The Scissor Test. Within the first few weeks of me joining TBC, Steve gave me the direction that he wanted to be able to walk around a Prufrock with a pair of scissors, be able to cut any wire, and the machine should still be able to mine. Obviously this was a hypothetical exercise, but the goal was real. What followed was a deep system-wide failure mode effects analysis and a complete redesign of the machine’s electrical system to be able to pass the scissor test. There are still a few single points of failure where the complexity or cost tradeoff doesn’t make sense to design out, but for the most part Prufrock now passes the scissor test. Being robust to a single failure is obviously important, but equally as important is observability of those failures. Without observability, a failure can lay latent in the system without anyone noticing for years and then when the backup fails the system will still go down. For this reason we make sure to instrument each redundant connection so when any failure happens we instantly know, get a notification, and can schedule a repair for the next maintenance day - all while Prufrock keeps mining. That’s what lets these machines keep mining continuously with zero people in the tunnel. We’re hiring electrical engineers. Come help us keep pushing this further. Link to apply in the comments below 👇