This summer, in an effort to teach myself Autodesk Inventor 2012 I decided to construct a virtual Geneva wheel. I have made actual Geneva wheels in the past using a pre-existing templates but I had no idea how to lay out this mechanism from scratch.
After watching a few YouTube videos depicting Geneva wheels with a frustrating lack of useful information I finally dug up the necessary formulas in Ronald A. Walsh’s Handbook of Machining and Metalworking Calculations. Some portions of this book are available for viewing on Google Books.
The video is pretty clear. What is really satisfying about this geometry is that everything is based off of two right triangles. Once I understood this, the math became a lot less mystifying.
(Note: These calculations are practical in that I have made accommodations for the tolerances required if the mechanism is expected to actually function. This is represented by value t and can be varied depending on the size of the overall Geneva and the materials it is to be constructed from.)
UPDATE: I noticed that this calculator and visualization tool was posted a few months ago in the YouTube comments section. Very nice! Thanks for posting user wjf213!