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Re: traction control

To: ddahlgren@snet.net
Subject: Re: traction control
From: rtmack <RTMACK@pop3.concentric.net>
Date: Sat, 01 Dec 2001 15:17:35 -0600
Dave:

adressing your comments individually:

> you said...

> You can integrate the analog signal for an average deal or just apply a low 
>pass filter
> with a real big cap that works way down in frequency.  8 or 10 hz is easy 
>enough to do so
> the changes are gradual.. adds about 1.00 to the simple version so now we are 
>up to
> 11.00....
>

>> >>  cool!  I would approach it with programming-- but it may be cheaper, 
>easier, and
>> >>  better-responding using pure analog electronics, as you suggest.
>> >>  when can we get one, and how much will it cost?
>> >
> >
> > you said...

>  weight is the biggest problem to go fast once you get into the 300 range. do 
>the math.
> Plus it hurts you from the very start to the very end but in different ways. 
>At the
> start it takes more to get moving at the end the rolling resistance is 
>substantial. On
> the Golden Rod (I use only for example as it was well documented) the rolling 
>resistance
> was 90% of the power required...
>
>           I have that book, too (Forbes Aird's Aeordynamics for Racing and 
>Performance
>           Cars-- ??).  I'm not convinced anyone knows how to "do the math" 
>correctly.
>           Aird himself points out that there are two things wrong with those 
>mathematical
>           conclusions (pp. 16-17):
>              + the Goldenrod's designer (W. Korff) used an (obviously 
>inappropraite)
>                equation for tire drag that probably results in a value that 
>is far too
>                large
>
>              + Goldenrod is one of the most aero-efficient cars to ever run 
>on the salt--
>                so the effect of tire drag will be proportionately larger for 
>it than for
>                most LSR machines
>
> You said...
> The real problem is the coefficient of friction on the salt. From what I have 
>learned
> and information I have gathered from data acquisition systems on different 
>cars and
> talking to many who have a clue is that the best you might hope for is 0.61 g 
>acell
> rate.
>
>
>> > That supports my own unscientific suspicions (based on much less research 
>on my part).
>>
you said...

> Funny this number is the same whether it was a 1100 lb car with 1500 cc 
>engine or
> Tom Burklands car from what he told me... So if you get to that point the 
>only way to go
> faster is with distance... or in the case of most cars they will hit terminal 
>velocity
> before the 4 mile marker as they are out of power with that acell rate, the 
>speed equals
> the power available. The other little bit of info is that the best rates of 
>acceleration
> do have some slip on the order of 5 to 10% so if you run a TC you would want 
>to allow
> about 15% and have it pull power out only to that point. Doing it this way i 
>suspect it
> would be much smoother as you are never really trying to have it hunt for 
>zero slip.
>
>
>> > Among our LSR people, the old drag racers I've talked too seem to agree 
>that the best
>> > accelleration is with a little slip, as you suggest.  My friends who race 
>Federal Mogul
>> > Funny Cars usually seem to tune for a little slip, as well. At this point, 
>I think
>> > everyone is still guessing a little w/regard to how much slip would be 
>best.
>> > Therefore, I think the best "off the shelf" system would have a "tuneable" 
>slip-rate
>> > (which would require something like a tunable bandpass filter on your 
>pure-analog
>> > system).
>> > I agree that allowing a constant, small slip should help produce a 
>smoother operation.
>> >
>>
> >
> > >
> > > Pork Pie said...
> > > So the question for traction, is not a question for a traction control - 
>it's a
> > > question of the compromise of downforce and resistance.
> > > If you got enough power you can increase the downforce, which will 
>eliminate the
> > > traction/grip problem.
> >

and I responded...
>         If you do this, I think you will soon get into the realm that Tom 
>Bryant theorized
was the cause of Earl Wooden's tire failure:  you simply overload the tires-- 
too much
downforce + torque (see Tom Bryant's response to this thread).  I think the 
first thing to
do is to minimize the resistance so you don't need to ask  the tires for so 
much (the
True/Costella car that you worked on appears to be a good example of this idea).

> then you responded to me...
> All the Goodyear stuff that was labeled for LSR use has a speed load rating 
>why not just
> believe it.  Add what down force you can until you exceed the rating then 
>back up a bit
> and that is what you have to work with. BTW a tires grip does not always 
>increase with
> force applied to it. There is an optimum amount and when you exceed it you 
>get on the
> other side of the curve too. Read "Fundamentals of Vehicle Dynamics" Thomas 
>Gillespie
> from SAE press.
>
>> > I agree about believing the tire's load rating.  I did not know that you 
>can reach a
>> > point where the friction force of a tire declines w / increasing load 
>(before the
>> > blowout)-- but I had wondered about it.  Don't have that book, but I'll 
>get a copy.
>>
> Dave Dahlgren ( who does understand exactly what we are doing or at least 
>trying to
> accomplish)

Dave, your knowledge is widely known among LSR people, and they have every 
right to respect
your opinion much more than they would mine.  It is human nature.  I thank you 
very much for
your support.
Best Regards,
Russ Mack

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