Taken at the center of mass and aligned with Moments of inertia: ( pounds * square inches ) Principal axes of inertia and principal moments of inertia: The SolidWorks model provides for the L-beam part the following mass properties data: You must specify the moments and products of inertia relative to this frame. Its origin is at the center of mass and its axes are parallel to those of the local reference frame. This frame coincides with the inertia frame of resolution. You must specify the center of mass relative to this frame.įrame I is a custom solid frame included for your convenience. This frame is located at the lower corner of the L-shape on one of the two longitudinal ends of the beam. It coincides with what SolidWorks users refer to as the output coordinate system of the part model. The visualization pane shows two frames, one labeled R and the other I.įrame R is the local reference frame of the solid. In the visualization pane, click the Toggle visibility of frames button. The beam geometry is imported from a STEP file previously exported from a SolidWorks model. Open the File Solid block and explore its Geometry parameters. A simple model opens with a File Solid block representing the L-beam solid. At the MATLAB command prompt, enter smdoc_lbeam_inertia. Use the mass properties data provided in this example for a SolidWorks model of the beam. Then, specify them explicitly in a solid block by setting the inertia parameterization to Custom. Try It: Reference a SolidWorks Modelĭetermine the inertia parameters for the L-beam shape shown in the figure. For individual CAD parts, use the STEP file import feature of the solid block and set the Inertia > Type parameter to Calculate from Geometry.įor more information, see CAD Translation. This option may suit you only if you have a complete CAD assembly model. You must export your CAD model in a valid XML format, meaning one that conforms to the Simscape Multibody XML schema, before you can import it. CAD import is based on the smimport function, which parses a multibody description file in XML format and generates an equivalent block diagram with all block parameters prespecified-inertia parameters included. Rather than reference the inertia data in a CAD assembly model, you can import that model into the Simscape Multibody environment. I = ( I x x − I x y − I x z − I y x I y y − I y z − I z x − I z y I z z ) CAD Import as an Alternative Specify the calculated parameters explicitly in a Brick Solid block using a Custom inertia parameterization. Determine its mass, center of mass, moments of inertia, and products of inertia. Try It: Specify a Custom InertiaĬonsider the rectangular beam shown in the figure. The frame position is always that of the center of mass, but its orientation relative to a solid geometry, when using a solid block, may not always coincide with the principal axes of inertia. In imported shapes, it depends on how, relative to the local zero coordinate, the part geometries were modeled.Īs a best practice, always consider the placement of the inertia frame of resolution when specifying the elements of the inertia matrix explicitly, particularly when using a solid block. In Extruded Solid and Revolved Solid shapes, the frame placement depends closely on how you define the geometrical cross-sections. The same, however, is not generally true of Extruded Solid or Revolved Solid solid shapes, nor is it of those imported via STEP or STL files. This is the inertia frame of resolution assumed in the highly symmetrical preset shapes of the solid blocks. For this reason, the principal axes of inertia can be a convenient frame in which to specify the inertia matrix elements. The number of nontrivial inertia matrix elements that you must specify is in this case reduced to three-the principal moments of inertia. However, its origin coincides instead with the local center of mass. Its axes are parallel to those of the local reference frame, associated with frame port R and correspondingly labeled R. The inertia matrix captures the spatial distribution of matter about a local frame referred to here as the inertia frame of resolution. It is possible, however, to modify a solid geometry file so that the two frames no longer match. In solids with imported CAD shapes, this frame is generally that assumed by your CAD application in its inertia calculations. The center of mass is defined with respect to the local reference frame of the block. Recall that the products of inertia are the off-diagonal elements of the inertia matrix. An alternate convention exists in which a minus sign does not accompany the mass integrals. The products of inertia are defined using a negated convention, one with a minus sign inserted, explicitly, in the mass integrals.
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