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Flywheel Diameter

  1. Oct 9, 2006 #1

    moo

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    Hey all,

    I realize that when weight is moved from the center of a flywheel toward the outer edge (or a larger diameter wheel is used), the capacity for energy storage increases. But I have no idea how to calculate how much that increase actually is, or whether the increase remains constant (proportionately) between the two as RPMs increase.

    Anyone have a formula handy for this? Hopefully with enough footnotes for a "non-engineer" who doesn't know many standardized formula abbreviations...

    Thanks, moo
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    Last edited: Oct 9, 2006
  2. jcsd
  3. Oct 9, 2006 #2

    berkeman

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    Staff: Mentor

  4. Oct 9, 2006 #3

    brewnog

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    Gold Member

    Sure, a common problem.

    For a solid disc:

    I = mk^2 = (mr^2) / 2 = (p*pi**b*r^4) / 2

    Where I is the moment of inertia of your wheel, m its mass, p the material's density, b the disc's thickness, r its radius, and k the radius of gyration.

    k = r / (sqrt 2)

    Now, energy stored:

    E = (Iw^2)/2

    Where w is the angular velocity of your wheel, (2*pi*N) where N is the number of revolutions per second.

    Sorry about the lack of fancy text, write it out on paper!

    For non-disc-like flywheels, you will easily be able to find I geometrically; if you struggle give us a shout or have a quick look in a mechanics book.

    You following?
     
  5. Oct 9, 2006 #4

    moo

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    Thanks guys, that should do the trick. :wink:

    moo
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