At 07:49 AM 11/1/99 , Todd Green wrote:
>>At 07:50 PM 10/28/99 , Engstrom wrote:
>>>>> [ I wrote g_uasge = max(cur)/max(peak); ]
>>
>>>> Ignoring the transition component, you'd want something like:
>>>>
>>>> g_usage = sqrt((cur_lat/peak_lat)^2 + (cur_accel/peak_accel)^2)
>>>>
>>>Now, usage at any point in the run is calculated as the highest of three
>>>numbers.
>>> 1) Total G percentage - this number is the distance from the
>>> origin (or center of the friction circle) of the total Gs that
>>> the car is currently pulling divided by the distance from
>>> the origin of the edge of the friction circle that touches
>>> a line that runs from the origin through the total G point
>>> that the car is currently pulling.
>>
>>Okay. I think the math for this would be the g_usage I gave above,
>>where you use the appropriate friction circle for your speed.
>
>In my original post on this, I didn't mean for my "max" function to be
>taken literally in the mathematical sense, but just locgically in the
>sense that GEEZ thinks you should be maximizing one of the three data
>channels. While your math is close, it isn't exactly what you want. In
>addition to quantizing for speed (the idea of a friction cylinder) you'd
>also have to quantize for the vector angle for (at least) two reasons.
>The first is that you can brake much harder than you can accelerate. If
>you use your formula above, acceleration is always going to be some
>fraction of peak usage as soon as you hit the brakes.
Well, if you go back to my original post (not the snippet cut from it),
you will see I said "where peak_accel depends upon the direction of
curr_accel", but...
> The second is
>that tires aren't linear in their ability to generate g's with respect
>to the angle of the force.
Wow! Geez tracks the actual peak point for every point on the friction
circle (tube)!?!? That seems somewhat improbable... OR, does Geez have a
standard formulation for how tires vary with respect to the angle of force
and then computes based on the peak lat, accel, braking forces?
>
>A third consideration could be quantizing over time. Say the first half
>of the course was wet or on a different surface. Clearly your absolute
>g's are going to be different for differing conditions. I guess my
>point is that Byron has probably put quite a bit more thought into
>getting useful usage numbers than we can surmise on this list.
Whoa--- now how would Geez figure that out? How would it know whether
the course was wet or you were just not handling the elements on that
side of the course very well? Somehow I don't think Geez is that clever.
>
>However, I still think GEEZ has a limitation by not looking at the rate
>of change in acceleration, like it does for lat g's. You should not be
>"penalized" for acceleration going through the center of the friction
>circle (as you do in straight line braking.)
Agreed... and as I said before, I think you'd need two rates there, as
you can go from max accel to max brake much quicker than vice-versa.
But why do you think Geez doesn't look at that?
Brian
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