My common solution to boot issues that lock me out is,
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Get a USB Live distro (always good to have a backup lying around)
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Boot into live distro
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Chroot into the broken distro (Arch wiki has an article on this)
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Fix any bugs that I can find and/or reinstall the bootloader
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Test, repeat until the problem has been found and fixed
Hope it helps any newcomers!
Woah those are some cool properties, I wonder how hard these gears would be to manufacture at home? I'm looking at implementing my own custom gear reductions in servos but I don't think my 3d prints will mesh well enough or withstand long usage