LocostUSA.com

Learning how to build Lotus Seven replicas...together!
It is currently July 17, 2018, 7:52 am

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 38 posts ]  Go to page Previous  1, 2, 3  Next
Author Message
 Post subject: Re: CC&AR Revisited
PostPosted: March 30, 2017, 6:49 pm 
Offline

Joined: February 8, 2014, 10:47 pm
Posts: 489
Location: Cornholio OR "Where the magic happens"
Seems to me it will bind up as the geometry changes will require forces greater than the actuating forces available?

Which takes us back to "any suspension will work if you don't let it!"

_________________
Yaaaaaaay! The profile link is fixed!


Top
 Profile  
Reply with quote  
 Post subject: Re: CC&AR Revisited
PostPosted: March 31, 2017, 1:00 am 
Offline
User avatar

Joined: November 11, 2013, 4:47 am
Posts: 875
Location: No. Nevada
I'm interested in this.
Hoping to find time to make a mock-up to test it out on a table.

_________________
If I must be a one-man PC free zone, so be it!


Top
 Profile  
Reply with quote  
 Post subject: Re: CC&AR Revisited
PostPosted: March 31, 2017, 1:25 am 
Offline
User avatar

Joined: April 26, 2008, 6:06 pm
Posts: 2949
Location: Under the weather. (Seattle)
DaveH wrote:
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.
Correct, but unlike a traditional anti-roll bar, this only acts only when there is an applied lateral load. In a straight line there would be no appreciable increase in wheel rate for a single wheel bump.

DaveH wrote:
If this suspension reduces the effect of body roll on caster, do you need less caster (not good) or less inherent camber gain?
I don't follow. What 'effect of body roll on caster' is being reduced, and why is needing less caster not good? Caster is actually not the best way to achieve camber gain, since it's steering angle dependent rather than lateral load dependent. Technically, as long as you have the freedom of design to achieve the other geometric requirements and have another means of driving camber gain under lateral load, then caster in and of itself is not actually necessary.

DaveH wrote:
Also, this seems like scrub radius would move all over the place.
Again, I don't follow. I wouldn't expect the dynamic scrub radius changes due to movement of the center of pressure of the tire to be substantially greater than that of a more conventional geometry. Or do you maybe mean lateral tire scrub? Yeah, there would be some of that with my lowered roll center type geometry.


Bent Wrench wrote:
Seems to me it will bind up as the geometry changes will require forces greater than the actuating forces available?
How so? I'd actually argue that this 'should' (at least in theory) let the suspension work more than a conventional geometry of similar capabilities.


RichardSIA wrote:
Hoping to find time to make a mock-up to test it out on a table.
Go for it! Although I wouldn't recommend copying the image of 'my' geometry to test...While it's representative of the general concept, it's not exactly 'correct'. :wink:

_________________
-Justin

Also follow my build on blogspot, tumblr, or instagram and twitter (GarageOdyssey)


Top
 Profile  
Reply with quote  
 Post subject: Re: CC&AR Revisited
PostPosted: March 31, 2017, 11:18 am 
Offline
User avatar

Joined: January 28, 2016, 7:59 pm
Posts: 99
Location: Omaha, Nebraska
Would it do funny things with bump steer?

_________________
Aedifico ergo sum.


Top
 Profile  
Reply with quote  
 Post subject: Re: CC&AR Revisited
PostPosted: March 31, 2017, 12:12 pm 
Offline
User avatar

Joined: April 26, 2008, 6:06 pm
Posts: 2949
Location: Under the weather. (Seattle)
It's not so much bump steer that would be a problem, as roll steer. I believe the steering geometry could be set to minimize steering effects in two wheeled bump for most spindles, since there is minimal camber change of the spindle taking place. However, the system needs to pivot on a horizontal axis between the lower ball joint and tie rod end if it is going to prevent steering effects from the camber compensation in roll. So that would limit spindle options.

_________________
-Justin

Also follow my build on blogspot, tumblr, or instagram and twitter (GarageOdyssey)


Top
 Profile  
Reply with quote  
 Post subject: Re: CC&AR Revisited
PostPosted: March 31, 2017, 2:15 pm 
Offline

Joined: May 11, 2009, 5:15 pm
Posts: 17
Driven5 wrote:
DaveH wrote:
If this suspension reduces the effect of body roll on camber, do you need less caster (not good) or less inherent camber gain?
I don't follow. What 'effect of body roll on caster' is being reduced, and why is needing less caster not good? Caster is actually not the best way to achieve camber gain, since it's steering angle dependent rather than lateral load dependent. Technically, as long as you have the freedom of design to achieve the other geometric requirements and have another means of driving camber gain under lateral load, then caster in and of itself is not actually necessary.


My fingers were moving faster than my brain - I meant effect on camber, not caster.

Caster contributes to steering centering and overall steering effort and feel. Very low levels of caster result in a numb feel to the steering.


Top
 Profile  
Reply with quote  
 Post subject: Re: CC&AR Revisited
PostPosted: March 31, 2017, 4:45 pm 
Offline
User avatar

Joined: April 26, 2008, 6:06 pm
Posts: 2949
Location: Under the weather. (Seattle)
DaveH wrote:
My fingers were moving faster than my brain - I meant effect on camber, not caster.
In that case, it would require less static camber to achieve the same dynamic camber on the loaded (outside) tire.

DaveH wrote:
Caster contributes to steering centering and overall steering effort and feel. Very low levels of caster result in a numb feel to the steering.
Only in a round about way. Trail is what you're actually describing. Since spindle geometry is generally fixed, caster adjustments affect trail. However, if designing from scratch, you could theoretically design a spindle with zero (or even negative) caster and still have the requisite trail. Look at a a caster wheel on any number of everyday items like shopping cars and whatnot. Plenty of trail to function, but zero caster.

_________________
-Justin

Also follow my build on blogspot, tumblr, or instagram and twitter (GarageOdyssey)


Top
 Profile  
Reply with quote  
 Post subject: Re: CC&AR Revisited
PostPosted: March 31, 2017, 5:10 pm 
Offline
User avatar

Joined: April 26, 2008, 6:06 pm
Posts: 2949
Location: Under the weather. (Seattle)
Driven5 wrote:
DaveH wrote:
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.
Correct, but unlike a traditional anti-roll bar, this only acts only when there is an applied lateral load. In a straight line there would be no appreciable increase in wheel rate for a single wheel bump.
Something else to add, is that unlike a traditional anti-roll bar which should apply an equal and opposite force at either end of the bar, this would apply a force proportional to the load being carried by the tire on the opposite side of the car. So while a 100 lb of anti-roll effect at the wheels for a traditional bar might apply 50 lb to compress the inboard (extended) suspension and 50 lb to extend the outboard (compressed) suspension, for the same total anti-roll effect this might apply 65 lb to compress the inboard suspension and 35 to extend the outboard suspension. Thus, the anti-jacking effect I previous mentioned.

_________________
-Justin

Also follow my build on blogspot, tumblr, or instagram and twitter (GarageOdyssey)


Top
 Profile  
Reply with quote  
 Post subject: Re: CC&AR Revisited
PostPosted: April 1, 2017, 3:10 pm 
Offline
User avatar

Joined: July 4, 2006, 5:40 pm
Posts: 1916
Location: Novato, CA
As someone who is only now, after 3+ years of driving a car I built myself, beginning to feel that parts aren't going to come flying off while I'm motoring down the freeway, I think the simpler the components, the better.


Top
 Profile  
Reply with quote  
 Post subject: Re: CC&AR Revisited
PostPosted: April 1, 2017, 4:23 pm 
Offline

Joined: February 20, 2015, 12:04 pm
Posts: 281
Location: Cotswolds - UK
nick47 wrote:
As someone who is only now, after 3+ years of driving a car I built myself, beginning to feel that parts aren't going to come flying off while I'm motoring down the freeway, I think the simpler the components, the better.


Damned right!

The CC&AR is/was interesting, but is just one in a long line of dual roll centre/camber compensation ideas that go back to the Trebron and Fairthorpe TX systems of the 60's and 70's. They invariably add complication and cause as many problems as they solve. Actually, the Torix Bennett Fairthorpe was probably the simplest and most practical. Faced with the complexity of CC&AR, I'd probably go for a lightweight, properly located beam axle like the Lotus 58, which does almost the same job but with a lot less complication.

The CC&AR felt distinctly 'odd' to me when I drove it in its Dax Rush implementation...as though there were some strange, slightly floaty disconnect between steering and suspension at the front end. The other problem was that it allowed/required relatively soft springs to work properly, which was great for grip and ride comfort, but not so good for pitch control. If you watch any of the videos on YouTube of Duncan Cowper's fearsome Dax Rush on track, you'll see that it's like a nodding dog under braking and acceleration.


Top
 Profile  
Reply with quote  
 Post subject: Re: CC&AR Revisited
PostPosted: April 1, 2017, 7:16 pm 
Offline
User avatar

Joined: April 26, 2008, 6:06 pm
Posts: 2949
Location: Under the weather. (Seattle)
Sam_68 wrote:
The CC&AR is/was interesting, but is just one in a long line of dual roll centre/camber compensation ideas that go back to the Trebron and Fairthorpe TX systems of the 60's and 70's. They invariably add complication and cause as many problems as they solve. Actually, the Torix Bennett Fairthorpe was probably the simplest and most practical. Faced with the complexity of CC&AR, I'd probably go for a lightweight, properly located beam axle like the Lotus 58, which does almost the same job but with a lot less complication.

The CC&AR felt distinctly 'odd' to me when I drove it in its Dax Rush implementation...as though there were some strange, slightly floaty disconnect between steering and suspension at the front end. The other problem was that it allowed/required relatively soft springs to work properly, which was great for grip and ride comfort, but not so good for pitch control. If you watch any of the videos on YouTube of Duncan Cowper's fearsome Dax Rush on track, you'll see that it's like a nodding dog under braking and acceleration.
Yes, this would ultimately function very similarly to the Torix Bennett rear suspension...Although for all it's simplicity, I wonder just how' optimized' the geometry was actually capable of being. Interestingly enough, rather than literally being a trailing arm suspension with cross linking for cornering camber correction, my thought process started out more at the opposite end of the spectrum, as a swing axle with cross linking for straight line camber correction. The relative complexity of adding one pushrod and one rocker per side doesn't turn me off from this any more than it would an inboard suspension.

I certainly appreciate the fact that you've actually driven a Dax Rush with CC&AR. Can you provide more details on your experience and the balance, capabilities, and control/feedback? I'm really not surprised that it initially felt somewhat odd. How much time were you able to spend behind the wheel to acclimate yourself to the unfamiliar reactions? Do you think any of it had to do with their use of bushings, rather than spherical joints? Did it otherwise generally seem to deliver on their claims?

Regarding pitch control, I'm not sure I see how this is a 'problem' for a street car. Most street cars are sprung softly enough that they have considerable pitch anyways, well at least by racing standards, and this would not be much (if any) softer sprung than the equivalent conventional 'street' suspension I was originally planning on. Thus, the pitch motions shouldn't be much different either, except that this type of system would prevent the pitch motions from sacrificing grip.

_________________
-Justin

Also follow my build on blogspot, tumblr, or instagram and twitter (GarageOdyssey)


Top
 Profile  
Reply with quote  
 Post subject: Re: CC&AR Revisited
PostPosted: April 2, 2017, 4:12 am 
Offline

Joined: February 20, 2015, 12:04 pm
Posts: 281
Location: Cotswolds - UK
Driven5 wrote:
Can you provide more details on your experience and the balance, capabilities, and control/feedback?

Honest answer is, no, not really: I drove the factory demonstrator, on public roads. Not for a huge distance and not at the sort of pace that would show up any serious shortcomings. So all I can offer is first impressions (and even that was a long time ago).

Having discussed my experience with owners of the cars, they claim that the steering feel issue doesn't exist/is easily acclimatized to, so maybe it was a simple case of 'bumpsteer' equivalent, with the geometry being slightly out on the car that I drove. The suspension movement as the chassis rises and falls (Dax used to have a very lightly sprung bare chassis that they use to take to the shows, to demonstrate the suspension as a 'party trick') was enough to make you seasick just watching it, though, and it felt like a little of that motion was being transmitted to the steering on the car that I drove... very hard to describe, but it felt like there was some sort of 'floating' linkage in the steering.

Accuracy of geometry may be another Achille's heel of the system: spaceframes are not the most dimensionally perfect structures, even when you jig them up as carefully as you can. You can tolerate and dial-out any minor inaccuracies with a conventional double wishbone system. Given its additional complexity, it would be reasonable to assume that CC&AR is less tolerant and needs to be more carefully set up (IIRC, the factory used to do the suspension assembly on the CC&AR cars, whereas they trusted customers to bolt together the normal wishbone cars).

Pitch control on a street car is a problem because of suspension travel/ground clearance, when the street car is as low slung as a Seven.

Bottom line is that since it failed to demonstrate any clear advantage in racing, why would you want to risk the additional complexity, cost and oddities in the first place, other than to be different for the sake of being different?


Top
 Profile  
Reply with quote  
 Post subject: Re: CC&AR Revisited
PostPosted: April 2, 2017, 3:52 pm 
Offline
User avatar

Joined: November 11, 2013, 4:47 am
Posts: 875
Location: No. Nevada
Ahh, now I wonder if this can be used to fix a rear swing axle?
Thinking mostly of Spitfiire and early GT6.
Really tired today but my first thought is that with fixed length axle there would be binding issues?
Need to mock this up!
After a nap.

_________________
If I must be a one-man PC free zone, so be it!


Top
 Profile  
Reply with quote  
 Post subject: Re: CC&AR Revisited
PostPosted: April 2, 2017, 5:51 pm 
Offline

Joined: February 20, 2015, 12:04 pm
Posts: 281
Location: Cotswolds - UK
Yes, fixed length axle is always a problem, unless you can use it as a link. Nothing a pair of Rotoflexes won't sort out, though?


Top
 Profile  
Reply with quote  
 Post subject: Re: CC&AR Revisited
PostPosted: April 2, 2017, 6:36 pm 
Offline
User avatar

Joined: April 26, 2008, 6:06 pm
Posts: 2949
Location: Under the weather. (Seattle)
Sam_68 wrote:
Bottom line is that since it failed to demonstrate any clear advantage in racing, why would you want to risk the additional complexity, cost and oddities in the first place, other than to be different for the sake of being different?
Then again, there were also plenty of people who once professed these exact same sentiments about double wishbone suspensions...

_________________
-Justin

Also follow my build on blogspot, tumblr, or instagram and twitter (GarageOdyssey)


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 38 posts ]  Go to page Previous  1, 2, 3  Next

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: Google [Bot] and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
POWERED_BY