n smikle's LMP car

[PlatinumZealot]

Ok, lets see what happens.

[PlatinumZealot]

Check out the control arms on the Zonda R.

http://www.autoblog.com/photos/pagani-z ... l/#1336907

Why are the mounting axes angled like that? Like the Arms rotate a little forwards as the wheel travels.

http://www.autoblog.com/photos/pagani-z ... l/#1336904

[PlatinumZealot]

I have to put he steering rack behind the front axle. How should I set it to have good ackerman behaviour?

[marcush.]

I have to put he steering rack behind the front axle. How should I set it to have good ackerman behaviour?

what is GOOD for a racecar in terms of pro ackerman? The tyrecharcateristic will decide on how much pro or anti Ackerman you will need.
Ackermann will show its force when more steering angle is needed ,so in slower corners..you are likely to have less vertical force on the inner front tyre...so the question is how much slipangle does the immer less loaded tyre want compared to the outer higher loaded tyre ...so if your car does lift the front inner wheel at the slightest turn anyways..forget ackerman...
You may also be surprised by pro-ackerman turning the inner wheel a lot more so all your packaging has to cater for wheelmovements you don´t need to go quicker!
(thats for example an issue with Lotus elise where the inner wheel does come very close to the tub ,and geometric bind is also an issue with suspension travel ....giving interesting sideeffects to your ARB characteristics..
So do your race tyres need more slipangle with decreasing vertical load would be the reason to want pro ackermann behaviour ..and that would favour your back of axle positioning of the rack ...

[PlatinumZealot]

Tell the truth.. I have no tyre data and I don't know where to get them.. I only have a tyre size that I think the car will use. I sort of want it like a street sport car that is converted to a race; a car that can work well with many tyres. The car is supposed to behave similar to one of those FR race cars, like the ferrari 599 or the Corvette.

From your experience which ackermann, positive or negative is used on such cars? (599 and Corvette).

I am also encountering some issues with camber due to steering movement. What is the best way for the camber angle to relate to the steering angle?
For example do you want the camber to increase/decrease when toeing in or toe out?

[marcush.]

Tell the truth.. I have no tyre data and I don't know where to get them.. I only have a tyre size that I think the car will use. I sort of want it like a street sport car that is converted to a race; a car that can work well with many tyres. The car is supposed to behave similar to one of those FR race cars, like the ferrari 599 or the Corvette.

From your experience which ackermann, positive or negative is used on such cars? (599 and Corvette).

I am also encountering some issues with camber due to steering movement. What is the best way for the camber angle to relate to the steering angle?
For example do you want the camber to increase/decrease when toeing in or toe out?

I can only advise to try and get as much information from the Jts of the world or
try and build a wide range of adjustability into the car ,preferably one adjustment not affecting the other(Ackerman adjustment by shims ,also sterring toe adjustment by shims =so you can quickly evaluate where to go.
look up front uprights of Merc/RB/MACS one of those has ackermann shim adjusters.clever.
use one type of adjusting shims.so you save a lot of spares you neeed to carry!
shims are a lot better when it comes to make equick changes and not having to measure up the whole thing again and again.you setup the car in the morning and do so when your finished and compare with what you have done.ready.repeatable.

I don´t think any data from other cars is useful ,the elise liked the anti-ackerman for the kumho tyres for example,but what to derive from this?

as for the camber change in turn -Kingpinangle will reduce your camber on the outside wheel as on the inside .very often the kPA cannot be zero ,because of the axis then having the need to be in middle of the wheel ..so you really will lack space for the brakes etc as all has to be ppackaged into the outer half of the rim.So you compromise there,as having a lot of offset will increas scrub dramatically..and thats a bad thing either.
With caster you add negative camber on the outer wheel and positive camber on the inner wheel when turning ..this is of course desireable.But also there are limits of how much can be done.
this is not to be confused with caster trail .. !
So make up your mind how you could achieve the adjustability so at least you can
tailor the car to the tyres if you feel its not working for you.And its good fun to adjust the car and optimise..

[PlatinumZealot]

I don´t think any data from other cars is useful ,the elise liked the anti-ackerman for the kumho tyres for example,but what to derive from this?

I want to use those FR cars as a guide. The actual geometry is of interest to me. This can help me to see If I am on the right track. I made a movable wireframe model representing the members of the suspension. I intend to dial in the dimensions of the suspension now and see how it behaves over a range of motions, but there are so many variables that is why I would like to see it is approached on those top performing Front engine race cars (ferrari 599 and corvette).

[marcush.]

I don´t think any data from other cars is useful ,the elise liked the anti-ackerman for the kumho tyres for example,but what to derive from this?

I want to use those FR cars as a guide. The actual geometry is of interest to me. This can help me to see If I am on the right track. I made a movable wireframe model representing the members of the suspension. I intend to dial in the dimensions of the suspension now and see how it behaves over a range of motions, but there are so many variables that is why I would like to see it is approached on those top performing Front engine race cars (ferrari 599 and corvette).

I got some real world measurements of the corvette z06 somewhere... chassis points ,wishbone dimensions ,upright dimensions.I´ll look into it .Still i´m nor convinced what you are trying to achieve by duplicating suspension layouts.
you don´t know what led those to the decisions they took and as I think you will use spherical bearings your starting point is not elastokinematics anyways.

[PlatinumZealot]

Ok.. tracking back a little bit, I implemented the roll centre method and now I have found my roll center (axis). It is about an inch below the ground at the front of the car.

Now that I have it (and I can also change it if i wish) what do I do with it?

[747heavy]

you may find some useful informations about tire characteristics here.
Sorry it´s mainly for road car tires, but still better than nothing - I would think

http://www.nhtsa.gov/staticfiles/saferc ... 10-561.pdf

There is a difference between a force based roll centre and a geometrical roll centre (roll axis).
You will need to included at least vertical tire deflection in your geometrical roll centre model, to get a useful approximation of "real" roll centre/roll axis location.

you may find some useful and interesting information for you here

Enjoy:

http://www.vehicledynamics-expousa.com/ ... kianov.pdf
http://www.theoryinpracticeengineering. ... alysis.pdf
http://www.neohio-scca.org/comp_clinic/ ... cs2007.pdf

[PlatinumZealot]

OK thanks for the information. I am really trying to approach this in a systematic manner (engineering approach) and that is what I am finding very difficult with all the roundabout and "rule of thumb" articles on the internet. Then again, I don't necessarily want to get too deep if I do not have the proper tools.

There is a lot to digest, it. This is why I left this part for last.

[MadMatt]

That looks like a nice project mate, any update on it ?

[PlatinumZealot]

Thanks, I hadn't really touched it for a while. I only just made some updates last week.

I have recently decided to go with a aero-centric philosophy for this car so I have narrowed the chassis, placing the driver in the middle. I guess you can say the RedBull RB7 influenced me somewhat.
The compromise is that there is going to be a raise in centre of gravity since the driver will now sit on the drive shaft tunnel. I think the possible gains in downforce will be well worth it.

Very Narrow chassis. Hoping to put some large venturi tunnels at the sides. Keep in mind this car is gonna be 2 meters wide.. hehehe..

[PlatinumZealot]

I am still having some lingering concerns over the roll centre. I read the Mclaren F1 wiki, which says that the Mclaren F1 had identical roll centers front and rear....

OK.. you know what. Somebody just tell me where to put it. front and back.. and where should the roll axes intercept from and back.

Please and thanks...


Moving on to something else now.. (I hope you guys see now why i didn't waste time finalising the frame - I can change it anytime)

[Caito]

They're probably gonna jump all over me. But... who cares. Adjustability would be good, so you could try what is best to you.

Put the front roll center above the ground, and below the COG. Restrain its movement in between the wheels.

Same for the rear, put it higher than the front.

Make the rear roll center move "in compass" with the front. If one moves left, the other moves left. Don't let one move to the right and the other to the left.


Yes I'm guilty because it's all BS, and how can I know if that's better? I don't, it's just a starting point. After all KRC is just.... ok, no, I don't want to start that discussion again.



There you go, you can move on with your project. If you get all the time with roll center(or suspension kinematics) you're going nowhere. Don't put all the beans on one basket.


Bye!


Hope it helps.



Caito.-