Hi Luke,

I haven't really decided what kind of vehicle to build on yet. Nyathi's outer dimensions were determined by the need (wish) to fit in a 6m shipping container. Relaistically, if I go bigger, a high-top container, or even an open-top container probably will be too small. So I have a blank sheet of paper to start with.

We want to be able to live inside, to give us the possibility of travelling in colder climes. (Nyathi was designed to live outside, as we wanted to be "camping", and we planned our route and timetable to make that possible and pleasant).

We also still want to be able to go anywhere that wheeled traffic can go, and be reasonably self-sufficient for a couple of weeks. I am leaning towards a 'Mog, but wary of the complexity. The slow speed is also unattractive, but we like to travel slowly anyway. Besides, a comparable vehicle could very rarely do even 100km more in a day than a slower Unimog.

My biggest fear of a compromise is ending up with a vehicle that has almost all the drawbacks of smaller campers, and almost all the costs and other problems of a big truck. I'll tell you what, you go first, and tell me how it worked out!? :-)

Back to the diff thing: I'll grant you that I didn't give much thought to the actual figures I used in my sums, but it's hard to work out what actually happens unless one quantifies the principles with some numbers. Now that I have thought it over, 2000Nm doesn't seem an unreasonable number to pull a 2000kg car up a gradient. (200Nm from the engine, and a 10:1 overall gear ratio in, say, 2nd gear?).

As you can see, I am not fully employed at the moment! :-)

Hi Peter: I wasn't aware that any Rovers made use of worm-type Torsen diffs(?) Or do you mean if you fit a Torsen as an after-market diff? Are you saying the use of ETC makes the performance of the Torsens worse, or that they are just terrible anyway?

(Of course LSDs and Torsens both make use of friction to slow the spinning wheel, but they do so by slowing the planetary gears, and not the shafts. That's why the friction clutches and worms don't present quite the same wearing-out problems as the brake pads in the case of a TCS. I'll leave it to a braver person than me to try and analyse a mixed ETC/Torsen scenario with some torque numbers!)

Cheers,

Michael...




[This message has been edited by SandyM (edited 11 November 2005).]

(QUOTE)

(In practice, TCSs tend to substitute independently progressive braking with a series of momentary "grabs" at a wheel. The frequency of these grabs does much the same thing as progressive braking, but a bit more sloppily. A system with independent braking pressures at each wheel would be hugely complex, I imagine. But the overall effect of the simpler system is very similar to what I described.)

Michael,
Sorry, thought you were talking about using LF Braking...
In this paragraph about braking - I see you were saying that in Theory, the TC should cut in in one progressive pulse. In Practice, if it did this the engine would stall before we can add throttle, thats why it has to pulse, so it slows the wheel even more progressively.


I understand the Diff Dynamics that the torque loss depends on the resistance level on the wheel, more wheelspin/less grip = less torque to both wheels, not just a single wheel.
What happens in Practice on the ground is the nice heavy hub, wheel and tyre on the end of the halfshaft have Momentum and this is why alot of the time when a wheel spins out (even in contact with the ground) the effect is total loss of resistance, it just keeps on spinning until the terrain changes enough to overcome the momentum - like a total lift off the ground.

I see what you mean with the extra power requirements theory, but again in practice, the fact that we are in low range with the CDL engaged - (lessening the power required) means there is plenty of torque there to overcome this.

Theres no doubt that the rear and front lockers are going to get you further in a straight line, but the TC system works a treat and has less potential to damage transmission it also means you can fight the wheel instead of having to constantly flick switches on and off.

When we are Teaching people to drive LR products, we still place the emphisis on ground reading and correct momentum, with the TC as something that will kick in if its needed.

Im just going for a spin on me bike, with its nice efficient chain drive and no diffs !!!
Cheers Guys
Grif

Torsen ‘worm’ type diffs have screw cogs for their planetaries. Initially they were incapable of dealing with really torquey engines and stripped regularly.
Detroit bought rights to the design and applied their metallurgy knowledge to it, creating the Detroit Trutrac (sp?) which is nicely toughened up.

I’m trying to work out the meaning of Peter’s “terrible” in large parts of the continent that’s come to mean good (the way “wicked” has been twisted in English)

“Live in” vehicles: A new thread perhaps?

Luke, I didn't know Detroit bought the torsen rights, but I have to say I have always been confused by all the various brand names and variations of each type of diff. I seem to remember the Easton(?), which was also a torsen type(?).

The torsen concept was very elegant - worm gears can drive, but they can't be driven. So by using them in the planetary system, the half-shafts can force the planetary gears to turn back and forth (as when cornering, the outer wheel speeds up and the inner slows down), but the crownwheel can't turn the planetary gears at all (which it would like to do when torque drops at one wheel, such as when traction is lost).

I can see why they would strip, though - if you open up a torsen, you can't help admiring the engineering feat required to fit all those carefully cut worm gears into a casing the size of a diff!

Grif, I am not really on a crusade against TC, though reading back what I wrote, it may seem like it! I stand by my observation about power sapping, even though most often it's not an issue because of low gearing. I have experienced it only once as a noticeable problem, when towing heavy trailers up steep (asphalt) mountain passes. Getting up the passes in dry weather, the TD5s needed low range 2nd and 3rd. When the asphalt got heavily rained on, the TD5s with ETC really struggled, even in low range 1st! And when we got to the top, I reckon the brakes had worked harder than if we had been going down the hill - they were extremely hot.

On the other hand, we only had one vehicle without ETC (and no axle lockers), and he couldn't make it to the top! So ETCis very effective, no question about that. It follows that whenever power is sapped by ETC, it is because wheels are spinning, and at that point, an otherwise-identical vehicle without ETC will be stuck.

Have fun on the bike, Grif - I assume you have given thought to converting it from 2x1 to 2x2??? http://www.horizonsunlimited.com/ubb/smile.gif

Rgds,

Michael...

Luke,

Thanks for the input. And yes, it's great fun with an expanding family. Never knew a baby could be this much fun actually! http://www.horizonsunlimited.com/ubb/smile.gif

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Hi Sandy, Hi Luke,

the aftermarket improved "Torsen" diffs are from Quaife (www.quaife.co.uk) - as the worm gears are parallel to the halfshaft-axis, there ist even more teething in contact and some friction plates deliver a base load.

Yes, seems someone taught me english dialect: The Quaife-equpipped Rovers with ETC are marvellous. http://www.horizonsunlimited.com/ubb/wink.gif

Regards,
Peter

Thanks for clearing up that misunderstanding, Peter. I have heard good things about the Quaife, although never actually used one or seen one in use, to my knowledge.

Rgds,

Michael...