frayed

Reactive, proactive, casual, I don't think it matters. All that does matter is whether you can detect something unnatural happening at the rear axle. I predict that the technology will be transparent to the driver except for increased precision and superior turn in.

Whether it's a robust system is a different question. We can all hypothesize but in the end it's going to take time and track miles to understand what the system's limitations are. PAG is not infallible, of course, with lots of angry folks about CL's, coolant hoses, gen 1 ceramics, RMS leaks, etc etc but most technologies used on the GT cars didn't detract from the driver experience. The only one I can think of is first gen PASM on the 997 GT3.

In terms of involvement I'm much more concerned about electric steering. You can only polish a turd so much. If it really is good as the hydraulic steering in the last GT cars I'd be excited but I'm not optimistic.

Bill_C4S

If Nissan's engineers could master the challenge of RWS on the racing version of the R32 GT-R in the early 1990's...I seriously doubt such presents a challenge to Porsche's over 20yrs later....

and further from AP on the ability to switch RWS on/off:

"FS: Can Rear Wheel Steering be turned off and how much weight does it add?

AP: It was planned to make it switchable and so I stated this already in earlier interviews. This is still under discussion at the moment because of the influence on ESP systems, which was not so clear some weeks (months) ago. So my initial statements might have been a little premature, sorry.
Well see what we do, but it is definitely very cool proof positive when you can compare back to back. Weight of the system is easily compensated by improved agility and stability, as well as more "feel" for the car. System weight is about 7 kgs, the need for a bigger battery adds another 6."


http://flatsixes.com/cars/911-gt2gt3...interview-gt3/

frayed

While I tend to agree and wouldn't buy the car if I thought it a huge risk, to be fair Nissan had a lot of development time on their system. At first glance Porsche's version may be mechanically straightforward but its integration with the stability control system (steering angle, speed, yaw, throttle position, braking, slip angle etc etc) makes RWS electronically complicated. So much so that AP says there will be no toggle switch.

I bet we'll see software upgrades during the model cycle further refining the 1's and 0's. The chances for a glitch in the matrix would seem to be high.

Mike in CA

I don't mean to be pedantic, but I continually see references to "electric steering" which IMO is misleading. In fact, a mechanical connection still exists from the steering wheel to the front wheels; it's only the power assist that involves an electric motor. This gives me hope that, as claimed, a modification of control software for the assist can resolve whatever negatives the system might have.

blake

+1. I believe this was designed into the system. I expect lots of tweaking including a so-called "Kussumaul setting for RWS" for the proper software config over time...

ShakeNBake

It's pretty much a function of the design. Hydraulic applies assist in parallel with your input and has no/few moving parts that move with the rack/steering shaft.

With electric, the motor and gearbox are directly connected to the sheering shaft or rack, and the motor must move/rotate as inputs move through the system. The motor and geartrain has a lot of friction and rotational mass, and this dampens the feedback passing through the system from the wheels to the steering wheel.

Electric is infinitely more tuneable and can be made to feel more precise.

Eventually they will figure out how to solve the friction/inertia issue, maybe with a direct linear motor. Who knows - but it's a general fact feedback is gone with electric systems. Some people may prefer the precision/active feel over feedback...would be nice to have both.

Mike in CA

I absolutely agree that the design of the system is critical. Looking at the depiction in this vid, though, I confess that I don't see friction as an issue; the electric motor is essentiallly frictionless, and there is no "gearbox" involved, only a direct belt drive of the steering rack. I'm no expert, but I suspect inertia is not a major factor either, as the mass of the entire steering assembly is going to be a bigger factor in the reaction time of the system than the inertia inherent in the electric motor.

I think the major issue with most EM steering systems is the way they are programmed to respond to and filter road feedback and conditions. Porsche knows they went to far with this programming in the Carrera and realize that it wasn't appropriate for the GT3. AP says they have resolved the issue, and again, I'm hopeful that he's right.

P.S. Nothing wrong with your speakers; the audio for this clip is kaput....

ShakeNBake

I guess you're the expert.

We had a tough time designing robotic actuators that were able to transmit forces back through the system while still maintaining controlled output. It's complex motion control that I'm sure has progressed light years in the last 10 years since i left that industry. But I can see that inertia would pose a challenge, these are very powerful motors.

Mike in CA

No reason to be sarcastic. As I said, I don't claim to be an expert. You said that friction in the gearbox and motor would be an issue and my layman's eyes didn't see that in the design of the steering rack in the vid. Sharing ideas is a big part of RL for me and I'd sincerely appreciate learning from your experience with this subject.

frayed

As always its not the technology thats the culprit but the implemenation of the technology. How many cars with hydraulic steering have we all driven with non existent feedback? Pretty much every one of 157 rentals I've had in the last 5 years.

Exactly.

But what surprises me is that PAG was *so* far off the mark with the 991 IMO. Of all things, steering is what separates the true drivers cars from the wannabes. What makes Lotus so awesome. . . the only rig that had superior feedback to my 997 cars (that I've driven).

The pain is that the 991 took a step backwards in terms of feel. The 997 did a great job filtering out all the nonsense from the 996 leaving behind what you need to feel. The 991 went too far IMO.

AP's comments about regaining the feel of the 4.0 leaves me some hope.

ShakeNBake

I said inertia and friction. Anything is possible - it's engineering. Their system is based on a recirculating ball linear geartrain, so it's worse than high inertia and friction, it's not backdrivable - meaning the motor cannot sense a force pushed back to it through the geartrain, so it makes it a bit difficult to react through a control loop completed by a sensor far away from the electric motor and allow those forces to persist without being dampened out by the motor trying to execute the command given to it by the driver. I'm sure they have done a good job allowing low frequency stuff back through - so like a change in surface levels, bump in the road, sudden loss of traction on one tire. I can't see how they can transmit high frequency stuff through like gavel texture, the tire gradually losing grip, etc, with that design - there is just too much indirect connection between the force input and the output. It's going to take a direct drive linear motor (no geartrain) to be able to get it right IMO. From everything I have read and experienced with the 991 and 981, my assumptions seem to fit the bill. High accuracy, basic feedback, no texture.

tmg57

What effect will RWS have on counter steer slide correction?

Nick

Presumably at higher speeds, the turning of the rear wheels the same direction as the front will lessen sliding but should not affect counter steering if sliding occurs.

neanicu

Found interesting Acura is now using a similar system with 1.8 degrees movement in their 2014 RLX :

http://www.acura.com/Features.aspx?m...allwheel_steer


"The rear wheels can pivot as much as 1.8 degrees in the same direction as the front wheels for smooth, stable and quick lane changes.
When cornering, the rear wheels angle slightly in the opposite direction from the front wheels (reverse-phase) to help rotate the car into the turn.
At low speeds, reverse-phase steering helps the RLX maneuver in tight areas.
In high-speed braking, each rear wheel angles inward, increasing braking ability and stability. "

ShakeNBake

I had this on a Prelude in London, back in 91....RWS is not a new concept.