Detailed Description

template<typename T>
class drake::multibody::RigidBody< T >

The term rigid body implies that the deformations of the body under consideration are so small that they have no significant effect on the overall motions of the body and therefore deformations can be neglected.

If deformations are neglected, the distance between any two points on the rigid body remains constant at all times. This invariance of the distance between two arbitrary points is often taken as the definition of a rigid body in classical treatments of multibody mechanics [Goldstein 2001]. It can be demonstrated that the unconstrained three-dimensional motions of a rigid body can be described by six coordinates and thus it is often said that a free body in space has six degrees of freedom. These degrees of freedom obey the Newton-Euler equations of motion. However, within a MultibodyTree, a RigidBody is not free in space; instead, it is assigned a limited number of degrees of freedom (0-6) with respect to its parent body in the multibody tree by its Mobilizer (also called a "tree joint" or "inboard joint"). Additional constraints on permissible motion can be added using Constraint objects to remove more degrees of freedom.

[Goldstein 2001] H Goldstein, CP Poole, JL Safko, Classical Mechanics (3rd Edition), Addison-Wesley, 2001.

Template Parameters

T	The scalar type, which must be one of the default scalars.

#include <drake/multibody/tree/rigid_body.h>

Public Member Functions
	RigidBody (const std::string &body_name, const SpatialInertia< double > &M_BBo_B=SpatialInertia< double >::Zero())
	Constructs a RigidBody named `body_name` with the given default SpatialInertia. More...

	RigidBody (const std::string &body_name, ModelInstanceIndex model_instance, const SpatialInertia< double > &M_BBo_B=SpatialInertia< double >::Zero())
	Constructs a RigidBody named `body_name` with the given default SpatialInertia. More...

BodyIndex	index () const
	Returns this element's unique index. More...

const std::string &	name () const
	Gets the `name` associated with this rigid body. More...

ScopedName	scoped_name () const
	Returns scoped name of this frame. More...

const RigidBodyFrame< T > &	body_frame () const
	Returns a const reference to the associated BodyFrame. More...

void	Lock (systems::Context< T > *context) const
	For a floating RigidBody, lock its inboard joint. More...

void	Unlock (systems::Context< T > *context) const
	For a floating RigidBody, unlock its inboard joint. More...

bool	is_locked (const systems::Context< T > &context) const
	Determines whether this RigidBody is currently locked to its inboard (parent) RigidBody. More...

internal::MobodIndex	mobod_index () const
	(Advanced) Returns the index of the mobilized body ("mobod") in the computational directed forest structure of the owning MultibodyTree to which this RigidBody belongs. More...

bool	is_floating () const
	(Advanced) Returns `true` if this body is granted 6-dofs by a Mobilizer and the parent body of this body's associated 6-dof joint is `world`. More...

bool	has_quaternion_dofs () const
	(Advanced) If `true`, this body's generalized position coordinates q include a quaternion, which occupies the first four elements of q. More...

int	floating_positions_start () const
	(Advanced) For floating bodies (see is_floating()) this method returns the index of this RigidBody's first generalized position in the vector q of generalized position coordinates for a MultibodyPlant model. More...

int	floating_velocities_start_in_v () const
	(Advanced) For floating bodies (see is_floating()) this method returns the index of this RigidBody's first generalized velocity in the vector v of generalized velocities for a MultibodyPlant model. More...

std::string	floating_position_suffix (int position_index_in_body) const
	Returns a string suffix (e.g. More...

std::string	floating_velocity_suffix (int velocity_index_in_body) const
	Returns a string suffix (e.g. More...

double	default_mass () const
	Returns this RigidBody's default mass, which is initially supplied at construction when specifying this body's SpatialInertia. More...

const Vector3< double > &	default_com () const
	Returns the default value of this RigidBody's center of mass as measured and expressed in its body frame. More...

const UnitInertia< double > &	default_unit_inertia () const
	Returns the default value of this body B's unit inertia about Bo (body B's origin), expressed in B (this body's body frame). More...

RotationalInertia< double >	default_rotational_inertia () const
	Gets the default value of this body B's rotational inertia about Bo (B's origin), expressed in B (this body's body frame). More...

const SpatialInertia< double > &	default_spatial_inertia () const
	Gets the default value of this body B's SpatialInertia about Bo (B's origin) and expressed in B (this body's frame). More...

const T &	get_mass (const systems::Context< T > &context) const
	Gets this body's mass from the given context. More...

const math::RigidTransform< T > &	EvalPoseInWorld (const systems::Context< T > &context) const
	Returns the pose `X_WB` of this RigidBody B in the world frame W as a function of the state of the model stored in `context`. More...

const SpatialVelocity< T > &	EvalSpatialVelocityInWorld (const systems::Context< T > &context) const
	Evaluates V_WB, this body B's SpatialVelocity in the world frame W. More...

const SpatialAcceleration< T > &	EvalSpatialAccelerationInWorld (const systems::Context< T > &context) const
	Evaluates A_WB, this body B's SpatialAcceleration in the world frame W. More...

const SpatialForce< T > &	GetForceInWorld (const systems::Context< T > &, const MultibodyForces< T > &forces) const
	Gets the SpatialForce on this RigidBody B from `forces` as F_BBo_W: applied at body B's origin Bo and expressed in world frame W. More...

void	AddInForceInWorld (const systems::Context< T > &, const SpatialForce< T > &F_Bo_W, MultibodyForces< T > *forces) const
	Adds the SpatialForce on this RigidBody B, applied at body B's origin Bo and expressed in the world frame W into `forces`. More...

void	AddInForce (const systems::Context< T > &context, const Vector3< T > &p_BP_E, const SpatialForce< T > &F_Bp_E, const Frame< T > &frame_E, MultibodyForces< T > *forces) const
	Adds the SpatialForce on this RigidBody B, applied at point P and expressed in a frame E into `forces`. More...

const Vector3< T >	CalcCenterOfMassInBodyFrame (const systems::Context< T > &context) const
	Gets this body's center of mass position from the given context. More...

Vector3< T >	CalcCenterOfMassTranslationalVelocityInWorld (const systems::Context< T > &context) const
	Calculates Bcm's translational velocity in the world frame W. More...

SpatialInertia< T >	CalcSpatialInertiaInBodyFrame (const systems::Context< T > &context) const
	Gets this body's spatial inertia about its origin from the given context. More...

void	SetMass (systems::Context< T > *context, const T &mass) const
	For this RigidBody B, sets its mass stored in `context` to `mass`. More...

void	SetCenterOfMassInBodyFrame (systems::Context< T > *context, const Vector3< T > &com) const
	(Advanced) Sets this body's center of mass position while preserving its inertia about its body origin. More...

void	SetCenterOfMassInBodyFrameAndPreserveCentralInertia (systems::Context< T > *context, const Vector3< T > &center_of_mass_position) const
	Sets this body's center of mass position while preserving its inertia about its center of mass. More...

void	SetSpatialInertiaInBodyFrame (systems::Context< T > *context, const SpatialInertia< T > &M_Bo_B) const
	For this RigidBody B, sets its SpatialInertia that is stored in `context` to `M_Bo_B`. More...

template<typename ToScalar >
std::unique_ptr< RigidBody< ToScalar > >	CloneToScalar (const internal::MultibodyTree< ToScalar > &tree_clone) const
	(Advanced) This method is mostly intended to be called by MultibodyTree::CloneToScalar(). More...

Does not allow copy, move, or assignment
	RigidBody (const RigidBody &)=delete

RigidBody &	operator= (const RigidBody &)=delete

	RigidBody (RigidBody &&)=delete

RigidBody &	operator= (RigidBody &&)=delete

Methods to access position kinematics quantities.
The input PositionKinematicsCache to these methods must be in sync with context. These method's APIs will be deprecated when caching arrives.
const math::RigidTransform< T > &	get_pose_in_world (const internal::PositionKinematicsCache< T > &pc) const
	(Advanced) Extract this body's pose in world (from the position kinematics). More...

const math::RotationMatrix< T >	get_rotation_matrix_in_world (const internal::PositionKinematicsCache< T > &pc) const
	(Advanced) Extract the RotationMatrix relating the world frame to this body's frame. More...

const Vector3< T >	get_origin_position_in_world (const internal::PositionKinematicsCache< T > &pc) const
	(Advanced) Extract the position vector from world origin to this body's origin, expressed in world. More...

Methods to access velocity kinematics quantities.
The input VelocityKinematicsCache to these methods must be in sync with context. These method's APIs will be deprecated when caching arrives.
const SpatialVelocity< T > &	get_spatial_velocity_in_world (const internal::VelocityKinematicsCache< T > &vc) const
	(Advanced) Returns V_WB, this RigidBody B's SpatialVelocity in the world frame W. More...

const Vector3< T > &	get_angular_velocity_in_world (const internal::VelocityKinematicsCache< T > &vc) const
	(Advanced) Extract this body's angular velocity in world, expressed in world. More...

const Vector3< T > &	get_origin_velocity_in_world (const internal::VelocityKinematicsCache< T > &vc) const
	(Advanced) Extract the velocity of this body's origin in world, expressed in world. More...

Methods to access acceleration kinematics quantities.
The input AccelerationKinematicsCache to these methods must be in sync with context. These method APIs will be deprecated when caching arrives.
const SpatialAcceleration< T > &	get_spatial_acceleration_in_world (const internal::AccelerationKinematicsCache< T > &ac) const
	(Advanced) Returns A_WB, this RigidBody B's SpatialAcceleration in the world frame W. More...

const Vector3< T > &	get_angular_acceleration_in_world (const internal::AccelerationKinematicsCache< T > &ac) const
	(Advanced) Extract this body's angular acceleration in world, expressed in world. More...

const Vector3< T > &	get_origin_acceleration_in_world (const internal::AccelerationKinematicsCache< T > &ac) const
	(Advanced) Extract acceleration of this body's origin in world, expressed in world. More...

Public Member Functions inherited from MultibodyElement< T >
virtual	~MultibodyElement ()

ModelInstanceIndex	model_instance () const
	Returns the ModelInstanceIndex of the model instance to which this element belongs. More...

template<typename MultibodyPlantDeferred = MultibodyPlant<T>>
const MultibodyPlantDeferred &	GetParentPlant () const
	Returns the MultibodyPlant that owns this MultibodyElement. More...

void	DeclareParameters (internal::MultibodyTreeSystem< T > *tree_system)
	Declares MultibodyTreeSystem Parameters at MultibodyTreeSystem::Finalize() time. More...

void	SetDefaultParameters (systems::Parameters< T > *parameters) const
	Sets default values of parameters belonging to each MultibodyElement in `parameters` at a call to MultibodyTreeSystem::SetDefaultParameters(). More...

	MultibodyElement (const MultibodyElement &)=delete

MultibodyElement &	operator= (const MultibodyElement &)=delete

	MultibodyElement (MultibodyElement &&)=delete

MultibodyElement &	operator= (MultibodyElement &&)=delete

Friends
class	internal::RigidBodyAttorney< T >

Additional Inherited Members
Protected Member Functions inherited from MultibodyElement< T >
	MultibodyElement ()
	Default constructor made protected so that sub-classes can still declare their default constructors if they need to. More...

	MultibodyElement (ModelInstanceIndex model_instance)
	Constructor which allows specifying a model instance. More...

	MultibodyElement (ModelInstanceIndex model_instance, int64_t index)
	Both the model instance and element index are specified. More...

template<typename ElementIndexType >
ElementIndexType	index_impl () const
	Returns this element's unique index. More...

const internal::MultibodyTree< T > &	get_parent_tree () const
	Returns a constant reference to the parent MultibodyTree that owns this element. More...

const internal::MultibodyTreeSystem< T > &	GetParentTreeSystem () const
	Returns a constant reference to the parent MultibodyTreeSystem that owns the parent MultibodyTree that owns this element. More...

void	SetTopology (const internal::MultibodyTreeTopology &tree)
	Gives MultibodyElement-derived objects the opportunity to retrieve their topology after MultibodyTree::Finalize() is invoked. More...

systems::NumericParameterIndex	DeclareNumericParameter (internal::MultibodyTreeSystem< T > *tree_system, const systems::BasicVector< T > &model_vector)
	To be used by MultibodyElement-derived objects when declaring parameters in their implementation of DoDeclareParameters(). More...

systems::AbstractParameterIndex	DeclareAbstractParameter (internal::MultibodyTreeSystem< T > *tree_system, const AbstractValue &model_value)
	To be used by MultibodyElement-derived objects when declaring parameters in their implementation of DoDeclareParameters(). More...

Constructor & Destructor Documentation

◆ RigidBody() [1/4]

RigidBody ( const RigidBody< T > & )

delete

◆ RigidBody() [2/4]

RigidBody ( RigidBody< T > && )

delete

◆ RigidBody() [3/4]

RigidBody	(	const std::string &	body_name,
		const SpatialInertia< double > &	M_BBo_B = `SpatialInertia< double >::Zero()`
	)

explicit

Constructs a RigidBody named body_name with the given default SpatialInertia.

Parameters

[in]	body_name	A name associated with this body.
[in]	M_BBo_B	Spatial inertia of this body B about the frame's origin `Bo` and expressed in the body frame B. When not provided, defaults to zero.

Note: See Spatial Mass Matrix (Spatial Inertia) for details on the monogram notation used for spatial inertia quantities.

◆ RigidBody() [4/4]

RigidBody	(	const std::string &	body_name,
		ModelInstanceIndex	model_instance,
		const SpatialInertia< double > &	M_BBo_B = `SpatialInertia< double >::Zero()`
	)

Constructs a RigidBody named body_name with the given default SpatialInertia.

Parameters

[in]	body_name	A name associated with this body.
[in]	model_instance	The model instance associated with this body.
[in]	M_BBo_B	Spatial inertia of this body B about the frame's origin `Bo` and expressed in the body frame B. When not provided, defaults to zero.

Note: See Spatial Mass Matrix (Spatial Inertia) for details on the monogram notation used for spatial inertia quantities.

Member Function Documentation

◆ AddInForce()

void AddInForce	(	const systems::Context< T > &	context,
		const Vector3< T > &	p_BP_E,
		const SpatialForce< T > &	F_Bp_E,
		const Frame< T > &	frame_E,
		MultibodyForces< T > *	forces
	)		const

Adds the SpatialForce on this RigidBody B, applied at point P and expressed in a frame E into forces.

Parameters

[in]	context	The context containing the current state of the model.
[in]	p_BP_E	The position of point P in B, expressed in a frame E.
[in]	F_Bp_E	The spatial force to be applied on body B at point P, expressed in frame E.
[in]	frame_E	The expressed-in frame E.
[out]	forces	A multibody forces objects that on output will have `F_Bp_E` added.

Exceptions

std::exception if forces is nullptr or if it is not consistent with the model to which this body belongs.

◆ AddInForceInWorld()

void AddInForceInWorld	(	const systems::Context< T > &	,
		const SpatialForce< T > &	F_Bo_W,
		MultibodyForces< T > *	forces
	)		const

Adds the SpatialForce on this RigidBody B, applied at body B's origin Bo and expressed in the world frame W into forces.

◆ body_frame()

const RigidBodyFrame<T>& body_frame ( ) const

Returns a const reference to the associated BodyFrame.

◆ CalcCenterOfMassInBodyFrame()

const Vector3<T> CalcCenterOfMassInBodyFrame ( const systems::Context< T > & context ) const

Gets this body's center of mass position from the given context.

Parameters

[in] context contains the state of the multibody system.

Returns: p_BoBcm_B position vector from Bo (this rigid body B's origin) to Bcm (B's center of mass), expressed in B.

Precondition: the context makes sense for use by this RigidBody.

◆ CalcCenterOfMassTranslationalVelocityInWorld()

Vector3<T> CalcCenterOfMassTranslationalVelocityInWorld ( const systems::Context< T > & context ) const

Calculates Bcm's translational velocity in the world frame W.

Parameters

[in] context The context contains the state of the model.

Return values

v_WBcm_W The translational velocity of Bcm (this rigid body's center of mass) in the world frame W, expressed in W.

◆ CalcSpatialInertiaInBodyFrame()

SpatialInertia<T> CalcSpatialInertiaInBodyFrame ( const systems::Context< T > & context ) const

Gets this body's spatial inertia about its origin from the given context.

Parameters

[in] context contains the state of the multibody system.

Returns: M_BBo_B spatial inertia of this rigid body B about Bo (B's origin), expressed in B. M_BBo_B contains properties related to B's mass, the position vector from Bo to Bcm (B's center of mass), and G_BBo_B (B's unit inertia about Bo expressed in B).

Precondition: the context makes sense for use by this RigidBody.

◆ CloneToScalar()

std::unique_ptr<RigidBody<ToScalar> > CloneToScalar ( const internal::MultibodyTree< ToScalar > & tree_clone ) const

(Advanced) This method is mostly intended to be called by MultibodyTree::CloneToScalar().

Most users should not call this clone method directly but rather clone the entire parent MultibodyTree if needed.

See also: MultibodyTree::CloneToScalar()

◆ default_com()

const Vector3<double>& default_com ( ) const

Returns the default value of this RigidBody's center of mass as measured and expressed in its body frame.

This value is initially supplied at construction when specifying this body's SpatialInertia.

Return values

p_BoBcm_B The position of this rigid body B's center of mass Bcm measured from Bo (B's frame origin) and expressed in B (body B's frame).

◆ default_mass()

double default_mass ( ) const

Returns this RigidBody's default mass, which is initially supplied at construction when specifying this body's SpatialInertia.

Note: In general, a rigid body's mass can be a constant property stored in this rigid body's SpatialInertia or a parameter that is stored in a Context. The default constant mass value is used to initialize the mass parameter in the Context.

◆ default_rotational_inertia()

RotationalInertia<double> default_rotational_inertia ( ) const

Gets the default value of this body B's rotational inertia about Bo (B's origin), expressed in B (this body's body frame).

This value is calculated from the SpatialInertia supplied at construction of this body.

Return values

I_BBo_B body B's rotational inertia about Bo, expressed in B.

◆ default_spatial_inertia()

const SpatialInertia<double>& default_spatial_inertia ( ) const

Gets the default value of this body B's SpatialInertia about Bo (B's origin) and expressed in B (this body's frame).

Return values

M_BBo_B body B's spatial inertia about Bo, expressed in B.

◆ default_unit_inertia()

const UnitInertia<double>& default_unit_inertia ( ) const

Returns the default value of this body B's unit inertia about Bo (body B's origin), expressed in B (this body's body frame).

This value is initially supplied at construction when specifying this body's SpatialInertia.

Return values

G_BBo_B rigid body B's unit inertia about Bo, expressed in B.

◆ EvalPoseInWorld()

const math::RigidTransform<T>& EvalPoseInWorld ( const systems::Context< T > & context ) const

Returns the pose X_WB of this RigidBody B in the world frame W as a function of the state of the model stored in context.

◆ EvalSpatialAccelerationInWorld()

const SpatialAcceleration<T>& EvalSpatialAccelerationInWorld ( const systems::Context< T > & context ) const

Evaluates A_WB, this body B's SpatialAcceleration in the world frame W.

Parameters

[in] context Contains the state of the model.

Return values

A_WB_W this body B's spatial acceleration in the world frame W, expressed in W (for point Bo, the body's origin).

Note: When cached values are out of sync with the state stored in context, this method performs an expensive forward dynamics computation, whereas once evaluated, successive calls to this method are inexpensive.

◆ EvalSpatialVelocityInWorld()

const SpatialVelocity<T>& EvalSpatialVelocityInWorld ( const systems::Context< T > & context ) const

Evaluates V_WB, this body B's SpatialVelocity in the world frame W.

Parameters

[in] context Contains the state of the model.

Return values

V_WB_W this body B's spatial velocity in the world frame W, expressed in W (for point Bo, the body frame's origin).

◆ floating_position_suffix()

std::string floating_position_suffix ( int position_index_in_body ) const

Returns a string suffix (e.g.

to be appended to the name()) to identify the kth position in the floating base. position_index_in_body must be in [0, 7) if has_quaternion_dofs() is true, otherwise in [0, 6).

Exceptions

std::exception if called pre-finalize

Precondition: this is a floating body

See also: is_floating(), has_quaternion_dofs(), MultibodyPlant::Finalize()

◆ floating_positions_start()

int floating_positions_start ( ) const

(Advanced) For floating bodies (see is_floating()) this method returns the index of this RigidBody's first generalized position in the vector q of generalized position coordinates for a MultibodyPlant model.

Positions q for this RigidBody are then contiguous starting at this index. When a floating RigidBody is modeled with quaternion coordinates (see has_quaternion_dofs()), the four consecutive entries in the state starting at this index correspond to the quaternion that parametrizes this RigidBody's orientation.

Exceptions

std::exception if called pre-finalize

Precondition: this is a floating body

See also: is_floating(), has_quaternion_dofs(), MultibodyPlant::Finalize()

◆ floating_velocities_start_in_v()

int floating_velocities_start_in_v ( ) const

(Advanced) For floating bodies (see is_floating()) this method returns the index of this RigidBody's first generalized velocity in the vector v of generalized velocities for a MultibodyPlant model.

Velocities v for this RigidBody are then contiguous starting at this index.

Exceptions

std::exception if called pre-finalize

Precondition: this is a floating body

See also: is_floating(), MultibodyPlant::Finalize()

◆ floating_velocity_suffix()

std::string floating_velocity_suffix ( int velocity_index_in_body ) const

Returns a string suffix (e.g.

to be appended to the name()) to identify the kth velocity in the floating base. velocity_index_in_body must be in [0,6).

Exceptions

std::exception if called pre-finalize

Precondition: this is a floating body

See also: is_floating(), MultibodyPlant::Finalize()

◆ get_angular_acceleration_in_world()

const Vector3<T>& get_angular_acceleration_in_world ( const internal::AccelerationKinematicsCache< T > & ac ) const

(Advanced) Extract this body's angular acceleration in world, expressed in world.

Parameters

[in] ac velocity kinematics cache.

Return values

alpha_WB_W B's angular acceleration in world W, expressed in W.

◆ get_angular_velocity_in_world()

const Vector3<T>& get_angular_velocity_in_world ( const internal::VelocityKinematicsCache< T > & vc ) const

(Advanced) Extract this body's angular velocity in world, expressed in world.

Parameters

[in] vc velocity kinematics cache.

Return values

w_WB_W rigid body B's angular velocity in world W, expressed in W.

◆ get_mass()

const T& get_mass ( const systems::Context< T > & context ) const

Gets this body's mass from the given context.

Parameters

[in] context contains the state of the multibody system.

Precondition: the context makes sense for use by this RigidBody.

◆ get_origin_acceleration_in_world()

const Vector3<T>& get_origin_acceleration_in_world ( const internal::AccelerationKinematicsCache< T > & ac ) const

(Advanced) Extract acceleration of this body's origin in world, expressed in world.

Parameters

[in] vc velocity kinematics cache.

Return values

a_WBo_W acceleration of body origin Bo in world W, expressed in W.

◆ get_origin_position_in_world()

const Vector3<T> get_origin_position_in_world ( const internal::PositionKinematicsCache< T > & pc ) const

(Advanced) Extract the position vector from world origin to this body's origin, expressed in world.

Parameters

[in] pc position kinematics cache.

Return values

p_WoBo_W position vector from Wo (world origin) to Bo (this body's origin) expressed in W (world).

◆ get_origin_velocity_in_world()

const Vector3<T>& get_origin_velocity_in_world ( const internal::VelocityKinematicsCache< T > & vc ) const

(Advanced) Extract the velocity of this body's origin in world, expressed in world.

Parameters

[in] vc velocity kinematics cache.

Return values

v_WBo_W velocity of Bo (body origin) in world W, expressed in W.

◆ get_pose_in_world()

const math::RigidTransform<T>& get_pose_in_world ( const internal::PositionKinematicsCache< T > & pc ) const

(Advanced) Extract this body's pose in world (from the position kinematics).

Parameters

[in] pc position kinematics cache.

Return values

X_WB	pose of rigid body B in world frame W.

◆ get_rotation_matrix_in_world()

const math::RotationMatrix<T> get_rotation_matrix_in_world ( const internal::PositionKinematicsCache< T > & pc ) const

(Advanced) Extract the RotationMatrix relating the world frame to this body's frame.

Parameters

[in] pc position kinematics cache.

Return values

R_WB	rotation matrix relating rigid body B in world frame W.

◆ get_spatial_acceleration_in_world()

const SpatialAcceleration<T>& get_spatial_acceleration_in_world ( const internal::AccelerationKinematicsCache< T > & ac ) const

(Advanced) Returns A_WB, this RigidBody B's SpatialAcceleration in the world frame W.

Parameters

[in] ac acceleration kinematics cache.

Return values

A_WB_W this rigid body B's spatial acceleration in the world frame W, expressed in W (for point Bo, the body frame's origin).

◆ get_spatial_velocity_in_world()

const SpatialVelocity<T>& get_spatial_velocity_in_world ( const internal::VelocityKinematicsCache< T > & vc ) const

(Advanced) Returns V_WB, this RigidBody B's SpatialVelocity in the world frame W.

Parameters

[in] vc velocity kinematics cache.

Return values

V_WB_W this rigid body B's spatial velocity in the world frame W, expressed in W (for point Bo, the body frame's origin).

◆ GetForceInWorld()

const SpatialForce<T>& GetForceInWorld	(	const systems::Context< T > &	,
		const MultibodyForces< T > &	forces
	)		const

Gets the SpatialForce on this RigidBody B from forces as F_BBo_W: applied at body B's origin Bo and expressed in world frame W.

◆ has_quaternion_dofs()

bool has_quaternion_dofs ( ) const

(Advanced) If true, this body's generalized position coordinates q include a quaternion, which occupies the first four elements of q.

Note that this does not imply that the body is floating since it may have fewer than 6 dofs or its inboard body could be something other than World.

Exceptions

std::exception if called pre-finalize

See also: is_floating(), MultibodyPlant::Finalize()

◆ index()

BodyIndex index ( ) const

Returns this element's unique index.

◆ is_floating()

bool is_floating ( ) const

(Advanced) Returns true if this body is granted 6-dofs by a Mobilizer and the parent body of this body's associated 6-dof joint is world.

Note: A floating body is not necessarily modeled with a quaternion mobilizer, see has_quaternion_dofs(). Alternative options include a roll-pitch-yaw (rpy) parametrization of rotations, see RpyFloatingMobilizer.

Exceptions

std::exception if called pre-finalize,

See also: MultibodyPlant::Finalize()

◆ is_locked()

bool is_locked ( const systems::Context< T > & context ) const

Determines whether this RigidBody is currently locked to its inboard (parent) RigidBody.

This is not limited to floating bodies but generally Joint::is_locked() is preferable otherwise.

Returns: true if the body is locked, false otherwise.

◆ Lock()

void Lock ( systems::Context< T > * context ) const

For a floating RigidBody, lock its inboard joint.

Its generalized velocities will be 0 until it is unlocked.

Exceptions

std::exception if this body is not a floating body.

◆ mobod_index()

internal::MobodIndex mobod_index ( ) const

(Advanced) Returns the index of the mobilized body ("mobod") in the computational directed forest structure of the owning MultibodyTree to which this RigidBody belongs.

This serves as the BodyNode index and the index into all associated quantities.

◆ name()

const std::string& name ( ) const

Gets the name associated with this rigid body.

The name will never be empty.

◆ operator=() [1/2]

RigidBody& operator= ( RigidBody< T > && )

delete

◆ operator=() [2/2]

RigidBody& operator= ( const RigidBody< T > & )

delete

◆ scoped_name()

ScopedName scoped_name ( ) const

Returns scoped name of this frame.

Neither of the two pieces of the name will be empty (the scope name and the element name).

◆ SetCenterOfMassInBodyFrame()

void SetCenterOfMassInBodyFrame	(	systems::Context< T > *	context,
		const Vector3< T > &	com
	)		const

(Advanced) Sets this body's center of mass position while preserving its inertia about its body origin.

Parameters

[in,out]	context	contains the state of the multibody system. It is modified to store the updated com (center of mass position).
[in]	com	position vector from Bo (this body B's origin) to Bcm (B's center of mass), expressed in B.

Note: This function changes B's center of mass position without modifying G_BBo_B (B's unit inertia about Bo, expressed in B). Since this use case is very unlikely, consider using SetSpatialInertiaInBodyFrame() or SetCenterOfMassInBodyFrameAndPreserveCentralInertia().

Precondition: the context makes sense for use by this RigidBody.

Exceptions

std::exception if context is null.

Warning: Do not use this function unless it is needed (think twice).

◆ SetCenterOfMassInBodyFrameAndPreserveCentralInertia()

void SetCenterOfMassInBodyFrameAndPreserveCentralInertia	(	systems::Context< T > *	context,
		const Vector3< T > &	center_of_mass_position
	)		const

Sets this body's center of mass position while preserving its inertia about its center of mass.

Parameters

[in,out]	context	contains the state of the multibody system. It is modified to store the updated center_of_mass_position and the updated G_BBo_B (this body B's unit inertia about B's origin Bo, expressed in B).
[in]	center_of_mass_position	position vector from Bo to Bcm (B's center of mass), expressed in B.

Note: G_BBo_B is modified to ensure B's inertia about Bcm is unchanged. Although this function can work well when B's mass is concentrated at (or mostly near) a single point, it has questionable utility to generally account for inertia changes due to arbitrary center of mass changes. Consider using SetSpatialInertiaInBodyFrame() instead.

Precondition: the context makes sense for use by this RigidBody.

Exceptions

std::exception if context is null.

◆ SetMass()

void SetMass	(	systems::Context< T > *	context,
		const T &	mass
	)		const

For this RigidBody B, sets its mass stored in context to mass.

Parameters

[out]	context	contains the state of the multibody system.
[in]	mass	mass of this rigid body B.

Note: This function changes this body B's mass and appropriately scales I_BBo_B (B's rotational inertia about Bo, expressed in B).

Precondition: the context makes sense for use by this RigidBody.

Exceptions

std::exception if context is null.

◆ SetSpatialInertiaInBodyFrame()

void SetSpatialInertiaInBodyFrame	(	systems::Context< T > *	context,
		const SpatialInertia< T > &	M_Bo_B
	)		const

For this RigidBody B, sets its SpatialInertia that is stored in context to M_Bo_B.

Parameters

[out]	context	contains the state of the multibody system.
[in]	M_Bo_B	spatial inertia of this rigid body B about Bo (B's origin), expressed in B. M_Bo_B contains properties related to B's mass, the position vector from Bo to Bcm (B's center of mass), and G_Bo_B (B's unit inertia about Bo expressed in B).

Precondition: the context makes sense for use by this RigidBody.

Exceptions

std::exception if context is null.

◆ Unlock()

void Unlock ( systems::Context< T > * context ) const

For a floating RigidBody, unlock its inboard joint.

Exceptions

std::exception if this body is not a floating body.

Friends And Related Function Documentation

◆ internal::RigidBodyAttorney< T >

friend class internal::RigidBodyAttorney< T >

friend

The documentation for this class was generated from the following files:

drake/multibody/tree/fixed_offset_frame.h
drake/multibody/tree/rigid_body.h

Detailed Description

template<typename T> class drake::multibody::RigidBody< T >

Public Member Functions

Friends

Additional Inherited Members

Constructor & Destructor Documentation

◆ RigidBody() [1/4]

◆ RigidBody() [2/4]

◆ RigidBody() [3/4]

◆ RigidBody() [4/4]

Member Function Documentation

◆ AddInForce()

◆ AddInForceInWorld()

◆ body_frame()

◆ CalcCenterOfMassInBodyFrame()

◆ CalcCenterOfMassTranslationalVelocityInWorld()

◆ CalcSpatialInertiaInBodyFrame()

◆ CloneToScalar()

◆ default_com()

◆ default_mass()

◆ default_rotational_inertia()

◆ default_spatial_inertia()

◆ default_unit_inertia()

◆ EvalPoseInWorld()

◆ EvalSpatialAccelerationInWorld()

◆ EvalSpatialVelocityInWorld()

◆ floating_position_suffix()

◆ floating_positions_start()

◆ floating_velocities_start_in_v()

◆ floating_velocity_suffix()

◆ get_angular_acceleration_in_world()

◆ get_angular_velocity_in_world()

◆ get_mass()

◆ get_origin_acceleration_in_world()

◆ get_origin_position_in_world()

◆ get_origin_velocity_in_world()

◆ get_pose_in_world()

◆ get_rotation_matrix_in_world()

◆ get_spatial_acceleration_in_world()

◆ get_spatial_velocity_in_world()

◆ GetForceInWorld()

◆ has_quaternion_dofs()

◆ index()

◆ is_floating()

◆ is_locked()

◆ Lock()

◆ mobod_index()

◆ name()

◆ operator=() [1/2]

◆ operator=() [2/2]

◆ scoped_name()

◆ SetCenterOfMassInBodyFrame()

◆ SetCenterOfMassInBodyFrameAndPreserveCentralInertia()

◆ SetMass()

◆ SetSpatialInertiaInBodyFrame()

◆ Unlock()

Friends And Related Function Documentation

◆ internal::RigidBodyAttorney< T >

template<typename T>
class drake::multibody::RigidBody< T >