All Wheel Steering

[assquatch20]

So I don't post much, but I'm trying to slowly collect extra ideas for a project without getting overwhelming. I'm trying make an AWD Chevette, and the idea of active rear steering is coming to mind. I'm wanting an independent rear with maybe a Corvette subframe, but that's besides the point, kinda. Again, I don't wanna overwhelm with chassis and suspension questions, but I do have a ton. I've got homework to do, but I'm looking to make a full-tube car with the 'vette shell, and probably an entirely new floor and firewall, given the build goals.

At first it was an aim for a fully-mechanical system (no TC, PS etc.), engine management aside, and I'm still interested, but that brings me to the question: do I just gut a Prelude mechanical steering system or is there a way to rig something up with GM parts that are out there or? I'm assuming a custom shaft to connect front and rear, but I'd like to avoid electric motors and servos if possible. Electronic transfer cases might change my mind, and I eventually have ABS and the full works in it, but that's way off the mark, I think.

This isn't a necessity, just an idea. How could it be done feasibly? For chassis design, I'm gonna keep doing my reading.

[Jetfixr320]

GM has done it. https://en.wikipedia.org/wiki/Quadrasteer

[raustinss]

And the c3 sierras that had it had some very serious electronics and programming to make it function. My question is why ? , with such a short car and a small turning radius doesn't really seem to be something that would be beneficial. Not to mention the gm c3 system came off obviously a much larger vehicle so even if you got it to work. The programming would have to be modified to work with such a small car.

[srh3trinity]

Wasn't there a model of the Mitsubishi 3000gt that had all wheel steering?

[cpd004]

I thought the Prelude did way back in the day.

[andrewb70]

The second gen RX7s had passive rear steering. This was done with the use of a special link and bushing at the rear spindle.

Again, the question is why? Seems that the trouble to make it work would yield questionable benefits and possibly make handling worse.

Andrew

[dirty rick]

Before you get too deep, rear steering needs very little travel for anything but parking. Next depending on the speed and turning radius the rear wheels might actually need the steer opposite. And yes a short wheelbase is going to make rear steer even more sensitive, even downright scary.

[raustinss]

on a short wheelbase car that weighs less then 2000 lbs stock and has a turning radius that gm called the smallest in the world 30 feet ,im going to say the idea is cool ,way too involved to use and mainly useless..not needed

[ace_xp2]

Well, there'd be no reason for decrease turning radius steering on a chassis that small, but opposite steer will help reduce the the rotation rate of that car at high speed, which could help it feel more planted.

By the time it's all said and done a fully mechanical system swap seems like a lot of work for a car that could probably use a different proportionate response rate from most of those vehicles, which means you'd have to modify the mechanics of it to get it to work. I think that diving into a custom controlled electronic system might actually prove simpler at that point.

There's probably a ton of HICAS systems off the 240sx around, as the mad tyte drift crowd doesn't have much use for it and it adds a fair bit of weight, however it's electronic.

You know the Corvette Spindles are front steer right? Which means that most of the hydraulic systems won't work as they're based on a rack which would hit the differential. With toe arms up front, you'd want something like the porsche or Acura Individual actuators for each side, which is of course a fully electronic system.

[assquatch20]

It's the Porsche stuff that's selling me on the idea. The high-speed benefits, ya know. I believe their passive rear steer is what Mazda later modified, and nowadays they're using active electronic stuff.

Quadrasteer would be neat if converted, but I'd have to design a module GM no longer makes just to get one up and running, I'd say. I'm thinking the early Prelude mechanical setup with some hacking up could be adapted, but I'll agree with all the naysayers as well.

HICAS is a nicer option. The only Corvette bits that will necessarily be used in the build will likely be hubs and a T56, though. The subframe is looking less than ideal for the application, but I'd really like to explore the composite leaf spring thing for space/weight if it can perform.

[udloze]

I think the Infinity J30T had rear steering

[TheJDMan]

I gotta say, I owned a 76 Chevette and that car would turn on a dime due to the short wheelbase. I can't imagine one with all wheel steer. IMO, it would be a handful to drive.

[raustinss]

I had a 86 chevette scooter. That was the a"sport" version 2 doors,lol manual steering and brakes, was a joke to maneuver that thing around. Hence why I'm lost on the why?

[ace_xp2]

Did either of you read the bit about counter steering? it's in the thread...

[TheJDMan]

Did either of you read the bit about counter steering? it's in the thread...

Have you ever driven a Chevette?

[raustinss]

have you ever driven a chevette?

lol

[ace_xp2]

Okay, I'll go slower then...

So Chevette chassis very short right? Makes car twitchy at high speed right? So imagine if you could artificially lengthen the car at speed...

That's exactly what turning the rear tires into the corner effectively does, it's actually a fairly common set up in all wheel steer systems, when you go fast enough it starts to turn in with you, settling the chassis. That way you can have a small incredibly responsive chassis, which doesn't turn in to a twitchy mess at high speeds.

Simple enough?

[mikedc]

I get your train of thought on this. It's a clever idea, combining a short wheebase + artificially stabilizing it with additional steering.

I once read that GM played with the idea on a Camaro back around 1990-ish. They found that 1-2 degrees of turn-out (rear wheels turning the same direction as the fronts) produced a measurable stability gain, and 8-9 degrees made the car pretty much uncontrollable. IIRC the later GM truck option only ever moved the rear wheels by a couple of degrees too.

I have wondered if European WRC Rally cars might be a good usage for a 4WS setup. They are one of the only motorsports that really sees the need for both hi-speed cornering stability + low-speed short radius turning.



You lost me on the Chevette body, though. I can't see much reason to want one other than the size alone. There are other cooler small cars IMO.

If you are going for the anti-performance, anti-cool car image of it then I think Chevettes are getting too old. Even uncool cars become interesting-->cool when they are 30+ years old. IMO a busted-ass 1990s Cavalier would fit the anti-performance-car image better today.

[raustinss]

I guess you missed the part where everyone said how complex this would be to achieve?...I get counter steer but the risk doesn't seem like the reward

[assquatch20]

Heh it's only a chevette shell. Tube chassis. I'd mentioned the drivetrain in my intro thread, but it's going to be stupid amounts of power. Kind of a demo car. All wheel drive, as mentioned, and yes, loose surfaces, while remaining street worthy.

[raustinss]

If your getting that crazy with it, you could even stretch the wheelbase a inch or two without throwing off the looks of the car

[assquatch20]

If your getting that crazy with it, you could even stretch the wheelbase a inch or two without throwing off the looks of the car

I've considered it. I've got a straight parts car, and I know it's getting wider track, but it'll come down to whatever is a most ideal geometry. It would certainly help get the motor behind the front diff.

Not that it's related, but I'm gonna be chopping the top as well. Not sure if I want to tilt the A pillars back or shorten them, though. I'd like to make the car a little slicker for performance purposes anyhow, but the form is certainly the secondary function (lol) in design for this instance. I've come to feel that the cab being so damn tall is what makes the car so silly looking.

[raustinss]

I would lay them back...my two cents. Is it a Chevette sedan or two door scooter

[assquatch20]

It's a two door. I'll most likely do away with rear seating in favor of more leg and engine room, but I was contemplating an RX8 kinda setup, seeing as the parts car is a sedan. I could use some bits to accomplish this. Stretching the car a bit could allow this to remain possible. This will take forever.

[assquatch20]

Well I'm having a little tossup. It would seem like the 88-91 Prelude 4WS is the only mechanical one, and I think I could adapt it, if I can clear it around two driveshafts and three diffs. Given that I may do without power steering, the low speed stuff could be substantially tougher, but some with mechanical 4WS have removed the PS pump and don't seem to mind.

Of course, I've still gotta go find the gurus of such things and discuss adaptability.

[Bird of Prey]

I thought about it too . The only thing that came to mind was hydrolice like the rock crawlers use . But use low rider stuff to save weight and power . Going over the AWD and not using the hydrolic will be tough .

[assquatch20]

I thought about it too . The only thing that came to mind was hydrolice like the rock crawlers use . But use low rider stuff to save weight and power . Going over the AWD and not using the hydrolic will be tough .

I've been thinking about the crawler stuff lately as well. I think that's my next area to brush up on.

[HellPhish89]

Some hard physics on 4 wheel steering
http://www.control.lth.se/documents/2002/5697.pdf