SACC Power Steering

@racecarmike posted:

A little more about caster. Mostly cut and paste but slightly embellished by me.

"Caster:

The steering axis is angled such that a line drawn through it intersects the road surface slightly ahead of the center of the contact patch of the tire on the pavement by a distance called trail. The purpose of this is to provide a degree of self-centering for the steering—the wheel casters around in order to trail behind the axis of steering. This makes a vehicle easier to control and improves its directional stability (reducing its tendency to wander). Excessive caster angle will make the steering heavier and less responsive, although in racing large caster angles are used for improving camber gain in cornering. Caster angles over 7 degrees with radial tires are common. Power steering is usually necessary to overcome the jacking effect from the high caster angle.

The steering axis does not have to pass through the center of the wheel, so the caster can be set independently of the trail, which is the distance between where the steering axis intersects the ground, in side view, and the point directly below the axle.

Caster angle and trail both influence the steering, albeit in different ways: caster tends to add damping, while trail adds "feel" and returnability (to self-center)."

Take particular note of the last sentence.

I revised my very crude sketch to show the trail (which will vary depending on tire size and other design aspects) to illustrate how that can vary depending on how caster is added. The red car on the right side of the sketch (very simplified) shows some things we experimented with on our race cars. I don't have the drawing here so the dimensions are arbitrary just to illustrate the point. Design "B" worked OK but required lots of arm strength and was overly sensitive to steering inputs. For "C" and "D" I redesigned the front uprights from a forward spindle design to a trailing spindle design. That tamed the beast. The car was no longer overly sensitive to steering inputs and I didn't need to take Advil after the race. I was ready to install power steering before the change. The lap times improved, mostly because the car was much easier to drive.

Mike

So what you are saying is that something like 2/3 of the caster shim needs to be on the top and 1/3 of the shim on the bottom totaling either 4 or 6 degrees. That results in a significant amount of trail, i.e.,  with the spindle center being behind the centerline.

This results in a lighter feel, self centering and less sensitive to road chatter.

Wew! Brain hurts. How do you determine the "centerline"? It is only "theoretical". This is like the Internet. You can't touch it. It is just out there somewhere? How is that measurable? Only on paper?

How could you do that with offset bushings? They would have to be 1/3 less offset for the bottom? People don't know what offset bushings are now. You wann'a get me shot?

Where would anyone even get those? Out of the Ferrari race shop? Yikes!

Only 65? Very disappointing. Does it have a rev limiter?

The EPS units look big in the pictures posted. How is the clearance for your clutch foot and knees?

First, Correction:  "For "C" and "D" I redesigned the front uprights from a forward spindle design to a trailing spindle design."

Should be: For "C" and "D" I redesigned the front uprights from a trailing spindle design to a forward spindle design."  Sorry, it's been a while.

I haven't measured the space between the mounting tabs for the lower control arm bushings so I really don't know how much the bushings can be offset forward. I suspect not very much. I don't know if anyone ever made and sold offset bushings. It's likely a DIY project.

I designed custom upper control arms and modified the lower arms to facilitate the desired results. I avoid modifying anything welded to the body like the mounting tabs. The car will likely outlive me and someone down the line might want to install the factory arms, which I have.

Doug, My very crude sketches are only intended to illustrate a few basic concepts and options. Someone would need detailed dimensioned drawings of the entire chassis to plot out and accurately predict the outcome from changes. Curves need to be generated from full bump to full droop and from lock to lock. (center part of the curves count most). Being a dynamic system, all this data must be generated for most chassis attitudes and loading. It's mostly about the tire contact patch and the road surface. And that's only part of the fun.

The engine in (not actually installed yet) 5715 is an all aluminum 401 Clevor with EFI and lots of other goodies. The cam was selected for max power at 6300. You can rev it to 6950

Doug,

I have noticed no clearance issues with the SACC unit installed.

I don’t get into or drive the car any different than I did prior to the installation

Larry

@lf-tp2511 posted:

Doug,

I have noticed no clearance issues with the SACC unit installed.

I don’t get into or drive the car any different than I did prior to the installation

Larry

Do you need use the adjustment knob a lot?

I set it to a comfortable performance level and have not touched it in 5000 miles.

The upgrade is seamless in performance, car still tracks perfectly at cruising speeds, and I can confidently take hands off wheel when doing so  

Larry

Larry, how much positive caster is on your car?

Professionally done corner balancing and alignment

@lf-tp2511 posted:

I set it to a comfortable performance level and have not touched it in 5000 miles.

The upgrade is seamless in performance, car still tracks perfectly at cruising speeds, and I can confidently take hands off wheel when doing so  

Larry

I ask because I have three options. No adjust/default, automatic adjust, manual adjust.

The manual adjust doesn't back off for vehicle speed, the automatic does. It ramps down. The automatic requires a VSS. I'm thinking automatic.

@davidnunn posted:

Doug,

It's doubtful the SACC and EZ PS kits use the same EPAS motor as I'm told by Gerry Romack, who's driven Panteras equipped with both, that the systems feel VERY different.

I was just told that the difference in feel is not caused by the motor assembly used. It is likely in the "reprogramming" of the separate electronics control box from the original stock production application.

Dialing down the assist without a VSS can also be done by adding a torque sensor internally within the motor assembly by varying the teeth to different varying lengths that effect it's harmonics. That one is certainly beyond my realm of abilities.

There are now at least two aftermarket companies that have their programs re-written AND that at least one has an internal torque sensor which determines what speed you are traveling at WITHOUT a VSS. Just the vibrations it senses from the car in motion according to a pre-written menu.

It is done by adding an additional board into the control module.

There are several variations of the "manual control knob". One is fully manual. The second ramps down the boost according to speed no matter where the starting point is on the dial.

I could be completely wrong on this and can’t cite the basis for my beliefs, but….

I thought the potentiometer on the SACC unit determines the ….maximum…. amount of power assist available, and an internal torque sensor (OEM??) determines how much of that potential assist is delivered.

for instance, parallel parking will see a lot of wheel-turning friction which in turn is transmitted into the internal torque sensor calling for power assist to be delivered.

at highway speeds, there is little or no wheel-turning friction, and thus little or no power assist is delivered.

quite willing to be confirmed or contradicted on this  🤷‍♂️

Larry

Doug,

All EPAS units have an integral load sensor. That means the motor is off until it senses a load, such as when you turn the steering wheel. The motor then compensates and gives more or less assist, depending on the load. The potentiometer or VSS only sets a limit to that assist. I don't believe an EPAS unit can tell how fast the car is going, other than loads are typically greater at lower speeds. Unfortunately, that's not always the case.

The two "strategies" result in a very different "feel" for the driver. Gerry R. can describe these differences to you. I can only tell you about my own experience, which is with the EZ system. It never feels like power steering. At normal speeds my steering feels exactly like it did prior to EPAS installation.

DC Electronics has one EPAS system where the motor and load sensor are separate, for installations where space is very tight. 

I'm just quoting what I was told in a 2 hour phone conversation with the manufacturer.

It isn't that I am confused but there is an interpretation of the language as we speak it. The argument here, if it is an argument is over the use of synonyms. That being defined as a word similar but not exactly the same as the subject word.

If you are clever, you can notice the root of each of those words?

Yes it is torque sensing rather then speed sensing UNLESS you use Bruno's GPS plug in module which measures vehicle speed from the GPS satellite and eliminates any manual control knob entirely. That kind of makes his manual control almost obsolete now in my view?

It's like the Pantera radiator control fans. Do you want them to go on automatically like the later cars or have to turn them on manually like the early cars? Automatically for me.

Wasn't Jackie Stewart the guy who toasted the engine in the loaner Pantera because he didn't know he had to turn the fans on manually?

It appears that Bruno is THE source of all the aftermarket plug in power assist modification modules EVERYONE IS USING in their "kits". Those all work off of the Saturn Vue/Chevy Equinox CPU modules at the moment according to Bruno.

I'm told that he is the original designer of the EPAS system for GM.

I suppose that this is as complicated as you want to make it but the tech is changing almost as we speak. I'm just trying to keep up from yesterday.

This strikes me as somewhat similar to the aftermarket EFI cpu's where 10 years ago you needed a laptop and needed to program virtually everything into them and now you have a plug and play self learning cpu?

Tech marches on and it is to "one's own benefit" to wait for the latest development?