Wide open question.........

building a new grasser for 2007, so will be building it during 2006.........

I'd like to incorporate something that I think will enhance early corner handling, but maybe I am wrong.

I want a way of countersteering the rear (driving) wheels during corner entry roll movement, but without toeing both rear wheels out during squat.

Strictly speaking rear wheel or 4 wheel steering is illegal in the regs for Autograss racing, but I think it can be incorporated into a "normal" toe adjustment system.

The tricky bit is getting it to roll steer without altering toe during pitch changes.

I had an idea of using a rocker/bellcrank to mount the inboard end of the rear trailing arms, and operating the bellcranks vis the anti-roll bar, with adjustable stops to set the min and max movement........but then when the antiroll bar is unladen, the bellcranks will float and the toe will move around........
any ideas??

(thinking of some sort of clever over centre arrangement where the rollbar can move the rockers but they can't move themselves......................just can't picture how to do it.....not very good at clever linkages!)

[Edited on 11/12/05 by NS Dev]

[Edited on 11/12/05 by NS Dev]

a weissach axle in reverse ?

pardon my ignorance but wossat!?

ahhhhhhh, just googled!!

Yup, exactly a weissach axle in reverse, nicely put!

Any ideas on doing that but without rubber involved and only affecting the geometry in roll and not in pitch???

hmmm , can only thik of using the movement of a roll bar .

ie a mechanical link that uses the twisting movement to move a toe link outwards .

are u saying your motor doesnt turn in roll because of a locked diff or something .

what about setting up a weissach axle , with extra toe out as std

Yes, locked diff.

Initial turn in is ok, but then the requisite oversteer is purely power/track surface governed. If this could be induced after the initial turn-in has set the roll angle then I think the car would be easier to drive, and the key to autograss, easier to hold the inside line.

Any hint of understeer mid corner and somebody is in the gap.

Oversteer is easy to correct with steering input, but understeer means being animal with the brake and throttle which is never good for track positioning and controlled progress.

As I say, might be a daft idea but I think it might just work........need any tricks I can think of!!!

hmm , ill sleep on it !!

Wonder if you could achieve an effect by using cranks somewhat along the lines of the Dax suspension system which moves suspension pivot points and thus camber in roll but tied into steering arms instead?

might be possible, but I think I might be pushing my luck with the scrutineers if there is an obvious "steering arm" involved, rather than something that looks like a toe adjuster.

I am the club chief scrutineer so it'll be ok at my club but at other events I may not be so lucky!!

How about using a gas strut (as found in car tailgates) as the toe-link. You can buy these at different 'strengths' I think. RS Components sell 'em.

At max extension it won't give toe-out, but will compress to give toe-in. You would need to fiddle with the settings and the geometry to get it to work...

...just an idea, I haven't fully woken up yet!

quote:

---

Originally posted by NS Dev
might be possible, but I think I might be pushing my luck with the scrutineers if there is an obvious "steering arm" involved, rather than something that looks like a toe adjuster.

---

Why don't you do something similar to what Rover did on the 200.

Not sure how to describe it but ....

Mount the rear axle on a trailing arm system, then the chassis mounts for the trailing arms aren't mounted to the chassis at all. They are mounted to "something" that is mounted to the chassis (i think in the middle). Add a element of compliance into this mounting so that when the car starts to turn in, that flexes on its mounting causing the rear wheels to 'turn'.

Not double wishbone I'm afraid, it's trailing arm.

Old school but very good at keeping the wheel square to the track during huge pitch movement...............perhaps this pic will explain.......:



l25startatmap

nice to see you infront with the throttle pedel floored

(to those that haven't seen the car race, it really drops at the rear a lot when the power is applied)

thanks Mike!

Was a really good start (especially considering I was the least powerful car there!!) Shame it all went wrong in the first corner eh!!!

[Edited on 12/12/05 by NS Dev]

i never mentioned that bit!

see, you're your own worst enemy

Reading up on the weissach axle, it seems a good solution, i'm sure that the s/w i gave you ages ago can model that as well.

Still want you to look into auto camber adjustment as well. The way you shred the one side of the tyre in some races means it would have to be a benefit.

(plus could help mask some of this as well, but suspect it might be too much to adjust with the zero setup time you have)

have tyou decided on a class yet ? (7?)

I started think of a way to to do it using void bushes and additional control links but then --
thinking out of the box didn't Lotus use a 3 point subframe mounting on the FWD Elan to reduce understeer --- I think 2 of the mountings were void bushes.

quote:

---

Originally posted by MikeR
Why don't you do something similar to what Rover did on the 200.

Not sure how to describe it but ....

Mount the rear axle on a trailing arm system, then the chassis mounts for the trailing arms aren't mounted to the chassis at all. They are mounted to "something" that is mounted to the chassis (i think in the middle). Add a element of compliance into this mounting so that when the car starts to turn in, that flexes on its mounting causing the rear wheels to 'turn'.

---

But .... the roll stiffness would be up to how NS Dev designs it.

Also, somethings just occured to me, the max amount of movement we can design in is the max in/out travel in the drave shaft CV joints minus a little bit to stop the thing going solid.

Any idea how much this is ? How much we're looking for? It might just affect the approach.

Trouble is with a torsion beam the high roll stiffness comes with structure of the beam.

good stuff link
http://www.autozine.org/technical_school/suspension/tech_suspension21.htm

but i was thinking of attaching the trailing arms at the end of the beam as attached now to the chassis. The restistance to turn in the beam would be a factor of friction between the beam and the chassis (and i guess some mounting bush).

In the original setup isn't the beam used as a torsion / anti roll bar, hence the name? (at work, can't really look it up to check).

quote:

---

Originally posted by MikeR
But .... the roll stiffness would be up to how NS Dev designs it.

Also, somethings just occured to me, the max amount of movement we can design in is the max in/out travel in the drave shaft CV joints minus a little bit to stop the thing going solid.

Any idea how much this is ? How much we're looking for? It might just affect the approach.

---

[cough] megasquirt [cough]

I know, i know it involves some work but its about 500 pounds cheeper!!!

How much is your time worth again?

..........................if somebody can advise me how to run a 5 cyl engine with coil on plug ign on megasquirt then I am open to the idea.......not sure it's poss tho.

quote:

---

Originally posted by NS Dev
..........................if somebody can advise me how to run a 5 cyl engine with coil on plug ign on megasquirt then I am open to the idea.......not sure it's poss tho.

---

ms2 may be able to - its going to be more expensive tho .

with tuning time limited to the track ie you cant just go up up the road for a tune , an MBE or omex ecu etc, will be best , since you have little setup time ie to pay someone else to do it . Since tuning will be done on a dyno - making it easier will make it cheaper in the long run

ok, that's probably the best answer really, as the chap that I would be getting the Omex ecu from does the mapping too, and he is in my autograss club and is supplying me with a gearbox as well, and has just started installing a rolling road on his own site, as well as the one he uses at another site, so would be inclined to use him anyway.

MegasquirtnSpark

http://megasquirt.sourceforge.net/extra/setup-wheel.html

Sounds like what you need!

that's what I meant by the generic "megasquirt"

prob is getting it to work with 5 cylinders!

I believe a number of production cars (fwd mainly though) have a form of passive rear wheel steering to help handling. I'm sure I've been in one recently and it felt quite strange - must have been a pug 306. Will have to check.

But basically the system works on lateral load rather than roll, so there is no problem with straight line pitch change. The suspension bushes are designed to compress in such a way under lateral loading that the rear outside wheel toes out subtly. It was definately noticable on the pug (pretty sure it was a 306 now) but took some getting used to to predict. Certainly increased the neutrality on the FWD car.

I imagine it could be achieved on your car by having all your joints rigid (i.e. rose joints) except your toe link (provided it's at the rear) which is on rubber or otherwise slightly compressable. Then the outside rear wheel would be forced to toe out slightly under cornering loads. Obviously the amount of toe allowed and the load required to initiate it needs to be experimented with but should be a simple system and all but invisible to scrutineers.

Liam

thanks for the ideas, food for thought, thanks Liam, not keen on the rubber but I think there must be another way of doing it.....................if it is actually worthwhile, keen to find out tho!

bitchy comment sent via u2u

sure there are 5cylinder guys using megasquirt - i'll look them up for you.

(cause if you go megasquirt you can figure out how to do it before i do :p)

LOL

believe me , MSnS is a PIA , for 5 cyl , you need an audi dizzy , etc etc , trust me , id be doing it already if you could .

the problem is timing intervals , the software wont allow for the timing split on a 5 cyl , now fuelling is a different matter .

I do believe you!

That's why I made enquiries with Steve Walford about the Omex unit. I'll be investigating the MBE system as well.

I've been thinking about this roll steer as well. getting it to steer in lean but not in bounce.
I did a few sketch es on auto cad but not sure yet how i'm going to post them for you to look at. I've done it before so it can be done.(the posting that is)

Mike

you can email em to me on n.seviour@ntlworld.com

I have autocad so no probs

E-mail sent
now remember it was just a quick drawing so i could see it work in my head better.

Mike

mmmmm interesting!

I'll have another look when I am more awake!!

Certainly has the principles of something that could work, just need to understand the outer ends!

Thanks!

had project management moment at work.

We're looking at this the wrong way.

We're not trying to get rear-end steering. We're tying to get your back end to overstear more easily so you've less chance of understeer when cornering. There are other ways!

Weight transfer for one! Have your entire engine shift 10 mill sideways when you enter a corner

(try explaining that its supposed to do that to a scrutiener!)

For everyone else
Rescued attachment RWSRUN1j.jpg

Just think of the little purple circles at the end of each rod as rod ends
Rescued attachment RWSBOUNCE1.JPG

also there is no A-arms or trailing arms or such like showinf so you need to use your imagination a bit
Rescued attachment RWSROLL1.JPG

remember theese are just quick sketches so I could see it work in my head, so it's not a final design in any way

Mike

Had a conversation(argument) with someone at work about the rear steer , on a road going car with rear driven wheels I've always been under the impresion that when cornering right you would want the wheels to steerin to the corner to hold the car in to the apex?
He rekons that it should be the oposite it should steer out to get the back end round.
But if you steer out on a driven wheel does that not give mega oversteer?
I normally listen to what this boy has to say coz he used to build and race sidecars allover the place, but this time i think he could be wrong
I have an old mk2 80 quattro sitting at home and thats where i got the idea of rear steer in my locost and as far as i can tell on the workings on the rear suspention it steers in on a corner, but if 4 wheel drive still be the same though driving wheel steering in to the corner?

Mike

When Nissan did the 300 that had rear wheel steer. I *think* they programmed it so that it steered out of the bend at slow speed to increase the turning effect of the car and into the bend at high speed to increase stability.

This is a 10 year+ old design but they probably did the maths first.

I'm afraid the answer is not really that simple, Mike! What way you might want your rear wheels to steer totally depends on the natural characteristics of the vehicle, the driving conditions, and what you are trying to achieve with your 4 wheel steering. All active systems i'm aware of (skyline, honda prelude, early 90s F1 very briefly, for example) are capable of turning the rear wheels either way in a corner. The prelude turned it's rear wheels depending on the angle of the fronts - into a corner at low lock for high speed stability and stable lane changing, but outwards at high lock for reducing understeer. The F1 system was a complex mapped feedback system that kept the car neutral at all times - mainly correcting low speed understeer and high speed oversteer. Skyline system is designed for fun - using various inputs to work out the drivers intent, then usually decides he wants to hang the rear out in a massive power slide, and happily obliges flicking the rear wheels out then in to unstick the rear, but all the time keeping it under perfect control.

With a simple passive roll or lateral load actuated system you only have the choice to steer the rear wheels one way. NS Dev wants to increase oversteer and drive even more sideways so his rears want to steer outwards a bit. Production front wheel drive cars only really suffer from understeer so can also use the rears to shift the balance towards oversteer. Something like a seven is a bit trickier because they can suffer from either understeer or oversteer. However they tend to be predominantly oversteery, especially at higher speeds and with reasonable power. With a road going seven you might well want your rear wheels to steer into corners to increase high speed stability and reduce general oversteer - would certainly help some seven drivers i've seen on tracks! But any low speed understeer (especially in rear heavy becs) will be increased. A track based seven may want it the other way around to eliminate any understeer, and live with (or try and dial out with spring/damper adjustment) the extra high speed oversteer.

So hard to find the right answer. Totally depends on your intentions for the car. I would have thought increasing oversteer would be dangerous on a road going seven - ask all the people who've become intimate with roundabouts/hedges/ditches. I'd really like to see a nice active system on mine one day, but the complexity would be pretty daunting.

Hope that helps

Liam

[Edited on 18/12/05 by Liam]

Yep that sounds about right

Cheers

Mike

quote:

---

Originally posted by Liam
I'm afraid the answer is not really that simple, Mike! What way you might want your rear wheels to steer totally depends on the natural characteristics of the vehicle, the driving conditions, and what you are trying to achieve with your 4 wheel steering. All active systems i'm aware of (skyline, honda prelude, early 90s F1 very briefly, for example) are capable of turning the rear wheels either way in a corner. The prelude turned it's rear wheels depending on the angle of the fronts - into a corner at low lock for high speed stability and stable lane changing, but outwards at high lock for reducing understeer. The F1 system was a complex mapped feedback system that kept the car neutral at all times - mainly correcting low speed understeer and high speed oversteer. Skyline system is designed for fun - using various inputs to work out the drivers intent, then usually decides he wants to hang the rear out in a massive power slide, and happily obliges flicking the rear wheels out then in to unstick the rear, but all the time keeping it under perfect control.

With a simple passive roll or lateral load actuated system you only have the choice to steer the rear wheels one way. NS Dev wants to increase oversteer and drive even more sideways so his rears want to steer outwards a bit. Production front wheel drive cars only really suffer from understeer so can also use the rears to shift the balance towards oversteer. Something like a seven is a bit trickier because they can suffer from either understeer or oversteer. However they tend to be predominantly oversteery, especially at higher speeds and with reasonable power. With a road going seven you might well want your rear wheels to steer into corners to increase high speed stability and reduce general oversteer - would certainly help some seven drivers i've seen on tracks! But any low speed understeer (especially in rear heavy becs) will be increased. A track based seven may want it the other way around to eliminate any understeer, and live with (or try and dial out with spring/damper adjustment) the extra high speed oversteer.

So hard to find the right answer. Totally depends on your intentions for the car. I would have thought increasing oversteer would be dangerous on a road going seven - ask all the people who've become intimate with roundabouts/hedges/ditches. I'd really like to see a nice active system on mine one day, but the complexity would be pretty daunting.

Hope that helps

Liam

[Edited on 18/12/05 by Liam]

---