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6wd and Air Suspension


Simon_CSK
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I have been wanting a 6x6 vehicle for some time and thought a lot about it and am still thinking I would like to build one. I really like the air suspension on my P38 and if I was to build my six wheeler I would like it to have air suspension however what I don't like about the p38 is the complicated electronics that go with it.

Is there a simpler system? I was thinking along the lines of air pressure switches that inflate to a certain pressure and then switch off. Manual inflation perhaps.

Also would both bags on the rear axle be controlled together or independently?

Just looking for ideas.

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Is there a simpler system? I was thinking along the lines of air pressure switches that inflate to a certain pressure and then switch off. Manual inflation perhaps.

Also would both bags on the rear axle be controlled together or independently?

Some trucks use a valve connected to a rod on the axle that opens when the axle gets below a certain height, and closes when the axle gets above a certain height. Not very adjustable though, and not ideal for an off-road vehicle.

There have been plenty of threads on 6x6s on here, and all of them conclude the rear axles need to be connected. So connect the airbags per side, and you only need a 4x4 valve block for the air suspension as well :) Just keep the P38 system, it's really not that complicated.

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You have a couple of main options , you can link all four rear together , with single ride height sensing , or better have level sense on

each side . With that set up , you only need to have a pressurised air supply , and the level valves (mechanical ) control the air to each side. This is basically the system used on hgv trailer air suspension. By fitting a couple of air solenoids you can have a optionaloverride set up to raise or lower the suspension . HTSH

Re 6x6 you need to think about the double rear drive , as without off road can be less able than 4x4 . The double rear drive is about £6K the last time I enquired and that was a while back. When I had the tacr2a

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Are all your axles full-time driven (a proper 6x6) or is one axle going to be an idler ?

What is your intended use?

Unless you're producing a hardcore only-ever-going-to-be-used-off-roader, look at what commercial trucks do - when they're not fully loaded they use their gearbox and electric screw-jacks to decouple and lift one axle so its wheels are not driven/not touching the road. This can typically save 15% on fuel consumption.

Why drive unnecessary, power-sapping axles when they're not needed??

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The problem with linkinh everything is as you corner the air can freely flow from one side to another meaning lits of body roll unless you can mechanically limit it.

just inflating to a set pressure all the time won't account for different loads so you will get different ride heights, one of the main advantages of air is being able to level the vehicle.

Every lorry I've ever driven doesn't constantly assess and adjust the suspension as you drive as it's a dynamic load, it's constantly bouncing up and down and you don't want the suspension trying to react constantly. Once you've been loaded and before you set off you press a button which returns the vehicle to a pre programmed ride height. What I don't know is how it maintains this height taking account of any air leaks. Can it average out the measured ride height or does it monitor the pressure and average that out?

The trailers seem to be fully mechanical with a valve at the back for setting the height so getting hold of one of the valves could be interesting. (Or climbing under a trailer)

Of course the best thing about air suspension on lorries is you don't have to wind the trailer up and down when it's loaded before you hitch :D

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Vehicle will be a toy possibly a camper. Was thinking that the air suspension could also be used to self level when parked up. I am needing a new shell for my CSK so am going to salvage a full car to get it which will leave me with most of the parts to play with.Started thinking about a straight forward 6x6 Disco based on a Disco 1 shell but then I will have 4 cars to drive so thought a camper would be cool.

If I am going to do it it will be done properly so all singing and dancing. Will be 6 wheel drive.

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Have you looked at the air assist kits for pickups. You could have regular coils on the front and link the suspension on the back then just use the air assist to level the back.

Although I suspect you'll want more than that just because. .. lol

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I'm aware of maybe 4 solutions that could meet your needs, suggest a read of their websites to decide what sort of a system you'd consider.

To be fair the RR classic / P38 system is actually a very good system, because of the way that it conserves air use and uses a very clever dessicant air dryer arrangement. Unfortunatly relaibility always gets quoted... but really it's operating in a fairly harsh enviroment and is compated against a coil spring (non-electrical device of only only one component)

Top of the tree cost wise: AccuAir

, actually they do two systems, and electronic one + self levelling [although it uses air pressure sensors or height sensors [poteniometers] (as linked), or a purely mechanical system

There is also Dakota Digital Ride Height Cotroller (actually you have three options from the one controller .... air pressure sensors ..... ride height potentiometer sensors .... or a combination of the two ..... to be fair in my opinion this was the best option of the bunch as it's dynamic so will adjust as ou drive.... but it does not have the safety features of the RR Classic and P38 (i.e. it will maintain the pressure locked when you brake etc). .... also of note is that I can't find it on the website so may no longer be available....

There is the air bag it offering which is the "smartride" controller ... FB7000, FB8000 and FB9000, again very similar arrangement to the dakota digital ride height controller in that you get air pressure sensors, ride height sensors (potentiometers) and a combination of all three..... the catch is this one is not dynamic and basically allows you to set the heights at one of the various settings or pump them up and down (front, rear or individually).... this one has the easiest display im my opinion.... by not dynamic so would not correct for body roll or offroading (which the RR Classic / P38 one will do), plus you can get a bluetooth module and a smartphone app if you wish.

smartride manual here

Air bagit also do a manual system with guages and switches too: http://www.airbagit.com/v/vspfiles/pages/AirGaugesSw_PAGE.html

And then there is the arduino....

https://github.com/lucasvanlierop/air-suspension-controller

https://github.com/kvasilak/AirRide

https://github.com/HeMan/Suspension

http://www.instructables.com/id/lowering-suspension-projectArduino/

Suggestion .... air compressor .... this is the best I've found for FAD, psi & duty cycle

http://shop.air-zenith.com/200psiob2-black.aspx

manual

performance chart

if you can get a viair to beat it i'll be impressed.

Rob

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Good write up of options above, one other option only part covered is to buy the bags and solinoid air valve unit then just wire it to manual switches. It is then fully manual, down side is no automatic self leveling or active controls, plus side is cheap and pretty reliable.

For extra searchs look up the custom car low rider stuff it is the same system just used in a different way with different airbags, you can go as fancy and expensive or simple and cheap as you want.

An extra for any air suspension system is you get onboard air as well.

What ever system you run think carefully about where the air line runs go an protect them from wear and heat as much as possible.

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The problem with linkinh everything is as you corner the air can freely flow from one side to another meaning lits of body roll unless you can mechanically limit it.

You don't link the rear axles left/right, but front/back on each side. This gives you the bogie effect, and allows you to use non-6x6 components.

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.... from what I've read the difference between the RR classic + P38 air suspension system and the later or newer range rovers with indipendant suspension is they have a valve that links the left hand side to the right hand side (front + rear, 2 valves [not back to front as that is in the valveblock anyway]), so that they can link and shut off airflow to either side of the vehicle.... this provides air savings (and therefore fuel + noise savings too).

one of the things that all of the aftermarket air suspension systems do not do from what I've read is conserve airflow (although most are not dynamic either so they don't really have to....) and that is two things the range rover system does very well

... so if you think about body roll, say a bend toward the left for example, the vehicle will try to roll toward the right...

the air suspension will try to increase pressure on the right and may decrease pressure on the left...

when coming out of the bend the range rover system will repressurise the left with excess pressure from the right... where as an aftermarket dynamic system with 8 valves (air in + air out to each of the corners) will repressurise the left with air from the reciever and dump / depressurise the right ... none of which goes through a regenerative air dryer....

rob

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My issue with the P38 system, and I have about 4 valve blocks, compressors and other bits, is the electrickery connecting through the BECM. I have Air suspension on both the Disco and my P38 and would not go back to springs unless absolutely necessary. The Disco is currently being manually inflated because of a fault that I cannot find. (Not really had time to look) The P38 was sorted before the last MOT and now works brilliantly as it should.

I like the idea of manual inflation (Bagit) but had not really thought about the P£8 altering the dynamics when cornering which on a very large vehicle would be beneficial.

Robert thanks for the comprehensive post very interesting and will certainly explore more.

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The P38 system doesn't have any left/right connecting strategy (nor capability), nor does it do anything while cornering. The only thing it does is not level when braking. See the diagram and description below.

post-18506-0-64768600-1440487653_thumb.png

The L322 system does have the left/right linking. I think cornering adjustments are purely in an ACE-like system, but I could be wrong, I don't know much about the system on those cars.

The P38 system is also pretty much completely stand-alone. Pretty much the only link to the BeCM is for showing faults and lights on the dashboard.

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Simon

Yes, thats the problem with the RR and diso's is they decided at some point to integrate the ABS and the air suspension and get WABCO to do the lot in one BECM which although benefical to them on two fronts (a) probably cheaper as one unit, + shared infomation about cornering and vehicle speeds etc and (b) less chance of people like us reusing it elsewhere in another application.

the RR classic ais suspension controller in my opinion is a great idea as its stand alone and although it won't meet your 6x6 needs may give you (or someone else) an idea of how it should be done dynamically.

As usual there is always the spanner in the works .... insurance + liability should it not perform as intended and someone gets sued as a propriatary system ... hence the reason why so few may employ a dynamic system given the RR cassic + P38 empolyed inputs from the brake, and doors and speed sensor to hold off control when things were changing such as braking, people getting in and out / loading up or travelling at low speed etc.

Arduino is a great platform but there are caveats there too .... should you post anything about an automotive application on the arduino forum, a smart"£$$ will shortly arrive to inform you that the AMTEL microprocessors have a disclaimer in the front of all their manuals stating that they should not be used for automotive (or life critical) applications or systems .... hence its sometimes more benefical to just ask the question than disclose what its for ...

Elbekko, yup you are right about the balancing valve (which is of larger bore than the valve block ports ) ... I did say later / newer rangerovers but for the life of me could I remember L322

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a smart"£$$ will shortly arrive to inform you that the AMTEL microprocessors have a disclaimer in the front of all their manuals stating that they should not be used for automotive (or life critical) applications or systems

TBH every chip manufacturer prints that in every data sheet for everything - medial devices, transportation, heavy machinery, marital aids, etc etc. all on your own risk.

SimonR had PLC controlled air suspension on his 90 years ago, he might have some insight.

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Lots of complication is available, a triaxle trailer on air carrying upto 24 tonnes over the axles , can get a considerable weight transfer going thru roundabouts the mechanical system copes perfectly well with this side to side by using a level unit either side . There is a lift axle system by using another airbag (or two) depending on system that deflates the suspension airbag on that axle and then pressurises the lift bag/s . You also have the facility to raise or lower the ride height when stopped by hand operate valve.

On rigid vehicles you have similar options , plus some even have memory for selected heights , but are more electronic and therefore complicated. all though still very durable. The trailer system by design is dynamic , they even have a emergency dump facility for when they get over extended to prevent airbag damage . I think a more critical choice is the actual airbag type, and rate

to get a good ride comfort , some fitted to 4x4 are a bit lacking in that respect , a better result can be achieved by a well matched coil spring . JMHO

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Yes Simons snorklegrommet air suspension stuff was whatgot me looking into air suspension for my 90 and trying to understand it better ... From memory he used a PIC and a model submarine levelling control ... As I said before to him he did a good open source writeup on it for us noobs

I just find some of the disclaimers from people amd products interesting and wonder how anyone makes any progress and how we all survived this long... All about probability ... We did afterall get to the moon though using a slide rule as a design tool for the Apollo programme

Rob

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The disclaimers are there so you don't make a homebrew life-support machine with an ardunio and then sue Atmel when your granny conks out. Anyone making anything safety-critical has to take the risk on themselves or get a lot of lawyers gathered together to agree who guarantees what.

There's nothing stopping you making anything you like, it's just that whatever happens it's your problem not theirs.

It's the same with aerospace stuff - you can buy perfectly good nuts & bolts for peanuts but buying identical ones which are warranted airworthy by the manufacturer will set you back heaps.

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with regards to the Dakota Digital Ride Height Controller I mentioned above, I've had a response from Dakota that it is in fact no longer being manufactured (and they hold no further stock .... which is unfortunate as it was the only dynamic after market controller I could find (i.e. one that adjusts the ride height as you drive).

arduino it is in my opinion (or a RR classic / P38)

I have thought about trying to use two RR classic / P38 valve blocks and larger bore tubes for a quicker and tuneable response to body roll (i.e. quick response use both valve blocks in parallel... slower response required ... use on valve block).7

The other thing that is a good advantage of using a RR valve block is the electronic valve driver is a good stand alone cleverly designed device.... it uses PWM to open and hold open the valves .... but all you do is provide it with a "enable" / valve "open" signal and the PWM is all done in the driver.... two advantages here:

1) although the arduino can output PWM ... you don't really want to load the microprocessor with such a rudimentary task. (you could also use a DRV102 [high output drive] / DRV101 [low output drive] but you will need one for each valve to perform the same function)

2) PWM to drive a valve is actually very beneficial to both current draw and solenoid life.... it takes one amount of current to open the valve and another lesser amount of current to hold the valve in the open position.... hence by using a lesser amount of current you'll get a power saving and less heat going into the solenoid which will keep the coil cooler and give it a longer lifespan.

Hence in my scenario I was thinking about using two parrallel RR classic / P38 valve blocks + desiccant air dryers + the valve block drivers .... but then an arduino (or two) to drive it all (well that's the pipe dream...) + gyro and accelerometer + brake input + speed input + steering angle + air pressure and height sensors

why two arduino's ... well they are buttons and by using one to do the sensor algorithms ... and another to do the digital control bit it may improve response and noise response [trying to understand kalman filters at present (anyone got idiots guidance ... sorry way off topic but I know some of you have very diverse interests + careers hence please feel free to PM me)

And as tacr2man said ... nope you can't beat a coil spring for longevity and simplicity...

Rob

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the RR classic ais suspension controller in my opinion is a great idea as its stand alone and although it won't meet your 6x6 needs may give you (or someone else) an idea of how it should be done dynamically.

There's actually very little difference between the classic and P38a air suspension systems - having owned both, I'd say the classic version was the beta (tested out on customers in true LR style) and the P38a version the finished product. The P38a one is just a little more polished (slightly more control, less inclined to "dance" if you park on uneven ground), and as others have noted the integration with the BECM is just a couple or so of 12V on/off signal lines - the suspension controller doesn't need the BECM at all.

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Thanks nice to have a comparison as I've never owned neither, but remain in awe at its ingenuity... I understand that the classic eas was designed / cobbled together by an enthusiastic owner, who either approached LR or was approached by them, and gave them the design on the condition they set his up properly for him... Or that's the urban myth and unconfirmed rumour of the internet (neither confirmed by LR or the mysterious owner)

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There's actually very little difference between the classic and P38a air suspension systems - having owned both, I'd say the classic version was the beta (tested out on customers in true LR style) and the P38a version the finished product. The P38a one is just a little more polished (slightly more control, less inclined to "dance" if you park on uneven ground), and as others have noted the integration with the BECM is just a couple or so of 12V on/off signal lines - the suspension controller doesn't need the BECM at all.

Certainly Air Suspension was introduced on the Classic on the LSE model and my belief was that this was the test bed for the P38. To try and iron out the bugs for the new model launch.

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