How to design a cage?

[nose]

Hi there,

I do not know anything about cage design. So I would like to ask you to comment on the disgn below. Yes, I have done a lot of searching on the board and the www but did not find guidelines or design principles. But I have found a lot of cages where I did not understand why they are built the way they are and if they actually are a good design for the purpose.

There is a lot of engineering knowledge and practice on this boeard so please help me to built this cage right the first time.

I do some not too extreme wheeling in woods and would like to do some more stuff at higher speeds (trophy / rallye style). In general I would like to keep it simple and light weight, as my rig is not heavy.

Here is what the sketch means:
- B-pillar hoop (red main hoop) takes loads from side rolls and is bent in one piece for best load distribution.
- The B-pillar support structure (grey square tubes) distributes the load evenly into the body and is attached to it at many places. This neat idea is from Pal Blesvik from this board.
- B-pillar cross brace (yellow) keeps hoop from collapsing at side loads.
- C-pillars (green) take loads from front and rear roll. They are welded to the B-pillar hoop where the roof bars left and right are welded at to have a nice load path from front to rear.
- A-pillars take front rolls. There are two pillars which include the roof bar left and right.
- Cross braces above dash / window (blue) keep front section from collapsing or buckling sideways at loads from the top in case of a front roll.

Here are my questions:
1.) A-pillars: Should I bend the front section in one piece like the B-pillar hoop or as shown in the sketch in two pieces (but including the roof part left and right)?
2.) B-pillar cross brace: Should it go from drivers head to passenger lower side or the other way around (push versus pull)? Or a X?
3.) Roof section: should I add cross barces in a X-form or on stringer in the middle going from front to rear? Is it better to add a hard roof sheet metal?
4.) C-pillars: Cross bracing in X-form here instead of cross-bracing the B-pillar to create a sort of triangle with B-pillar hoop and C-pillar?

Mounting the cage is a bit complicated; which seems to be the way I do things.
My idea is to bolt the cage to the body. Then I bolt a plate that hold rubber bushings (the small leaf spring bushings) to the other side. The bushing is then bolted to the frame at welded attachement points. I would like to have the bushings at the front frame outriggers left and right to meet the A-pillars, at the frame right below lower bar of B-pillar support structure and where the C-pilars meet the frame.
This way I have a felexible, not vibrating but still tough connection between body and frame, no holes in the body and still can take the body off.

All your comments and suggestions are greatly appreciated.

Best regards,

Norbert

[Foxfab]

B pillar support isnt necessary IMHO. Just have the legs of the B pillar hoop go to the frame and X the B pillar hoop instead of just one diagonal. Gusset Gusset Gusset.

I just read some of your lengthy post, sandwich the body with two plates bolted together where the b pillar would hit the body so that you can still remove the body and theres only 4 little holes per side.

[OKIE ZUK]

Since you're not running extreme, your design will be fine. As you step up the trails you run, add more later to your cage.

[Reflexx]

Nose,

Looks like you've done your homework! I'm not a cage designer, but I do design various products. Here's what I'd add (or consider):

1. Search Amazon for race car fabrication / construction. While 4x4 cage building books might not exist, the race care guys have many. same principals apply.

2. Are you designing a cage for an off-road race truck or nascar? in which case go to a race fab shop or you might die in a crash. No cage can withstand all crashes at high speed impacts.

3. I'm assuming that we're talking about your Samurai. 1.5" or 1.625 (.093+ wall) tubing is plenty. Bigger is overkill and looks a little goofy on our trucks.

4. A trail / rock-crawling 4x4 will not see high speed impacts, unless you flop off a long steep climb (or a Moab cliff). In which case, even a pro-built/frame attached/ultra-cage might not help.

5. as for your design, imagine putting tremendous pressure at any one point on your cage. Then imagine what would bend/give break off / puncture you / etc..

6. as you've figured out "triangulation" is key. Your "B" hoop is incredibly strong because you've added the (yellow) crossbrace. It's two triangles. But as with all things, it's a compromise. How far away is the back of your head to that cross brace? Perhaps you cannot bang it in a regular driving position, but what if your truck is tumbling around?

7. on your diagram, imagine if I was to push in the direction of the arrow that says "cross brace above window". It would buckle in that direction, no triangles to stop it! The stress is at the welds between the blue and white tubes and they will tear and/or bend.

8. You could add a similar brace over your head. But then again ,it would be directly over your or your passenger's head (bang / ouch)

9. I would suggest only two changes. Add an X over your head and replace the yellow brace with another (matching?) X. I don't mean a corner to corner X but like a letter X (more vertical than horizontal). this way it might not be directly over/behind your head.

10. the green C pillars are fine, unless you've got passengers. I would move them further back and mount them to the bed behind the wheelwells. IF you mount them to the wheel wells, your thru bolts might hit your tires. if you might have passengers some day, I'd just repeat the "A" pillars w/o the dash crossbrace.

11. Gussets - are mini triangles and can have a HUGE effect on strength. a short piece of tube 6-10" in every corner might be as good as the "X" or cross braces and look a hell of a lot better. there are pre-fabbed braces with cool designs out there.

12. Body mount vs frame mount. This can be a long argument. But my cage(s) are mounted to the body with .188 (3/16) thick and wide plates, with matching plates underneath. grade 8 bolts & nylocks. the argument is always "what if your body breaks off the frame", well then it will be body and cage and seats go one way, frame and else goes another way.

13. You're right in attaching the frame to the body in as many places as possible, but not "welded on"

14. A cage (in my opinion) is like a motorcycle. Use once and throw away. I've had three helmets save my life in serious moto crashes, I retire those helmets. IF you have a "serious" roll and you cage looks "OK" how do you know? it might have cracks and next time its useless. can you say "pancake?"

15. consider a cage that's already made (or copy it). Rock4xfab or petroworks or calmini or davesport all make good products. Samurai guys are cheap (no denying), but $10 helmets are for $10 heads.

16. Or do what I did, buy a cage and add on what you think will make it better. I bought the petroworks cage (beautiful design) and added cross braces, welded it (instead of bolted), added padding, etc. But since I'm going to a stretched samurai, I might just buy the two front tubes of the petro cage and do the rest myself or get in touch with Rock4x or have Okiezuk make one or...

This has got to be the longest thing I've posted in my life!!!

just my $2.00 worth (inflation, ya know)

Reflexx

www.RXDi.com

[Reflexx]

some pics:

My first cage (circa 1992) just added on to the stock hoop: (it's for sale in So Cal)



Current cage (Petroworks) before I added bracing / extra tubes / handholds / hammerite paint: (also for sale along with a custom grey safari top!)


Reflexx

[stocker75]

A cage, like anything on your 4x4, should be based on your intended use. You seem to have already pondered this.

The first thing I tell people about cages is to remember that there is no such thing as "safe," just relative safety. We have all drivien 4x4s at one point or another with relatively no rollover protection without thinking a thing of it. So, you're on the right track, trying to make your rig safer.

The biggest design concerns I run into is maximizing safety while minimizing the intrusion of the cage into the function of my vehicle. With an extreme rock rig you sacrifice practicality--crawling through tiny openings, banging knees getting in, losing storage space and luxuries like cup holders. With a daily driver/mild trail rig you want to be able to retain your top, adjust your seat, and get in and out without whacking your noggin (for most people).

As for making everything removeable, it is a good enough idea but in my experience, you rarely end up removing the stuff very often, it takes longer to do with some trade-offs, and it might not be any harder to cut it aparts and weld it back together if you had to remove something. In a perfect world you'd have your truck close to where you want it prior to cage building--like the engine swap done, the body lift on, suspension settled, etc. But, it's not always that simple.

Also, when building a cage, it is often a matter of where you want to build in failure. Meaning--some rigs, like a rock rig, might have a slow, easy rollover and you would want the cage to hold up without any damage and be usable for additional rollovers. Other times, you want insurance in the worst case scenario. Namely--a one-time use cage. If it saves your ass you aren't concerned with totalling it or the vehicle out. People will debate this point, though, and its no excuse to build a poorly designed or week cage.

A lot of bench builders will preach and preach about cross bracing, and there is no argument that the triangle is your friend. For all of the arguments there are few examples of failed cages out there to study. Look at all of the designs you can find, borrow ideas from other sources (off road racing, etc.). Then, start building. You'll probably modify your designs as you build your first cage, anyway. Good luck.

[nose]

Hello,

thanks for all your inputs.

Your are right, without an X in the roof area the cage could give in. As I am very tall I have to look into how much space there actually is above my head. I want enough clearance even for running with a helmet (required where I come from).

Yep, I also will let the C-pillars go to the very rear end of the frame.

I was thinking about adding a X between the C-pillars to care the spare tire. To still be able to carry bulky stuff I wanted to make this X a bolt on to be removable.

Does it make sense to bolt such an X into the cage or is welding the only way to go?

Thanks and keep you comments coming.

best regards,

nose

[OKIE ZUK]

Use 1 1/2" X .120 wall tubing. To start out build basic, then add. I dought too many guys have rolled (tested cage, not on purpose) as many times as I have. This picture is of my cage after 3 barrel rolls, with an endo at the end. It has been in many previous rolls also. Notice targa bar smashed, but windshield still intack. Also I'd suggest running front shoulder harness set-up in the rear for passengers, if you add to the rear.

[OKIE ZUK]

Here's how it landed.

[OKIE ZUK]

This was after 3 endos at Hot Springs, on a trail called Quicksand. Yes, I recommend a cage, if you run extreme stuff. My passenger on the right is 6'3" tall and we both made it out ok.

[Foxfab]

Also look at the minimum standards required for racing such as UROC's rules. There's a minimum for a reason.

For those with cable modems, here's a movie of my non-suzuki comp rig testing out its cage

http://www.yankeetoys.org/black900rr...s/PA300058.mov

[nose]

Yep, I need a cage.
I rolled my first zuk @ 60mph off the highway and down a small hill. Ice on the road. Luckily the factory sheet metal roll bar (European models do not have the tube roll bar) held up. If a door would have opened I would hae had trouble to walk away.

So I would like to have at least the protection needed for wheeling.

Thanks again for your input.

nose

[Rockrat]

Here are a few shots for you to give a maybee some inspiration or new ideas, obveuosly no one will be sitting in the back of this rear stly cage but oh well



before completion


front dash bar and you get the idea of the trianglation around your head area


Mine the top is a Nascar style halo with the dr. and passanger front A-pillar uprights come up and travel in line to cause the X in the top of the passanger area of the cab

[jp008]

Holy freeking tires Batman.

I like the blower though

Nice work as usual Scott

[Tusker]

Nose. I know the feeling. I am an engineer and majored in structural engineering (20 years ago ) and still felt myself in a funk about how to design my cage. The education is nice and helpful, but there is no substitute for the knowledge and experience of those who have done gymnastics in their rigs. My best freind was also a big help to me in that he is a 30+ year fireman and seen at least a thousand high speed rollover accidents. He owns a Zuk as well and felt absolutely confident that my design (which isn't much if any different than a lot of the otrher cages you will see in Zuks) would get me through almost anything.

I agree with Okie Zuk that the 1.5" x 0.120 wall tube as a good size. You can go bigger, but with a good design, it is not necessary IMHO. Make sure the wall thickness you use is at least 0.120". Once a tube gets pinched by an impact load it is severely weakened.

Joints are the place where most structures tend to fail, so don't put joints in the critical stress areas if you can help it, and as stated above, gusset the connections thoroughly. I believe that the one-piece "A" hoop is stronger than what you have drawn. However, it is much harder to do properly and as long as your jointing is sound, I don't think it matters much in a lightweight Sami.

Bracing is a good idea as it stiffens the cage significantly. To be effective, braces should be diagonal. The downside is that they tend to get in the way. Also, unless you mount the cage to the frame, I think it is somewhat of a wasted effort to brace the cage since it is likely to be torn off of the sheetmetal before it completely collapses if well built. If you want to brace, brace the "b" hoop diagonally. A single brace adds a lot of strength. You get a little bit more from double braces, but not awhole lot.

The last thing to consider is looks. I have seen some cages out there that were ok structurally, but were hideous Rockrat is the master at combining form and function in a host of different designs. There are a lot of other good examples out there too.

Here is a shot of mine. Good luck.

[Reflexx]

Gents,

In my earlier post I mentioned that Cages are "one time use" items. Let me clarify. A good cage will withstand a few rolls, depending on "where" you roll it.

If your in the dunes, the sand gives as your cage goes over and over. probably minimal damage. I know, I've done it.

If your at Moab (solid rock) one roll might toast your cage. Just be sane and use your judgment. somewhere here I read that a guy cut his cage off after a bad roll, and continued to wheel!!!! That's just nuts.

If your on a wooded trail with normal dirt (like back east) your cage can survive a few tumbles. Just give it a good once over.

Reflexx

[Reflexx]

Tusker,

that cage is a beauty. did you DIY or is that from a fab shop? how about some more pics???

thanks,

Reflexx

[AnotherCanuck]

Originally Posted by Reflexx

12. Body mount vs frame mount. This can be a long argument. But my cage(s) are mounted to the body with .188 (3/16) thick and wide plates, with matching plates underneath. grade 8 bolts & nylocks. the argument is always "what if your body breaks off the frame", well then it will be body and cage and seats go one way, frame and else goes another way.

13. You're right in attaching the frame to the body in as many places as possible, but not "welded on"


Reflexx

www.RXDi.com

Of all that has been posted I would only disagree on #12 and the mounting plates. I think you are setting yourself up for trouble by having the upper and lower plated the same size. I've been told (and stand to be corrected if I'm wrong) that the plate on the cage side should only be 75% of the size of the plate on the frame side. This ensures that you do not merely rip the body off the cage and have it beat the crap out of you. Having both plates the same size makes it easier for the body to 'pass' the plate on hard impact. If they are different in size they are working against one another on impact from either direction, hopefully that makes sense...

[Reflexx]

Another,

I stand corrected, you are 100% right. I can't argue with logic, and that's exactly what I will do on my new cage!

Reflexx

[SilverZuk]

Being the cheap bastard that I am.
I used the factory bar and added supports from the rear frame to the bar and made a hoop and A pillars. I recommend putting a bend in the hood above the passengers head for added strength and head clearance.
I am going to add a door bar from the A pillar beside the seat to the B pillar (factory bar) and bars straight up from the frame rails to the factory bar behind the seats before next season.
I have flopped this one a few times with no damage. It’s not ready for a multi-roll and drive away yet until I complete it and add gussets.
Most any cage is better than none though.

I outlined the cage so you can see what is there (including booger welds).
Notice the bend in the hood above my head. This makes head clearance better and the over all strength better from a force straight down from the top.

[Tusker]

Originally Posted by Reflexx

Tusker,

that cage is a beauty. did you DIY or is that from a fab shop? how about some more pics???

thanks,

Reflexx

Thanks. It is a complete DIY job (and what a job............ I have a WHOLE new respect for those who bend tube for a living). Here is a link to the post I did on it.

http://www.pirate4x4.com/forum/showt...highlight=cage

Silverzuk also makes a great point. Adding a slight bend in the cage, especially in the head bars, can help tremendously. With the slight "bulge" outward, the bars don't have to start collapsing inward from point loads to reach "developmental strength". Here is a pic that kind of shows what I did on my head bars in the front.

[Rockrat]

The last thing to consider is looks. I have seen some cages out there that were ok structurally, but were hideous Rockrat is the master at combining form and function in a host of different designs. There are a lot of other good examples out there too.

Thanks for the Comp Tusker,, dont generaly here much on the cages we do anymore. As noted above on floor plates inside plates 1.5 time the width of the tube,, and the outside plate larger so you dont get a cooky cutter effect in a hard impact. We use 4x5" under and a 4x4 inside both 3/16" I have see alot of aftermarket cages that only use 1/8" plate which is a stip no wider then the tube and only had 2 bolts in it..

[nose]

Hi,

thanks a lot to all of you. I really appreciate your comments and pics. You all have built very nice cages.

I am going to keep windshield, doors and factory sheet-metal roll bar. At least I want to be able to bolt it on during winter.

What is the common knowledge on how far the head has to be away from the bars?
I would like to mount the B-hoop further in the rear than the stock roll bar (which my model does not have anyways) or have it leaning slightly backwards (or is this a No-No?).

Thanks again + best regards,

nose

[Tusker]

The problem with moving the "B" hoop is that there is a thickened area in the wheel wells that the stock hoop mounts too. If you move away from this, your hoop-to-body connection will likely be weaker (and the "B" hoop is the one in particular you want to keep intact ). Leaning it is ok, but if you get it leaned very much, you will want to start adding diagonal bracing running along the axis of the vehicle (from the top of the "B" hoop to the floor area of the "C" hoop).

On the head bars, I put mine as far away (and tucked up to the roof) as they would go. I also did the angling with them to push them away from my head as far as possible while minimizing the opening size in the cage.

[bulletproof]

Originally Posted by OKIE ZUK

Use 1 1/2" X .120 wall tubing. To start out build basic, then add. I dought too many guys have rolled (tested cage, not on purpose) as many times as I have.

I HAVE!!!!