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Calculating the Moment of Inertia of a loaded flywheel

  1. Sep 29, 2015 #1

    I need to calculate the moment of inertia of this flywheel so I can calculate the torque I need.

    T= I*alpha

    Attached is an image of the flywheel the cam follower that will be attached to the shaft (left shaft in this picture). When calculating the Moment of Inertia, what mass do I use? The mass of the cam follower will be atleast 100KG (another load will be on top of that).

    Can I just use I=1/2 * M*R^2

    I will need a torque larger than what is required to rotate the loaded flywheel as the load will be variable.


    Attached Files:

  2. jcsd
  3. Sep 29, 2015 #2


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    As for your purpose, the formula will be close enough. It's the formula for a solid cylinder ( there is a groove at the outside of your wheel ).

    The exact formula/definition is

    I = r2⋅dm.

    Remember the inertia of the axle and the motor, assuming they are rotating as well.

    T = I * dω/dt
    Last edited: Sep 29, 2015
  4. Sep 29, 2015 #3
    Thanks but for the equation

    I=MR^2 do I use the mass of the flywheel (in KG) or the entire assembly? (The cam shaft plus the load on top of it aka 150 KG). The flywheel will need to rotate with that load which will move vertically up and down.

  5. Sep 29, 2015 #4


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    As for the rotating parts ( wheel+axle+motor ) you must calculate the inertias individually, then add these inertias.

    As for the load, you must place its mass at a distance = R from the center axis. As for the inertia it dosn't matter if the load is moving vertically or horizontally, but when the load is moved vertically, it will result in a torque, which has nothing to do with inertia.

    Tload = m*g*R, even if dω/dt = 0.
  6. Sep 29, 2015 #5
    Sorry just so we are on the same page I made a side view of the entire assembly. So the rectangle on the far right is the fly wheel. The horizontal shaft connected to it is the offset shaft (that will cause the platform (the other horizontal rectangle) to move up andr e down. The cam (the rectangle with the X) is attached to the shaft. Finally the box on the very top is the load which is resting on the plat form. In this picture it would be moving in a circular motion but I used linear bearings so restrict it to vertical motion.

    So for your equation Tload = m*g*R

    the R would be from the center of the fly wheel to the center of mass of the box (load)?

    Attached Files:

  7. Sep 29, 2015 #6


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    Sorry, I'm a kind of an extra terrestrial here ( don't understand technical english well ), so somebodies assistance needed.

    R is the distance from the center of the wheel to the center of the wire carrying the load.
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