Well CC I have an sd 4 with a single Z lead screw but these can wiggle a bit and effect print quality.
but the dual z should be more stable as both sides of the bed are supported not just one side.
So some general advice and info then will attempt to answer your question.
First of all go to the ROBO3D site and download the getting started pdf file.
https://drive.google.com/file/d/0B10g8o … view?pli=1
Then read through the control program documents in this case matter control seems to be the recommended software and last but not least look over the Slic3r documentation . you will likely have to look over these a few times. If most of it seems like Greek or GEEK do not worry you will understand it in time. Get a feel for the layout of the manuals and what setting effect the print and how. When you have a question go back and find the answer.
Also IIRC Robo 3d has a forum, join it and you have a second resource to ask questions of users.
Now for you question
here is partial answer from the manual. The z limit switches sit on coupler nuts it is important that these are properly seated.
Sorry to cause you concern just make you the z axis is properly aligned and lubricated and the z stop is set correctly . you just have to to check 2 instead of one.
Hope this help you .
http://manual.slic3r.org/
http://www.mattercontrol.com/
Tin
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