I am trying to design a gearbox for a project i have. I have calculated a fair few things about what i want to get from the gearbox, but now i have came to design the gear box i have got bogged down with all the various things, so help please if you can. Data is Input:7850 rpm Output: 1975 rmp Power that is transmitted is 29.75kw Permissable bending stress is 380mpa and shear stress 280. I am going to use a modulus of 3 for the gear tooth. I want to use 4 gears, but little unsure on what gears to use? Application is to take a motion from an electric motor and output, much like a gearbox is a Drill. I am a little unsure, well lost really, on how to calculate the ideal number of teeth for Gears 1, 2, 3 and 4, and there diameter and width. Is there a minimum width to dia ratio? Application is a small generator. Thanks for any help.