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 Building My Home Made Caravan by JR 
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Joined: Sun Feb 28, 2010 1:53 am
Posts: 396
Location: narre warren south
Post Re: Building My Home Made Caravan by JR
ALLAN,

You better lift your game JR is going to run you over here, and at the rate he's going he finish his before you as well.

Robert.


Fri Apr 29, 2011 8:05 am Profile

Joined: Mon Apr 20, 2009 9:37 am
Posts: 122
Location: Gawler, South Australia
Post Re: Building My Home Made Caravan by JR
hi jr
after 100' and 100' of posts and input, comments you are about to lay it on the line
all of those comments about other builds and do's and donts are being scrutinised to the enth degree and are making there way to your computer now....... lol
look forward to your posts
cheers
Andrew


Fri Apr 29, 2011 10:00 am Profile
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Joined: Mon Nov 05, 2007 3:09 am
Posts: 2078
Location: Newcastle
Post Re: Building My Home Made Caravan by JR
Stage 2 the Chassis/Suspension Cont.

Air Supply System for the Air Bags

Each air bag is treated independently and has its own air inlet and drain valve and a glycerine filled pressure gauge. Glycerine is used in gauges that are exposed to high vibration and high frequency pressure changes this is to protect the mechanical movement in the gauge.

The air supply is from a stainless steel air receiver and the air receiver is supplied from an ARB air compressor which is controlled with a pressure switch set at 800KPA. The air receiver also has its own gauge. The air compressor output goes via a filter strainer and a shut off solenoid valve to prevent air leaking back through the compressor from the receiver.

The compressor has been replaced with an ARB compressor and the filter is not shown in the photo
Attachment:

Air system.jpg [ 122.51 KiB | Viewed 1559 times ]

The van level is set using a proximity limit switch on each suspension arm which activates an LED at the control station when the van is at the correct height. The proximity switch is basically a very robust switch that changes state when a magnetic field is interrupted from a metal spade passing between the magnetic field and a magnetic sensitive switch.
Attachment:

Switch.jpg [ 72.64 KiB | Viewed 1559 times ]

The control station also has an air outlet which can be used to blow tyres up and if the ARB compressor fails air can be fed back into the receiver from another source. After the bags are set at the correct height I switch the electrical supply off to the compressor and LEDS with a manual switch in the control station.

Air Control Station access is via an outside door on LHS of van
Attachment:

Air control station.jpg [ 158.84 KiB | Viewed 1559 times ]

When under a static state pressure stays constant in the air bags regardless of the height setting. Once the bag takes up the weight of the van the bag can then raise the van just by increasing the volume of air in the bag. Only at the very start and end of the bag travel does the pressure vary this can be seen in the air bag specifications graph.
Note the difference in pressure from the LHS to the RHS. The RHS is the heavy side of the van but once the van if fully loaded the bag pressure is about 50KPa different. RHS loaded running pressure is usually 450KPa.

JR
:razz:


Sat Apr 30, 2011 2:44 am Profile
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Joined: Wed Feb 25, 2009 12:02 pm
Posts: 398
Location: Croydon VIC
Post Re: Building My Home Made Caravan by JR
Excellent thread JR and I am glad I talked you into it. Just hope it does not become a rod for your back and you get some enjoyment out of re-living the build, because I know everyone else will.

Thanks again for making the effort.

Cheers
ALLAN

PS I did not know you towed around your very own nuclear power station. LOL. Or is that your whisky still?

_________________
Computer Engineer. 100 Series TD.
Home building a 21ft off-roader called "The Expedition".
Steel Chassis, Simplicity Suspension, Aluminium Frame.
Paulownia Cabinetry, All 12 volt & Self Sufficient.
When its finished WE retire.


Sun May 01, 2011 12:46 pm Profile
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Joined: Mon Nov 05, 2007 3:09 am
Posts: 2078
Location: Newcastle
Post Re: Building My Home Made Caravan by JR
Hi Allan,
Appreciate your comments, I am getting enjoyment of reliving the build. I think you inspired me to have ago with all your photos and I hope I don’t bore people to much with all the text I just like to try an explain the process.

JR
:razz:


Tue May 03, 2011 1:28 am Profile
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Joined: Mon Nov 05, 2007 3:09 am
Posts: 2078
Location: Newcastle
Post Re: Building My Home Made Caravan by JR
Stage 2 the Chassis/Suspension Cont.

Placement of the axles:
How to know where to place the axle was I big worry as once you committed to a location there was no way out without major mods. The only option is to move water tanks or spare wheels to help change the weight distribution. I had two locations for the spare tyre in my plan as that was the easiest option to do if required as even moving the water tanks would not be easy once the tank filling lines were fitted.

To try and get the axle location right I decided to go back in time about forty years to my engineering days and used moments about a point clockwise and anticlockwise to calculate wheel location. You know the lever on a fulcrum thing where you can lift a weight twice as heavy as the force you apply with a lever twice as far from the pivot point of the weight.

The big problem with this is you need to know the weight of everything on and in the van. That’s no problem when working out the weight of the chassis as steel sections have an exact weight per metre. But when it comes to wooden cupboards and glass shower doors and so on it can get a bit difficult. I found myself going to shops with scales and weighing items, even sheets of three ply for the walls.

A spread sheet was developed in XL and it contained about 320 inputs and many of these values arise from many other values. Also you need to know the centre of gravity of every item and its exact location X and Y.

Each item needs to be considered what effect it has on the front to rear and side to side to get an exact weight each item places on each wheel and the tow ball.

All these calculations would probably not be necessary building a van with four wheels and with a standard layout.

Part of XL Spread Sheet
Attachment:

Spread sheet.jpg [ 248.15 KiB | Viewed 1509 times ]


Things to consider when designing a caravan chassis:
Engineering a chassis to carry a certain weight does require a fair amount of engineering skills so it is best to stick to known and proven designs, basically copy a chassis similar to the size and weight you are going to require.

My old Jayco chassis was my template and as I knew its weaknesses I just improved the design to allow for its short comings.

Basically you are going to start with two main chassis rails and work from there. Below are some things to consider when designing your chassis.
1.Wheel location and suspension mounting points
2.Spacing of two main chassis rails
3.Wheel width and clearances under mudguards side to side and on top (wheel travel)
4.Tow ball coupling height
5.How to attach mud guards
6.Water tank size, best to know or have the tanks before you start as some can be quite wide to fit between chassis rails
7.Water tank location and filling lines need to be considered so not to end up running a torturous path straight in is best
8.Grey water tank location if you are fitting one
9.Allow for water tank protection shields and how you will attach them
10.Allow for flooring joins if you are using sheets of ply and also internal walls so as to have a chassis member under these points, using one single sheet of material for the floor may be a better option, I used five sheets of ply 8x4x1/2”
11.Consider plumbing and shower outlet so not to end up with the outlet in the centre of a chassis rail
12.Consider hand brake cable supports
13.Fitting a rear bumper and spare tyre
14.Stabilising jacks
15.Gas bottles and gas regulator
16.Electrics, usually run through the chassis so work out what you are going to do and run a draw wire for later
17.Gas line routing
18.How to attach the wall frame to the chassis
19.Extra tow points and tire down points for chains and shackles if you are camping in strong wind.
Attachment:

Chassis plan.jpg [ 63.75 KiB | Viewed 1509 times ]


Making the chassis
Important Tools for making chassis
MIG welder (250amp)
14” (355mm) Electric metal cut off saw
4” Angle grinder
8” bench grinder
Two good quality battery drills
Most other tools are just the normal tools you would have in your garage

I chose to use DuraGal for the chassis as it is a proven product, there were many others but at the time I could not get any detail on their strength or specifications. The reason I used DuraGal is because it is higher tensile strength than standard RHS.

To maintain that strength you must not galvanise as that will soften it and DuraGal is already galvanised on the outside. The secret of DuraGal is that it is rolled after it is galvanised and the rolling increases the tensile strength.

Galvanising a chassis usually buckles and distorts the chassis so it will need to be straightened naturally a galvanised chassis has advantages.

Welding
As I had some experience welding with a stick welder from my earlier trade days (fitter and turner) I thought using a MIG would not be too difficult but after running what looked like a perfect weld and destruction testing it I was put back some as the first strike with a hammer the weld failed.

I really wish I had done a MIG welding course as getting the voltage and wire feed speed exactly right is very important. After consulting with the people I bought the welder off and about two weeks on and off I managed to get the weld right.
Welding upside down and vertical is not as easy as welding horizontal so I decided to make a pair of stands that would allow me to rotate the chassis to allow horizontal welding most of the time.
One of two stands to rotate the chassis
Attachment:

Stand.jpg [ 142.44 KiB | Viewed 1509 times ]


JR
:razz:


Tue May 03, 2011 1:45 am Profile
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Joined: Mon Nov 05, 2007 3:09 am
Posts: 2078
Location: Newcastle
Post Re: Building My Home Made Caravan by JR
Stage 2 the Chassis/Suspension Cont.

Making and setting up the two main chassis rails
I decided to use the laminate system for the chassis main rails, put simply instead of running one large RHS section I used two smaller RHS sections. One 100x50x3 and one 50x50x3 and the ‘A’ frame was 100x50x3. So the main chassis rails where 150mm deep and the front third 200mm deep where the ‘A’ Frame overlapped then stepped back to 150mm deep.

‘A’ Frame 100x50x3 RHS to chassis which consisted of 100x50x50 RHS and a 50x50x3 RHS
Attachment:

A frame to chassis.jpg [ 63.53 KiB | Viewed 1510 times ]


The draw bar was strengthened with pre-tensioned rod

Main draw bar strengthener ¾” solid rod mounting brackets
Attachment:

Draw bar strengthener brackets.jpg [ 104.32 KiB | Viewed 1510 times ]

Draw bar tensioned with ¾” turn buckle
Attachment:

Draw bar strengthener.jpg [ 132.7 KiB | Viewed 1510 times ]


JR
:razz:


Tue May 03, 2011 1:53 am Profile
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Joined: Mon Nov 05, 2007 3:09 am
Posts: 2078
Location: Newcastle
Post Re: Building My Home Made Caravan by JR
Stage 2 the Chassis/Suspension Cont.

Strengthening main chassis rails to support the van full weight on a small area of the chassis
The localised area of the chassis that the full van weight is supported on by the air bag suspension was strengthened one metre forward and back from the support point with side strengthening plates 6mm thick and 100mm holes in the plate to reduce the weight.
2000x150x6mm side plate strengthener’s one carton of beer.
Having these plates drawn up in PC CAD made it easy for a fabrication shop to cut them out on their automated profile plasma cutting machine.

Cost quoted was $400 for their draftsman to draw the side plate profile and one carton of beer to cut it out, so handing over a USB memory stick with a CAD drawing done was only one carton of beer for the profile cutter to cut it out.
Attachment:

Side strengthener drawing.jpg [ 43.36 KiB | Viewed 1498 times ]

Side view of a chassis strengthening plate
Attachment:

Chassis side plate.jpg [ 125.97 KiB | Viewed 1498 times ]

Top view of two side plates, one on either side of main chassis rail
Attachment:

Top view of side plates.jpg [ 89.35 KiB | Viewed 1498 times ]


Actually the main chassis rails full cross section metal thickness where the additional strengthening plates were mounted worked out at 6 + 3 + 3 + 6 = 18mm, a bit over the top.

JR
:razz:


Tue May 03, 2011 5:46 am Profile
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Joined: Mon Nov 05, 2007 3:09 am
Posts: 2078
Location: Newcastle
Post Re: Building My Home Made Caravan by JR
Stage 2 the Chassis/Suspension Cont.

Starting to prepare components before welding chassis together

Some of the side outer frame running from main chassis rails out
Attachment:

Outer brackets.jpg [ 218.65 KiB | Viewed 1458 times ]


Rear bumper bar mounting bracket with skid plate
Attachment:

Bumper bar mount and skid plate.jpg [ 186.56 KiB | Viewed 1458 times ]


Welding brackets for the bumper bar mounting on main chassis rail
Attachment:

first weld.jpg [ 129.86 KiB | Viewed 1458 times ]


JR
:razz:


Sun May 08, 2011 3:09 am Profile
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Joined: Mon Nov 05, 2007 3:09 am
Posts: 2078
Location: Newcastle
Post Re: Building My Home Made Caravan by JR
Stage 2 the Chassis/Suspension Cont.

Making the Chassis straight, square and level

I went high tech here and used a length of string a water level gauge a tape measure and an engineer’s square.
Attachment:

Tools.jpg [ 120.47 KiB | Viewed 1458 times ]


The water level gauge consists of about 10mts of ½” clear plastic hose one end attached to the bottom of a 20ltr container of water mounted about three feet off the ground and the last 5ft of hose at the other end attached longwise to a length of conduit or a 2 x 1. By placing the conduit vertically on one corner of the chassis and marking the water level on the conduit gave me a reference and then pack the chassis on the other corners to reproduce the same reading on the gauge.
Measuring the diagonals and using a water gauge the chassis can be perfectly square and level within 0.5mm or better.
Note: this is not needed if you have a perfectly level garage floor which is not likely.

Setting the main chassis rails on the ground and set up the cross members to join the two main rails ready to tack weld
Attachment:

Packing chassis.jpg [ 297.39 KiB | Viewed 1458 times ]


Rotating the chassis
Attachment:

Chassis 90 degrees.jpg [ 122.33 KiB | Viewed 1458 times ]


Setting up the suspension was a very tedious job, the sugar glider suspension has adjustment for tow in and out but is very limited. I was advised by Withers to set the front of the wheel/tyre 2mm in. I set the suspension up then went for lunch and when I returned to start tack welding the suspension support brackets to the chassis I did a final check and found the thing had moved almost 1mm.
After some time I realised that it hadn’t moved, the entire chassis was moving as the afternoon went on. My garage faces north and as the sun slowly moved into the garage the chassis warmed up and expanded. I closed the roller doors and after some time the suspensions set up stayed put and I was able to tack and weld the suspension to the main cross member.

JR
:razz:


Sun May 08, 2011 3:22 am Profile
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