Flex3Drive 3rd gen mount for CR-10

This is a mount for Mutley's excellent flex3drive (version 3) found at https://flex3drive.com/flex3drive/.

The flex3drive allows you to keep the stepper motor mounted in the same location as stock but gives you a direct drive extruder; it does this by driving the extruder itself with a flexible cable. Excellent for all types of filament, but it is particularly good for flexible filaments.

I expect Mutley will probably eventually make a "prettier" mount, but this one works and is on my prin