Add site semantics to weld constraint. Fixes #1896
PiperOrigin-RevId: 675112981 Change-Id: Ie4c01440d54116075df89f480591700762892cbd
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Taylor Howell
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Copybara-Service
Copybara-Service
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2da15cf137
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60a1921b34
+36
-9
@@ -4372,7 +4372,8 @@ ball joint outside the kinematic tree. Connect constraints can be specified in o
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satisfied in the configuration in which the model is defined.
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- :ref:`site1<equality-connect-site1>` and :ref:`site2<equality-connect-site2>` (both required). When using this
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specification, the two sites will be pulled together by the constraint, regardless of their position in the default
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configuration.
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configuration. An example of this specification is shown in
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`this model <https://github.com/google-deepmind/mujoco/blob/main/test/engine/testdata/equality_site.xml>`__.
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.. _equality-connect-name:
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@@ -4421,11 +4422,11 @@ ball joint outside the kinematic tree. Connect constraints can be specified in o
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:at:`site1`: :at-val:`string, optional`
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Name of a site belonging to the first body participating in the constraint. When specified, :at:`site2` must also be
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specified. The (:at:`site1`, :at:`site2`) specification is a more flexible alternative to the (:at:`body1`,
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:at:`anchor`) specification, and is different in two ways. First, the sites are not required to overlap at the
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default configuration; if they do not overlap then the sites will "snap together" at the beginning of the
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simulation. Second, changing the site positions in ``mjModel.site_pos`` at runtime will correctly change the position
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of the constraint (i.e. the content of ``mjModel.eq_data`` has no effect when this semantic is used).
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specified. The (:at:`site1`, :at:`site2`) specification is a more flexible alternative to the body-based
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specification, and is different in two ways. First, the sites are not required to overlap at the default
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configuration; if they do not overlap then the sites will "snap together" at the beginning of the simulation. Second,
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changing the site positions in ``mjModel.site_pos`` at runtime will correctly change the position of the constraint
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(i.e. the content of ``mjModel.eq_data`` has no effect when this semantic is used).
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.. _equality-connect-site2:
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@@ -4442,7 +4443,15 @@ This element creates a weld equality constraint. It attaches two bodies to each
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freedom between them (softly of course, like all other constraints in MuJoCo). The two bodies are not required to be
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close to each other. The relative body position and orientation being enforced by the constraint solver is the one in
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which the model was defined. Note that two bodies can also be welded together rigidly, by defining one body as a child
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of the other body, without any joint elements in the child body.
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of the other body, without any joint elements in the child body. Weld constraints can be specified in one of two ways:
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- Using :ref:`body1<equality-weld-body1>` (and optionally :ref:`anchor<equality-weld-anchor>`,
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:ref:`relpose<equality-weld-relpose>`, :ref:`body2<equality-weld-body2>`). When using this specification, the
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constraint is assumed to be satisfied at the configuration in which the model is defined.
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- :ref:`site1<equality-weld-site1>` and :ref:`site2<equality-weld-site2>` (both required). When using this
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specification, the frames of the two sites will be aligned by the constraint, regardless of their position in the
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default configuration. An example of this specification is shown in
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`this model <https://github.com/google-deepmind/mujoco/blob/main/test/engine/testdata/equality_site.xml>`__.
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.. _equality-weld-name:
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@@ -4459,8 +4468,9 @@ of the other body, without any joint elements in the child body.
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.. _equality-weld-body1:
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:at:`body1`: :at-val:`string, required`
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Name of the first body.
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:at:`body1`: :at-val:`string, optional`
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Name of the first body participating in the constraint. Either this attribute and must be specified or :at:`site1`
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and :at:`site2` must be specified.
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.. _equality-weld-body2:
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@@ -4483,6 +4493,23 @@ of the other body, without any joint elements in the child body.
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this parameter is the same as for connect constraints, except that is relative to body2. If :at:`relpose` is
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specified, body1 will use the pose to compute its anchor point.
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.. _equality-weld-site1:
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:at:`site1`: :at-val:`string, optional`
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Name of a site belonging to the first body participating in the constraint. When specified, :at:`site2` must also be
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specified. The (:at:`site1`, :at:`site2`) specification is a more flexible alternative to the body-based
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specification, and is different in two ways. First, the sites are not required to overlap at the default
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configuration; if they do not overlap then the sites will "snap together" at the beginning of the simulation. Second,
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changing the site position and orientation in ``mjModel.site_pos`` and ``mjModel.site_quat`` at runtime will
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correctly change the position and orientation of the constraint (i.e. the content of ``mjModel.eq_data`` has no
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effect when this semantic is used, with the exception of :ref:`torquescale<equality-weld-torquescale>`).
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.. _equality-weld-site2:
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:at:`site2`: :at-val:`string, optional`
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Name of a site belonging to the second body participating in the constraint. When specified, :at:`site1` must also be
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specified. See the :ref:`site1<equality-weld-site1>` description for more details.
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.. _equality-weld-torquescale:
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:at:`torquescale`: :at-val:`real, "1"`
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+2
-2
@@ -642,9 +642,9 @@
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| | | +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
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| | | | :ref:`name<equality-weld-name>` | :ref:`class<equality-weld-class>` | :ref:`body1<equality-weld-body1>` | :ref:`body2<equality-weld-body2>` | |
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| | | +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
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| | | | :ref:`relpose<equality-weld-relpose>` | :ref:`anchor<equality-weld-anchor>` | :ref:`active<equality-weld-active>` | :ref:`solref<equality-weld-solref>` | |
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| | | | :ref:`relpose<equality-weld-relpose>` | :ref:`anchor<equality-weld-anchor>` | :ref:`site1<equality-weld-site1>` | :ref:`site2<equality-weld-site2>` | |
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| | | +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
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| | | | :ref:`solimp<equality-weld-solimp>` | :ref:`torquescale<equality-weld-torquescale>` | | | |
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| | | | :ref:`active<equality-weld-active>` | :ref:`solref<equality-weld-solref>` | :ref:`solimp<equality-weld-solimp>` | :ref:`torquescale<equality-weld-torquescale>` | |
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| | | +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
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+------------------------------------+----+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
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| |_| equality |br| |_| |L| | | .. table:: |
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+15
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@@ -2,7 +2,7 @@
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Changelog
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=========
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Version 3.2.3 (Sep 12, 2024)
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Version 3.2.3 (Sep 16, 2024)
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----------------------------
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General
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@@ -24,15 +24,23 @@ General
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detection is handled with a new native code path, rather than `libccd <https://github.com/danfis/libccd>`__.
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This feature is in early stages of testing, but users who've experienced issues related to collsion detection are
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welcome to experiment with it and report any issues.
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5. Added a new way of defining :ref:`connect<equality-connect>` equality constraints, using two sites rather than bodies.
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The new semantic is useful when the assumption that the constraint is satisfied in the base configuration does not
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hold. In this case the sites will "snap together" at the beginning of the simulation. Additionally, changing the site
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positions in ``mjModel.site_pos`` at runtime can be used to modify the constraint.
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.. youtube:: kcM_oauk3ZA
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:align: right
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:width: 240px
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5. Added a new way of defining :ref:`connect<equality-connect>` and :ref:`weld<equality-weld>` equality constraints,
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using two sites. The new semantic is useful when the assumption that the constraint is satisfied
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in the base configuration does not hold. In this case the sites will "snap together" at the beginning of the
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simulation. Additionally, changing the site positions (``mjModel.site_pos``) and orientations
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( ``mjModel.site_quat``) at runtime will correctly modify the constraint definition. This
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`example model <https://github.com/google-deepmind/mujoco/blob/main/test/engine/testdata/equality_site.xml>`__ using
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the new semantic is shown in the video on the right.
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6. Introduced **free joint alignment**, an optimization that applies to bodies with a free joint and no child bodies
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(simple free-floating bodies): automatically aligning the body frame with the inertial frame. This feature can be
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toggled individually using the :ref:`freejoint/align<body-freejoint-align>` attribute or globally using the compiler
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:ref:`alignfree<compiler-alignfree>` attribute. The alignment diagonalizes the related 6x6 inertia sub-matrix, leading
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to both faster simulation and more stable simulation of free bodies.
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:ref:`alignfree<compiler-alignfree>` attribute. The alignment diagonalizes the related 6x6 inertia sub-matrix,
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leading to both faster simulation and more stable simulation of free bodies.
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While this optimization is a strict improvement, it changes the semantics of the joint's degrees-of-freedom.
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Therefore, ``qpos`` and ``qvel`` values saved in older versions (for example, in :ref:`keyframes<keyframe>`) will
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