The ratio is generally determined by three main
factors:
Number of teeth per part
Segmentation of fixed part,
input part and output part
Number of planet stages
There are several formulas for
the calculation of the ratio that depend on how the parts of the
gearbox are used. For example if the sun wheel is fixed and the
hollow wheel is the input, you have to use a different formula than
if the hollow wheel works as output.
You can find the suitable formulas in the table below:
Hollow wheel fixed
Pinion gear fixed
Planet shaft fixed
In pinion gear
i = 1+ (z3/z1)
In hollow wheel
i = 1 + (z1/z3)
In pinion gear
i = - (z3/z1)
Out planet shaft
Out planet shaft
Out hollow wheel
In planet shaft
i = 1/(1+(z3/z1))
In planet shaft
i = 1/(1+(z1/z3))
In hollow wheel
i = - (z1/z3)
Out pinion gear
Out hollow wheel
Out pinion gear
In = Input
Out = Output
If the planetary gearbox for example consists of 2 stages, you only
have to change z1 into z4 within your calculation formula.
The overall ratio of multi-stage planetary gearboxes
is calculated with the following fomula:
iges = i1*i2*....*in
The overall ratio is the product of all stage-ratios
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