Wishbones attachment question !

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polarboy
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Joined: Fri Dec 04, 2009 12:09 am

Re: Wishbones attachment question !

Post by polarboy » Thu Jul 31, 2014 11:07 pm

marcush. wrote:that fastener can be called anything..as it is your bespoke design ...you would not dare to rob one of IKEAs spares department would you?
I cannot fatom such things are avaialable of the shelf in the Quality you Need

http://www.formula1-dictionary.net/Big/ ... ng_big.jpg

btw -who came up with that IKEA idea in formula1? 321 ..yes of course it was John Barnard ..is there anything in Formula 1 of today NOT invented or introduced by him??????

Benneton B191 was the car .
As they say in pantomime "OH NO HE DIDNT"
Don't know about other cars but the cam fixing was run on the Lotus 102 in the 1990 season .102 was a Mike Coughlan designed car(thou Frank Dernie seems to get most of the credit ! )
Coughlan was co designer with Barnard on the 191
Thou Mike came up with the idea all the actual nuts and bolts design work was done by a guy called Hamish Monroe and when they started off the idea was shown to him using cam fixings from Texas DIY (remember them ?)
Items that made it to the car were quite a bit different and a lot stronger !!!
Spent many a happy hour building noses,building the cam set up into the boxes and setting up the location pins on the chassis at Team Lotus

firasf1dream
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Joined: Fri Apr 18, 2014 8:26 pm

Re: Wishbones attachment question !

Post by firasf1dream » Tue Aug 12, 2014 8:59 am

thanks a lot guys,
i must read the book Race Car Vehicle Dynamic for more general info

marcush.
268
Joined: Tue Mar 09, 2004 3:55 pm

Re: Wishbones attachment question !

Post by marcush. » Tue Aug 12, 2014 9:15 am

polarboy wrote:
marcush. wrote:that fastener can be called anything..as it is your bespoke design ...you would not dare to rob one of IKEAs spares department would you?
I cannot fatom such things are avaialable of the shelf in the Quality you Need

http://www.formula1-dictionary.net/Big/ ... ng_big.jpg

btw -who came up with that IKEA idea in formula1? 321 ..yes of course it was John Barnard ..is there anything in Formula 1 of today NOT invented or introduced by him??????

Benneton B191 was the car .
As they say in pantomime "OH NO HE DIDNT"
Don't know about other cars but the cam fixing was run on the Lotus 102 in the 1990 season .102 was a Mike Coughlan designed car(thou Frank Dernie seems to get most of the credit ! )
Coughlan was co designer with Barnard on the 191
Thou Mike came up with the idea all the actual nuts and bolts design work was done by a guy called Hamish Monroe and when they started off the idea was shown to him using cam fixings from Texas DIY (remember them ?)
Items that made it to the car were quite a bit different and a lot stronger !!!
Spent many a happy hour building noses,building the cam set up into the boxes and setting up the location pins on the chassis at Team Lotus
I thought Coughlan was a Barnard cadet at Mclaren ...but anyways the principle is quite the same as on every DZUS or whatever quarterlock fastener.

firasf1dream
1
Joined: Fri Apr 18, 2014 8:26 pm

Re: Wishbones attachment question !

Post by firasf1dream » Wed Aug 13, 2014 7:48 pm

Ali F1 wrote:FirasF1Dream - Read my blog to help you find suspension angles (Geometries) !

http://www.ali-f1.blogspot.co.uk/2014/0 ... tries.html

You as the designer should calculate your geometries to find the angles of your wishbones.
how can this principle of Instant Center work if the upper and lower wishbone in F1 are parallel ?!
Last edited by firasf1dream on Thu Aug 14, 2014 12:17 pm, edited 2 times in total.

mep
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Location: Germany

Re: Wishbones attachment question !

Post by mep » Wed Aug 13, 2014 9:53 pm

Then the instant centre is in infinite, which results in the roll centre to be on the ground plane.

firasf1dream
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Joined: Fri Apr 18, 2014 8:26 pm

Re: Wishbones attachment question !

Post by firasf1dream » Thu Aug 14, 2014 12:16 pm

mep wrote:Then the instant centre is in infinite, which results in the roll centre to be on the ground plane.
how is that ?! damn the dynamics course lol worst course and best in the same time ! it was in the fisrt year second semester that we took it !

for the wheel itself it's the contact point between the tyre and the ground but for the suspension how is that it's on the ground ? isn't that every joint of the wheel and wishbone has it's own instant center ?

Tim.Wright
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Re: Wishbones attachment question !

Post by Tim.Wright » Thu Aug 14, 2014 1:08 pm

Read up on 2D rigid body kinematics and 4-bar linkages and think about how this theory can be applied to a suspension to determine the wheel movements and the load paths during roll (specifically how much force goes through the spring and how much through the links). Its a simplification of the 3D case, but in my experience its quite accurate.

This will give you the knowledge you need. Until then, try to avoid reading any automotive specific treatments on instant centres and roll centres until you understand the fundamentals. Most of the classical theories are gross simplifications and are misleading or flat out wrong.
Not the engineer at Force India

mep
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Location: Germany

Re: Wishbones attachment question !

Post by mep » Thu Aug 14, 2014 9:50 pm

Tim.Wright wrote:Until then, try to avoid reading any automotive specific treatments on instant centres and roll centres until you understand the fundamentals. Most of the classical theories are gross simplifications and are misleading or flat out wrong.
Do you have examples of this?

Tim.Wright
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Re: Wishbones attachment question !

Post by Tim.Wright » Fri Aug 15, 2014 1:25 pm

mep wrote:
Tim.Wright wrote:Until then, try to avoid reading any automotive specific treatments on instant centres and roll centres until you understand the fundamentals. Most of the classic theories are gross simplifications and are misleading or flat out wrong.
Do you have any examples of this?
Yes, there are shirtloads.

[rant=1]

I'm not going to name names because its a small world I work in. I will name the concepts though. The problems are all related to incorrect use of the "geometric" roll centre. This is the one found by projecting so many lines from various points in the suspension that its impossible the the resulting intersection point cannot posses mystical properties.

Many books, websites and seminars will lead you to believe that the geometric roll centre is actually the fundamental mechanism governing suspension roll which is not correct. The geometric roll centre is merely a very basic model, used to simplify all the lateral dynamics of a cornering car down to a single degree of freedom model which is valid under some very simplified conditions. This method is not useless - in fact I use it occasionally to calculate different elastic setups because I've found that its not bad at predicting trends of balance and roll between different elastic setups. But if I want to accurately calculate the tyre forces or roll angle - especially in limit conditions, I use other methods (often a full vehicle simulation).

The main problem of the geometric roll centre (due to its name) is that people think that the chassis rolls about the roll centre and that it acts like a pin joint in determining the tyre forces.

Bill Mitchell showed here that body movements and tyre forces need to be approached considering the left and right wheels seperately AND knowing the contact patch lateral forces if you want accurate results. Erik Zapletal confirms here (in his usual condescending style) that the roll movement depends the left/right lateral tyres forces and the force-line or n-line slopes (even with the roll centre in outer space) and also addresses the vertical jacking effect. Danny Nowlan is also using a similar method to Bill Mitchell in his articles and software. S.M. Sincere (SAE Paper 983033) has shown that non-linearities in wheel rates are also a factor in determining the roll angle and move the actual roll centre away from the geometric one. Basically, the industry is slowly moving away from classical roll centre theory, but unfortunately large segments of the education system are not.

The main issue with classic roll centre theory is that it ignores the difference between the left and right lateral tyre forces which can be responsible for a significant portion of the roll angle and vertical load transfer forces. The above people demonstrate this

The fact that there is such a knowledge gap between classical roll centre theory and the actual behaviour of a car has led to various myths and wives-tales being propogated through (often expensive) books, journals, magazines, seminars. I have read, or been told the following during my lifetime:
  1. Roll centres should never pass through the ground as it causes instabilities and gives give bad driver feedback
  2. Lateral roll centre migration must be minimised because it makes a vehicle "inconsistent" and difficult to tune.
  3. Front and rear roll centres must move in the same direction in cornering otherwise handling will be inconsistent in corners
  4. Rear roll centres should be higher than the front because the "CG axis" of the car is inclined up towards the rear
  5. Vertical weight forces cause rolling moments about the geometric roll axis which lead to changes in the roll angle and extra lateral load transfer.
  6. Letting the roll centre pass through the contact patch of a tyre will effectively lock that side of the suspension solid. It also causes cancer.
  7. Roll centre height variation during roll must be minimised otherwise the LLTD balance will change with roll (fun fact: it will change even with a rock solid RCH)
All of them are complete BS and you can see many of them hide behind the conveniently unquantifiable smoke screens of "bad driver feedback" or "inconsistent handling" which is effectively saying "god works in mysterious ways".

When I was at the start of my career in vehicle dynamics I wasted massive amounts of time trying to understand the phenomena from my list. In the end, as my general engineering skills improved (a process helped by ignoring most automotive texts and drawing loads of free body diagrams myself) I realised/proved to myself not only that every point on the above list is BS, but I have in my time analysed race and road cars which break rules 1, 2, 3, 4 and 6 and show no ill effects. Some of these cars were even analysed at an extremeley deep level using wheel force sensors, slip sensors and comparing them with various calculations. Points 5 and 7 can be proved to be BS with a simple free body diagram.

In addition to that, In all of my (short) career, I've never ever heard of any stories, even from the people who propogate this stuff, about any peculiar handling problems that were ever objectively isolated to one of these roll centre effects (from my list) and then were subsequently cured by changing the geometry to "fix" the roll centre behaviour. Never.

This is why I suggested avoiding automotive texts if you want to learn about suspension. There are some good ones (usually in german) but most of the others will "teach" you rubbish that will take years to unlearn. This was my experience at least, and as you can possibly tell I'm still a little annoyed about it. It took me about 3-4 years to unlearn all the crap I'd "learnt" and to finally understand how a vehicle rolls and pitches. It turns out that it just follows the normal laws of physics.

[rant=0]
Not the engineer at Force India

firasf1dream
1
Joined: Fri Apr 18, 2014 8:26 pm

Re: Wishbones attachment question !

Post by firasf1dream » Fri Aug 15, 2014 2:45 pm

Tim.Wright wrote:Read up on 2D rigid body kinematics and 4-bar linkages and think about how this theory can be applied to a suspension to determine the wheel movements and the load paths during roll (specifically how much force goes through the spring and how much through the links). Its a simplification of the 3D case, but in my experience its quite accurate.

This will give you the knowledge you need. Until then, try to avoid reading any automotive specific treatments on instant centres and roll centres until you understand the fundamentals. Most of the classical theories are gross simplifications and are misleading or flat out wrong.
i was just checking about it, well i know these stuff ! i took them i university nothing new, so u mean all i have to do is refresh my memory about the Instant Center and how to find it in all cases including parallel bars and i will be good to go ?

Lycoming
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Re: Wishbones attachment question !

Post by Lycoming » Fri Aug 15, 2014 10:34 pm

Tim.Wright wrote: Rear roll centres should be higher than the front because the "CG axis" of the car is inclined up towards the rear
I was always told that this was done to make weight transfer happen more quickly at the rear to allow the rear to "catch up" to the front during turn in. CG axis inclination seems to me like a weird generalization of a 2D concept into 3D space, when we already have a 3D concept of center of gravity location.
Tim.Wright wrote:Vertical weight forces cause rolling moments about the geometric roll axis which lead to changes in the roll angle and extra lateral load transfer.
How did that one come about? I was always told that the only factors that affect weight transfer are mass, center of gravity height, wheelbase/track and magnitude of contact patch force in the ground plane.
Tim.Wright wrote:Letting the roll centre pass through the contact patch of a tyre will effectively lock that side of the suspension solid. It also causes cancer.
Well, as far as I can tell, everything seems to cause cancer.

Luke
2
Joined: Thu Nov 07, 2013 6:32 am

Re: Wishbones attachment question !

Post by Luke » Wed Aug 20, 2014 12:49 am

mep wrote:Then the instant centre is in infinite, which results in the roll centre to be on the ground plane.
not quite.

yes the instant centre is infinite, but it wont effectively be on the ground. the force line from the contact patch will angle up parallel to the arms, so there will be a vertical component applied to the chassis from the suspension, so therefor the RC isn't on the ground.

another way to think of it is to remove the springing, move the wheel up and down. Is it purely a vertical path? If not the RC isnt on the ground. there is a Y component to the Z input, so a Y input will result in a Z reaction.

sorry to high jack the thread.

In saying all this, with these cars kinematics is at best a second order concern as there is little suspension movement...will be interesting when the 18" gets introduced :)

Tim.Wright
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Re: Wishbones attachment question !

Post by Tim.Wright » Wed Aug 20, 2014 8:15 am

Luke wrote: sorry to high jack the thread.
Image

But apart from that what you said is correct. The front view kinematics of the front axle on the current F1 cars have practically parallel arms which slope up to the middle of the car. Therefore the force line (or n-line or whatever you want to call it) will slope up at more or less the same angle.
Lycoming wrote:
Tim.Wright wrote: Rear roll centres should be higher than the front because the "CG axis" of the car is inclined up towards the rear
I was always told that this was done to make weight transfer happen more quickly at the rear to allow the rear to "catch up" to the front during turn in.
Not meant as a personal dig, but that sounds like just another cult saying. The sooner people move away from religious, hand-wavy explanations and use proper physics then the discussion can move forward. I think also a lot of people would be disappointed with how small the delay is between the geometric load transfer and the elastic load transfer, especially on stiffly sprung race cars.
Not the engineer at Force India

trinidefender
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Re: Wishbones attachment question !

Post by trinidefender » Wed Aug 20, 2014 4:34 pm

Tim.Wright wrote:
mep wrote:
Tim.Wright wrote:Until then, try to avoid reading any automotive specific treatments on instant centres and roll centres until you understand the fundamentals. Most of the classic theories are gross simplifications and are misleading or flat out wrong.
Do you have any examples of this?
Yes, there are shirtloads.

[rant=1]

I'm not going to name names because its a small world I work in. I will name the concepts though. The problems are all related to incorrect use of the "geometric" roll centre. This is the one found by projecting so many lines from various points in the suspension that its impossible the the resulting intersection point cannot posses mystical properties.

Many books, websites and seminars will lead you to believe that the geometric roll centre is actually the fundamental mechanism governing suspension roll which is not correct. The geometric roll centre is merely a very basic model, used to simplify all the lateral dynamics of a cornering car down to a single degree of freedom model which is valid under some very simplified conditions. This method is not useless - in fact I use it occasionally to calculate different elastic setups because I've found that its not bad at predicting trends of balance and roll between different elastic setups. But if I want to accurately calculate the tyre forces or roll angle - especially in limit conditions, I use other methods (often a full vehicle simulation).

The main problem of the geometric roll centre (due to its name) is that people think that the chassis rolls about the roll centre and that it acts like a pin joint in determining the tyre forces.

Bill Mitchell showed here that body movements and tyre forces need to be approached considering the left and right wheels seperately AND knowing the contact patch lateral forces if you want accurate results. Erik Zapletal confirms here (in his usual condescending style) that the roll movement depends the left/right lateral tyres forces and the force-line or n-line slopes (even with the roll centre in outer space) and also addresses the vertical jacking effect. Danny Nowlan is also using a similar method to Bill Mitchell in his articles and software. S.M. Sincere (SAE Paper 983033) has shown that non-linearities in wheel rates are also a factor in determining the roll angle and move the actual roll centre away from the geometric one. Basically, the industry is slowly moving away from classical roll centre theory, but unfortunately large segments of the education system are not.

The main issue with classic roll centre theory is that it ignores the difference between the left and right lateral tyre forces which can be responsible for a significant portion of the roll angle and vertical load transfer forces. The above people demonstrate this

The fact that there is such a knowledge gap between classical roll centre theory and the actual behaviour of a car has led to various myths and wives-tales being propogated through (often expensive) books, journals, magazines, seminars. I have read, or been told the following during my lifetime:
  1. Roll centres should never pass through the ground as it causes instabilities and gives give bad driver feedback
  2. Lateral roll centre migration must be minimised because it makes a vehicle "inconsistent" and difficult to tune.
  3. Front and rear roll centres must move in the same direction in cornering otherwise handling will be inconsistent in corners
  4. Rear roll centres should be higher than the front because the "CG axis" of the car is inclined up towards the rear
  5. Vertical weight forces cause rolling moments about the geometric roll axis which lead to changes in the roll angle and extra lateral load transfer.
  6. Letting the roll centre pass through the contact patch of a tyre will effectively lock that side of the suspension solid. It also causes cancer.
  7. Roll centre height variation during roll must be minimised otherwise the LLTD balance will change with roll (fun fact: it will change even with a rock solid RCH)
All of them are complete BS and you can see many of them hide behind the conveniently unquantifiable smoke screens of "bad driver feedback" or "inconsistent handling" which is effectively saying "god works in mysterious ways".

When I was at the start of my career in vehicle dynamics I wasted massive amounts of time trying to understand the phenomena from my list. In the end, as my general engineering skills improved (a process helped by ignoring most automotive texts and drawing loads of free body diagrams myself) I realised/proved to myself not only that every point on the above list is BS, but I have in my time analysed race and road cars which break rules 1, 2, 3, 4 and 6 and show no ill effects. Some of these cars were even analysed at an extremeley deep level using wheel force sensors, slip sensors and comparing them with various calculations. Points 5 and 7 can be proved to be BS with a simple free body diagram.

In addition to that, In all of my (short) career, I've never ever heard of any stories, even from the people who propogate this stuff, about any peculiar handling problems that were ever objectively isolated to one of these roll centre effects (from my list) and then were subsequently cured by changing the geometry to "fix" the roll centre behaviour. Never.

This is why I suggested avoiding automotive texts if you want to learn about suspension. There are some good ones (usually in german) but most of the others will "teach" you rubbish that will take years to unlearn. This was my experience at least, and as you can possibly tell I'm still a little annoyed about it. It took me about 3-4 years to unlearn all the crap I'd "learnt" and to finally understand how a vehicle rolls and pitches. It turns out that it just follows the normal laws of physics.

[rant=0]
From this I have a question. Why then are roll centres in the rear generally higher than roll centres in the front? Just here to learn.

Tim.Wright
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Re: Wishbones attachment question !

Post by Tim.Wright » Wed Aug 20, 2014 5:20 pm

trinidefender wrote: From this I have a question. Why then are roll centres in the rear generally higher than roll centres in the front? Just here to learn.
My honest opinion is I believe that most people do it because thats the way it has usually been done. Then some others do it because they have some hand-wavy theory to support it. Though I know of a couple of production supercars on the market now which don't follow this trend.

Until now I've not seen a decent analysis of the problem, so there is very little good literature on roll centre placement. Its a slightly complicated problem to analyse and I guess the people who understand it are not inclined (or allowed) to share this knowledge.

There might be a real reason but as of now I haven't uncovered it. It is something I'm researching at the moment though because I would like to know definitively....
Not the engineer at Force India