Pulley to pulley calculations

YuccaFlatsRanch · #1 02/09/08, 08:00 PM

If I have a 3 inch pulley driving a 13 inch pulley how do I easily figure comparative rotations and comparative power??

ace admirer · #2 02/09/08, 08:10 PM

rpm is porportional to diameter.... the small will turn 13/3 x rpm of the larger.. the larger will turn 3/13 x rpm of the smaller...the torque will be inverse of the rpm.

Batt · #3 02/09/08, 08:22 PM

Think of it as a length of rope around both pullys. If the 3" pulley makes 1 revolution then 9.42 " of rope goes around the pulley. Meanwhile the 13" pulley will use 40.84 inches of rope to make 1 full revolution. So 1 rev on the 3" pulley = a little under 1/4 revolution on the 13" pulley.

tyusclan · #4 02/10/08, 07:26 AM

Multiply the diameter of the drive pulley (on the motor) by the rpm of the motor, then divide that by the diameter of the driven pulley.

For example, if the 3" is on the motor and the motor is turning 1725 rpm, and you multiply 3 X 1725 you get 5175. Divide 5175 by 13 and you get 398. So the rpm of the 13" pulley would be 398.