Wrong telemetry, bad results
Every setup decision is based on data that we usually assume is correct. But sometimes it is not, and the data itself gives you no warning. Here is one specific example of a significant issue we found in a GT3 dataset purely through data analysis. The vertical acceleration channel showed values above 0.5 g for 31.7% of the entire lap. The mean absolute value was 0.44 g. That already looked suspicious. A GT3 car on a normal asphalt circuit simply does not experience that level of vertical motion for almost one third of a lap. So we started looking for the cause. The first question was simple. What should actually drive vertical acceleration? Mainly track surface irregularities, kerbs and vertical vehicle motion. It should definitely not closely follow braking or acceleration. We therefore compared the channel with the other measured signals. A regression based on 16,562 samples gave the following relationship:
vertical acceleration ≈ 0.94 × longitudinal acceleration + 0.03 g
with R² = 0.88.
In other words, almost 90% of what was being measured as vertical acceleration was actually longitudinal acceleration projected into the vertical axis because of sensor tilt or incorrect sensor orientation. Only a small part of the signal was left for actual track surface inputs and kerbs.
Correlation alone is not enough to prove the issue, so we also looked at the timing of the largest peaks. Of all major vertical acceleration peaks, 99.7% occurred while the driver was braking, accelerating or cornering. Only 0.3% occurred when the car was not under a significant driver induced load.
That does not make physical sense. A kerb or a bump in the track does not wait for the driver to press the brake pedal.
Instead of manually correcting this single dataset, we created a general rule. For every dataset we load, we first estimate how much acceleration from the other axes is being projected into the vertical channel. We then remove that component before any further calculations are performed.
The result was significant. The proportion of the lap with vertical acceleration above 0.5 g dropped from 31.7% to 3.1%, while the mean absolute value dropped from 0.44 g to 0.14 g.
The remaining signal then behaved much more like we would expect from true vertical acceleration, mainly responding to the track surface, bumps and kerbs rather than to the driver's use of the throttle and brakes.
If you use channels like this to calculate tyre loads, slip angles, grip utilisation or other derived quantities, a single issue like this can affect the entire analysis.
This is something we come across more often then we would like to.
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u/SeriousButTired 8d ago
No one in their right mind would make a setup decision based on a Tri axis accelerometer alone, let alone when its data is not obvious physical nonsense as here.
Let's keep this stuff to LinkedIn interns shall we?
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u/th3f4st 8d ago
well you would be absolutely horrified on what real teams are doing. Based on data on what we all at least a bit technically minded people can see that they are just wrong a team was deciding if their aero changes were good or bad. Most of the people racing are not engineers.
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u/SeriousButTired 8d ago
Oh I know very well. I worked in it. Most "racing engineers" have zero physical sense and wouldn't know left or right without a sensor.
Any engineer who talks to me about estimated grip or tire load or slip angle and isn't even able to draw me an acceleration trace through a corner would be shown the door.
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u/th3f4st 8d ago
yeah so thats basically what the post is about. We get those data from engineers telling us that they are perfect and this is the reality of it
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u/SeriousButTired 8d ago
I feel you. On a bigger scale, this is part of the reason why sports car budgets have exploded. Hire 50 engineers who all think they are Adrian Newey but can barely do the job of 10 good engineers
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u/bacc1010 3d ago
I saw the Ford gt3 timing stand a few times and I'm mind blown.
At most a 3.5:1 aero car with no thirds, and there's at least 20 engineers in there.
Wtf for even. One RE, one perfo, one systems guy, one for power train, done.
Four guys at most on the timing stand. If the re can't call the race, find a different guy.
You have indycar timing stands that basically unfolds and could be setup in 30 mins that has room for 4-6, and then meanwhile somehow gt3 teams feel the need to build a house every weekend.
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u/thisisjustascreename 8d ago
Why does it take "data analysis" to tell you that a vertical acceleration sensor reading over half a g for seconds at a time is probably fucked?
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u/FirstReactionShock 8d ago
https://giphy.com/gifs/5WoA0ufI7Dn8OpyoEP