Spur Gear - Circular Pitch (19.722mm) - Pitch Diameter (280.276mm)

20/3/17: Added: further inspiration: http://www.thingiverse.com/thing:2190190

Inspirations:

1. Alex Crease inspired me to make the GearBot & to learn about gear mechanisms:
   http://3dprint.com/89688/3d-printed-gearbot-project
   www.instructables.com/id/GearBot-A-Dual-Speed-Gear-Driven-Bot
   www.instructables.com/id/Basic-Gear-Mechanisms/?ALLSTEPS

2. ProfDrafting's videos are instructional and easy to learn: https://youtu.be/_rH5mXvYLjQ
   I have learnt a lot of 3D modelling (Autodesk 123D Design) from her.