If you need to know standards and basics of gear train design, go to this website :
http://www.sdp-si.com/catalogs.htm . Their books of small standard drive compenents and the Drive Component Design textbook are both really helpful. The textbook has all of your tolerances for press fits and helps you learn the basics of backlash etc. in a drive train. It also has a special section on robotics in the back. All of the books can be viewed online or ordered.
Hope that helped some.
Aaron