Physsim::FSABAlgorithm Class Reference

Class for an articulated body using Featherstone's algorithm for forward dynamics. More...

#include <FSABAlgorithm.h>

Inheritance diagram for Physsim::FSABAlgorithm:

List of all members.

Public Member Functions
virtual void	load_state (BasePtr object, bimap< BasePtr, BasePtr > *correspondence)
	Implements Base::load_state().
virtual void	save_state (BasePtr object, bimap< BasePtr, BasePtr > *correspondence) const
	Implements Base::save_state().
virtual void	clone (BasePtr &cloned, bimap< BasePtr, BasePtr > *obj_map=NULL) const
	Implements Base::clone().
virtual void	calc_fwd_dyn (RCArticulatedBodyPtr body, ReferenceFrameType rftype)
	Computes the joint accelerations (forward dynamics) for a manipulator.
virtual void	apply_impulse (RCArticulatedBodyPtr body, const Vector3 &j, const Vector3 &k, const Vector3 &contact_point, RigidBodyPtr link)
	Implements RCArticulatedBodyFwdDynAlgo::apply_impulse().
virtual void	load_from_xml (XMLTreeConstPtr node, std::map< std::string, BasePtr > &id_map)
	Implements Base::load_from_xml().
virtual void	save_to_xml (XMLTreePtr node, std::list< BaseConstPtr > &shared_objects) const
	Implements Base::save_to_xml().
Public Attributes
ReferenceFrameType	_rftype
	The reference frame all quantities are computed in.
std::vector< SVector6 >	_v
	The spatial velocities.
std::vector< SVector6 >	_a
	The spatial accelerations.
std::vector< SMatrix6 >	_Iiso
	The spatial isolated inertias.
std::vector< SMatrix6 >	_I
	The articulated body inertias.
std::vector< SVector6 >	_Z
	The articulated body spatial zero accelerations.
std::vector< SVector6 >	_c
	The spatial coriolis vectors.
std::vector< SMatrixN >	_Is
	The expression I*s.
std::vector< MatrixNN >	_sIs
	The temporary quantity sIs.
std::vector< VectorN >	_mu
	The temporary expression Q - I*s'*c - s'*Z.

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Detailed Description

Class for an articulated body using Featherstone's algorithm for forward dynamics.

Implements Featherstone's algorithm for articulated bodies. Featherstone's algorithm runs in O(n) time [n = # of joints]. This implementation is based on Brian Mirtich's Ph. D. thesis, and remains pretty consistent with it. There are a couple of changes, to produce a nice implementation. The user need not be concerned with these issues, but they are useful to know for debugging.

1. Mirtich labels his links from 1..n, and considers the base to be link 0; the total number of links is considered to be n, rather than n+1. I make the total number of links n+1 and treat the links the same as the base. I do this so that the user thinks of the base as a link for purposes of link connectivity.
2. Mirtich labels his joints from 0..n-1. When labeling the link in Mirtich's style, link i and joint i match up (joint i is link i's inner joint). When labeling the link in my style, joint i-1 is the corresponding joint for link i.

Note that one critical note for manipulator setup is that the base is the first link in the list of links.

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Member Function Documentation

void FSABAlgorithm::calc_fwd_dyn	(	RCArticulatedBodyPtr	body,
		ReferenceFrameType	rftype
	)			[virtual]

Computes the joint accelerations (forward dynamics) for a manipulator.

Featherstone Algorithm taken from Mirtich's thesis (p. 113). Note that Mirtich's numbering is a little funny; I decrement his joint indices by one, while leaving his link indices intact.

Implements Physsim::RCArticulatedBodyFwdDynAlgo.

void FSABAlgorithm::apply_impulse	(	RCArticulatedBodyPtr	body,
		const Vector3 &	j,
		const Vector3 &	k,
		const Vector3 &	contact_point,
		RigidBodyPtr	link
	)			[virtual]

Implements RCArticulatedBodyFwdDynAlgo::apply_impulse().

Precondition:

forward dynamics have been computed already by calc_fwd_dyn()

Implements Physsim::RCArticulatedBodyFwdDynAlgo.

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

• /home/drumwrig/Physsim/include/Physsim/FSABAlgorithm.h
• /home/drumwrig/Physsim/src/FSABAlgorithm.cpp

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