Independent Suspension Design

[Witchdoctor]

Here are the close to final design of my independent suspension trailer chassis.

After all the trouble we had trying to get the camper on the tray of the truck we decided to design & build a trailer to take the camper, while i'm at it i can design in some extra storage.

As it grows i will update.

David

[Slunnie]

Reminds me of the old VW swing arm suspension geometry! I'm guessing that it will need to adjust to a specific ride height with the varying loads. Have you considered hinging the suspension from a cross member rather than from the spine of the trailer - I just say this because it will always retain your chosen camber angle(s) and it may improve handling and stability. This may have already been discussed previously.

Is the aim to reduce the ride height etc or for something cool and different? Irrespective, I like it.

[Blknight.aus]

you're airbags arent going to like that unless you put some wedge angle on to deal with the relative motion of the bag through its arc.


I assume that you're going to fit self levelling airbag controls so that you dont have to worry about the wheel camber changing with varying load?

[roverrescue]

if you run that design.
I would run a sway bar to enable some left to right dynamic load sharing.
I built up some swing arms on soft coils.
Hated the varying camber, hated the lack of cross axle load sharing. Changed it over to a solid axle with triangulated 4 link. Tis now awesome.

Name one solid engineering reason why a sigle axle trailer should have totally independently suspended hubs?

S

[superquag]

Reminds me of a South Australian invention around 25+ years ago, "Sway-Allay".
Aimed at the solid beam axle/cart-springs which was then the 'standard' for caravans.

Basically, a pair of triangle arms hinged near the spine,attached to the axle at the apex and base....then the axle between the triangle bases (L and R) was cut out. Instant independant suspension !

The original spring/shocks setup was left untouched.

It certainly did as it was designed, reduced caravan swaying especially on the Bendy Bits. :p

From fading memory, it was sold to a rustproofing company...who made a dog's breakfast of fitting them... and subsequently went out of business.

[slug_burner]

Shock absorbers as required for length of suspension travel

https://www.aulro.com/afvb/images/imported/2012/05/898.jpg

Maybe I should have said select either air bag A or B configuration for suspension travel.

I note that truck bogies use the air bag outboard of the axle as per B. They are not after a lot of suspension travel but load handling so the lever (radius arm) can be used to their advantage on the airbags pressure handling capability to provide the necessary spring rate.

[DRanged]

Mate dont try and re invent the wheel so to speak. I went down the same path and ended up building a solid axle on RR coils using RR trailing arms, A frame and small adjustable shocks. Works like a treat. Will put up a photo if you like.

Justin

[Sprint]

The CRUISEMASTER® Range (http://www.vehiclecomponents.com.au/component/content/article/138)

Vehicle components make some top quality gear, and I doubt you'll easily find any better trailer suspension kits.....

[Witchdoctor]

Thanks guys for all you input about location & angle of the air springs.

I'm not the person that builds an item my self just like the ones on the shelf. i believe that the design can be improved for my requirements, so i will give it a shot. I have taken some of your tips & added them into the design, but will be sticking to the original setup.
The drawing are with the 3D CAD man, so real work on this project should start any day.
I'l keep posting images & updates.

Cheers
David

[roverrescue]

Have fun David,
I like your attitude (sounds a bit like me) just be prepared to change it all around if it doesnt meet the mark!!! When I built up that boat trailer with swing arms that didnt work as well as I would like, the challenge was changing the axle and link config without altering my chassis mounts as the chassis had been hot dipped gal! Ended up working well - bit of good luck over good management I would think!

With your centrally located swing arms, you will have some pretty serious longitudinal loads along the bushing as opposed to axial loads that bushes are made for. I would be making them super strong. What bushes will you use at the central chassis pivots? Will the bushes incorporate toe adjustment? Out of interest what section are you intending to build the swing arms out of?

And another small tip, a trailer wont ever need more travel than 100mm up and 100mm down from ride height. By limiting your individual swing arm travel to 200mm at the hub you will control some of the wildly changing camber and funky dynamic loadings that central swing arms will result in. By the nature of a fixed central pivot at the tow hitch, trailer hubs never articulate relative to each other EXCEPT when one wheel or the other (not both) hits a significantly large object (hole or lump) at speed. Having another look at you design, with regards to lateral loads on the air spring and shock stroke, you might need to limit the travel even more than 200mm? Can the fancy CAD file be animated to show the angles when each swing arm travels up and down 100mm from the static ride height in the current images?

Have fun!

Steve

[Tank]

Thanks guys for all you input about location & angle of the air springs.

I'm not the person that builds an item my self just like the ones on the shelf. i believe that the design can be improved for my requirements, so i will give it a shot. I have taken some of your tips & added them into the design, but will be sticking to the original setup.
The drawing are with the 3D CAD man, so real work on this project should start any day.
I'l keep posting images & updates.

Cheers
David
One important thing to remember is that when your wheel travels up, say over a rock or hump the pivot point will travel down, reducing ground clearnce at the pivot point, that's why live axles are better off-road, Regards Frank.

[It'sNotWorthComplaining!]

Have a look at my swag web site, there are lots of camper trailer build threads and independent axles designs.
here's one of them.

CT build revision 2 (http://myswag.org/forum/index.php'topic=20270.0)

[Witchdoctor]

Still working on the CAD man to draw the trailer, he has to much on his plate at this time.

The wishbone arms will be made out of chromo tube with plate in stress areas & mounting points, still working out the design of adjustable tow-in on the arms, but happy with the overall setup.
More soon!

David

[Dougal]

I think a monolink with panhard is about as simple and elegant as trailer suspension can get. An alternative with a similar amount of work is two radius arms, one of which is triangulated to provide lateral location.

IMO independent trailer suspension is only necessary when you need to get really low and can't have an axle tube/beam underneath.

[Witchdoctor]

Just an update.

The CADing started this weekend :D, i have most of the required components in the shed ready to go once the digital design is completed. The engineer is happy with the design but there may be some small changes as we proceed.

Im looking at using Profender shocks, they are getting good reviews from the USA

Im getting excited now that this project will start moving again, this thing needs to be usable for our Christmas trip to Fraser

Cheers
David

[roverrescue]

great work - keep us updated!

what bushes are you decided on for the swing arms?

S

[Witchdoctor]

My suspension guys has recommended the bushes from the 75 series cruiser rear fixed spring setup with greasable pins, due to the size of them & they are very common. We did look at a pressed type but they not very serviceable out in the bush.

Cheers
David

[roverrescue]

those 75 leafer bushes really are a solid unit and easy to source.

Obviously not having the cad to see exactly i still wonder if your swing arm design will badly load what are essentially rotating bushes. With central arms pivoting only laterally without any longitudinal rake, your bushes will get hammered in the longitudinal plane every big hit the tyre takes.essentially the tyre will try to twist the two bushes from the central mount

I fear those bushes will be short lived under these circumstanses.

I would look into the lower control arm bushes on a heavy duty mcpherson strut setup to ensure good bush life. Acknowledging that a mac strut has more structural rigidity owing to the upper arm

S

[Witchdoctor]

Things are starting to happen.

It took awhile to find a person to digitise my drawings but it has finally started, should have something to look at late next week.

Purchased the Air Springs from OS they should land any day. Also picked up the DO35 V2 hitch from Vehicle Components, very helpful salesman, had a good look at their hydraulic disc brake setup.

Have organised an engineer to do some load & stress testing of the design once it is digitised.
Coming along slowly.

Cheers
David

[Witchdoctor]

Ordered & payed for my pair of Profender Piggy Back 2.0 shocks should get them this week.
Engineer gets the drawing Thursday, so i should be making a start on the build next week. Been a long time coming:o
Still cannot decide what finish to put on the frame of the trailer for protection, Powder coat, two pack, hot dip gal or S5 Zinc coating. Iv'e also heard that the sand blaster can do a protection coating that will go the distance. Sill got time to work it all out

Cheers
David

[Dougal]

Galvanised beats everything until you have to modify it.

[Witchdoctor]

Hot dip gal is great, but a big draw back is the heat will buckle the big flat sections so the pro's say :mad:.
So i think i have to rule it out.

David

[Dougal]

Hot dip gal is great, but a big draw back is the heat will buckle the big flat sections so the pro's say :mad:.
So i think i have to rule it out.

David

What sort of big flat sections do you have? Zinc-spray and electroplating are your best options if you have platework. Corrugated deck panels must survive hot-dip fine, plenty of commercial trailers are done that way.

[Witchdoctor]

Dougal,

The trailer has three ribs that are 1.8m wide in the shape of an inverted roof truss with a depth of 470mm.
S im thinking of the zinc spray option.

Cheers
David

[Witchdoctor]

My Profender Piggy back 2.0 remote canister shocks have arrived. I'm very impressed these are big shocks will take a beating.
I had the engineer look over my design all looks good, tests come back clean but he suggested a couple of personal changes nothing big that i will take on board. Still waiting on the air spring to show up :(.
I will now be looking for a laser cutting company on the Gold Coast area to do the cutting for me.
I have found a complete from wheel nut to wheel nut front axle from a Disco to use the hub & disc brake assembly that will give me the correct stud pattern for the sawtooth wheels to match the tow vehicle.

Cheers
David

[roverrescue]

If you run with front stub axles - just knock the CV spindle bearing from the guts of it
That way you only need to machine the axle flanges a small amount to accept the stubs

You could always machine flat the backside of the stub axle but then you lose the location properties of the step and they become custom stubs if you were to scour the stub (pretty unlikely) and needed a replacement

What travel will the springs/shocks be limited to?

S

[Witchdoctor]

100mm of up travel & 200mm of down travel.
Will post some pictures over the weekend of the gear.

Cheers

[roverrescue]

Very nice indeed - as I mentioned above you will never use 200 of down travel on a trailer so if geometry gets the better of the central swings arms limit it
I really like the central spine concept - I look forward to seeing how you pull this all together
Great build

S

[Witchdoctor]

An image of the Profender shocks :D.

[roverrescue]

Them be pretty flash for a trailer!!!!
Did you consider running an air/strut to make the suspension more compact?
I think their would be some merit in doing this
S

[Bush65]

An image of the Profender shocks :D.
It's hard to be sure from that pic, but it sure looks like that shockie has spherical bearings. IMHO these are high maintenance when used in our long distances in dusty/muddy conditions as they are not sealed.

[Witchdoctor]

Bush65, your right they are spherical bearings, something i will have to keep a good eye on.

David

[philco]

Those set ups are similar to the Macpherson strut ? thats what first came to my mind when i saw them.
I think the best axle i ever came across is the AL-KO axle. no springs or shocks only the rubber bush. We have had a camper for 25 years with the AL-KO axle and its never had any maintenance and still works as good as the first day we got it.
They work really good under load.

[Witchdoctor]

Air spring should arrive Friday fingers crossed. They sent me an image before they packaged them up.

I got myself a rear end (complete) out of a Range Rover. We decided that the rear would be easier to work with for the purpose we need.
Getting closer to a start.

[Witchdoctor]

The air springs arrived, picked up the rear R/R rear axle.
We will start stripping the axle down this week, now i'm having trouble getting hold of the 2" Chromo for the arms.
The parts that need laser cutting goes away next week :)

I'm getting excited

Cheers

[roverrescue]

Not that I have been involved in the use of chromoly but from what I have been informed - unless you have the perfect welding procedure that maintains strength in the HAZ you may as well just use seamless tube and a boring weld

Less bling though ;)

Those short arms on your trailer design could be made of cheese and would probably still hold together!!!! 50mm chromoly - well - just wow

Steve

[Slunnie]

Yep, it cracks. Without checking, I think its meant to be post heat treated also. I'd use mild steel, but each to their own.


Here it is: I know a lot..... anyway, here it is.
http://www.interlloy.com.au/data_sheets/hollow_bar/4140.html

[roverrescue]

"I'd use mild steel,"

I must be tighter than you Simon 'cos I use not only mild steel but last time I checked nb32H has a seam down the inside ;)

my theory is its still stronger than a landy rear arm and on a trailer has tonne less loading - it works and makes bushings easy

Witchdoctors trailer is gonna be flash! I cant wait to see it built!

Steve

[Dougal]

If by chromoly you mean 4130, then yes it can crack after welding. It's the 0.3% carbon content which means you need to use a low hydrogen method.

I would use RHS/SHS for your links instead. Strength is close to 4130 (typically 350MPa yield for SHS/RHS) but the low carbon content means welding is much less involved.

[Psimpson7]

I will now be looking for a laser cutting company on the Gold Coast area to do the cutting for me.


Which end of the coast are you? There is Gold Coast Laser in Ormeau, and All Plates in Molendinar. I have used both multiple times and would recommend either.

[Witchdoctor]

Thanks for the names of the laser cutters Psimpson7.

Made a start on the RR rear axle striped it all down, will replace all the seals but the bearings are in good shape so i will keep them. Dropped the callipers in to get rebuilt, lucky the pistons still moved in & out. Ordered new brake rotors as they were bad shape.
I kept 300 mm of the axle tube for the moment, i only need enough of the old tube to mount the new shock mounts too, from there it will be 4130 tube. The Chromo is hard to get hold of at the moment, had to get it out of Sydney. Should get the bits back from the laser cutter late next week :D

Cheers
David

[Witchdoctor]

Here are the progress images to date.

[Witchdoctor]

Got the re built callipers back from South Coast Brakes all nice and new looking. The pistons were badly scored so new ones were fitted. I'm going to clean up the rotors and get them skimmed. The hub assembly will then be waiting for the 4130 axles to be made.
I'm getting excited [bigsmile]

[Witchdoctor]

I'm now doing the lay out and drawings for the new nose section on the camper trailer.
All the wheels and tyres on both the tow vehicle and trailer will be identical, do i really need to carry two spares on the camper all the time. I'm trying to find a place that is out of the way in the camper, when we do a large trip i can always put the extra one up on the rack on the camper. This will give me more room for other gear in the nose of the camper.

Would appreciate your thoughts on this one.

Cheers
David

[roverrescue]

David,
By two spares on the trailer do you mean then having three spares total for six on the ground?

We drag boats all over the cape and take two spares total that can fit either boat trailer or vehicle.

Your having a bad trip to do three tyres none of which cannot be repaired with plugs or tubes! And if its that bad you could always rockup the trailer grab a wheel for the vehicle ad go for new rubber!

Does this make sense?/?

IMHO
Just have one spare on the vehicle.
One spare on the trailer
carry plugs & tubes then call it good.

S

[Witchdoctor]

Thanks roverrescue,
Thats all easy for me to understand. We had two spare on board for our last desert trip. One for truck one for trailer is how it will be.
Dropped the cast rear hub assembly to the engineers shop to build the 4130 axles today :D

Cheers
David

[Witchdoctor]

I'm getting really excited now, all the laser cut ribs & brackets are in my hot little hands.
We are starting to assemble this thing Saturday, with axle fabrication next weekend.
:D:D:D

Cheers
David

[Witchdoctor]

Made good progress on the trailer today, all the bits are welded onto the backbone tube. Axle & suspension next weekend.

Cheers
David

[roverrescue]

Looking good

love the axle stands ;)

Out of interest,
what are the dimensions of the main tube? And if you dont mind the length of the tube from hitch to trailer structure?

Steve

[Witchdoctor]

That axle stand made the welding a breeze, weld then rotate.
The main tube is 165.2 mm with 5 mm wall thickness.
Hitch to nose of box is 900 mm as per drawing but i can stretch this out to 1200 mm if i feel the need. My idea was to have enough length from the hitch to camper to jack knife the trailer without hitting the rear panels of the truck.

Geeze i'm having fun with this build [happycry]

Cheers
David

[Witchdoctor]

Well i got my cut down axle hubs back from the engineer shop, very happy with their work. These are the bits that will hang off the chromo pipe.
The original axle tube was cut down leaving 20mm were the cast flange tapers in. An over size pipe was then machine to fit inside the axle tube, the inside of the pipe was then machined down to take the 2" chromo pipe.
Hope this is easy to understand.

[roverrescue]

That should just about hold ;)
Have you a welding procedure for the chromoly to steel junction?

All coming along nicely though!

S

[Witchdoctor]

The chromo gets pushed though to the very inside of the new steel pipe then welded to that section of steel only. There will be no welding of the chromo to steel on the outside.
Hope this image helps.

Cheers
David

[roverrescue]

I acknowledge that you are using an alloy with known properties of tensile strength
But that 2" pipe seems mighty thin walled for your axle/swing arms?
Obviously it will pass a multitude of engineering calculations when new but surely after 5 years of use when corrosion starts to work at the HAZ you might wish for a little more structure?
Have you gone the route of chromoly in order to save unsprung weight?

S

[Witchdoctor]

Here is an update on the days progress. We did not make as much progress as last Saturday but we spent a load of time nutting out problems with will help us with progress tomorrow.

Cheers
David

[Witchdoctor]

Todays update, all the chromo arms are tact in place. Very impressed with the weight so far well within the design ideals. Im now having trouble finding Defender alloy wheels at a reasonable price for this build.

Cheers
David

[slug_burner]

Looking good.

We all like a build with progress pictures

[Witchdoctor]

Todays update,

We got all the things I had hoped to get done, we got all the chromo axles fully welded, the air spring mounting ring ground into shape & welded onto the axle.
The suspension rib was half fabricated ready for load testing in the morning, every thing is working as I had designed. Next two days will be fiddle bits like hitch & wiring.

Cheers
David

[Dougal]

How much bending load can those arms take?

[Witchdoctor]

One can buy product and be happy & others build things and be rewarded.

How much load will the arms take? Thats what RnD is all about. I am building a prototype, i have done computer load tests i have had an engineer look over the design. so now i build it, do some static testing if that passes we take it into the field for controlled testing.

We had a smell fail to day, the rib that hold the air bag was not braced enough and failed, that took five hours to rectify. The chassis now has its 700Kg static load in place at ride hight with no problems.

To days update.

[roverrescue]

So if that is it with its load
is it just the photo that gives it the degree or two of positive camber "look"

I did wonder about the top spring mount - seemed a little underdone to me shade tree engineering background!

Good to see this thing being dragged around though!

S

[Witchdoctor]

Spent a large portion of the morning working out the location of the shocks, this was not as simple as first thought. Shock travel in both directions, ensure the shock is not topping out or bottoming out and max stroke length without hitting any other part of the suspension. Have to order a set of limiting straps.
With all that worked out we finished tacking on all the other bits that make up the suspension rib.

The trailer sat out side with its 700Kg static load over night with nothing changed or moved or broken this morning. As we removed the load I dumped air out of the air spring. The photo shows were the wheels were sitting with no load and only 5PSI of air in the springs.

Cheers
David

[roverrescue]

hmmmmmm

S

[Slunnie]

Flash shocks for a trailer!

[Witchdoctor]

rover, the hmmmm worries me!

I was looking for a shock that would cop a flogging & would not give up. I run Billies on my trucks & love them, but for the some coin i got big buggers with remote canisters, should do the job + i love shinny bits :D

Cheers

[Homestar]

Have you thought about any form of auto leveling for the airbags? Maybe a proportioning valve or something to reduce or increase the pressure via an arm attached to the swing arm? Just wondering how you are going to manage this so the tyres don't get destroyed?

Looking good though, keep the pics coming.:)

Cheers - Gav

[roverrescue]

Witchdoctor
I promise you I love this build
I like the central spine - I like the tube you have used
I like the "ribs" supporting the outside structure
I like the overall vibe of the thing

I just couldnt be satisfied with that suspension geometry
I fear this thing as you show it will ride poorly (left to right load transfer) and it will wear tyres horribly

Is it possible to perhaps re design the swing arms to incorporate an upper link arm from your central pivot???
Still keep your centrally located geometry but using upper and lower links (think mcpherson strut) to ensure consistent alignment throughout wheel travel

Or alternatively make a solid axle and "one link" geometry from the central spine

I just think that NOW is the time to sort the geometry issue not in 100km when you realise you are not happy with it???

Steve

[Witchdoctor]

Hi Steve,

I really appreciate you honest input to my build.

My chassis design idea has come from the Tatra king frame suspension design.
It is not identical but very similar in operation.
Have a peek at this video, these guys have been using this design for many years. Time will tell if i have got it right or failed badly.

Awesome Off Road Truck Video - YouTube

I am looking into an auto levelling kit for the future.

David

[slug_burner]

Auto leveling.:eek: An air compressor and two schrader valves, it is not like it is a luxury vehicle that needs to self level after putting a trailer behind it. I suspect the trailer will be used with a similar mass most of the time and self leveling would be an unnecessary complication. KISS.

But it would be cool to see it adjusting to compensate for 100 liters of water in the tank.


Ag Wholesalers | Farming Supplies | Schrader Valve 1/8" BSPT Stainless Steel - 5 Pack | Southern Downs | Queensland Agricultural Supplies (http://www.agwholesalers.com.au/schrader-valves/schrader-valve-5-pack.html#)

[roverrescue]

mighty sexy twuck video
I bet tatra trucks wear tyres on the black stuff
Trailers are tripods, those tucks gain stability from wheel track and multiple axles
Your trailer has neither
Narrow track and no front rear load shift

I still like it but maybe plan a one link while its rough. Run it and see how goes. Change if need be?

S

[Witchdoctor]

Small up date.
My limiting straps arrived, ordered Tuesday they arrived Thursday from The Off-Road Shop in SA
I got prices on metal spraying the chassis, this includes blasting, metal spray & top coat colour.
This process can be done on cold surfaces with no distortion of the large flat surfaces, the chassis should last 30 years before service if any may be required.
I'm hoping to send the chassis away for this all to be done mid next week, i still have a few things to to this Saturday.

Cheers
David

[Witchdoctor]

Big day today, but it did not look like we achieved much. All the bits are now in place ready for field testing, i could not get any images of it complete as it was to dark.:mad:
A couple of images of the cut out of the hitch mount.

Cheers
David

[Witchdoctor]

Took same images this morning of the weekend progress.

Hitch in place.
Shock in finished position as well as the limiting traps.
Control testing this coming weekend :D

Cheers
David

[Witchdoctor]

I have a question for the members that are running air springs.
We have the same air pressure in both air springs but the trailer is high on one side, the load is even across the trailer.
Does anyone have an idea why this is happening?

We have just completed our off road(slow) 700kg load test, every thing went really well, tried really hard to roll the trailer pushing it over some really interesting terrain. I'm not saying we could not get it to roll over but i needed to know that the suspension was not aiding the trailer to roll over, considering the load is a water tank full with the load centre 1.4m of the ground.

Very happy with the weekend results.

Cheers
David

[Witchdoctor]

Right some images from the weekend.
Very happy with the departure angle.
I really love the hitch, never used this type before.

Cheers
David

[Bush65]

I have a question for the members that are running air springs.
We have the same air pressure in both air springs but the trailer is high on one side, the load is even across the trailer.
Does anyone have an idea why this is happening?

We have just completed our off road(slow) 700kg load test, every thing went really well, tried really hard to roll the trailer pushing it over some really interesting terrain. I'm not saying we could not get it to roll over but i needed to know that the suspension was not aiding the trailer to roll over, considering the load is a water tank full with the load centre 1.4m of the ground.

Very happy with the weekend results.

Cheers
David
Many people incorrectly assume pressure adjusts height of air springs.

Pressure x effective area = load. So the pressure changes to suit the load and vice versa.

To change the height you add more air to increase height or remove air to lower. For the same load, the pressure is constant as air is added or removed, assuming the change in air spring height is about the middle of the recommended operating range.

That said, the effective area does change over the operating height of the air spring, particularly associated with the piston diameter. Note all of my comments are for reversible sleeve type air springs like you are using.

[Witchdoctor]

Thanks John,

My understanding was if the air springs are equal & the load is also equal one would expect that with the same pressure in each spring the load would then sit level, very simplistic. I'm now thinking that the springs are not identical after all. I do not have a problem with putting more air in one spring to make the load look level.

We will just have to do more testing, i'm still very happy with were we are at so far.
This weekend i will be starting the electrical to get it ready for registering.

Thanks Martin for the Boost wheels for this project.

Cheers
David

[Bush65]

Many people incorrectly assume pressure adjusts height of air springs.

Pressure x effective area = load. So the pressure changes to suit the load and vice versa.

To change the height you add more air to increase height or remove air to lower. For the same load, the pressure is constant as air is added or removed, assuming the change in air spring height is about the middle of the recommended operating range.

That said, the effective area does change over the operating height of the air spring, particularly associated with the piston diameter. Note all of my comments are for reversible sleeve type air springs like you are using.


Thanks John,

My understanding was if the air springs are equal & the load is also equal one would expect that with the same pressure in each spring the load would then sit level, very simplistic. I'm now thinking that the springs are not identical after all. I do not have a problem with putting more air in one spring to make the load look level.

We will just have to do more testing, i'm still very happy with were we are at so far.
...

Cheers
David
Comparing air springs to coil springs for our suspensions is like comparing chalk to cheese.

Static and kinetic energy from the application of load is transformed into strain energy in the material of coil springs as they deflect (extension and compression) – recall that natural laws deem that energy cannot be created or destroyed, but only change form.

For air springs, static and kinetic energy from the application of load change the pressure, volume and temperature of the trapped air in compliance with gas laws.

The usual/useful data provided for coil springs are diameter, length (free and minimum compressed), and spring rate. From these values it is simple to evaluate load vs deflection, etc.

Because air springs are often used as vibration isolation mounts and actuators, as well as suspension springs, manufacturers provide a wide range of air spring data. Firestone refer to these three applications as Airmount, Airstroke, and Airride in their air spring data.

The useful air spring data for our purposes are those for static and dynamic performance. The info in this post is for reversible sleeve type air springs.

Static data is often given in chart or table form. The first pics below are static data for a Firestone air spring assembly using a 1T14C-1 bellows, which I have guessed, similar to what you are using. For the chart, the 'Y' axii are 'Volume' (of trapped air) on the left, and 'Force' on the right side. Spring 'Height' is read from the 'X' axis (bottom).

Note the family of 'Constant Pressure Curves' for a number of pressure values within the allowable operating range. These curves plot the 'Force' as the air spring is compressed from the maximum to minimum height while the air pressure in kept constant.

Force = pressure x effective area. The shape of each constant pressure curve is a function of how the 'Effective Area' changes between the maximum to minimum height. The sketch below illustrates effective area for air springs. Effective area of reversible sleeve air springs is smaller near maximum height when the piston is withdrawn from the bellows. Near minimum height the shape near the piston base increases the effective area, while the bellows travels over a parallel region of a piston the effective area is constant.

The range of recommended static ride height happens to be within the region where the the effective area remains reasonably constant. On the constant pressure curves it is the range of heights where the force remains reasonably constant. For these particular air springs with 1T14C-1 bellows, between approximately 180mm (7”) and 280mm (11”).

The shaded area on the left side of the chart, indicates the region of spring height to be avoided when the spring is under load (high pressure), otherwise bellows damage can/will occur. It is permissible however for the spring to extend into this area when the suspension unloads (droop or rebound).

It should be apparent now that to maintain a particular static ride height (within the recommended range), pressure rises when the load is increased, and lowers when the load is reduced.

The other curve (from top left to bottom right) is the 'Volume Curve' which is a measure the volume of air left inside the air spring as the height changes while the pressure is constant, 7 bar or 100 psi, in this case.

Now it should be apparent that to change the static ride height (within the recommended range), at constant load, the air pressure remains reasonably constant, but the amount (volume) of air in the spring needs to be increased to raise the height, and reduced to lower the height.
Note the above discussion on air pressure and volume is for static (stationary) conditions.

When the vehicle moves the springs compress and rebound to absorb bumps and motion can be great as the axle articulates while 4 wheel driving. The amount of air in the spring remains constant as it compresses (or extends). Pressure increases and the volume reduces as the spring is compressed, and vice versa. The amount of air is constant, but its density changes with pressure and volume variations. The air temperature also changes slightly, but with normal use it is not significant.

The last pic is a diagram of Dynamic Load vs Deflection for a 1T15M-11 reversible sleeve air spring – I don't have a dynamic load diagram for the 1T14C-1 bellows. The starting point for each curve is the static height in the mid point of the recommended range (18” in this example). Starting pressures of 20, 40, 60, 80 and 100 psig are plotted. Dynamic Load is read on the 'Y' axis and spring height on the 'X' axis.

Looking at the curve starting at 18” for 100 psig, we read the dynamic load on the left axis of about 7000 pounds force.

If we find the point on this same curve for a compressed height of 15” (bottom axis), we can read the corresponding dynamic load from the left axis at 9800 lb. If we were to look at the static data chart for this air spring, we could read the new pressure, 138 psig (for 15” and 9800 lb). If the the spring extends to 21”, we see that the dynamic load has reduced to 5200 lb and the pressure has reduced to 77 psig.

Similar dynamic data for air springs can be determined using the static data sheet and the following gas law for pressure and volume:
P1 V1 ^1.38 = P2 V2 ^1.38 (for normal vehicle operation).

A spreadsheet makes it reasonably simple to determine the dynamic data for the Design Load and Ride Height, given a static data sheet for the air spring we are using.

Create a table with 8 columns for; Height, Static Load, Volume, Effective Area, Absolute Pressure, Gauge Pressure, Dynamic Load, and G-force. The table should have rows for different heights over the range of interest.

For the following example, assume 9” is our design static ride height, so make 3 rows for 11”, 9” and 7” spring length. Assume also that our design spring load is 2000 lb.

In the middle row, for static ride height, the data for each column are found or calculated as follows:
1.) Static Load, This value is obtained on the closest constant pressure curve, at the required ride height. This static load may be a little higher or lower than our actual design load. Use the 60 psi curve, or the 60 psi column in the Force Table, and read static load 1890 lb

2.) Volume, This value is taken from the 'Volume at 100 psig ' in the Force Table at the ride height, or from the 100 psig volume curve. For this example we see the volume is 280 cubic inches at 9” height

3.) Effective Area, Calculated using the pressure value of the constant pressure curve and the static load found in the step 1.). Effective Area = Static Load / Pressure, i.e. EA = 1890 lb / 60 psi = 31.5 square inches.

4.) Gauge Pressure, The Design Load divided by the effective area from the previous step 3.).
P1 = 2000 lb / 31.5 in^2 = 63.5 psi

5.) Absolute Pressure, This is gauge pressure from step 4.) plus atmospheric pressure (14.7 psi).
P1a = 63.5 + 14.7 = 78.2 psia

6.) Dynamic Load at point 1, equals the Design Load, i.e. 2000 lb

7.) G, This is the ratio of dynamic load / design load , i.e. 2000/2000 = 1.0 for this row.

Now find the data for the extended height (11") row as follows:
8.) Static Load, This value is obtained using the same constant pressure curve (or column in the Force Table) as before (step 1.), and the new extended spring height. Static load = 1770 lb at 60 psi and 11” height.

9.) Volume, This value is taken from the 100 psig Force Table at the new extended spring height, or from the 100 psig volume curve. Volume = 347 cubic inches at 11” height

10.) Effective Area, Calculated using the pressure value of the constant pressure curve and the static load found for the new extended spring height at step 8.). Effective Area = Static Load / Pressure = 1770 / 60 = 29.5 square inches.

11.) Absolute Pressure, This is calculated using the gas law given above;
P2 = P1 x (V1 / V2) ^1.38 where:
P1 is the absolute pressure found at step 5.)
V1 is the volume found at step 2.)
V2 is the volume found at step 9.)
P2a = 78.2 x (280 / 347)^1.38 = 58.2 psia

12.) Gauge Pressure, The absolute pressure from step 11.) minus atmospheric pressure (14.7 psi).
P = 58.2 – 14.7 = 43.5 psi

13.) Dynamic Load = Effective Area x pressure using: effective area at step 10.), and pressure at step 12.)
Dynamic Load = 29.5 x 43.5 = 1282 lb

14.) G, This is the ratio of dynamic load divided by design load, using dynamic load at step 13.)
G = 1282 / 2000 = 0.64

Repeat steps 8.) to 14.) for the compressed height (7") row, using the new compressed height instead of extended height.

After this our Dynamic Load table should look like:
11, 1770, 347, 29.5, 58.2, 43.5, 1282, 0.64
9, 1890, 280, 31.5, 78.2, 63.5, 2000, 1.0
7, 1920, 211, 32.0, 115.6, 100.8, 3227, 1.61

Now plot the dynamic load vs deflection curve through the 3 points representing dynamic load and spring height.
1282 lb at 11”, 2000 lb at 9”, and 3227 lb at 7”.

Note in this example the curve is approximate, but we could improve it by determining values over more heights at smaller deflection increments.

We can also calculate the spring rate (load / deflection) from our curve (spring rate = the slope of the tangent to the dynamic load vs deflection curve) and natural frequency if required.

Natural frequency is a useful value that should be used more often when choosing vehicle suspensios. For good performance over a range of general and off road conditions use values of natural frequency around 1.35 Hz for front springs and 1.688 Hz at the rear – motion/ride will be bad if the front is not less than the rear.
https://www.aulro.com/afvb/images/imported/2012/10/657.jpg

https://www.aulro.com/afvb/images/imported/2012/10/658.jpg

https://www.aulro.com/afvb/images/imported/2012/10/659.jpg

https://www.aulro.com/afvb/images/imported/2012/10/660.jpg

[Witchdoctor]

Thanks John,
Really appreciate the air spring info.

Made a start on the wiring on the trailer.

Cheers
David

[Witchdoctor]

Doing the wiring took me much longer than i thought, but it is now complete.
When i hooked the trailer to tow vehicle no power to trailer, bugger. Then i had to start tracking the problem on the truck. The plug on the bar had not seen any maintenance :( for a while. pulled it apart still on power then track to the tail lights the wiring is scotch locked into the wiring of the vehicle lights, not happy. Tomorrow i will change all that & get it all working ready for registration next week :cool:

Cheers
David

[slug_burner]

Did you check that the placement of your lights is as per requirements? Min of 350mm high and max of 400mm in from the side of trailer. Applies to tail and indicators, stop lamps just have to have 600mm or more between them, height limits are the same for all.

[Pedro_The_Swift]

All your airlines and bags should be available from any decent truck spares shop,, I'd use Festo fittings and line, they will also carry the ride height gear you will need.
What compressor are you running?
Having read the thread, did I miss the part where you keep air in the bags? external compressor into schrader? no cross linking?
You can buy small festo pressure guages that will sit quite happily in the system.
Though, to be honest I think a ride height valve way over the top for this,,

[Witchdoctor]

slug_burner,
Had a good read of the trailer laws just now. Stop/tail max distance in from out side of vehicle to edge of light 400mm, this goes for the indicator as well. No higher than 1500mm & no lower than 350mm. Your were spot on.

Mine are well inside these on all accounts.

I was confident but thanks for putting drought in my mind, so i had a re-read.

Cheers
David

[slug_burner]

slug_burner,
Had a good read of the trailer laws just now. Stop/tail max distance in from out side of vehicle to edge of light 400mm, this goes for the indicator as well. No higher than 1500mm & no lower than 350mm. Your were spot on.

Mine are well inside these on all accounts.

I was confident but thanks for putting drought in my mind, so i had a re-read.

Cheers
David

After I had a look, I thought that your indicators were the only ones of concern on the 400mm issue. I can't estimate where the extreme outer of your trailer will be. I'm glad your ok, sorry if it caused you undue concern.

[Witchdoctor]

Trailer passed rego :o
Now to start building the nose of the camper, i have 12 working days to have this thing ready for Fraser Isl.

Cheers
David

[Shamo]

Yeah, don't like it. Fair enough you built it and designed it yourself, but sometimes there are reasons other systems are so widely and commonly used haha.

Goodluck regardless.

Cheers,
Shamo

[Witchdoctor]

Shamo,

What are the reasons other designs are widely used?

I understand that there are people everywhere that are not, for what ever reason able to design & build items that they wish to have. That is where a shop comes into play. Then there are people in this club that are happy to share there builds with us, so that they may inspire other members to get the confidents to at the least have a go, at anything.

Just lucky for me i like it! And many other do too! :D

Cheers
David

[Homestar]

Yeah, don't like it. Fair enough you built it and designed it yourself, but sometimes there are reasons other systems are so widely and commonly used haha.

Goodluck regardless.

Cheers,
Shamo

Yes, the commonly used designs are easy to copy and build, and in general show no new initiative in how they go together. Also, you have the sheep factor - because someone does it one way, everyone follows. Sort of sounds like you drive a Toyota...:D

I think the central spine will be very strong - a lot stronger than conventional designs. The only part of the suspension I see a potential for an issue is how the tyres will wear, but David has gone over that before and he can manage this with the airbags.

Then there's the satisfaction in designing and building something yourself.

Most others comments on this build have been constructive, and I'm not sure why you are just hanging it on him because you don't like it....

Keep the criticism constructive mate, you only make yourself look like a dill openly laughing at someone like that, and it's not considered good form on a forum such as this that holds such high standards.

I am looking forward to see how it all comes out and how it performs in he real world.

Regards - Gavin

[Dougal]

Yes, the commonly used designs are easy to copy and build, and in general show no new initiative in how they go together. Also, you have the sheep factor - because someone does it one way, everyone follows. Sort of sounds like you drive a Toyota...:D

I would be a lot more positive about this build had the swingarms pivoted the other way or been paired up in a double-wishbone type design. I suspect others feel the same.

This design was used on the Corvairs.
https://www.aulro.com/afvb/images/imported/2012/11/926.jpg

It is famous for all the wrong reasons: http://en.wikipedia.org/wiki/Unsafe_at_Any_Speed#.22The_Sporty_Corvair.22

[Homestar]

You could be right Dougal, I'm no expert on suspension design. I await the outcome of the real road trials. My last post was more about the way Shamo bagged the whole thing needlessly. I'm all for constructive criticism, and there has been plenty of that on the thread, not laughing at someone for having a go.

Cheers - Gav

[Witchdoctor]

Spent the weekend road testing the trailer over different types of road surfaces with about 200K's on the chassis :). Its now ready to be sand blasted & metal sprayed then powder coated, i'm hoping to have it back in a week. Put the chassis over the weigh-bridge, i had calculated without wheels & tyres the chassis should weigh 200Kg, the rolling chassis weighed 260Kg very happy :o. With the weight of the camper the total should be just over 1000Kg fully setup.

Cheers
David

[Pedro_The_Swift]

Those are two awesome pics David,,
Its great to see someone "build a dream":clap2:

it looks strong as!:eek:

[Nova]

Great looking trailer, nice design that is unique and unusual while still being practical.

If it is not too much bother, could you detail how you built the stub axles? I gather from reading earlier in the thread that you used D2 front hubs and RRC rear axle/brakes plus the ends of the rear axle to mount the whole assembly. Do you mind going into detail what went where and how it worked? I am looking to convert a 6 stud LC pattern trailer to Disco hubs to match my D2, just need stub axles (and disc/drum brakes) so i can unbolt the existing drums and hubs and bolt on new D2 stubs with brakes. Trying to talk to trailer shops is fun, no-one wants to know about it, too hard they say.

Cheers,
Nova

[Witchdoctor]

Nova,
The hubs, actually all were from an old RR. I need the disc brake assembly & something to attach to the new arms. I left about 20 mm of axle tube away from the hub casting for just this purpose. An engineer shop machined the inside of the axle tube to enable a steel sleeve to fit inside. That was also machined inside to fit the 2" Chromo axle to fit inside. This could be machined to match your own axle size. You will need to know a good machine shop as it was not cheep! I still had to linish a couple of sections on the outer of the hub to get the Defender alloys to fit as well as using a 4mm spacer ring to aid fitting.
If you would like me to send a couple of hi res image of my assembly just send a PM & i will email them to you.
Hope this helps.

Cheers
David

[Nova]

I sent you a PM, thanks.

Cheers,
Nova

[Witchdoctor]

I'm now getting excited, the chassis is back & i can now start going forward with putting it back together.
Saturday we are going to start putting it back together & fit the camper on, then make a start on the nose section, running out of time but at least it will be useable if not complete.

Tried to get as close as powder coat colour could get to the truck paint Galway Green.

Cheers
David

[Witchdoctor]

It's finally starting to look like the drawing from the beginning.
Got all the gear back on the chassis today including the tray top camper for the first test drive, very happy :D.
Loads of work to start tomorrow, hoping to make good progress on the front section, then it will really look like the drawings.
I'm still waiting no a pair of material limiting straps for the USA, will have to stick with the chain for now.

Will have to change this to a camper build thread shortly.

Cheers
David

[Pedro_The_Swift]

I'm surprised you had to go to the states for limiting straps,,
even if you want sexy branded ones with bolt on ends,,:D
https://www.aulro.com/afvb/images/imported/2012/12/1125.jpg

most truck places can supply loop types in various lengths

[slug_burner]

I'm surprised you had to go to the states for limiting straps,,
even if you want sexy branded ones with bolt on ends,,:D
https://www.aulro.com/afvb/images/imported/2012/12/1125.jpg

most truck places can supply loop types in various lengths

Is there a limiting strap in sight in the above photo?

[Pedro_The_Swift]

That would be the cable-tied thing with McKenzie on it,,
its actually two,,

[slug_burner]

That would be the cable-tied thing with McKenzie on it,,
its actually two,,

Looks like a cable sheath, although a little hard to tell if the top of the picture has the sheath with electrical cables breaking out or a fancy check strap that needs a metal weaved sheath?

[Witchdoctor]

Pedro, the local limiting straps are over the top price wise. That is the only reason i'm getting mine from the USA, chain will work fine for now.
I have a set of Mckenzie's that are to long & cost me $100 + freight with no colour option. Got a blue set for $52 delivered.
Thanks for the tips.

Cheers
David

[Witchdoctor]

Made a start on the nose section of the old camper, got the base tacked together and started on the vertical frame sections and compartments.
This was no easy task with a series of lines converging to a point at the front, looked easy but to a long time to work through and get right.
The frame is 50 x 25 x 2 mm with 25 x 25 x 2 mm and 50 x 50 x 2 mm. Outside skin will be 1.6 mm alloy sheet.
Sorry about the quality of the last image!

Cheers
David

[Witchdoctor]

Finished all the framing of the nose section & made a start on the outside skin. We got some good sections bonded onto the RHS frame with the black Fixtech, black goo seams to get on everything. The frame is also fixed to the chassis so no turning back now. I had more panels to bond on but ran out of clamps, should get the roof on to night and also make a start on the internal skin.
It's really taking shape now.

Cheers
David

[Witchdoctor]

Finished bonding all we could before Christmas break.
The roof is now on the nose and the old camper and nose section are now bonded onto the chassis with a few S/Steel nut-serts to assist hold down. Also cut in two extra brake lights as the stabiliser legs were blocking the view of them.
Had a delivery of shiny stuff, received our Dexter brake actuator for the disc brakes as well as the Redac remote brake controller.

Tomorrows job is fitting the wiring from the truck to camper to charge the twin batteries, also need to fit the duel battery to the 90.

Cheers
David

[Witchdoctor]

The night before we left for Fraser Isl i had to fill in the soon to be doors in the new nose section. I used a 20mm foam with alloy foil on both sides, then i used foil tape to tape it all in place. It looked rather rough for me but it worked, once we got to camp i just ran the sharp knife around three sides & they worked as they will with a hinge.
The trailer worked really well, the wheel travel is a little un nerving when looking in the side mirrors but the boys traveling behind said it was working great, handled the by passes very well.

Now to finish it off!

Cheers
David

[Witchdoctor]

Finally found a way to slow the rock & roll of the camper.

Getting an Antirock kit out of the US, very excited for it to land so i can fit it.
This has really put a damper on the progress of the camper so if it works i can start moving forward again on finishing it.

Cheers
David

[roverrescue]

Can I feel at least a little bit vindicated...
from post four of this build thread

"if you run that design.
I would run a sway bar to enable some left to right dynamic load sharing."

Anyways, great to see it out and rolling. Im sure you will get many years out of it!
Are there plans to fill in the guard sections. It just needs a little something more.
But I guess the way it is people can admire your suspension set up!

S

[Sitec]

A very interesting thread... Nice workshop by the way! There's a few machines in there I'd like in my own workshop!! I've never really got my head around 'single axle' trailers with independent suspension. With only 3 points of contact i.e:- the drawbar, the left wheel, and the right wheel, what are the benefits? Have plans to build a trailer some day and plan to use a beam axle on radius arms and airbags, but mounting the bags behind the axle so keeping the floor low. Trailers with a single axle need only enough travel to deal with its own weight..? If it was a double axle I'd see the need for decent travel. I'd be interested in what gains you think there are. Great build tho, and fantastic metalworking! Well done!

[Pedro_The_Swift]

Well Done on the build,, it must be extremely gratifying to see it work out so well,,

Matching black?:cool::cool:

[Witchdoctor]

roverescue,

Im no engineers but the design is what i wanted to build to limit problems from what i had seen with past suspension set ups. I appreciate your input early but i was not receptive to your thoughts.
I have had people explain to me in great detail how a sway bars would work on my trailer & this was very different to the way i thought they worked.

I built this trailer to withstand extended time on corrugated tracks, that was my main design criteria. I also like to test my brain!

Cheers
David

[roverrescue]

Please dont get me wrong David,
In no way am I telling you to suck eggs!
I will shout you beers when you end up passing through Cooktown ;)
I love the fact you started, carried through and completed this project.
Way too many people would have just copied Kimberleery etal inadequate swing arm suspension design.
You went and played with a design that you thought up AND that should be totally rewarded!

I guess it is more that I have played the single axle independent trailer suspension game and in my opinion (as Sitec mentions) independent is a bad joke being played on everyone who buys into it ;) A trailer is a tripod. There is absolutely no reason to have independent suspension and independent loses left-right dynamic load sharing.

I personally think swing arms have become popular because they are sexy.
AFAIK SugarGlider started it. In the 80s they were able to package swing arms for any dimension trailer with coils (unheard of in toyota land when leaves ruled) and the setup is compact.

Offroad trailers in my opinion do need to track the same as the tow vehicle - so if you are making generic suspension for trailer manufactirers swing arms are easy as you just bolt/weld them on at the correct width.

But it is also my opinion that trailers must have left right dynamic load sharing for stability on broken ground.

So if you run swing arms (especially on soft spring rates ) then you really need to link left to right with sway bars

Or you could just run a solid axle and any other combination of links. Radius arms with panhard, triangulated four link or parralel four link with panhard, or follow TrackTrailer and run cross arms as your main links and then single pivot radius arms.

David,
I am very keen to see how you set up the antirock/ARB units and if they fix the twitches...

Out of interest would your current chassis design allow some parrallel links to be mounted on the main cross bar that leads the wheel well?
Potentially if that cross bar is structural or can be tied in so it is, you could run parralel lowers from them back to a solid axle and then run triangulating uppers from you current leading bushes?

The first (and last) independent single axle I built was on a gal dipped chassis.
The suspension sucked badly in dynamic situations and wrt to tyre wear.
It was a fiddle but i was able to manipulate the existing galvanized swing arm pivot connections to accept a triangulated four link design.
That trailer is now 3 years old and going strong.
Obviously not perfect as I had to work with an already galvanised setup
But MkII happens to be a chassis Im laying out in the shed at the moment... this one is a chassis for a camper trailer (the original above was a boat trailer)

I have a .DXF for the rough design when I get my act together Ill take some purdie pictures and post a build in AULRO.


Peace (and there are cold beers in fridge for ya David)

Steve

[Witchdoctor]

Righto that beer will be called for when i eventually do the Cape :D

Steve, when i started having problems with the boat effects of the suspension i looked back through the posts & found your post about the sway bar. I have a number of very experienced suspension mates, two are from the off road racing arena that backed your idea with a very good explanation which eased my miss understanding of the sway bar.
I appreciate all members & mates giving me their thoughts & ideas on most things that i build as i'm no a no it all, so i take all comments on board.

Thanks for your help as it has helped, keep them coming.

David

[roverrescue]

If you have bought the antirock gear then cest la vie
but if not perhaps think about a suspension re-design???
A solid axle with triangulated fourlink on that chassis with those springs and dampers should work nicely.

Airbags and dampers locations will not need to change.
Your bomber axle tubes can remain and most of the swing arm material can be incorporated?
(just a note I am going to emulate your sleeving and welding technique for the flange/ stub axles on this new build)

With the triangulated fourlink, I went with a stepped axle (65 SHS 6)
The step in the middle could be accused of being done to give more clearance but really it gives verticle separartion of the upper links from the parrallel lowers.

Anyways - keep the good build going!!!!

S

[Witchdoctor]

My Antirock Kit has arrived today:p
So Saturday ill be trying the install i'm hoping.

Cheers
David

[Witchdoctor]

Made a start on the Antirock Kit.

Got the front mounts fabricated & bolted in position, next Saturday we will get the other mounts & hangers in position ready for testing.

Cheers
David

[Witchdoctor]

Finished the setup tonight.

Got everything together, this thing works really great, it has reduced the body roll massively. I will need to do some fine tuning through the week, very happy with the kit.
I will post some images real soon.

Cheers
David

[Witchdoctor]

Ok some images, now this is not complete as everything needs cleaning up before going to the powder coating.

Cheers
David

[tacr2man]

When you go on the corrugations those antirock ball ends are going to get a right beating ! A good few years back now some guys from LROC WA built a fuel carrying trailer for a Canning trip they did, that was coil , might be some info on that they had quite a few interesting tech problems but got it sorted in the end IIRC

[Witchdoctor]

For an update on my off-road camper.

Camper Trailer Touring did a photo shoot on it down at the Condamine Gorge track last weekend, it is not complete but that was not an issue with them.
It will be the feature custom camper in issue 58, no idea when that will be on the stands.

Cheers