". Driver is 6'4" and all leg. My DIY shifter:



That 3rd tube bracing the footwell ends up at a massive junction on the pass side. Along the way it supports the pedals and electrical panel: