For the past 3 weeks we have been working on improving and expanding the capabilities of the AO-100 from Aleph Objects.
We noticed a few areas that could be improved. After loosing the Z axis alignment a few times, we started experiencing really bad wobble. Like really really bad. I think this is from flexing the x ends too far, but even after loosening and realigning we still experienced it. We found brass bushings and designed a mount so that the end of the bushing is at the same height as the nozzle. I remembered from a comment on thingiverse.com/thing:4740 how keeping the bushings at the same level as the nozzle would ensure the nozzle can rotate, but not translate, therefore reducing wobble. We also used nophead's coupler from thingiverse.com/thing:9622. In hind sight I would have printed the one from the Mendel90.
Next task was to add support for dual materials. Our original plan was to use two eMinebea motors (http://store.trinitylabs.com/trinitylabs-micro-extruder-gearhead-motor-and-options/). Since the consensus on their functionality is mixed, we went with a mirrored jonas'-greg's-wade. We designed a simple carriage with two fans and the extruders rotated. Using slic3r 0.8.4 and dob71's Marlin fork (https://github.com/dob71/Marlin) we were able to get dual materials working pretty well. Our original hope was to use PVA and ABS. There is very little data available about printing with PVA, so we were surprised (and a little frustrated :P) to find out PVA and ABS do not stick together. We are currently looking into other options such as PLA/ABS and ABS/PEO. If you have anymore info about sacrificial support for ABS, please let me know!
Edit: I forgot the SCAD's for the x carriage and lower x bushing. will upload tomorrow.
I would like to give a big thanks to Mill-Max Mfg for letting me open source this work. On that note, if you are interested in more info about our setup, please find me on IRC (sjkelly) or email me. Don't contact Mill-Max, they make really nice electronic headers and things(made in the USA!), not RepRaps... :D