Vehicle stability off road.

[Strange Rover]

Its fairly easy to set up the links to cancle out the driveshaft torque twist although doing this isnt necessarly the best way to go.

Sam

[modman]

bill, any feedback as to whether the forced artic. on nigels hybrid helps with the torque twist?
from what people who have seen it climb say it never seems to scrabble like rangies in the same situation do.
david

[ISUZUROVER]

bill, any feedback as to whether the forced artic. on nigels hybrid helps with the torque twist?
from what people who have seen it climb say it never seems to scrabble like rangies in the same situation do.
david

Any more details on how this forced articulation system works - for those of us who won't have access to the 4x4 mag it is appearing in.

[daddylonglegs]

Yes Ben I experimented with my Hybrid Landy tonight. and I can drive the left front wheel up a vertical bank almost to the point of toppling and if I release the clutch but not allow the vehicle to roll back again, it stabilizes.
Reengage the clutch, it starts to go over, disengage clutch, safe again . Another thing I noticed tonight is when climbing diagonally out of a Wombat gully, the truck stayed much flatter when the front difflock was in compared to when I tried it unlocked.
And Sam, I did work out a while ago that it could be possible to design a suspension linkage so that the roll centre (axis) was higher than the centre of gravity, but because I wanted to keep my vehicle suitable for all round use I rejected the idea as too space intrusive. I was thinking "A" frames front and rear but mounted several inches higher on the axle than say on a Rangey. What are your thoughts?
Regards Bill.

[JK]

Surely,rather than driveshaft torque,it is the effect of the pinion climbing the crownwheel that causes "torque twist".

It's the same thing.

[ozhumvee]

As a matter of interest the Humvee weighs less than a lot of Cruisers and not much more than my troopy. The weighbridge 'wet' weight (not production weight minus fuel, oils, coolant etc) and complete with proper seats and everything required for ADR compliance is 2.7t.
Kevlar composite and aluminium body helps keep the weight down.
It is also relatively softly sprung, cruiser and patrol drivers are surprised by the ride especially over rough roads, most comment that 'wish my vehicle rode as well as this'.

[daddylonglegs]

Ben, I will try to explain the forced articulation in words, but iI wish I was able to drive this computer properly so that I could draw it for you.
I bolt a Landrover two shaft Implement drive box to the chassis just behind the t/case. I then run drive shafts from this to both the front and rear axle housings and attatch them more or less concentric with the axles roll centre. Therefore when the front axle articulates say in a clockwise direction, the angular difference between the front axle and the vehicle chassis is transferred via the driveshafts, through the implement box which reverses the rotation and forces the rear axle to articulate in an anticlockwise direction. As I mentioned in a previous post there are some losses due to backlash in the 3 driveshaft slip joints.
If space or cost is not an issue, the same or better results can probably be acheived hydraulically, pneumatically or via two longditudal/diagonal
torsion bars.
Bill.

[JK]

Interesting Bill. Some of the guys are running similar setups (in principle) on the shaft drive RC crawlers to counter the torque twist. Because many of the trucks run a cantilever shock linkage they can connect the FL canti to the RL cantilever and likewise the FR to the RR with long linkages.

This forces the same effect that you describe where the front is forced to articulate the same amount but opposite to the rear. By all reports it works very well.

Only downside is that they cancel out any shock absorption but that's OK cos they aren't looking for driver comfort

I know I'm banging on about the RC stuff but they are very accurate models of the full-scale stuff. We can go a lot more crazy cos the cost of a rollover is a lot cheaper.

[daddylonglegs]

Thanks jk. I have been unable to play the Vids from your website on this old steam powered computer, but the stills were very interesting and informative, and show those RC rigs have pretty amazing capabilities. As and when funds permit i think I wouldn't mind buying and building up an RC rig . Different ideas can be tried and proven much more quickly than re-engineering a full size vehicle and many of the principals should still work when scaled up. Regards Bill.

[ISUZUROVER]

Cheers Bill, that is very interesting.

[DFENDA]

Bill,
Would your idea of countering the torque twist be similar to Glen Dobbins hydraulic suspension on his ram raider 40 series featured in 4wd monthly

Peter

[Gwagensteve]

Sorry for the delay in posting on this thread, It's fascinating. My G certainly picks up WAY more on the left than onthe right. In fact I never recall my G every getting spooky when the RHS was up, only the left.

However, it always always feels fine until it picks up a wheel, then it feels like the car is going to fall over. This only happens though with a big compound angle.

The key to this (IMHO) is roll stiffness. The G has very soft springs and very similar roll stiffness front to rear. (but low in both cases)

I have lots of experience with Sierras, and in all repects, a coil sierra and a leaf sierra are identical except the suspension design. The Leaf cars pick up in a very predictable way, and I can't ever recall a big difference in behaviour from one side to the other. However, the coil sierra has high front roll stiffness (three link with outboard mounted coilovers) and very low rear roll stiffness with three link and very inboard mounted coils.

I think that the reason rockcrawlers are running rear swaybars now is to force the front down.

I don't think that compressing one side or the whole suspension in the front will help once a wheel comes off the ground, it will still go all light and adding power will induce a twist. - when my car gets spooky, it is when the front end goes to droop.

Same thing with "forced" but passive articulation - once a front wheel is in the air and the rear starts to fall over ( which will happen beyond a certain compound angle, regardless of car) adding power will cause the car to twist. I have seen video of the Scorpion falling over on a compound angle- once the front end started to get under the cars COG ( viewed from the front) and power was applied over it went.

The photo of my car was taken on KillerHill in Murrindindi, on a very high compound angle. how come the big angles always put the LHF up?

[christover1]

[christover1]

me too

[/img]

[bigjedd]

This is certainly a thought provoking thread. After reading this and thinking about it for a while I just thought Imight add my thoughts to the discussion.

I am wondering if more than just the torque effect of the motor, drivshafts, and body flexing that is at work here.

On drag cars when the power was applied the torque would cause the front of the vehicle to lift and create a wheel stand as the tyres dug into the bitumen and the torque transferred to the crown wheel under power. As the wheels began to get traction and propel the vehicle forward the front would come down.

As was stated earlier if the rear wheels were to be cemented down the torque effect would be to try and lift the front of the vehicle around the crownwheel and if the torque was high enough and the vehicle light enough it could conceivably flipover.

Imagine the drill bit in a hand drill is the rear axle and the hand drill is the crown wheel and pinion. when the drill gets stuck the hand drill rotates in the opposite direction to the drill bit. Perhaps this lifting force is what is contributing to the wheellift being that the high side of the vehicle in the sample given would be closest to the cog. On the driver side the twisting effect of the motor and drive line would tend to be away from the normal direction of rotation and so not be so pronounced.

I am interested to find out what the difference in comparison would be if this test was done in both two wheel drive and four wheel drive.

[daddylonglegs]

Sorry, I haven't visited this thread for a few days.
Yes, it is strange that the people who originally made all those tracks cambered them the wrong way. Perhaps they drove everywhere in reverse gear!
BigJed. The difference between 2wd and 4wd is similar to the test I did climbing out of Wombat gully with and without front difflock engaged.
When disengaged the tendency to wind over its rear axle was much more pronounced because the left front wheel was either off the ground or had so little weight on it that the truck was effectively only 2wd anyway.
With front lock engaged the rear axle did not have to work as hard and the truck completed the climb out without tilting over as much.
Peter, I think glen dobbins system is much more versatile that the system I described, in that my system is passive and depends on gravity and the normal forces generated by the vehicles motion, wheras Glen can force his wheels down with hydraulic pressure. He can also counter the effect of side slopes.
I was just watching an old video of the2001 US rockcrawling championships and noticed that the more stiffly sprung trucks looked a lot more unsteady in off camber situations than vehicles with more articulate setups. Having said that, the truck that won was a J10 Jeep with fairly firm leaf springs front and rear. Walker Evans S10 Chevy with that weird front hung "A' frame seemed to have no articulation at all and was not competitive in that event.
Bill.

[TuffRR]

The photo of my car was taken on KillerHill in Murrindindi, on a very high compound angle. how come the big angles always put the LHF up?

Knowing that particular hill, I'd say it has very little to do with torque effects and more to do with gravity!!!

[Gwagensteve]

Interesting this about this hill is that there is a line that can be driven in it without the car picking up at all. after about one million tries, a sierra on the same day as mine was photographed climbed it like it was a flat track. -see the photo

I reckon that (in theory) this stiffer the car and more roll stiffness you have the better it will climb, and of course, the less torque reaction effect you have. Even if the front is picking up, a stiffer, higher roll stiffness rear will help to prevent that torque reaction instability.

Hence the applications of rear swaybars in sooo many rockcrawlers. I reckon that too many people build big travel in the rear ( becuse it is easy) and don't work hard enough to get the front to work. when we put sierra rear springs onthe front of a sierra we gain 1.5" of wheelbase, but gain about 4" of droop in the front. this REALLY changes the way the car climbs and almost eliminates the wierd picking up effects. The front will go to full articulation well before the rear, even when climbing moderately. (everything has limits) The rear has much higher roll stiffness than the rear due to spring spacing. ( this is the case for most leaf cars, while IMHO most coil cars have lower rear roll stiffness ( or feel like they do) than front due to bushing design, no swaybars, or higher COG.

By the way, the tourqu effect is FAR worse in an auto, where high torque can be applied with very low HP, and a car can be driven all the way up/over and then stopped ( pucker factor ) which is cool, but when you try to restart, boy does it hop around on tippytoes then!

[jeep97tj]

Alright it has been 2 years since this thread was started, and rock crawling has come a long way, so how do i get rid of my torque twist??

With the air shocks, 6:1 tcase and 39s Im suffering bad Is there any thing i can change on my supension to reduce this??

[Wendle]

Alright it has been 2 years since this thread was started, and rock crawling has come a long way, so how do i get rid of my torque twist??

With the air shocks, 6:1 tcase and 39s Im suffering bad Is there any thing i can change on my supension to reduce this??

a combination of very low anti-squat values, low spring rates, and very little rear axle bump travel from ride height works very well.
that might not suit your particular application though.

[Bentzook]

This is my forced articulation theory in 1.

[jeep97tj]

That is what my zuk looks like when i boot it up a hill . It bounces alittle aswell so it looks like i will be moving my upper arm mounts. Thanks

[GRIMACE]

this thread is good glad it has been brought up again.

a small winch on the rear left to pull the body back down to the diff (which is trying to rotate away from the body from to much traction and torque) would be a small startin point

I like bills forced artic setup and am thinkin of takin it to the next level... Ill build the gravitronII and make a thread about goin through yet another layer of gravity

[RUFF]

That is what my zuk looks like when i boot it up a hill . It bounces alittle aswell so it looks like i will be moving my upper arm mounts. Thanks

Are you sure you have enough oil in your shocks? Sounds like they are too soft.

[jeep97tj]

Front is 1" over full and the rear is full, using 7.5w oil

[christover1]

I use heavy duty springs on drivers side and normal/softer on passenger side.
This works for me to reduce front left pick-up without spending huge.
New bushes certainly helped heaps, too.

Its psychologicaly more scarey for me when passenger side is higher

christover

[Cheezy4x4]

We have spent alot of time on R+D and are trying alot on buggies ATM.
Playing around with tailshaft rotations and rear engines ect.
With the Rodent buggy we built the harder you drive at a hill the harder the front wheels push down (good for up hills but not as good down).

[hando]

Wow guys. Interesting for sure.

I reckon that 1000ft/lb of torque is wrong. V8 supercars don't even put out that much.

[ISUZUROVER]

Wow guys. Interesting for sure.

I reckon that 1000ft/lb of torque is wrong. V8 supercars don't even put out that much.

That is because they don't have the gearing of a 4x4. You can get unimogs with 2L engines that have 10000ft.lbs of torque.

[jeep97tj]

So no 1 else has this problem with air shocks? could it be because i have the air shocks sitting so low that there is not enough pressure in them?

When it happens the low side is just about fully compressed and the high side is nearly full extended, theses are with 16" shocks .