MSF doesn't use belts or tensioners. It has no idlers. If you count each part including every screw, nut and washer it's only about 100 parts. Most printers are over 600 parts. It uses a system I call "Rubber Rack and Pinion" Basically sections of belt fixed to the edge of the X and Y axis. The entire X axis is suspended on one threaded rod and motor. This eliminates backlash in the Z axis. The X and Y motors are very slightly canted in relation to the rubber rack so as to engage on the front and back of each belt tooth. This eliminates backlash in the X and Y directions. The prints are amazing! Most of the things I make are set with a coarse layer height but when you set Monkey to .1 mm layers it really shines. MSF has changed a bit since that pic. It now has a glass bed that covers the entire platform and it has no heated bed. I'm working on a second version that is made of printed parts and is easier to assemble. Enjoy!