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1988 U1300L RW1 Working gears Dual Tanks AC Rigged for Camping Plus: 91 F250 HD 4x4
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Math aside, it is chock full of cool line drawings eh? DIN3 plate info, for example:

Make a good t-shirt print

A similar set of documents exists for the round cabs, I have it... someplace. It's not near as comprehensive as the square cab documentation though.
Holy moment diagrams Trevman, that's a torque-load of data points!!!!

But your hallowed MB engineers avoided the real math. They put the Mog on a set of steps. No rolling downslope here as the axle loads are directly over the contact patch on the level platforms/ measurement surfaces. Good stuff for a staid German coach builder, but what is a poor rock-crawler to do?

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Couldn't do much with the screenshot, but the bottom line is that static tipping is just not a good model for the dynamics of a downhill run. I have noodled some more on my last best post, and think that it is also deficient in the modeling. I am messing with it, but it is really tedious work, and no way to prove/ disprove the results.

One takeaway from this post is that the next time I am facing a steep downhill, I will put the Mog in "hopping up the stairs mode". No roll-overs, that way.

All in fun, of course.

Edit: Trev, I am thinking that MB must publish uphill/ downhill/ sidehill slope limits for all models of Unimog. Any idea of where to access such data, for at least the 406/ 416 and SBU's? The interesting part would be how they test or calculate for this, and what sort of safety margin (if any) they incorporate. So many variables on the up/ down slopes, it could be a nightmare they avoid. But if the data is there, it would be cool to see how it compared to calculations.

Lee


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1988 U1300L RW1 Working gears Dual Tanks AC Rigged for Camping Plus: 91 F250 HD 4x4
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Hi All...

Ok.. before the Math and the engineering makes me confused more, i have some last questions and requests.

* Trev : if you can find and share the similar Round cap documents, it will be very appreciated.

* Lee : As per your calculations, we understand that Net Downforce for 406 in Steady mode on 45 degree slope is = 361#.

So.. what is this value rougly for 416 and SBU? ( if you can calculate and serve here, it will be very very comparative in terms of adding extra weight to equalize the 406 conditions compared to 416 and SBU).

REGARDS.
Elbruz.
Elbruz,

I would caution you not to take my drawings and calculations too exactly. What I would say is that the there is some useful information to be gleaned from the analysis I did. Basically, the issue with the 406 is the short wheelbase, and how far forward the CM is. Making a 406 into a 416 equivalent is not a realistic goal, for those reasons. Adding weight will help on the downhills, but it will also alter behavior on the flats and uphill, as well. My guess is that a modest amount of weight as far back and as low as practical is probably a good thing, as has been observed by other members here.

The biggest take-away that I would offer is to drive very conservatively on steep downhills. As previously posted, this means using engine braking (gear choice) to the maximum extent possible. Irregularities, such as dropping off even small ledges, can be enough to initiate an endo, because of the dynamic forces. The modeling and math for this gets so tough, that the MB engineers direct the coach builders to do a skid pad test, to verify calculated results for sideways tippers. And those calculations are easy, compared to the downhill run. Notice the MB documentation for front/ back tipping is based on measuring on a set of steps. With the tires sitting on horizontal surfaces, there is no moment induced in the axle/ tire assembly, that would translate into (downhill) acceleration of the truck. Total wusses, running from serious problems! Pure static tip-over.

Another suggestion I have, based on the analysis, is to be in a gear that holds back, with the engine in the middle of the rpm range. If you feel a forward lurch (aka a forward somersault) the best thing is to ACCELERATE. This will pull the front end out ahead of the CM, as much as is possible, and may keep you upright. Braking is the WORST response, the dynamic goes to one of Conservation of Momentum, and you accelerate the flip. The big problem with your (finally revealed) nosedive is that this is NOT a downhill tip-over, but rather a diagonal corkscrew failure at one corner of the vehicle. I can't even imagine how to model, much less calculate that scenario. It is best left to practical experience, as to what to avoid to stay safe.

On the subject of modeling, it is easy to do calculations: the ones I showed are all simple math (really). The hard part is setting up what to calculate, and herein, I had to do a bunch of simplifications and assumptions. I have been thinking some more on this, and believe that my model came out about how it should, but partly by accident or serendipitous circumstances. The biggest issue is how to model the net ground force at the contact patch of each tire, and I chose to assume that would be at the leading (downhill ) edge. I doubt that this is correct, and moving back even a fraction of the contact patch for center of net force is a big change. There is also the issue of coefficient of friction at the contact patch. If one is on loose material, all bets are off, as sliding may well occur before tipping. See the MB documentation posted by Trev, for validation of this.

If I get really inspired, I may do a more sophisticated model and calculate forces and moments at both axles, as they are intertwined, as you might suspect. If so, I will post, but don't hold your breath; it is a LOT of work, and I have spent an inordinate amount of time on this already. Still, I find the education and enlightenment valuable to me personally, so it is all good.

Meanwhile, have fun and stay safe.

Lee
 

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Holy moment diagrams Trevman, that's a torque-load of data points!!!!

But your hallowed MB engineers avoided the real math. They put the Mog on a set of steps. No rolling downslope here as the axle loads are directly over the contact patch on the level platforms/ measurement surfaces. Good stuff for a staid German coach builder, but what is a poor rock-crawler to do?
So what you are saying is in your normal day to day driving, steps don't pop out of just anywhere? Cause by the looks of things, wild platforms and steps are not just in videogames:
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I believe they covered that with the "an evaluation of the vehicle-device combination by means of a practical driving test is required (influence of driving dynamics). " And I think Mercedes is more interested in how the attached boom mower affects stability vs rock crawling But it could be argued that offroad trails need trimming as well, why not by Unimog!

ie, get out, test your equipment (with proper safety equipment!), as no calculation can cover every aspect in every situation.

I've got lots and lots of documents but they are far too large to attach here, and I've shared them in the past via dropbox, google drive, etc but then you have to maintain those services (everything is free...like a puppy...) and the links are long since dead as I've let my dropbox lapse. I can't recall any rolling downslope in the documents but I'll open a few and check. Doesn't help a lot of it's in German and though I OCR'd it when I scanned it, I don't know the proper terms for searching and Google translate only goes so far.

Edit, come to think of it there is a section on traversing side slopes in one or more of them...lemme look.
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Awesome stuff. I thought I had seen the SBU entry/ exit/ up slope/ down slope angles somewhere before, undoubtedly posted on the Forum. As for elbruz, that data will not hold for his 406, of that I am sure.

If the camera was level, then the side-tipping axle in both photos is 34 degrees, measured graphically with an adjustable triangle, on screen. Not something I'd want to be doing alone in a remote location.

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So what you are saying is in your normal day to day driving, steps don't pop out of just anywhere? Cause by the looks of things, wild platforms and steps are not just in videogames:
View attachment 2626469
Trev,

I still have problems with the EPC. Can you look up the part number for this set of steps? I want to take a set with me on my next trip to Canyonlands. I think this could be more useful than a winch, much as I love my A50.

Lee
 

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Here's a great video if you have 15min to spare, I set the thumbnail to the side-slope demonstration, just because ;), there's more side testing at 3:23 :

They even have a rock pit at 1:32 and 13:10, if you didn't think the Unimog 406 capable before, this video should change anyone's mind

 

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See at 4:40, the truck eases down over the 100% (45 degree) test slope. The driver touches the brakes, and the rear wheels start to lift off. Validation that my original calculations, however flawed, end up giving a more-or-less correct summation of the situation. Better to be lucky than good, we take'm however we can get'em.

Basically, at 45 degrees downslope, BE VERY CAREFUL, the truck is right on the edge of somersaulting.

Edit: Notice also the different amounts of tire showing above the test slope curb. If the curb is parallel to the actual track, then this also demonstrates the significant difference in loaded radius/ contact patch between F & R. It would have been really great to see the slope without the curb blocking. Then I could re-assess my modeling of the tire/ slope interface, and have a better conformity to reality.
 

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Keep in mind that Terrain can not only cause you to flip sooner, but can also increase the angle of your dangle. Flat ground scenarios can be misleading and don’t tell the whole dynamic story. I have done some things in my trucks that on the face of it is not possible, but once you analyze the terrain it becomes clear how you can pull it off.

Also rolling through an obstacle without stopping can easily get you past rollover point and back again before disaster strikes.
 

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Discussion Starter #56
So. I had asked that video scene in my previous post.

If 416's rear axle lifts up in that 45 degree. Then 406 can not ease down that 45 degree.
 

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Discussion Starter #57
So. I had asked that video scene in my previous post.

If 416's rear axle lifts up in that 45 degree. Then 406 can not ease down that 45 degree.
 

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So. I had asked that video scene in my previous post.

If 416's rear axle lifts up in that 45 degree. Then 406 can not ease down that 45 degree.
It dawned on me after posting that the truck at 4:40 was a longer wheelbase 416 (I think?). And therefore, it is likely that the 406 is more unstable, or may not be able to negotiate the 45 degree downslope. This would imply that my calculations were dangerously optimistic.

Lee
 

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Up on George Bulls mountain, he has a cool chunk of rock that the glaciers made just right so you can pull up on it and in the correct spot the Mog is perfectly balanced on one front wheel and one rear wheel. Its kinda neat to get out and with just a push of your hand, rock it one way to be on three wheels then rock it the other way to be on a different three wheels.

the spot is a little less dramatic than the photo in Trevs post (which I cannot apparently insert here for some reason) but gave me a good memory I thought some would like.
 
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