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Solid Geometry

SimMechanics™ provides a set of shapes that you can use to represent rigid bodies. You can specify the shapes directly in the Solid block dialog box.

Simple Shapes

Shapes range from simple to advanced. Simple shapes require a small number of dimensional parameters. The following simple shapes are available.

  • Cylinder — Cylinder with custom dimensions, centroid at the solid reference frame origin, and symmetry axis along the solid reference frame z-axis.

  • Sphere — Sphere with custom dimensions and center located at the solid reference frame origin.

  • Brick — Brick with custom dimensions along the three Cartesian axes and centroid located at the block reference frame.

  • Ellipsoid — Ellipsoid with custom dimensions with centroid located at the block reference frame.

  • Regular Extrusion — Extruded solid with constant cross-section along the z-axis and centroid located at the block reference frame. The constant cross-section is a regular polygon with a custom number of sides.

Simple shapes are easier to use than advanced shapes. When modeling a rigid body, consider using a simple shape as a first approximation. After successful model assembly, you can add detail to the rigid body. The following figure shows the four simple shapes, ordered left to right: cylinder, Sphere, Brick, and Ellipsoid.

The Regular Extrusion shape is more versatile than other simple shapes. With this shape, you can model solids with constant cross sections. Cross-sections can have any number of sides, but all lengths and internal angles are equal.

The following figure shows a set of shapes you can model with the Regular Extrusion shape.

Advanced Shapes

Advanced shapes include:

  • General Extrusion — Extruded solid with custom cross-section swept along the z-axis and centroid located at the block reference frame.

  • Revolution — Solid of revolution with constant cross-section revolved about the z-axis and centroid located at the block reference frame.

The shapes require a MATLAB® cross-section matrix. To be valid, the matrix must observe a set of rules. See Cross-Section Coordinates.

General Extrusions

For extrusions with irregular cross-section, SimMechanics provides a General Extrusion geometry. This geometry is among the most versatile in SimMechanics. You can use it to model shapes with an increased level of detail.

This shape requires a MATLAB matrix that contains the cross-section coordinates. The matrix must follow a set of rules that are specific to the shape. See Revolution and General Extrusion Cross-Sections.

The following figure shows some shapes you can model with General Extrusion.

For General Extrusion examples, see:

Solids of Revolution

Solids that have a constant cross-section about an axis are solids of revolution. To model these solids, use the Revolution shape.

The Revolution shape requires a MATLAB matrix that contains the cross-section coordinates. The matrix must follow a set of rules specific to the Revolution geometry. See Revolution and General Extrusion Cross-Sections.

The following figure shows some shapes you can model with Revolution.

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