Add mjContact.solreffriction, mjModel.pair_solreffriction and related implementation, allowing contact reference acceleration to be different for normal and frictional contact directions. This is required for e.g. elastic frictional collisions.
PiperOrigin-RevId: 538513357 Change-Id: Id9eb910fe791cf898c712030cb2c0fc481389c91
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Yuval Tassa
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Copybara-Service
Copybara-Service
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@@ -1630,6 +1630,8 @@ if omitted.
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.. _default-pair-solref:
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.. _default-pair-solreffriction:
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.. _default-pair-solimp:
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.. _default-pair-gap:
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@@ -4299,6 +4301,20 @@ element.
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:at:`solref`, :at:`solimp`
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Constraint solver parameters for contact simulation. See :ref:`CSolver`.
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.. _contact-pair-solreffriction:
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:at:`solreffriction`: :at-val:`real, "0 0"`
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Contact reference acceleration, in the friction dimensions. This attribute has the same semantics as other
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:at:`solref` attributes (described in :ref:`CSolver`), with two important distictions:
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- The default :at-val:`"0 0"` means "use the same values as :at:`solref`".
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- This attribute only takes effect for :ref:`elliptic friction cones<option-cone>`, since pyramidal cones mix normal
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and frictional forces.
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Note that as with other :at:`solreffriction` attributes, the constraint violation is identically 0. Therefore, when
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using positive semantics :at:`solreffriction[1]` is ignored, while for negative semantics :at:`solreffriction[0]` is
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ignored. See :ref:`CSolver` for more details.
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.. _contact-pair-margin:
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:at:`margin`: :at-val:`real, "0"`
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+5
-3
@@ -305,7 +305,9 @@
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| | | +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
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| | | | :ref:`condim<default-pair-condim>` | :ref:`friction<default-pair-friction>` | :ref:`solref<default-pair-solref>` | |
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| | | +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
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| | | | :ref:`solimp<default-pair-solimp>` | :ref:`gap<default-pair-gap>` | :ref:`margin<default-pair-margin>` | |
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| | | | :ref:`solreffriction<default-pair-solreffriction>` | :ref:`solimp<default-pair-solimp>` | :ref:`gap<default-pair-gap>` | |
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| | | +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
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| | | | :ref:`margin<default-pair-margin>` | | | |
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| | | +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
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+------------------------------------+----+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
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| |_| default |br| |_| |L| | | .. table:: |
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@@ -827,9 +829,9 @@
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| | | +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
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| | | | :ref:`geom2<contact-pair-geom2>` | :ref:`condim<contact-pair-condim>` | :ref:`friction<contact-pair-friction>` | |
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| | | +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
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| | | | :ref:`solref<contact-pair-solref>` | :ref:`solimp<contact-pair-solimp>` | :ref:`gap<contact-pair-gap>` | |
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| | | | :ref:`solref<contact-pair-solref>` | :ref:`solreffriction<contact-pair-solreffriction>` | :ref:`solimp<contact-pair-solimp>` | |
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| | | +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
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| | | | :ref:`margin<contact-pair-margin>` | | | |
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| | | | :ref:`gap<contact-pair-gap>` | :ref:`margin<contact-pair-margin>` | | |
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| | | +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
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+------------------------------------+----+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
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| |_| contact |br| |_| |L| | | .. table:: |
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@@ -63,6 +63,13 @@ Simulate
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General
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^^^^^^^
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- Added :ref:`mjContact.solreffriction<mjContact>`, allowing different :ref:`solref<CSolver>` parameters for the normal
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and frictional axes of contacts when using :ref:`elliptic friction cones<option-cone>`. This attribute is required
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for elastic frictional collisions, see associated
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`example model <https://github.com/deepmind/mujoco/blob/main/test/engine/testdata/bounce_recoil.xml>`__ mimicking the
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spin-bounce recoil behaviour of `elastic rubber balls <https://www.youtube.com/watch?v=uFLJcRegIVQ&t=3s>`__.
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This is an advanced option currently only supported by explicit :ref:`contact pairs<contact-pair>`, using the
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:ref:`solreffriction<contact-pair-solreffriction>` attribute.
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- Added :ref:`mjd_inverseFD` for finite-differenced inverse-dynamics derivatives.
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- Added functions for operations on banded-then-dense "arrowhead" matrices. Such matrices are common when doing direct
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trajectory optimization. See :ref:`mju_cholFactorBand` documentation for details.
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+19
-17
@@ -50,32 +50,33 @@ typedef enum mjtTimer_ { // internal timers
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mjNTIMER // number of timers
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} mjtTimer;
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struct mjContact_ { // result of collision detection functions
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struct mjContact_ { // result of collision detection functions
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// contact parameters set by geom-specific collision detector
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mjtNum dist; // distance between nearest points; neg: penetration
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mjtNum pos[3]; // position of contact point: midpoint between geoms
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mjtNum frame[9]; // normal is in [0-2]
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mjtNum dist; // distance between nearest points; neg: penetration
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mjtNum pos[3]; // position of contact point: midpoint between geoms
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mjtNum frame[9]; // normal is in [0-2]
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// contact parameters set by mj_collideGeoms
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mjtNum includemargin; // include if dist<includemargin=margin-gap
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mjtNum friction[5]; // tangent1, 2, spin, roll1, 2
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mjtNum solref[mjNREF]; // constraint solver reference
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mjtNum solimp[mjNIMP]; // constraint solver impedance
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mjtNum includemargin; // include if dist<includemargin=margin-gap
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mjtNum friction[5]; // tangent1, 2, spin, roll1, 2
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mjtNum solref[mjNREF]; // constraint solver reference, normal direction
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mjtNum solreffriction[mjNREF]; // constraint solver reference, friction directions
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mjtNum solimp[mjNIMP]; // constraint solver impedance
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// internal storage used by solver
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mjtNum mu; // friction of regularized cone, set by mj_makeConstraint
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mjtNum H[36]; // cone Hessian, set by mj_updateConstraint
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mjtNum mu; // friction of regularized cone, set by mj_makeConstraint
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mjtNum H[36]; // cone Hessian, set by mj_updateConstraint
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// contact descriptors set by mj_collideGeoms
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int dim; // contact space dimensionality: 1, 3, 4 or 6
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int geom1; // id of geom 1
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int geom2; // id of geom 2
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int dim; // contact space dimensionality: 1, 3, 4 or 6
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int geom1; // id of geom 1
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int geom2; // id of geom 2
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// flag set by mj_instantianteEquality
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int exclude; // 0: include, 1: in gap, 2: fused, 3: no dofs
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int exclude; // 0: include, 1: in gap, 2: fused, 3: no dofs
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// address computed by mj_instantiateContact
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int efc_address; // address in efc; -1: not included
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int efc_address; // address in efc; -1: not included
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};
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typedef struct mjContact_ mjContact;
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struct mjWarningStat_ { // warning statistics
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@@ -1056,8 +1057,9 @@ struct mjModel_ {
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int* pair_geom1; // id of geom1 (npair x 1)
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int* pair_geom2; // id of geom2 (npair x 1)
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int* pair_signature; // (body1+1) << 16 + body2+1 (npair x 1)
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mjtNum* pair_solref; // constraint solver reference: contact (npair x mjNREF)
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mjtNum* pair_solimp; // constraint solver impedance: contact (npair x mjNIMP)
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mjtNum* pair_solref; // solver reference: contact normal (npair x mjNREF)
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mjtNum* pair_solreffriction; // solver reference: contact friction (npair x mjNREF)
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mjtNum* pair_solimp; // solver impedance: contact (npair x mjNIMP)
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mjtNum* pair_margin; // detect contact if dist<margin (npair x 1)
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mjtNum* pair_gap; // include in solver if dist<margin-gap (npair x 1)
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mjtNum* pair_friction; // tangent1, 2, spin, roll1, 2 (npair x 5)
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