Did I miss something? Or is this list not correct?
Dimensions for new subframe
As soon as I have these items, I can start my new subframe.
In the book "Build your own Overland Camper", the author recommends rectangular hollow steel of 100x50x3mm. What dimensions do you have?
How much space do you recommend between the original and the subframe?
In the Mercedes manual you'll find a subframe that consists of 1 beam in the center. Most of the subframes I find on the internet contains 2 beams. What would you recommend?
Thanks for your help.
Ivan
Ivan, if you had been on this forum long enough, you would know that the (my) Universal Answer is:
It Depends.
As for list, I don't have access to EPC, and don't have a U3000. If you miss something, you can always place another order. Basically, you want the two simplest cross-beams (no vee cuts), and hardware. The long bolts and sleeves are critical; they are the bump stops that limit angular motion of the subframe and body, before they would crunch the cross members themselves.
I am a very firm believer in highly integrated design. Without the first pass at the design/ layout of your camper, there is no absolute way to answer any of the remaining questions, except maybe for one.
1) On the Atlas subframe, the longitudinal tubes are 80 x 80 x 4 mm wall thickness. I am pretty sure they are high strength steel, what we in the US would call an A50 steel (typical structural shapes are A36 grade). This makes a big difference in the tube size/ wall thickness required to meet a given load condition. By using higher grade steel and then cutting a LOT of lightening holes, Atlas can make a very light frame.
Further thoughts, not in order posed:
A) Manufacturing methods and materials are highly relatable to quantity of items produced. M-B is producing a lot of frames, relative to Atlas. Therefore, they employ different means to achieve the (same) desired result. M-B can justify stamped and special roll-formed sections, as the cost of dies, etc. is quickly repaid in time and material savings. I suspect that the single large rectangular section (in the M-B manuals) is due to these considerations, as opposed to "best way to build a subframe". For Atlas, stock sections are imperative, along with plasma cutting and custom bending of plate materials (which is pretty cost effective at their quantities). For the solo builder, the "Brute Force Method" generally has to prevail, due to sheer cost and availability of special equipment. What this is getting to is, you have to decide whether to pay for high strength steel, whether to do lightening holes, etc. A lot of this comes down to what your skill level is in both engineering and fabrication, or what you can get help with. As noted by others, simpler and heavier may be a perfectly fine solution. However, weight does carry a penalty, of some sort or another.
B) Engineering. Two beams help distribute the loads of the camper body onto the subframe, which can be an important criteria. If you are going hard-core high tech for your shell (carbon fiber, perhaps?) you can use the shell to self-support side and end body overhangs beyond the subframe. If the shell (read: floor) is not designed with an appropriate structure (it may be lighter, as well as cheaper), then you will need to consider a full perimeter frame, to pick up the wall loads directly, and prevent the floor bowing down over the ends of the subframe. The Atlas subframe is quite a bit undersized, relative to the body that it supports.
C) How much space.....?? Not sure now to address this one. See 3.2/ 121 of the M-B manual that you posted, which has a note to see further specs. I presume there is more information available from M-B.
Atlas lowers the top of the subframe relative to M-B standards. Michael D. told me it was 75 mm lower, which is the amount they bump up into the floor of their bodies, to maintain adequate clearance over the tire/ shock tower. When I measure my U1300L firebody, I have the top of subframe only about 28mm lower on the truck frame rails than the bottom of the metal floor/ top of frames of the existing firebody. One thing is certain, that the center of the F&B pivot bolts must both be coincident with the top of the truck frame rails at the rear, which is the higher of the two. Atlas maintains this, as well.
So, after the long-winded lecture, here is the cross-section and dimensions (blue)of the existing firebody on my U1300L RW1. The section and dimensions (red) of the Atlas subframe are also shown. All dimensions are CNC type (see zero/ zero labelled) in millimeters. The sections are composites, that show relationships, NOT one true section, all in order to show shock tower clearance requirements and tire location and clearances.
Disclaimer: This is NOT an engineered drawing. For Reference ONLY. Any user must make their own decisions as to actual design.
But it might help the effort.
Lee
EDIT/ ADDED:
B.1) I believe there is good support (!) for the two beam approach, on a pure engineering basis. M-B makes the point that MOST of the load is transferred from expedition body through the subframe to the TWO clamps that wrap the tubular truck frame crossmember. Per the Atlas section, the two tubes stack directly over the clamp locations. Two cheeks with gussets, and shear connections between, are a very efficient design, per the load path. Forms a braced square over the tube, which is itself the basis of the rigid structure. The subframe stays in harmony with the tube, and therefore the center of, the truck frame. Also quite amenable to individual construction, no special shapes required. And the (half) load at each clamp is then distributed along the length of the body by the associated square tube. The gussets and triangle plates to carry the pivots then brace the pair of longitudinal tubes against racking (torsional) forces. I like elegance, and this design has it.
Edit:
Forgot to add the new dimension from top of Atlas frame down to top of 365 tire. It is reduced by 28 mm, so it is172 mm here. Obviously, clearance to bottom of actual floor/ tire well of body is a dependency, and must be built to suit.
