Go Back   Team-BHP > Buckle Up > 4x4 & Off-Roading > 4x4 Technical


Reply
 
Thread Tools Search this Thread
Old 1st February 2011, 23:18   #76
Team-BHP Support
 
Samurai's Avatar
 
Join Date: Jan 2005
Location: B'lore-Manipal
Posts: 22,045
Thanked: 13,496 Times
Default

Quote:
Originally Posted by SPIKE ARRESTOR View Post
For a layman- There are four forces which play a role here:-

1. Weight of the vehicle
2. Force due to lateral acceleration (read Rolling in off-road parlance)
3. Height of Center of gravity (C.G.)
4. Wheel track


Now can someone tell me if there is any term which mentions about spring and suspension stiffness? NO! So what I had been harping continuously was correct, the graph is wrong. Since no terms related to suspension feature in these equations, there is no relation between Suspension characteristics and the amount of weight transfer when on road and off- road.
In other words, you just described how a huge piece of brick would behave. You know, a monolith rectangular block.

Quote:
Originally Posted by SPIKE ARRESTOR View Post
This is my last post on this thread, I think I have had enough, no point in breaking my head. I rest my case here. :-)
Wait, don't walk away. I am not finished yet.

Now, a vehicle is not just a monolith rectangular block. It is a monolith rectangular sprung on two sets of axles, which can move independently up and down when forced. When somebody as strong as Arka presses down on one side of the Jeep, the top part will tilt to that side. How much it will tilt, depends on the softness/hardness of the suspension. My Jeep has much softer suspension, so it will tilt more than the average Jeep. So the tilt depends on the suspension stiffness. When the top part tilts, the CG also shifts to that side to some extent. Ok, depends on the axis of the tilt too. If the axis of the tilt above the CG, the CG will shift to the tilting side. If the CG is below the axis of tilt, I think it remains where it is. Not too sure.

Anyway, let's get some pictures here.

Consider a Jeep standing on flat ground. I haven't shown the leaf-springs, so assume it.

Name:  Flat.jpg
Views: 486
Size:  17.4 KB

This time let us lift one wheel, so that the axle makes 10 degrees angle against the ground. The near leaf-spring will get compressed and far leaf-spring gets stretched. Therefore the body only makes half as tilt or 5 degree angle against the ground. Axle at 10 deg, and body at 5 deg.

Name:  10.jpg
Views: 506
Size:  28.3 KB

Let us further lift it until the tyre fouls the wheel well, say it takes 20 degrees against the ground to achieve it. The body would tilt another 5 degrees. Now we have reached the max articulation. Axle at 20 deg, and body at 10 deg.

Name:  15.jpg
Views: 735
Size:  31.3 KB

Let us further lift the wheel, say another 20 degree. This time body will also move as much. After the max articulation point, the entire Jeep acts like a monolith and would move as a single block. Axle will be at 40 deg, body at 30 deg.

Name:  monolith.jpg
Views: 526
Size:  41.2 KB

I hope that explains why latitudinal CG doesn't shift as much as the wheel lift until the max articulation point. After that your brick theory holds good.

As you see, I have not used any formula to explain my thought. This is the best I can do to explain in a layman's words. If you think all the above is pure BS, you don't have to reply.

Quote:
Originally Posted by pjbiju View Post
But once it reaches its limits, then the graph should be linear, as if there was no suspension at all. Does this make sense?
Call the Y axis as Body Tilt instead of Vehicle lift, then we are in agreement. For me vehicle is not a monolith brick. The sprung body and unsprung wheels/axles can tilt/lift somewhat separately.

Last edited by Samurai : 1st February 2011 at 23:24. Reason: back-to-back post
Samurai is offline   (1) Thanks Reply With Quote
Old 2nd February 2011, 00:07   #77
Senior - BHPian
 
The Wolf's Avatar
 
Join Date: Jan 2005
Location: Bangalore
Posts: 1,116
Thanked: 58 Times
Default Re: Articulating on Articulation

Would agree with Arka and Samurai. In simple terms under articulation the CG shift is non linear however at max suspension compression (at the lifted wheel end) the shift of CG to the other side becomes linear (1deg lift:1unit of CG shift). In case of the Thar crde the CG shift point will be lesser than that of a vehicle with higher capacity of articulation, hence the Thar crde may have lifted a front wheel where others were'nt.

Lastly: Just say if we slice a jeep into half (from front to rear) and weigh the 2 pieces individually there would be difference in the weights. Pls factor that in the articulation load and release computations. A monolith has the same effect both sides, a jeep wont. Hope this adds a perspective to our understanding...in simple layman terms

Last edited by The Wolf : 2nd February 2011 at 00:09.
The Wolf is offline   Reply With Quote
Old 2nd February 2011, 01:13   #78
AVR
BHPian
 
AVR's Avatar
 
Join Date: Apr 2008
Location: Ahmedabad
Posts: 929
Thanked: 511 Times
Default Re: Articulating on Articulation

Sharath your posts make a lot of sense while Spike at the same time makes me nostalgic about what I studied in "Dynamics" in the 6th semester.

While comparing a IFS (Softer spring rates) with a solid axle (harder spring rates), is it also safe to assume that a IFS vehicle would have a slower shift of CG as compared to the solid axle till a certain level which we define as a bump stop as the solid axle would be more closer to linear than the IFS given harder spring rates. I say slower as am assuming a solid axle vehicle would be typically closer to a monolithic brick than an IFS one?

Further, Beyond that point there would be a sharp transition to a more or less linear relationship resulting in a more sudden rolling experience which could possibly take an inexperienced offroader by greater surprise as compared to a solid axle vehicle which would essentially have a more gradual transition? For an engineer I put it across in rather plain English but am also thinking aloud here.

Cheers,
Adi

Last edited by AVR : 2nd February 2011 at 01:16. Reason: Afterthoughts :)
AVR is offline   Reply With Quote
Old 2nd February 2011, 08:21   #79
Senior - BHPian
 
svsantosh's Avatar
 
Join Date: Mar 2008
Location: Hosur
Posts: 3,308
Thanked: 1,252 Times
Default Re: Articulating on Articulation

All you engineering guys make this a very complicated read.

From my perspective, under extreme flex, there are 3 parameters deciding what happens next.

a) Ground Level
b) Suspension setup (IFS/Leafs/Solid...)
c) Wheel Well (Remember the 35" monstor @ anaconda)

a) Ground level is important because not every time articulation happens where ONLY 1 wheel lifts, and causes its diagonal opposite to lift. Most of the time, (recent anaconda 1st obstacle was a good example) - the diagonal wheels are kissing the tub, while other diagonals are flexing OUT at max. Solid axles have a advantage here, because they are designed to do that. PS - Wider 57/54 make it look like cake walk and hardly loose their C.o.G.

b) Thinking about it - Can a IFS be designed in such a way that the limitation of the front suspension travel, can be over compensated with the rear flexing more than our ol' jeeps, of course making the chassis tilt a bit (make it a stressed member in between) - all this still leading to a scenario where the Thar would have its 4 wheels under extreme flex, albeit with a slight/big body tilt leading to shift in C.o.G.

I think this is what you B.Engg are fighting about, I am not sure...

c) How many of us ever bump our jeeps/ypsys into the bump stops. Hardly...Reason being we end up limiting our flex at wheel wells (scratch marks can be seen on all 4 wells). Does the thar design allow it to flex till the bumps? Spikey, please answer. At least the front looks it will. because it is IFS and wont flex so much into a well like a solid... Rear of the thar from S.A pics looks like it flexs enormously over a ol jeep, is it a conscious design factor?

Last edited by svsantosh : 2nd February 2011 at 08:27.
svsantosh is offline   Reply With Quote
Old 2nd February 2011, 08:56   #80
Team-BHP Support
 
Samurai's Avatar
 
Join Date: Jan 2005
Location: B'lore-Manipal
Posts: 22,045
Thanked: 13,496 Times
Default Re: Articulating on Articulation

According to Spike, suspension has nothing to do with articulation, because the formula doesn't have a variable for it. Apparently he thinks we are all talking crap, so he doesn't want to respond.

Therefore, we have no choice but marinate in our ignorance and simple-minded understanding of articulation.
Samurai is offline   Reply With Quote
Old 2nd February 2011, 10:13   #81
Senior - BHPian
 
headers's Avatar
 
Join Date: May 2006
Location: Greater Chennai
Posts: 4,548
Thanked: 424 Times
Default Re: Articulating on Articulation

Quote:
Originally Posted by svsantosh View Post
c) How many of us ever bump our jeeps/ypsys into the bump stops. Hardly...Reason being we end up limiting our flex at wheel wells (scratch marks can be seen on all 4 wells).
Sir, I beg to differ. We always limit the suspension travel with our bump stops in our Jeeps and Gypsies. There is no other way. The setting of a bump stop is just before your shocks / springs max out!!

I am 100% sure THAR will have its suspension flex until the bump stop. How BIG that bump stop is, IS the question.
headers is offline   Reply With Quote
Old 2nd February 2011, 10:32   #82
Senior - BHPian
 
SPIKE ARRESTOR's Avatar
 
Join Date: Nov 2009
Location: Deutschland
Posts: 2,653
Thanked: 679 Times
Talking Re: Articulating on Articulation

Quote:
Originally Posted by Samurai View Post
According to Spike, suspension has nothing to do with articulation, because the formula doesn't have a variable for it. Apparently he thinks we are all talking crap, so he doesn't want to respond.

Therefore, we have no choice but marinate in our ignorance and simple-minded understanding of articulation.
Sharath are you insane? When did I say that suspension has nothing to do with articulation. Please read my posts I have continuously maintained that suspension characteristics have nothing to do with Lateral weight transfer and and hence shift in CG. I am not advocating any vehicles lack / abundance of articulation. I am against the graph which has little or no reasoning, fueled with Microsoft Imagination.

Spike

PS- I have a weird feeling on how you came out with the graph. The curve shown by you for (maximum articulation 3rd curve towards right) resembles the path traced by the right wheel when the left wheel is inside a ditch, at the same time the wheels keep slipping and sliding away towards the right. Is that simple in layman terms?

Last edited by Jaggu : 2nd February 2011 at 12:31. Reason: Editing the personal remark. Hope you understand. Thanks
SPIKE ARRESTOR is offline   Reply With Quote
Old 2nd February 2011, 10:38   #83
Senior - BHPian
 
ex670c's Avatar
 
Join Date: Nov 2004
Location: Chennai
Posts: 2,454
Thanked: 1,789 Times
Default Re: Articulating on Articulation

Quote:
Originally Posted by Samurai View Post
According to Spike, suspension has nothing to do with articulation, because the formula doesn't have a variable for it. Apparently he thinks we are all talking crap, so he doesn't want to respond.

Therefore, we have no choice but marinate in our ignorance and simple-minded understanding of articulation.
Hi Sharath,

While we are talking articulation, I think, Spike was talking about CG and Lifting a wheel, on a Side-Slope (Bank).

We need his help to come up with something for the RTI Ramp (Articulation Test).

Regards,

Arka
ex670c is offline   Reply With Quote
Old 2nd February 2011, 11:05   #84
Team-BHP Support
 
Samurai's Avatar
 
Join Date: Jan 2005
Location: B'lore-Manipal
Posts: 22,045
Thanked: 13,496 Times
Default Re: Articulating on Articulation

I related articulation with shift in lateral CG, because for me they are related. Articulation depends on suspension characteristics. The lateral shift in CG depends on articulation, according to me, which many have agreed. That means lateral shift in CG depends on articulation, which in turn depends on suspension. That is the connection as I understand.

Since you are not able to explain stooping down to our level, we have no choice but believe in crude graphs.

Last edited by Jaggu : 2nd February 2011 at 12:36. Reason: Deleting off the personal bit. Thanks
Samurai is offline   Reply With Quote
Old 2nd February 2011, 11:41   #85
BHPian
 
sreejeshmp's Avatar
 
Join Date: May 2007
Location: Bangalore
Posts: 623
Thanked: 571 Times
Default Re: Articulating on Articulation

This thread is getting more interesting and lots of new things to learn for me like jeep drivers.

I would like to share a simple experience that I shared with my brother when he was 3-4 years old. I took a stone and dropped to ground and I asked Why this stone reached the ground, He just answered me that There is nothing to hold the stone !! If there was a chair in between my hand and ground it will not reach the ground !!.

What I understand from the discussion between spike and samurai is the different point of view of same problem One is thinking as a custom builder and other one as production builder.Like one deriving equations from Theory and another one deriving from Practical experience.
sreejeshmp is offline   Reply With Quote
Old 2nd February 2011, 11:59   #86
Senior - BHPian
 
ex670c's Avatar
 
Join Date: Nov 2004
Location: Chennai
Posts: 2,454
Thanked: 1,789 Times
Default Re: Articulating on Articulation

Quote:
Originally Posted by SPIKE ARRESTOR View Post
I don't know many things and I openly admit that. I would prefer to remain silent on things which I don't know rather than making vague comments on things which I don't know / have never tried / can provide proof of (just now I read someone suggesting for a traction bar if the propeller shaft angle changes more than 3-5 degrees), what is the basis for this 3-5 degrees? I hope you are getting my point.
Hi Spike,

If the sentence is read as Differential Pinion Angle changes more than 3-5 Degree, then is right.

And then the Basis for 3-5 Degrees is experience.

He is BE & MS from UK, and manufactures Precision Automotive Components.

His Gypsy is one of the BEST OFF-ROAD vehicles in the country (with facts). Have you driven his vehicle to understand what he has done to his suspension, including failed shackle lifts. He suggests from his experience.

He can mention it even more vaguely as "if your differential pinion is pitching too much then you should consider a Traction Bar".


Regards,

Arka

PS - For the Layman - Axle Wrap Prevention
ex670c is offline   Reply With Quote
Old 2nd February 2011, 12:12   #87
BHPian
 
Join Date: Dec 2008
Location: Planet E.A.R.T.H.
Posts: 140
Thanked: 7 Times
Default Re: Articulating on Articulation

Quote:
Originally Posted by SPIKE ARRESTOR View Post
Sharath are you insane? When did I say that suspension has nothing to do with articulation. Please read my posts I have continuously maintained that suspension characteristics have nothing to do with Lateral weight transfer and and hence shift in CG. I am not advocating any vehicles lack / abundance of articulation. I am against the graph which has little or no reasoning, fueled with Microsoft Imagination.

Spike

PS- I have a weird feeling on how you came out with the graph. The curve shown by you for (maximum articulation 3rd curve towards right) resembles the path traced by the right wheel when the left wheel is inside a ditch, at the same time the wheels keep slipping and sliding away towards the right. Is that simple in layman terms?

What we laymen are saying is that in a vehicle with good articulation (suspension characteristics), the tendency to roll (due to Lateral weight transfer and and hence shift in CG) is less as compared to a vehicle with limited articulation on the same terrain.

Last edited by Jaggu : 2nd February 2011 at 12:39. Reason: Editing out the personal remarks. Thanks
'72 Bullet is offline   Reply With Quote
Old 2nd February 2011, 12:29   #88
Team-BHP Support
 
Jaggu's Avatar
 
Join Date: May 2004
Location: Bangalore
Posts: 17,496
Thanked: 6,779 Times
Default Re: Articulating on Articulation

Quote:
Originally Posted by SPIKE ARRESTOR View Post
regarding vehicle toppling at the "Robinson Point" (pardon me Robi, I have to be specific), it had nothing to do with articulation. I was keeping quiet on this as it would hurt others sentiments, as I am being questioned, I have to answer this. It was purely driver error, I did not see it but I have Eye witness account on this.
I was there and i can assure you the second jeep topple was a driver error. This might not be directly related to articulation.

Quote:
Originally Posted by '72 Bullet View Post
What we laymen are saying is that in a vehicle with good articulation (suspension characteristics), the tendency to roll (due to Lateral weight transfer and and hence shift in CG) is less as compared to a vehicle with limited articulation on the same terrain.
Yes this is what i really want to know. As far as i could understand the nature of suspension is involved because it controls the way in which weight is transfered, at what rate and to what extent. Hence i feel suspension plays a part.

ps: Guys i feel that the discussion is getting slightly personal from many fronts. As a member request you guys to focus more on sharing such amazing technical info with all of us.

pps: As a moderator i will be watching

Last edited by Jaggu : 2nd February 2011 at 12:51.
Jaggu is offline   Reply With Quote
Old 2nd February 2011, 12:55   #89
Senior - BHPian
 
SPIKE ARRESTOR's Avatar
 
Join Date: Nov 2009
Location: Deutschland
Posts: 2,653
Thanked: 679 Times
Default Re: Articulating on Articulation

Quote:
Originally Posted by Samurai View Post
According to Spike, suspension has nothing to do with articulation, because the formula doesn't have a variable for it. Apparently he thinks we are all talking crap, so he doesn't want to respond.
Samurai, I would like you /someone else to provide facts which make me believe that the graph shown by you is right. As simple as that. till then it is only speculation with IF's and BUT's.

Last edited by .anshuman : 2nd February 2011 at 15:21. Reason: Off-topic content removed. Let's please stick to the topic being discussed here. Thanks for anticipated co-operation.
SPIKE ARRESTOR is offline   Reply With Quote
Old 2nd February 2011, 14:23   #90
Senior - BHPian
 
svsantosh's Avatar
 
Join Date: Mar 2008
Location: Hosur
Posts: 3,308
Thanked: 1,252 Times
Default Re: Articulating on Articulation

Quote:
Originally Posted by headers View Post
Sir, I beg to differ. We always limit the suspension travel with our bump stops in our Jeeps and Gypsies. There is no other way. The setting of a bump stop is just before your shocks / springs max out
You must be right, my jeep has some unique rims that no is able to identify. It is zero, may be even +ve offset!! and all it does scraps the tub and limits further articulation. I will push it to its limits this weekend and shall observe the 'bump stops' and revist this line of mine...

And drop the 'sir' Vikram, not after we got aquainted face-face...

Last edited by .anshuman : 2nd February 2011 at 15:24. Reason: Post edited as one of the quoted posts were deleted.
svsantosh is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Articulation @ Bidaraguppe lake and water wading at Dhakshina Thirupathi hisunil 4x4 Excursions 41 7th March 2011 12:48
Do Diff locks compensate for lack of articulation? tsk1979 4x4 Technical 86 3rd April 2010 12:35


All times are GMT +5.5. The time now is 08:46.

Copyright 2000 - 2017, Team-BHP.com
Proudly powered by E2E Networks