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 chassisImportant 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.
WeldingAs 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 chassisAttachment:
Stand.jpg [ 142.44 KiB | Viewed 1509 times ]
JR