From: Ashton Crusher on 28 Apr 2010 00:38 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 28 Apr 2010 03:49 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 28 Apr 2010 07:39 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 28 Apr 2010 19:01 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 28 Apr 2010 19:05
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. |