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Torque & rpm

  1. Aug 30, 2013 #1
    Dear Engineers,

    Asslam u Alaikum(May peace be upon all of you)

    I have machine A, rotates at 3000 rpm and required torque to rotate is 10 NM.
    I want to operator this machine with an other machine B(motor) of 1500 rpm which can gives the torque of 7 NM max.
    bc i m Electrical person and don't know much about this so I hv following questions

    1. Can I operate it by using 2 gears,1 to shaft of machine A and 2nd to the shaft of machine B?
    2. How can i calculate the gears size to meet the torque and rpm?
    3. will the load of machine B increase in this case, even using gears? bc I don't want big difference in current.


    Last edited by a moderator: Aug 30, 2013
  2. jcsd
  3. Aug 30, 2013 #2


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    If machine A requires 3000rpm with a torque of 10Nm, it needs a power of 3000rpm*10Nm*2pi = 3.1kW.
    Your motor can deliver a maximum of 1500rpm*7Nm*2pi = 1.1kW. Gears cannot produce energy out of nowhere - there is no way to operate machine A with your design values with motor B. You have to reduce revolution frequency or torque, or use a more powerful motor.
  4. Aug 30, 2013 #3


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    For an idealized motor, max torque occurs at zero rpm (stalled) and max rpm occurs with zero torque (no load). Maximum power occurs at 1/2 max rpm with 1/2 the max torque. As mentioned above, you need a more powerful motor.
  5. Aug 30, 2013 #4
    thanks for your reply

    So is there any way to increase rpm of machine A using gears on machine B, i. e. by increasing the torque of machine B and using a rather larger gears set, I mean what will happen if i use a motor A of 750 rpm which gives the torque of 14 NM.
  6. Aug 31, 2013 #5


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    Motor A, machine A? I am confused.

    Gears can increase rpm and reduce torque, or reduce rpm and increase torque - always with some losses of course.
    If your motor cannot deliver the given maximal torque value at the given rpm value, you also have to take into account the effect rcgldr mentioned.
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