Bodies

Model body geometries, inertias, colors, and frames

Model the bodies of an articulated mechanical assembly. Bodies can be rigid or flexible, the latter being free to deform when acted upon by a force or torque. All bodies are characterized by their physical properties, among them geometry, inertia, and color. Flexible bodies have the additional properties of stiffness, damping, and discretization level.

Rigid bodies are based on the Solid block, the File Solid block, or, in special cases, their equivalents of variable mass and geometry. You can find the latter in the Body Elements > Variable Mass library. Use the File Solid block to import a body from a 3-D part file. Flexible bodies are based on the General Flexible Body block—a representation of a slender body with a specified cross section.

A single Solid, File Solid, or General Flexible Beam block may suffice to completely model a body. More often, several are required. The body is then a composite of simpler body elements fixed to one another. Frame connection lines between the blocks establish the necessary rigid connections between the body elements. Rigid Transform blocks, normally inserted in the connection lines, provide the relative positions and orientations required for proper assembly.

Simscape Blocks

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File SolidSolid element with properties derived from external file
GraphicMarker with graphic properties
InertiaMass element with fixed inertial properties
SolidSolid element with geometry, inertia, and color
General Flexible BeamSlender extrusion with elastic properties for deformation
General Variable MassMass element with variable inertial properties
Variable Brick SolidSolid brick with variable mass and size
Variable Cylindrical SolidSolid cylinder with variable mass and size
Variable Spherical SolidSolid sphere with variable mass and size
SplineCubic interpolating plane curve or space curve
Reference FrameNon-inertial reference frame
Rigid TransformFixed spatial relationship between frames
World FrameInertial reference frame

Functions

smnewOpen Simscape Multibody model template and block library
sm_libOpen the Simscape Multibody block library

Topics

Bodies

Bodies Workflow

Bodies, the core constituents of a multibody model, comprise body elements, each in turn comprising frames and attributes. Modeling a body is more than adding a block to a model. Here are some general steps to keep in mind when modeling one.

Modeling Bodies

Bodies are representations that you create of physical parts—gears, pistons, levers—for later assembly into multibody systems, a piston engine serving as an example. Here is an introduction to bodies as well as the blocks and tools commonly used to represent one in a model.

Compounding Body Elements

A typical body is a collection of solids and other body elements. In this sense, it is a compound unit. Learn how you can use compounding to create complex geometries and inertias from simpler ones.

Geometry

Representing Solid Geometry

Geometry is a key attribute of solids and of the bodies they comprise. You can specify the shape and size of a solid using the Solid block. Here is an introduction to the types of shapes that you can specify (or import) using this block.

Modeling Extrusions and Revolutions

General Extrusion and Revolution are the most versatile of the preset solid shapes. Their cross-sections are custom and set by coordinate matrices that you specify. Here is an introduction to both the shapes and the cross-sections that define them.

Inertia

Representing Solid Inertia

Inertia quantifies the resistance of a body to changes in motion and is among the most important attributes in a model. Here is an introduction to the types of inertias that you can represent in a model as well as the blocks and parameterizations that you can use to do so.

Specifying Custom Inertias

"Inertia" is a general term often used to mean mass, center of mass, the moments of inertia, and the products of inertia. Learn more about these inertia parameters and how they are defined in the Simscape Multibody environment.

Specifying Variable Inertias

Not all inertias remain constant during simulation. Some can vary and it is often their changing parameters that most matter in a model. Learn more about variable inertias and how you can specify their parameters in a model.

Frames

Working with Frames

Frames are axis triads that encode the position and orientation of body elements in a body. Learn about frames as a means to connect body elements and about rigid transforms as a means to offset those elements.

Creating Connection Frames

Often, you must create new frames for use in joint and constraint connections. Learn how you can create such frames and how joints and constraints affect their placements in a body.

Creating Custom Solid Frames

All solids have a local reference frame but you can create other, custom, frames, for connection in a model. Learn how you can perform this task using the frame creation panel of the Solid block.

Visualization

Manipulate the Color of a Solid

Color helps to differentiate bodies and contributes to the effectiveness of a multibody visualization. Learn about the color parameters that you can specify and their impact on the appearance of your bodies.

Visualize a Model and Its Components

Visualization is not only a central part of a multibody simulation, it is an essential tool in modeling bodies and verifying their shapes, sizes, frame placements, and colors. Here is an overview of the visualization utilities available in the Simscape Multibody environment and the roles they play in your modeling workflow.

Featured Examples