I love this idea!!! So simple yet so perfect
The trick here is to use some of that springiness.
Put the lead screw into nthe coupler, and bottom it out in the 8mm portion. Tighten grub screws appropriately. When you attach it to the 5mm motor shaft, stretch the coupler gently forcing firm contact between the motor shaft and the TR8 lead screw. Keep that tension while you tighten the motor grub screws. Thenfirm contact between motor and screw shaft will prevent the coupler from introducing backlash.
I used that technique for my leadscrew based 3D printer for the X and Y axes. It’s getting a bit old now, but I still use it after years of use. I use regular anti-backlash nuts, which work well enough to keep overshoot and ringing to an acceptable level.
I remember also seeing this in the V1 docs, I think in the Primo assembly instructions. Maybe also in the LR2 instructions. I never read the LR3 instructions though, since mine was a beta program build.
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