EDIT: This PDF contains very detailed electrical information for the EEs who wanna go through the complaint: https://www.autoevolution.com/pdf/news_attachements/breaking-nhtsa-petition-shows-tesla-s-sudden-unintended-acceleration-is-real-and-curable-217525.pdf
Last year at /r/RealTesla, a Chinese video of a car rocketing at full speed for 1+ minutes before crashing / killing a pedestrian made the rounds. We all recognized it as one of the weirder cases of “Sudden Unintended Acceleration”, and I think that particular video really changed some minds.
While a lot of SUA events are from driver-error, it began a search into why Teslas seemed to be getting more SUA above-and-beyond the industry normal. This investigation (now filed under NHTSA) suggests that the ADC could be miscalibrated during a load-dump (or other electrical surge-like) scenario.
If the ADC associated with the accelerator pedal is off, then the Tesla will have the pedal at the wrong level of acceleration until the next calibration event, which is not going to happen until over a minute later.
This is extremely similar to that Chinese runaway Tesla, and perfectly seems to explain it. I’m glad that someone seems to have gotten to the bottom of this.
This is actually more damning of Tesla, though. The fact this is normal behavior means anybody working in this space should know and would therefore compensate for high and low voltage scenarios. Then consider the fact that the new LiPo 12v battery is only 6.9Ah and you’re basically discharging it at 14.5C to get 100A. The relationship of voltage sag to current draw in a LiPo battery isn’t exactly unknown science. The Model 3 flooded battery is 45 Ah, and claims to have ~ 400 CCA rating. I’m not sure what the sag would look like there, but based on these crashes I bet it’s just as bad.
As I mentioned on Discord, if you exposed the FSD computer or even infotainment computer to this kind of huge voltage range, the best outcome would be software crashes because of spurious values in logic circuits. So they clearly knew to compensate for this in the power supplies for these computers. Using simple voltage dividers and op-amps as the reference for the ADCs and then skipping the gain compensation in the DSP is unbelievably lazy.
Worse, IMO, is the fact that TI calls out that you should either design or use a voltage reference generator, of which they offer several compatible with the DSP. Two seconds on the site and I found REF34-Q1 which is an automotive grade component with a cut off voltage of Vout + 50mV. And of course the design guide, data sheet, and other documentation describe how to best use this component in an automotive environment. In other words, this is lazy software and lazy hardware design when there are countless reference designs available.
Of course, the fact that so many systems run from this same 12v line on the inverter boards calls into question how they are properly isolated and protected from such dramatic voltage drops. You’ve got CAN, LIN, the FET drivers, etc. all running off this same rail. When the inverter boards started blowing up, I assumed it was because Tesla wrote a unified firmware for controlling new and old FETs and they were perhaps overdriving some of them and causing them to blow. But now I’m wondering if there isn’t something rooted in hardware causing the issue. If the AC compressor or PAS cause large voltage swings, is it possible that this is causing another reference somewhere to be incorrect which in turn causes FETs to switch improperly and blow each other up? There’s a lot of field and position sensors in the drive units, so I could see this happening more now than ever before.