Anti-ackerman steering

[ChaosMaster]

Hey guys, sorry, new here. Doing some research on the Pro Ackerman steering for an open wheel front sus setup (Uni Project, SAE). The more I read, the more confused I get though, could someone please outline the pros and cons of going Pro and Anti Ackerman? Circuit doesn't really have any tight corners, mostly medium and one long wide one, although not banked.

[marcush.]

obviously any ackerman setup influence will have more influence with steering lock applied.
Ackerman is trying to cater for the different turn radii of inner and outer wheel when cornering but with a car you do not really need this ..you want to maximise grip on all corners .
As the inner wheel sees less load it also can carry less load and potentially does maximise its grip at lower -not bigger slip angles so depending on tyre characteristic you may well find out anti ackerman does improve toal grip.
You can of course find out by testing if your ackerman characterisatics are suiting the tyres.
I´d think ackerman is something that should be kept adjustable with a race car.

[Tommy Cookers]

there will also be effects on steering angle with suspension extension/compression in cornering ('bump steer?)

ie due to (unavoidable?) geometrical conflicts of steering arms motion relative to motion of upright ?
(this could swamp your Ackerman tuning, unless you have minimal suspension travel)

apologies if you are already on top of this !

[Greg Locock]

"I´d think ackerman is something that should be kept adjustable with a race car."

Not according to the three serious race engineers I know. Life is too short.

use toe as fake ackerman to determine where you'd like to be for each corner, then set it somewhere in the middle. if you have time.

[Jersey Tom]

There are serious race series in which Ackermann is indeed kept adjustable.

[hardingfv32]

There are serious race series in which Ackermann is indeed kept adjustable.

Mechanic adjustable, not in car driver adjustable.... correct?

Brian

[GSpeedR]

Correct.

[olefud]

If you know your center of turning with slip angles, your can calculate a classical Ackerman geometry –though the correction may feedback and change your solution. Keep in mind that the turning thrust from tire graphs is a vector quantity and the thrust not through the turn center dumps into tire drag, which may or may not be all bad. This latter point could explain anti-Ackerman in F-1, but this is just IMO.

Ackerman is independent of bump steer as long as you keep your steering link and suspension link parallel and equal length.

Tires vary but many tolerate greater slip angles under light load than with a heavy loading, or at least they used to.

[marcush.]

well -formula 1 is adjustable..you can see it very clear on mclarens front upright .the shims are indeed there NOT for toe adjustment but altering the steering arm geometry.The tierod has additional provision for adjusting only toe...(not visible in this pic)

[ChaosMaster]

Having adjustable Ackerman would be ideal, however this is a University project, of which is only funded by sponsors. Forget fine tuning, any sort of track testing (on the final race track anyway) is out of the question. This is a race against other Universities after all, nothing professional. And it's more for experience than anything. Obviously, we have some toe and camber adjustments. All previous designs didn't have any Ackerman involved so this is a first for us, which is why I'm trying to figure out if Pro or Anti ackerman should be the way to go. Haven't actually seen any Anti ackerman setups though, much less adjustable ones, would anyone have any links?

[Jersey Tom]

Having adjustable Ackermann was pretty simple when I was doing this stuff at university. Shouldn't take more than a couple minutes to change and do a quick test driving around in a parking lot.

[ChaosMaster]

Having adjustable Ackermann was pretty simple when I was doing this stuff at university. Shouldn't take more than a couple minutes to change and do a quick test driving around in a parking lot.

Really? Any design ideas and such? I'm not even sure how to calculate the Ackermann angles. Uni hasn't taught us any of this stuff, so it's really based on our own research.

[marcush.]

sorry it is really really easy -as tom said :
You could for examble fix outer joint of the toelink to the upright by using a bracket .This bracket could be bolted to a corresponding surface of the upright .By adding and removing shims you can alter the position of the svivelpoint towards more or less ackerman.
You will alter toe settings by this of course ,so you need to adjust the toelink length after all adjustments.(I would design the system with toelink adjustment using the same shims than bracket fixing to the hub -so you could swap shim from toelink towards bracket adjusting Ackerman WITHOUT affecting toesettings....this will be a very quick way of adjusting ackerman on the fly with not much time available)

[Jersey Tom]

Having adjustable Ackermann was pretty simple when I was doing this stuff at university. Shouldn't take more than a couple minutes to change and do a quick test driving around in a parking lot.

Really? Any design ideas and such? I'm not even sure how to calculate the Ackermann angles. Uni hasn't taught us any of this stuff, so it's really based on our own research.

I had zero formal education in anything vehicle related at uni either. Get used to and in the practice of learning things on your own - helps a lot in the professional world. Why wait for someone to give you an explanation when you can figure it out yourself.

Easiest way to figure out how it all works is to make something like a dynamic 2d sketch in Solidworks, play around with it and see how the steer angles work out for various steering geometries. Comes down to arrangement of tie rods and steering links on the upright. As mentioned earlier, can be done via brackets and such.

[marcush.]

If you can´t visuualize it ..it gets difficult ..at least for me..I can actually see the concept in my head -no solidworks or autodesk necessary.
If you have no idea what your tyre or driver or track needs -you need quick and repeatable possibilities to dial in the geometry -there is NO possibility to align the car on the fly .so the shim concept -separating adjustments camber ,caster ,Toe etc and having a wide window of adjustment is king and exactly this is what a good design should deliver.