chenlin/Mujoco_WASM
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Polynomial stiffness and damping https://youtu.be/aKa3ZlEF9_Y

Browse Source 
PiperOrigin-RevId: 884607673
Change-Id: If8088dbf37fed1055304778a7eb84dec52cba920
This commit is contained in:
Yuval Tassa
2026-03-16 13:24:44 -07:00
committed by Copybara-Service
parent aec1b45dce
commit efae9157a7
38 changed files with 1093 additions and 176 deletions
Download Patch File Download Diff File Expand all files Collapse all files
doc/XMLreference.rst
+41 -13
View File
@@ -2268,9 +2268,14 @@ rotations as unit quaternions.
.. _body-joint-stiffness:
:at:`stiffness`: :at-val:`real, "0"`
Joint stiffness. If this value is positive, a spring will be created with equilibrium position given by springref
below. The spring force is computed along with the other passive forces.
:at:`stiffness`: :at-val:`real, "0 0 0"`
Joint stiffness coefficients :math:`a, b, c`. A positive :math:`a` produces the standard restorative linear spring
force :math:`f = -a x`, where :math:`x` is the joint displacement from equilibrium given by
:ref:`springref<body-joint-springref>`.
If the optional second and third components are set, they define a nonlinear
polynomial spring force :math:`f(x) = -(a x + b x^2 + c x^3)`.
See :ref:`Polynomial forces<gePolynomial>` for details.
.. _body-joint-range:
@@ -2373,12 +2378,18 @@ rotations as unit quaternions.
.. _body-joint-damping:
:at:`damping`: :at-val:`real, "0"`
Damping applied to all degrees of freedom created by this joint. Unlike friction loss which is computed by the
constraint solver, damping is simply a force linear in velocity. It is included in the passive forces. Despite this
simplicity, larger damping values can make numerical integrators unstable, which is why our Euler integrator handles
:at:`damping`: :at-val:`real, "0 0 0"`
Damping coefficients :math:`a, b, c`.
A positive :math:`a` produces the standard dissipative linear damping force :math:`f(v) = -a v`,
where :math:`v` is the joint velocity. Despite its simplicity,
larger damping values can make numerical integrators unstable, which is why our Euler integrator handles
damping implicitly. See :ref:`Integration <geIntegration>` in the Computation chapter.
If the optional second and third components are set, they define a nonlinear polynomial damping force
:math:`f(v) = -(a v + b v |v| + c v^3)`.
Note the anti-symmetrization of the quadratic term, ensuring that the force is an odd function of
velocity. See :ref:`Polynomial forces<gePolynomial>` for details.
.. _body-joint-frictionloss:
:at:`frictionloss`: :at-val:`real, "0"`
@@ -5025,15 +5036,32 @@ length X, as in the clip on the right of `this example model
.. _tendon-spatial-stiffness:
:at:`stiffness`: :at-val:`real, "0"`
Stiffness coefficient. A positive value generates a spring force (linear in position) acting along the tendon.
.. youtube:: aKa3ZlEF9_Y
:aspect: 2:1
:align: right
:width: 35%
:at:`stiffness`: :at-val:`real, "0 0 0"`
Tendon stiffness coefficients :math:`a, b, c`. A positive :math:`a` generates a linear spring force
:math:`f(x) = -a x`, acting along the tendon. Here :math:`x` is the tendon displacement
defined by :ref:`springlength<tendon-spatial-springlength>`.
If the optional second and third components are set, they define a nonlinear polynomial spring force
:math:`f(x) = -(a x + b x^2 + c x^3)`. See :ref:`Polynomial forces<gePolynomial>` for details.
The clip on the right is of
`this model <https://github.com/google-deepmind/mujoco/blob/main/test/engine/testdata/passive/poly_stiffness.xml>`__.
.. _tendon-spatial-damping:
:at:`damping`: :at-val:`real, "0"`
Damping coefficient. A positive value generates a damping force (linear in velocity) acting along the tendon. Unlike
joint damping which is integrated implicitly by the Euler method, tendon damping is not integrated implicitly, thus
joint damping should be used if possible.
:at:`damping`: :at-val:`real, "0 0 0"`
Damping coefficients :math:`a, b, c`.
A positive :math:`a` produces the standard dissipative linear damping force :math:`f(v) = -a v`.
If the optional second and third components are set, they define a nonlinear polynomial damping force
:math:`f(v) = -(a v + b v |v| + c v^3)`.
Note the anti-symmetrization of the quadratic term, ensuring that the force is an odd function of
velocity. See :ref:`Polynomial forces<gePolynomial>` for details.
.. image:: images/XMLreference/tendon_armature.gif
:width: 30%