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Confusion with Motor Sizing

  1. May 22, 2013 #1
    Hello all,

    I an trying to size a motor to drive two mechanisms but am having some real trouble getting my head around the required torque.

    First let me explain what we have. Basically there are two mechanisms where I have plotted the speed and torque requirements on this graph
    Initial_Torque_Requirements.png
    as you can see the v230 mechanism only runs between 0 to 1500 RPM where as the v24 mechanism runs from 0 to 6000 RPM but with very different torque requirements.

    I need to size a motor in terms of RPM and Torque that will run both mechanisms however I'll have to do something to limit the speed of the v230 mechanism to 1500 rpm.

    What happens to the torque requirements in this situation? Are they added together? If a motor is driving one mechanism is the torque already present for the other mechanism or is additional torque required?

    I am envisaging the mechanics somewhat like this
    Concept.png
    I soft of have the speeds sorted in as much as I believe they are correct but I am struggling with the amount of torque required by the motor.

    Could someone please advise on this? Or maybe (i'm sure) there is a simpler way to achieve this in a less complicated fashion?

    Thanks very much guys.
     
  2. jcsd
  3. May 23, 2013 #2
    I would approach it by calculating the power needed by each mechanisme: P = T*\omega. Since the sum of the powers needed is what should be provided by the drive it should be fairly forward. Of course there will be some losses due to friction
     
    Last edited: May 23, 2013
  4. May 23, 2013 #3
    First thing is how you are driving both, sheaves or is your first gearbox dual output?

    A simplistic answer is that your motor will have to have a torque equal or greater than that of the two drives combined (after considering losses from the gearboxes).

    Second, if your gearbox is 4:1, your torque ratio is 4:1.
     
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