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Minimalist Cage Designs

[memphis]

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So... since the tech is here I thought I'd start a new thread since I am looking for information that pre-dates 2010. Since then everyone is all about curved tube chassis and zero new tech at Pirate.

Building a cage is way down the list but I'd like to start some good discussion about it.

I am building a CJ2a/3a and space is at a premium.
A properly designed is 100% better than no cage but this is not a desert runner, no high speed stuff but it will be used on the street. So with that in mind, I'd like to keep myself safe on the street and not ring my bell since I won't be wearing a helmet on the road, off road is a different story.

I love Meisers Rango cage... and it is something I will likely duplicate

20121020_121924.jpg


Is there a minimum tube size I can use? If I use smaller material can I increase the wall thickness to compensate for strength?

Let's get some discussion going!
 

YotaAtieToo

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Why go smaller and thicker?

1.5"x120 is good for lighter rigs I just did a cage for Wilson on his samurai out of 1.5" chromo, we did 120 A-C pillar run and 090 everything else.

Personally I like 1 3/4" I think it just looks more correctly sized.

The cage pictured is basically how I would do it, I'm a fan of running the tube from the A pillar to the C pillar instead of hoops running side to side. Looks better and is more functional imo.
 

gt1guy

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[memphis said:
;n46225]

A properly designed is 100% better than no cage but this is not a desert runner, no high speed stuff but it will be used on the street. So with that in mind, I'd like to keep myself safe on the street and not ring my bell since I won't be wearing a helmet on the road, off road is a different story.

Is there a minimum tube size I can use? If I use smaller material can I increase the wall thickness to compensate for strength?

Let's get some discussion going!


OD of the tube has more of an impact on resistance to bending than wall thickness does.

I'm in the same boat as far as being driven on the street. I went to great lengths to keep the cage away from my melon.
 

dnsfailure

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I don't see why not to use 1.75". it doesn't look too thick for a small jeep. The majority of mine is 1.75" .120, with a few 1" .120 for mounting the seats, belts, and grab handles. Mine is similar to Brennan's, with a few extra pieces in there.
 

jhama78

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Rango's cage is bitchin for sure.. Is jesse haines on here yet? He has built some awesome minimalist cages on his flatties over the years as well. Following along to get ideas for a future project or two.
 
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needs overhead protection, going to the roof on anything other than flat ground is asking for some serious problems.
 

Eric

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General rule of thumb for tube diameter is under 4k lbs then 1.5" x 0.120" is good, between 4k - 5k lbs use 1.75" x 0.120, over 5k lbs use 2" x 0.120". This is more or less what various sanctioning bodies require.

Here are some pics of the "minimalist" cage for my TJ-looking buggy. I still want to add some crosses in the back (to mount a spare tire) but have not come up with a design that I like.

As designed in Solidworks:

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Transferred into Bendtech:

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As built:

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Weasel

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needs overhead protection, going to the roof on anything other than flat ground is asking for some serious problems.

I've seen alot of cages that the top B pillar connector folds in when the rig rolls over backwards or forwards, even on slow once overs. I can't really imagine the cage not racking over if you laid it over on it's side, without a X.
 
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I've seen alot of cages that the top B pillar connector folds in when the rig rolls over backwards or forwards, even on slow once overs. I can't really imagine the cage not racking over if you laid it over on it's side, without a X.

i was referring to a rock impaling the occupants.

i would not feel comfortable in the cage the OP posted
 

OC IH

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General rule of thumb for tube diameter is under 4k lbs then 1.5" x 0.120" is good, between 4k - 5k lbs use 1.75" x 0.120, over 5k lbs use 2" x 0.120". This is more or less what various sanctioning bodies require.

Here are some pics of the "minimalist" cage for my TJ-looking buggy. I still want to add some crosses in the back but have not come up with a design that I like.

As designed in Solidworks:


I’m interested in your thoughts on these (see red ovals). What will they connect to in the front? Any concern about the hoop at the A pillar handling the load mid tube?

cage-001-x.jpg


While we build the suspension in our Scout we’re thinking about the cage we will eventually build. It came up now since it seems logical to brace the front shock hoops to the A pillar hoop. Then, where does the load go from there?
 
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I’m interested in your thoughts on these (see red ovals). What will they connect to in the front? Any concern about the hoop at the A pillar handling the load mid tube?

While we build the suspension in our Scout we’re thinking about the cage we will eventually build. It came up now since it seems logical to brace the front shock hoops to the A pillar hoop. Then, where does the load go from there?

it prebuckles the a pillar on the endo, so it collapses when it hit the brow bar.
 

Eric

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i was referring to a rock impaling the occupants.

i would not feel comfortable in the cage the OP posted
Depends on what you are doing. Its similar, probably better, than a factory TJ cage and I've seen those hold up remarkably well. Of course you are not going to take it out desert racing and it probably would not fare too well during a 300 foot barrel roll but out on the "easier" trails it serves fine for a "minimalist" cage. And then we have this guy:

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Eric

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I’m interested in your thoughts on these (see red ovals). What will they connect to in the front? Any concern about the hoop at the A pillar handling the load mid tube?
These pieces connect to some tube work in the front that is permanently welded to the frame. They are there for aesthetics and are not intended to be primary load bearing structure. The frame itself is 2" x 4" x 0.188" tube. There are a number of places on the cage, and the front tube work, where I intentionally deviated from "proper" node design for (mostly) aesthetic reasons. This is a full-frame rock crawling trail rig that will see very low speed flops onto the side or roof. If racing was part of the picture I would have built a full-tube space frame.
 
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gt1guy

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I think the biggest problem when designing a cage, is the simple fact that we don't get to decide when/where/how we roll over.

I'm in the same boat as OP in the fact that the rig will also be driven on the road. To me, getting cut off at 75mph on the freeway could easily be "worst case scenario", even if I didn't plan to go crazy offroad. That's a high speed crash.

A poorly designed cage can become just as dangerous as not having one. I think a proper X in the B-pillar is the single most important part of any cage.
 

'84 Bronco II

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Cages are something that are kind of hard to analyze, so it comes down to what makes you feel comfortable/best judgement. There are some best practices that should followed to get the best results and I'll list a few:
  • Keep your tubes as straight as possible and avoid bends
    • Tubes are likely to buckle at bends and you are pre-yielding the material, so the tubing will undergo less deformation before it tears and breaks. If you must have a bend in the tube, make it at a node.
  • Minimize unsupported spans
    • The longer the section of tube is without other tubes connecting to it, the more likely it is to buckle.
  • Make sure you merge your nodes
    • You want the theoretical centerlines of of all the tubes that are coming together at a joint to intersect at a single imaginary point (node)
    • BAD
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    • GOOD
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  • Triangulation! :flipoff2:
    • Triangulation creates stiffness and resists bending by keeping the tubing in pure tension and compression. Think about your design; if the welded joints were hypothetically replaced with spherical joints, would your cage still be rigid and just as strong? If not, you need more triangulation!
    • BAD
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    • GOOD
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  • Use the best material you can afford
    • 4130 > 1020 DOM (A513 Type 5) > 1020 CREW (A513 Type 2) > 1020 HREW (A513 Type 1)
  • Attach your seats and belts to the cage, and attach the cage to the frame
    • You want to stay with the cage if it separates from the vehicle, and you want the cage attached solidly and not just by some flimsy sheetmetal.

Now, there is a big difference between how a cage needs to be built to survive a high-speed rollover, end-over-end rolls, or multiple rolls versus your typical flop or half roll that occurs on the trail. For the more violent types of rolls, you definitely don't want to skimp on your cage and are going to want to follow all the rules I outlined above; however, I have seen poorly/under-built cages (including factory Jeep cages) survive impressively well during serious rollovers. In the end, anything is better than nothing, but your cage could very well be the thing that saves your life. So, how good is good enough? Well, only you can really answer that question, but I think you should attempt to build something that could survive a pretty serious roll over, even if you "don't do anything too crazy" with your flat fender.

Here are some examples of factory Jeep cages (crappy) holding up surprisingly well:
This guy rolled over two complete times on Black Bear Pass (Here's the in-cab video:https://www.youtube.com/watch?v=UxcY...&frags=pl%2Cwn)
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This guy rolled on Tomboy Road (Imogene Pass)
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All that said, I would add an "X" to the main hoop behind the seats on the Rango cage or some other form of lateral triangulation at a minimum. I would also seriously consider putting an "X" in the roof panel as well to add more triangulation and help prevent rocks or other objects from protruding into the cabin when you are upside down. Some door bars would also be a really good idea to keep you in, objects out, and add yet more triangulation into the design. As for material, I think 1020 DOM is a happy medium between strength and and cost. If you can't afford DOM, at least get CREW over HREW since it only costs slightly more and is marginally stronger. For size, you could probably get away with 1.5" dia. .120" wall as light as a flat fender is, but I would probably go 1.75" dia. .120" wall myself if you aren't going to be making it out of 4130. Tube diameter is the main factor in the stiffness of the tube, and wall thickness is the main factor in dent/crush resistance. Sure, you can trade diameter for thickness to an extent to maintain bending strength with thicker wall, smaller diameter tubing (easy mathematical formula to determine equivalent bending resistance), but it takes a lot of additional wall thickness to make up for even slight reductions in tubing diameter. You can also use stronger materials to compensate for thinner walls and/or smaller diameter (again, easy to determine equivalencies using math), but unless you are building a race car where every last pound counts, it is much more economical to use larger diameter/thicker wall lower grade material. Also, like a good painter who knows when to put down the brush, you need to know when to put down the welder. I see a lot of people who use a whole lot of unnecessary material, or don't use their material effectively (excessive bends, missed nodes, lacking triangulation) and end up with a lot of extra weight up high in their rig (ironically making a roll over more likely :laughing:) and excessive material costs.
 
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Toreadorranger

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I think a people tend to get confused on what is minimalist and what is insufficient. Like mentioned above there are a lot of "cages" that make me nervous even looking at them. The no crossbracing 4 pillar cages make cringe.

I’m interested in your thoughts on these (see red ovals). What will they connect to in the front? Any concern about the hoop at the A pillar handling the load mid tube?

While we build the suspension in our Scout we’re thinking about the cage we will eventually build. It came up now since it seems logical to brace the front shock hoops to the A pillar hoop. Then, where does the load go from there?

I would add another door bar from the back of that shock brace to the node at the bottom of the B pillar if you end up using that design. The other thing to consider is that if the cage is hard mounted to the frame, the frame is now part of the structure, which I think a lot of people tend to forget. While not always ideal, that does add quite a bit of strength to the entire structure.
 

92 Green YJ

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General rule of thumb for tube diameter is under 4k lbs then 1.5" x 0.120" is good, between 4k - 5k lbs use 1.75" x 0.120, over 5k lbs use 2" x 0.120". This is more or less what various sanctioning bodies require.

Here are some pics of the "minimalist" cage for my TJ-looking buggy. I still want to add some crosses in the back (to mount a spare tire) but have not come up with a design that I like.

As designed in Solidworks:



Transferred into Bendtech:



As built:






I’m curious about the thought behind the tabs that appear to attach to the tub along the rear section. I’ve not seen that done before. Designed to strengthen the body by tieing it into the cage? Keeping body flex down?
 

Eric

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I’m curious about the thought behind the tabs that appear to attach to the tub along the rear section. I’ve not seen that done before. Designed to strengthen the body by tieing it into the cage? Keeping body flex down?
Its actually not a tub. Those rear quarters are just skins that attach to the frame and cage with tabs! The floor and inner wheel wells also bolt in.
 

dnsfailure

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That's a nice looking cage Eric! But I'm not sure I would call that a "minimalist" cage. Though I guess it depends on what type of wheeling you're doing. For simple trail riding and occasional sketchy moments, I wouldn't consider that "minimalist". Maybe it's on the slim side for more hardcore stuff?

Anyway, I like the cage discussion stuff, we need more cage and safety tech. :cool2:
 

92 Green YJ

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Its actually not a tub. Those rear quarters are just skins that attach to the frame and cage with tabs! The floor and inner wheel wells also bolt in.

Gotcha. That makes sense. Looks great! I’m going to hopefully start my cage next week. Just ordered a notcher and some other goodies to help from Trick Tools last night. Gonna measure my old cage to get me a ballpark estimate of how much tube to get and get the order I. To IMS for steel tomorrow
 

OC IH

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I think a people tend to get confused on what is minimalist and what is insufficient. Like mentioned above there are a lot of "cages" that make me nervous even looking at them. The no crossbracing 4 pillar cages make cringe.



I would add another door bar from the back of that shock brace to the node at the bottom of the B pillar if you end up using that design. The other thing to consider is that if the cage is hard mounted to the frame, the frame is now part of the structure, which I think a lot of people tend to forget. While not always ideal, that does add quite a bit of strength to the entire structure.

This was a sort of diagonal “slow” 30 MPH or so end over end roll. Witnesses said it went over two times. I don’t remember it. All I can say is we lived.

After studying how the body buckled and the frame bent I look forward to a cage stiffening everything up a bit. This also got me to go look at the old videos of Scout crash testing. Like this https://www.youtube.com/watch?v=daZG...Cj2w&index=716. They basically collapse right at the A pillar when the frame bends so, yes, everything will be tied into the frame.

IMG_4605.JPG
 

YotaAtieToo

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To all those who are cringing at a simple 4 point cage, what does your daily driver look like?

I see where you are coming from and I'm usually a "prepare for the worst, hope for the best" type of guy, but it's not always feasible to put a wrc spec cage in every rig.

Also, just because a cage moved or a bar bent, doesn't mean that it didn't do its job. It's going to be damn near impossible to build a cage that won't take damage on a high speed roll.
 

Weasel

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To all those who are cringing at a simple 4 point cage, what does your daily driver look like?

I see where you are coming from and I'm usually a "prepare for the worst, hope for the best" type of guy, but it's not always feasible to put a wrc spec cage in every rig.

Also, just because a cage moved or a bar bent, doesn't mean that it didn't do its job. It's going to be damn near impossible to build a cage that won't take damage on a high speed roll.

Well that's true but if I flop my daily driver over it's going to be damaged and then fixed. Do you want to rebuild or repair the cage when it flops over? I realize that's not the point of the cage but its side factor. If your going to put the time into a cage you should make it functional as well. I've seen pretty good damage to cages that were involved in crawling speed endo or reverse endo.

Has it really come down to IBB is putting fashion in front of function?
 

SLOWPOKE693

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Its actually not a tub. Those rear quarters are just skins that attach to the frame and cage with tabs! The floor and inner wheel wells also bolt in.

We would know that already if you'd post a fawkin build thread! Yer killin me with these teaser shots.......

:flipoff2:
 

YotaAtieToo

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Well that's true but if I flop my daily driver over it's going to be damaged and then fixed. Do you want to rebuild or repair the cage when it flops over? I realize that's not the point of the cage but its side factor. If your going to put the time into a cage you should make it functional as well. I've seen pretty good damage to cages that were involved in crawling speed endo or reverse endo.

Has it really come down to IBB is putting fashion in front of function?

If your cage is damaged from a flop, then yes, it's not strong enough.

I was more referring to higher speed stuff. Which is much more likely to happen in a DD than a crawler.

My point is that each person has different needs or standards. The more simple cages aren't necessarily wrong, as they'll most likely serve their purpose even if they do get tweaked.

​​​​​
 

gt1guy

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If your cage is damaged in a flop and you walked away.......it did it's job. You may be cutting it out to install a new one, but it did do it's job. I think the first thing we need to admit is........a roll cage is a consumable. The more complex a cage is, the more abuse it can take before it's time for the sawzall, but at some level of crash every cage reaches it's end of life.

In the spirit of the thread title.............what should be done on a minimalist cage so you're not replacing it every time you tip over? Say you're starting with the simple 4 point cage.

First, I'd think a diagonal from the top of the B on the dvr side to the bottom of the B on the pass side would help greatly.

Second, a diagonal, V, or X above the driver/passenger, turning the big open rectangle into triangles.

Third, two struts running to the rear from the top of the B corners down to the tub. Believe it or not, this is to keep the top of the A from moving to the rear in an endo.

Fourth, everything tied into the frame and not just bolted to the tub.


This wouldn't add a lot of weight or get in your way too bad (the B diag), but would add a ton of strength to the cage.
 
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