Newbie: Disco 6x6 from Spain

[Nigelw]

Mmmmmmmmmmmm...like it! It seems that two wheel stubs axles have been mounted in a rocker and then the rocker has been bolted to a single axle casing. Simple and effective.

Independent susp. front axle used at middle of chassis will certainly ease thing: no trailing arms, no A frame, no up-down moving diff that exceeds short propshafts angles...but wheel articulation will be far less than that of a beam axle, and I should find a same ratio as others diff.

Ratios are only ring and pinion sets, you can get them to match the front and back axles, as for articulation, it really won't be that important on the middle axle as it will be more stability on obstacles and terrain, the articulation needs are of the front and rear axles to enable the mid axle to bite and gain traction that will claw up or support you on the wat down, not acting so much as a see saw but I can't see a need for a centre axle to need as much articulation as the front and rear, and also looking at it from the point of view from space needs inside the vehicle, if it has too much articulation you need a faily substantial wheel box for it to go up in to and thus will have very limited passenger/load space as it will be a big wheel box from just behind the drivers seat to the rear door if bobbed as well!!!

For me it would be better tan trying to use a live beam axle in the centre, plus the torsion bars would be nice and close to the chassis without the need to worry for coil spring dislocation. Personally that's the route I would look to follow.

[o_teunico]

That´s true about wheel boxes. In my original mix-axle layout the wheel box (wich will act as seat box too) will be the same as that on rear axle (about 20-23cm tall) because my intention of using a rear std Discovery axle will make the up-travel of mid axle the same as the rear std one (limited by distance between axle casing and chassis-bumo stop).

A CappiTruck Jeep style layout was discussed here http://forums.lr4x4.com/index.php?showtopic=31845&page=2 Certainly this will require the extra tall wheel boxes you mentioned.

An idea taken from Bill van Snorkel´s design: some device that enables me from elevating rearmost or middle axle to my desire.

Maybe an hidraulic ram with "dead position" for inter linked bogie-style performance, fully extended for elevated rear axle and fully collapsed for elevated mid-axle.

A lockable rear axle steering could make 100" two axle "normal" Discovery by just the flick of a switch (or lever)

[o_teunico]

Maybe I will need some shallow racing style seats, but thin there is room enough under seats for a wheel box

http://imageshack.us/photo/my-images/203/p4060417.jpg/

[bill van snorkle]

Hi Teunico. I'm not sure that it is a good idea for me to jump into this thread, as I have long since abandoned the idea that I could build a 6x6 that would be superior in most crosscountry conditions when compared to my current portal axled 4x4. Anything's possible of course but having given it some serious thought for the past couple of years, such a vehicle would need to have a scaled down version of a Scammell Explorer or road grader type gear driven walking beam type rear bogie to allow for the maximum possible articulation so that the weight of the airborne rearmost axle doesn't become a massive counterweight when cresting a steep hill or hummock. What happens on crests with conventional twin rear axles is that the wheels on the middle axle effectively become the fulcrum of a see saw, and the weight of the rearmost axle,once it runs out of articulation, plus all the weight of the chassis/body rearward of the middle axle centreline pulls down with gravity and lifts or unloads the wheels of the front axle, so that in certain circumstances the only wheels providing traction are the wheels on the middle axle.

The other option I would have liked to have tried to build would be the shortest possible wheelbase 4x4 , but with a powered 'trailer' attached that only articulated in pitch and roll, but not yaw as in a conventional trailer, because experience with powered trailers attached to 101 FC Landrovers revealed that the trailer could push the prime mover on its side in certain circumstances.The result I would aim for would be similar to the prototype of the original Gamma Goat, built in Switzerland by Miel'e if I remember correctly. There was a short video clip a while back of one climbing up and over a wall.

Bill.

[Nigelw]

Hi Teunico. I'm not sure that it is a good idea for me to jump into this thread, as I have long since abandoned the idea that I could build a 6x6 that would be superior in most crosscountry conditions when compared to my current portal axled 4x4. Anything's possible of course but having given it some serious thought for the past couple of years, such a vehicle would need to have a scaled down version of a Scammell Explorer or road grader type gear driven walking beam type rear bogie to allow for the maximum possible articulation so that the weight of the airborne rearmost axle doesn't become a massive counterweight when cresting a steep hill or hummock. What happens on crests with conventional twin rear axles is that the wheels on the middle axle effectively become the fulcrum of a see saw, and the weight of the rearmost axle,once it runs out of articulation, plus all the weight of the chassis/body rearward of the middle axle centreline pulls down with gravity and lifts or unloads the wheels of the front axle, so that in certain circumstances the only wheels providing traction are the wheels on the middle axle.

The other option I would have liked to have tried to build would be the shortest possible wheelbase 4x4 , but with a powered 'trailer' attached that only articulated in pitch and roll, but not yaw as in a conventional trailer, because experience with powered trailers attached to 101 FC Landrovers revealed that the trailer could push the prime mover on its side in certain circumstances.The result I would aim for would be similar to the prototype of the original Gamma Goat, built in Switzerland by Miel'e if I remember correctly. There was a short video clip a while back of one climbing up and over a wall.

Bill.

I much prefer that idea Bill, although the Gamma Goat will be very old hat now, this is a pic of a concept vehicle from Mercedes

I think this would be much more appealing personally, it could combine the most compact 4X4 and also when coupled to the powered trailer it would be an amazing 6X6!!

[o_teunico]

Hi Bill,

Your point of view will allways be well apreciated. Your experience on 6x6 is priceless!

Dieseldog, Mercedes´aproach to GammaGoat design looks good. It will be great to make such thing with a Landy and make it road-legal.

In my off-roading experience (limited to 88" Santana and Disco) I have found turning circle one of the most limiting factor in Galician woods.

Mid-axled 6x6 with front and rear steering will give me an excellent turning circle, but I don´t know if i could be able to make it road-leagal and how will it behave at highway speeds. Maybe a lockable rear steering+elevated mid axle will give best of both worlds: excellent off-road capabilities and standard-like road behaviour.

[Nigelw]

Hi Bill,

Your point of view will allways be well apreciated. Your experience on 6x6 is priceless!

Dieseldog, Mercedes´aproach to GammaGoat design looks good. It will be great to make such thing with a Landy and make it road-legal.

In my off-roading experience (limited to 88" Santana and Disco) I have found turning circle one of the most limiting factor in Galician woods.

Mid-axled 6x6 with front and rear steering will give me an excellent turning circle, but I don´t know if i could be able to make it road-leagal and how will it behave at highway speeds. Maybe a lockable rear steering+elevated mid axle will give best of both worlds: excellent off-road capabilities and standard-like road behaviour.

Yes legality will be your biggest dictator but perhaps there is an amateur built SVA* type system where by it could be fully evaluated and tested if needs be?

Just thinking about the lifting of an axle set the idea of using a pair of macpherson air over shock springs and mounting them to the front or back of the bogie system, where by the shock absorbers would dampen the articulation of the bogies and when needed the airbag could be inflated to push either the back or front set of wheels down there by raising one set off the ground, air off and back to 6X6!

I personally think it over complicates things too much with either beam or independent wishbone type axles as you are trying to cram so much into 34" of space from output flange to prop flange to retain 100" wheel base, now if you were to try it with the extra 10" given by the wheel base of a 110 then maybe but still too tight and probably why many 6X6 vehicles don't lift an axle and also why they are always much longer, a 90 6X6 would be a real mission but I doubt very much without using hydrostatic drive whether you could make it work within the vehicles original length, maybe bobtailing is not much of an option either for the swinging bogies as the axle position as it is with the bogies on would probably see the rear most of the quarters re modeled as the wheel will be punching into the bottom of the D pillar!!

Sorry but running out of ideas my end, and especially with wanting to stay within such a tight wheel base!!

*(my apologies for that sequence of letters and by no means am I implying that it won't work blah, blah, blah)

[bill van snorkle]

There are 2 main engineering hurdles that must be addressed for a Landrover based version of the concept vehicle to work IMO.
The first is to get a sufficiently short wheelbase for the prime mover, but with enough propshaft length to allow good suspension articulation without incurring severe universal joint angles. On my old 6x6 I acheived that by mounting the rear axles back to front so that the differential pinions faced towards the rear of the vehicle and the diffs were offset to the left instead of right. On to each rear diff I bolted a gear driven drop box that raised the height of the input shafts in addition to lining them up with the transfercase output shaft.With vehicle on level ground the propshafts were almost straight and level with just 3 degrees of U joint angle to keep the needle bearings rolling. The wheelbase from front axle to leading rear axle was 74 inches and distance from axle centreline to transfercase output flange was around 10 inches from memory,but the leading propshaft was about 20 inches long, consisting of 2 wide angle Rangerover slip joints and about 2 1/2 inches of tubing.
The second engineering hurdle would be to build the 'trailer' tow/drive hitch so that the towing and driving mediums are concentric with each other and have enough universal joint articulation to allow the 'trailer' to acheive the kind of angles relative to the prime mover that are illustrated in those Mercedes concept vehicle photos.It is morning over here and I have to go out for the day, so I will try to address that issue tonight, but I'm not too sure yet how to do that without having too long a wheelbase between the prime mover rear axle and the 'trailer' axle. The 101Fc powered trailer hitch I thing had 60 degrees of articulation.I once had a tractor double Carden CV joint that operated to 70 degrees but it was only designed to run at a little over 1000rpm maximum.Maybe that is enough for the short duration that the outfit would be clambering up and over those extreme obstacles.
Bill.

[o_teunico]

I have been thinking about those 100" wheelbase between first and third axle beeing not enough...

I could move front axle+engine+gearbox (if I relocate batteries and change viscous coupling fan for electric front ones) for about 4"/100mm. Front wings and wheel arches will need slight modifications.

Rear axle could be relocated 7 inch further back with the kit used by http://www.4x4-xsoffroad.fr/ for making Defender 90 a 100" one.

This will see a 111" Disco.

[o_teunico]

I have also been thinking on linked second and third axle. Is it really a must?

Maybe some looooooooooooong shocks + x-prings will be enough to maintain contact between wheels and terrain.

[o_teunico]

About making it road legal...if I weld radius arms and A frame mounts for mid axle, along with spring seats/buckets, I could use it temporaly as a normal 4x4 Disco from monday to friday. On saturday morning I will swap rear axle (unbraked while testing) to welded mounts in middle of chassis , install a rearmost steering axle, with a slave cylinder moved by a master one located in the standard steering shock absorber mounts at front axle, and test it off-road at private land.

In sunday afternoon everithing will be reverted for road-legal monday run.

After some months testing this way, if approved, it will be made road-legal 6x6, if not, will be maintained in 4x4 form. One car, two configurations.

[bill van snorkle]

I played the Jeep video you posted DieselDog, it appears to have the same gear driven walking beams that have been available for Humvees, although Engasa in Brazil made similar units to convert trucks to tandem rear drive. That video also brought up an important point to me, and that is one of gearing. The jeep appeared to be a bit high geared, which would not allow it to take full advantage of the 6x6's cross country potential. Before I built my 6x6 I developed it's 4x4 abilities as far as I could with difflocks, flexible front suspension and low gearing.No point in having all that potential if your engine /transmission cannot generate enough torque to keep the wheels turning in extreme terrain at crawling speeds. the Disco's overall ratio in low low of around 44:1 isn't anything like enough for a high mobility 6x6.I would consider 65:1 crawl ratio the minimum acceptable for this type of vehicle. My old 6x6 had an 86:1 low low, which seemed great back then, although I have found the 275:1 low low low ratio of my 4x4 very useful on a number of occasions. Lower ratio crownwheels and pinions will help the Disco a bit, but are not as strong as the standard ratio, and if suspension articulation is insufficient there will be circumstances offroad where almost all the vehicles weight and drive torque will be concentrated on one diff, so they had better be strong. An Ashcroft crawler box would take care of the gearing, but apart from the expence, the PTO facility to drive the additional transfercase would be lost, so a diff mounted drop box would then be required to drive the additional axle assembly.

Bill

[bill van snorkle]

O-Teunico, I know they are getting a bit ancient and hard to find, but the best LandRover chassis for 6x6 conversions is from the Series One LWB 107'' pickup. The 'kick up' for the rear suspension starts at the same point as for the SWB but the chassis rails are longer and stronger and depending on transmission arrangement would allow for a primary wheelbase of 74'' without drastic modification.Fitting the Disco mechanicals and suspension components to one of those would save a lot of headaches with chassis work.

bill.

[bill van snorkle]

That suspended axle idea has resurrected my "half-track" project that I sketched some years ago.

It has nothihg to do with Centaur style half tracked Landys.

It would be just one chassis width track under t-box. This track will act as a skid plate and, when vehicle´s ramp-over angle was reached, will help the car crawling over the obstacle. This could be achived by car´s wheels pushing the car or by the track´s own motion, beeing obtained from PTO, hydraulic or electric motor.

Just an old-school pen and paper sketch I have made just minutes ago

And another one for the inter-linked coil suspension that will enable bogie style performance off-road

If you deleted the coil springs between the axle and cranked arms and substituted link rods,and inverted the cranked arms, you could sandwich a single heavy duty coil spring between the cranked arms in the location where you have an arrow pointing to 'rod'.Delete the 'rod' to allow the coil spring to do its thing. Similar to WW2 german 6x4 light artillary tractor, the Kruppe Protz KFZ 70.

BTW, the British/European method of determining the wheelbase of a 6x6 vehicle is to measure from the centreline of the front axle to mid distance between the 2 rear axles. So for example, if the distance between front axle and leading rear axle is 80 inches and the distance between the leading rear axle and the rearmost axle is 40 inches, then the vehicles wheelbase is said to be 100 inches,but would be described as

"100" BC 40'' , BC meaning distance between centres.So the turning circle in theory will be that of a 100 inch 4x4. The USA would describe the wheelbase as 80'' +40''.

Another thing to consider is that rear wheel steering generally requires much stronger CV joints than are usually used for front wheel steering.Disco CVs are really too small and weak for the job. Maxidrive Engineering found that they required the huge 115mm dia 101 FC cv joints to give good reliability on their 4 wheel steering conversions to Defenders.

[bishbosh]

If an improved turning circle is your main driver for this project I would suggest you simply fit fiddle brakes.

[Nigelw]

As opposed to doing a lot of moving of components why not make life a little simpler and not bother bobtailing or majorly moving the entire drive train and power plant forward and just cut the middle out of the chassis?

that would make fabbing up the back end much easier for the third axle to sit under, and then it would just be a shorter prop needed, the rear axle could follow a live beam axle from a 101 and a through drive from the rear of the disco axle, the 101 axle would make life so simple as it sits on leaf springs!!!

[FridgeFreezer]

I'd consider buying a 6x6 Volvo C304/6 and... um... actually if you do that you may as well bin the Discovery...

But if you really wanted you could steal the axles which are set up for 6x6 drive, plus give you portals, better gearing & difflocks.

Or shorten the 6x6 Volvo, which gives a very effective vehicle about the same length as a 110:

If the Disco engine is any good I suppose that would be worth dropping in to the Volvo.

Here's the same picture from the other side (apologies for V8bertha's face, it's always like that):

As you can see, they can hide behind each other.

[bill van snorkle]

I get the impression Fridge that there are still numbers of 6x6 Volvos around in the UK, is that so?

The propshaft from the transfercase to the leading rear axle on that Volvo pictured must be very short. Is it long enough to permit full articulation?

bill.

[bill van snorkle]

I have also been thinking on linked second and third axle. Is it really a must?

I seem to be useless at providing internet links, but if you Google '6x6 LandRover 101 cresting a dune', there is a short youtube video showing just how ineffective a 6x6 can be even on a minor obstacle when fitted with non linked suspension.

Note as the front wheels begin to climb the dune, the wheels on the leading rear axle lift off, thus concentrating the trucks weight on the 2 rearmost wheels and they bog down. After a couple of run ups the wheels on the leading rear axle reach the crest of the dune, but then the rearmost wheels lift off, thus concentrating the vehicles weight on the leading rear wheels and they bog down. Notice also how the leading axles wheels have now become the fulcrum of the see saw that I mentioned in an earlier post, and the wheels on the trucks front axle have unloaded.

[o_teunico]

Chopping chassis at middle will involve lot´s of calculations by an engineer and tests at mechanical lab for making it approved by spanish MoT and make it road legal.

Nice VOLVO, but have never seen one of those in Spain.

Bill, I think this is the 101 video you mentioned

Here is another one where we can see the see saw fulcrum problem in a ENASA/Pegaso BMR from spanish army

I was thinking that maybe some soft springs + x-prings will make it to behave like a walking beam. Just think in a situation like hte 101 in the dune:

-Front axle goes up to the dune

-Mid axle tends to be airborne BUT x-prigs push it to touch ground

-As part of the waight from mid axle has been tranfered to rear one, it´s soft spring will collapse AND thus lower the wehicles tail.

At the top of the dune, just the oposite: mid axle is compressed and rearmost one pushed to ground by x-prings.

Certainly rear CVs should be heavy duty ones and 4.75 cwp + lockers a must.

I will have a look at Kruppe´s suspension design.

BTW, how is a 275:1 ratio achieved?

[o_teunico]

Bishbosh, I have experienced fiddle brakes in farm tractors and aren´t as effective as they were suposed to be. I was quite dissapointed.

[q-rover]

Although I see you may be getting the Disco for free, i agree with Fridge in that why not get

a ready made 6x6? Although it would mean no project, by the sounds of it getting a modified

6x6 Disco approved in Portugal won't be easy anyway, and how much of a budget are you looking

at for the project?

http://www.shropshiregunbus.co.uk/vehicles.asp

[o_teunico]

Nice Pinzgauers!

In Spain ANY modifications MUST be approved by MoT. Some time ago I contacted an engineering company and a pack of: snorkel, coils, shocks, wheels and oversized 32" tyres for the disco was a 500 Eur. bill, just for paperwork. And these were moddifications that needed no calculations or extra trength tests...

My budget? Errr...I´m unemployed now, so it´s not going to be a short term project.

For about 1000 Eur I can grab my hands in a non road legal Disco for sourcing the axle+hardware, the extra LT230 and propshafts I will need and the rest of the car will be canibalished for parts and thus help to maintain road-going the Disco I have.

[o_teunico]

Mmmmmm...interesting

[o_teunico]

Yesterday I took some measurements on the Disco so I could confirm that there is enough space in the body for a mid axle.

White masking tape indicates a 50" wheelbase

And yes, there is enough space betwen seat base and door for a inner wheel arch. Thats great because moving the seat was not an option because spanish regulations ask for a strenght test (not cheap) if you modify seat locating points and want to maintain it road legal.

Moving engine forward will not be as easy as I thought...there are 4" betwen engine and radiator (this could be moved forward about 8" if desired, up to the bumper) but I´m not sure if the turbo and/or engine mount will foul the PAS box.

If I want to chop it at the ends I have nearly 16" at back and 4" at front. Redesigned front bumper will shorten the car by another 4" and rear one about 8". In total I could make the Disco 32" shorter.

Unfortunately I don´t see how I could use walking beam or similar arrangement without altering mid seat row´s door/access.