Suspension Specific Bunfight Thread.

[bill van snorkle]

The front axle located by an ''A'' frame may lead to bump steer issues, although I built a hybrid, and a 6x6 once with a Watts linkage up front, which basically does the same thing, and bump steer never felt bad on either.

Bill.

[jacks906]

just had a skim read of this topic but what would happen in a cross axel (kinda way) situation would it not also belly out as the oppsing corners were pushed up and the others will push down

also just coz i cant work out what will happen, if you have an indy set up with a large amount of travel what happens with the drive shafts as the wheels drop will it not disconnect or are the arms set up in a way to address this

dave

[Night Train]

With an independent suspension the wheel moves up and down in an arc around the point where the track control arm or wish bone is connected to the chassis. The drive shaft would, normally, also move in a similar arc and a small amount of sliding in the cv joint would allow for that change in length.

To get a large amount of up and down range the track control arm needs to be long and in some cases have been attched to the opposite side of the chassis. The longer arm means that the drive shaft will need to have a wider range of extension and this could be allowed for with a sliding joint as found on a standard prop shaft. Another area of restriction is the length of the drive shaft which is limited by the width of the diff housing and the track of the vehicle. Longer drive shafts allow a greater range of movement but mean that the diff needs ot be really narrow or the vehicle needs to be really wide. As always, compromise comes in as does some weird and wonderful design alternatives.

[jacks906]

^^^^^^^^^^^^cheers night train^^^^^^^^^^^^

all makes sense now

i was thinkin the wheel an hub will stay vertical and true but never thought of the arc it would take

think will stick with me ridged axels

but will be keepin me eye on the thread see how it comes on

dave

[simonr]

As I suspect often happens - now my truck is nearing completion - I've had a better idea!

I've always had a bit of a fascination with walking machines - and even built a few 4 and six legged versions on a small scale.

I was watching people driving at Slab on the Howlin' Wolf and was thinking that although in some circumstances a walking machine would be good - much of the time, wheels are better. Feet come in to their own when traction is very limited and on very steep slopes / cross-axles.

Then there is the topical issue of how to get whatever you build through an SVA test.

An idea struck me which could satisfy all three.

Imagine a regular, road going flat-bed pickup, something fairly light weight like a Bedford Rascal. On the rear bed, build a 'contraption' with a pair of legs which, when extended arch up over the cab plus another lower profile pair at the rear. They need a knee and a single axis hip joint to allow the 'foot' to be raised, lowered and moved forwards and backwards. The leg itself will be springy enough to absorb side to side movement needed while cornering.

The foot on each leg consists of a hydraulic motor with a wheel attached on a two axis swivel such that it can steer (via regular hydraulic steer pump) but also rotate such that the wheels turn into big, circular pad feet.

On the road, and when you need to go fast, the 2wd truck wheels are on the ground and the rest raised above. In this configuration it is just a truck with an unusual load - no SVA required.

When you get to a site, you lower the hydrostatic wheels and drive around on those. Hydrostatic drive works well, except when you try to make it go fast. This way, you don't have to. 10 to 15mph would be fine.

When you loose traction, you roll the wheels (or even just one or two as necessary) to become feet and use the foot to push you out of the hole.

The cost of all the valving and rams would be frightening. In fact, even if you started with a hydrostatic drive vehicle - the cost would be frightening. I guess this is why you don't often see such things!

Si

[Paul Wightman]

Simon, you been licking the fungus off the garage wall again?

[jacks906]

you could in away do it to anything (but maybe wont be as extreme as legs but) by using the original parts an setup but swappin the struts an springs for some hydrolic/phewmatic rams etc would give you the advantage of being able to lower or raise any corner

dave

[Night Train]

I've seen recovery trucks push themselves along a bit when stuck by using their extending underlift. The army has been known to use their DROPS (big hook) pallet as a pusher to help them out of holes by unloading it against the ground and pushing the truck out in the process before reloading. I have also seen excavators and JCB's shift thenselves around using their back hoe bucket. So what you really need is a one legged Land Rover made with a back hoe arm off a JCB on the back. I believe they made one on a 110 chassis around 1990.

However, two back hoes would be even better, one on each side.