A MobilizedBody is Simbody's fundamental body-and-joint object used to parameterize a system's motion by constructing a multibody tree containing each body and its unique "mobilizer" (internal coordinate joint). More...

#include <MobilizedBody.h>

Inheritance diagram for SimTK::MobilizedBody:

Classes
class	Ball
	Three mobilities – unrestricted orientation modeled with a quaternion which is never singular. More...

class	BendStretch
	Two mobilities: The z axis of the parent's F frame is used for rotation (and that is always aligned with the M frame z axis). More...

class	Bushing
	Six mobilities – arbitrary relative motion modeled as x-y-z translation followed by an x-y-z body-fixed Euler angle sequence, though with a singularity when the middle angle is +/- 90 degrees. More...

class	Custom
	The handle class MobilizedBody::Custom (dataless) and its companion class MobilizedBody::Custom::Implementation can be used together to define new MobilizedBody types with arbitrary properties. More...

class	Cylinder
	Two mobilities – rotation and translation along the common z axis of the inboard and outboard mobilizer frames. More...

class	Ellipsoid
	Three mobilities – coordinated rotation and translation along the surface of an ellipsoid fixed to the parent (inboard) body. More...

class	Free
	Unrestricted motion for a rigid body (six mobilities). More...

class	FreeLine
	Five mobilities, representing unrestricted motion for a body which is inertialess along its own z axis. More...

class	FunctionBased
	This is a subclass of MobilizedBody::Custom which uses a set of Function objects to define the behavior of the MobilizedBody. More...

class	Gimbal
	Three mobilities – unrestricted orientation modeled as a 1-2-3 body-fixed Euler angle sequence, though with a singularity when the middle angle is +/- 90 degrees. More...

class	Ground
	This is a special type of "mobilized" body generated automatically by Simbody as a placeholder for Ground in the 0th slot for a SimbodyMatterSubsystem's mobilized bodies; don't create this yourself. More...

class	LineOrientation
	Two mobilities, representing unrestricted orientation for a body which is inertialess along its own z axis. More...

class	Pin
	Provides one rotational mobility about the common z axis of the F and M frames of the mobilizer. More...

class	Planar
	Three mobilities – z rotation and x,y translation. More...

class	Screw
	One mobility – coordinated rotation and translation along the common z axis of the inboard and outboard mobilizer frames. More...

class	Slider
	One mobility – translation along the common x axis of the F (inboard) and M (outboard) mobilizer frames. More...

class	SphericalCoords
	Three mobilities – body fixed 3-2 (z-y) rotation followed by translation along body z or body x. More...

class	Translation
	Three translational mobilities describing the Cartesian motion of a point. More...

class	Universal
	Two mobilities – rotation about the x axis, followed by a rotation about the new y axis. More...

class	Weld
	Zero mobilities. More...

Public Types
enum	Direction { Forward = 0, Reverse = 1 }
	Constructors can take an argument of this type to indicate that the mobilizer is being defined in the reverse direction, meaning from the outboard (child) body to the inboard (parent) body. More...

typedef Pin	Torsion
	Synonym for Pin mobilizer. More...

typedef Pin	Revolute
	Synonym for Pin mobilizer. More...

typedef Slider	Prismatic
	Synonym for Slider mobilizer. More...

typedef Translation	Cartesian
	Synonym for Translation mobilizer. More...

typedef Translation	CartesianCoords
	Synonym for Translation mobilizer. More...

typedef BendStretch	PolarCoords
	Synonym for BendStretch mobilizer. More...

typedef Ball	Orientation
	Synonym for Ball mobilizer. More...

typedef Ball	Spherical
	Synonym for Ball mobilizer. More...

Public Types inherited from SimTK::PIMPLHandle< MobilizedBody, MobilizedBodyImpl, true >
typedef PIMPLHandle < MobilizedBody, MobilizedBodyImpl, PTR >	HandleBase

typedef HandleBase	ParentHandle

Public Member Functions
	MobilizedBody ()
	The default constructor provides an empty MobilizedBody handle that can be assigned to reference any type of MobilizedBody. More...

	MobilizedBody (MobilizedBodyImpl *r)
	Internal use only. More...

Mobilizer locking and unlocking
Every MobilizedBody object supports locking and unlocking of the mobilizer it contains. You can lock the mobilizer's position, velocity, or acceleration. In all cases the generalized accelerations udot of a locked mobilizer are prescribed. If you lock just the accelerations, then velocity and position remain free. If you lock velocity, then the generalized speeds u are prescribed to specified values, accelerations udot are prescribed to zero, and positions will remain free. If you lock position (the default locking level) then the generalized coordinates q are prescribed to specified values and the speeds u and accelerations udot are prescribed to zero. Prescribed values may be obtained from the current state, or set explicitly. The lock() and lockAt() methods when called at position level will modify q in the given state if necessary to satisfy the locked position, and will set u to zero. When called at velocity level they will modify u if necessary to satisfied the locked velocity, but will leave q unchanged. You can also specify that a mobilizer is locked by default (at acceleration, velocity, or position level). In that case the prescribed value is recorded when the state is realized to Stage::Model, using values taken from the state at that time. If this mobilizer is driven by a Motion object, locking overrides that while the lock is active; when unlocked the Motion object resumes control.
void	lock (State &state, Motion::Level level=Motion::Position) const
	Lock this mobilizer's position or velocity at its current value, or lock the acceleration to zero, depending on the `level` parameter. More...

void	lockAt (State &state, Real value, Motion::Level level=Motion::Position) const
	Lock this mobilizer's q, u, or udot to the given scalar `value`, depending on `level`. More...

void	lockAt (State &state, const Vector &value, Motion::Level level=Motion::Position) const
	Lock this mobilizer's q, u, or udot to the given Vector `value`, depending on `level`. More...

template<int N>
void	lockAt (State &state, const Vec< N > &value, Motion::Level level=Motion::Position) const
	Lock this mobilizer's q, u, or udot to the given Vec<N> `value`, depending on the `level`. More...

void	unlock (State &state) const
	Unlock this mobilizer, returning it to its normal behavior which may be free motion or may be controlled by a Motion object. More...

bool	isLocked (const State &state) const
	Check whether this mobilizer is currently locked in the given `state`. More...

Motion::Level	getLockLevel (const State &state) const
	Returns the lock level if the mobilizer is locked in the given `state`, otherwise Motion::NoLevel. More...

Vector	getLockValueAsVector (const State &state) const
	Return the q, u, or udot value at which this mobilizer is locked, depending on the lock level, as a Vector of the appropriate length. More...

MobilizedBody &	lockByDefault (Motion::Level level=Motion::Position)
	Change whether this mobilizer is initially locked. More...

bool	isLockedByDefault () const
	Check whether this mobilizer is to be locked in the default state. More...

Motion::Level	getLockByDefaultLevel () const
	Returns the level at which the mobilizer is locked by default, if it is locked by default, otherwise Motion::NoLevel. More...

State Access - Bodies
These methods extract already-computed information from the State or State cache, or set values in the State.
const Transform &	getBodyTransform (const State &state) const
	Extract from the state cache the already-calculated spatial configuration X_GB of body B's body frame, measured with respect to the Ground frame and expressed in the Ground frame. More...

const Rotation &	getBodyRotation (const State &state) const
	Extract from the state cache the already-calculated spatial orientation R_GB of body B's body frame x, y, and z axes expressed in the Ground frame, as the Rotation matrix R_GB. More...

const Vec3 &	getBodyOriginLocation (const State &state) const
	Extract from the state cache the already-calculated spatial location of body B's body frame origin Bo, measured from the Ground origin Go and expressed in the Ground frame, as the position vector p_GB (== p_GoBo). More...

const Transform &	getMobilizerTransform (const State &state) const
	At stage Position or higher, return the cross-mobilizer transform X_FM, the body's inboard mobilizer frame M measured and expressed in the parent body's corresponding outboard frame F. More...

const SpatialVec &	getBodyVelocity (const State &state) const
	Extract from the state cache the already-calculated spatial velocity V_GB of this body's reference frame B, measured with respect to the Ground frame and expressed in the Ground frame. More...

const Vec3 &	getBodyAngularVelocity (const State &state) const
	Extract from the state cache the already-calculated inertial angular velocity vector w_GB of this body B, measured with respect to the Ground frame and expressed in the Ground frame. More...

const Vec3 &	getBodyOriginVelocity (const State &state) const
	Extract from the state cache the already-calculated inertial linear velocity vector v_GB (more explicitly, v_GBo) of this body B's origin point Bo, measured with respect to the Ground frame and expressed in the Ground frame. More...

const SpatialVec &	getMobilizerVelocity (const State &state) const
	At stage Velocity or higher, return the cross-mobilizer velocity V_FM, the relative velocity of this body's "moving" mobilizer frame M in the parent body's corresponding "fixed" frame F, measured and expressed in F. More...

const SpatialVec &	getBodyAcceleration (const State &state) const
	Extract from the state cache the already-calculated spatial acceleration A_GB of this body's reference frame B, measured with respect to the Ground frame and expressed in the Ground frame. More...

const Vec3 &	getBodyAngularAcceleration (const State &state) const
	Extract from the state cache the already-calculated inertial angular acceleration vector b_GB of this body B, measured with respect to the Ground frame and expressed in the Ground frame. More...

const Vec3 &	getBodyOriginAcceleration (const State &state) const
	Extract from the state cache the already-calculated inertial linear acceleration vector a_GB (more explicitly, a_GBo) of this body B's origin point Bo, measured with respect to the Ground frame and expressed in the Ground frame. More...

const SpatialVec &	getMobilizerAcceleration (const State &state) const
	TODO: Not implemented yet – any volunteers? At stage Acceleration, return the cross-mobilizer acceleration A_FM, the relative acceleration of body B's "moving" mobilizer frame M in the parent body's corresponding "fixed" frame F, measured and expressed in F. More...

const MassProperties &	getBodyMassProperties (const State &state) const
	Return a reference to this body's mass properties in the State cache. More...

const SpatialInertia &	getBodySpatialInertiaInGround (const State &state) const
	Return a reference to the already-calculated SpatialInertia of this body, taken about the body's origin (not its mass center), and expressed in the Ground frame. More...

Real	getBodyMass (const State &state) const
	Return the mass of this body. More...

const Vec3 &	getBodyMassCenterStation (const State &state) const
	Return this body's center of mass station (i.e., the vector fixed in the body, going from body origin to body mass center, expressed in the body frame.) The State must have been realized to Stage::Instance or higher. More...

const UnitInertia &	getBodyUnitInertiaAboutBodyOrigin (const State &state) const
	Return a reference to this body's unit inertia matrix in the State cache, taken about the body origin and expressed in the body frame. More...

const Transform &	getInboardFrame (const State &state) const
	Return a reference to this mobilizer's frame F fixed on the parent body P, as the fixed Transform from P's body frame to the frame F fixed to P. More...

const Transform &	getOutboardFrame (const State &state) const
	Return a reference to this MobilizedBody's mobilizer frame M, as the fixed Transform from this body B's frame to the frame M fixed on B. More...

void	setInboardFrame (State &state, const Transform &X_PF) const
	TODO: not implemented yet. More...

void	setOutboardFrame (State &state, const Transform &X_BM) const
	TODO: not implemented yet. More...

State Access - Mobilizer generalized coordinates q and speeds u
These methods extract q- or u-related information from the State or State cache, or set q or u values in the State.
int	getNumQ (const State &state) const
	Return the number of generalized coordinates q currently in use by this mobilizer. More...

int	getNumU (const State &state) const
	Return the number of generalized speeds u currently in use by this mobilizer. More...

QIndex	getFirstQIndex (const State &state) const
	Return the global QIndex of the first q for this mobilizer; all the q's range from getFirstQIndex() to QIndex(getFirstQIndex()+getNumQ()-1). More...

UIndex	getFirstUIndex (const State &state) const
	Return the global UIndex of the first u for this mobilizer; all the u's range from getFirstUIndex() to UIndex(getFirstUIndex()+getNumU()-1). More...

Motion::Method	getQMotionMethod (const State &state) const
	Determine how generalized coordinate q values are being determined. More...

Motion::Method	getUMotionMethod (const State &state) const
	Determine how generalized speed u values are being determined. More...

Motion::Method	getUDotMotionMethod (const State &state) const
	Determine how generalized acceleration udot values are being determined. More...

Real	getOneQ (const State &state, int which) const
	Return one of the generalized coordinates q from this mobilizer's partition of the matter subsystem's full q vector in the State. More...

Real	getOneU (const State &state, int which) const
	Return one of the generalized speeds u from this mobilizer's partition of the matter subsystem's full u vector in the State. More...

Vector	getQAsVector (const State &state) const
	Return as a Vector of length getNumQ() all the generalized coordinates q currently in use by this mobilizer, from this mobilizer's partion in the matter subsystem's full q vector in the State. More...

Vector	getUAsVector (const State &state) const
	Return as a Vector of length getNumU() all the generalized speeds u currently in use by this mobilizer, from this mobilizer's partion in the matter subsystem's full u vector in the State. More...

Real	getOneQDot (const State &state, int which) const
	Return one of the generalized coordinate derivatives qdot from this mobilizer's partition of the matter subsystem's full qdot vector in the State cache. More...

Vector	getQDotAsVector (const State &state) const
	Return as a Vector of length getNumQ() all the generalized coordinate derivatives qdot currently in use by this mobilizer, from this mobilizer's partition in the matter subsystem's full qdot vector in the State cache. More...

Real	getOneUDot (const State &state, int which) const
	Return one of the generalized accelerations udot from this mobilizer's partition of the matter subsystem's full udot vector in the State cache. More...

Real	getOneQDotDot (const State &state, int which) const
	Return one of the generalized coordinate second derivatives qdotdot from this mobilizer's partition of the matter subsystem's full qdotdot vector in the State cache. More...

Vector	getUDotAsVector (const State &state) const
	Return as a Vector of length getNumU() all the generalized accelerations udot currently in use by this mobilizer, from this mobilizer's partion in the matter subsystem's full udot vector in the State cache. More...

Vector	getQDotDotAsVector (const State &state) const
	Return as a Vector of length getNumQ() all the generalized coordinate second derivatives qdotdot currently in use by this mobilizer, from this mobilizer's partion in the matter subsystem's full qdotdot vector in the State cache. More...

Vector	getTauAsVector (const State &state) const
	Return the generalized forces tau resulting from prescribed (known) acceleration, corresponding to each of this mobilizer's mobilities, as a Vector of length nu=getNumU(). More...

Real	getOneTau (const State &state, MobilizerUIndex which) const
	Return one of the tau forces resulting from prescribed (known) acceleration, corresponding to one of this mobilizer's mobilities as selected here using the `which` parameter, numbered from zero to getNumU()-1. More...

void	setOneQ (State &state, int which, Real v) const
	Set one of the generalized coordinates q to value `v`, in this mobilizer's partition of the matter subsystem's full q vector in the State. More...

void	setOneU (State &state, int which, Real v) const
	Set one of the generalized speeds u to value `v`, in this mobilizer's partition of the matter subsystem's full u vector in the State. More...

void	setQFromVector (State &state, const Vector &v) const
	Set all of the generalized coordinates q to value `v` (a Vector of length getNumQ()), in this mobilizer's partition of the matter subsystem's full q vector in the State. More...

void	setUFromVector (State &state, const Vector &v) const
	Set all of the generalized speeds u to value `v` (a Vector of length getNumU()), in this mobilizer's partition of the matter subsystem's full u vector in the State. More...

void	setQToFitTransform (State &state, const Transform &X_FM) const
	Adjust this mobilizer's q's to best approximate the supplied Transform which requests a particular relative orientation and translation between the F "fixed" frame and M "moving" frame connected by this mobilizer. More...

void	setQToFitRotation (State &state, const Rotation &R_FM) const
	Adjust this mobilizer's q's to best approximate the supplied Rotation matrix which requests a particular relative orientation between the "fixed" frame F and "moving" frame M connected by this mobilizer. More...

void	setQToFitTranslation (State &state, const Vec3 &p_FM) const
	Adjust this mobilizer's q's to best approximate the supplied position vector which requests a particular offset between the origins of the F "fixed" frame and M "moving" frame connected by this mobilizer, with any q's (rotational or translational) being modified if doing so helps satisfy the request. More...

void	setUToFitVelocity (State &state, const SpatialVec &V_FM) const
	Adjust this mobilizer's u's (generalized speeds) to best approximate the supplied spatial velocity `V_FM` which requests the relative angular and linear velocity between the "fixed" and "moving" frames connected by this mobilizer. More...

void	setUToFitAngularVelocity (State &state, const Vec3 &w_FM) const
	Adjust this mobilizer's u's (generalized speeds) to best approximate the supplied angular velocity `w_FM` which requests a particular relative angular between the "fixed" and "moving" frames connected by this mobilizer. More...

void	setUToFitLinearVelocity (State &state, const Vec3 &v_FM) const
	Adjust any of this mobilizer's u's (generalized speeds) to best approximate the supplied linear velocity `v_FM` which requests a particular velocity for the "moving" frame M origin in the "fixed" frame F on the parent where these are the frames connected by this mobilizer. More...

SpatialVec	getHCol (const State &state, MobilizerUIndex ux) const
	Expert use only: obtain a column of the hinge matrix H corresponding to one of this mobilizer's mobilities (actually a column of H_PB_G; what Jain calls H* and Schwieters calls H^T). More...

SpatialVec	getH_FMCol (const State &state, MobilizerUIndex ux) const
	Expert use only: obtain a column of the mobilizer-local hinge matrix H_FM which maps generalized speeds u to cross-mobilizer spatial velocity V_FM via V_FM=H_FM*u. More...

Basic Operators
These methods use state variables and Response methods to compute basic quantities which cannot be precomputed, but which can be implemented with an inline combination of basic floating point operations which can be reliably determined at compile time. The method names and descriptions use the following terms: Body or ThisBody: the Body B associated with the current MobilizedBody. ThisBody is implied when no other Body is mentioned. Ground: the "MobilizedBody" G representing the Ground reference frame which never moves. AnotherBody: the Body A being referenced, which in general is neither ThisBody nor Ground. Station: a point S fixed on ThisBody B, located by a position vector p_BS (or more explicitly, p_BoS) from the B-frame origin Bo to the point S, expressed in the B-frame coordinate system. Vector: a vector v fixed on ThisBody B, given by a vector v_B expressed in the B-frame coordinate system. Direction: a unit vector u fixed on ThisBody B, given by a unit vector u_B expressed in the B-frame coordinate system. Frame: an origin and coordinate axes F fixed on ThisBody B, given by a transform X_BF that locates F's origin (a Station) in B and expresses each of F's axes (Directions) in B. Origin: the Station located at (0,0,0) in ThisBody frame B, that is, body B's origin point. MassCenter: the Station on ThisBody B which is the center of mass for B. GroundPoint, GroundVector: a Point P or Vector v on the Ground "Body" G. These are measured and expressed in the Ground frame, as p_GP or v_G. AnotherBodyStation, AnotherBodyVector, etc.: a Station S or Vector v on AnotherBody A. These are measured and expressed in the A frame, as p_AS or v_A. Mobilizer frame M: the mobilizer's outboard "moving" frame, fixed to ThisBody B. Mobilizer frame F: the mobilizer's inboard "fixed" frame, fixed to the parent body P.
Transform	findBodyTransformInAnotherBody (const State &state, const MobilizedBody &inBodyA) const
	Return X_AB, the spatial transform giving this body B's frame in body A's frame. More...

Rotation	findBodyRotationInAnotherBody (const State &state, const MobilizedBody &inBodyA) const
	Return R_AB, the rotation matrix giving this body B's axes in body A's frame. More...

Vec3	findBodyOriginLocationInAnotherBody (const State &state, const MobilizedBody &toBodyA) const
	Return the station on another body A (that is, a point measured and expressed in A) that is currently coincident in space with the origin Bo of this body B. More...

SpatialVec	findBodyVelocityInAnotherBody (const State &state, const MobilizedBody &inBodyA) const
	Return the angular and linear velocity of body B's frame in body A's frame, expressed in body A, and arranged as a SpatialVec. More...

Vec3	findBodyAngularVelocityInAnotherBody (const State &state, const MobilizedBody &inBodyA) const
	Return the angular velocity w_AB of body B's frame in body A's frame, expressed in body A. More...

Vec3	findBodyOriginVelocityInAnotherBody (const State &state, const MobilizedBody &inBodyA) const
	Return the velocity of body B's origin point in body A's frame, expressed in body A. More...

SpatialVec	findBodyAccelerationInAnotherBody (const State &state, const MobilizedBody &inBodyA) const
	Return the angular and linear acceleration of body B's frame in body A's frame, expressed in body A, and arranged as a SpatialVec. More...

Vec3	findBodyAngularAccelerationInAnotherBody (const State &state, const MobilizedBody &inBodyA) const
	Return the angular acceleration of body B's frame in body A's frame, expressed in body A. More...

Vec3	findBodyOriginAccelerationInAnotherBody (const State &state, const MobilizedBody &inBodyA) const
	Return the acceleration of body B's origin point in body A's frame, expressed in body A. More...

SpatialVec	findMobilizerReactionOnBodyAtMInGround (const State &state) const
	Return the spatial reaction force (moment and force) applied by the mobilizer to body B at the location of the mobilizer frame M (fixed to body B, but not necessarily at the body frame origin), expressed in Ground. More...

SpatialVec	findMobilizerReactionOnBodyAtOriginInGround (const State &state) const
	Return the spatial reaction force (moment and force) applied by the mobilizer to body B but shifted to the B frame origin, and expressed in Ground. More...

SpatialVec	findMobilizerReactionOnParentAtFInGround (const State &state) const
	Return the spatial reaction force (moment and force) applied by the mobilizer to the parent (inboard) body P at the location of the inboard "fixed" mobilizer frame F (fixed to body P, but not necessarily at the P frame origin), expressed in Ground. More...

SpatialVec	findMobilizerReactionOnParentAtOriginInGround (const State &state) const
	Return the spatial reaction force (moment and force) applied by the mobilizer to the parent (inboard) body P at the location of the P frame origin, and expressed in Ground. More...

Vec3	findStationLocationInGround (const State &state, const Vec3 &stationOnB) const
	Return the Cartesian (ground) location that is currently coincident with a station (point) S fixed on body B. More...

Vec3	findStationLocationInAnotherBody (const State &state, const Vec3 &stationOnB, const MobilizedBody &toBodyA) const
	Given a station S on this body B, return the location on another body A which is at the same location in space. More...

Vec3	findStationVelocityInGround (const State &state, const Vec3 &stationOnB) const
	Given a station fixed on body B, return its inertial (Cartesian) velocity, that is, its velocity relative to the Ground frame, expressed in the Ground frame. More...

Vec3	findStationVelocityInAnotherBody (const State &state, const Vec3 &stationOnBodyB, const MobilizedBody &inBodyA) const
	Return the velocity of a station S fixed on body B, in body A's frame, expressed in body A. More...

Vec3	findStationAccelerationInGround (const State &state, const Vec3 &stationOnB) const
	Given a station fixed on body B, return its inertial (Cartesian) acceleration, that is, its acceleration relative to the ground frame, expressed in the ground frame. More...

Vec3	findStationAccelerationInAnotherBody (const State &state, const Vec3 &stationOnBodyB, const MobilizedBody &inBodyA) const
	Return the acceleration of a station S fixed on body B, in another body A's frame, expressed in body A. More...

void	findStationLocationAndVelocityInGround (const State &state, const Vec3 &locationOnB, Vec3 &locationOnGround, Vec3 &velocityInGround) const
	It is cheaper to calculate a station's ground location and velocity together than to do them separately. More...

void	findStationLocationVelocityAndAccelerationInGround (const State &state, const Vec3 &locationOnB, Vec3 &locationOnGround, Vec3 &velocityInGround, Vec3 &accelerationInGround) const
	It is cheaper to calculate a station's ground location, velocity, and acceleration together than to do them separately. More...

Vec3	findMassCenterLocationInGround (const State &state) const
	Return the Cartesian (ground) location of this body B's mass center. More...

Vec3	findMassCenterLocationInAnotherBody (const State &state, const MobilizedBody &toBodyA) const
	Return the point of another body A that is currently coincident in space with the mass center CB of this body B. More...

Vec3	findStationAtGroundPoint (const State &state, const Vec3 &locationInG) const
	Return the station (point) S of this body B that is coincident with the given Ground location. More...

Vec3	findStationAtAnotherBodyStation (const State &state, const MobilizedBody &fromBodyA, const Vec3 &stationOnA) const
	Return the station (point) on this body B that is coincident with the given station on another body A. More...

Vec3	findStationAtAnotherBodyOrigin (const State &state, const MobilizedBody &fromBodyA) const
	Return the station S of this body that is currently coincident in space with the origin Ao of another body A. More...

Vec3	findStationAtAnotherBodyMassCenter (const State &state, const MobilizedBody &fromBodyA) const
	Return the station S of this body that is currently coincident in space with the mass center Ac of another body A. More...

Transform	findFrameTransformInGround (const State &state, const Transform &frameOnB) const
	Return the current Ground-frame pose (position and orientation) of a frame F that is fixed to body B. More...

SpatialVec	findFrameVelocityInGround (const State &state, const Transform &frameOnB) const
	Return the current Ground-frame spatial velocity V_GF (that is, angular and linear velocity) of a frame F that is fixed to body B. More...

SpatialVec	findFrameAccelerationInGround (const State &state, const Transform &frameOnB) const
	Return the current Ground-frame spatial acceleration A_GF (that is, angular and linear acceleration) of a frame F that is fixed to body B. More...

Vec3	expressVectorInGroundFrame (const State &state, const Vec3 &vectorInB) const
	Re-express a vector expressed in this body B's frame into the same vector in G, by applying only a rotation. More...

Vec3	expressGroundVectorInBodyFrame (const State &state, const Vec3 &vectorInG) const
	Re-express a vector expressed in Ground into the same vector expressed in this body B, by applying only rotation. More...

Vec3	expressVectorInAnotherBodyFrame (const State &state, const Vec3 &vectorInB, const MobilizedBody &inBodyA) const
	Re-express a vector expressed in this body B into the same vector expressed in body A, by applying only a rotation. More...

MassProperties	expressMassPropertiesInGroundFrame (const State &state) const
	Re-express this body B's mass properties in Ground by applying only a rotation, not a shift of reference point. More...

MassProperties	expressMassPropertiesInAnotherBodyFrame (const State &state, const MobilizedBody &inBodyA) const
	Re-express this body B's mass properties in another body A's frame by applying only a rotation, not a shift of reference point. More...

High-Level Operators
High level operators combine State Access and Basic Operators with run-time tests to calculate more complex MobilizedBody-specific quantities, with more complicated implementations that can exploit special cases at run time.
SpatialMat	calcBodySpatialInertiaMatrixInGround (const State &state) const
	Return the mass properties of body B, measured from and about the B origin Bo, but expressed in Ground and then returned as a Spatial Inertia Matrix. More...

Inertia	calcBodyCentralInertia (const State &state, MobilizedBodyIndex objectBodyB) const
	Return the central inertia for body B, that is, the inertia taken about body B's mass center Bc, and expressed in B. More...

Inertia	calcBodyInertiaAboutAnotherBodyStation (const State &state, const MobilizedBody &inBodyA, const Vec3 &aboutLocationOnBodyA) const
	Return the inertia of this body B, taken about an arbitrary point PA of body A, and expressed in body A. More...

SpatialVec	calcBodyMomentumAboutBodyOriginInGround (const State &state)
	Calculate body B's momentum (angular, linear) measured and expressed in Ground, but taken about the body origin Bo. More...

SpatialVec	calcBodyMomentumAboutBodyMassCenterInGround (const State &state) const
	Calculate body B's momentum (angular, linear) measured and expressed in Ground, but taken about the body mass center Bc. More...

Real	calcStationToStationDistance (const State &state, const Vec3 &locationOnBodyB, const MobilizedBody &bodyA, const Vec3 &locationOnBodyA) const
	Calculate the distance from a station PB on body B to a station PA on body A. More...

Real	calcStationToStationDistanceTimeDerivative (const State &state, const Vec3 &locationOnBodyB, const MobilizedBody &bodyA, const Vec3 &locationOnBodyA) const
	Calculate the time rate of change of distance from a fixed point PB on body B to a fixed point PA on body A. More...

Real	calcStationToStationDistance2ndTimeDerivative (const State &state, const Vec3 &locationOnBodyB, const MobilizedBody &bodyA, const Vec3 &locationOnBodyA) const
	Calculate the second time derivative of distance from a fixed point PB on body B to a fixed point PA on body A. More...

Vec3	calcBodyMovingPointVelocityInBody (const State &state, const Vec3 &locationOnBodyB, const Vec3 &velocityOnBodyB, const MobilizedBody &inBodyA) const
	TODO: not implemented yet – any volunteers? Return the velocity of a point P moving on body B, in body A's frame, expressed in body A. More...

Vec3	calcBodyMovingPointAccelerationInBody (const State &state, const Vec3 &locationOnBodyB, const Vec3 &velocityOnBodyB, const Vec3 &accelerationOnBodyB, const MobilizedBody &inBodyA) const
	TODO: not implemented yet – any volunteers? Return the velocity of a point P moving (and possibly accelerating) on body B, in body A's frame, expressed in body A. More...

Real	calcMovingPointToPointDistanceTimeDerivative (const State &state, const Vec3 &locationOnBodyB, const Vec3 &velocityOnBodyB, const MobilizedBody &bodyA, const Vec3 &locationOnBodyA, const Vec3 &velocityOnBodyA) const
	TODO: not implemented yet – any volunteers? Calculate the time rate of change of distance from a moving point PB on body B to a moving point PA on body A. More...

Real	calcMovingPointToPointDistance2ndTimeDerivative (const State &state, const Vec3 &locationOnBodyB, const Vec3 &velocityOnBodyB, const Vec3 &accelerationOnBodyB, const MobilizedBody &bodyA, const Vec3 &locationOnBodyA, const Vec3 &velocityOnBodyA, const Vec3 &accelerationOnBodyA) const
	TODO: not implemented yet – any volunteers? Calculate the second time derivative of distance from a moving point PB on body B to a moving point PA on body A. More...

Construction and Misc Methods
These methods are the base class services which are used while building a concrete MobilizedBody, or to query a MobilizedBody to find out how it was built. These are unlikely to be used by end users of MobilizedBodies.
const Body &	getBody () const
	Return a const reference to the Body contained within this MobilizedBody. More...

Body &	updBody ()
	Return a writable reference to the Body contained within this MobilizedBody. More...

MobilizedBody &	setBody (const Body &)
	Replace the Body contained within this MobilizedBody with a new one. More...

int	addBodyDecoration (const Transform &X_BD, const DecorativeGeometry &geometry)
	Add decorative geometry specified relative to the new (outboard) body's reference frame B. More...

int	addBodyDecoration (const DecorativeGeometry &geometry)
	Convenience method for use when the `geometry` is supplied in the body frame. More...

int	addOutboardDecoration (const Transform &X_MD, const DecorativeGeometry &geometry)
	Add decorative geometry specified relative to the outboard mobilizer frame M attached to body B. More...

int	getNumOutboardDecorations () const
	Return the count of decorations added with addOutboardDecoration(). More...

const DecorativeGeometry &	getOutboardDecoration (int i) const
	Return a const reference to the i'th outboard decoration. More...

DecorativeGeometry &	updOutboardDecoration (int i)
	Return a writable reference to the i'th outboard decoration. More...

int	addInboardDecoration (const Transform &X_FD, const DecorativeGeometry &geometry)
	Add decorative geometry specified relative to the inboard mobilizer frame F attached to the parent body P. More...

int	getNumInboardDecorations () const
	Return the count of decorations added with addInboardDecoration(). More...

const DecorativeGeometry &	getInboardDecoration (int i) const
	Return a const reference to the i'th inboard decoration. More...

DecorativeGeometry &	updInboardDecoration (int i)
	Return a writable reference to the i'th inboard decoration. More...

MobilizedBody &	setDefaultMassProperties (const MassProperties &m)
	If the contained Body can have its mass properties set to the supplied value `m` its mass properties are changed, otherwise the method fails. More...

const MassProperties &	getDefaultMassProperties () const
	Return the mass properties of the Body stored within this MobilizedBody. More...

void	adoptMotion (Motion &ownerHandle)
	Provide a unique Motion object for this MobilizedBody. More...

void	clearMotion ()
	If there is a Motion object associated with this MobilizedBody it is removed; otherwise, nothing happens. More...

bool	hasMotion () const
	Check whether this MobilizedBody has an associated Motion object. More...

const Motion &	getMotion () const
	If there is a Motion object associated with this MobilizedBody, this returns a const reference to it. More...

MobilizedBody &	setDefaultInboardFrame (const Transform &X_PF)
	Change this mobilizer's frame F on the parent body P. More...

MobilizedBody &	setDefaultOutboardFrame (const Transform &X_BM)
	Change this mobilizer's frame M fixed on this (the outboard) body B. More...

const Transform &	getDefaultInboardFrame () const
	Return a reference to this mobilizer's default for the frame F fixed on the parent (inboard) body P, as the fixed Transform from P's body frame to the frame F fixed to P. More...

const Transform &	getDefaultOutboardFrame () const
	Return a reference to this MobilizedBody's default for mobilizer frame M, as the fixed Transform from this body B's frame to the frame M fixed on B. More...

	operator MobilizedBodyIndex () const
	This is an implicit conversion from MobilizedBody to MobilizedBodyIndex when needed. More...

MobilizedBodyIndex	getMobilizedBodyIndex () const
	Return the MobilizedBodyIndex of this MobilizedBody within the owning SimbodyMatterSubsystem. More...

const MobilizedBody &	getParentMobilizedBody () const
	Return a reference to the MobilizedBody serving as the parent body of the current MobilizedBody. More...

const MobilizedBody &	getBaseMobilizedBody () const
	Return a reference to this MobilizedBody's oldest ancestor other than Ground, or return Ground if this MobilizedBody is Ground. More...

const SimbodyMatterSubsystem &	getMatterSubsystem () const
	Obtain a reference to the SimbodyMatterSubsystem which contains this MobilizedBody. More...

SimbodyMatterSubsystem &	updMatterSubsystem ()
	Obtain a writable reference to the SimbodyMatterSubsystem which contains this MobilizedBody. More...

bool	isInSubsystem () const
	Determine whether the current MobilizedBody object is owned by a matter subsystem. More...

bool	isInSameSubsystem (const MobilizedBody &mobod) const
	Determine whether a given MobilizedBody `mobod` is in the same matter subsystem as the current body. More...

bool	isSameMobilizedBody (const MobilizedBody &mobod) const
	Determine whether a given MobilizedBody `mobod` is the same MobilizedBody as this one. More...

bool	isGround () const
	Determine whether this body is Ground, meaning that it is actually body 0 of some matter subsytem, not just that its body type is Ground. More...

int	getLevelInMultibodyTree () const
	Return this body's level in the tree of bodies, starting with ground at 0, bodies directly connected to ground at 1, bodies directly connected to those at 2, etc. More...

MobilizedBody &	cloneForNewParent (MobilizedBody &parent) const
	Create a new MobilizedBody which is identical to this one, except that it has a different parent (and consequently might belong to a different MultibodySystem). More...

Real	getOneFromQPartition (const State &state, int which, const Vector &qlike) const
	This utility selects one of the q's (generalized coordinates) associated with this mobilizer from a supplied "q-like" Vector, meaning a Vector which is the same length as the Vector of q's for the containing matter subsystem. More...

Real &	updOneFromQPartition (const State &state, int which, Vector &qlike) const
	This utility returns a writable reference to one of the q's (generalized coordinates) associated with this mobilizer from a supplied "q-like" Vector, meaning a Vector which is the same length as the Vector of q's for the containing matter subsystem. More...

Real	getOneFromUPartition (const State &state, int which, const Vector &ulike) const
	This utility selects one of the u's (generalized speeds) associated with this mobilizer from a supplied "u-like" Vector, meaning a Vector which is the same length as the Vector of u's for the containing matter subsystem. More...

Real &	updOneFromUPartition (const State &state, int which, Vector &ulike) const
	This utility returns a writable reference to one of the u's (generalized speeds) associated with this mobilizer from a supplied "u-like" Vector, meaning a Vector which is the same length as the Vector of u's for the containing matter subsystem. More...

void	applyOneMobilityForce (const State &state, int which, Real f, Vector &mobilityForces) const
	This utility adds in the supplied generalized force `f` (a scalar) to the appropriate slot of the supplied `mobilityForces` Vector, which is a "u-like" Vector. More...

void	convertQForceToUForce (const State &state, const Array_< Real, MobilizerQIndex > &fq, Array_< Real, MobilizerUIndex > &fu) const
	Given a generalized force in the q-space of this mobilizer, convert it to the equivalent generalized mobility force (u-space force). More...

void	applyBodyForce (const State &state, const SpatialVec &spatialForceInG, Vector_< SpatialVec > &bodyForcesInG) const
	This utility adds in the supplied spatial force `spatialForceInG` (consisting of a torque vector, and a force vector to be applied at the current body's origin) to the appropriate slot of the supplied `bodyForcesInG` Vector. More...

void	applyBodyTorque (const State &state, const Vec3 &torqueInG, Vector_< SpatialVec > &bodyForcesInG) const
	This utility adds in the supplied pure torque `torqueInG` to the appropriate slot of the supplied `bodyForcesInG` Vector. More...

void	applyForceToBodyPoint (const State &state, const Vec3 &pointInB, const Vec3 &forceInG, Vector_< SpatialVec > &bodyForcesInG) const
	This utility adds in the supplied force `forceInG` applied at a point `pointInB` to the appropriate slot of the supplied `bodyForcesInG` Vector. More...

Public Member Functions inherited from SimTK::PIMPLHandle< MobilizedBody, MobilizedBodyImpl, true >
bool	isEmptyHandle () const
	Returns true if this handle is empty, that is, does not refer to any implementation object. More...

bool	isOwnerHandle () const
	Returns true if this handle is the owner of the implementation object to which it refers. More...

bool	isSameHandle (const MobilizedBody &other) const
	Determine whether the supplied handle is the same object as "this" PIMPLHandle. More...

void	disown (MobilizedBody &newOwner)
	Give up ownership of the implementation to an empty handle. More...

PIMPLHandle &	referenceAssign (const MobilizedBody &source)
	"Copy" assignment but with shallow (pointer) semantics. More...

PIMPLHandle &	copyAssign (const MobilizedBody &source)
	This is real copy assignment, with ordinary C++ object ("value") semantics. More...

void	clearHandle ()
	Make this an empty handle, deleting the implementation object if this handle is the owner of it. More...

const MobilizedBodyImpl &	getImpl () const
	Get a const reference to the implementation associated with this Handle. More...

MobilizedBodyImpl &	updImpl ()
	Get a writable reference to the implementation associated with this Handle. More...

int	getImplHandleCount () const
	Return the number of handles the implementation believes are referencing it. More...

Related Functions
(Note that these are not member functions.)
typedef MobilizedBody	Mobod
	Mobod is the approved abbreviation for MobilizedBody. Feel free to use it if you get tired of typing or seeing the full name. More...

Additional Inherited Members
Protected Member Functions inherited from SimTK::PIMPLHandle< MobilizedBody, MobilizedBodyImpl, true >
	PIMPLHandle ()
	The default constructor makes this an empty handle. More...

	PIMPLHandle (MobilizedBodyImpl *p)
	This provides consruction of a handle referencing an existing implementation object. More...

	PIMPLHandle (const PIMPLHandle &source)
	The copy constructor makes either a deep (value) or shallow (reference) copy of the supplied source PIMPL object, based on whether this is a "pointer semantics" (PTR=true) or "object (value) semantics" (PTR=false, default) class. More...

	~PIMPLHandle ()
	Note that the destructor is non-virtual. More...

PIMPLHandle &	operator= (const PIMPLHandle &source)
	Copy assignment makes the current handle either a deep (value) or shallow (reference) copy of the supplied source PIMPL object, based on whether this is a "pointer sematics" (PTR=true) or "object (value) semantics" (PTR=false, default) class. More...

void	setImpl (MobilizedBodyImpl *p)
	Set the implementation for this empty handle. More...

bool	hasSameImplementation (const MobilizedBody &other) const
	Determine whether the supplied handle is a reference to the same implementation object as is referenced by "this" PIMPLHandle. More...

Detailed Description

A MobilizedBody is Simbody's fundamental body-and-joint object used to parameterize a system's motion by constructing a multibody tree containing each body and its unique "mobilizer" (internal coordinate joint).

A MobilizedBody connects a new body (the "child", "outboard", or "successor" body) with a mobilizer and a reference frame to an existing MobilizedBody (the "parent", "inboard", or "predecessor" body) that is already part of a SimbodyMatterSubsystem. In the topology of the multibody tree, the parent mobilized body is always closer to Ground ("inboard") than is the child.

This is the base class for all MobilizedBody classes, which include a body and a particular kind of mobilizer. Each built-in MobilizedBody type is a local subclass within MobilizedBody, so the built-ins have names like MobilizedBody::Pin. All concrete MobilizedBody classes, including the built-ins, are derived from MobilizedBody. There is a MobilizedBody::Custom class available for defining your own mobilizer types.

Normally, a MobilizedBody's motion is unknown and Simbody calculates it using forward dynamics where the motion results from external or internal forces. However, a MobilizedBody may be locked or controlled by an associated Motion object which defines how it is to move; those are inverse dynamics conditions in which the motion is known but the generalized forces required to produce that motion are to be determined. In general a system may contain a mix of forward- and inverse-dynamics mobilizers, and mobilizers may be switched between forward and inverse dynamics during simulations.

The MobilizedBody class supports a large number of methods useful for obtaining and modifying body-specific and mobilizer-specific information and for performing useful computations. These are organized in three sets:

State Access
Basic Operators
High Level Operators

State Access methods simply extract already-calculated data from the State or State Cache, or set state values. They involve no additional computation, have names beginning with "get" and "upd" (update) and return references to the requested quantities rather than calculated values. We divide these into routines which deal with bodies and routines which deal with mobilizers and mobilities.

Basic Operators use State Access methods to compute basic quantities which cannot be precomputed, such as the velocity of an arbitrary point, using an inline combination of basic floating point operations which can be reliably determined at compile time. These have names beginning with "find" or a more specific verb, as a reminder that they do not require a great deal of computation.

High Level Operators combine responses and basic operators with run-time tests to calculate more complex quantities, with more complicated implementations that can exploit special cases at run time. These begin with "calc" (calculate) as a reminder that they may involve substantial run time computation.

There is also a set of methods used for construction, and miscellaneous utilities.

Mobilizer Terminology and Notation

Refer to the figure below for the terminology we use when discussing mobilizers and mobilized bodies.

Terminology and notation for mobilized bodies

The figure shows the coordinate frames used in describing the mobility of MobilizedBody B with respect to its inboard parent body P. Everything blue in the figure is associated with B. The origin point O of each frame is labeled. A new MobilizedBody with body frame B is added to the multibody tree by choosing a parent body P that is already present in the tree. There are two frames associated with the mobilizer: the "fixed" frame F that is attached to the parent, and the "moving" frame M that is attached to the new body B. Frame F is specified by giving its transform X_PF relative to the P frame. Frame M is specified by giving its transform X_BM relative to the B frame. At run time the transform X_FM between the two mobilizer frames represents translation and rotation of the mobilizer. That motion is parameterized via generalized coordinates q and generalized speeds u, the specific meaning of which is a unique property of each type of mobilizer.

In the API below, we'll refer to the current ("this") MobilizedBody as "body B". It is the "object" or "main" body with which we are concerned. Often there will be another body mentioned in the argument list as a target for some conversion. That "another" body will be called "body A". The Ground body is abbreviated "G".

We use Fo to mean "the origin of frame F", Bc is "the mass center of body B". R_AF is the rotation matrix giving frame F's orientation in frame A, such that a vector v expressed in F is reexpressed in A by v_A = R_AF*v_F. X_AF is the spatial transform giving frame F's origin location and orientation in frame A, such that a point P whose location is measured from F's origin Fo and expressed in F by position vector p_FP (or more explicitly p_FoP) is remeasured from frame A's origin Ao and reexpressed in A via p_AP = X_AF*p_FP, where p_AP==p_AoP.

Theory

For the mathematical and computational theory behind Simbody's mobilizers, see

the paper Seth, A.; Sherman, M.A.; Eastman, P.; Delp, S.L. "Minimal formulation of joint motion for biomechanisms" Nonlinear Dynamics 62:291-303 (2010), or
the Simbody Theory Manual.

Member Typedef Documentation

typedef Pin SimTK::MobilizedBody::Torsion

Synonym for Pin mobilizer.

typedef Pin SimTK::MobilizedBody::Revolute

Synonym for Pin mobilizer.

typedef Slider SimTK::MobilizedBody::Prismatic

Synonym for Slider mobilizer.

typedef Translation SimTK::MobilizedBody::Cartesian

Synonym for Translation mobilizer.

typedef Translation SimTK::MobilizedBody::CartesianCoords

Synonym for Translation mobilizer.

typedef BendStretch SimTK::MobilizedBody::PolarCoords

Synonym for BendStretch mobilizer.

typedef Ball SimTK::MobilizedBody::Orientation

Synonym for Ball mobilizer.

typedef Ball SimTK::MobilizedBody::Spherical

Synonym for Ball mobilizer.

Member Enumeration Documentation

enum SimTK::MobilizedBody::Direction

Constructors can take an argument of this type to indicate that the mobilizer is being defined in the reverse direction, meaning from the outboard (child) body to the inboard (parent) body.

That means that the mobilizer coordinates and speeds will be defined as though the tree had been built in the opposite direction. It does not actually affect which body is the inboard one and which is the outboard; it just affects the definitions of the generalized coordinates q and speeds u that parameterize the motion of the outboard body with respect to the inboard one. This is a topological setting and can't be changed dynamically.

Enumerator
Forward	Use default definitions for q and u (inboard to outboard).
Reverse	Define q and u in the reverse order (outboard to inboard).

Constructor & Destructor Documentation

SimTK::MobilizedBody::MobilizedBody ( )

inline

The default constructor provides an empty MobilizedBody handle that can be assigned to reference any type of MobilizedBody.

SimTK::MobilizedBody::MobilizedBody ( MobilizedBodyImpl * r )

explicit

Internal use only.

Member Function Documentation

void SimTK::MobilizedBody::lock	(	State &	state,
		Motion::Level	level = `Motion::Position`
	)		const

Lock this mobilizer's position or velocity at its current value, or lock the acceleration to zero, depending on the level parameter.

The prescribed position or velocity is taken from state and recorded. If the lock is at the position (q) level then the generalized speeds u for this mobilizer are set to zero in the state. If the mobilizer was already locked, the new lock specification overrides it. The state must already have been realized to at least Stage::Model and will be lowered to Stage::Model on return since a lock is an Instance-stage change.

void SimTK::MobilizedBody::lockAt	(	State &	state,
		Real	value,
		Motion::Level	level = `Motion::Position`
	)		const

Lock this mobilizer's q, u, or udot to the given scalar value, depending on level.

When locking at the position level (the default), this mobilizer's q in state is set to value, and u in state is set to zero. When locking at velocity level, this mobilizer's u in state is set to value but the q is left unchanged. This signature of lockAt(), taking value as a scalar, is only permitted for mobilizers that have just a single q and u, such as a Pin or Slider mobilizer. See the other signatures of lockAt() for multi-coordinate mobilizers.

void SimTK::MobilizedBody::lockAt	(	State &	state,
		const Vector &	value,
		Motion::Level	level = `Motion::Position`
	)		const

Lock this mobilizer's q, u, or udot to the given Vector value, depending on level.

When locking at the position level (the default), this mobilizer's q's in state is set to value, and its u's in state are set to zero. When locking at velocity level, this mobilizer's u's in state are set to value but its q's are left unchanged. The Vector must be the expected length, either nq=getNumQ() for the default Motion::Position level, or nu=getNumU() for Motion::Velocity or Motion::Acceleration levels.

See Also: getNumQ(), getNumU()

template<int N>

void SimTK::MobilizedBody::lockAt	(	State &	state,
		const Vec< N > &	value,
		Motion::Level	level = `Motion::Position`
	)		const

Lock this mobilizer's q, u, or udot to the given Vec<N> value, depending on the level.

When locking at the position level (the default), this mobilizer's q's in state is set to value, and its u's in state are set to zero. When locking at velocity level, this mobilizer's u's in state are set to value but its q's are left unchanged. The size N of the given Vec must match the expected length, either nq=getNumQ() for the default Motion::Position level, or nu=getNumU() for Motion::Velocity or Motion::Acceleration levels.

See Also: getNumQ(), getNumU()

void SimTK::MobilizedBody::unlock ( State & state ) const

Unlock this mobilizer, returning it to its normal behavior which may be free motion or may be controlled by a Motion object.

If the mobilizer is already unlocked nothing happens.

bool SimTK::MobilizedBody::isLocked ( const State & state ) const

inline

Check whether this mobilizer is currently locked in the given state.

Motion::Level SimTK::MobilizedBody::getLockLevel ( const State & state ) const

Returns the lock level if the mobilizer is locked in the given state, otherwise Motion::NoLevel.

Vector SimTK::MobilizedBody::getLockValueAsVector ( const State & state ) const

Return the q, u, or udot value at which this mobilizer is locked, depending on the lock level, as a Vector of the appropriate length.

If the mobilizer is not currently locked, a zero-length Vector is returned.

MobilizedBody& SimTK::MobilizedBody::lockByDefault ( Motion::Level level = Motion::Position )

Change whether this mobilizer is initially locked.

On construction the mobilizer is unlocked by default; you can change that here. To respecify that the motion is unlocked, use Motion::NoLevel as the level. This is a topological change; you'll have to call realizeTopology() again and get a new State if you call this method. If the default lock is at the position or velocity level, the required q or u value is recorded at the time a state is realized to Stage::Model. A default Motion::Acceleration lock always prescribes the accelerations udot to zero.

bool SimTK::MobilizedBody::isLockedByDefault ( ) const

inline

Check whether this mobilizer is to be locked in the default state.

Motion::Level SimTK::MobilizedBody::getLockByDefaultLevel ( ) const

Returns the level at which the mobilizer is locked by default, if it is locked by default, otherwise Motion::NoLevel.

const Transform& SimTK::MobilizedBody::getBodyTransform ( const State & state ) const

Extract from the state cache the already-calculated spatial configuration X_GB of body B's body frame, measured with respect to the Ground frame and expressed in the Ground frame.

That is, we return the location of the body frame's origin, and the orientation of its x, y, and z axes, as the Transform X_GB. This notation is intended to convey unambiguously the sense of this transform, which is as follows: if you have a station (body fixed point) S on body B, represented by position vector p_BS (a.k.a. p_BoS) from the origin Bo of B to the point S and expressed in the B frame, then p_GS=X_GB*p_BS where p_GS (== p_GoS) is the position vector from the Ground origin Go to the point in space currently coincident with S and expressed in the Ground frame. The inverse transformation is obtained using the "~" operator where ~X_GB=X_BG, so that p_BS = ~X_GB*p_GS. This response is available at Position stage.

const Rotation& SimTK::MobilizedBody::getBodyRotation ( const State & state ) const

inline

Extract from the state cache the already-calculated spatial orientation R_GB of body B's body frame x, y, and z axes expressed in the Ground frame, as the Rotation matrix R_GB.

The sense of this rotation matrix is such that if you have a vector v fixed on body B, represented by the vector v_B expressed in the B frame, then v_G=R_GB*v_B where v_G is the same vector but re-expressed in the Ground frame. The inverse transformation is obtained using the "~" operator where ~R_GB=R_BG, so that v_B = ~R_GB*v_G. This response is available at Position stage.

const Vec3& SimTK::MobilizedBody::getBodyOriginLocation ( const State & state ) const

inline

Extract from the state cache the already-calculated spatial location of body B's body frame origin Bo, measured from the Ground origin Go and expressed in the Ground frame, as the position vector p_GB (== p_GoBo).

This response is available at Position stage.

const Transform& SimTK::MobilizedBody::getMobilizerTransform ( const State & state ) const

At stage Position or higher, return the cross-mobilizer transform X_FM, the body's inboard mobilizer frame M measured and expressed in the parent body's corresponding outboard frame F.

const SpatialVec& SimTK::MobilizedBody::getBodyVelocity ( const State & state ) const

Extract from the state cache the already-calculated spatial velocity V_GB of this body's reference frame B, measured with respect to the Ground frame and expressed in the Ground frame.

That is, we return the linear velocity v_GB of the body frame's origin in G, and the body's angular velocity w_GB as the spatial velocity vector V_GB = {w_GB, v_GB}. This response is available at Velocity stage.

const Vec3& SimTK::MobilizedBody::getBodyAngularVelocity ( const State & state ) const

inline

Extract from the state cache the already-calculated inertial angular velocity vector w_GB of this body B, measured with respect to the Ground frame and expressed in the Ground frame.

This response is available at Velocity stage.

const Vec3& SimTK::MobilizedBody::getBodyOriginVelocity ( const State & state ) const

inline

Extract from the state cache the already-calculated inertial linear velocity vector v_GB (more explicitly, v_GBo) of this body B's origin point Bo, measured with respect to the Ground frame and expressed in the Ground frame.

This response is available at Velocity stage.

const SpatialVec& SimTK::MobilizedBody::getMobilizerVelocity ( const State & state ) const

At stage Velocity or higher, return the cross-mobilizer velocity V_FM, the relative velocity of this body's "moving" mobilizer frame M in the parent body's corresponding "fixed" frame F, measured and expressed in F.

Note that this isn't the usual spatial velocity since it isn't expressed in G.

const SpatialVec& SimTK::MobilizedBody::getBodyAcceleration ( const State & state ) const

Extract from the state cache the already-calculated spatial acceleration A_GB of this body's reference frame B, measured with respect to the Ground frame and expressed in the Ground frame.

That is, we return the linear acceleration a_GB of the body frame's origin in G, and the body's angular acceleration b_GB as the spatial acceleration vector A_GB = {b_GB, a_GB}. This response is available at Acceleration stage.

const Vec3& SimTK::MobilizedBody::getBodyAngularAcceleration ( const State & state ) const

inline

Extract from the state cache the already-calculated inertial angular acceleration vector b_GB of this body B, measured with respect to the Ground frame and expressed in the Ground frame.

This response is available at Acceleration stage.

const Vec3& SimTK::MobilizedBody::getBodyOriginAcceleration ( const State & state ) const

inline

Extract from the state cache the already-calculated inertial linear acceleration vector a_GB (more explicitly, a_GBo) of this body B's origin point Bo, measured with respect to the Ground frame and expressed in the Ground frame.

This response is available at Acceleration stage.

const SpatialVec& SimTK::MobilizedBody::getMobilizerAcceleration ( const State & state ) const

inline

TODO: Not implemented yet – any volunteers? At stage Acceleration, return the cross-mobilizer acceleration A_FM, the relative acceleration of body B's "moving" mobilizer frame M in the parent body's corresponding "fixed" frame F, measured and expressed in F.

Note that this isn't the usual spatial acceleration since it isn't expressed in G.

const MassProperties& SimTK::MobilizedBody::getBodyMassProperties ( const State & state ) const

Return a reference to this body's mass properties in the State cache.

The State must have been realized to Stage::Instance or higher.

const SpatialInertia& SimTK::MobilizedBody::getBodySpatialInertiaInGround ( const State & state ) const

Return a reference to the already-calculated SpatialInertia of this body, taken about the body's origin (not its mass center), and expressed in the Ground frame.

The State must have been realized to Stage::Position or higher.

Real SimTK::MobilizedBody::getBodyMass ( const State & state ) const

inline

Return the mass of this body.

The State must have been realized to Stage::Instance.

const Vec3& SimTK::MobilizedBody::getBodyMassCenterStation ( const State & state ) const

inline

Return this body's center of mass station (i.e., the vector fixed in the body, going from body origin to body mass center, expressed in the body frame.) The State must have been realized to Stage::Instance or higher.

const UnitInertia& SimTK::MobilizedBody::getBodyUnitInertiaAboutBodyOrigin ( const State & state ) const

inline

Return a reference to this body's unit inertia matrix in the State cache, taken about the body origin and expressed in the body frame.

The State must have been realized to Stage::Instance or higher.

const Transform& SimTK::MobilizedBody::getInboardFrame ( const State & state ) const

Return a reference to this mobilizer's frame F fixed on the parent body P, as the fixed Transform from P's body frame to the frame F fixed to P.

If this frame is changeable, the result comes from the State cache, otherwise it is from the MobilizedBody object itself. The State must have been realized to Stage::Instance or higher.

const Transform& SimTK::MobilizedBody::getOutboardFrame ( const State & state ) const

Return a reference to this MobilizedBody's mobilizer frame M, as the fixed Transform from this body B's frame to the frame M fixed on B.

If this frame is changeable, the result comes from the State cache, otherwise it is from the MobilizedBody object itself. The State must have been realized to Stage::Instance or higher.

void SimTK::MobilizedBody::setInboardFrame	(	State &	state,
		const Transform &	X_PF
	)		const

TODO: not implemented yet.

Set the location and orientation of the inboard (parent) mobilizer frame F, fixed to this mobilizer's parent body P.

See Also: setDefaultInboardFrame()

void SimTK::MobilizedBody::setOutboardFrame	(	State &	state,
		const Transform &	X_BM
	)		const

TODO: not implemented yet.

Set the location and orientation of the outboard mobilizer frame M, fixed to this body B.

See Also: setDefaultOutboardFrame()

int SimTK::MobilizedBody::getNumQ ( const State & state ) const

Return the number of generalized coordinates q currently in use by this mobilizer.

State must have been realized to Stage::Model.

int SimTK::MobilizedBody::getNumU ( const State & state ) const

Return the number of generalized speeds u currently in use by this mobilizer.

State must have been realized to Stage::Model.

QIndex SimTK::MobilizedBody::getFirstQIndex ( const State & state ) const

Return the global QIndex of the first q for this mobilizer; all the q's range from getFirstQIndex() to QIndex(getFirstQIndex()+getNumQ()-1).

UIndex SimTK::MobilizedBody::getFirstUIndex ( const State & state ) const

Return the global UIndex of the first u for this mobilizer; all the u's range from getFirstUIndex() to UIndex(getFirstUIndex()+getNumU()-1).

Motion::Method SimTK::MobilizedBody::getQMotionMethod ( const State & state ) const

Determine how generalized coordinate q values are being determined.

Parameters

[in] state Must be realized to Instance stage.

Motion::Method SimTK::MobilizedBody::getUMotionMethod ( const State & state ) const

Determine how generalized speed u values are being determined.

Parameters

[in] state Must be realized to Instance stage.

Motion::Method SimTK::MobilizedBody::getUDotMotionMethod ( const State & state ) const

Determine how generalized acceleration udot values are being determined.

Parameters

[in] state Must be realized to Instance stage.

Real SimTK::MobilizedBody::getOneQ	(	const State &	state,
		int	which
	)		const

Return one of the generalized coordinates q from this mobilizer's partition of the matter subsystem's full q vector in the State.

The particular coordinate is selected using the which parameter, numbering from zero to getNumQ()-1.

Real SimTK::MobilizedBody::getOneU	(	const State &	state,
		int	which
	)		const

Return one of the generalized speeds u from this mobilizer's partition of the matter subsystem's full u vector in the State.

The particular coordinate is selected using the which parameter, numbering from zero to getNumU()-1.

Vector SimTK::MobilizedBody::getQAsVector ( const State & state ) const

Return as a Vector of length getNumQ() all the generalized coordinates q currently in use by this mobilizer, from this mobilizer's partion in the matter subsystem's full q vector in the State.

Vector SimTK::MobilizedBody::getUAsVector ( const State & state ) const

Return as a Vector of length getNumU() all the generalized speeds u currently in use by this mobilizer, from this mobilizer's partion in the matter subsystem's full u vector in the State.

Real SimTK::MobilizedBody::getOneQDot	(	const State &	state,
		int	which
	)		const

Return one of the generalized coordinate derivatives qdot from this mobilizer's partition of the matter subsystem's full qdot vector in the State cache.

The particular coordinate is selected using the which parameter, numbering from zero to getNumQ()-1.

Vector SimTK::MobilizedBody::getQDotAsVector ( const State & state ) const

Return as a Vector of length getNumQ() all the generalized coordinate derivatives qdot currently in use by this mobilizer, from this mobilizer's partition in the matter subsystem's full qdot vector in the State cache.

Real SimTK::MobilizedBody::getOneUDot	(	const State &	state,
		int	which
	)		const

Return one of the generalized accelerations udot from this mobilizer's partition of the matter subsystem's full udot vector in the State cache.

The particular coordinate is selected using the which parameter, numbering from zero to getNumU()-1.

Real SimTK::MobilizedBody::getOneQDotDot	(	const State &	state,
		int	which
	)		const

Return one of the generalized coordinate second derivatives qdotdot from this mobilizer's partition of the matter subsystem's full qdotdot vector in the State cache.

The particular coordinate is selected using the which parameter, numbering from zero to getNumQ()-1.

Vector SimTK::MobilizedBody::getUDotAsVector ( const State & state ) const

Return as a Vector of length getNumU() all the generalized accelerations udot currently in use by this mobilizer, from this mobilizer's partion in the matter subsystem's full udot vector in the State cache.

Vector SimTK::MobilizedBody::getQDotDotAsVector ( const State & state ) const

Return as a Vector of length getNumQ() all the generalized coordinate second derivatives qdotdot currently in use by this mobilizer, from this mobilizer's partion in the matter subsystem's full qdotdot vector in the State cache.

Vector SimTK::MobilizedBody::getTauAsVector ( const State & state ) const

Return the generalized forces tau resulting from prescribed (known) acceleration, corresponding to each of this mobilizer's mobilities, as a Vector of length nu=getNumU().

If this mobilizer has prescribed accelerations udot due to an active lock or Motion object, the set of generalized forces tau that must be added in order to produce those accelerations is calculated at Acceleration stage. There is one scalar tau per mobility and they can be returned individually or as a Vector. The return value is zero if this mobilizer is currently free.

Real SimTK::MobilizedBody::getOneTau	(	const State &	state,
		MobilizerUIndex	which
	)		const

Return one of the tau forces resulting from prescribed (known) acceleration, corresponding to one of this mobilizer's mobilities as selected here using the which parameter, numbered from zero to getNumU()-1.

See Also: getTauAsVector() for more information

void SimTK::MobilizedBody::setOneQ	(	State &	state,
		int	which,
		Real	v
	)		const

Set one of the generalized coordinates q to value v, in this mobilizer's partition of the matter subsystem's full q vector in the State.

The particular coordinate is selected using the which parameter, numbering from zero to getNumQ()-1.

void SimTK::MobilizedBody::setOneU	(	State &	state,
		int	which,
		Real	v
	)		const

Set one of the generalized speeds u to value v, in this mobilizer's partition of the matter subsystem's full u vector in the State.

The particular coordinate is selected using the which parameter, numbering from zero to getNumU()-1.

void SimTK::MobilizedBody::setQFromVector	(	State &	state,
		const Vector &	v
	)		const

Set all of the generalized coordinates q to value v (a Vector of length getNumQ()), in this mobilizer's partition of the matter subsystem's full q vector in the State.

void SimTK::MobilizedBody::setUFromVector	(	State &	state,
		const Vector &	v
	)		const

Set all of the generalized speeds u to value v (a Vector of length getNumU()), in this mobilizer's partition of the matter subsystem's full u vector in the State.

void SimTK::MobilizedBody::setQToFitTransform	(	State &	state,
		const Transform &	X_FM
	)		const

Adjust this mobilizer's q's to best approximate the supplied Transform which requests a particular relative orientation and translation between the F "fixed" frame and M "moving" frame connected by this mobilizer.

This set of methods sets the generalized coordinates, or speeds (state variables) for just the mobilizer associated with this MobilizedBody (ignoring all other mobilizers and constraints), without requiring knowledge of the meanings of the individual state variables. The idea here is to provide a physically-meaningful quantity relating the mobilizer's inboard and outboard frames, and then ask the mobilizer to set its state variables to reproduce that quantity to the extent it can.

These methods can be called in Stage::Model, however the routines may consult the current values of the state variables in some cases, so you must make sure they have been set to reasonable, or at least innocuous values (zero will work). In no circumstance will any of these methods look at any state variables that belong to another mobilizer; they are limited to working locally with just the current mobilizer.

Routines which specify only translation (linear velocity) may use rotational coordinates to help satisfy the translation requirement. An alternate "Only" method is available to forbid modification of purely rotational coordinates in that case. When a mobilizer uses state variables which have combined rotational and translational character (e.g. a screw joint) consult the documentation for the derived MobilizedBody class to find out how that mobilizer responds to these routines.

There is no guarantee that the desired physical quantity will be achieved by these routines; you can check on return if you're worried. Individual mobilizers make specific promises about what they will do; consult the documentation. These routines do not throw exceptions even for absurd requests like specifying a rotation for a sliding mobilizer. Nothing happens if there are no mobilities here, i.e. Ground or a Weld mobilizer.

void SimTK::MobilizedBody::setQToFitRotation	(	State &	state,
		const Rotation &	R_FM
	)		const

Adjust this mobilizer's q's to best approximate the supplied Rotation matrix which requests a particular relative orientation between the "fixed" frame F and "moving" frame M connected by this mobilizer.

See Also: setQToFitTransform()

void SimTK::MobilizedBody::setQToFitTranslation	(	State &	state,
		const Vec3 &	p_FM
	)		const

Adjust this mobilizer's q's to best approximate the supplied position vector which requests a particular offset between the origins of the F "fixed" frame and M "moving" frame connected by this mobilizer, with any q's (rotational or translational) being modified if doing so helps satisfy the request.

See Also: setQToFitTransform()

void SimTK::MobilizedBody::setUToFitVelocity	(	State &	state,
		const SpatialVec &	V_FM
	)		const

Adjust this mobilizer's u's (generalized speeds) to best approximate the supplied spatial velocity V_FM which requests the relative angular and linear velocity between the "fixed" and "moving" frames connected by this mobilizer.

Routines which affect generalized speeds u depend on the generalized coordinates q already having been set; they never change these coordinates.

See Also: setQToFitTransform()

void SimTK::MobilizedBody::setUToFitAngularVelocity	(	State &	state,
		const Vec3 &	w_FM
	)		const

Adjust this mobilizer's u's (generalized speeds) to best approximate the supplied angular velocity w_FM which requests a particular relative angular between the "fixed" and "moving" frames connected by this mobilizer.

See Also: setQToFitTransform(), setUToFitVelocity()

void SimTK::MobilizedBody::setUToFitLinearVelocity	(	State &	state,
		const Vec3 &	v_FM
	)		const

Adjust any of this mobilizer's u's (generalized speeds) to best approximate the supplied linear velocity v_FM which requests a particular velocity for the "moving" frame M origin in the "fixed" frame F on the parent where these are the frames connected by this mobilizer.

See Also: setQToFitTransform(), setUToFitVelocity()

SpatialVec SimTK::MobilizedBody::getHCol	(	const State &	state,
		MobilizerUIndex	ux
	)		const

Expert use only: obtain a column of the hinge matrix H corresponding to one of this mobilizer's mobilities (actually a column of H_PB_G; what Jain calls H* and Schwieters calls H^T).

This is the matrix that maps generalized speeds u to the cross-body relative spatial velocity V_PB_G via V_PB_G=H*u. Note that although H relates child body B to parent body B, it is expressed in the ground frame G so the resulting cross-body velocity of B in P is also expressed in G. The supplied state must have been realized through Position stage because H varies with this mobilizer's generalized coordinates q.

See Also: getH_FMCol()

SpatialVec SimTK::MobilizedBody::getH_FMCol	(	const State &	state,
		MobilizerUIndex	ux
	)		const

Expert use only: obtain a column of the mobilizer-local hinge matrix H_FM which maps generalized speeds u to cross-mobilizer spatial velocity V_FM via V_FM=H_FM*u.

Note that H and V here are expressed in the parent body's (inboard) frame F. The supplied state must have been realized through Position stage because H varies with this mobilizer's generalized coordinates q.

See Also: getHCol()

Transform SimTK::MobilizedBody::findBodyTransformInAnotherBody	(	const State &	state,
		const MobilizedBody &	inBodyA
	)		const

inline

Return X_AB, the spatial transform giving this body B's frame in body A's frame.

Cost is 63 flops. If you know that one of the bodies is Ground, use the 0-cost response getBodyTransform() instead of this operators. This operator is available in Position stage.

See Also: getBodyTransform()

Rotation SimTK::MobilizedBody::findBodyRotationInAnotherBody	(	const State &	state,
		const MobilizedBody &	inBodyA
	)		const

inline

Return R_AB, the rotation matrix giving this body B's axes in body A's frame.

Cost is 45 flops. If you know that one of the bodies is Ground, use the 0-cost response getBodyRotation() instead of this operators. This operator is available in Position stage.

See Also: getBodyRotation()

Vec3 SimTK::MobilizedBody::findBodyOriginLocationInAnotherBody	(	const State &	state,
		const MobilizedBody &	toBodyA
	)		const

inline

Return the station on another body A (that is, a point measured and expressed in A) that is currently coincident in space with the origin Bo of this body B.

Cost is 18 flops. This operator is available at Position stage. Note: "findBodyOriginLocationInGround" doesn't exist because it would be the same as the no-cost response method getBodyOriginLocation().

See Also: getBodyOriginLocation()

SpatialVec SimTK::MobilizedBody::findBodyVelocityInAnotherBody	(	const State &	state,
		const MobilizedBody &	inBodyA
	)		const

inline

Return the angular and linear velocity of body B's frame in body A's frame, expressed in body A, and arranged as a SpatialVec.

Cost is 51 flops. If you know inBodyA is Ground, don't use this routine; use the response method getBodyVelocity() which is free. This operator is available in Velocity stage.

See Also: getBodyVelocity()

Vec3 SimTK::MobilizedBody::findBodyAngularVelocityInAnotherBody	(	const State &	state,
		const MobilizedBody &	inBodyA
	)		const

inline

Return the angular velocity w_AB of body B's frame in body A's frame, expressed in body A.

Cost is 18 flops. If you know inBodyA is Ground, don't use this routine; use the response method getBodyAngularVelocity() which is free. This operator is available in Velocity stage.

See Also: getBodyAngularVelocity()

Vec3 SimTK::MobilizedBody::findBodyOriginVelocityInAnotherBody	(	const State &	state,
		const MobilizedBody &	inBodyA
	)		const

inline

Return the velocity of body B's origin point in body A's frame, expressed in body A.

Cost is 51 flops. If you know inBodyA is Ground, don't use this routine; use the response method getBodyOriginVelocity() which is free. This operator is available in Velocity stage.

See Also: getBodyOriginVelocity()

SpatialVec SimTK::MobilizedBody::findBodyAccelerationInAnotherBody	(	const State &	state,
		const MobilizedBody &	inBodyA
	)		const

inline

Return the angular and linear acceleration of body B's frame in body A's frame, expressed in body A, and arranged as a SpatialVec.

Cost is 105 flops. If you know that inBodyA is Ground, don't use this operator; instead, use the response method getBodyAcceleration() which is free. This operator is available in Acceleration stage.

See Also: getBodyAcceleration()

Vec3 SimTK::MobilizedBody::findBodyAngularAccelerationInAnotherBody	(	const State &	state,
		const MobilizedBody &	inBodyA
	)		const

inline

Return the angular acceleration of body B's frame in body A's frame, expressed in body A.

Cost is 33 flops. If you know inBodyA is Ground, don't use this operator; instead use the response method getBodyAngularAccleration() which is free. This operator is available at AccelerationStage.

See Also: getBodyAngularAcceleration()

Vec3 SimTK::MobilizedBody::findBodyOriginAccelerationInAnotherBody	(	const State &	state,
		const MobilizedBody &	inBodyA
	)		const

inline

Return the acceleration of body B's origin point in body A's frame, expressed in body A.

Cost is 105 flops. If you know that inBodyA is Ground, don't use this operator; instead, use the response method getBodyOriginAcceleration() which is free. This operator is available at Acceleration stage.

See Also: getBodyOriginAcceleration()

SpatialVec SimTK::MobilizedBody::findMobilizerReactionOnBodyAtMInGround ( const State & state ) const

Return the spatial reaction force (moment and force) applied by the mobilizer to body B at the location of the mobilizer frame M (fixed to body B, but not necessarily at the body frame origin), expressed in Ground.

This operator is available at Acceleration stage. Cost is about 120 flops.

See Also: findMobilizerReactionOnParentAtFInGround(); findMobilizerReactionOnBodyAtOriginInGround(); SimTK::SimbodyMatterSubsystem::calcMobilizerReactionForces()

SpatialVec SimTK::MobilizedBody::findMobilizerReactionOnBodyAtOriginInGround ( const State & state ) const

Return the spatial reaction force (moment and force) applied by the mobilizer to body B but shifted to the B frame origin, and expressed in Ground.

This operator is available at Acceleration stage. Cost is about 90 flops.

See Also: findMobilizerReactionOnParentAtOriginInGround(); findMobilizerReactionOnBodyAtMInGround(); SimTK::SimbodyMatterSubsystem::calcMobilizerReactionForces()

SpatialVec SimTK::MobilizedBody::findMobilizerReactionOnParentAtFInGround ( const State & state ) const

Return the spatial reaction force (moment and force) applied by the mobilizer to the parent (inboard) body P at the location of the inboard "fixed" mobilizer frame F (fixed to body P, but not necessarily at the P frame origin), expressed in Ground.

This operator is available at Acceleration stage. Cost is about 140 flops.

See Also: findMobilizerReactionOnBodyAtMInGround(); findMobilizerReactionOnParentAtOriginInGround(); SimTK::SimbodyMatterSubsystem::calcMobilizerReactionForces()

SpatialVec SimTK::MobilizedBody::findMobilizerReactionOnParentAtOriginInGround ( const State & state ) const

Return the spatial reaction force (moment and force) applied by the mobilizer to the parent (inboard) body P at the location of the P frame origin, and expressed in Ground.

This operator is available at Acceleration stage. Cost is about 110 flops.

See Also: findMobilizerReactionOnBodyAtOriginInGround(); findMobilizerReactionOnParentAtFInGround(); SimTK::SimbodyMatterSubsystem::calcMobilizerReactionForces()

Vec3 SimTK::MobilizedBody::findStationLocationInGround	(	const State &	state,
		const Vec3 &	stationOnB
	)		const

inline

Return the Cartesian (ground) location that is currently coincident with a station (point) S fixed on body B.

That is, we return locationInG=X_GB*stationOnB which means the result is measured from the Ground origin and expressed in Ground. In more precise notation, we're calculating p_GS = X_GB * p_BS for position vectors p_GS and p_BS. Cost is 18 flops. This operator is available at Position stage.

Vec3 SimTK::MobilizedBody::findStationLocationInAnotherBody	(	const State &	state,
		const Vec3 &	stationOnB,
		const MobilizedBody &	toBodyA
	)		const

inline

Given a station S on this body B, return the location on another body A which is at the same location in space.

That is, we return locationOnA=X_AB*locationOnB, which means the result is measured from the body A origin and expressed in body A. In more precise notation, we're calculating p_AS = X_AB * p_BS, which we actually calculate as p_AS = X_AG*(X_GB*p_BS). Cost is 36 flops. Note: if you know that one of the bodies is Ground, use one of the routines above which is specialized for Ground to avoid half the work. This operator is available at Position stage or higher.

Vec3 SimTK::MobilizedBody::findStationVelocityInGround	(	const State &	state,
		const Vec3 &	stationOnB
	)		const

inline

Given a station fixed on body B, return its inertial (Cartesian) velocity, that is, its velocity relative to the Ground frame, expressed in the Ground frame.

Cost is 27 flops. If you know the station is the body origin (0,0,0) don't use this routine; use the response getBodyOriginVelocity() which is free. This operator is available at Velocity stage.

See Also: getBodyOriginVelocity()

Vec3 SimTK::MobilizedBody::findStationVelocityInAnotherBody	(	const State &	state,
		const Vec3 &	stationOnBodyB,
		const MobilizedBody &	inBodyA
	)		const

inline

Return the velocity of a station S fixed on body B, in body A's frame, expressed in body A.

Cost is 93 flops. If you know inBodyA is Ground, don't use this operator; instead use the operator findStationVelocityInGround() which is much cheaper. This operator is available in Velocity stage.

See Also: findStationVelocityInGround()

Vec3 SimTK::MobilizedBody::findStationAccelerationInGround	(	const State &	state,
		const Vec3 &	stationOnB
	)		const

inline

Given a station fixed on body B, return its inertial (Cartesian) acceleration, that is, its acceleration relative to the ground frame, expressed in the ground frame.

Cost is 48 flops. If you know the station is the body origin (0,0,0) don't use this routine; use the response getBodyOriginAcceleration() which is free. This operator is available at Acceleration stage.

See Also: getBodyOriginAcceleration()

Vec3 SimTK::MobilizedBody::findStationAccelerationInAnotherBody	(	const State &	state,
		const Vec3 &	stationOnBodyB,
		const MobilizedBody &	inBodyA
	)		const

inline

Return the acceleration of a station S fixed on body B, in another body A's frame, expressed in body A.

Cost is 186 flops. If you know that inBodyA is Ground, don't use this operator; instead, use the operator findStationAccelerationInGround() which is much cheaper. This operator is available in Acceleration stage.

void SimTK::MobilizedBody::findStationLocationAndVelocityInGround	(	const State &	state,
		const Vec3 &	locationOnB,
		Vec3 &	locationOnGround,
		Vec3 &	velocityInGround
	)		const

inline

It is cheaper to calculate a station's ground location and velocity together than to do them separately.

Here we can return them both in 30 flops, vs. 45 to do them in two calls. This operator is available at Velocity stage.

void SimTK::MobilizedBody::findStationLocationVelocityAndAccelerationInGround	(	const State &	state,
		const Vec3 &	locationOnB,
		Vec3 &	locationOnGround,
		Vec3 &	velocityInGround,
		Vec3 &	accelerationInGround
	)		const

inline

It is cheaper to calculate a station's ground location, velocity, and acceleration together than to do them separately.

Here we can return them all in 54 flops, vs. 93 to do them in three calls. This operator is available at Acceleration stage.

Vec3 SimTK::MobilizedBody::findMassCenterLocationInGround ( const State & state ) const

inline

Return the Cartesian (ground) location of this body B's mass center.

Cost is 18 flops. This operator is available at Position stage.

Vec3 SimTK::MobilizedBody::findMassCenterLocationInAnotherBody	(	const State &	state,
		const MobilizedBody &	toBodyA
	)		const

inline

Return the point of another body A that is currently coincident in space with the mass center CB of this body B.

Cost is 36 flops. This operator is available at Position stage.

Vec3 SimTK::MobilizedBody::findStationAtGroundPoint	(	const State &	state,
		const Vec3 &	locationInG
	)		const

inline

Return the station (point) S of this body B that is coincident with the given Ground location.

That is we return locationOnB = X_BG*locationInG, which means the result is measured from the body origin Bo and expressed in the body frame. In more precise notation, we're calculating p_BS = X_BG*p_GS. Cost is 18 flops. This operator is available at Position stage.

Vec3 SimTK::MobilizedBody::findStationAtAnotherBodyStation	(	const State &	state,
		const MobilizedBody &	fromBodyA,
		const Vec3 &	stationOnA
	)		const

inline

Return the station (point) on this body B that is coincident with the given station on another body A.

That is we return stationOnB = X_BA * stationOnA, which means the result is measured from the body origin Bo and expressed in the body frame. Cost is 36 flops. This operator is available at Position stage.

See Also: findStationLocationInAnotherBody()

Vec3 SimTK::MobilizedBody::findStationAtAnotherBodyOrigin	(	const State &	state,
		const MobilizedBody &	fromBodyA
	)		const

inline

Return the station S of this body that is currently coincident in space with the origin Ao of another body A.

Cost is 18 flops. This operator is available at Position stage.

Vec3 SimTK::MobilizedBody::findStationAtAnotherBodyMassCenter	(	const State &	state,
		const MobilizedBody &	fromBodyA
	)		const

inline

Return the station S of this body that is currently coincident in space with the mass center Ac of another body A.

Cost is 36 flops. This operator is available at Position stage.

Transform SimTK::MobilizedBody::findFrameTransformInGround	(	const State &	state,
		const Transform &	frameOnB
	)		const

inline

Return the current Ground-frame pose (position and orientation) of a frame F that is fixed to body B.

That is, we return X_GF=X_GB*X_BF. Cost is 63 flops. This operator is available at Position stage.

SpatialVec SimTK::MobilizedBody::findFrameVelocityInGround	(	const State &	state,
		const Transform &	frameOnB
	)		const

inline

Return the current Ground-frame spatial velocity V_GF (that is, angular and linear velocity) of a frame F that is fixed to body B.

The angular velocity of F is the same as that of B, but the linear velocity is the velocity of F's origin Fo rather than B's origin Bo. This operator is available at Velocity stage. Cost is 27 flops.

SpatialVec SimTK::MobilizedBody::findFrameAccelerationInGround	(	const State &	state,
		const Transform &	frameOnB
	)		const

inline

Return the current Ground-frame spatial acceleration A_GF (that is, angular and linear acceleration) of a frame F that is fixed to body B.

The angular acceleration of F is the same as that of B, but the linear acceleration is the acceleration of F's origin Fo rather than B's origin Bo. This operator is available at Acceleration stage. Cost is 48 flops.

Vec3 SimTK::MobilizedBody::expressVectorInGroundFrame	(	const State &	state,
		const Vec3 &	vectorInB
	)		const

inline

Re-express a vector expressed in this body B's frame into the same vector in G, by applying only a rotation.

That is, we return vectorInG = R_GB * vectorInB. Cost is 15 flops. This operator is available at Position stage.

Vec3 SimTK::MobilizedBody::expressGroundVectorInBodyFrame	(	const State &	state,
		const Vec3 &	vectorInG
	)		const

inline

Re-express a vector expressed in Ground into the same vector expressed in this body B, by applying only rotation.

That is, we return vectorInB = R_BG * vectorInG. Cost is 15 flops. This operator is available at Position stage.

Vec3 SimTK::MobilizedBody::expressVectorInAnotherBodyFrame	(	const State &	state,
		const Vec3 &	vectorInB,
		const MobilizedBody &	inBodyA
	)		const

inline

Re-express a vector expressed in this body B into the same vector expressed in body A, by applying only a rotation.

That is, we return vectorInA = R_AB * vectorInB. Cost is 30 flops. This operator is available at Position stage. Note: if you know one of the bodies is Ground, call one of the specialized methods above to save 15 flops.

MassProperties SimTK::MobilizedBody::expressMassPropertiesInGroundFrame ( const State & state ) const

inline

Re-express this body B's mass properties in Ground by applying only a rotation, not a shift of reference point.

The mass properties remain measured in the body B frame, taken about the body B origin Bo, but are reexpressed in Ground.

MassProperties SimTK::MobilizedBody::expressMassPropertiesInAnotherBodyFrame	(	const State &	state,
		const MobilizedBody &	inBodyA
	)		const

inline

Re-express this body B's mass properties in another body A's frame by applying only a rotation, not a shift of reference point.

The mass properties remain measured in the body B frame, taken about the body B origin Bo, but are reexpressed in A.

SpatialMat SimTK::MobilizedBody::calcBodySpatialInertiaMatrixInGround ( const State & state ) const

inline

Return the mass properties of body B, measured from and about the B origin Bo, but expressed in Ground and then returned as a Spatial Inertia Matrix.

The mass properties are arranged in the SpatialMat like this:

        M=[      I_Bo      crossMat(m*Bc) ]
        [ ~crossMat(m*Bc)   diag(m)     ]

where I_Bo is the inertia taken about the B frame origin Bo, and Bc is the vector p_BoBc from B's origin to its mass center.

The Spatial Inertia Matrix for Ground has infinite mass and inertia, with the cross terms set to zero. That is, it looks like a 6x6 diagonal matrix with Infinity on the diagonals.

Required stage: Stage::Position, unless objectBodyB == GroundIndex

Inertia SimTK::MobilizedBody::calcBodyCentralInertia	(	const State &	state,
		MobilizedBodyIndex	objectBodyB
	)		const

inline

Return the central inertia for body B, that is, the inertia taken about body B's mass center Bc, and expressed in B.

/

Required stage: Stage::Instance

Inertia SimTK::MobilizedBody::calcBodyInertiaAboutAnotherBodyStation	(	const State &	state,
		const MobilizedBody &	inBodyA,
		const Vec3 &	aboutLocationOnBodyA
	)		const

inline

Return the inertia of this body B, taken about an arbitrary point PA of body A, and expressed in body A.

TODO: this needs testing!

SpatialVec SimTK::MobilizedBody::calcBodyMomentumAboutBodyOriginInGround ( const State & state )

inline

Calculate body B's momentum (angular, linear) measured and expressed in Ground, but taken about the body origin Bo.

SpatialVec SimTK::MobilizedBody::calcBodyMomentumAboutBodyMassCenterInGround ( const State & state ) const

inline

Calculate body B's momentum (angular, linear) measured and expressed in Ground, but taken about the body mass center Bc.

Real SimTK::MobilizedBody::calcStationToStationDistance	(	const State &	state,
		const Vec3 &	locationOnBodyB,
		const MobilizedBody &	bodyA,
		const Vec3 &	locationOnBodyA
	)		const

inline

Calculate the distance from a station PB on body B to a station PA on body A.

We are given the location vectors (stations) p_Bo_PB and p_Ao_PA, expressed in their respective frames. We return |p_PB_PA|.

Real SimTK::MobilizedBody::calcStationToStationDistanceTimeDerivative	(	const State &	state,
		const Vec3 &	locationOnBodyB,
		const MobilizedBody &	bodyA,
		const Vec3 &	locationOnBodyA
	)		const

inline

Calculate the time rate of change of distance from a fixed point PB on body B to a fixed point PA on body A.

We are given the location vectors p_Bo_PB and p_Ao_PA, expressed in their respective frames. We return d/dt |p_BoAo|, under the assumption that the time derivatives of the two given vectors in their own frames is zero.

Real SimTK::MobilizedBody::calcStationToStationDistance2ndTimeDerivative	(	const State &	state,
		const Vec3 &	locationOnBodyB,
		const MobilizedBody &	bodyA,
		const Vec3 &	locationOnBodyA
	)		const

inline

Calculate the second time derivative of distance from a fixed point PB on body B to a fixed point PA on body A.

We are given the position vectors (stations) p_Bo_PB and p_Ao_PA, expressed in their respective frames. We return d^2/dt^2 |p_PB_PA|, under the assumption that the time derivatives of the two given vectors in their own frames is zero.

Vec3 SimTK::MobilizedBody::calcBodyMovingPointVelocityInBody	(	const State &	state,
		const Vec3 &	locationOnBodyB,
		const Vec3 &	velocityOnBodyB,
		const MobilizedBody &	inBodyA
	)		const

inline

TODO: not implemented yet – any volunteers? Return the velocity of a point P moving on body B, in body A's frame, expressed in body A.

Vec3 SimTK::MobilizedBody::calcBodyMovingPointAccelerationInBody	(	const State &	state,
		const Vec3 &	locationOnBodyB,
		const Vec3 &	velocityOnBodyB,
		const Vec3 &	accelerationOnBodyB,
		const MobilizedBody &	inBodyA
	)		const

inline

TODO: not implemented yet – any volunteers? Return the velocity of a point P moving (and possibly accelerating) on body B, in body A's frame, expressed in body A.

Real SimTK::MobilizedBody::calcMovingPointToPointDistanceTimeDerivative	(	const State &	state,
		const Vec3 &	locationOnBodyB,
		const Vec3 &	velocityOnBodyB,
		const MobilizedBody &	bodyA,
		const Vec3 &	locationOnBodyA,
		const Vec3 &	velocityOnBodyA
	)		const

inline

TODO: not implemented yet – any volunteers? Calculate the time rate of change of distance from a moving point PB on body B to a moving point PA on body A.

We are given the location vectors p_Bo_PB and p_Ao_PA, and the velocities of PB in B and PA in A, all expressed in their respective frames. We return d/dt |p_BoAo|, taking into account the (given) time derivatives of the locations in their local frames, as well as the relative velocities of the bodies.

Real SimTK::MobilizedBody::calcMovingPointToPointDistance2ndTimeDerivative	(	const State &	state,
		const Vec3 &	locationOnBodyB,
		const Vec3 &	velocityOnBodyB,
		const Vec3 &	accelerationOnBodyB,
		const MobilizedBody &	bodyA,
		const Vec3 &	locationOnBodyA,
		const Vec3 &	velocityOnBodyA,
		const Vec3 &	accelerationOnBodyA
	)		const

inline

TODO: not implemented yet – any volunteers? Calculate the second time derivative of distance from a moving point PB on body B to a moving point PA on body A.

We are given the location vectors p_Bo_PB and p_Ao_PA, and the velocities and accelerations of PB in B and PA in A, all expressed in their respective frames. We return d^2/dt^2 |p_AoBo|, taking into account the time derivatives of the locations in their local frames, as well as the relative velocities and accelerations of the bodies.

const Body& SimTK::MobilizedBody::getBody ( ) const

Return a const reference to the Body contained within this MobilizedBody.

This refers to an internal copy of the Body that is owned by the MobilizedBody.

Body& SimTK::MobilizedBody::updBody ( )

Return a writable reference to the Body contained within this MobilizedBody.

This refers to an internal copy of the Body that is owned by the MobilizedBody. Calling this method invalidates the MobilizedBody's topology, so the containing System's realizeTopology() method must be called again.

MobilizedBody& SimTK::MobilizedBody::setBody ( const Body & )

Replace the Body contained within this MobilizedBody with a new one.

Calling this method invalidates the MobilizedBody's topology, so the containing System's realizeTopology() method must be called again. A reference to this MobilizedBody is returned so that this can be chained like an assignment operator.

int SimTK::MobilizedBody::addBodyDecoration	(	const Transform &	X_BD,
		const DecorativeGeometry &	geometry
	)

inline

Add decorative geometry specified relative to the new (outboard) body's reference frame B.

Note that the body itself may already have had some decorative geometry on it when it was first put into this MobilizedBody; this just adds more and the returned index is larger. Use the underlying Body object's accessors to find this decorative geometry again. The given geometry object is copied here; we do not keep a reference to the supplied object.

int SimTK::MobilizedBody::addBodyDecoration ( const DecorativeGeometry & geometry )

inline

Convenience method for use when the geometry is supplied in the body frame.

This is the same as addBodyDecoration(Transform(),geometry).

int SimTK::MobilizedBody::addOutboardDecoration	(	const Transform &	X_MD,
		const DecorativeGeometry &	geometry
	)

Add decorative geometry specified relative to the outboard mobilizer frame M attached to body B.

If body B already has decorative geometry on it, this just adds some more, but kept in a separate list from the body decorations and inboard decorations. Returns a unique index that can be used to identify this outboard decoration later (numbered starting from zero for outboard decorations only).

int SimTK::MobilizedBody::getNumOutboardDecorations ( ) const

Return the count of decorations added with addOutboardDecoration().

const DecorativeGeometry& SimTK::MobilizedBody::getOutboardDecoration ( int i ) const

Return a const reference to the i'th outboard decoration.

DecorativeGeometry& SimTK::MobilizedBody::updOutboardDecoration ( int i )

Return a writable reference to the i'th outboard decoration.

int SimTK::MobilizedBody::addInboardDecoration	(	const Transform &	X_FD,
		const DecorativeGeometry &	geometry
	)

Add decorative geometry specified relative to the inboard mobilizer frame F attached to the parent body P.

If body P already has decorative geometry on it, this just adds some more, but kept in a separate list from the body decorations and outboard decorations. Returns a unique index that can be used to identify this inboard decoration later (numbered starting from zero for inboard decorations only).

int SimTK::MobilizedBody::getNumInboardDecorations ( ) const

Return the count of decorations added with addInboardDecoration().

const DecorativeGeometry& SimTK::MobilizedBody::getInboardDecoration ( int i ) const

Return a const reference to the i'th inboard decoration.

DecorativeGeometry& SimTK::MobilizedBody::updInboardDecoration ( int i )

Return a writable reference to the i'th inboard decoration.

MobilizedBody& SimTK::MobilizedBody::setDefaultMassProperties ( const MassProperties & m )

inline

If the contained Body can have its mass properties set to the supplied value m its mass properties are changed, otherwise the method fails.

Calling this method invalidates the MobilizedBody's topology, so the containing matter subsystem's realizeTopology() method must be called again. A reference to this MobilizedBody is returned so that this can be chained like an assignment operator.

const MassProperties& SimTK::MobilizedBody::getDefaultMassProperties ( ) const

inline

Return the mass properties of the Body stored within this MobilizedBody.

void SimTK::MobilizedBody::adoptMotion ( Motion & ownerHandle )

Provide a unique Motion object for this MobilizedBody.

The MobilizedBody takes over ownership of the Motion object and is responsible for cleaning up its heap space when the time comes. This is a Topology-changing operation and consequently requires write access to the MobilizedBody which will propagate to invalidate the containing Subsystem and System's topology. There can only be one Motion object per mobilizer; this method will throw an exception if there is already one here.

void SimTK::MobilizedBody::clearMotion ( )

If there is a Motion object associated with this MobilizedBody it is removed; otherwise, nothing happens.

If a Motion is deleted, the containing System's topology is invalidated.

bool SimTK::MobilizedBody::hasMotion ( ) const

Check whether this MobilizedBody has an associated Motion object.

This does not tell you whether the Motion object is currently enabled or in use; just whether it is available.

const Motion& SimTK::MobilizedBody::getMotion ( ) const

If there is a Motion object associated with this MobilizedBody, this returns a const reference to it.

Otherwise it will throw an exception. You can check first using hasMotion(). Note that there is no provision to obtain a writable reference to the contained Motion object; if you want to change it clear the existing object instead and replace it with a new one.

See Also: hasMotion()

MobilizedBody& SimTK::MobilizedBody::setDefaultInboardFrame ( const Transform & X_PF )

Change this mobilizer's frame F on the parent body P.

Calling this method invalidates the MobilizedBody's topology, so the containing matter subsystem's realizeTopology() method must be called again. A reference to this MobilizedBody is returned so that this can be chained like an assignment operator.

MobilizedBody& SimTK::MobilizedBody::setDefaultOutboardFrame ( const Transform & X_BM )

Change this mobilizer's frame M fixed on this (the outboard) body B.

Calling this method invalidates the MobilizedBody's topology, so the containing matter subsystem's realizeTopology() method must be called again. A reference to this MobilizedBody is returned so that this can be chained like an assignment operator.

const Transform& SimTK::MobilizedBody::getDefaultInboardFrame ( ) const

Return a reference to this mobilizer's default for the frame F fixed on the parent (inboard) body P, as the fixed Transform from P's body frame to the frame F fixed to P.

This default Transform is stored with the MobilizedBody object, not the State.

const Transform& SimTK::MobilizedBody::getDefaultOutboardFrame ( ) const

Return a reference to this MobilizedBody's default for mobilizer frame M, as the fixed Transform from this body B's frame to the frame M fixed on B.

This default Transform is stored with the MobilizedBody object, not the State.

SimTK::MobilizedBody::operator MobilizedBodyIndex ( ) const

inline

This is an implicit conversion from MobilizedBody to MobilizedBodyIndex when needed.

This will fail unless this MobilizedBody is owned by some SimbodyMatterSubsystem. We guarantee that the MobilizedBodyIndex of a mobilized body is numerically larger than the MobilizedBodyIndex of its parent.

MobilizedBodyIndex SimTK::MobilizedBody::getMobilizedBodyIndex ( ) const

Return the MobilizedBodyIndex of this MobilizedBody within the owning SimbodyMatterSubsystem.

This will fail unless this MobilizedBody is owned by some SimbodyMatterSubsystem. We guarantee that the MobilizedBodyIndex of a mobilized body is numerically larger than the MobilizedBodyIndex of its parent.

const MobilizedBody& SimTK::MobilizedBody::getParentMobilizedBody ( ) const

Return a reference to the MobilizedBody serving as the parent body of the current MobilizedBody.

This call will fail if the current MobilizedBody is Ground, since Ground has no parent.

const MobilizedBody& SimTK::MobilizedBody::getBaseMobilizedBody ( ) const

Return a reference to this MobilizedBody's oldest ancestor other than Ground, or return Ground if this MobilizedBody is Ground.

That is, we return the "base" MobilizedBody for this MobilizedBody, meaning the one which connects this branch of the multibody tree directly to Ground.

const SimbodyMatterSubsystem& SimTK::MobilizedBody::getMatterSubsystem ( ) const

Obtain a reference to the SimbodyMatterSubsystem which contains this MobilizedBody.

This will fail unless this MobilizedBody is owned by some SimbodyMatterSubsystem.

SimbodyMatterSubsystem& SimTK::MobilizedBody::updMatterSubsystem ( )

Obtain a writable reference to the SimbodyMatterSubsystem which contains this MobilizedBody.

This will fail unless this MobilizedBody is owned by some SimbodyMatterSubsystem.

bool SimTK::MobilizedBody::isInSubsystem ( ) const

Determine whether the current MobilizedBody object is owned by a matter subsystem.

bool SimTK::MobilizedBody::isInSameSubsystem ( const MobilizedBody & mobod ) const

Determine whether a given MobilizedBody mobod is in the same matter subsystem as the current body.

If the bodies are not in a subsystem, this routine will return false.

bool SimTK::MobilizedBody::isSameMobilizedBody ( const MobilizedBody & mobod ) const

Determine whether a given MobilizedBody mobod is the same MobilizedBody as this one.

For this to be true the handles must not be empty, and the implementation objects must be the same object not separate objects with identical contents.

bool SimTK::MobilizedBody::isGround ( ) const

Determine whether this body is Ground, meaning that it is actually body 0 of some matter subsytem, not just that its body type is Ground.

int SimTK::MobilizedBody::getLevelInMultibodyTree ( ) const

Return this body's level in the tree of bodies, starting with ground at 0, bodies directly connected to ground at 1, bodies directly connected to those at 2, etc.

This is callable after realizeTopology(). This is the graph distance of the body from Ground.

MobilizedBody& SimTK::MobilizedBody::cloneForNewParent ( MobilizedBody & parent ) const

Create a new MobilizedBody which is identical to this one, except that it has a different parent (and consequently might belong to a different MultibodySystem).

Real SimTK::MobilizedBody::getOneFromQPartition	(	const State &	state,
		int	which,
		const Vector &	qlike
	)		const

This utility selects one of the q's (generalized coordinates) associated with this mobilizer from a supplied "q-like" Vector, meaning a Vector which is the same length as the Vector of q's for the containing matter subsystem.

Real& SimTK::MobilizedBody::updOneFromQPartition	(	const State &	state,
		int	which,
		Vector &	qlike
	)		const

This utility returns a writable reference to one of the q's (generalized coordinates) associated with this mobilizer from a supplied "q-like" Vector, meaning a Vector which is the same length as the Vector of q's for the containing matter subsystem.

Real SimTK::MobilizedBody::getOneFromUPartition	(	const State &	state,
		int	which,
		const Vector &	ulike
	)		const

This utility selects one of the u's (generalized speeds) associated with this mobilizer from a supplied "u-like" Vector, meaning a Vector which is the same length as the Vector of u's for the containing matter subsystem.

Real& SimTK::MobilizedBody::updOneFromUPartition	(	const State &	state,
		int	which,
		Vector &	ulike
	)		const

This utility returns a writable reference to one of the u's (generalized speeds) associated with this mobilizer from a supplied "u-like" Vector, meaning a Vector which is the same length as the Vector of u's for the containing matter subsystem.

void SimTK::MobilizedBody::applyOneMobilityForce	(	const State &	state,
		int	which,
		Real	f,
		Vector &	mobilityForces
	)		const

inline

This utility adds in the supplied generalized force f (a scalar) to the appropriate slot of the supplied mobilityForces Vector, which is a "u-like" Vector.

Note that we are adding this not setting it so it important that mobilityForces be initialized to zero before making a set of calls to applyOneMobilityForce().

void SimTK::MobilizedBody::convertQForceToUForce	(	const State &	state,
		const Array_< Real, MobilizerQIndex > &	fq,
		Array_< Real, MobilizerUIndex > &	fu
	)		const

Given a generalized force in the q-space of this mobilizer, convert it to the equivalent generalized mobility force (u-space force).

This uses the kinematic coupling matrix N that appears in equation (1) qdot=N*u. Here we compute (2) fu = ~N*fq (that's N transpose, not inverse).

Simbody deals with generalized forces in mobility (u) space, but sometimes these are more convenient to generate in generalized coordinate (q) space. In that case this utility method is useful to perform the conversion from q space to u space that is necessary for communicating the force to Simbody.

Parameters

[in]	state	A State already realized through Position stage, from which this mobilizer's kinematic coupling matrix N(q) is obtained.
[in]	fq	This is a generalized force in the space of the generalized coordinates q rather than the generalized speeds u. The length of `fq` must be nq, the number of q's currently being used by this mobilizer in the given `state`. (This can depend on a Model-stage state variable.)
[out]	fu	This is the generalized force in mobility space (the space of the generalized speeds u) that is equivalent to `fq`. `fu` will be resized if necessary to length nu, the number of u's being used by this mobilizer.

Theory

The physical quantity power (force times velocity) must not change as a result of a change of coordinates. Hence we must have ~fq*qdot==~fu*u which follows from equations (1) and (2): multiply (1) by ~fq to get

    ~fq*qdot= ~fq*N*u
            = ~(~N*fq)*u
            = ~fu*u           from equation (2).

For any mobilizer where qdot==u this simply copies the input to the output. Otherwise a multiplication by ~N is done, but that is very fast since N has already been computed. Cost depends on type of mobilizer but is unlikely to exceed 25 flops.

void SimTK::MobilizedBody::applyBodyForce	(	const State &	state,
		const SpatialVec &	spatialForceInG,
		Vector_< SpatialVec > &	bodyForcesInG
	)		const

This utility adds in the supplied spatial force spatialForceInG (consisting of a torque vector, and a force vector to be applied at the current body's origin) to the appropriate slot of the supplied bodyForcesInG Vector.

Note that we are adding this not setting it so it is important that bodyForcesInG be initialized to zero before making a set of calls to applyBodyForce().

void SimTK::MobilizedBody::applyBodyTorque	(	const State &	state,
		const Vec3 &	torqueInG,
		Vector_< SpatialVec > &	bodyForcesInG
	)		const

This utility adds in the supplied pure torque torqueInG to the appropriate slot of the supplied bodyForcesInG Vector.

Note that we are adding this not setting it so it is important that bodyForcesInG be initialized to zero before making a set of calls to applyBodyTorque().

void SimTK::MobilizedBody::applyForceToBodyPoint	(	const State &	state,
		const Vec3 &	pointInB,
		const Vec3 &	forceInG,
		Vector_< SpatialVec > &	bodyForcesInG
	)		const

This utility adds in the supplied force forceInG applied at a point pointInB to the appropriate slot of the supplied bodyForcesInG Vector.

Notes:

we are adding this not setting it so it is important that bodyForcesInG be initialized to zero before making a set of calls to applyForceToBodyPoint().
pointInB represents a fixed station of B and is provided by giving the vector from body B's origin to the point, expressed in the B frame, while the applied force (and resulting body forces and torques) are expressed in the ground frame.

Friends And Related Function Documentation

typedef MobilizedBody Mobod

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

MobilizedBody.h

Classes

Public Types

Public Member Functions

Related Functions

Additional Inherited Members

Detailed Description

Mobilizer Terminology and Notation

Theory

Member Typedef Documentation

Member Enumeration Documentation

Constructor & Destructor Documentation

Member Function Documentation

Theory

Friends And Related Function Documentation