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Old 09-08-2011, 03:30 PM   #1
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Default In the design stages

I am just working on starting the design of my toterhome conversion. I started modeling my framework up so i can keep an eye on what it is going to weigh. I will be putting at least one slideout in it, so i am hoping i can get a solid model from the mfg to put it into my model. The box will be going on a 87 Freighliner FLD-120. I will post up some pictures of the truck when i get a chance. This will be my first project of this size, the framework so far is 3" Sq. .120" wall thickness for the floor frame, and 2"sq for the wall and ceiling. I am open for suggestions or things to watch out for on this project. Like i said i am just getting started designing.

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Old 09-08-2011, 06:38 PM   #2
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I am getting ready to do the same project. Were did you get your design program from?
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Old 09-09-2011, 01:57 AM   #3
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What are your measurements ?
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Old 09-09-2011, 07:18 AM   #4
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I am a mechanical design engineer by trade, so the software is what i use at work. It is Solid Edge, and is very pricey.

The box is 18 feet long, 102" wide, 91" Inside height.

I will be using the truck to pull a 36' Fifth Wheel car trailer pulling a dirt modified racecar.
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Old 09-09-2011, 04:19 PM   #5
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Can you keep posting your design pictures. that would help me alot with my box build and what materials you are using for the frame.
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Old 09-09-2011, 04:38 PM   #6
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Great looking design from your program. I am jealous.

The 3x3 is probably overkill for your floor, 2x3 would be just as strong positioned correctly and a lot lighter. The .120 wall could probably be lighter gauge as well. Certainly the wall could be much lighter gauge. It is real easy to go overboard on strength (objectively not a bad thing) but weight is critical, both for fuel mileage, and for not overloading the front axle, which is real easy to do. You be amazed at what plywood, wall board, aluminum and even fabric and carpet add up to in a unit that size. Your twin screw truck won't be nearly as bad as my single, at least your front rear can take some of the box weight. Also keep that in mind when positioning fresh/gray/black tanks as to keeping weight to the rear.

Good luck! Dave
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Old 09-09-2011, 10:03 PM   #7
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For those on a budget you can do quite a lot with Google Sketchup, allows for full 3D modeling and some rendering. There is a great online collection of materials, componants, and even some 3d truck models. Best part is the basic version is available by download for free. I am just starting the design of my future truck conversion and will be using a combination of Sketchup and Autocad software I use for my business. Makes it nice to be able to walk thru your model before actually start cutting steel. When you have a design you like, may not be a bad idea to run it by a structural engineer to see where you might save some weight, and or need to beef up a bit. For those home builders a few bucks spent at an engineer may well save a lot more down the road.

Dave
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Old 09-17-2011, 10:02 PM   #8
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Guys be very careful, you have to plan every thing out, it is super SUPER easy to overload that front axle. Your Over-the-road-highway truck was designed for a 40K trailer with 15-20k on the pin, now you have next to nothing on the pin, and now all the entire weight of that box WILL BE equally spread like 50/50 on the front and rear axles.

Think about that original design, for optimal highway operation, load capacity, truck ride, and of course fleet cost, The spec as light of a front axle to save overall weight and ride comfort for the truck, as most of the time they need all the capacity they can on the drivers.

To overcome this problem, most coach builders will hang a bunch of the box rear of the rear axle to leverage the weight off the steer axle like a huge teeter totter, using the center of the drives as the pivot. An extreme example of this is a front engine'd Class A or Van based Class C, they all have those real long tails to pivot the pounds off the steer axle. (its also why you may never see a diesel E450 based Class C as the engine itself is too heavy once even a lightweight stick and aluminum RV body is loaded on it.)

When a Truck conversion involves streching the wheelbase front axle weight adds up even quicker (as mine did.)

The design, shown in the OP looks to be a toterhome box. Those balance ONLY with the fiver hooked to the back of the truck. Try to run bobtail to take 8 buds to tailgate at the football game, and that front axle is way past ugly.

I search racing junk once a week, I cringe at what my 80K might buy now as a finished RV with this economy. I also cringe at those long stretched trucks and wonder how big of water tanks the must have just to pivot the weight off the front axles. There is no doubt some very over weight trucks out there and its just a matter of time before some LEO starts scaling us.

Even if you think you may never get scaled, some day you will want to sell your $50-100K investment, you will have to disclose somewhere in that transaction that the front axle is over its limit.

I'll try to follow this thread a bit closer, good luck with your projects guys!
-blizzND
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Old 09-18-2011, 07:51 PM   #9
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blizzND is a pretty smart guy. And he's got lots of experience to speak from.
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Old 09-18-2011, 09:33 PM   #10
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This discussion of weight location, front axle capacity, rear axle weight, overhang, etc. reminds of getting my pilots license 40 years ago.

We were taught to do weight and balance calculations be essentionally measuring the weight of something (fuel, oil, front seat passenger, rear seat passenger, baggage, etc.) and its location in the plane as a distance from a known point (datum); knowing the center of gravity of the empty plane, and then calculating the loaded CG. Couldn't something similar be done with these truck builds? Using Excel it would seem to be to be easy. Start out by weighing the empty chassis, establish a starting CG, and go from there.

Anyone have thoughts?
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