How to change Moment of inertia and center of gravity of a model?

[Anonymous]

Hello All,

I have following details of a model:

Mass:

COG X:

COG Y:

COG Z:

Ix:

Iy:

Iz:

Obviously when i create a 3D model it has different properties.

i want to replace the properties of a model with the above known values.

can some one please guide on how to do this?

[swalton · Accepted solution]

I typically do this:

1. Download or model from scratch MyPart.ipt to represent the component.
2. Create a new Material: "Weightless"
   1. Set the density of the new material to as small as Inventor will accept
3. Assign the Weightless material to MyPart.ipt
4. Create a new part: COG_Placeholder.ipt
   1. Model a 1 inch (or 1 cm) cube, centered at the origin
   2. Override the weight of the cube with the known correct weight of MyPart.ipt
5. Create a new assembly: MyPart.asm
6. Place MyPart.ipt in MyPart.asm and constrain it to the origin
7. Place COG_Placeholder.ipt in MyPart.asm and constrain it at the desired COG location.
8. Verify that the COG of MyPart.asm matches the desired COG
9. Use MyPart.asm in upstream assemblies, or anywhere else I need the corrected COG.

This will give you a reasonable approximation of the known mass and COG location.  It will not give you the correct Mass Moments of Inertia. 

If you need correct Mass Moments of Inertia, you may have to adjust the density of MyPart.ipt, and add internal voids to the part.  It will be a manual trial and error process.

[Anonymous]

Hello Steve,

Thanks for the response.

can i do this to a whole assembly?

to a (.iam) file?

I have modeled as shown in the attachment but its an .iam file.

[Anonymous]

Is there any way that i could change the Moment of Inertia of the model as i want?

[swalton]

As I understand it, Inventor calculates Mass Moments of Inertia based on the object's 3d geometry and mass distribution.  It is not a property that the user can set or override.

How are you trying to use the MMI information in your design process?  Maybe there is another way you can get what you need.  

[swalton]

Sure, you can do this for a complete assembly. 

COG is calculated based on the location of each mass particle in the component.  Setting one very small component to the mass of the entire assembly, and setting all the others to a minimum mass,  the COG result is dominated by the location of the small component.  This tricks Inventor into reporting COG data that matches reality without having full information about the size, shape, and material of the various components in the assembly.