pivoting frames and mounting campers

[Badmiker]

I just realized I was not clear above.

I was thinking like Coachgeo was thinking. Jack between the frame and the subframe, not the subframe and the ground. So little 6 ton bottle jacks kinda things.

We are looking at big 6x6 jobbies with a ~20' habitat so the rocking should be pretty minimal. We didn't notice it in our Class A 27'. We did hate trying to level that bastard though.

 

[Victorian]

Independent Air suspension is the answer for leveling.

I'm following this conversation about subframes with great interest. Agreed, there are many people out there with very simple mounting systems. From a supplier/manufacturer standpoint, we can not endorse these "non proven" home build constructions. I personally have seen several "profesional" build subframes fail that resulted in VERY expensive repairs. My advice: let an engineer (with a proven track record) design the subframe. It's not worth it to try and re-invent the wheel every single time. Think about the forces that are involved!

 

[Sitec]

Good to see a pic of Ulrich's truck under full flex! Agreed re levelling body. Air suspension or blocks are the simplest solutions. Trying to jack a rigid body that's fixed to a flexible chassis won't get the desired levelling. Trying to jack a fixed body from the ground requires long jacks and puts the body under unnecessary stress.

 

[Ramdough]

I just realized I was not clear above.

I was thinking like Coachgeo was thinking. Jack between the frame and the subframe, not the subframe and the ground. So little 6 ton bottle jacks kinda things.

We are looking at big 6x6 jobbies with a ~20' habitat so the rocking should be pretty minimal. We didn't notice it in our Class A 27'. We did hate trying to level that bastard though.

You would be inducing torsion into your camper box and defeating the purpose of a torsion free subframe.

Blocks are safer. Still no torsion applied to the camper.


Sent from my iPad using Tapatalk

 

[Sitec]

I'm still of the opinion that trying to lift and level a rigid box (that's not designed to be stressed) using jacks between it and the chassis will only serve to load and stress the box and probably twist the chassis a little... A correctly engineered 4 point mount should allow the chassis to do what it requires without stressing the box. 2 of those 4 points are fixed between the chassis and the body (the central point of pivot), leaving you only 2 to jack near.. and these wouldn't achieve what you want.. I'm with the others.. Stick to blocks under the wheels. Just my opinion though.

 

[Coachgeo]

I'm still of the opinion that trying to lift and level a rigid box (that's not designed to be stressed) using jacks between it and the chassis will only serve to load and stress the box and probably twist the chassis a little... A correctly engineered 4 point mount should allow the chassis to do what it requires without stressing the box. 2 of those 4 points are fixed between the chassis and the body (the central point of pivot), leaving you only 2 to jack near.. and these wouldn't achieve what you want.. I'm with the others.. Stick to blocks under the wheels. Just my opinion though.

FIXED POINTS arrg "oh wha ta fo liam" ..... my apologies and thank you for correcting me. I removed my post so not to steer someone incorrectly. I honestly totally forgot about the fixed point(s) in a 4 point pivot subchassis. So yes then there would be torsion and I would have to agree with you.

 

[Sitec]

FIXED POINTS arrg "oh wha ta fo liam" ..... my apologies and thank you for correcting me. I removed my post so not to steer someone incorrectly. I honestly totally forgot about the fixed point(s) in a 4 point pivot subchassis. So yes then there would be torsion and I would have to agree with you.

Nah, all good fella, I'd leave the post there, as it provokes thought and discussion. That's what the forum's here for. We're all learning, and this thread is of great interest to me, as I am yet to mount my body on my truck. A question not asked is when it can go wrong.
I have a plan for a 4 point mount where the 2 fixed points are about a meter behind the cab, either side of the chassis external sides with point 3 in the center of the chassis just in front of the rear axle, and point 4 in the center of the chassis right at the back. This allows the chassis to twist along its central point but keeps the front of the living box on a similar plane with the rear of the cab for the pass thru access hatches. I'd mount cab spring/shock absorber struts on either side of points 3 and 4 to dampen roll etc... But, all that said, I am still sat on the fence as to wether its even necessary, because there's several forum members here who run simple body to chassis setup's with minimal allowance for twist, have covered huge distances and have had no issues. I'll get round to sketching it one day as a picture tells a thousand words!! Cheers for now.

 

[IdaSHO]

FYI, for those interested in the 2011-2016 SuperDuty 3/4 and 1-tons...

Im in the process of building a custom flatbed for my 2011.

This is the chassis flex I'm seeing with just 8" under right front and left rear.
The truck has a bit more flex in it (totally stock), but this test was enough to verify tire clearances when flexed.

A 3-point mount really shows it off. It is quite a good deal of chassis flex, that would definitely destroy a camper if hard mounted.

 

[Sitec]

Some nice looking fabrication going on there!

 

[IdaSHO]

Thanks

Certainly a lot going on all at once with this build.

Chassis was extended to create space for the large cross-body box, integrated stairs for camper, large over cab storage rack, aux fuel tank built into bed, aux air tank built into bed, 3-point pivoting frame setup, integrated under-body boxes, etc... etc...

 

[Darwin]

IdaSho, any pictures of how you attached to flatbed to the frame? I am guess springs at the front and bolted at the rear with 'guides' welded in to keep it from shifting side to side?

Edit: nevermind I see the single pivot point in the back

 

[IdaSHO]

Here are some better shots of the business end of the pivoting frame...

front cradle.

Chassis extension and single pivot in the rear

 

[Darwin]

IdahSho, looks nice. It appears with the method you are using vs. a spring mount that you would be able to keep the height of the box lower to the frame rails.

 

[Coachgeo]

IdahSho, looks nice. It appears with the method you are using vs. a spring mount that you would be able to keep the height of the box lower to the frame rails.

disagree.... captured spring mounts keep it much lower... but do agree with you that Idahsho's set up is one of the most compressed 3pt pivots I've seen. confused though.... IdahSho.... your pivot at the rear appears to sit a good bit lower than the fixed points at the front... maybe that does not matter since it is only pivot spot...??

Am I correct that your rear set up pivots under the chassis instead of above like most??

How does the habitat attach to the rear pivot framework?

 

[Sitec]

Coachgeo, I picked up on the different height of the front pivot points too... In theory they need to be on the same plane as the rear pivot... but after thinking about it, as they are a 'fore and aft' pivot at the front and are only being used on a 3 point system, the central pivot plane becomes irrelevant (to a point). If however there was a 4th pivot point, then yes, the front points would have to be lower. I plan to use a similar system to IdaSHO's on my 6m body, but will be using 4 mounts. My first two pivots will be in the center plane of the chassis rail ( mounted on the LH and RH outside faces of the chassis) about a meter back from the cab, the third will be at 3m back, sitting centrally between the two 'C' sections of the chassis, and the 4th will be in the same position between the two 'C' sections but about a meter in from the rear.