Pulleys 1 and 2 rotate about fixed axes A and B. Crossed belt 3 runs over pulleys 1 and 2, contacting the pulleys with both of its sides. The transmission ratio from pulley 1 to pulley 2 is i₁₂=ω₁/ω₂=n₁/n₂=-(R₂/R₁) where ω₁, ω₂, n₁ and n₂ are the angular velocities and speeds (in rpm) of pulleys 1 and 2, and R₁ and R2 are the radii of pulleys 1 and 2.
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