Torsion-Free Sub-Frame
- Thread starter Bajaroad
- Start date
Bajaroad
Adventurer
FusoFG said:
Thanks for the response Tom.
I'm affraid I am not clearly communicating my ideas - sorry for that.
The airbags I'm describing are only supplemental, distributing the load more evenly - not like a truck air spring sys.
The engine mounts I am referring to are rated up to 4500lbs (EACH) depending on the model (I am looking at the series 22000) and they are fail safe, meaning they have a bolt that runs through them. Even if the polymer was to fail, the bolt would not allow a disconnect. If you look at Rob Gray's rig it's one of the biggest/heaviest I've seen, he got by fine with just 3 of these mounts - years of use.
Some of these rubber mounting products are rated to 10,000lbs, so its only a matter of applying them correctly. From my experience, I am more concerned with metal to metal connections on vibrating systems. Vibration and shock are killers. We develop DC Contactors for aerospace and ground vehicles (Bradley), and the first qualification test they want to do is shock and vibration. I'm sure I could get by without the shock mounts, but I believe they are a good benefit.
I hope to start cutting material in a week or two - I'll keep you posted on the progress.
Robthebrit
Explorer
Mounting the cab on shocks is a really good idea but you have to keep some sort of tension otherwise it'll be boat. My mog was factory modified for this and the difference in ride quality is huge. The cab is 4 point mounted, there are two flexible rubber mounts at the rear and two shocks at the front - typically there is a solid mount at the front and sligtly different rubber mounts at the rear. This saves everything in the cab from taking a beating when on dirt. Air ride seats save the people in the cab even more, I can barely tell I am on dirt unless I go fast.
Rob
Rob
Robthebrit
Explorer
A mog typically has a single connection at the front but its not used for tipping the cab. There is a set of flanges on the front of the cab which are used for tipping and in general its a royal pita as you have to pry bar the front of the cab up a few inches. Lots of people don't do this and just tip using the front hinge.
The system on my cab is actually better and I can tip by cab anywhere without any special hardware. The front hinge is not even there, the shocks on the front of the cab don't go to the frame, they go to a flange which is bolted to the frame with some rubber torsion pivots. To tip the cab all I do pull out a few blots, disconnect the steering and lift the back. The previous owner welded an extendable bar under the back of the cab and with that a few strong people can lift it or if you are not feeling strong you can use a high lift.
I am sure a similar system would work on the fuso but it will require some modifications. I can send pictures if you are interested.
Rob
The system on my cab is actually better and I can tip by cab anywhere without any special hardware. The front hinge is not even there, the shocks on the front of the cab don't go to the frame, they go to a flange which is bolted to the frame with some rubber torsion pivots. To tip the cab all I do pull out a few blots, disconnect the steering and lift the back. The previous owner welded an extendable bar under the back of the cab and with that a few strong people can lift it or if you are not feeling strong you can use a high lift.
I am sure a similar system would work on the fuso but it will require some modifications. I can send pictures if you are interested.
Rob
charlieaarons
Explorer
Bajaroad I bet you have you the best built strongest camper box and subframe money can buy said:
Robthebrit
Explorer
What Charlie says is true for all properly configured multipoint/pivot mounts, nothing special about the Unicat system. The pickup beds on my other unimogs have a 3 point mounts too.
As Unimogs go the U500 is not that bendy, its designed as a semi rigid frame. The UHNs (U3000,U4000 and U5000) still use the ladder type frames as used in the older 1300s and 406/416s. You can get a huge amount of twist across the frame, multi point mounts are essential and on these mogs everything is mounted in a 3 point system including the cab, engine and tranny.
Rob
As Unimogs go the U500 is not that bendy, its designed as a semi rigid frame. The UHNs (U3000,U4000 and U5000) still use the ladder type frames as used in the older 1300s and 406/416s. You can get a huge amount of twist across the frame, multi point mounts are essential and on these mogs everything is mounted in a 3 point system including the cab, engine and tranny.
Rob
Bajaroad
Adventurer
You Mog guys are preaching to the choir - I'm on board with the properly designed 3-pt system.
My point is that a properly designed 3-pt system is not necessarily adequate for a weight bearing flatbed and the bed will respond significantly to inertial or gravitational loads depending on the load and shear strength of the flatbed. I've done the FEA analysis on my flatbed frame sitting on 3pts - a camper box on top makes all the difference.
A 4-pt system that you describe should reduce that response by about half if the two outsides mounts are in the middle. That's probably the best approach for my flatbed, but I want the subframe to follow the cab as much as possible, so I'm going to stick with 3pts and a supplimental air springs.
Just to argue . . . I will say your subframe does respond to inertial loads, it's just that the response is too small to notice. Continue to increase the inertial load and the response increases more or less linearly.
Thanks for the discussion.
My point is that a properly designed 3-pt system is not necessarily adequate for a weight bearing flatbed and the bed will respond significantly to inertial or gravitational loads depending on the load and shear strength of the flatbed. I've done the FEA analysis on my flatbed frame sitting on 3pts - a camper box on top makes all the difference.
A 4-pt system that you describe should reduce that response by about half if the two outsides mounts are in the middle. That's probably the best approach for my flatbed, but I want the subframe to follow the cab as much as possible, so I'm going to stick with 3pts and a supplimental air springs.
Just to argue . . . I will say your subframe does respond to inertial loads, it's just that the response is too small to notice. Continue to increase the inertial load and the response increases more or less linearly.
Thanks for the discussion.
Robthebrit
Explorer
Bajaroad said:
I don't think thats much of an argument, in theory you are 100% correct.
Rob
Bajaroad
Adventurer
Vertical location of pivot point on 3PT subframe
Has anyone thought about the vertical location of the pivot point in relation to the twisting frame?
I would assume when the frame twists the axis of that rotation is centered between the frame rails, and this location would be the ideal location of the pivot axis.
Has anyone thought about the vertical location of the pivot point in relation to the twisting frame?
I would assume when the frame twists the axis of that rotation is centered between the frame rails, and this location would be the ideal location of the pivot axis.
Bajaroad
Adventurer
?
Why would the optimum twist be at the step-up. The modulus is highest at the step-up.
My question was about the location of the axis of rotation of the twist - see attached. If the 3pt pivot point is not on this axis then it will have a laterial component (sideways movement) when the frame twists. I worry this will place stress on the two stationary points.
Why would the optimum twist be at the step-up. The modulus is highest at the step-up.
My question was about the location of the axis of rotation of the twist - see attached. If the 3pt pivot point is not on this axis then it will have a laterial component (sideways movement) when the frame twists. I worry this will place stress on the two stationary points.
Robthebrit
Explorer
My camper has lower pivots and the box is directly mounted to them to get it as low as possible. I don't think it could go any lower without the frame and box contacting at max flex. I posted pictures elsewhere but I am not sure where.
Rob
Rob
sprale
Observer
Adjustable shocks on sub-frame
Has anyone thought of/tried using adjustable shocks on the sub-frame? You could tighten it up for use on smoother maintained roads, then soften them up for use on unmaintained surfaces. This could help control body roll on more heavily used roads where traveling with traffic would mean higher safety needs, while still providing off-road flexibility with a simple adjustment. I'm sure someone could be creative enough to run a remote adjuster inside the cab.
Has anyone thought of/tried using adjustable shocks on the sub-frame? You could tighten it up for use on smoother maintained roads, then soften them up for use on unmaintained surfaces. This could help control body roll on more heavily used roads where traveling with traffic would mean higher safety needs, while still providing off-road flexibility with a simple adjustment. I'm sure someone could be creative enough to run a remote adjuster inside the cab.