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Add quadratic stiffness to flex.

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PiperOrigin-RevId: 827409919
Change-Id: I3dff8ea49fb1726fec4acf5b91138d6d52c4bfba
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Alessio Quaglino
2025-11-03 03:00:18 -08:00
committed by Copybara-Service
parent d4f13b4abc
commit 3a7aa84e53
10 changed files with 161 additions and 65 deletions
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doc/XMLreference.rst
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@@ -3540,15 +3540,25 @@ saving the XML:
:align: right
:width: 240px
Trilinear flexes are much faster than the previous two options, and are the preferred choice if the expected
deformations can be captured by the reduced parametriation. For example, see the video on the right comparing `full
<https://github.com/google-deepmind/mujoco/blob/main/model/flex/gripper.xml>`__ and `trilinear
Trilinear and quadratic flexes are much faster than the previous two options, and are the preferred choice if the
expected deformations can be captured by the reduced parametriation. For example, see the video on the right
comparing `full <https://github.com/google-deepmind/mujoco/blob/main/model/flex/gripper.xml>`__ and `trilinear
<https://github.com/google-deepmind/mujoco/blob/main/model/flex/gripper_trilinear.xml>`__ flexes for modeling
deformable gripper pads.
Note that the choice of dof parametrization affects the deformation modes of the flex but has no effect on the
accuracy of the collision geometry, which always takes into account the high-resolution mesh of the flex.
**quadratic**
Three translational dofs per corner, edge, face, and volume of the bounding box of the flex, for a total of 81 dofs
for the entire flex, independent of the number of vertices. The positions of the vertices are updated using
quadratic interpolation over the bounding box. While this option requires more degrees of freedom than trilinear
flexes, it enables curved deformation modes, while the only modes achievable for trilinear flexes are
strech/compression and shear.
Note that a higher interpolation order generally requires a smaller time step for stability, although usually not as
large as with the "full" option and a fine mesh.
.. _body-flexcomp-type:
:at:`type`: :at-val:`[grid, box, cylinder, ellipsoid, disc, circle, mesh, gmsh, direct], "grid"`