Weight and Center of Gravity Calculator

The Weight and Center of Gravity Calculator can be accessed from the Analysis Analysis Weight and Center of Gravity command. The requirements for this tool are as follows:

1. You must have a mass density assigned for the material for each part in your model.
2. You must have performed the Analysis Analysis Check Model command.
3. If you do not assign a value for gravity in the Analysis Parameters dialog, you will be prompted to enter one before the calculations are performed. The value is entered using the Model Units.

Once the results are calculated, the Model Information section at the top of the dialog will list the volume, weight, center of gravity, mass moment of inertia and mass product of inertia values for the entire assembly. The spreadsheet section will list these values for each individual part of the assembly. All results use the Model Units.

An HTML report of these values can be created by pressing the HTML button. A csv file, which can be opened in a spreadsheet program, can be created by pressing the Export button. In addition, two text files are created by the processor. Use a text editor (such as NotePad or Word) to open these statistics (.LG9) and summary (.WCG) files.

Tip: When creating an HTML report, you can replace the Autodesk logo with a custom logo. Use the Reporting Tab to specify the custom logo.

The mass moment of inertia is by default calculated about the axes passing through the origin (0,0,0). Use the parallel axis theorem and a hand-calculation to calculate the mass moment of inertia about a different axis.

Attention: The mass moment of inertia about the longitudinal axis, I1 is not calculated for line elements (beams, trusses, and so on). Only the mxR ² effect is considered, where R is the distance from the reference point to the element. The mass moment of inertia about the other axes, I2 and I3, are calculated based on the slender rod formula (I2 = I3 = MxL ² /12).

If the model includes parts created from 2D elements, the statistics (.LG9) and summary (.WCG) files contain the area and area moment of inertia of the 2D cross section. Similar results can be obtained for cross sections drawn in a sketch. See the page Meshing Overview: Creating and Modifying Geometry in the FEA Editor: Drawing Planes.

Attention: The results for 2D axisymmetric elements are based on a full revolution, not 1 radian.

Tip: Another result of the Weight and Center of Gravity calculator is the ability to display the volume of each element in the Results environment (Results Contours Other Results Element Properties Volume). The volume can also be used in custom calculations (Results Contours Other Results Custom Results Manager). The file containing the volume results is deleted whenever any analysis is performed; thus, it may be necessary to rerun the weight and center of gravity calculator to display the volume results.

Nodal forces and moments have no effect on the weight and center of gravity results.

Lumped masses and lumped mass moments of inertia may or may not be included in the weight and center of gravity calculation depending on the analysis type. Also, the results with masses of different values in the X, Y, and Z directions may be based on the X mass only. Refer to the weight and center of gravity summary file (.WCG) to see how it is treated for each situation.

Parent topic: Setting Up and Performing the Analysis