# Epicyclic gear:modules for the sun,planet and ring gear

marellasunny
Is the module(M) of the sun,planet and ring gear in a 'planetary gear set' equal to each other always? Is it possible for M to be different for each of the gears in the set?[-Applications of this?]

$$PCD_{Ring}=PCD_{Sun}+2*PCD_{Planet}\Rightarrow N_{Ring}=N_{Sun}+2*N_{Planet}$$

is valid only when the modules of all the 3 gear types are same.

where,
PCD- pitch circle diameter
N- no. of teeth