How to draw the 3-D figure in (a) with cubes

I have read a paper about robotics-- Hybrid head mechanism of the groundhog-like mine rescue robot.

And I want to draw the 3-D picture of the robot's workspace as in http://imgur.com/OzKz0E3. I know how to draw the workspace with mesh but do not know how to draw it with cubes as in (a). It seems the cube picture is more clear. Is there anyone who can give me some codes how to draw the workspace with cubes?