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Remove grid from composite types.

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Replaced it with flexcomp in the models.

PiperOrigin-RevId: 730070619
Change-Id: Icbc69e4c6784c6252743f689a1eafb6482d0c393
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Alessio Quaglino
2025-02-23 01:29:20 -08:00
committed by Copybara-Service
parent b90ff3f0b1
commit 0fcd20f0da
14 changed files with 191 additions and 568 deletions
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doc/modeling.rst
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@@ -1193,47 +1193,10 @@ a more complete treatment, see again the :ref:`deformable <CDeformable>` section
flex, see the folder `elasticity/ <https://github.com/google-deepmind/mujoco/tree/main/model/plugin/elasticity>`__ for
several examples.
**1D grid**.
**Grid**.
|image6| |image7|
.. code-block:: xml
<composite type="grid" count="20 1 1" spacing="0.045" offset="0 0 1">
<joint kind="main" damping="0.001"/>
<tendon kind="main" width="0.01"/>
<geom size=".02" rgba=".8 .2 .1 1"/>
<pin coord="1"/>
<pin coord="13"/>
</composite>
The grid type can create 1D or 2D grids, depending on the :at:`count` attribute. Here we illustrate 1D grids. These
are strings of spheres connected with tendons whose length is soft-equality-constrained. The softness can be adjusted.
Similar to particles, the element bodies here have slider joints but no rotational joints. The plot on the right
illustrates pinning. The :el:`pin` sub-element is used to specify the grid coordinates of the pinned bodies, and the
model compiler does not generate joints for these bodies, thereby fixing them rigidly to the parent body (in this case
the world). This makes the string in the right plot hang in space. The same mechanism can be used to model a whip for
example; in that case the parent body would be moving, and the first element body would be pinned to the parent.
**2D grid**.
|image8| |image9|
.. code-block:: xml
<composite type="grid" count="9 9 1" spacing="0.05" offset="0 0 1">
<skin material="matcarpet" inflate="0.001" subgrid="3" texcoord="true"/>
<geom size=".02"/>
<pin coord="0 0"/>
<pin coord="8 0"/>
</composite>
A 2D grid can be used to simulate cloth. What it really simulates is a 2D grid of spheres connected with
equality-constrained tendons (not shown). The model compiler can also generate skin, enabled with the :el:`skin`
sub-element in the above XML. Some of the element bodies can also be pinned, similar to 1D grids but using two grid
coordinates. The plot on the right shows a cloth pinned to the world body at the two corners, and draping over our
capsule probe. The skin on the right is subdivided using bi-cubic interpolation, which increases visual quality in the
absence of textures. When textures are present (left) the benefits of subdivision are less visible.
The grid composite type has been removed. It is recommended to use 2D flex :ref:`deformable objects <CDeformable>` for
simulating thin elastic structures.
**Cable**.