Calculate Moment of Inertia?

[Anonymous]

I need to calculate the change in moment of intertia due to modifing a simple angled beam from 120 x 120 x 10 to 120 x 112 x 10.  Inventor has a function for moments but it rotates the center plane to something like VxV in the link below.  Is there a way to calculate this to X-X?  The instructions on this function are not very clear to me.  I'm also no expert with Inventor.  Thanks

  http://www.roymech.co.uk/Useful_Tables/Sections/Angles_dim_prop.htm

[Anonymous · Accepted solution]

do it in sketch mode, click tools, measure, region properties then calculate...

I only touched on this yesterday and would be interested if there was a better way, say properties of a boundry patch or similar

[JDMather]

Something like this?  (see attached)

[Anonymous]

That worked but I had to move teh origin to the centroid.  Thanks!

[Anonymous]

Where is that calculator from?

[Anonymous]

The same problem here:

I have to calculate profile's Moment of inertia and resistance in X and Y directions, with given parameters like this:

Inventor Region properties gives such results:

Area is correct, but the rest isn't (comparing to the table).

I think the problem is with the centroid - the X and Y zero points are slightly shifted in the original calculations. 

Is it possible to carry out such calculations with moved centre point in Inventor?

[Anonymous]

HI,

Can MOI be measured for a 3d shape?

I design and make cricket bats and am keen to calculate the changes of MOI on different shapes.

Thanks in advance,

David

[Anonymous]

Hi David, 

With your question, yes, MOI can be measured both for 2D and 3D shape. You can try using 2 Moment of Inertia calculator,  one is from skyciv the other one is from autodesk, it's also free. Have a look https://www.autodesk.com/education/free-software/featured.

Both of them are good resources.

Hope it helps.

Good luck! 

C. 

[Kai.Farrar]

I have noticed that the region properties only calculate correctly when the sketch is located on the XY plane.

[andrewdroth]

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@Kai.Farrar wrote:

I have noticed that the region properties only calculate correctly when the sketch is located on the XY plane.

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Is this true?

[johnsonshiue]

Hi Andrew,

I don't think that is true. We do have bugs in Regional Properties but it is not about calculation on different sketch planes. It should work in any 2D sketch regardless of the plane. I will need to see an example showing otherwise.

Many thanks!

[Kai.Farrar]

I have attached screen shots of identical areas drawn on different planes.

The one drawn on the XY plane is correct.

The one drawn on the ZY plane is backward.

The centroid location is wrong too.

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@johnsonshiue wrote:

Hi Andrew,

I don't think that is true. We do have bugs in Regional Properties but it is not about calculation on different sketch planes. It should work in any 2D sketch regardless of the plane. I will need to see an example showing otherwise.

Many thanks!

---

[johnsonshiue]

Hi Kai,

I cannot seem to reproduce it on 2019.2. The images you shared indeed are wrong. What release are you on?

Many thanks!

[Kai.Farrar]

I am also on Inventor 2019.2

[johnsonshiue]

Hi Kai,

Attached is the file I created based on the image. It seems to work fine for me on 2019.2. Do you mind sharing a file showing the problem?

Many thanks!

[Kai.Farrar]

I get the same bad results with your file as when I create my own.

Is there a setting or something that is messing this up?

[johnsonshiue]

Hi Kai,

I think I know the difference. Go to Tools -> Application Options -> General -> Physical properties. You probably have "Calculate inertial properties using negative integral" option unchecked. Mine is checked by default.

Below is an excerpt of the option and how it works.

https://help.autodesk.com/view/INVNTOR/2019/ENU/?guid=GUID-A8E50133-E4FF-4459-B2AE-9568D2C9F565

Calculate inertial properties using the negative integral

Controls how the inertial properties are reported in the Properties dialog box Physical tab, and on the clipboard.

When selected, the negative integral, and either the Global or Center of Gravity is selected in the Properties dialog box, Physical tab, Inertial Properties section. The data shown is the rigid body inertia tensor of the selected component. Any of the off diagonal elements (Ixy, Iyz, Ixz) can be negative or positive, depending on the coordinate system and the component mass distribution.

When cleared, the positive integral flips the sign of the off diagonal elements to report only the integral part of the value.

Many thanks!

[Kai.Farrar]

That is checked for me too.

I unchecked it and calculated the region properties of the 5x10 rectangles again and got the same results.

[SER4]

Looks like 2019 at least you can do Inspect->Analysis->Section

https://knowledge.autodesk.com/support/inventor/learn-explore/caas/CloudHelp/cloudhelp/2019/ENU/Inve....

for a Cross Section Analysis! (Make sure to do the Advanced one).

[joshua.nenadich]

Hello, 

I am an undergraduated student developing an AUV. I am currently trying to find the MOI of our design and would like to know how I can do so for the 3D assembly we have.