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The cybertruck steer by wire IIRC has dual redundant everything including power supplies (the redundant one is powered by a DC-DC converter from the HV battery)

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That's great, but are they also running redundant, independently-developed software stacks? Because software failure seems to be the issue here.

Disregard me, I'm dumb.

All the electrical steering columns designs I've seen have used redundant sensors (often groups of them) specifically for that reason. The physical steering wheel to the shaft is still a SPOF, but it's also a "dumb" part where the only failure cases are mechanical. Eliminating failures there is straightforward engineering.

Yeah, I should have spent an extra 10 seconds thinking of the problem here and I'd have realised you can have multiple sensors going to different software on one steering column...

Multi-version approaches to developing software aren't as good at reducing common-mode failures as many people expect[1].

[1] J. C. Knight and N. G. Leveson, “An experimental evaluation of the assumption of independence in multiversion programming,” IIEEE Trans. Software Eng., vol. SE-12, no. 1, pp. 96–109, Jan. 1986, doi: 10.1109/TSE.1986.6312924.

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