MultibodyElement< T > Class Template Reference

Detailed Description

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

A class representing an element (subcomponent) of a MultibodyPlant or (internally) a MultibodyTree.

Examples of multibody elements are bodies, joints, force elements, and actuators. After a Finalize() call, multibody elements get assigned a type-specific index that uniquely identifies them. By convention, every subclass of MultibodyElement provides an index() member function that returns the assigned index, e.g.,

/** Returns this element's unique index. */
BodyIndex index() const { return this->template index_impl<BodyIndex>(); }

Some multibody elements are added during Finalize() and are not part of the user-specified model. These are called "ephemeral" elements and can be identified using the is_ephemeral() function here. Examples include

• free joints added to connect lone bodies or free-floating trees to World
• fixed offset frames added when joints are modeled by mobilizers
• all mobilizers.

Template Parameters

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

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

Public Member Functions
virtual	~MultibodyElement ()
ModelInstanceIndex	model_instance () const
	Returns the ModelInstanceIndex of the model instance to which this element belongs. More...
template<typename = void>
const MultibodyPlant< T > &	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...
bool	is_ephemeral () const
	Returns true if this MultibodyElement was added during Finalize() rather than something a user added. More...
void	set_is_ephemeral (bool is_ephemeral)
	(Internal use only) Sets the is_ephemeral flag to the indicated value. More...
Does not allow copy, move, or assignment
	MultibodyElement (const MultibodyElement &)=delete
MultibodyElement &	operator= (const MultibodyElement &)=delete
	MultibodyElement (MultibodyElement &&)=delete
MultibodyElement &	operator= (MultibodyElement &&)=delete

Protected Member Functions
	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...
int	ordinal_impl () const
	Returns this element's unique ordinal. 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...
virtual void	DoSetTopology (const internal::MultibodyTreeTopology &tree)=0
	Implementation of the NVI SetTopology(). More...
virtual void	DoDeclareParameters (internal::MultibodyTreeSystem< T > *)
	Implementation of the NVI DeclareParameters(). More...
virtual void	DoSetDefaultParameters (systems::Parameters< T > *) const
	Implementation of the NVI SetDefaultParameters(). 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...
bool	has_parent_tree () const
	Returns true if this multibody element has a parent tree, otherwise false. More...

Friends
class	internal::MultibodyTree< T >
class	MultibodyElementTester

Constructor & Destructor Documentation

MultibodyElement() [1/5]

MultibodyElement ( const MultibodyElement< T > &  )

delete

MultibodyElement() [2/5]

MultibodyElement ( MultibodyElement< T > &&  )

delete

~MultibodyElement()

virtual ~MultibodyElement ( )

virtual

MultibodyElement() [3/5]

MultibodyElement ( )

protected

Default constructor made protected so that sub-classes can still declare their default constructors if they need to.

MultibodyElement() [4/5]

MultibodyElement ( ModelInstanceIndex  model_instance )

explicitprotected

Constructor which allows specifying a model instance.

MultibodyElement() [5/5]

MultibodyElement ( ModelInstanceIndex  model_instance, int64_t  index  )

explicitprotected

Both the model instance and element index are specified.

Member Function Documentation

DeclareAbstractParameter()

systems::AbstractParameterIndex DeclareAbstractParameter ( internal::MultibodyTreeSystem< T > *  tree_system, const AbstractValue &  model_value  )

protected

To be used by MultibodyElement-derived objects when declaring parameters in their implementation of DoDeclareParameters().

For an example, see Joint::DoDeclareParameters().

DeclareNumericParameter()

systems::NumericParameterIndex DeclareNumericParameter ( internal::MultibodyTreeSystem< T > *  tree_system, const systems::BasicVector< T > &  model_vector  )

protected

To be used by MultibodyElement-derived objects when declaring parameters in their implementation of DoDeclareParameters().

For an example, see RigidBody::DoDeclareParameters().

DeclareParameters()

void DeclareParameters

(

internal::MultibodyTreeSystem< T > *

tree_system

)

Declares MultibodyTreeSystem Parameters at MultibodyTreeSystem::Finalize() time.

NVI to the virtual method DoDeclareParameters().

Parameters

[in]

tree_system

A mutable copy of the parent MultibodyTreeSystem.

Precondition

'tree_system' must be the same as the parent tree system (what's returned from GetParentTreeSystem()).

DoDeclareParameters()

virtual void DoDeclareParameters ( internal::MultibodyTreeSystem< T > *  )

protectedvirtual

Implementation of the NVI DeclareParameters().

MultibodyElement-derived objects may override to declare their specific parameters.

DoSetDefaultParameters()

virtual void DoSetDefaultParameters ( systems::Parameters< T > *  ) const

protectedvirtual

Implementation of the NVI SetDefaultParameters().

MultibodyElement-derived objects may override to set default values of their specific parameters.

DoSetTopology()

virtual void DoSetTopology ( const internal::MultibodyTreeTopology &  tree )

protectedpure virtual

Implementation of the NVI SetTopology().

For advanced use only for developers implementing new MultibodyTree components.

Implemented in Joint< T >.

get_parent_tree()

const internal::MultibodyTree<T>& get_parent_tree ( ) const

protected

Returns a constant reference to the parent MultibodyTree that owns this element.

Exceptions

std::exception

in debug builds if has_parent_tree() is false.

GetParentPlant()

const MultibodyPlant<T>& GetParentPlant

(

)

const

Returns the MultibodyPlant that owns this MultibodyElement.

Note

You can only invoke this method if you have a definition of MultibodyPlant available. That is, you must include drake/multibody/plant/multibody_plant.h in the translation unit that invokes this method; multibody_element.h cannot do that for you.

Exceptions

std::exception

if there is no MultibodyPlant owner.

GetParentTreeSystem()

const internal::MultibodyTreeSystem<T>& GetParentTreeSystem ( ) const

protected

Returns a constant reference to the parent MultibodyTreeSystem that owns the parent MultibodyTree that owns this element.

Exceptions

std::exception

in debug builds if has_parent_tree() is false.

has_parent_tree()

bool has_parent_tree ( ) const

protected

Returns true if this multibody element has a parent tree, otherwise false.

index_impl()

ElementIndexType index_impl ( ) const

protected

Returns this element's unique index.

is_ephemeral()

bool is_ephemeral

(

)

const

Returns true if this MultibodyElement was added during Finalize() rather than something a user added.

(See class comments.)

model_instance()

ModelInstanceIndex model_instance

(

)

const

Returns the ModelInstanceIndex of the model instance to which this element belongs.

operator=() [1/2]

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

delete

operator=() [2/2]

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

delete

ordinal_impl()

int ordinal_impl ( ) const

protected

Returns this element's unique ordinal.

set_is_ephemeral()

void set_is_ephemeral

(

bool

is_ephemeral

)

(Internal use only) Sets the is_ephemeral flag to the indicated value.

The default if this is never called is false. Any element that is added during Finalize() should set this flag to true.

SetDefaultParameters()

void SetDefaultParameters

(

systems::Parameters< T > *

parameters

)

const

Sets default values of parameters belonging to each MultibodyElement in parameters at a call to MultibodyTreeSystem::SetDefaultParameters().

Parameters

[out]

parameters

A mutable collections of parameters in a context.

Precondition

parameters != nullptr

SetTopology()

void SetTopology ( const internal::MultibodyTreeTopology &  tree )

protected

Gives MultibodyElement-derived objects the opportunity to retrieve their topology after MultibodyTree::Finalize() is invoked.

NVI to pure virtual method DoSetTopology().

Friends And Related Function Documentation

internal::MultibodyTree< T >

friend class internal::MultibodyTree< T >

friend

MultibodyElementTester

friend class MultibodyElementTester

friend

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

• drake/multibody/tree/multibody_element.h