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RTG crane design calculation

  1. Apr 6, 2017 #1
    Hi guys...
    appreciate if somebody can help me on the design calculation of the RTG crane....
    I am stuck to understand the following formulas, used by MITSUBISHI to calculate as follow:

    1. Moment of inertia for hoisting
    = [Lifting weight (kg) x Lifting velocity^2 (m/min)^2] / [π^2 x motor rpm^2]
    = [(52,920 kg) x (23 m/min)^2] / [(3.142)^2 x (1,000)^2]
    = 2.84 kgm^2

    Please help guys....tq
     
    Last edited by a moderator: Apr 6, 2017
  2. jcsd
  3. Apr 6, 2017 #2

    berkeman

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    Staff: Mentor

    Welcome to the PF.

    Could you post the source for these equations? Is there a picture of the crane, or a figure that goes with your question? Is this for schoolwork?
     
  4. Apr 6, 2017 #3
    I got this formula from the crane manufacturer document. It is a partial calculation used to calculate the required motor horsepower for hoisting.
    You can go here to look fornthe crane i meant
    http://www.gosan.net/imagenes_aplicaciones/puerto/grua_rtg_grande.jpg
     
  5. Apr 6, 2017 #4
    This picture is no help at all in understanding what MMOI is required.
     
  6. Apr 6, 2017 #5

    berkeman

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    Staff: Mentor

    And the equation that was originally posted is more of a force equation, no? Not a MOI calculation. And MOI isn't involved much int power lifting for a crane...
     
  7. Apr 6, 2017 #6
    The pi
    The picture is just to answer mr berkeman request "the picture of the crane".
    Yes, i myself also cannot understand the calculation and seeking help here...
     
  8. Apr 6, 2017 #7
    Sir...
    The calculation is made by the japanese. Maybe there was translation issue. Maybe it is not MOI. Maybe you are true (force)... i am not sure... seek your help to clarify the formula used...
     
  9. Apr 6, 2017 #8
    This is my understanding...
    The final unit is kgm^2. So it is MOI.
    This value is later used to calculate the acceleration force. This is justified as MOI is the resisting force in acceleration...
     
  10. Apr 7, 2017 #9

    JBA

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    For those wanting the basis and context of this calculation see pg. 8 of the below document
    http://dl.mitsubishielectric.com/dl/fa/document/manual/inv/sh060004eng/sh060004engb.pdf

    And for the referenced Tech Note no. 30 calculation see pg 133 of the below document
    http://dl.mitsubishielectric.com/dl/fa/document/manual/inv/sh060003eng/sh060003engg.pdf

    I found all of this through a determined websearch, your welcome

    In the end, I don't see how the Note 31 pg 8 Moment of Inertia equation is somehow a substitute for one of the Note 30 pg 131 Moment of Inertia formulas

    Maybe someone else can figure this out.
     
  11. Apr 8, 2017 #10
    You are very hepful sir. I thank you so much
     
  12. Apr 10, 2017 #11
    Dear JBA
    I found the formula as link given is similar with the design calculation, but only the crane designer put a figure in front:

    Load MOI = 4 x W x (V/2π x rpm)^2

    What does the "4" stands for?

    tq
     
  13. Apr 10, 2017 #12

    JBA

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    The formula in your first post reads as follows:
    If you look at the above formula you see that 2π is used where only π is used in the first post formula (converting that first formula to the same format as the above one gives: Load MOI = W x (V/π x rpm)^2). The result of the second formula is that the (2π)^2 in the denominator cancels out the 4 in the numerator, so the two equations are actually identical. As to why the crane designer used 2π instead of simply π and then cancelled the 2 out with the 4 in front, I don't have a clue.
     
  14. Aug 15, 2017 at 4:36 AM #13
    How do you determine speed and acceleration of crane?
     
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