Inertia

class compas_fab.robots.Inertia(inertia_tensor, mass, center_of_mass)[source]

Bases: object

The moments of inertia represent the spatial distribution of mass in a rigid body.

It depends on the mass, size, and shape of a rigid body with units of [mass * m**2]. The moments of inertia can be expressed as the components of a symmetric positive-definite 3x3 matrix, with 3 diagonal elements, and 3 unique off-diagonal elements. Each inertia matrix is defined relative to a coordinate frame or set of axes.

Attributes

• inertia_tensor (list of float) – A symmetric positive-definite 3x3 matrix: | ixx ixy ixz | | ixy iyy iyz | | ixz iyz izz | with [ixx, iyy, izz] as the principal moments of inertia and [ixy, ixz, iyz] as the products of inertia.

• mass (float) – The mass of the object in kg.

• center_of_mass (Point) – The center of mass of the object in meters.

Examples

>>> inertia = Inertia([[0] * 3] * 3, 1., Point(0.1, 3.1, 4.4))
>>> inertia
Inertia([[0, 0, 0], [0, 0, 0], [0, 0, 0]], 1.0, Point(0.100, 3.100, 4.400))
>>> inertia.principal_moments
[0, 0, 0]

Notes

Assuming uniform mass density, inertial data can be obtained using the free software MeshLab, refering to this great tutorial: http://gazebosim.org/tutorials?tut=inertia

Methods

__init__(inertia_tensor, mass, center_of_mass)	Initialize self.
calculate_inertia_tensor(cls, mesh)	Returns the inertia tensor.

Attributes

principal_moments

Returns the diagonal elements of the inertia tensor [ixx, iyy, izz]