Anyone still believe in 4WS?

[Chuckster]

I've read all the past posts on 4WS several times now and wonder if there are any new thoughts churning about out there now?

My interest is from the perspective of a high powered Solo car that lifts the front wheels a little in some slow corners. If it ain't turning-already--well, you get the picture.

Has everyone come to the conclusion that fiddle brakes are really the answer?

Thanks!

[Chuckster]

I've read all the past posts on 4WS several times now and wonder if there are any new thoughts churning about out there now?

My interest is from the perspective of a high powered Solo car that lifts the front wheels a little in some slow corners. If it ain't turning-already--well, you get the picture.

Has everyone come to the conclusion that fiddle brakes are really the answer?

Thanks!

[Buckingham]

Any time you have the ability to dynamically control another degree of freedom of a system, you have the opportunity to increase the operational performance of the system. It all comes down to execution, whether its the mechanical design of the system, the control strategy used, or the theory upon which the control strategy is based. Theoretically, every car should be able to be made faster by adding properly engineered 4WS.

[Rex]

Exactly - 4WS makes a car faster in SOME things. But it makes other things more difficult and/or slower. For example, opposite steer makes slaloms a breeze, but makes it awfully hard to apply power at corner exit. Parallel steer has pretty much the opposite effect. So with a basic proportional system you gain something, but lose something else. I have always felt that a "smart" system that is actively controlled (or maybe a very trick mechanical system) would be necessary to see any real overall gains.

[absolutepressure]

The 3000GT VR-4 has 4WS. It has opposite steering at slow speeds (maybe up to 40ish?) and parallel steering at higher speeds. You should see how they do it.

[BamaJeff]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by absolutepressure:
The 3000GT VR-4 has 4WS. It has opposite steering at slow speeds (maybe up to 40ish?) and parallel steering at higher speeds. You should see how they do it. </div></BLOCKQUOTE>

As well as the Z32 (1990-1996 Nissan 300ZX TwinTurbo). It has "HICAS" (High Capacity Actively Controlled Suspension).

More can be read about it here:
http://en.wikipedia.org/wiki/HICAS

[TG]

One website had this graph showing what the steering response of the old 4ws preludes was
http://www.autozine.org/technical_school/traction/tech_pic_traction_4ws.jpg

It parallel steers up to a point for small changes (like at high speed) while goes into opposite lock for larger (slower) steering. The site mentioned it was operated through an eccentric shaft and planetary gear... nothing too complicated like the HICAS systems.

[Mr. White]

Our car (F2007-V2) has 4WS. During tests we have noticed a perceptible improvement of car agility.. Designers love it, drivers enjoy it.. want more?? http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Steve Yao]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mr. White:
Our car (F2007-V2) has 4WS. During tests we have noticed a perceptible improvement of car agility.. Designers love it, drivers enjoy it.. want more?? http://fsae.com/groupee_common/emoticons/icon_wink.gif </div></BLOCKQUOTE>

Back to back lap times with it on and with it off/disconnected.

How does it feel when countersteering during oversteer recovery? Seems like nonlinear car response would be terrible for such a critical situation.

[Jersey Tom]

I can see it being cool for low speed and offroad driving and maybe the first first bit of turn in.. but in the middle of a corner if you already have a balanced car that's pushing all the tires to their peak, maximum grip slip angle.. what does it gain you?

[Matt N]

... stuff to break?

[TG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mr. White:
Our car (F2007-V2) has 4WS. During tests we have noticed a perceptible improvement of car agility.. Designers love it, drivers enjoy it.. want more?? http://fsae.com/groupee_common/emoticons/icon_wink.gif </div></BLOCKQUOTE>

Mr. White,

I remember seeing your setup in photos, but from what I remember, you guys had it disconnected at competition, why was that?

[VFR750R]

The trick ( I think ) would be rear steering proportional to front steering rate and not angle. This could give you the transitional benefits perhaps without sacrificing mid corner.

[Mr. White]

[to SEY] for low rear steering angles, in countersteering 4WS helps the driver, quickly reducing the toe of the rear laden wheel.. the car is very easy to drive! increasing rear steering angles the car becomes too "rough".

[to Jersey Tom] 4WS helps reducing the actual slip angle of the rear wheels, and allows to cut down the front steering angle for a given path (just as reducing the wheelbase).. so even in the middle of the corner you have some advantages.. even if, as you say, the best benefits are in the very first bit of the turn and in slalom.

[to TG] During FSTUD 2005 competition, the system was too "young".. no tests=too problems..

Sorry for verbose post!!!

[Steve Yao]

So, are you saying as long as the driver catches it quickly, before rear slip angles get too large, its ok, but otherwise..."rough"? Is that a euphemism for "unstable"?

Lap times?

[Mr. White]

No, I say that if you set the maximum rear steering angle to a low value (lower than the limit imposed by rules) the car is esay to drive, and 4WS helps you even in countersteering.. For a higher maximum rear steering angle the car becomes not so easy to control..
you can see some manoeuvers of our 2005 car with working 4WS here:
http://www.pcm.unifi.it/FORMULA_STUDENT/ITA/FILM/skid_4ws.wmv
http://www.pcm.unifi.it/FORMULA_STUDENT/ITA/FILM/slalom_4ws.wmv
http://www.pcm.unifi.it/FORMULA_STUDENT/ITA/FILM/step_steer_4ws.wmv

[Steve Yao]

Ok. So keeping the total amount of rear steer conservative seems to drive ok, but any more and its unstable...

Nice videos.

Doing donuts must be super easy. http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Mr. White]

eheh.. doing donuts has never been so easy!

See you @ FSAE West!

[Rex]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mr. White:
Designers love it, drivers enjoy it.. want more?? </div></BLOCKQUOTE>

Design JUDGES, on the other hand, don't really care for it at all unless you can PROVE that it's considerably faster than a traditional setup. Or at least they didn't back in 2002. You can tell them it helps negotiate slaloms, or that it makes turn-in "feel" better, or that it feels like the back wheels are on ice if you apply too much power at corner exit even at angles lower than dictated by the rules - but without quantitative analysis and data it doesn't count for much.

We never did enough lap time testing to get conclusive/reliable results, but it certainly wasn't night and day different in terms of lap times. Most of the gains from full-time-opposite 4WS are probably perceived rather than actual.

[absolutepressure]

IMO, your back end kicked out because you have opposite steering. If you had parallel, I don't think that would've happened, and it seems like that's the way to go in lane changing type maneuvers. It seems like any quick direction changes with opposite make the rear end flick out and cause oversteer, but I do see how it could help end oversteer sooner during opposite lock. I don't know if yours is mechanical or electronic, but if you had a NOS like button on the wheel that changed it to parallel for slalom situations, that would be cool. It would also be cool to see what would happen in the middle of a turn while switching between the two.

[Rex]

The system I'm talking about was hydraulic, and could be switched (not on the fly) via a valve setup. You're right that with parallel steer it was rock solid at corner exit. But it also wouldn't clear minimum radius hairpins.

I really think opposite is the way to go for slaloms. Some of our other drivers might have different opinions, but it always felt like the faster setup to me. Kind of the same theory as making a narrower rear track - makes it pretty easy to get around the slalom cones. Again, I wish we had data.

A system that's a bit "smarter" is clearly the right answer - but such a system could also be a huge failure "magnet" given the complexity involved so we decided to focus our energies on other things.