Anti-ackerman steering

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Caito
Caito
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Anti-ackerman steering

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zgred wrote:Image
Does it seem to me, or there's some Anti-ackerman going on?

Bye bye

Caito.-
Last edited by mx_tifoso on Mon Aug 30, 2010 8:12 pm, edited 1 time in total.
Reason: Split from RB6 thread.
Come back 747, we miss you!!

marcush.
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Re: Red Bull RB6

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the only car not sporting anti ackerman is the Lotus AFAIK

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PlatinumZealot
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Re: Red Bull RB6

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Interesting. What effect does anti-ackerman on the F1 car? More turn in?
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marcush.
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Re: Red Bull RB6

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n smikle wrote:Interesting. What effect does anti-ackerman on the F1 car? More turn in?
anti ackerman takes into consideration the optimum slip angle for the tyre at reduced vertical load(inner wheel ).
If your inner wheel stays on the ground at cornering speeds and you have PRO ackerman the inner wheel has to have more steering angle=more slip angle but has much less vertical load ..so youre not using the inner wheel properly you are abusing it a bit .
As we have learned tyres do not like to be punished at low vertical loads ..
With ANTIackermann the inner wheel has less steering angle than the outer wheel but has more grip.(unless your tyre would like more slip angle at lower vertical load)
The maximum lock of the outward tyre in the corner can be increased of course ,as the inner wheel does not steer more than the outer wheel.clearance wise its much better and aerowise for sure as the inner wheel does not block /modify the airflow as much when there is not much lock available un the inside..
definitely not good for pushing the car around in the pits ,but at racing speeds more than worth a thought to have anti .

Edited and clarified due to a typo rendering the statement useless.
Last edited by marcush. on Sun Aug 29, 2010 10:00 am, edited 1 time in total.

tok-tokkie
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Re: Red Bull RB6

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marcush. wrote:
n smikle wrote:Interesting. What effect does anti-ackerman on the F1 car? More turn in?
anti ackerman takes into consideration the optimum slip angle for the tyre at reduced vertical load(inner wheel ).If your inner wheel stays on the ground at cornering speeds and you have pro ackerman the inner wheel has to have more steering angle=more slip angle but has much less vertical load ..so youre not using the inner wheel properly you are abusing it a bit .
As we have learned tyres do not like to be punished at low vertical loads ..
With pro ackermann the inner wheel has less steering angle than the outer wheel but has more grip.(unless your tyre would like more slip angle at lower vertical load)

The maximum lock of the outward tyre inthe corner can be increased of course ,as the inner wheel does not steer more than the outer wheel.clearance wise its much better and aerowise for sure as the inner wheel does not block /modify the airflow as much when there is not much lock available un the inside..
definitely not good for pushing the car around in the pits ,but at racing speeds more than worth a thought.
I think there is a typo. The first pro ackerman should be anti ackerman?

marcush.
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Re: Red Bull RB6

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opps right!but wrong ..it´s the other ways round .Anti ackerman has less steering on the inside wheel.
But thanks a lot for paying attention..well appreciated.
Last edited by marcush. on Sun Aug 29, 2010 10:01 am, edited 1 time in total.

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raymondu999
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Re: Red Bull RB6

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marcush. wrote:
n smikle wrote:Interesting. What effect does anti-ackerman on the F1 car? More turn in?
anti ackerman takes into consideration the optimum slip angle for the tyre at reduced vertical load(inner wheel ).
If your inner wheel stays on the ground at cornering speeds and you have PRO ackerman the inner wheel has to have more steering angle=more slip angle but has much less vertical load ..so youre not using the inner wheel properly you are abusing it a bit .
As we have learned tyres do not like to be punished at low vertical loads ..
With ANTIackermann the inner wheel has less steering angle than the outer wheel but has more grip.(unless your tyre would like more slip angle at lower vertical load)
The maximum lock of the outward tyre in the corner can be increased of course ,as the inner wheel does not steer more than the outer wheel.clearance wise its much better and aerowise for sure as the inner wheel does not block /modify the airflow as much when there is not much lock available un the inside..
definitely not good for pushing the car around in the pits ,but at racing speeds more than worth a thought to have anti .

Edited and clarified due to a typo rendering the statement useless.
While I do appreciate your effort to impart this excellent piece of knowledge... could you summarise in human terms? All these engineering terms boggle the mind :shock:
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marcush.
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Re: Red Bull RB6

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I always try not to be engineerish... :mrgreen: ask expensive...

Ackerman is one steering layout geometrie and widely used in the automotive sector.
The idea behind it is :
the outer wheels have to cover a larger radius (r+track width) than the inner ones so it cannot be that you would need the same steering angle for inner and outer wheel .

So a full ackermann layout will mount the steering arms on the upright in such a manner that lines drawn through svivel points of upright , svivel points of steering toelink to steering arm will intersect exactly in the middle of the rear axle.
Steering action will now provide a steerangle x for the outside wheel and steering angle y of the inside wheel.the axlelines will intersect in the cornercentrepoint.
Image

This idea does not taking into account slip angles or tyre grip at all its justgeometry.

Racing cars very rarely drive geometrically ,there is always a component of slip
involved to maximise grip.going through the corner the tyre generates lateral grip.
This grip is maximum under a certain slipping angle .above and below that slip angle the grip will be less ..so you want to see optimum slip angle while cornering .
BUT Tyres are also load sensitive .so under a certain load the tyre might want to see 5° slip angle at double load it might want to see 6° slip angle and at half the vetical load the slip angle might be best at 2° ..

Now we are entering the corner introducing steering angle to change direction :
The coernering will introduce a shift of carnerweights/loads towards the outside wheels increasing vertical load.The driver will adjust the steering wheel to maximise the available grip during his aim to make the corner ...Too much ..the car washes out (lack of grip) too little the car leaves the track as the radius is too big.But there is also the inside tyre ...not carrying half axle load anymore but say a quarter of the original load.tyres are load sensitive..so what happens to the optimum slip angle ..it changes.if it does not change I need the same slip angle inside outside ..so no ackerman at all.If the unloaded tyre wants more slip angle .then I need pro ackermann and more slip angle introduced.
But ..it could be that our tyre wants to see less slip angle and we are going towards anti ackerman .

How do we know what the tyre needs ? you will have to either ask Tom ..but maybe his collegues will not be willing to tell or they don´t know..so you need to evaluate and see what is increasing grip on the track ...
This can be evaluated in limits by adjusting toe ...as this will of course alter the position of the front wheels to one another ...and you will see if toe in or out will increase your cornering grip...(g-force).


I´m happy to get this removed or moved by the mods as I feel it does not belong here.
Last edited by marcush. on Sun Aug 29, 2010 11:54 am, edited 2 times in total.

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mep
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Re: Red Bull RB6

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it should get its own topic maybe together with that CoG CoP issue

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747heavy
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Re: Red Bull RB6

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just to add a graphic for Marcus explaination of anti-ackerman geometry.
maybe that makes the "why do it" easier to understand.

Image
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raymondu999
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Re: Anti-ackerman steering

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Right. That diagram from Marcush says a lot. Thanks :mrgreen:
Just a question though. The outside wheel in a turn is always either getting more load or getting the same-ish load, for a longer period of time. How does anti ackerman help with that? Also, how does this affect how camber is set up?
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marcush.
marcush.
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Re: Anti-ackerman steering

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The steering geometry will ,in this compromise allow for more front total grip ,as both tyres can operate nearer their peak performance (in allowing both front tyres to assume best slipangle for the load they are subject to)

Of course as always this is a compromise as with rising speeds /downforce and depending on just how much load you are transferring optimum ackerman is a movable target obviously and compromise for each corner ,fuel load ,allast placement,spring and ARB setttings...another multiple variable equation to be solved there.. :mrgreen:
thankfully the graph posted by 747h clearly shows the peak of tyre load bearing capability is rather a round curve so the compromise should be to avoid the inside tyre to trop out of the accepable window of slip angles.

Jersey Tom
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Re: Anti-ackerman steering

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Don't forget about combined slip effects (ie braking)... and weight jacking / dynamic camber changes through caster.

Can do some trick stuff... like have the steering start off reverse-Ack at low steer angles and pro-Ack at high steer angles, or the other way around.

Just one more tuning tool to pick how much work each tire does. One more thing that can be used as an advantage, or one more thing that you can screw up.
Grip is a four letter word. All opinions are my own and not those of current or previous employers.

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mep
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Re: Anti-ackerman steering

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One thing I noticed by checking some graphs, the effect of the slip angle is almost reduces when you put little load on the tire. Check the brown curve. The curve becomes flat so the slip angle isn't that important anymore and the peak of grip is almost gone.
What I don't really get is why botter about the actual slip angle of a inside (unloaded) tyre?

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marcush.
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Re: Anti-ackerman steering

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there is a lot to this,mep.
look at touringcars ..lots of three wheeling motion ....look at sportscars ,F1 ...in some corners your inside front will not touch the ground...so the whole thing of ackerman is of course irrelevant there.
But:
Why not use all four tyres to the max?You got excessive traction capabilities to throw away 100% of lateral grip of 1 of the front tyres?
Haven´t some teams had big difficulties with front end grip this year? when fronts were bigger ,it seems reasonable to unload the inner tyre completely but with a loss of front footprint i would do everything to use all I got at the front.(That implies not to allow too much roll / squat at the rear ..as the bump /droop at the rear will quickly lift one of the fronts(just look at a rear puncture ..instantly the opposite front will be unloaded )
so it´s a very difficult battlefield.
basically you do not want the same toe settings for differnt steering angles /different types of corners .
Setting up a race car you will quickly find out different settings of toe will improve your car in certain areas and will make you slower on others.So the adjustment of anti7proackerman will help you find the best compromise.If your car does not have its (front)wheels planted ..ackerman will not help or hurt.

also what crosses my mind..if you unload the inner wheel anyways..maybe there is an AERO advantage to run the inner wheel straightened??? ....