File:Fixed Diff A.svg

A fixed differential gear system. This arrangement has all gears with external teeth, and has typical ratio of between 10:1 and 50:1. The ratio is given by:

${\displaystyle m_{G}={\frac {N_{S2}N_{P1}}{N_{S2}N_{P1}-N_{S1}N_{P2}}}}$

where:

${\displaystyle N_{S1}}$ is the number of teeth on the No. 1 Sun gear (S1, yellow)

${\displaystyle N_{S2}}$ is the number of teeth on the No. 2 Sun gear (S2, green)

${\displaystyle N_{P1}}$ is the number of teeth on the No. 1 Planet gear (P1, dark blue, on the left)

${\displaystyle N_{S2}}$ is the number of teeth on the No. 2 Planet gear (P2, dark blue, on the right)