Simbody
3.6

Enforce that a fixed station on one body remains coincident with a fixed station on a second body, as though there were a ball joint connecting them at those points. More...
Public Member Functions  
Ball (MobilizedBody &body1, MobilizedBody &body2)  
Connect the origin of body1 to the origin of body2. More...  
Ball (MobilizedBody &body1, const Vec3 &defaultPoint1, MobilizedBody &body2, const Vec3 &defaultPoint2)  
Connect body1 and body2 at given station points, given in the body frame of the corresponding body. More...  
Ball ()  
Default constructor creates an empty handle. More...  
void  setPointOnBody1 (State &state, const Vec3 &point_B1) const 
Change the station point on body 1 at which this Constraint acts. More...  
void  setPointOnBody2 (State &state, const Vec3 &point_B2) const 
Change the station point on body 2 at which this Constraint acts. More...  
const Vec3 &  getPointOnBody1 (const State &state) const 
Return from the given state the constrained station on body 1, in the body 1 frame. More...  
const Vec3 &  getPointOnBody2 (const State &state) const 
Return from the given state the constrained station on body 2, in the body 2 frame. More...  
Ball &  setDefaultPointOnBody1 (const Vec3 &defaultPoint_B1) 
Change the default station location on body 1. More...  
Ball &  setDefaultPointOnBody2 (const Vec3 &defaultPoint_B2) 
Change the default station location on body 2. More...  
const Vec3 &  getDefaultPointOnBody1 () const 
Return the default location for the station point on body 1, as a vector in the body 1 frame. More...  
const Vec3 &  getDefaultPointOnBody2 () const 
Return the default location for the station point on body 2, as a vector in the body 2 frame. More...  
Ball &  setDefaultRadius (Real r) 
For visualization only, you can override the default radius used by this Constraint to draw itself. More...  
Real  getDefaultRadius () const 
Retrieve the radius being used for visualization of this Constraint. More...  
MobilizedBodyIndex  getBody1MobilizedBodyIndex () const 
Return the MobilizedBodyIndex corresponding to body 1. More...  
MobilizedBodyIndex  getBody2MobilizedBodyIndex () const 
Return the MobilizedBodyIndex corresponding to body 2. More...  
Vec3  getPositionErrors (const State &state) const 
Return the current positionlevel constraint error for this Constraint. More...  
Vec3  getVelocityErrors (const State &state) const 
Return the current velocitylevel constraint error for this Constraint. More...  
Vec3  getAccelerationErrors (const State &) const 
Return the current accelerationlevel constraint error for this Constraint. More...  
Vec3  getBallReactionForceOnBody1 (const State &) const 
Return the force currently being applied by this Constraint to the point of body 1 that is coincident in space with the constrained point on body 2. More...  
Vec3  getBallReactionForceOnBody2 (const State &) const 
Return the force currently being applied by this Constraint to body 2, at its constrained station point. More...  
Vec3  getMultipliers (const State &state) const 
Return the three Lagrange multipliers associated with the three acclerationlevel constraint equations generated by this Constraint. More...  
Public Member Functions inherited from SimTK::Constraint  
Constraint ()  
Default constructor creates an empty Constraint handle that can be used to reference any Constraint. More...  
Constraint (ConstraintImpl *r)  
For internal use: construct a new Constraint handle referencing a particular implementation object. More...  
void  disable (State &) const 
Disable this Constraint, effectively removing it from the system. More...  
void  enable (State &) const 
Enable this Constraint, without necessarily satisfying it. More...  
bool  isDisabled (const State &) const 
Test whether this constraint is currently disabled in the supplied State. More...  
bool  isDisabledByDefault () const 
Test whether this Constraint is disabled by default in which case it must be explicitly enabled before it will take effect. More...  
void  setDisabledByDefault (bool shouldBeDisabled) 
Normally Constraints are enabled when defined and can be disabled later. More...  
operator ConstraintIndex () const  
This is an implicit conversion from Constraint to ConstraintIndex when needed. More...  
const SimbodyMatterSubsystem &  getMatterSubsystem () const 
Get a const reference to the matter subsystem that contains this Constraint. More...  
SimbodyMatterSubsystem &  updMatterSubsystem () 
Assuming you have writable access to this Constraint, get a writable reference to the containing matter subsystem. More...  
ConstraintIndex  getConstraintIndex () const 
Get the ConstraintIndex that was assigned to this Constraint when it was added to the matter subsystem. More...  
bool  isInSubsystem () const 
Test whether this Constraint is contained within a matter subsystem. More...  
bool  isInSameSubsystem (const MobilizedBody &mobod) const 
Test whether the supplied MobilizedBody is in the same matter subsystem as this Constraint. More...  
int  getNumConstrainedBodies () const 
Return the number of unique bodies directly restricted by this constraint. More...  
const MobilizedBody &  getMobilizedBodyFromConstrainedBody (ConstrainedBodyIndex consBodyIx) const 
Return a const reference to the actual MobilizedBody corresponding to one of the Constrained Bodies included in the count returned by getNumConstrainedBodies(). More...  
const MobilizedBody &  getAncestorMobilizedBody () const 
Return a const reference to the actual MobilizedBody which is serving as the Ancestor body for the constrained bodies in this Constraint. More...  
int  getNumConstrainedMobilizers () const 
Return the number of unique mobilizers directly restricted by this Constraint. More...  
const MobilizedBody &  getMobilizedBodyFromConstrainedMobilizer (ConstrainedMobilizerIndex consMobilizerIx) const 
Return a const reference to the actual MobilizedBody corresponding to one of the Constrained Mobilizers included in the count returned by getNumConstrainedMobilizers(). More...  
const SimbodyMatterSubtree &  getSubtree () const 
Return a subtree object indicating which parts of the multibody tree are potentially affected by this Constraint. More...  
int  getNumConstrainedQ (const State &, ConstrainedMobilizerIndex) const 
Return the number of constrainable generalized coordinates q associated with a particular constrained mobilizer. More...  
int  getNumConstrainedU (const State &, ConstrainedMobilizerIndex) const 
Return the number of constrainable mobilities u associated with a particular constrained mobilizer. More...  
ConstrainedUIndex  getConstrainedUIndex (const State &, ConstrainedMobilizerIndex, MobilizerUIndex which) const 
Return the index into the constrained mobilities u array corresponding to a particular mobility of the indicated ConstrainedMobilizer. More...  
ConstrainedQIndex  getConstrainedQIndex (const State &, ConstrainedMobilizerIndex, MobilizerQIndex which) const 
Return the index into the constrained coordinates q array corresponding to a particular coordinate of the indicated ConstrainedMobilizer. More...  
int  getNumConstrainedQ (const State &) const 
Return the sum of the number of coordinates q associated with each of the constrained mobilizers. More...  
int  getNumConstrainedU (const State &) const 
Return the sum of the number of mobilities u associated with each of the constrained mobilizers. More...  
QIndex  getQIndexOfConstrainedQ (const State &state, ConstrainedQIndex consQIndex) const 
Map one of this Constraint's constrained q's to the corresponding index within the matter subsystem's whole q vector. More...  
UIndex  getUIndexOfConstrainedU (const State &state, ConstrainedUIndex consUIndex) const 
Map one of this Constraint's constrained U's (or mobilities) to the corresponding index within the matter subsystem's whole u vector. More...  
void  getNumConstraintEquationsInUse (const State &state, int &mp, int &mv, int &ma) const 
Find out how many holonomic (position), nonholonomic (velocity), and accelerationonly constraint equations are currently being generated by this Constraint. More...  
void  getIndexOfMultipliersInUse (const State &state, MultiplierIndex &px0, MultiplierIndex &vx0, MultiplierIndex &ax0) const 
Return the start of the blocks of multipliers (or acceleration errors) assigned to this Constraint. More...  
void  setMyPartInConstraintSpaceVector (const State &state, const Vector &myPart, Vector &constraintSpace) const 
Set the part of a complete constraintspace vector that belongs to this constraint. More...  
void  getMyPartFromConstraintSpaceVector (const State &state, const Vector &constraintSpace, Vector &myPart) const 
Get the part of a complete constraintspace vector that belongs to this constraint. More...  
Vector  getPositionErrorsAsVector (const State &) const 
Get a Vector containing the position errors. More...  
Vector  calcPositionErrorFromQ (const State &, const Vector &q) const 
Matrix  calcPositionConstraintMatrixP (const State &) const 
Matrix  calcPositionConstraintMatrixPt (const State &) const 
Matrix  calcPositionConstraintMatrixPNInv (const State &) const 
void  calcConstraintForcesFromMultipliers (const State &, const Vector &lambda, Vector_< SpatialVec > &bodyForcesInA, Vector &mobilityForces) const 
This operator calculates this constraint's body and mobility forces given the complete set of multipliers lambda for this Constraint. More...  
Vector  getVelocityErrorsAsVector (const State &) const 
Get a Vector containing the velocity errors. More...  
Vector  calcVelocityErrorFromU (const State &, const Vector &u) const 
Matrix  calcVelocityConstraintMatrixV (const State &) const 
Matrix  calcVelocityConstraintMatrixVt (const State &) const 
Vector  getAccelerationErrorsAsVector (const State &) const 
Get a Vector containing the acceleration errors. More...  
Vector  calcAccelerationErrorFromUDot (const State &, const Vector &udot) const 
Vector  getMultipliersAsVector (const State &) const 
Get a Vector containing the Lagrange multipliers. More...  
void  getConstraintForcesAsVectors (const State &state, Vector_< SpatialVec > &bodyForcesInG, Vector &mobilityForces) const 
Given a State realized through Acceleration stage, return the forces that were applied to the system by this Constraint, with body forces expressed in Ground. More...  
Vector_< SpatialVec >  getConstrainedBodyForcesAsVector (const State &state) const 
For convenience, returns constrained body forces as the function return. More...  
Vector  getConstrainedMobilityForcesAsVector (const State &state) const 
For convenience, returns constrained mobility forces as the function return. More...  
Real  calcPower (const State &state) const 
Calculate the power being applied by this Constraint to the system. More...  
Matrix  calcAccelerationConstraintMatrixA (const State &) const 
Matrix  calcAccelerationConstraintMatrixAt (const State &) const 
void  setIsConditional (bool isConditional) 
(Advanced) Mark this constraint as one that is only conditionally active. More...  
bool  isConditional () const 
(Advanced) Get the value of the isConditional flag. More...  
Public Member Functions inherited from SimTK::PIMPLHandle< Constraint, ConstraintImpl, 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 Constraint &other) const 
Determine whether the supplied handle is the same object as "this" PIMPLHandle. More...  
void  disown (Constraint &newOwner) 
Give up ownership of the implementation to an empty handle. More...  
PIMPLHandle &  referenceAssign (const Constraint &source) 
"Copy" assignment but with shallow (pointer) semantics. More...  
PIMPLHandle &  copyAssign (const Constraint &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 ConstraintImpl &  getImpl () const 
Get a const reference to the implementation associated with this Handle. More...  
ConstraintImpl &  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...  
Additional Inherited Members  
Public Types inherited from SimTK::Constraint  
typedef Rod  ConstantDistance 
Synonym for Rod constraint. More...  
typedef Ball  CoincidentPoints 
Synonym for Ball constraint. More...  
typedef Ball  Spherical 
Synonym for Ball constraint. More...  
typedef Weld  CoincidentFrames 
Public Types inherited from SimTK::PIMPLHandle< Constraint, ConstraintImpl, true >  
typedef PIMPLHandle< Constraint, ConstraintImpl, PTR >  HandleBase 
typedef HandleBase  ParentHandle 
Protected Member Functions inherited from SimTK::PIMPLHandle< Constraint, ConstraintImpl, true >  
PIMPLHandle ()  
The default constructor makes this an empty handle. More...  
PIMPLHandle (ConstraintImpl *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 nonvirtual. 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 (ConstraintImpl *p) 
Set the implementation for this empty handle. More...  
bool  hasSameImplementation (const Constraint &other) const 
Determine whether the supplied handle is a reference to the same implementation object as is referenced by "this" PIMPLHandle. More...  
Enforce that a fixed station on one body remains coincident with a fixed station on a second body, as though there were a ball joint connecting them at those points.
Uses three positionlevel (holonomic) constraint equations to prevent relative translation in three orthogonal directions.
At construction you specify the two bodies to be connected by the Constraint, and give default values for a station on each body. The State is initialized with those default stations, but you can change them later.
The constraint is enforced by an internal (nonworking) force applied at the spatial location of the point on body 2, on material points of each body that are coincident with that spatial location. Note that this is somewhat asymmetric when the ball is not properly assembled – it acts as though the contact occurs at the point on body 2, not at the point on body 1. That is critical to ensure that Newton's 3rd law is satisified – the action and reaction must occur at the same point.
The assembly condition is the same as the runtime constraint – the two points can be brought together by driving the perr to zero.
SimTK::Constraint::Ball::Ball  (  MobilizedBody &  body1, 
MobilizedBody &  body2  
) 
Connect the origin of body1 to the origin of body2.
That is, the default stations will both be (0,0,0). You can change those later in the State using setPointOnBody1() and setPointOnBody2().
SimTK::Constraint::Ball::Ball  (  MobilizedBody &  body1, 
const Vec3 &  defaultPoint1,  
MobilizedBody &  body2,  
const Vec3 &  defaultPoint2  
) 
Connect body1 and body2 at given station points, given in the body frame of the corresponding body.
You can change those later in the State using setPointOnBody1() and setPointOnBody2().

inline 
Default constructor creates an empty handle.
Change the station point on body 1 at which this Constraint acts.
Provide the station location in the body 1 local frame. This overrides the default point that was supplied on construction. This is an Instancestage change.
Change the station point on body 2 at which this Constraint acts.
Provide the station location in the body 2 local frame. This overrides the default point that was supplied on construction. This is an Instancestage change.
Return from the given state the constrained station on body 1, in the body 1 frame.
Return from the given state the constrained station on body 2, in the body 2 frame.
Change the default station location on body 1.
This is a topological change meaning you'll have to call realizeTopology() again after changing the default point. If you want to change the constrained station during a simulation, use setPointOnBody1() instead to override it in a State.
Change the default station location on body 2.
This is a topological change meaning you'll have to call realizeTopology() again after changing the default point. If you want to change the constrained station during a simulation, use setPointOnBody2() instead to override it in a State.
const Vec3& SimTK::Constraint::Ball::getDefaultPointOnBody1  (  )  const 
Return the default location for the station point on body 1, as a vector in the body 1 frame.
Note that this is not necessarily the station point being used for any given State; use getPointOnBody1() for that.
const Vec3& SimTK::Constraint::Ball::getDefaultPointOnBody2  (  )  const 
Return the default location for the station point on body 2, as a vector in the body 2 frame.
Note that this is not necessarily the station point being used for any given State; use getPointOnBody2() for that.
For visualization only, you can override the default radius used by this Constraint to draw itself.
Real SimTK::Constraint::Ball::getDefaultRadius  (  )  const 
Retrieve the radius being used for visualization of this Constraint.
MobilizedBodyIndex SimTK::Constraint::Ball::getBody1MobilizedBodyIndex  (  )  const 
Return the MobilizedBodyIndex corresponding to body 1.
MobilizedBodyIndex SimTK::Constraint::Ball::getBody2MobilizedBodyIndex  (  )  const 
Return the MobilizedBodyIndex corresponding to body 2.
Return the current positionlevel constraint error for this Constraint.
This is the vector between the constrained stations on body 1 and body 2, which would be zero if this constraint were perfectly satisfied. The returned vector is measured in the Ancestor body frame. The given state must be realized through Position stage.
Return the current velocitylevel constraint error for this Constraint.
This is the relative velocity between the material points of body 1 and body 2 that are coincident with the constrained station point on body 2; note that this is subtly different from the time derivative of the position error vector. The returned vector is measured in the Ancestor body frame. The given state must be realized through Velocity stage.
Return the current accelerationlevel constraint error for this Constraint.
This is the relative acceleration between the material points of body 1 and body 2 that are coincident with the constrained station point on body 2; this is precisely the time derivative of the velocity error vector (but not exactly the second time derivative of the position error). The returned vector is measured in the Ancestor body frame. The given state must be realized through Acceleration stage.
Return the force currently being applied by this Constraint to the point of body 1 that is coincident in space with the constrained point on body 2.
The force vector is expressed in body 1's local frame.
Return the force currently being applied by this Constraint to body 2, at its constrained station point.
The force vector is expressed in body 2's local frame.
Return the three Lagrange multipliers associated with the three acclerationlevel constraint equations generated by this Constraint.
Although these are related to reaction forces, if that's what you're interested in you should use getBallReactionForcesOnBody1() or getBallReactionForceOnBody2() instead; the definition of the multipliers is somewhat arbitrary and will not always be easy to interpret as forces. The given state must be realized through Acceleration stage.