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 various solid blocks, 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 Brick 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.
|File Solid||Solid element with properties derived from external file|
|Graphic||Marker with graphic properties|
|Inertia||Mass element with fixed inertial properties|
|Inertia Sensor||Sensor to measure the inertial properties of body groups or mechanisms|
|Brick Solid||Solid brick element with geometry, inertia, and color|
|Cylindrical Solid||Solid cylindrical element with geometry, inertia, and color|
|Ellipsoidal Solid||Solid ellipsoidal element with geometry, inertia, and color|
|Extruded Solid||Solid extruded element with geometry, inertia, and color|
|Revolved Solid||Solid revolved element with geometry, inertia, and color|
|Spherical Solid||Solid spherical element with geometry, inertia, and color|
|General Flexible Beam||Slender extrusion with elastic properties for deformation|
|General Variable Mass||Mass element with variable inertial properties|
|Reduced Order Flexible Solid||Flexible body based on a reduced-order model|
|Variable Brick Solid||Solid brick with variable mass and size|
|Variable Cylindrical Solid||Solid cylinder with variable mass and size|
|Variable Spherical Solid||Solid sphere with variable mass and size|
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.
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.
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 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.
General Extruded Solid and Revolved Solid blocks 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.
Use the Reduced Order Flexible Solid block to model a deformable body of arbitrary geometry. Start with the CAD geometry of the body, produce a finite-element mesh, and generate reduced-order data to use with the block.
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.
"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.
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 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.
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.
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.
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.
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.