pivoting frames and mounting campers

[4x4Canterman]

Thanks rruff. I reckon it is helping to stiffen the frame. All the c channel rails and rhs cross beams are fully welded on every surface. The chequer plate floor sheet is welded everywhere also. This tray has been made to be strong. My point is that the frame still flexes even with the bracing of a decent steel bed. I will test and photograph it again with the tray removed for a comparison. Thanks for the link

 

[Zuber]

Why is the rear DS so short which causes such a steep angle?
Kevin

DS = Drive Shaft?
The Core models have a different transfer case. It's like the Merican pickups. In 2WD the power passes directly through, no gear stack to move the output drive shaft to the bottom of the case like the Fuso. Also, the gear train is stationary in 2WD, the shaft just passes through. The front DS output is low.

 

[The Artisan]

DS = Drive Shaft?
The Core models have a different transfer case. It's like the Merican pickups. In 2WD the power passes directly through, no gear stack to move the output drive shaft to the bottom of the case like the Fuso. Also, the gear train is stationary in 2WD, the shaft just passes through. The front DS output is low.

I get that but rule of thumb is 4 to 10% angle on driveshaft that rear is much more than that
Kevin

 

[nnamssorxela]

Hi all, I'm collecting materials for my flatbed build on my 2003 Ford F250 (crew cab long bed). Since it's an '03 Ford, it has a C-channel frame, and since it's a 250; it's a "1 ton" truck and I never plan to load more than that. I have a 10' slide in camper to get me going, but I would love to eventually build or buy a flatbed style camper, and I don't want to have to rebuild the bed when it comes time. If you're unfamiliar with the ford trucks, the long bed is ~8' and has 4 sets of bolts keeping it in place from the top down (very similar to IdaSHO's frame about 10 pages back).

As of now I'm planning on making the flatbed's main rails that run on top of the truck frame out of 3" C-channel as it is stronger and lighter than 2"x3" 3/16" tube. Initially I was going to have the cross bars made of 2"x3" 0.120 tube, but using the same 3" C-channel would add less than 10lbs overall to the frame, and be much stronger (this may be 2" to reduce the height, but need to measure). On top of that I will have 1.75" extruded aluminum planks. I do have an overhang on the camper, and plan on having 4-5" of clearance between the top of the cab and the bottom of the overhang to allow for flex (not sure if this is too much or too little). Trying to keep bed weight down to keep the payload high.

Suffering through some paralysis by analysis and trying not to over think this.

- Sounds like 3 and 4 point pivoting frames are overkill for a passenger truck that is not heavy duty, and captive springs are the best bet to keep it functional and simple.
- Can I just use all of the 8 existing mounting points with captive spring bolts (with simple guides on each end to keep the bed centered) or does one end need to be hard mounted?
- If I need to hard mount one end, does it matter which end is fixed?
- When hard mounting, can I bolt straight through from the top down using the existing mounting points, or does it need to be "hinged" with a bolt/bushing mounted from the side?

I consider myself a fairly decent fabricator and I'm at a great point to design the bed the best way possible.

 

[rruff]

Use tubing not C-channel for your subframe. The "problem" you are solving by having a subframe is a lack of torsional stiffness in the truck's main frame, and a C-channel subframe will be similarly flexy. C-channel is only strong (and stiff) in the vertical dimension. The subframe needs to be a platform that is stiff in all dimensions, but primarily torsion.

Near the beginning of this video the Earthcruiser mounting is shown. They are using what appear to be the soft Energy Suspension PU universal body mounts in a addition to springs. On the first position (front two mounts) they have the PU mounts only (this would be the "rigid" point), while the second and third positions have springs in addition to the PU mounts.

Note that the subframe is tubing and not that large.

 

[nnamssorxela]

Excellent points. The MMI rating of c-channel I'm looking at is only for straight down deflection, not the twist that I need to compensate for. I really like the poly/spring combo. It seems easy to incorporate with almost no design compromise from my original solid mounting plans I had before I saw the light of flexible subframes.

All the spring hardware can be kept in the channel portion of the OEM frame on my truck, and I just need to have a subframe pocket big enough for the poly bushings.

 

[rruff]

Seeing them use only 6 of those PU mounts is making me question my design. I have 8, and the weight I have on them is surely less than half the Earthcruiser load. Maybe I should only use 4...

The guy at Energy Suspension told me they'd support 800 lbs each, but I did my own calculations with generic PU data and thought that was optimistic. But if this is how the Earthcruisers mounts have been made for years, then they must hold up ok.

 

[nnamssorxela]

I was thinking the same thing. My plan is to have 8 sets of the 70A 1/2" thick bushes with no sleeve, only washers. Not a big deal to have a few extra, and when the truck is level on road a few more contact patches will surely distribute the load a little better. Probably going with 4" gold springs from McMaster on the front 6 mounting points. Seems most have the captive end of the frame at the back. I'll be doing top down on the existing bed mounts.

 

[rruff]

That should work fine. I don't know about advantages of having the fixed point at the rear, but if you want a passthrough, I'd definitely fix the front. Also, I kinda like having the cab and camper line up.

I've been scratching my head regarding Earthcruiser mounts. They really do look like the Energy Suspension soft mounts (dimensions look right), only they have nuts that are too large. Then it dawned on me... I think they removed the inner sleeve and have 3/4" bolts instead of the 1/2". That makes sense... I think the sleeve is mostly there to make it easy to set the right preload, and you can just torque them down hard.

Which brings me back to how much load they can carry. The Isuzu NPR these are based on has a payload capacity of at least 6,800 lbs. Nearly all of this would be in the habitat and supported by the PU mounts... so with 6, over 1,000 lbs each. 4 of them should be plenty for my <2,000 lbs then. It would help in my case since the rear mounts are on the centerline and will act as a pivot of sorts. And the front ones need to accomodate a little pivoting motion as well.

 

[Alloy]

That should work fine. I don't know about advantages of having the fixed point at the rear, but if you want a passthrough, I'd definitely fix the front. Also, I kinda like having the cab and camper line up.

I've been scratching my head regarding Earthcruiser mounts. They really do look like the Energy Suspension soft mounts (dimensions look right), only they have nuts that are too large. Then it dawned on me... I think they removed the inner sleeve and have 3/4" bolts instead of the 1/2". That makes sense... I think the sleeve is mostly there to make it easy to set the right preload, and you can just torque them down hard.

Which brings me back to how much load they can carry. The Isuzu NPR these are based on has a payload capacity of at least 6,800 lbs. Nearly all of this would be in the habitat and supported by the PU mounts... so with 6, over 1,000 lbs each. 4 of them should be plenty for my <2,000 lbs then. It would help in my case since the rear mounts are on the centerline and will act as a pivot of sorts. And the front ones need to accomodate a little pivoting motion as well.

Without the sleeve hopefully there's something to prevents the threads of the bolt from cutting the urethane.

Without a sleeve the fixed mounts may want to lean over while braking.

I also wonder if the load rating is static or peak.

Once the box goes on I was wondering how easy they are to service. Looks like there's only room for the open end of a wrench.

 

[rruff]

Good points. I was told that the 800 lb load/per was static.

The problem of threads cutting the PU could be solved with bolts that only have that last bit threaded.

Sleeve or no sleeve, I don't see a difference in the ability to lean or tilt. They should do that either way... in fact I'm banking on it since I want the rear ones to tilt without too much resistance. But I don't think leaning over while braking is much of an issue since it will be a small movement, and it will spring back as soon as the deceleration is over.

If you can get a wrench in there, it shouldn't be a problem to remove the bolt out the bottom.

If you are interested in the Earthcruiser Core, the guy who made the video above has many on his youtube channel and also has a thread on ExPo.

 

[Sitec]

- Sounds like 3 and 4 point pivoting frames are overkill for a passenger truck that is not heavy duty, and captive springs are the best bet to keep it functional and simple.

There's an even easier way to decide which of the options will be best for your truck... If there is a tray on it currently, remove it. Then cross axle the cab chassis on a dirt mound or bank and watch how much your empty chassis twists before the suspension moves or a wheel lifts... Our 12 tonne Mercedes has a massive amount of twist (12" or more) before the axle springs do any real work. This twist will then be transmitted through your Habitation Box so it either needs to be a heavy RHS frame with diagonal bracing so it can withstand the load, or it needs to be mounted on some pivots. I have had the job of welding/repairing cracked bodies on overland trucks that were rail on rail mounted, and this along with visually seeing the massive amount of flex on our truck told me that a pivot system was the way to go. If the vehicle is going to be on 95% tarmac or good dirt roads then rail on rail would probably be fine, but if like us you want to get out to some remote areas with undulating tracks and creek crossings, then look to pivots.

I'm also of the belief that all the pivot points should be within the center axis of the chassis rails, and not on a seperate subframe above the chassis, but that's another story all together! If you want to see my take on it, look at the thread Mercedes 1222a the beginning in the Unimog and MB section.

 

[nnamssorxela]

Alloy, like rruff said, I can't imagine that a sleeve with do any more damage than a smooth shank bolt, and at 1/2" thick poly with 1 ton spread between 8 mounts; I suspect it will be pretty planted under braking. I don't have the knowhow to calculate this, just going from the gut.

Sitec, Thanks for your input. I saw your posts earlier in this thread and checked out your build as well. Pretty serious, and your payload is higher than my entire rig!

I think to make the project progress rapidly, I'm going to keep it simple. If I run into issues or feel like I want something with pivots, I can do that if/when my current camper falls apart, and I go to build a custom one. I find it easy to get lost dreaming and I have to reel myself back to reality.

My F250 has a hump in the frame over the axle which necessitates having little risers to lift the frame over the hump. I think this alone will greatly help my design, and the "fixed" end will be able to compress the poly mounts as needed. I do not anticipate hardcore offroading with this rig, being that it has quite a poor turning radius for the trails I'm familiar with. This is my preliminary design so far. The "feet" are 1/4" thick, and the main bars and cross bars are 2"x3" 1/8" thick tube (0.120" wall). The bolts will come up from the bottom and have a 2" washer and nut on the end that would be inside of the foot, sandwiching the poly.

 

[rruff]

Are the mounts directly on top of the frame rails? How will the springs be mounted?

 

[The Artisan]

Are the mounts directly on top of the frame rails? How will the springs be mounted?

Looks like under?
Kevin