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Moment of Inertia values incorrect/different than Inventor?

Question asked by Mike Grieb on Nov 2, 2013
Latest reply on Nov 3, 2013 by Mike Grieb

For a lot of complicated reasons, I have an assembly in Solidworks 2013 x64 SP4.0 that has been remodeled in Inventor 2012. I am finding a large discrepancy between the Mass Moment of Inertia between the programs and I'm not sure which is correct but some quick hand calcs lead me to believe that Solidworks is coming up wrong?

 

Here is what I have done to try and identify the issue:

1. Every part was verified to have a material assigned in both programs

2. Weights and center of gravity of every assembly was verified and consistent between the programs

3. Weight, Volume, and CG of both assemblies is the same

4. Coordinate systems are setup the same

 

Inventor is saying the principal inertias are:

Px = 15.5 kg-m^2

Py = 594.685 kg-m^2

Pz = 598.402 kg-m^2

where Solidworks says:

Px = 8.66 kg-m^2

Py = 212.63 kg-m^2

Pz = 217.67 kg-m^2

 

That's off by about a factor of 2. I do have some mass properties of some individual components overridden but it seems to be affecting both calculations. I checked inertias of individual components and the programs agree but when you look at the inertias of the sub-assemblies they are different.

 

Any ideas would be appreciated.

 

Solidworks Mass Properties Below:

 

 

Mass properties of 50994-90001_EOAT ASSEMBLY

Configuration: MaxProduct

Coordinate system: -- default --

* Includes the mass properties of one or more hidden components/bodies.

Mass = 692.57 kilograms

Volume = 0.11 cubic meters

Surface area = 7.92 square meters

Center of mass: ( meters )

X = 0.49

Y = -0.01

Z = 0.19

Principal axes of inertia and principal moments of inertia: ( kilograms * square meters )

Taken at the center of mass.

Ix = (1.00, 0.02, 0.02) Px = 8.66

Iy = (-0.02, 1.00, -0.01) Py = 212.63

Iz = (-0.02, 0.01, 1.00) Pz = 217.67

Moments of inertia: ( kilograms * square meters )

Taken at the center of mass and aligned with the output coordinate system.

Lxx = 8.80 Lxy = 3.65 Lxz = 3.73

Lyx = 3.65 Lyy = 212.56 Lyz = 0.02

Lzx = 3.73 Lzy = 0.02 Lzz = 217.60

Moments of inertia: ( kilograms * square meters )

Taken at the output coordinate system.

Ixx = 34.79 Ixy = 1.19 Ixz = 68.97

Iyx = 1.19 Iyy = 402.50 Iyz = -0.96

Izx = 68.97 Izy = -0.96 Izz = 381.62

One or more components have overridden mass properties:

Product<1><MaxProduct>@50994-95001_ClampAssembly<1><MaxProduct>

B12-3000is motor & brake 3D CAD Drawing_A06B-0078-B503<1><Default>@50994-95005_ServoAssembly<1><Default>

20HL_BSJ_I_24_1_X18R8_1_000_2_FC_3_00_BS@50994-95005_ServoAssembly

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