Vehicle stability off road.

[GRIMACE]

hmm this is very interesting - what the story seems to be is its easier to lift your front passenger side and flip than your front drivers side and flip....... And I just noticed in two of troys frestyle videos.....

The freestyle 4 with mostly stock not to hard core vehicles lifted the passenger wheel alot more than the drivers wheel (if ever) and also they got caught up on a flattish crossed up section where the front passenger side tyres just didnt want to get enough presure to the ground.


On the outer limits wild weekend video the cliff face that BJ gets up and others attempt all of them pull the front passenger wheel of the gorund and the vehicle rotates around numerous amounts of time ? ? ?


SO I SAY THIS IS DEFFINATELY AN OBVIOUS AFFECT and also when i put the boot in my rangie if it doesnt spit out a diff it always tilts front passenger side up and rear drivers side down. On an steep up hill climb this could be the single thing that could case a serious rollover or a safe climb
e.g. you come up to a heavily rutted area where your rear drivers side wheel is goin to be at the lowest point - you begin to loose traction and momentum so you put the boot in - torque causes shit loads of twist bringin your front passenger wheel high off the ground cause you to roll.
You could try it slowly but you would loose to much momentum and not get up the hill............ hmm got me thinkin.

Duel batterys on the front passenger corner shift light stuff to the driver side front, remove any heavy object in the rear drivers side of the vehicle

[antt]

i agree grimace. in my vit when i had the locker installed, i have noticed a severe increase in the torque load compressing the front drivers side, and lifting the passenger side when ya take off from a stop on the bitumen

[bj on roids]

i agree grimace. in my vit when i had the locker installed, i have noticed a severe increase in the torque load compressing the front drivers side, and lifting the passenger side when ya take off from a stop on the bitumen

i can pick a front wheel off the ground.


I prefer to sit on the low side, cause although it feels worse, you are actually closer to the ground

[Wendle]

I prefer to sit on the low side, cause although it feels worse, you are actually closer to the ground

low side rocks! i like to pick up small beetles off the ground for snacks with my teeth while i am wheeling!

seriously though, the high side can throw you around quite a lot, even in a pretty gentle flop..

torque lift is torque lift, all cars will do it, the easiest way to slow it up when climbing is stiffer rear springs.

[MissDrew]

Its all torque

Oh and I hate being on the high side, I much more prefer to be on the low side as I just look out the window at the ground and forget about how bad an angle it feels.

[daddylonglegs]

I suppose that the next thing we should try to determine is.
What influence does suspension design have on vehicle stability in these situations? Does a "ramp Queen" with great suspension travel and articulation roll over more easily than a similar vehicle with firmer springs?
Would an airbag on the right hand rear corner that you could inflate be an advantage here? Is the front axle limiting cable on Sam Overtons MogRover an attempt to minimise this effect? And if so, would it be more effective if it were anchored more left of centre?Why is Sam Keck's Zook so successfull when it nearly always seems to be laying on its side.
I know that suspension Roll geometry differences from one type of vehicle to another vary greatly and can determine whether one vehicle will lose stability when another does not, but I am just interested in learning other peoples thoughts and experiences on this subject.
Regards Bill.

[stumped]

got nuffin useful to say, but this is one of the most interesting and useful threads i've read

good to know this stuff... will be more careful on drivers side down angles now

[JK]

Yep it's all due to the torque twist.

The chassis will roll in the opposite direction to that which the driveshafts are spinning. Equal and opposites and all that.

Our RC crawlers are notorious for the torque twist effect cos of the much bigger relative difference between the unspring / sprung weight (with the unsprung weight being significantly lighter with respect to the axles etc). This effect is much more pronounced than in 1:1 rigs.

Super flexy rigs are terrible for this effect and are inherently unstable. They lift wheels all the time where the resistance to forward motion exceeds the stabilising effect of the weight of the truck and suspension stiffness.

To control the twist effects, shaft drive trucks are now developing along the path of limited flex and stiffer suspension. A low CoG is essential as higher CoG compounds the torque twist effect. We are also finding that longer WB helps to control torque twist.

Torque twist is also worse if lockers are in on a high traction surface and you are trying to turn in the direction of the unstable side.

If you are interested in seeing the torque twist effect in our RC crawlers, download this vid. Two of the trucks are shaft drive and suffer badly while the other (The MudCow) has the transmissions and motors integral to the axles so zero torque twist.

http://www.mudcow.com/Videos/Oxford_22Jan03.wmv 10.5Mb

BTW, the same effects are experienced in boats which is why counter-rotating props were developed. Similar concept to the counter rotating prop shafts that daddylonglegs mentioned above. Cool idea.

[antt]

Is the front axle limiting cable on Sam Overtons MogRover an attempt to minimise this effect? And if so, would it be more effective if it were anchored more left of centre?

you'll find that this is actually there to compress the front suspension when climbing a large ledge/step etc. puts the COG further forward which helps with traction on the front, and also lessens the impact of the front suspension trying to throw the tires off the rock face

[daddylonglegs]

Thanks for the input gents . It just occurred to me that in rock crawling for instance, If you reduced the amount of torque that the propshafts
(driveshafts) had to transmit by installing extremely low diff or portal axle ratios, then this torque twist should also be correspondingly reduced. does that make sense?
Also very interesting that vehicles with low unsprung mass(IFS/IRS) suffer more than rigid axles. I suspected as much when watching a Pinzgauer a side slope.Quite scary!
Regards Bill.

[JK]

Thanks for the input gents . It just occurred to me that in rock crawling for instance, If you reduced the amount of torque that the propshafts
(driveshafts) had to transmit by installing extremely low diff or portal axle ratios, then this torque twist should also be correspondingly reduced. does that make sense?
Also very interesting that vehicles with low unsprung mass(IFS/IRS) suffer more than rigid axles. I suspected as much when watching a Pinzgauer a side slope.Quite scary!
Regards Bill.

Interesting couple of comments there Bill.

Yep totally agree that less torque at the driveshafts would translate to less torque twisting of the chassis. This effect can be easily modeled on a workbench with our RC stuff.

Strangely enough I was also thinking about independent suspension and torque twist on the drive home yesterday... he he this thread has got me thinking

Independently suspended RC truck don't seem to suffer from torque twist at all and I think that this is more due to the resolution of the torque forces in the geometry of the double wishbones and pivot locations. They also seem to have far less and stiffer suspension travel so this might be another reason. I wonder if the independent suspension setup in the Pinz type is negatively effected by the drop hubs creating a greater eccentricity or something...

I have seen vids of the Victorian Pinz guys in action climbing very steep rutted tracks and they look plain scary on this sort of terrain. Always lifting front wheels and often lifting the entire front end off the ground as the rear axles push them up the hill. Yup give me a 4b in this terrain any day.

[Wendle]

it isn't all generated from the tailshafts though, the inertia of the engine and flywheel has a lot to do with it. rev the fark out of your truck when it is sitting in neytral, dead still, and you'll still feel the torque lift. tilt the truck up 45 degrees so that most of its weight is sitting on the rear links, or front half of the rear leaf springs, and that little bit of inertia changes into a lot.

[JK]

A little doesn't change into a lot it it just that your truck is closer to the point of instability so it takes less to destabilise it.

Agreed the engine twists in it's mounts as you rev it equal and opposites and all that but I think that by far the greatest destabilising effect is due to the massive amount of torque at the driveshafts working against the suspension and the vehicle CoG / stability, especially when a truck is close to it's limit of stability.

[daddylonglegs]

Dirt pigs,My head is spinning and about ready to explode because of an idea I have just had for a full size rock buggy, based on that twin engine RC vehicle.
If you build one with Suburu 4wd engine transmission units at both ends you would eliminate torque twist, but as was discovered years ago with twin engined Minimokes and Citroens, there are situations on steep climbs when due to weight transfer the rear unit had insufficient torque and would stall and the front unit would have insufficient traction and would madly spin its wheels. but if you had a solid mechanical connection between the front and rear transmissions, such as a drive shaft from the output of the Suburu gearbox that was originally meant to drive the rear axle, this independant stalling or wheel spinning could not occur. Hower, and the swelling in my head is beginning to subside, that interconnecting drive shaft will introduce a degree of torque twist, but possibly a lot less than a conventionally driven rig.

[JK]

OK then, what about an connecting chain or belt rather than by shaft?

Also, if geared down sufficiently the torque stalling would be less of a problem.

Yep the electric trucks also suffer from the motor stall as you described with the dual engined cars. It can be controlled in the electric rigs through lower gearing which generates more torque at the wheels, fooling with brushes (e.g. install softer brushes in the rear motor = better conduction of current) and wiring the motors in parallel so that they receive equal current and in effect produce the same torque. Parallel wiring effectively acts like a viscous centre differential.

If you wanted to go really radical in a fullsize rig, electric drive would be awesome if the problems of energy storage and weight could be overcome. Hydraulic is another way but also heavy, messy and SLOW.

If you are interested in more vids of the RC crawlers, head to my website www.mudcow.com and go to the videos page.

[daddylonglegs]

Silly me. I just looked at a Suburu and noticed they have more or less conventional north south, rather than east west engine transmission units, so you would still get the same torque twist effect as we have been discussing all along. Are their any soft roader type 4wd's out there with Eastwest engine transaxles.
I did look at hydraulic drive recently because there are a lot of scissor lift cherry picker type trucks around nowdays with hydraulic/planetary geared wheel motors, but I cannot rationalise spending that kind of money on a vehicle that is not suitable for multipurpose use.
Bill.

[JK]

I don't think that you would because the diff and transmission are locked together and therefore can't twist reletive to each other.

And now that I think about it a fully independent suspension vehicle wouldn't torque twist either cos the diffs and chassis are locked structurally therefore the diffs can't flex relative to the suspension. Doh... I should have thought of this earlier....

[daddylonglegs]

PS. Thanks for the links. i will check them out tonight when I have more time. Regards Bill.

[DIRTY ROCK STAR]

I agree with Heath, just my 2 cents.

I think it is all about perception and the way things feel to you.

[LOCKEE]

Can't believe it, a smart thread.

Bill is the mad proffessor of 4wding who actually builds and uses the stuff that circulates in his head.

[GRIMACE]

Bill is a great thinker and I look up to him for that - I often thing shit but never know how to get it out and admire people who put there thoughts into action unlike my own that just dwindle around amougnst all the other crap that goes on in my head.


THIS THREAD ROCKS.


ok now for my input - its not just the left front that comes off the ground its also the opposite force of the right rear that whats to compress down, sorta like a crossed up situation. So the people saying that to move all the heavy stuff to the right hand side isnt a good idea.

I am getting drunk as we speak so all this crap could be unter bullshit (as my signature suggests) but I think that it is hard to sort out this torque problem just by shifting weight more to one side.

I think you need to place stiffer springs in the rear right hand corner and front left hand corner and then place the wieght more centrally throughout the vehicle, but then i think this will be just like a normally wegihted vehicle with normal weighted springs and then i get confused and cant think and shit like that...................

But keep up the good shit fella and hopefully someone clears the shit in the way so i can see exactly what I am trying to discover


ok i better put this bucket bong outside

[bru21]

another train of thought. what about lots of little effects adding up.
ie, torque of motor - switch to transverse

torque of drive shafts - reduce diameter

panhard rods - under sudden load they shift to one side which may add to the problem. - a frames (hydraulic steer to combat draglink)

lastly i think vehicle balance. if you balance an obgect on an edge than move it off balance ever so slightly it falls in that direction, hence a small unbalancing force becomes a huge rollover action with gravitational effects. so does the driver torque etc cause that unballancing force, hebce body roll.

cheers, enjoy those sweet friday beers. i am

[slosh]

Could have already been mentioned, but putting the winch cable onto the left hand side of diff and pulling that corner of the truck down ( and thus rear right side up) while going up/ across hills should help a bit, as per the Mogrover. Simple to do, for trucks with winches at least.

[daddylonglegs]

Thanks guys but I am just an ordinary 4wd enthusiast who occasionally has too much time on his hands. Unfortunately that situation will change once my wife catches up with me.
Regards Bill.

[-Scott-]

There are enough stories here from people who wheel harder than me (OK, so that's not difficult ) for me to accept that this is a real phenomenon (if I spelled that correctly I need another drink. )

It is the torque of the drive shaft creating the problem. In low 1st the torque of the drive shaft is many times greater than the torque of the motor, so it will be the dominant force (or torque, to be more precise.) For those who don't believe me, grab Bill's Landy and demonstrate problem in high range, 4th gear.

Cheers,

Scott

(going for another drink anyway...)

[ozhumvee]

Bill
I've been 4 wheeling in Toyota's for 30 years so was aware of the torque effect on instabilty on sideslopes. I had noticed it and when I think about it I and lots of others unconciously pick the right hand line so that the sideslope counteracts it.
As has been suggected earlier in the thread IFS does seem to minimise if not cancel the effect out.
On the Humvee which has drop hubs, independant suspension and rigidly mounted diffs both ends I can honestly say that I haven't noticed it at all.
A CofG about 50 mm above floor level (which is a complete opposite to a laden troopy) does make a huge difference to stability off road.
The torque available at the wheels is pretty awesome after low range and then the 1.92 :1 reduction in the hubs, If I can get the front wheels up against a vertical wall it will climb it from a dead stop till the rear bumper touches the ground. what is funny though is that when you get up there it doesn't feel scary in the least.
Peter

[daddylonglegs]

Yes Peter, I think that the Humvee due to its extremely low centre of gravity is probably not a vehicle where torque twist would be a problem.
However, i am not really convinced at this stage that Independant suspension is not affected. I think the forces at work are the same, but a solid axle vehicle overturns in 2 stages. Stage 1,Transmission torque causes the vehicle to roll on its suspension until it reaches the critical balance point, and stage 2 takes over and the whole vehicle overturns.
On independant suspension there is generally less articulation and therefore less roll before the upper wheels lift and the vehicle overturns. So the perception is that the vehicle is on a sideslope that exceeds its static rollover angle and that transmission torque plays very little part.
I do not have an independantly suspended vehicle to experiment with. so I could be completely wrong. Bill

[ozhumvee]

The Humvee doesn't have a lot of travel but due to the wide stance and low CofG it rarely becomes a problem especially as you can BTM and lock the diffs so as long as one wheel is on the deck it will proceed.

[J Top]

Surely,rather than driveshaft torque,it is the effect of the pinion climbing the crownwheel that causes "torque twist".
Smokey Yunick recognised that engine torque caused Indy cars to push outwards in the early 70's and built a reverse rotation chev indy car which,
when booted into the corner, pulled the car down into the bend.
Some dirt track guys tried running a 2 gear drop-box,gearbox with the diff turned over to regain forward motion,however they found they were unloading the inside corner in the bends and, even with a locked diff, losing drive as the pinion climbed the C/W the other way.
J Top

[ISUZUROVER]

I have noticed the torque effect first hand as well.

On the Hummer though - I think the reason it isn't noticeable are the really heavy weight, wide stance and low CoG. It would require much more driveline torque to tilt a big heavy wide vehicle with extremely stiff springs like a hummer. I think with a lighter, narrower, higher CoG all independent suspension vehicle it would be more apparent.

This is a pic of my truck doing exactly what you are talking about Bill. If I stopped moving all 4 wheels were on the ground - when I started driving - no matter how slowly - it would lift the front left wheel off the ground.