Date: Thu, 5 Aug 1999 15:25:07 -0400 (EDT)
From: "Mark J. Andy" <marka@telerama.com>Subject: Re:
Software vs. Hardware
Mark Andy writes:
>Have you ever looked at two runs side by side using
Geez? That course map isn't accurate at all. Don't
get me wrong, it provides a handy reference to help
you locate areas of the course, but using it
to compare lines or anything that requires much
accuracy is a waste of time. This isn't Byron's fault
(I assume), its that the accelerometers have error
like any other measuring device.
#define DataAcquisitionGeek
{
Not quite. Modern 'chip' accelerometers are typically
accurate to within hundredths of a g. The inaccuracy
probably stems from the method used to compute the
course position. The accurate way to plot course
position would be to use an inertial navigation
system, like aircraft use. That requires sensors for
linear acceleration (which GEEZ, Edelbrock, etc. all
have) and for rotational acceleration (which none of
them have). Linear accelerometers are getting dirt
cheap because every airbag module in the world uses
one. Rotational sensors are *very* expensive,
especially the ones that can sense enough degrees per
second to keep up with a sharp turn or spin. (Lab
exercise: Go out and spin your car and see if GEEZ
can correct for it on the course map! :) I don't
doubt Byron has come up with some clever
approximations, but getting a true position plot with
only two accelerometers ain't possible.
In addition, course position and speed are calculated
from the acceleration data by mathematical
integration. (I almost said "derived" by integration,
silly me...) Errors in the acceleration data will
accumulate in the speed and position calculation.
That would tend to make the numbers less accurate
towards the end of the run. Might not matter in a 60
second autocross, but I bet you'd start to notice
after 20 minutes of track time.
}
> I wonder how much more accurate those maps would
be if Byron had an independent measure of vehicle
speed like the Edlebrock system apparenntly supplies?
The speed data would obviously be improved
(theoretically at least) but I doubt position would be
affected, unless you could somehow use it to correct
for the cumulative error in acceleration.
I guess the point of my rambling is, it's silly to
argue about which system is perfect; *none* of them
are, because perfect costs too much. Try as many as
you can and use the one that best helps you to go
faster. YMMV...
Cheers,
Craig Blome
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