Roll Cage design

[PoorMans180SX]

My car is in need of a roll cage. This will not be a street driven car and you can assume that whoever is riding in it will be wearing a helmet at all times. I'm talking a serious time attack/some drift cage, not just your basic 6-point.

Forgive my poor MS paint skills, but I've come up with several designs that I find intriguing, but I was hoping I could get some advice on the REAL importance of certain bars and their stiffening properties.

I know I could design some crazy monkey-bar setup, but I do want it to be somewhat lightweight. This cage will be made from Chromoly. If you want to give some advice on size and whatnot that will be cool, but I think I will ultimately let the shop decide (If I can find a good enough one)

This was the setup I was decided on for a long time (until I discovered some others). The downbars you see underneath the middle harness bar connect to the transmission tunnel.


I've noticed a lot of crossbars lately:


I'm starting to like this setup more and more for it's lightness and stiffness (the strut bar would do double duty as a harness bar):


I'm thinking this is probably the stiffest setup I can come up with without going crazy. I've also added a traingulated strut bar in, which I haven't seen on many S-chassis, but I have recently on several professional race cars, input?:


This is the classic setup I see in pretty much every full-cage drift S-chassis:


I got this design from a setup I saw in a S13 coupe:


And something similar to this from a Fastback shell on here (olive green, carbon doors? I've got photos) Obviously you could tie this into the C-pillars:


by the way the front downbars are to comply with some of the latest regulations and would pass through the strut towers completely. Any advice is appreciated. Like I said, they are just MS paint drawings, so feel free to edit and repost as you like. Thanks.

[UNITEDMASTER]

Hello, I really like your use of MS paint. Itss gonna be intereesting to hear the comments that follow!!!

[UNITEDMASTER]

[quote=UNITEDMASTER;1427303]Hello, I really like your use of MS paint. Its gonna be interesting to hear the comments that follow!!! Im a fabricator also,all the desighns are cool,only thing I saw is some of the missing the main hoop diagnol. If your going molly thats gonna cost (time in TIGing it & tight fit notches).

[LB.Motoring]

Not To scale.


hahaha

looks good.

I donno about those top corners, around the top box, Id do dimple Die corners...

[ch1873857]

heh, you want light weight, your going to have to use some crazy aluminum alloy tubing because thats going to be pretty heavy, better have the power to back this design up. even chromoly. your looking at about $1k of piping at least, and a crazy amount of man hours to build it. so extremely expensive. i just think you are over doing it man. and your design isnt the greatest at all. nothing makes sense. i would have to redo it to show you. eh.. i'll give it a shot

[chmercer]

um where are the front tubes supposed to be going

you have too much pipe in there

why would you build a cage from chromoly anymore, totally pointless, wall thickness must be consistent regardless of material which invalidates any benefit from chromoly. read the rule book. or read about roll cages. what am i talking about this is zilvia.

anyway using a strut bar as a harness bar is retarded and unsafe. you want your harness bar to be as close as possible to yourself. you want minimal excess webbing so you have less stretch. and you want it up by your shoulders. not like down by your lower back.

Xing the roof halo is stupid, so much weight up high (worst place) for no reason.

also the rear part (im assuming you got that from some kind of drag racer cage picture where they have to tie into the rear frame rails for the rules/helps with launching) is stupid.

if you went into a chassis shop with any of those pictures they would just say youre retarded and build you a cage that looks like everyone elses cage. dont reinvent the wheel.



make that

the sooner you realise the reason you want all that shit is for cool points and nothing else, the better off youll be

[Silverbullet]

OT: nice MS Paint skills. You should consider learning AutoCAD. haha.

[Gaelen]

if you give me some ideas of what you want I would be happy to copy it for you in solidworks

heres one i did a while ago


and yes i know it's missing things...it was never finished

[Wiisass]

You need to look at loads and how you want them transmitted. Think about where they come from and where they're going. Just drawing a bunch of bars is pointless.

[bwake 5]

haha those are rediculously overdone

[O3DigitalBath]

kinda looks like a kids playground...

[PoorMans180SX]

Well, I didn't get a lot from all that except that I'm overdesigning. I'm definitely sticking with X-door bars, and the corner reinforcements. Both are key to cage stiffness and safety. I'll take out one bar in the X in the halo, but a crossbar is necessary for stiffness. And I'll add a harness bar into my design. I'm not looking for "cool points" I'm looking for maximum chassis stiffness. What materials does everyone recommend then? Isn't Chromoly still the stiffest, safest, lightest metal to make cages out of? Sorry I'm not up to date on my latest cage requirements, I'm looking at NASA and SCCA specs now.

Another point I forgot: I know it would be best to triangulate the front strut towers with the dash bar horizontally (Or run a setup similar to DSG's Maxi) but it's basically impossible with the brake booster and clutch cylinder location and a VQ in the engine bay.

[cdlong]

Originally Posted by Turbo711

I'm looking for maximum chassis stiffness.

i just wanted to comment on this idea that you've mentioned a few times that i'm not sure anyone has commented on.

maximum chassis stiffness isn't the goal. if you wanted that, just make the chassis out of one block of steel. obviously you don't want to do that because it would weigh a ton. stiffness is a compromise (just like virtually everything else) with weight. you want to make the chassis stiff enough and safe enough but add as little weight as possible. the chassis will always flex, better to accept that sooner than later.

now, how you do that should be left to the experts.

on a side note, the strut tower braces can be added later. and there are bolt in braces that do pretty much the same thing. basically a sheet metal piece that fills in the space between the strut tower, fender, and firewall. i can't seem to find any at the moment, but maybe someone else knows of one.

[chmercer]

what are you doing with this car

most classes you cant run pipe into the engine compartment

are you building a wrc car. what is going on here

chromoly is steel. steel weighs the same as steel. i dont want to give you the whole lesson on it right now maybe search on google or something. but yeah make it out of dom tubing

noone puts any braces into the halo thats totally pointless just make the cage that i said

x the doors if you are going to be doing some 8 second drag passes or something

why not just X the passenger compartment. that would help with "key cage stiffness". run a bar from above the drivers head to the bottom of the passenger a pillar bar. that would make it MEGA STIFF. and you could X it. so rad.

save yourself some trouble and just do what i said

just saw your sig, dont acid dip your car it will fuck your chassis up, that only works on like old ass domestics where everything is welded, too much body glue nowadays

why are there so many people who have like no background knowledge whatsoever in the shit that they talk about. like did you just start drawing triangles on a napkin and think you wanted a cage.

take it to a chassis shop, and say you want a cage that will pass scca tech, and tell them how much money you have to spend, and walk out the door. let the people who know what they are doing make you the cage.

[GoodOl'S13]

Originally Posted by chmercer

what are you doing with this car

most classes you cant run pipe into the engine compartment

are you building a wrc car. what is going on here

chromoly is steel. steel weighs the same as steel. i dont want to give you the whole lesson on it right now maybe search on google or something. but yeah make it out of dom tubing

noone puts any braces into the halo thats totally pointless just make the cage that i said

x the doors if you are going to be doing some 8 second drag passes or something

why not just X the passenger compartment. that would help with "key cage stiffness". run a bar from above the drivers head to the bottom of the passenger a pillar bar. that would make it MEGA STIFF. and you could X it. so rad.

save yourself some trouble and just do what i said

just saw your sig, dont acid dip your car it will fuck your chassis up, that only works on like old ass domestics where everything is welded, too much body glue nowadays

why are there so many people who have like no background knowledge whatsoever in the shit that they talk about. like did you just start drawing triangles on a napkin and think you wanted a cage.

take it to a chassis shop, and say you want a cage that will pass scca tech, and tell them how much money you have to spend, and walk out the door. let the people who know what they are doing make you the cage.

With that being said, its seems that people have started to think that the more tubing in a cage the "COOLER" it is. Just go and talk to a chassis shop and they should help you out by showing designs for your car. If you want more info on the drab green fastback PM me.

[SicBastard]

Chromoly is the lightest, but the ENTIRE cage has to be heat treated after ALL of the welding is done in order to get the strength back. Because nearly no one does this chromoly is illeagle for a few sanctioning bodies as of Jan 2007.

It looks like you gleaned the important points from the posts above. Don't make an X when a single cross bar will triangulate. Chmercer is dead on about the harness bar, it needs to be about level with the top of your shoulders.

Most importantly read and re-read the rule books of the sanctioning body that you want to race under. Many sanctioning bodies will allow you to petition for acceptance of a cage that has been approved for another.

[shortandsour]

look and learn
http://e30m3performance.com/tech_art..._symposium.htm

[UNITEDMASTER]

Originally Posted by shortandsour

look and learn
http://e30m3performance.com/tech_art..._symposium.htm

Hello I was going to also suggest that site to look at,most of the cages posted can be seen here,of course with some variations

[chmercer]

chromoly steel is not lighter than erw steel or dom steel. dont spread misinformation. read up before you type.

[PoorMans180SX]

Well, I'm not quite sure what classes I want to race in, but I'm definitely reading up on those spec sheets. I'm hoping to do time attacks.

What's wrong with a WRC style cage?

Anyways, I am actually taking this information in and will be applying it.
Thanks Chmercer, you gave me quite the schooling.

[240sxaddict]

ok, time attack... you'd probably want to practice at some hpde level courses first right? yep...and have you ever looked up those sanctioning bodies rules(SCCA and NASA)? Let me see if I can find whats completely stupid/non-legal in your designs.

1) cages cannot travel through the firewall.
2) 6-8 points is max
3) overhead Xbrace is useless and definietly in the way
4) your main hoop must have on diagonal support bar and harness bar at the appropriate shoulder level. I only see this in one of your drawings.
5) the section rearward of the rear strut towers is useless. if the strut section doesnt flex if properly tied into the rollcage neither will the rear. plus the aforementioned extra points reason.

ok sure, you want to do time attack and they dont have specifics listed as to design of rollcage except it wont be accepted if it looks unsafe. your best bet is still to go along with scca/nasa specs because chances are the tech inspectors who are checking out the cages do it for multiple events/organizations and most likely know SCCA/NASA rules. and this is so you can still run your car legally at other events to keep your driving skills up and ready for the challenge. plus, a bare 6point cage costs an average of $1500 at a tuner shop... now add all those other braces... "poor with big plans" wont cut it there.

BTW... I design and build cages, not just talking out my ass here.

[infinitexsound]

most of that shit u dont even need....

[PoorMans180SX]

Thanks for all the advice and that link guys. I honestly came into this with an open mind hoping something like this would happen, I'm more than open to advice. I've redesigned my cage, let me upload it and you can tell me what you guys think. I've done a lot more research as well.

oh, and Chmercer, thanks for the acid dip warning.

[PoorMans180SX]

Got a lot of it from that M3 site. Obviously if I decide to run in a class that doesn't allow firewall penetration then I won't be running those bars.

[ch1873857]

raise your harness bar.. the diagonal bar has to be one piece but the harness bars are separate. at least raise the drivers side to the hieght of your shoulders like said before.

[PoorMans180SX]

Originally Posted by ch1873857

raise your harness bar.. the diagonal bar has to be one piece but the harness bars are separate. at least raise the drivers side to the hieght of your shoulders like said before.

Yes, I will definitely get seats and look at my shoulder height before I get the cage, these were merely drawings, not final designs.

To the other guys, I know my chassis is still going to flex, I'm not a newb. I just wanted to limit this flex to the minimum amount with out going super overboard on the bars, which I obviously did (at first) anyway.

And yes, I will be stitch/seam welding the chassis before the cage is installed.
And yes, I will be tieing the cage into the A and B pillars, still deciding if the roof is necessary.

[Wiisass]

Originally Posted by Turbo711

To the other guys, I know my chassis is still going to flex, I'm not a newb. I just wanted to limit this flex to the minimum amount with out going super overboard on the bars, which I obviously did (at first) anyway.

But do you know what the minimum amount is? And how you can limit that? Are you going to model the unibody and the cage in a program a little more sophisticated than Paint? Do you even know what a good value for torsional rigidity for your chassis would be?

Until you can answer those questions, I wouldn't worry about adding tons of bars and connecting every possible piece of the car together with a 1.5" or 1.75" piece of steel tubing.

Like I said before, the key to a good cage design is to look at the loads and how they're transmitted through the chassis and the cage. And learn good structure design, learn what a node is, how bars are supposed to intersect, how to efficiently triangulate.

Like someone said above, when you go crazy with bars and don't really have a good reason for it, you're quickly approaching the limit of diminishing returns. You're adding more weight and you aren't adding any stiffness or safety. You need to look at the rulebooks and find out what you can and can't do. And the best mechanical design won't always work the best in the car, sometimes compromises need to be made for fitting components, one of which can be the driver.

So keep it simple and make it clean, make sure the bars are transmitting forces clearly and not adding bending moments to bars or any of that other shit that you see on more than half the cages out there.

By the way, are you going to try and make this cage yourself? If you aren't, the more extra worthless stuff you add, is just going to drive the price of the cage up. And even if you're doing it yourself, it's still going to add a decent amount to the cost.

[240sxaddict]

stitch weld the chassis... then add rollcage.... and you have one stiff chassis

[TheWolf]

"I want maximum stiffness"

I highly doubt you have a way to measure if you're going stiffer or not. So why with the fancy drawings?


Only advice I can give is go with a basic 6 point and tie it into the a-pillars and the roof. The rest is quite subjective.

[ch1873857]

^someone who knows what hes talking about.

no need to tie it into your roof either