Cerberus PUP / GT2 carriage, combined from a DXF extrusion of the carriage and STL for the belt/magnetic ball holder. Interestingly enough the git repo doesn’t contain this part as a printed part. Instead the carriage (which the roller bearings screw into) is cut from aluminum and the belt/magnetic ball holder is a printed part. Since I wanted to print the entire part, I had to extrude the DXF in Inventor, and then combine the STL for the belt/magnetic ball holder and the resulting STL from the DXF in Sketchup of all things since Inventor doesn’t work well with STL meshes. After that, I had to run the resulting part through Netfabb to clean it up before I could print it.
Is that split in the u shape to tension the 3rd roller? I like it. No need for an eccentric bushing 
Yep!