# RTG crane design calculation

1. Apr 6, 2017

### Ridzuan

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

Last edited by a moderator: Apr 6, 2017
2. Apr 6, 2017

### 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?

3. Apr 6, 2017

### Ridzuan

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

4. Apr 6, 2017

### Dr.D

This picture is no help at all in understanding what MMOI is required.

5. Apr 6, 2017

### 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...

6. Apr 6, 2017

### Ridzuan

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...

7. Apr 6, 2017

### Ridzuan

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...

8. Apr 6, 2017

### Ridzuan

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...

9. Apr 7, 2017

### JBA

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.

10. Apr 8, 2017

### Ridzuan

You are very hepful sir. I thank you so much

11. Apr 10, 2017

### Ridzuan

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

12. Apr 10, 2017

### JBA

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.

13. Aug 15, 2017

### cranelift

How do you determine speed and acceleration of crane?

14. Aug 20, 2017

### Ridzuan

For my case, the speed was request by the operation team, based on the operation performance record