simscape.multibody.MassDistribution Class

Namespace: simscape.multibody
Superclasses: simscape.multibody.Inertia

Construct custom mass distribution

Since R2022a

Description

Use an object of the simscape.multibody.MassDistribution class to construct a custom mass distribution that explicitly specifies the mass, center of mass, moments of inertia, and products of inertia. The mass distribution has an implicit reference frame. If you use a simscape.multibody.MassDistribution object to specify the mass distribution of a solid, the implicit reference frame is coincident with the reference frame of the solid.

Class Attributes

Sealed	true
ConstructOnLoad	true
RestrictsSubclassing	true

For information on class attributes, see Class Attributes.

Creation

Description

mdmass = simscape.multibody.Massdistribution constructs a custom mass distribution using default values.

mdmass = simscape.multibody.Massdistribution(mass) constructs a custom mass distribution and sets the total mass to mass.

mdmass = simscape.multibody.Massdistribution(mass,com) constructs a custom mass distribution and also sets the specified center of mass to com.

mdmass = simscape.multibody.Massdistribution(mass,com,moi) constructs a custom mass distribution and also sets the moments of inertia to moi.

mdmass = simscape.multibody.Massdistribution(mass,com,moi,poi) constructs a custom mass distribution and also sets the products of inertia to poi.

Properties

Mass — Total mass

simscape.Value(1,"kg") (default) | simscape.Value(M,"Mass unit")

Total mass, specified as a simscape.Value object that represents a scalar with a unit of mass. The scalar can be positive or negative. Use a negative value to capture the effect of a void or cavity in a compound body that comprises multiple solids. The total mass of the compound body must be positive.

Example: simscape.Value(16,"lbm")

Attributes:

GetAccess	public
SetAccess	public
NonCopyable	true

CenterOfMass — Center-of-mass coordinates

simscape.Value([0 0 0]',"m") (default) | simscape.Value([x y z],"Length unit") | simscape.Value([x y z]',"Length unit")

Center-of-mass coordinates, specified as a simscape.Value object that represents a 3-by-1 or 1-by-3 array with a unit of length. The coordinates are resolved in the implicit reference frame of the mass distribution.

Example: simscape.Value([0 0 5],"mm")

Attributes:

GetAccess	public
SetAccess	public
NonCopyable	true

MomentsOfInertia — Diagonal elements of inertia matrix

simscape.Value([0 0 0]',"kg*m^2") (default) | simscape.Value([I_xx I_yy I_zz],"mass*length^2") | simscape.Value([I_xx I_yy I_zz]',"mass*length^2")

I_xx, I_yy, and I_zz elements of the inertia matrix, specified as a simscape.Value object that represents a 3-by-1 or 1-by-3 array with a unit of mass*length^2.

The quantities, I_xx, I_yy, and I_zz, are the moments of inertia with respect to the axes of a frame whose origin is coincident with the center of mass and whose axes are parallel to the implicit reference frame. The moments of inertia are the diagonal elements of the inertia matrix

$$\left(\begin{array}{ccc}{I}_{xx}& & \\ & I_{yy}& \\ & & I_{zz}\end{array}\right),$$

where:

• $$I_{xx}={\displaystyle \underset{m}{\int }\left(y^2+z^2\right)dm}$$

• $$I_{yy}={\displaystyle \underset{m}{\int }\left(x^2+z^2\right)dm}$$

• $$I_{zz}={\displaystyle \underset{m}{\int }\left(x^2+y^2\right)dm}$$

Example: simscape.Value([12 15 10],"kg*cm^2")

Attributes:

GetAccess	public
SetAccess	public
NonCopyable	true

ProductsOfInertia — Off-diagonal elements of inertia matrix

simscape.Value([0 0 0]',"kg*m^2") (default) | simscape.Value([I_yz I_zx I_xy],"mass*length^2") | simscape.Value([I_yz I_zx I_xy]',"mass*length^2")

I_yz, I_zx, and I_xy elements of the inertia matrix, specified as a simscape.Value object that represents a 3-by-1 or 1-by-3 array with a unit of mass*length^2.

The quantities, I_xy, I_yz, and I_zx are the products of inertia with respect to the axes of a frame whose origin is coincident with the center of mass and whose axes are parallel to the implicit reference frame. The products of inertia are the off-diagonal elements of the inertia matrix

$$\left(\begin{array}{ccc}& I_{xy}& I_{zx}\\ I_{xy}& & I_{yz}\\ I_{zx}& I_{yz}& \end{array}\right),$$

where:

• $$I_{yz}=-{\displaystyle \underset{m}{\int }yzdm}$$

• $$I_{zx}=-{\displaystyle \underset{m}{\int }zxdm}$$

• $$I_{xy}=-{\displaystyle \underset{m}{\int }xydm}$$

Example: simscape.Value([-2 3 1],"kg*cm^2")

Attributes:

GetAccess	public
SetAccess	public
NonCopyable	true

Methods

Public Methods

inertiaMatrix	Compute inertia matrix
principalMomentsOfInertia	Compute principal moments of inertia
principalToReferenceTransformation	Compute 3-D rigid transformation between principal and reference frames
transform	Transform inertia to different frame

Version History

Introduced in R2022a