Parametric lower Z (motor) mounts for AO / MendelMax printers

I really like the AO-100 style motor mounts, but ran into challenges editing the STLs for some of the things I was trying to do (e.g. testing different rod sizes, adding a membrane on the rod mount screw holes to improve the print).

I put this together loosely based on the AO design to make it easier for me to tweak.


Please note that this is a complete redesign -- though I'm happily also releasing under the GPL, and really appreciate the Lulzbot design. Also while I've tried to make sure