pivoting frames and mounting campers

Christian

Adventurer
Hi Ramdough. Well, all but the lock outs/hydraulic system are built. I have the two outer pivots no more than 100mm from the rear hanger of the front springs about 400mm behind the cab, keeping the cab and body faces in a fairly similar plane at all times. I have two central pivots, the first is located on the rear springs front hanger cross member and the second on the rear spring rear hanger cross member. These are all tack welded to the body and are yet to be fully welded. I've since added another central pivot at the very rear of the truck. All pivot points are on the center line of the chassis. I have then twisted the truck chassis (rear lh dual wheels 400mm off the ground) to the point where the lower lockers just touch the body to check that it all worked without any of the tack welds going bang, which it did. To double check what you mentioned about binding, I then unbolted and removed each locking bolt in the pivots and tapped each pin with the hammer to see how much load they were under. To my surprise they would tap out with ease and have minimal to no load on them. I must have got something right! :) Re the hydraulic setup, I have gone away from this due to weight, the time involved and cost to do it. I now plan to utilize 2 (poss 4) stumpy 100mm x 100mm coil springs between the body and chassis these will be sat with no or minimal tension when the truck is flat, and will only be compressed as the chassis twists. Here's a pic of the chassis twisted and the body straight. it was in this position that the pins would tap out. :)

View attachment 575883
FYI

Unicat has a YouTube video coming out tomorrow on subframe design.


Sent from my iPhone using Tapatalk

The guy from UNICAT actually describes Sitecs system, but calling it a 3-point... I guess you could view a 4-point as a 3-point with a mirror axis. The thing we can take from the UNICAT live stream is that you can add as many central points as you wish (theoretically), as long as they are all located on the central pivot axis of the chassis.
They surely do have proven track record!
 
Last edited:

Victorian

Approved Vendor : Total Composites
The guy from UNICAT actually describes Sitecs system, but calling it a 3-point... I guess you could view a 4-point as a 3-point with a mirror axis. The thing we can take from the UNICAT live stream is that you can add as many central points as you wish (theoretically), as long as they are all located on the central pivot axis of the chassis.
They surely do have proven track record!
I watched it too... Funny to see my old boss talk about stuff we repeated soo many time in the shop when I was working there. When it comes to subframes, they really know what they are talking about. I'm not aware of any frames/mounts ever failing coming from that shop. On the other hand, we had several rigs from other well know manufacturers show up with big structural failures! I have seen this on several North American made ones too...
Generally speaking, subframe design and builds are still a specialty in North America with not many that have a proven track record. Best places are currently: Overland Adventure Trucks in Olympia WA , Acela Trucks in Belgrad MT and ITB in Surrey BC. Only Overland Adventure trucks is selling and manufacturing them as a stand alone item.
 

Alloy

Well-known member
Here's the rear pivot point which sits lower in the rear of the chassis as the chassis depth is shallower in the rear. It is in line with the two pivots in front of it. I'm not looking for huge travel like some vehicles. I'm aiming for around 50mm allowable upward travel between a chassis rail and habitation box rail.. 100mm in total. This will allow the chassis to follow basic humps and bumps off road without stressing the body, but then still gives me full suspension travel as well if I really get into the rough... The body I'm using/modifying was originally built for mine spec work in Outback Australia so is already over engineered and was designed to be 'rail on rail'. I have left an accurate 100mm between the habitation box rails and the chassis rails so if I have any issues, i can easily slide a length of RHS in each side and make it 'fixed'.

View attachment 576031
Did you choose 50mm to keep the OA height down?
 

Sitec

Adventurer
Did you choose 50mm to keep the OA height down?

Hi Alloy. Not really, though doing it the way I have has assisted in keeping the overall height at 3.55m. I have the pivot points in the center of the rail as I think that's where they need to be, and the 50mm chassis rail to body rail travel is at 50mm as the pivot center to rail distance is about half what the pivot point to edge of body is, and I only wanted a 100mm travel gap between the body... Much more and it would have looked odd from outside. Hope that makes sense.. I have also gone with a 100mm clearance gap between the habitation box and the chassis, so that if for any reason my 5 point system does not work as intended, I can slide a piece of 100 x 50 RHS in between the chassis and box and quickly make it 'rail on rail' without major mods... Lets hope it all works eh! :)
 
Last edited:

Sitec

Adventurer
The guy from UNICAT actually describes Sitecs system, but calling it a 3-point... You can add as many central points as you wish (theoretically), as long as they are all located on the central pivot axis of the chassis.
Spot on. The only drawback with the way I have done it is that by having the outer support pivot points of the 4 point system at the front then means that the travel between body and chassis at the rear is huge... (hold a ruler at one end and twist it at the other). If the outer support pivots are mid mounted (as normally found), then travel is halved at each end. The advantage of my system is that movement between the cab and habitation box is minimal as the outer support pivots are at the front. As I'm not after huge twist, but looking to share the twist load between the chassis and suspension as my habitation box is very strong, I am allowing a percentage of chassis twist, but letting the leaf springs do the rest.
 

Christian

Adventurer
Spot on. The only drawback with the way I have done it is that by having the outer support pivot points of the 4 point system at the front then means that the travel between body and chassis at the rear is huge... (hold a ruler at one end and twist it at the other). If the outer support pivots are mid mounted (as normally found), then travel is halved at each end. The advantage of my system is that movement between the cab and habitation box is minimal as the outer support pivots are at the front. As I'm not after huge twist, but looking to share the twist load between the chassis and suspension as my habitation box is very strong, I am allowing a percentage of chassis twist, but letting the leaf springs do the rest.
That sounds interesting! and you know the positives and the downsides. I have actually thought about this a lot through several years. I have read just about all the discussions, theories and real-world experience. I started a project on a Volvo TGB just because the frame is rigid. but two kids later, it was too small even before it was finished.

So we bought a Mercedes LAF 1113B, much larger, but with a flexible chassis. Ok, it's not that big, approx. 7.5m/24.5ft. So I want to make it a fully integrated, so we can utilize the cab space while camping. I know this goes againt all canon here, but that's what we want.

So I'm trying to design a subframe that´s a bit unusual:

Up front there will be two heavy LORD cab mounts, which will support the front weight and control the front both vertically and horizontally.
These will also keep the subframe and chassis in alignment up front, so controls (gearshift, gas pedal etc.) will not be affected by movement.

Approx. above the rear axle there will be a Watts linkage which will control the rear side to side, but allow chassis flex and vertical displacement.

Behind the rear axle there will be an airbag on each side. These will support the weight of the subframe in the rear. On-road these will be inflated and controlled individually. Off-road they will be connected to allow air from one to go to the other. This way they will allow the chassis to flex.

I believe this should work, and have run FEA on the subframe. A bonus will be isolating the box from the chassis vibrations.

Please look it over and give me all your thoughts both positive and negative, as long as they are constructive!

PS: the yellow shadows are an interference block I have used to make sure I did not design anything that would interfere with the chassis while flexing...
TChassis VI v9 1.pngChassis VI v9 2.pngChassis VI v9 3.pngChassis VI v9 4.pngChassis VI v9 6.pngChassis VI v9 7.pngChassis VI v9 8.png
 

Recommended books for Overlanding

Vehicle-dependent Expedition Guide
by Tom Sheppard
From $136.95
999 Days Around Africa: The Road Chose Me
by Dan Grec, Dan Grec
From $19.95
Motorcycle Messengers: Tales from the Road by Writers who...
by Lois Pryce, Mark Richardson, Carla King, Sam Manic...
From $9.99

mog

Mammutbändiger
Up front there will be two heavy LORD cab mounts, which will support the front weight and control the front both vertically and horizontally.
These will also keep the subframe and chassis in alignment up front, so controls (gearshift, gas pedal etc.) will not be affected by movement.
Nothing against LORD mounts (we used them quite a bit in aviation applications), but there have been some less than stellar results in the overland/expo applications.
Perhaps as BAH in that thread pointed out, having a large enough washer to 'captive' the mount if the rubber portion fails?
 

Alloy

Well-known member
Hi Alloy. Not really, though doing it the way I have has assisted in keeping the overall height at 3.55m. I have the pivot points in the center of the rail as I think that's where they need to be,


You mean horizontally and vertically?



and the 50mm chassis rail to body rail travel is at 50mm as the pivot center to rail distance is about half what the pivot point to edge of body is, and I only wanted a 100mm travel gap between the body... Much more and it would have looked odd from outside.

You mean too large of air gap between the chassis rail and the body rail?


Hope that makes sense.. I have also gone with a 100mm clearance gap between the habitation box and the chassis,


Now you've got me wondering.........habitation box?


Nice stone retaining wall by the way!



so that if for any reason my 5 point system does not work as intended, I can slide a piece of 100 x 50 RHS in between the chassis and box and quickly make it 'rail on rail' without major mods... Lets hope it all works eh! :)
 

Christian

Adventurer
Nothing against LORD mounts (we used them quite a bit in aviation applications), but there have been some less than stellar results in the overland/expo applications.
Perhaps as BAH in that thread pointed out, having a large enough washer to 'captive' the mount if the rubber portion fails?
Thanks and of course! I have read the accounts of the Unfortunate Unimog. LORD actually describes how these mounts can be “safetied” using a big washer, just like i.e. a standard Landcruiser body mount, and I plan on doing just that.
If I can find a supplier, I plan on using J-21159-9, they have a rated static axial load of 11.39kN/2.560lb and according to a LORD representative should handle 5-8 times that momentarily. The only thing I’m not sure about is their ability to isolate the actual vibrations from chassis and engine.
 

Alloy

Well-known member
Nothing against LORD mounts (we used them quite a bit in aviation applications), but there have been some less than stellar results in the overland/expo applications.
Perhaps as BAH in that thread pointed out, having a large enough washer to 'captive' the mount if the rubber portion fails?
I've seen lots of rubber/neoprene fail. The material does not have a good cycle life. Happens allot with suspension components from a company called Moryde International. Their components have to be inspected yearly.
 
Top