Phone case designs with working gears, that demonstrate simple mechanical principles. Designed for Iphone 4/4s/5/5s/. There are 3 different cases, see bottom.
Getting the gears to stay in place is a little tricky since the pins aren't really the right size. I'm sure when assembling crazy glue would work just fine. We ended up used a hot glue gun to actually melt the plastic and fuse the the pins to the back of the case. Once you get it assembled its a lot of fun and spinning it is surprisingly amusing.
This is an example of how working mechanical intricacy can contribute to decorations in every day lifestyle. The possibilities of 3D printing are actually limitless.
Side Rack and Pinion
Gear and Piston