Two identical pulleys 3 and 4 rotate freely on fixed axle 6 about fixed axis D-D. Belt 5 runs over pulleys 3 and 4, contacting the pulleys with both of its sides, and over identical guide pulleys 1 and 2 which rotate about parallel fixed axes B and A. The transmission ratio from pulley 1 to pulley 2 is i₁₂=-1. Looking along axis D-D in the direction of the arrow, pulleys 3 and 4 rotate at the same speed but in opposite directions.
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