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 Post subject: CC&AR Revisited
PostPosted: March 16, 2017, 3:16 am 
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Now I know that we've previously discussed the Walker/DAX Camber Compensation and Anti-Roll (CC&AR) suspension (http://walker-partnership.com/cc&ar_text.htm) a few times before. And while I also know that it's not perfect (namely 1 wheel bump camber like a live axle [very minor IMHO], complexity and component count [minor IMHO], and packaging [that can be improved IMHO]), it does offer numerous very interesting attributes as well. Something I decided to explore further.

For those that don't know, it's a mechanical linkage that connects the upper left control arm to a rocker that the upper right control arm is mounted to, and vice versa. In doing so, it pushes the UCA mounts outward in pure bump (preventing unwanted negative camber gain), pulls the UCA mounts inward in pure droop (preventing unwanted positive camber gain), adds extra negative camber gain to the outside tire and extra positive camber gain to the inside tire in roll, and has an anti-roll (and anti-jacking) component when lateral loads are applied to the tires.

Image

Even though I had already spent considerable time figuring out a conventional suspension geometry for the rear that I was pretty happy with, and was getting close on the front, I still wanted to better understand this. Also, I felt that they were missing something in their application of this concept. They built a car that has a compliant ride but corners extremely flat and with no real camber loss/gain to speak of as a result of it. This may be great for very wide and low profile tires. But since most tires actually develop the max cornering grip at a non-zero camber angle, this seemed to actually be undermining the full potential of the design. I mean, what's the point of camber compensation in roll if you don't have (allow) any roll in the first place? So I used the magic of Excel to create (multiple iterations of) a CC&AR calculator that I could manipulate.

The first thing I did was move the cross link from being between both UCA's, to having it be actuated by the LCA to vary the opposite UCA position. Admittedly, part of this was to get around the patent, which specifically stated cross linking the uppers. However, I just recently found that Walker did not continue paying to maintain the patent on the CC&AR system, so it has since expired anyways. During this more recent research, I also found an RC car manufacturer (Serpent) that has created a system linked essentially in the manner I'm talking about (upper to opposite lower) for their DLS (Direct Link System).

Image

First of all though, for what I was trying to achieve, the suspension had to be allowed to roll. This meant lowering the roll center, which Walker/DAX claim is simply at the intersection of the two LCA lines of action. Even if I'm not sure I buy that, I'm confident min will be at least a few inches lower. Would it be enough lower to allow the movement I'd like to see? I'm not totally sure, but I think it should certainly do more so than the Walker/DAX layout. It also helped with the packaging considerably, even if not the complexity or parts count. Might even be adaptable to a production car chassis some day. There is also the anti-roll and anti-jacking component, but as far as I can tell that actually should not be overly strong in preventing roll, but will still hopefully be enough to (at least mostly) balance out the suspension with minimal (or 'no') need for sway bars. Of course this is all very much hypothetical still and based on very rough math at this point, but if you couldn't tell by now, I'm strongly considering putting this hypothesis to the test on my build... Whenever I get manage to get going on it again. :oops:

And here's the big explanation of why: The typical 'independent' suspension has somewhere in the ballpark of 1.0 degree of camber gain per inch in bump, and 0.5 degree of camber recovery per degree of roll. So lets put that into roughly approximated numbers aimed at maximizing cornering grip, while keeping streetable suspension rates. If the car corners at 2 degrees of body roll, that means the suspension needs to have -3 degrees of static negative camber to get -2 degrees of dynamic negative camber on the loaded wheel. Unfortunately, as the unloaded tire (that wants positive camber) tries to assist, it has -4 degrees negative camber. As the suspension is loaded (the more important end) in a straight line, it also gains another degree of negative camber. So this too is -4 degress, which is certainly not optimal for acceleration/braking either. It does help the unloaded end, but sill leaving it at -2 degrees.

Meanwhile, I have found a rear geometry for the Thunderbird spindles, that I believe will allow for a very street friendly -0.5 degree static negative camber. In doing so, it will achieve the same -2 degrees dynamic negative camber in roll on the loaded wheel, but also +1 degree dynamic positive camber on the unloaded wheel. In both bump (loaded) and droop (unloaded) scenarios for straight line performance, it very closely maintains the -0.5 degrees dynamic negative camber, actually moving closer to 0 at the limits of acceleration/deceleration based suspension movement. At more extreme suspension movements due to flying through the air and then slamming back into the ground, the suspension does wander a little further, but no more than 1.5 degrees at absolute maximum two wheeled bump travel. So at the same loaded cornering wheel angle, it is vastly improved on the unloaded cornering wheel angle, substantially improved wheel angle in two-wheel bump, and even noticeably improved wheel angle in two-wheel droop. This should increase total grip in all steady state maneuvers, as well as improve tire wear patterns across a wide variety of driving. Additionally, it actually compresses the suspension slightly in roll (anti-jacking) that would hunker the car down that much more while the majority of anti-roll rate is also fully damped.

Just thought I'd share some of what I've found as I've played with this over the last year, and open it up for public consumption/discussion.

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 Post subject: Re: CC&AR Revisited
PostPosted: March 16, 2017, 3:44 pm 
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I is not smart enough to know if you're right or wrong, but it's interesting at the very least. I like the concept.

Go ahead and spend another 50-60 hours on it and then let those who have spent zero time on it castrate you. It should be fun in any case.

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 Post subject: Re: CC&AR Revisited
PostPosted: March 16, 2017, 4:17 pm 
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It would be interesting to see two cars on the same track, identical other than this suspension, and to compare times. That's the only way to know whether it's any better.

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 Post subject: Re: CC&AR Revisited
PostPosted: March 16, 2017, 8:44 pm 
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Patent ran out, hmmmm. :idea:

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 Post subject: Re: CC&AR Revisited
PostPosted: March 17, 2017, 11:48 am 
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carguy123 wrote:
Go ahead and spend another 50-60 hours on it and then let those who have spent zero time on it castrate you. It should be fun in any case.
Yeah, that sounds about right...LOL


KB58 wrote:
It would be interesting to see two cars on the same track, identical other than this suspension, and to compare times. That's the only way to know whether it's any better.
It would...Same as with pretty much every other type of suspension design out there too. I believe precious few instances are on record of otherwise identical cars running totally different types of suspensions being compared back-to-back, and yet we have all still managed to come to the conclusion that some are 'better' than others...Even within the same suspension type. Of course even then, the results might only apply to that particular geometry, for that driver, on that track, on that day.

This also implies that 'better' is only found at the track. Indeed, I had considered figuring out how I could incorporate both my previously selected traditional geometry and this interchangeably so that I could do such a comparison...And still might. I was even going to additionally provide a second set of UCA mounting points for purely straight-line use. However, I'm not sure that would be worth the time/effort to do so. I mean, it's not like I expect to have people beating down my door to buy or learn how to build such a system even if it works. Obviously Walker/DAX didn't. And while I haven't come across many first hand accounts about how they actually drive with the CC&AR system, of what little I found, I don't recall any of it being negative.

But as we all know, every suspension is a compromise of sorts, although some more so than others. My traditional suspension was designed around my interpretation of geometry for a 'sporty street' car, which I'm sure some people would be able to tear apart as being amateurishly designed (because it is), would also intentionally not be optimized for any one type of track use (road course or drag) anyways...Including being 'too soft' for maximum track performance. So it really wouldn't be a fair fight on any track. I suppose I could spend a bunch of time reconfiguring back and forth to compare them on the street, then do a road course alignment and spend a bunch of time reconfiguring back and forth at an track day to get a few minutes of actual driving time on each to compare, then reconfigure the traditional suspension to the drag strip mounting points and spend a bunch of time reconfiguring back and forth at a test and tune to get a few passes with each to compare. But to what end? Do the majority of people who are critical, or at the very least skeptical, of the Walker/DAX CC&AR due to presumptions, assumptions, and technicalities take what the people who invented it and/or have actually driven it have to say at face value? I'm not saying they necessarily should either, but I'm also not setting out to prove anything to anybody other than myself.

In my opinion, the most meaningful comparison from conventional to CC&ar might actually be in judging differences in driver feel and feedback. But even then, if it's a noticeably 'different' feeling most people would probably interpret that to be 'unsettling' anyways, if it's a feeling they're simply not used to. And while such a system may provide an overall advantage in a purely race setting against a conventional suspension tuned specifically for that type of racing, due to more contact patch more of the time, my intention is exploiting this concept more for its (potentially) superior 'multi-purpose' capabilities without ever having to reconfigure or realign it before/after an event for the drive home.


RichardSIA wrote:
Patent ran out, hmmmm. :idea:
Yep. That's a large part of the reason I think most 'patentable' ideas are actually better off just being put into the 'public domain' anyways.

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 Post subject: Re: CC&AR Revisited
PostPosted: March 17, 2017, 1:21 pm 
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Funny thing is that I have independently given thought to a similar system using cams to correct geometry.
Basically gave up on it due to concerns over binding, likely high wear, and lack of time.
With the patent gone on this system I have a GT6 that has not had the rear suspension built yet.
Not a lot of room at the rear for the extra linkage, unless I give up cargo space, not a major concern as it's biased toward hill-climb type use.

Now, where to get enough detail to build it?

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 Post subject: Re: CC&AR Revisited
PostPosted: March 17, 2017, 2:45 pm 
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RichardSIA wrote:
With the patent gone on this system I have a GT6 that has not had the rear suspension built yet.
Not a lot of room at the rear for the extra linkage...
The patent only covered cross linking the uppers. Cross link lower to opposite upper, and the patent no longer applies anyways...As well as allowing for packaging that could potentially stay entirely below the existing structure and componentry. Something more along the lines of this...


Attachments:
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CCAR.jpg [ 72.71 KiB | Viewed 2464 times ]

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 Post subject: Re: CC&AR Revisited
PostPosted: March 17, 2017, 5:15 pm 
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One thing I'm a little confused about is negative camber on the front. Autocrossing I see the need for more than just a little neg camber to maximize cornering bite. Is that a factor of the suspension or the tire?

It seems that due to tire deformation it would be tire so staying flat would limit tire performance, non?

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 Post subject: Re: CC&AR Revisited
PostPosted: March 17, 2017, 6:32 pm 
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Not sure if it means much but I seem to recall most of Serpent's factory drivers removing that suspension and installing a normal upper arm.

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 Post subject: Re: CC&AR Revisited
PostPosted: March 18, 2017, 2:46 am 
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carguy123 wrote:
One thing I'm a little confused about is negative camber on the front. Autocrossing I see the need for more than just a little neg camber to maximize cornering bite. Is that a factor of the suspension or the tire?

It seems that due to tire deformation it would be tire so staying flat would limit tire performance, non?
I'm not sure whether I my description was too vague, or if you think even more camber generation is required...But my dynamic camber references above are relative to the ground, not the chassis. So at 2 degrees body roll, the outboard wheel would have -2 degrees camber relative to the ground (-4 degrees relative to the body), and the inboard wheel has +1 degree camber (+3 degrees relative to the body). So both wheels are cambered into the turn relative to the load they're carrying.


a.moore wrote:
Not sure if it means much but I seem to recall most of Serpent's factory drivers removing that suspension and installing a normal upper arm.
That is interesting, although not particularly concerning to me either. The vastly differing constraints between RC cars and full-size, as well as all of the unknown implementation variables, lead me to especially believe that correlation does not imply causation here.

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 Post subject: Re: CC&AR Revisited
PostPosted: March 18, 2017, 8:58 am 
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That was my thought - it would be interesting to see how camber and load sensitive rubber and foam RC car tires are compared to a fully pneumatic tire. It was my understanding that camber on onroad cars running foam tires was more of a tool to promote even wear versus maximizing grip but take this with a grain of salt - this is coming from a guy that primarily raced 1/8 scale buggies.

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 Post subject: Re: CC&AR Revisited
PostPosted: March 18, 2017, 2:25 pm 
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Related, be careful designing anything too "clever." That is, it may have some trait you want to adjust, but due to its cleverness, doesn't respond as expected. A lot of time can be spent fussing with a new system which may not be measurably better than a more traditional suspension. Or maybe it is, keep us posted.

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 Post subject: Re: CC&AR Revisited
PostPosted: March 18, 2017, 7:41 pm 
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Driven5 wrote:
I believe precious few instances are on record of otherwise identical cars running totally different types of suspensions being compared back-to-back


Famously, the Shelby GT-350R. They built an independent rear suspension for one of the prototypes, and ran it against a live axle car on the track. The IRS showed no advantage in lap times.


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 Post subject: Re: CC&AR Revisited
PostPosted: March 21, 2017, 1:36 am 
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KB58 wrote:
Related, be careful designing anything too "clever." That is, it may have some trait you want to adjust, but due to its cleverness, doesn't respond as expected.
...Like the handling balance effects from the built-in anti-roll geometry.

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 Post subject: Re: CC&AR Revisited
PostPosted: March 30, 2017, 5:51 pm 
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Has anyone done a full free body diagram of this in cornering? I'd be interested in seeing how the lateral forces from the contact patch translate to that upper control arm pivot. Putting some quick and dirty arrows on the diagram tells me it's increasing weight transfer between the tires, sort of acting like an anti roll bar.

The interaction between camber, caster, and steering axis inclination is also a little different here. Normally in the front suspension, you have caster and camber gain adding effective camber in cornering, with body roll and SAI subtracting. If this suspension reduces the effect of body roll on camber, do you need less caster (not good) or less inherent camber gain?

Also, this seems like scrub radius would move all over the place.


Last edited by DaveH on March 31, 2017, 2:02 pm, edited 1 time in total.

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