"Sandmation, Teeter Totter" is a "sand animated" teeter totter. This thing is my rendition of an antique toy originally presented in "Carpentry And Mechanics For Boys" by A. Neely Hall in 1918. I've taken quite a few liberties in my 3D printed miniaturized version such as to fit the average build area, reduce 3D printed induced friction, maximize run time, and finally to use the heads of the unwitting riders to tap the sand hopper in order to loosen the sand flow. As was the original design, this is a fussy project as it only works correctly with patience and good balance, yet it is still a grand illustration of animated toys available for children almost a hundred years ago. Video of prototype is here: https://www.youtube.com/watch?v=vDA6zitL7MA. Designed using Sketchup Make 2015, and printed in PLA on a Makerbot Replicator 2 using Makerware 2.3.3.42 "Standard" Settings (.2mm layer height, 2 shells, 10% infill). Parts I purchased: 1) Very fine colored sand (hobby, craft store, Amazon). Study "Assembly.skp". Print and assemble all pieces as shown in "Assembly.skp". After printing, remove the hold down tabs from "Hopper.stl" and "Pivot.stl". Test fit and trim, file, sand, etc. all parts as necessary for smooth movement of moving surfaces, and tight fit for non moving surfaces. Depending on the colors you chose and your printer settings, more or less trimming, filing and/or sanding will be required. "Pivot.stl" must move freely on its axle. Assemble as shown in "Assembly.skp". Comment if you have questions.