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Opposing airbags could do this to firm up the ride. ORI use high pressure in a shock form. Bags allow air compressors to change air settings rather than nitrogen tanks.
Reliability of rods and seals vs. bags puts bags on top.
 

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Two frame mounted bags with a link sandwiched between. Pressure top bag to lift. Pressure bottom bag to preload top bag. Eventually you end up at ride height with desired preload or spring rate. Firm rate with low ride height. You need large diameter bags or high pressure compressors because you loose load from negative force.
 

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Discussion Starter #104
Read and re-read and re-read this, but I'm not sure I'm following you. Sorry.
 

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I'm just reading to learn here, but it reminded me of an article I read awhile ago: http://www.tirerack.com/images/suspension/praxis/pdf/0311_scc_prax2.pdf

I think on re-reading it what he is saying is right, but only applies to applications like an air shock; I think an air bag acts more like a tire... Are there any good calculators out there that factor in the way air bags really work?

Jesse: I think hydrodynamic is suggesting an air bag setup that works more like ori or bike shocks, where the lower bag essentially acts against the upper to give you a way to adjust the spring rate at a given height.
 

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Two frame mounted bags with a link sandwiched between. Pressure top bag to lift. Pressure bottom bag to preload top bag. Eventually you end up at ride height with desired preload or spring rate. Firm rate with low ride height. You need large diameter bags or high pressure compressors because you loose load from negative force.
The original scorpion did the apposing air bags in the rear only to fight the rear jacking (high antisquat) created from the one link. As I recall it got named the scorpion because of the original rear jacking issue.

See if this link works. You can see it when he flexes out. The scorpion was a very interesting design...not just one of the first tube rock crawlers.

129 9801 Scorpion Mk1 Over The Top Sideview Photo 1
 

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Understand what you're saying about spring-rates and airbags. That's a problem with my Audi. When you lower the ride-height, the suspension gets 'softer' and when you raise it, it gets 'firmer', which is pretty much exactly the opposite of how it ought to work
This is not typically how an air spring works, there are several ways that this can occur but you are not likely to come across anything like this you would buy in the aftermarket. You will almost always see that the lower the ride height, the higher the spring rate. You are generally decreasing the volume of the spring as you go lower: spring volume dictates spring rate, functional spring diameters affect your pressure. Same concepts directly apply to air shocks.

You should be able to get everything you want out of a single air spring, just needs to be correctly sized. I don't care much for the convoluted style springs, a rolling lobe style gives much better characteristics and generally more travel. Look at Firestone 140/95 springs.
 

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Discussion Starter #109
Two frame mounted bags with a link sandwiched between. Pressure top bag to lift. Pressure bottom bag to preload top bag. Eventually you end up at ride height with desired preload or spring rate. Firm rate with low ride height. You need large diameter bags or high pressure compressors because you loose load from negative force.
I got it! Finally. Adjust the pressure on the lower bag to get the desired spring rate and adjust the the upper bag works like a negative spring (like pressure on the rebound side of a piston in an air-shock). Makes perfect sense and it' a concept I'm totally familiar with in other applications, just hadn't occurred to me to apply that idea to airbags in this application. Duh!
I'm just reading to learn here...
Me too.

...but it reminded me of an article I read awhile ago: http://www.tirerack.com/images/suspension/praxis/pdf/0311_scc_prax2.pdf

I think on re-reading it what he is saying is right, but only applies to applications like an air shock; I think an air bag acts more like a tire... Are there any good calculators out there that factor in the way air bags really work?

Jesse: I think hydrodynamic is suggesting an air bag setup that works more like ori or bike shocks, where the lower bag essentially acts against the upper to give you a way to adjust the spring rate at a given height.
Thanks for the link. Reading that article meow. Am sure there's a lot of good information out there about airbags. Never had much of a reason to learn anything more about them than the obvious. Bet the stuff the manufacturers have published would be a good place to start. You know, just to cover the basics.

Oh, and thanks for helping me to understand what Hydro was suggesting.

The original scorpion did the apposing air bags in the rear only to fight the rear jacking (high antisquat) created from the one link. As I recall it got named the scorpion because of the original rear jacking issue.
Of course I remember that! Soni's scorpion had a pretty major impact on me. Was one of the main reasons I got so interested in designing/building off-road vehicles. By the way, Soni is still making cool stuff.
This is not typically how an air spring works, there are several ways that this can occur but you are not likely to come across anything like this you would buy in the aftermarket. You will almost always see that the lower the ride height, the higher the spring rate. You are generally decreasing the volume of the spring as you go lower: spring volume dictates spring rate, functional spring diameters affect your pressure. Same concepts directly apply to air shocks.
I replaced the stock airbags on my allroad with Arnott airbags and they have metal collars around the bags. Assumed that was an attempt to manipulate the spring-rates as the airbags compress. But the performance is pretty close to stock, which is to say, it's horrible. Terrible. Dunno how/why, but the suspension definitely seems a lot 'softer' when it's lower. Made perfect sense to me, and I'm honestly kinda surprised by what you're telling me. Mostly because a balloon that's only partially inflated is so much easier to compress than a ballon that's got a lot more air in it. Would have attributed that to the stretchiness of the rubber being in a more relaxed state with less air in it. No?

You should be able to get everything you want out of a single air spring, just needs to be correctly sized. I don't care much for the convoluted style springs, a rolling lobe style gives much better characteristics and generally more travel. Look at Firestone 140/95 springs.
Thanks. Lots to learn.
 

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Discussion Starter #110
Hey Hydro, while I've got your attention... Would you please take a minute to read this, and the discussion that follows. Have been talking to Joe and we're both pretty much convinced that this idea is solid, and could/should be pivotal tech, but nobody seems too excited about it. Sent you a PM when it first came up, hoping that you'd weigh-in. Would really like to incorporate this kind of steering into whatever I end up building, and I would consider putting it on my motorhome too, but I'm not trying to build a 20,000lb guinea pig...
 

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This is not typically how an air spring works, there are several ways that this can occur but you are not likely to come across anything like this you would buy in the aftermarket. You will almost always see that the lower the ride height, the higher the spring rate. You are generally decreasing the volume of the spring as you go lower: spring volume dictates spring rate, functional spring diameters affect your pressure. Same concepts directly apply to air shocks.

You should be able to get everything you want out of a single air spring, just needs to be correctly sized. I don't care much for the convoluted style springs, a rolling lobe style gives much better characteristics and generally more travel. Look at Firestone 140/95 springs.
To help clear up confusion. Characteristics of rolling lobe or sleeve is different than convoluted.
Suspension linkage further complicates what the bag is doing.

My convolute example is at ride height, the bag is close to volume capacity which takes more pressure to stretch the bag to get to desired height. The bag is tight and stiff and the air volume is preloaded for trail impact loads. Lowest ride height has the lowest preload and softest spring rate.
Sleeves and pistons do not preload the same way.
 

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I've been reading some more on these airbags trying to understand things... (please correct me if I mistate anything here, I'm still trying to figure this all out).

The first thing I found (that seems obvious now) is that each bag has its own characteristics. You might be able to say general things about different types (convoluted, reversible sleeve, etc) but to really know how a specific bag is going to work on your application, you need to get the data sheets.

Firestone has some literature that was helpful to me, in particular their design guide

They have basic data sheets available at the literature link, however, you have to contact the compay for more detailed information and curves. I was looking at one in particular a model no W013585426, I sent an online request for data sheets and had them by the end of the day, although it does still seem to be lacking some info.

An interesting thing (about the above part) is depending on the load, height and pressure, it will act anywhere from very 'progressive' (compressing the bag considerably raises the spring rate) to nearly linear, where compressing the bag doesn't change the spring rate much at all (like a plain coil spring would behave).

Another interesting thing about this particular bag, assuming I'm looking at the charts right, as you fill the bag for certain load cases, you may actually see a decrease in pressure as the ride height increases--kind of counterintutive! Basically volume is increasing and the pressure area is increasing as you fill it, or at least that's how it looks to me.

I also played around with some numbers looking at the way airshocks behave... again, assuming I didn't screw something up (which is entirely possible) it appears that for a plain air shock, set at a given pressure:

-As you compress the shock, the spring rate increases.
-As you extend it, the spring rate decreases

-Adding an opposing chamber (like an ORI, mountain bike shock, etc) can help bring the spring rate closer to a constant.
-Assuming you have minimal flow restrictions, adding a resevoir inline would do something similar.

A question for you guys: I found the Firestone HD app guide, does anyone know of something similar that would be a better match for light trucks/jeeps etc?
 

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Burst pressure is a major concern with off road loading. Once that 150 psi charge gets compressed you can be in the 300-600 psi range quickly. I run the 200 psi Slam SS bag and have not had a bag failure at 200 psi with off road loading that cracked the frame. They have a 400 psi bag that is super stiff and it can handle more but requires more pressure to get to max height.

Air volume of lines and valves accumulate to change spring rate. Accumulator tanks can be valved off and on to instantly change spring rate.
 

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Discussion Starter #114
That's pretty interesting. Makes perfect sense though, using air tanks and valving to change volumes and spring rates. Feel like an infant just starting to explore all the endless possibilities. Thanks!

Nothing more to say about the hydraulic steering linkage stuff though? Was really hoping that might have turned into a more fruitful conversation. Seems like that could be such a pivotal breakthrough and I'm still not seeing why it wouldn't work.
 
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