Sun bevel gear 1 is rigidly attached to the base. Planet bevel gear 2 rotates about axis OB of carrier 3 which, in turn, rotates about fixed axis OA. Axes OA and OB intersect at point 0. 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+sin(δ₁)/sin(δ₂) where r₁ and r₂ are the radii of contacting circles on the pitch cones of gears 1 and 2, z₁ and z₂ are the numbers of teeth of gears 1 and 2, δ₁ and δ₂ are the pitch cone angles of gears 1 and 2, and δ is the centre angle (angle between axes OA and OB). If angle δ=δ₁+δ₂= 90° (mitre gears) then the transmission ratio equals i₂₃=1+cot(δ₂)=1+tan(δ₁).
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