These are the printable pieces of the Hello, Velo project on Instructables.
Hello, Velo is a device for making your bicycle more awesome! It contains a GPS and a SIM card, so it always knows where it is and can send and receive text messages. Forgot where you locked your bike? Send it a text and ask! Headed home from work and need to let your significant other know your arrival time? Hello, Velo can detect that and send the message for you.
I printed all these parts from PLA using support material. Orientation is not very important for the "holder", but the "collar" and "back" should be printed so that the ring is in-plane (to prevent breaking during mounting). The collar can be customized to fit your own bike's stem/seatpost/top tube radius; the default pieces I've included here are for a 36mm diameter stem. Note that it's a good idea to make this a bit big so you can put rubber or another material between to keep everything from slipping apart.
Note: using Customizer for this part can take a loooooong time. All the source for the parts is included in the one .scad file that is included in this repository.