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Torque of a spinning flywheel

  1. Dec 15, 2014 #1
    Hello, I would like to know the amount of torque required when the flywheel starts? I know that once at speed the flywheel doesn't require torque. I would also like to know what size of slip ring induction motor to run as the below mentioned speed.

    The weight of the flywheel is= 6500 kg
    ( wt. shaft, flywheel boss and wall 2700 kg + mass 3800 kg = total 6500 kg )
    RPM= 1550

    Thanks for your help.
  2. jcsd
  3. Dec 15, 2014 #2


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    Staff: Mentor

    The amount of torque required depends on its moment of inertia and how fast you want it to spin up.
  4. Dec 15, 2014 #3

    jack action

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    Last edited by a moderator: May 8, 2017
  5. Dec 16, 2014 #4
    ...and angular acceleration alpha is approximately closely enough by delta angular velocity / delta time.
  6. Dec 16, 2014 #5
    Thanks russ_watters, isn't how fast I want the fly wheel to spin the RPM? And if you don't mind how am I supposed to calculate the moment of inertia? Sorry for the trouble as am still an amateur at this thanks
  7. Dec 16, 2014 #6
    By RPM we usually mean the speed of rotation after the flywheel is up to speed. russ_watters and the other posters are talking about acceleration. How long do you want it to take to go from 0 RPM to max RPM? The shorter the time, the more torque you'll need.

    You can find the moment of inertia on this table: http://en.wikipedia.org/wiki/List_of_moments_of_inertia
    Note that multiple values are listed for each shape. The subscript tells you which axis you are rotating about.
  8. Dec 16, 2014 #7

    jack action

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    No, it's the angular accelration α that I mentioned in my post. As tygerdawg mentioned, the average angular acceleration is αavg = ( RPMfinal - RPMinitial ) / time.

    This the I in the equation of my previous post.

    If it is a solid disc:
    170px-Moment_of_inertia_solid_cylinder.svg.png 29bac02573ea5d0bbf08a7506e4e9b37.png

    If it is a ring:
    185px-Moment_of_inertia_thick_cylinder_h.svg.png bb27a6644113c6a25f841acabb3a003e.png

    For other basic shapes: http://en.wikipedia.org/wiki/List_of_moments_of_inertia

    Calculation method for more complex shapes: http://en.wikipedia.org/wiki/Moment_of_inertia#Calculating_moment_of_inertia_about_an_axis
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