Matter Control printing file types (.obj)?

I have recently purchased and setup a RoBo 3D R1, run test prints, watched videos, become familiarized, etc. with this 3D unit. However, I am trying to learn how to print files from a "*.obj" format. The literature and website information states that the R1 will print from ".stl AND .obj" files but I do not see any option to do so within MatterControl. I have utilized SketchUp to create my first file for printing and I have saved it in both .skp and .obj formats; I don't see an option to save/export from SketchUp into .stl format, which is why I only have it in the other two formats. Can anyone please help me to learn what the steps would be to either convert the stated file types into .stl or to load a .obj file directly into MatterControl for printing? I would greatly appreciate it!

Thanks-RD