Internal sun gear 1 is rigidly attached to the base. Planet gear 2 rotates about axis A of carrier 3 which, in turn, rotates about fixed axis B. Taking the sign of the angular velocities ω₂ and ω₃ of gear 2 and carrier 3 into account, the transmission ratio of the mechanism is i₂₃=ω₂/ω₃=1-r₁/r₂=1-z₁/z₂ where r₁ and r₂ are the pitch radii, and z₁ and z₂ are the numbers of teeth of gears 1 and 2. The paths of points of gear 2 are hypocycloids.
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