4WS as stability control?

I'm building a car with two front-wheel-drive power trains, one in front and one in back. Initially, I was planning on locking the rear steering rack and calling it done... but when I drink too much caffeine in the evening I lie awake staring at the ceiling thinking about stuff.

In my mind, it should be possible to do a couple of interesting things with the rear steering already in place, but it seems too easy in my head to not already be commonplace. I was hoping someone could point out a fundamental reason that this is a bad idea. Aside, of course, from my drinking buddies code running into a bug and driving me into a wall.

I'm thinking that given input from a rotary encoder on the steering column, a controller could be built that would manipulate a servo to steer the rear wheels, increasing steering quickness and behavior based on user setting, or with additional input of an accelerometer, and speed sensor from the tranny, rear steer could be used to ensure neutral handling characteristics regardless of how you throw the car into the corner. Not saying it will necessarily go through the corner faster for a good driver could, but it will at least be consistently pointed at the apex when you slide off the outside of the corner or into the wall. It would seem that by having software control over rear steer you could make the handling 'feel' any way you want to by simply manipulating the software controlling the rear steer servo.

Yeah, there would have to be some electronic voodoo involved, but I happen to know some pretty talented witch doctors.

Using 4WS for stability control seems, in my mind, a fundamentally more efficient way of controlling vehicle heading than pulsing the brakes and in effect scrubbing speed which is my understanding of how current stability control systems work.

But if it were that easy, everyone would be doing it. And I can't find a whole lot of examples of such. Plan A: just fix the rear steering rack with the wheels pointed straight ahead. But I'm going to think about this some...

In reply to sporqster: 4ws is very complicated and for it work in all conditions slow and highspeed ect the angles need alot of tuning based on vehicle speed ect...... and if you absolutly over cook it its not going to help in how an actual stability control system does. why fix the rear rack still in the car. connect the tierods at the angle you want them to allow for the amount of toe change you want during accell and brakeing. just weld in some mounts and fab up some inner tierods or adapters and your good to go. less to break. and yes current vehicle stability does hit the brakes but not just hit them. it controls pressure to each individual wheel allowing the vehicles dynamics to be completely changed. the system also alters throttle position and even will shift the transmission in some autocars.

In reply to sporqster:

Its far from new or untried. Google "four-wheel steering" and you get a lot of hits from an article on Wikipedia to links to cars (and trucks, tractors and construction equipment) with it.

The phrase "active four-wheel steering" generally describes systems where the rear steering is computer controlled.

I think I would remove the rear rack all together and find a place to mount the tierods so that you get some passive rear steer using car roll and suspension angles to toe in or two out the rear wheels

hmm: http://www.littlelamborghini.com/ifac-cts-2006011-01aug-0603yoo.pdf

Mazda GD chassis cars were had with active 4ws or "passive" 4ws. Both in the name of stability.

GM QuadraSteer is one of the best operating systems I have driven. I drove the prototype trucks when they were in development and the computers were open to modify several of the settings. The most fun setting to change was what they called "Crossover"...where the wheels went from low speed opposite steer to parallel steer for high speed stability.

The basic change between standard "No rear steer" to opposite steer On cut lap time on a triangle shaped course from about 18sec to about 15-16 sec.

On the full autoX course we keep stepping up the crossover speed until we got to near 70mph and that really livened up the extra-cab long bed truck we were driving and cut lap times. GM set the basic crossover to 45mph for the average consumers safety.

Prelude 4WS

Correct me if I'm wrong but I believe the old Prelude 4WS system was purely mechanical. Might want to look into adapting that system to your needs.

Although the idea for passive 4ws like mad_machine suggested would be how I would approach it.

coll9947 wrote: Prelude 4WS Correct me if I'm wrong but I believe the old Prelude 4WS system was purely mechanical. Might want to look into adapting that system to your needs. Although the idea for passive 4ws like mad_machine suggested would be how I would approach it.

Correct, 4WS-equipped third gen Preludes, like the one shown in that video, are mechanical 4WS. A lot of people like them, and although I have no personal experience, I hear it's a pretty trouble-free setup. However, I read that most reviewers could not determine if a third gen Prelude was 4WS or 2WS just by driving it.

With the exception of GM's Quad steer trucks, 4WS seems gimmicky at best. No manf. used it for more than a few years before dropping it. To expensive and troublesome for minimum benefit.

Now, if you could do this, I'd say go for it.

http://www.youtube.com/watch?v=XVQ4RimajTk

I do both. Just sayin'.