Prusa MK3 Einsy RPi Zero Access

**Update 2018/02/13:** Alternate Base with heat bed nylon support holder added back in.

**Update 2018/01/28:** Alternate Cover with clip to hold camera adapter.

This is a rework of Prusa's "Einsy-base" file from Github. I knocked out an opening to access the RPi Zero, reworked the vents, and added a removable cover. There is also an added slot to access the lower screw used to mount the base to the frame. The Pi cover is held on by screws commonly used on computer case fans, like these. ht