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View Poll Results: Diff locks or Articulation, what do you choose?
Diff locks - I think they are more important than articulation 21 61.76%
Articulation - With excellent articulation, diff locks are not really needed 13 38.24%
Voters: 34. You may not vote on this poll

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Old 25th March 2010, 09:00   #46
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Quote:
Originally Posted by '72 Bullet View Post
One reasoning is that as the gravitational (wheel down) force is going to work on the COG, the higher up it is, the more of it is going to be diverted into pulling you backwards. Does that sound right or is it just me? A diagram of course would help here.
During lateral load transfer conditions (cross articulation), the suspension should do all the hardwork i.e. it should flex, otherwise the wheels will be in air. I am attaching a pic for clarification.

Quote:
Originally Posted by '72 Bullet View Post
On a gradient, the wheel down force will be Tan A X Tmax and in this case, Tan 45 is 1/2. (I seem to forgetting alot of my basic triginometry, so am not 100% sure, Spike pls. help).
The lower your CG the lower the chances of rollover, there are two things which determine rollover 1. CG. 2. Track width (there is a relation between these two which most of you may be knowing).

Spike
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Old 25th March 2010, 09:09   #47
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Spike: Can you give the numbers for a mm540 for the above? This will make non technical students like me understand better
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Old 25th March 2010, 09:31   #48
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Quote:
Originally Posted by '72 Bullet View Post
Interesting.. Was thinking that articulation may help the vehicle squat (or weight transfer in another way) and somehow help it.
If the surface is even, articulation has no role. If all tyres are subjected to same amount of traction, diff locks have no role. Considering the above conditions at cet par, whether you can climb a hill or not becomes a mathematical function of traction and momentum. Once the gradient overrides the available traction, momentum becomes key.

Like in any scientific analysis, when we are discussing effect of steepness or gradient, one has to consider it at cet par (cēterīs pāribus). You can't bring other IFs and BUTs into the equation. If you are not from scientific/engineering background, this might take some time to adjust.

Quote:
Originally Posted by fiery enzyme View Post
@ Arka, Why LSD in the front when you can have the locker? Its only going to be called in when it is needed anyway (I'm not talking air lockers here, im referring to free wheeling hubs). I'm saying we as well as might go all out.
Lockers are entirely different from free wheeling hubs. If you don't lock the FWH, you are in 2WD. When you lock the FWH, you will be in 4WD. On the other hand, Lockers determine how your differential behaves in case of lack of traction in any wheel.

Last edited by Samurai : 25th March 2010 at 09:32.
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Old 25th March 2010, 10:32   #49
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Quote:
Originally Posted by fiery enzyme View Post
This is why 'pump the throttle' technology was invented

@ Arka, Why LSD in the front when you can have the locker? Its only going to be called in when it is needed anyway (I'm not talking air lockers here, im referring to free wheeling hubs). I'm saying we as well as might go all out.

@ 72 bullet, Good articulation becomes a necessity if the uphill track is very uneven. A good example is the track that vinod put pictures of. Right?
Hi Bala,

Pumping The Throttle is basically to build up and retain the Fly-Wheel Momentum.

Front Locker, will make the vehicle very-very hard to steer in 4WD, and considering the Chennai OTR scenario it is Overkill.

It will further reduce the ability to rapidly change direction.

Absolutely right about the Articulation and Climbs.

Regards,

Arka
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Old 25th March 2010, 10:50   #50
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Post Traction

Traction means Resistance or Traction=Reaction Balancing.

Traction Limit- production tires on a dry paved surface can generate coefficient of friction of 0.7-0.8

In the figure attached (pic 4)the red line shows the application of brake force/brake torque, the direction of which is opposite to the direction of wheel rotation(marked in blue). The weight of the vehicle and the braking force is marked in black arrows. Please note that the brake force and the braking force are different, brake force is the force applied to the wheel cylinders whereas braking force is the opposing reaction which comes from the road loads. What happens if the brake force exceeds the braking force? Simple, your wheels get locked. ABS works on this principle and controls the brake force only.

While accelerating from standstill on a plain road there are no roadloads corresponding to Aerodynamic forces and Gradients (Slopes), assuming no hitching loads the only force acting now is the weight on the wheels and the rolling resistance.

Once an acceleration level is attained aerodynamic loads, gradient loads may creep in depending on the conditions, rolling resistance although present it is less dominant. I am attaching a pic (3,5)which shows how rolling resistance changes.

Also showing (pic 1,2)the acceleration simulation of a vehicle with two types of road surfaces ('f'=1 and 'f'=0.6), notice the acceleration level attained. This is simply a case of Traction Limited Acceleration.
Hope this clarifies.

Spike

P.S. There are lot many topics like g-g diagram, friction circles which are based upon the basic funda i mentioned above,these are useful for study in Vehicle Dynamics.
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Do Diff locks compensate for lack of articulation?-1.jpg  

Do Diff locks compensate for lack of articulation?-2.jpg  

Do Diff locks compensate for lack of articulation?-5.jpg  

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Last edited by SPIKE ARRESTOR : 25th March 2010 at 10:58. Reason: photos jumbled up
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Old 25th March 2010, 11:55   #51
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SPike,
I knew that you were good in academics but never knew you have a good professor hidden in you! Wondeful

Spike lets take topic by topic and understand. We were talking about tractive force at wheel. Now in the give situation how do you calculate the tractive force for my MM540 for eg-

Engine- 12.2 kgm @ 2000 rpm
Transmission - Kia KMT 90 T 18
Tyre Dia - 29 inches

Can you explain us what would be the final torque at the wheel, considering transmission losses, rim weight, width of the tyre etc etc
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Old 25th March 2010, 12:06   #52
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Quote:
Originally Posted by Samurai View Post
If the surface is even, articulation has no role. If all tyres are subjected to same amount of traction, diff locks have no role. Considering the above conditions at cet par, whether you can climb a hill or not becomes a mathematical function of traction and momentum. Once the gradient overrides the available traction, momentum becomes key.

Like in any scientific analysis, when we are discussing effect of steepness or gradient, one has to consider it at cet par (cēterīs pāribus). You can't bring other IFs and BUTs into the equation. If you are not from scientific/engineering background, this might take some time to adjust.

Sir, I understand the cet par bit. The heart of the matter is that traction available on a gradient will be Tan A X Tmax (cet par). Period.

Now that this has been established, was wondering what other parameters come into
play. Terrain as you mentioned is one, what about COG?


Lockers are entirely different from free wheeling hubs. If you don't lock the FWH, you are in 2WD. When you lock the FWH, you will be in 4WD. On the other hand, Lockers determine how your differential behaves in case of lack of traction in any wheel.

Yes, lockers are different from FWH. What fiery enzyme is saying is that there's no harm having lockers up front as while driving on the road, the FWHs prevent them from coming into play and ruining your ride (in both senses).


No diagram from anyone as yet (spike please help). Diagram for this is very simple, just a vehicle going up a gradient and the forces applicable at COG being highlighted.

Last edited by '72 Bullet : 25th March 2010 at 12:07. Reason: change format
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Old 25th March 2010, 12:24   #53
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Post Calculations

Quote:
Originally Posted by vinod_nookala View Post
SPike,
I knew that you were good in academics but never knew you have a good professor hidden in you! Wondeful

Spike lets take topic by topic and understand. We were talking about tractive force at wheel. Now in the give situation how do you calculate the tractive force for my MM540 for eg-

Engine- 12.2 kgm @ 2000 rpm
Transmission - Kia KMT 90 T 18
Tyre Dia - 29 inches

Can you explain us what would be the final torque at the wheel, considering transmission losses, rim weight, width of the tyre etc etc
Vinod, this calculation would have been much simpler, had i known the torque available at the wheels (chassis dyno), or else you can use the thumb rule that i mentioned in my previous posts. If you wanna know the real calculations that would require a huge amount of data like the designed individual efficiencies of engine,clutch,transmission,propeller shafts (basically the whole power train), also the inertia and angular acceleration values of all these components will be required. I am attaching a equation which will give you some idea. Anyway, i will try to work out those calculations and post them after some time.

Spike

Courtesy- Vehicle Dynamics by Thomas Gillespie (beautiful book, considered as the Bible of Vehicle Dynamics)
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Old 25th March 2010, 12:32   #54
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Quote:
Originally Posted by '72 Bullet View Post
Sir, I understand the cet par bit. The heart of the matter is that traction available on a gradient will be Tan A X Tmax (cet par). Period.
Boss, the cet par comment was for the benefit of non-scientific background people who may be unfamiliar with that concept. I didn't mean you.

Quote:
Originally Posted by '72 Bullet View Post
Yes, lockers are different from FWH. What fiery enzyme is saying is that there's no harm having lockers up front as while driving on the road, the FWHs prevent them from coming into play and ruining your ride (in both senses).
Because it will be an overkill. Whenever you are in 4WD, you will have full lockers on the front. It will be hell to turn.

Quote:
Originally Posted by '72 Bullet View Post
No diagram from anyone as yet (spike please help). Diagram for this is very simple, just a vehicle going up a gradient and the forces applicable at COG being highlighted.
This is better left to Spike.
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Old 25th March 2010, 12:43   #55
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Post Forces acting on a vehicle

Quote:
Originally Posted by '72 Bullet View Post
No diagram from anyone as yet (spike please help). Diagram for this is very simple, just a vehicle going up a gradient and the forces applicable at COG being highlighted.
Your wish is answered, here it is:-
Please note that Da is Aerodynamic force, W is weight of vehicle, R is rolling resistance, F is tractive force Rh is hitch/drawbar force, h is height of CG from ground. Hope it is clear now.

Spike

P.S. There are people who even after knowing all these forces/diagrams don't feel this while they are behind the steering wheel, i consider myself lucky and proud that i know both. I think members here have a good "feel" of the vehicle. The basic intention of sharing this was to bring out simple concepts that we come across in our day to day lives. No one taught me (corporate life), i have learnt it the hard way.
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Last edited by SPIKE ARRESTOR : 25th March 2010 at 12:45. Reason: add info
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Old 25th March 2010, 12:50   #56
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Love the direction this is taking. Although being a non engineer some thing may fly above my head but reading it few times is opening mind to possibilities vis practical considerations.
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Old 25th March 2010, 13:21   #57
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Default merge

Articulating on ARTICULATION

http://www.team-bhp.com/forum/4x4-te...iculation.html (Articulating on Articulation)

Mods can the above thread merged with the current one?

Regards,

Arka
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Old 25th March 2010, 13:56   #58
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Quote:
Originally Posted by ex670c View Post
@ADC

The Rear Axle does most of the work on Road and Off-Road.

Between an LSD & Locker, LSD Front & Locker Rear.
This is because the LSD fades with regular use, and since it does not lock up its better on the Front Axle, relieves the steering during OTRs. On Road The Front LSD can be negated with FWHubs.

My Preference is LSD Front (with FWHubs) and Locker Rear.

Regards,

Arka


Quote:
Originally Posted by khan_sultan View Post
Yes, good input. locked rear diff will cover ~70% of your needs.

Again, a very good input and the way to go.


Thanks again Arka and KS for validating it.


But the thought that still lingers - with IFS and rear momentum, the front will lift easily on a up track or a hump and when it comes down, it really comes down hard With 100% torque going into one of the free wheels. All those wheelies out of a ditch, making great photos, will break or weaken things in the IFS system.

The rear traction is solved by momentum and LSD [good one], the front with selectable or even good auto lockers. Idea of thought is with IFS it is not an overkill but a necessity but it requires very good judicious use and will depend on the track terrain and 4wd instincts as they develop.


Another thing with LSD or autolocker in front, is that it will be reactive than being pro-reactive, ie, with selectable locker I am seeing the terrain, thought process is there and then selecting it as and when necessary, most probably in very short bursts of few seconds duration.

So with IFS system, listing the benefits with front locker in front with a good rear LSD [already supplied as OEM] at the back:

1. Keeping the front down, pulling action, solving the bad articulation of IFS.


2. Going through crawl motion over up obstacle rather than gunning up through pedal and momentum. As the IFS lands it takes up huge pressure, since the rear is giving all the momentum and traction, and the front wheel [right or left] which comes down first takes a huge impact, big obstacle, big jump something will break or at least will soon have to run to change tie rods and all.


3. Over a front LSD, a selectable locker will be proreactive, ie, before the situation develops where a front wheel is going on top.


But all said and done, with improving technologies a good auto locker is what is most required for a front differential of IFS system as a selectable locker [though the best] will require very good judgment all the time.

A front LSD will still act as a locker for quite sometime even in turning and steering should remain difficult, at least at the beginning of the turn?


This all theoretical for me, and definitely surely somewhere the argument of mine is not okay!. Please do give your views.

Last edited by adc : 25th March 2010 at 14:07.
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Old 25th March 2010, 14:19   #59
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Default Over-Reactive

Quote:
Originally Posted by adc View Post
another thing with LSD or autolocker in front, is that it will be reactive than being pro-reactive, ie, with selectable locker I am seeing the terrain, thought process is there and then selecting it as and when necessary, most probably in very short bursts of few seconds duration.

So with IFS system, listing the benefits with front locker in front with a good rear LSD [already supplied as OEM] at the back:


3. Over a front LSD, a selectable locker will be proreactive, ie, before the situation develops where a front wheel is going on top.

But all said and done, with improving technologies a good auto locker is what is most required for a front differential of IFS system as a selectable locker [thought the best] will require very good judgment all the time.

A front LSD will still act as a locker for quite sometime even in turning and steering should remain difficult, at least at the beginning of the turn?
Hi ADC,

I think you need to go for a few OTRs.
Open Invitation from the Chennai JEEPers.

Please Do ONLY the Following

If you have ONE Locker/LSD - Fit it in the Rear

If you have TWO Locker/LSD -Fit one at either end.
Front with FWHubs
.

If You have ONE Locker & ONE LSD - LSD Front & Locker Rear.
Front with FWHubs
.

If You have ONE Diff-Lock & ONE LSD - LSD Front & Diff-Lock Rear.
Front with FWHubs
.

If You have ONE Diff-Lock & ONE Locker - Locker Front & Diff-Lock Rear.
Front with FWHubs
.

If You have TWO Diff-Locks - One Front and One at the Back.
Engage Rear Locker First
.

LSD - Limited Slip Differential
Locker - Auto-Locker/Dog Clutch LSD/Aussie Locker/Lokka
Diff-Lock - Selectable (On/Off) ARB/OX/ECTED

Regards,

Arka

Last edited by ex670c : 25th March 2010 at 14:30. Reason: addl. info
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Old 25th March 2010, 14:38   #60
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Quote:
Originally Posted by SPIKE ARRESTOR View Post
Your wish is answered, here it is:-
Please note that Da is Aerodynamic force, W is weight of vehicle, R is rolling resistance, F is tractive force Rh is hitch/drawbar force, h is height of CG from ground. Hope it is clear now.

Spike

P.S. There are people who even after knowing all these forces/diagrams don't feel this while they are behind the steering wheel, i consider myself lucky and proud that i know both. I think members here have a good "feel" of the vehicle. The basic intention of sharing this was to bring out simple concepts that we come across in our day to day lives. No one taught me (corporate life), i have learnt it the hard way.

Finally we have the desired picture. So no matter how grippy your tyre, how torquey your engine there will come a gradient where your 4x4 will fail. Does anyone have any idea how to make calculations to calculate the gradeability of the various 4x4s on this forum.

Here, vehicle weight will play an interesting role too. Heavy Vehicle=more wheel down force BUT Heavy also means that force pulling backwards (Rhx in dia.) is more. So what is the relation between weight and gradebility? Is there an optimum weight which ensures max. gradebility?

This is an interesting performance characteristic, gradeability will determine whether a vehicle can make a climb on a rock slab (Like Arjun is attempting in http://www.team-bhp.com/forum/4x4-ve...ster-zuki.html (Arjun's Black Monster Zuki) post #46 )

Best regards to all.

Last edited by '72 Bullet : 25th March 2010 at 14:41. Reason: thread name missed out
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