From: Ashton Crusher on
On Tue, 27 Apr 2010 21:38:43 -0500, russotto(a)grace.speakeasy.net
(Matthew Russotto) wrote:

>In article <57q9t5lr4jhb5hervqhb2q51b3poff1eig(a)4ax.com>,
>Ashton Crusher <demi(a)moore.net> wrote:
>>>No. ABS is very close to threshold braking, but it is not. It is a very
>>>rapid sequence of going slightly beyond the threshold and then back to
>>>less than the threshold.
>>
>>Where you are getting that definition from? It makes no sense to me
>>and is contrary to what people have claimed in the past. What's your
>>definition of the "threshold" point?
>
>Take a chart of brake pressure (at the caliper or shoe) versus braking
>force applied to the road by that tire. It'll look basically like a
>line going from 0 upwards fairly linearly, leveling off slightly as it nears a
>peak, followed by a sharp dropoff to a horizontal line. Perfect
>threshold braking would be holding braking pressure right at that
>peak.

You've just described what ABS does in any practical sense. To say ABS
is qualitatively different then threshold braking is just splitting
hairs.
From: Alexander Rogge on
Ashton Crusher wrote:
> No modern ABS "guesses" at anything.

How could the ABS program know what I want to do when I touch the brake
pedal? It knows nothing except the wheel velocity and maybe how quickly
I depressed the pedal. In the examples of a sophisticated program, it
knows the velocity of the car and the angle of steering. What it cannot
know is my immediate intent, so it attempts to guess about what I want
the car to do next.

> When you say the cars you have tried miss the "optimum", how are you
> making that assessment?

Accelerate the car to 100, point at a mark on the track, and attempt to
stop. That's the standard for most car testing. I also attempt rapid
stops at much faster speeds.

> Most likely you are also basing your assessments on
> braking on dry pavement.

A dry surface was the subject under discussion.

> Although ABS will win there, where it really
> shines is on wet pavements and on pavements that have highly variable
> friction levels transversely and/or laterally.

The other option is to slow down so that you aren't driving too fast for
conditions.

> A 3 or 4 circuit ABS
> can easily handle such surfaces, a single circuit, i.e. human on the
> pedal, can't hope to handle it at anything close to what the ABS can
> do.

Yet, we seemed to drive without much difficulty before computers and ABS
programs. Most of the traction control results from the tyres, not
everything that rests on the tyres. Considering some comparative
examples of driving on snow and ice, the car with no traction control
system, rear-wheel drive and snow tyres can win over a car with 4-wheel
drive, an electronic traction-control system, and all-season tyres. The
most important components of maintaining traction are the tyres and the
driver.

There is too much reliance on these electronic control systems that were
intended to enable the car to be driven to new extremes, that are
instead used by some drivers as a crutch for common sense and having
proper equipment. Having proper tyres and a proper speed for conditions
can eliminate the need for ABS and other traction-control systems.

From: Dave__67 on
On Apr 27, 1:37 pm, Alan Baker <alangba...(a)telus.net> wrote:
> In article
> <e00930b2-999a-4467-adec-85b62b909...(a)v14g2000yqb.googlegroups.com>,
>
>
>
>  Dave__67 <spamTHIS...(a)yahoo.com> wrote:
> > On Apr 26, 2:41 pm, Alan Baker <alangba...(a)telus.net> wrote:
> > > In article
> > > <9bd36917-1c4c-48ba-bb9b-7061a9d6a...(a)z7g2000yqb.googlegroups.com>,
>
> > >  Dave__67 <spamTHIS...(a)yahoo.com> wrote:
> > > > On Apr 22, 9:04 pm, Ashton Crusher <d...(a)moore.net> wrote:
> > > > > On Thu, 22 Apr 2010 05:08:07 -0700 (PDT), Dave__67
>
> > > > > <spamTHIS...(a)yahoo.com> wrote:
> > > > > >On Apr 21, 11:55 pm, "Nick Naim" <orb...(a)ix.netcom.com> wrote:
> > > > > >> I pegged her at 70 years old plus minus.
> > > > > >> She pulled  out of a fast food on my left in a heart beat
> > > > > >> I,m in the left lane of thru traffic.
> > > > > >> I,m on the binders on ABS and they are working on overtime.
> > > > > >> I come to a stop 3 feet from her right front fender.
>
> > > > > >If your ABS is kicking on on dry clean pavement you need better tires-
> > > > > >you're throwing away stopping distance!
>
> > > > > >Dave
>
> > > > > How do y9ou figure that?  ABS works, wet or dry, to maximize the
> > > > > amount of time the tire is at or near peak friction level.  
>
> > > > No, it does not.
>
> > > > ABS is designed to allow you to still steer while mindlessly whomping
> > > > on the brakes. To do so it has to leave a little traction on the
> > > > plate.
>
> > > Again, not quite. ABS will reduce the amount of force applied to the
> > > brakes whenever conditions result in the tire starting to lock up.
>
> > > One of those conditions could be a change in the friction of the
> > > surface, but one could also be that you've turned the wheel.
>
> > > So there is no traction "left on the plate" in the way you meant.
>
> > > > Anyway, on dry pavement, if you can lock up the brakes, your brakes
> > > > are better than your tires. If you improve the grip of the tires
> > > > you'll stop faster.
>
> > > Not just on dry pavement. :-)
>
> > > --
> > > Alan Baker
> > > Vancouver, British Columbia
> > > <http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg>
>
> > If the algorithms and sensors were perfect, and there were no control
> > loop delay, sure.
>
> Sorry, but they don't have to be perfect. Just better than human. And
> give the speed of human reactions, that's not that hard.
>
> --
> Alan Baker
> Vancouver, British Columbia
> <http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg>

I'm stating clearly that ABS leaves some traction 'on the plate'
unused. The fact that an expert using skilled braking technique on dry
pavement can stop faster with the ABS off proves this
incontrovertibly.

I'm not debating improvements ABS gives in most circumstances compared
to human brake modulation


Dave.



From: Matthew Russotto on
In article <bbeft5hfniv2tfhknmpm1oh71jpbp3m65n(a)4ax.com>,
Ashton Crusher <demi(a)moore.net> wrote:
>
>I'm not too keen on the idea of "effective" being that when the
>pavement is wet is to go sliding out of control.

If you lock up all four wheels, the car does not go "sliding out of
control". It behaves in a quite predictable manner, sliding
straight in the direction it was going when the wheels locked up if on
a flat surface.

--
The problem with socialism is there's always
someone with less ability and more need.
From: Matthew Russotto on
In article <nreft51k6vg3gluv877sfni2jbkbsgupeh(a)4ax.com>,
Ashton Crusher <demi(a)moore.net> wrote:
>On Tue, 27 Apr 2010 21:38:43 -0500, russotto(a)grace.speakeasy.net
>(Matthew Russotto) wrote:
>
>>In article <57q9t5lr4jhb5hervqhb2q51b3poff1eig(a)4ax.com>,
>>Ashton Crusher <demi(a)moore.net> wrote:
>>>>No. ABS is very close to threshold braking, but it is not. It is a very
>>>>rapid sequence of going slightly beyond the threshold and then back to
>>>>less than the threshold.
>>>
>>>Where you are getting that definition from? It makes no sense to me
>>>and is contrary to what people have claimed in the past. What's your
>>>definition of the "threshold" point?
>>
>>Take a chart of brake pressure (at the caliper or shoe) versus braking
>>force applied to the road by that tire. It'll look basically like a
>>line going from 0 upwards fairly linearly, leveling off slightly as it nears a
>>peak, followed by a sharp dropoff to a horizontal line. Perfect
>>threshold braking would be holding braking pressure right at that
>>peak.
>
>You've just described what ABS does in any practical sense. To say ABS
>is qualitatively different then threshold braking is just splitting
>hairs.

No, ABS does not do that. ABS works by releasing pressure until the
wheels are no longer approaching lock, then re-applying until they
are, then releasing, etc. An ideal ABS would approach the same
effect as threshold braking, but the real ABS control loop is long and sloppy
enough that the difference is noticable.
--
The problem with socialism is there's always
someone with less ability and more need.