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Torque and RPM Analysis

  1. Aug 6, 2016 #1
    Please I need some help. I'm thinking that if I have a driving shaft with a torque of 10Nm and an RPM of 1000. If I add two 3 inches pulley on the shaft to transmit power to another shaft with a pair 6 inches pulley mounted on it and connected to the initial 3 inches via a belt. Will I have transmitted a total torque of 40Nm to this new bar and an RPM of 500?
  2. jcsd
  3. Aug 6, 2016 #2


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    The output will be 500rpm but the available torque will only be 20Nm (or less). Conservation of energy applies. If the belt was 100% efficient then Power Out = Power in.

    Power = torque(in Nm) * angular velocity(in Rads/S)

    So if you halve the rpm (angular velocity) you double the torque.

    Using two belts in parallel doesn't magnify the torque (unless the torque was limited by the belt slipping).

    It looks like your Power In is around 1000W. Belt drives can be 95% efficient so the Power Out is likely to be around 950W and at 500rpm that equates to 18Nm.
  4. Aug 6, 2016 #3
    Thank you so much Cwatters, its obvious power must always remain constant. Thank you for taking out time explain this to me. Cheers
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