I want a simple pop up. Is it better to buy or build.

Vic Harder said:
Has anyone ever bought a shell with the Short Cab Over and taken it apart to make a Long Cab Over? Or even more daringly, made an extra long cab over? I believe the longest FWC/ATC are 48" in the Cab Over. I am wondering about making a 5' Cab Over aka Queen bed, without having to use a pull out
Click to expand...
I think extending the camper body would be easy enough, longer and heavier top beams. But the roof lengthening would probably require a complete new structure.
 
Vic Harder said:
Has anyone ever bought a shell with the Short Cab Over and taken it apart to make a Long Cab Over? Or even more daringly, made an extra long cab over? I believe the longest FWC/ATC are 48" in the Cab Over. I am wondering about making a 5' Cab Over aka Queen bed, without having to use a pull out
Click to expand...
I had a short cab over Hawk. Thought about extending it to a longer cab over 48". After very little research it was easy to see it was faster and way cheaper to sell my Hawk and buy one with a 48" cab over. I would like a queen bed and the FWC flatbed model does have one. If you look at the picture below you can see they add an extra brace below the queen size cab over. This also so gives you under bed storage. IF they ever make a Hawk with this set up I might be tempted to buy one. It would raise the height of the camper.

FWC%20Fleet%20FB%207.jpg
 
Vic Harder said:
Has anyone ever bought a shell with the Short Cab Over and taken it apart to make a Long Cab Over? Or even more daringly, made an extra long cab over? I believe the longest FWC/ATC are 48" in the Cab Over. I am wondering about making a 5' Cab Over aka Queen bed, without having to use a pull out
Click to expand...
The sides of the cab-over part are basically cantilever beams. To cantilever further out with the same load capacity requires making the beam taller. FWC makes the compromise in favor of lower overall height instead of no slide-out bed support.

We would like to sleep N-S instead of E-W which requires about 80" of cantilevered length. I've not yet worked it out for our proposed flatbed build, but I'm thinking to use 250 lbs static tip load per beam as my design criteria. The depth of the resulting beam will yield under-bed storage for sure, even with a nice, comfy mattress up there. Keep in mind that w/o long drawers under the bed, or something similar, that under-bed storage requires popping the top for access.
 
I should note that I somewhat arbitrarily chose 250 lbs. per side (500 lbs total) to cover our weight up there along with the weight of the camper structure itself, mattress & bedding, and to compensate for the dynamic loading of our moving around.

Formula No. 22: http://www-classes.usc.edu/engr/ce/457/moment_table.pdf or here as well: https://archexamacademy.com/download/Structural%20Systems/beam%20diagrams/diagrams%20by%20waterman55.pdf

The variables & constants defined: https://www.scribd.com/document/226908732/Formulas-3-Beams-and-Diagrams

The two equations of real interest here are the Max Moment and the max deflection (deltamax). Both of these should be algebraically re-arranged to yield a value for I. I'm not sure what to use for max deflection, but I'm tempted to start with .125"

Which ever results in a larger "I" value is the value to use in designing the beam itself. Note that the value for E given in the third link is for steel only. Need to look up the value for whatever the beam is to be constructed of (aluminum, wood, etc.) before proceeding.

FWIW if this sort of thing intrigues you, this is the material covered in a Statics & Strengths of Materials class. If you just want the course book w/o taking the class I'll suggest Cheng's book of the title: "Statics & Strengths of Materials" because it presents the material at a Trigonometry level rather than a Calculus level of math. You'll still likely want to print out one of the first two links and stow it in the book. My class instructor did this for us.

Then need to research how to calculate the "I" of a built-up cross section. So far I'm not finding a simple & concise explanation of that on the net. Cheng's book does cover it.

A note: if you're thinking to build this inner wall structure like a trestle bridge you're making a lot of work for yourself. Keep it simple, build it more like an 'I' beam with box tubing or if wood, square sections for the flanges and a simple sheet or plate for the web.
 
ntsqd said:
The sides of the cab-over part are basically cantilever beams. To cantilever further out with the same load capacity requires making the beam taller. FWC makes the compromise in favor of lower overall height instead of no slide-out bed support.

We would like to sleep N-S instead of E-W which requires about 80" of cantilevered length. I've not yet worked it out for our proposed flatbed build, but I'm thinking to use 250 lbs static tip load per beam as my design criteria. The depth of the resulting beam will yield under-bed storage for sure, even with a nice, comfy mattress up there. Keep in mind that w/o long drawers under the bed, or something similar, that under-bed storage requires popping the top for access.
Click to expand...
 
ntsqd said:
I should note that I somewhat arbitrarily chose 250 lbs. per side (500 lbs total) to cover our weight up there along with the weight of the camper structure itself, mattress & bedding, and to compensate for the dynamic loading of our moving around.

Formula No. 22: http://www-classes.usc.edu/engr/ce/457/moment_table.pdf or here as well: https://archexamacademy.com/download/Structural%20Systems/beam%20diagrams/diagrams%20by%20waterman55.pdf

The variables & constants defined: https://www.scribd.com/document/226908732/Formulas-3-Beams-and-Diagrams

The two equations of real interest here are the Max Moment and the max deflection (deltamax). Both of these should be algebraically re-arranged to yield a value for I. I'm not sure what to use for max deflection, but I'm tempted to start with .125"

Which ever results in a larger "I" value is the value to use in designing the beam itself. Note that the value for E given in the third link is for steel only. Need to look up the value for whatever the beam is to be constructed of (aluminum, wood, etc.) before proceeding.

FWIW if this sort of thing intrigues you, this is the material covered in a Statics & Strengths of Materials class. If you just want the course book w/o taking the class I'll suggest Cheng's book of the title: "Statics & Strengths of Materials" because it presents the material at a Trigonometry level rather than a Calculus level of math. You'll still likely want to print out one of the first two links and stow it in the book. My class instructor did this for us.

Then need to research how to calculate the "I" of a built-up cross section. So far I'm not finding a simple & concise explanation of that on the net. Cheng's book does cover it.

A note: if you're thinking to build this inner wall structure like a trestle bridge you're making a lot of work for yourself. Keep it simple, build it more like an 'I' beam with box tubing or if wood, square sections for the flanges and a simple sheet or plate for the web.
Click to expand...
 
ntsqd said:
The sides of the cab-over part are basically cantilever beams. To cantilever further out with the same load capacity requires making the beam taller . . .
Click to expand...
Figuring cantilever beam loads is a simple statics problem. Your bigger problem is figuring out if the increased load is crating problems in the welded joints of the body of the camper.

Boatbuilder79 said:
Why not analyze it as a distributed load and use a factor of 1.6?
Click to expand...
An appropriately sized end load is an easy first order approximation of a distributed load, although calculating a distributed load is another well defined 'fill in your numbers' statics problem.
 
I want to do this on the back of an envelope, not need a Cray computer. Since I don't have to launch this into space I don't mind building in a little too much FS by contracting some of the variables down into a more manageable package. I see the point load at the end of the cantilevered beam as the most conservative case. That puts all of the distributed and point loads in the most extreme position.

As I would bring the beam well back into the main box part of the frame and the top "flange" tube clear to the rear corner I don't see welds being a problem.

Not being a Civil I don't see how a concrete design book is any help. In this case a "composite" beam isn't saying that it is comprised of fibres and resin or concrete and rebar. It is saying that it is a composition of different structural shapes.
 
This starts to sound like the makings of a gov't or Caltrans project.... "Over designed, over deadline and over budget..."

Just look at some to decide what you want/need in one and either buy a new one or find a used one close to your specs and get on with finishing it off. If you intend on camping in 2018 this would be the easiest, fastest albeit not necessarily the cheapest route.

No matter how you go about this....a few trips in one will tell you what you really should have done with and could have done without. Those who purchase their 2nd or 3rd camper have already figured this out...
 
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