Outer Limits 4x4 Board

Ok - I have had a crazy idea for a rock buggy for a while now, and since I will probably never build it I thought I would post it up here to see what everyone thought.

The idea is basically for a buggy chassis without suspension, but with controlled articulation.

The idea came about because although suspension on a buggy is good (e.g. antisquat in the right range helps), there are lots of bad things about suspension e.g. suspension unloading on climbs or side slopes, torque-flexing of the chassis/suspension, etc...

I though of 2 possible ideas:

(1) a centrally pivoting chassis (like a skidder) that is hydraulically controlled - hard part would be weight distribution between the two halves, and you can only have counter-steer, not crab steer. The advantage of this system is you could use two non-steering axles (more strength). It could also be setup to raise the centre of the vehicle when necessary to stop bellying out.

(2) a "strut" or "mast" projecting forward of a reasonable normally designed central chassi section. Each axle would then be located on a pivot so it could revolve (atriculate), but not move forwards or backwards. This design would have normal (steer/non-steer or steer/steer) axles at both ends. The articulation of the axles could be controlled by air-shocks at low pressure or some sort other method.

So, what does everyone else think? Is this a crazy idea? Is suspension critical on a buggy or only articulation?

Couple of reasons i could think of would be "bumping" a ledge, coming of a steep drop off or even scrambling for traction on a slightly more all terrain section of a course.

I think that there is more to suspension than antisquat, articulation etc, and a lot of that can be dialled in/out during design and through inbuilt adjustments - though it takes some research to learn and comprehend it. Suspension is also about stability, durability and comfort from bump and shock absorbtion which I think is important. Cheap is good though, and I suspect the spirit (not that I have followed the evolution of rules at all) of the legends class when it was RHS chassis, was to promote cheap donor chassis and simplicity for Joe hack to kit up and race on.

Don't get me wrong though, I like your thinking.

I think it would be awesome if all tracks had smooth transitions. Say you're rocketing up a steap climb and you hit a small step up just before the top, without any suppleness, you'll have wheels in the air then over you go. If some "give" or "suppleness" could be introduced to the system then it may just work.

If I am understanding u correctly, I think I've been pondering the same thing. The front axle on most tractors is on a pivot with no springs (back axle fixed of course to rest of tractor) and it's amazing what u can drive a 4wd one thru! It doesn't need smooth transitions either to climb up stuff.
Shame u can't use the front 4x4 diffs under WE rock rules, they would be so perfect no Dana would come close.

I don't think steering by articulation in centre would work- turning across an off camber situation would cause the buggy to falll over. Articulated tractors are lethal on hills.

If you were to add suspension (would be nice on drop offs!) it might be able to be added behind the front diff pivot like the rear swingarm on a bike, then rest of chassis behind that.

To control the flex maybe a disk brake and caliper mounted in line with pivot point and manually restrict movement or at least dampen it when needed.

Or maybe a better idea to have active rear suspension and leave the front free.

the idea is good but as mentioned, how smooth is the ride....
I thought about silly things such as the articulating chassis and then having a standard setup at each end with the diff able to articualte but only buy 5 or so inches.

So basically take a normal buggy set it up with 8" air shocks over each diff with an RTI of about 400, then make the adjustments and further mods to have it articulate at the centre...

Its all too hard for me to image, but i am sure sum of the more detailed enthusiast can work it out

Yes, the biggest drawback would be on dropoffs and ledges/uneven sections.

I did think that if the tyres were big enough and soft enough they would have some slight dampening effect???

It would be possible to build in some suspension as well, but would make the setup heavier and more complex.

Slosh - you are right that if using option 1, turning downhill on a sideslope would cause problems.

ISUZUROVER wrote:Yes, the biggest drawback would be on dropoffs and ledges/uneven sections.

Lucky there are not many of these at a Rock Crawling Comp.

Crazy Buggy Idea? Absolutly!

i think you mean like the lego crawler i made. works on the same principal, and ive always wanted to make a mini one to see how it would go.

that is cool

Spike_Sierra wrote:i think you mean like the lego crawler i made. works on the same principal, and ive always wanted to make a mini one to see how it would go.

Yeah, that is basically what I was talking about for idea (2). Each axle is fixed on a pivot and can only articulate.

Looks like your C of G is a bit high in that buggy though

tenic lego is so cool

It's a similar principle to many heavy earthmoving machines.

I'd still like some suspension capability for those sudden transitions. Having no "give" at all is asking for a rollover.

Problem is going to be rules for power delivery - dont many comps require single engine and driveshafts?

Managing driveshaft angles in this sort of setup could be a major pain - many of those types of earth movers use hydraulic or electric power transfer.

Beastmavster wrote:It's a similar principle to many heavy earthmoving machines.

I'd still like some suspension capability for those sudden transitions. Having no "give" at all is asking for a rollover.

Problem is going to be rules for power delivery - dont many comps require single engine and driveshafts?

Managing driveshaft angles in this sort of setup could be a major pain - many of those types of earth movers use hydraulic or electric power transfer.

The only difference is that lots of tractors and earthmovers have only one end that can articulate. If the pivot was built as close to the pinion as possible then I don't see that the driveshaft angles wouldn't work with a CD or CV propshaft.

ISUZUROVER wrote:

Beastmavster wrote:It's a similar principle to many heavy earthmoving machines.

I'd still like some suspension capability for those sudden transitions. Having no "give" at all is asking for a rollover.

Problem is going to be rules for power delivery - dont many comps require single engine and driveshafts?

Managing driveshaft angles in this sort of setup could be a major pain - many of those types of earth movers use hydraulic or electric power transfer.

The only difference is that lots of tractors and earthmovers have only one end that can articulate. If the pivot was built as close to the pinion as possible then I don't see that the driveshaft angles wouldn't work with a CD or CV propshaft.

You's be better off with the pivot higher in my opinion. With the increase in roll axis height, the chassis would be like a pendulum and be REALLY stable!

In Top Truck Challenge 03 there was a yellow 'Jeep' that had axles pivoting in the centre ala tractor front end with air bags controlling the articulation. Watching the footage it wanted to 'pig root'/hop alot when climbing and in the truck pull event but seemed to work fairly well in slow speed stuff.

http://www.fourwheeler.com/featuredvehi ... dex14.html

Cheers
Daryl

beebee wrote:
You's be better off with the pivot higher in my opinion. With the increase in roll axis height, the chassis would be like a pendulum and be REALLY stable!

Interesting idea - only problem I can see is the chassis can swing out further on side slopes, making the CofG worse (oh no - we are getting into Marcus's territory here...). As well as making any propshaft problems worse

derangedrover wrote:In Top Truck Challenge 03 there was a yellow 'Jeep' that had axles pivoting in the centre ala tractor front end with air bags controlling the articulation. Watching the footage it wanted to 'pig root'/hop alot when climbing and in the truck pull event but seemed to work fairly well in slow speed stuff.

http://www.fourwheeler.com/featuredvehi ... dex14.html

Cheers
Daryl

Interesting, any vids of it in action?

so something like this "RIP SAW"?
<http://videos.streetfire.net/Player.asp ... F5D02E2DAA>

bushy555 wrote:so something like this "RIP SAW"?
<http://videos.streetfire.net/Player.asp ... F5D02E2DAA>

That is nothing like what we are discussing here. It would suck at rock-crawling.

derangedrover wrote:In Top Truck Challenge 03 there was a yellow 'Jeep' that had axles pivoting in the centre ala tractor front end with air bags controlling the articulation. Watching the footage it wanted to 'pig root'/hop alot when climbing and in the truck pull event but seemed to work fairly well in slow speed stuff.

http://www.fourwheeler.com/featuredvehi ... dex14.html

Cheers
Daryl

Yeah, 03 was a different year indeed. Off track to what's been discussed already was the articulating chassis M37. All the shots I saw of it had wheels way up in the air. http://www.fourwheeler.com/featuredvehi ... dex13.html Apologies for the size of the pic. I wouldn't mind seeing any vids of either this, or the "Jeep" that competed in 03.

Interesting topic though. Barring the complexities of the driveshafts, clearance etc, The pivot height in relation to the COG, or even relative to vehicle mass is an intriguing thought. Practicalities aside of course.

Interesting stuff - here is another pic with the wheels on thr ground.



The reports of both these trucks in action bring up some interesting points - a (well designed) damped suspension system at each corner can stop or limit "axle tramp" - pig rooting, etc, and help keep the wheels on the ground. both of these trucks seem to have relatively no damping to the axle articulation, which it would seem the system needs if it is to work properly.

isnt this how a gama goat operates?