Fix typos and minor corrections in MuJoCo documentation and comments.
PiperOrigin-RevId: 875163889 Change-Id: Ic604d6235bf9cb999058f191e3ee41e47ec1a567
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@@ -495,7 +495,7 @@ are as follows:
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in mjData.contact actually has all 5 of them, even if condim is less than 6 and not all coefficients are used. In
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contrast, geoms have only 3 friction coefficients: tangential (same for both axes), torsional, rolling (same for both
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axes). Each of these 3D vectors of friction coefficients is expanded into a 5D vector of friction coefficients by
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replicating the tangetial and rolling components. See the :ref:`Contact<coContact>` section in the Computation
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replicating the tangential and rolling components. See the :ref:`Contact<coContact>` section in the Computation
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chapter for an intuitive description of the semantics of tangential, torsional and rolling coefficients.
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The contact friction coefficients are then computed according to the following rule: if one of the two geoms has
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@@ -1113,7 +1113,7 @@ Here we describe the XML attributes common to all sensor types, so as to avoid r
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:at:`noise`: :at-val:`real, "0"`
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The standard deviation of the noise model of this sensor. In versions prior to 3.1.4, this would lead to noise being
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added to the sensors. In release 3.1.4 this feature was removed, see :doc:`3.1.4 changelog <changelog>` for a
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detailed justification. As of subsequent versions, this attrbute serves as a convenient location for saving standard
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detailed justification. As of subsequent versions, this attribute serves as a convenient location for saving standard
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deviation information for later use.
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.. _sensor-cutoff:
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@@ -1454,7 +1454,7 @@ that applies to all edges of a given flex, which permits large time steps, or a
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where each element is in a constant stress state, which is equivalent to piecewise linear finite elements and achieves
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improved realism and accuracy. The edge-based model could be seen as a "lumped" stiffness model, where the correct
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coupling of deformation modes (e.g. shear and volumetric) is averaged in a single quantity. The continuum model enables
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instead to specify shear and volumetic stiffnesses separately using the `Poisson's ratio
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instead to specify shear and volumetric stiffnesses separately using the `Poisson's ratio
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<https://en.wikipedia.org/wiki/Poisson%27s_ratio>`__ of the material. For more details, see the `Saint Venant-Kirchhoff
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<https://en.wikipedia.org/wiki/Hyperelastic_material#Saint_Venant%E2%80%93Kirchhoff_model>`__ hyperelastic model.
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@@ -1631,7 +1631,7 @@ perfectly (and much better than a spring-damper would) because the constraints a
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large forces without destabilizing the simulation. But if the hand is forced to make contact with the table for example
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(right plot) it cannot simultaneously respect the contact constraint and track the mocap body. This is because the
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mocap body is free to go through the table. So which constraint wins? That depends on the softness of the weld
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constraint realtive to the contact constraint. The corresponding :at:`solref` and :at:`solimp` parameters need to be
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constraint relative to the contact constraint. The corresponding :at:`solref` and :at:`solimp` parameters need to be
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adjusted so as to achieve the desired trade-off. See the Modular Prosthetic Limb (MPL) hand model available on the
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MuJoCo Forum for an example; the plots below are generated with that model.
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@@ -1735,7 +1735,7 @@ dedicated section :ref:`therein<MjxPerformance>`.
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- Reduce the number of checked collisions using the
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:ref:`contype<body-geom-contype>` / :ref:`conaffinity<body-geom-conaffinity>` mechanism described in the
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:ref:`Collison detection<Collision>` section.
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:ref:`Collision detection<Collision>` section.
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- Modify collision geometries, replacing expensive collision tests (e.g. mesh-mesh) with cheaper primitive-primitive
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collisions. As a rule of thumb, collisions which have custom pair functions in the collision table at the top of
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`engine_collision_driver.c <https://github.com/google-deepmind/mujoco/blob/main/src/engine/engine_collision_driver.c>`__
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@@ -1766,7 +1766,7 @@ better visualize and understand the contact configuration and resulting forces.
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**Slip-preventing contact forces are outside the friction cone**
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This implies that the physics cannot prevent slip, even in principle. This occurs when:
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a. *The normal force is too small.* Ensure that the maximum force that can be applied by the gripper mutiplied by
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a. *The normal force is too small.* Ensure that the maximum force that can be applied by the gripper multiplied by
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the sliding friction coefficient is significantly greater than the weight of the object.
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b. *The sliding friction coefficient is too low.* Increase the sliding :ref:`friction<body-geom-friction>`
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coefficient.
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@@ -1774,7 +1774,7 @@ better visualize and understand the contact configuration and resulting forces.
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4 or 6 and choose appropriate friction coefficients.
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**condim 4** enables torsional friction, preventing rotation around the normal.
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**condim 6** also enables rolling friction, preventing rotation around the tangential directions.
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See the :ref:`Contact<coContact>` section for details and the specifc semantics of these coefficients.
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See the :ref:`Contact<coContact>` section for details and the specific semantics of these coefficients.
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**The geometry does not support the required forces or torques**
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This is a common real-world problem, solved by improved design of grippers and handles.
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@@ -1790,7 +1790,7 @@ better visualize and understand the contact configuration and resulting forces.
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High-frequency, low-amplitude vibrations are also a real-world problem in many industrial settings, but unlike in
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simulation, in the real world they are audible. Such vibration is often caused by controllers with very
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high gains and sometimes by stick-slip feedback from contacts or joints, resonating with the eigen-modes of the
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mechanism. The easist way to diagnose such vibration is to visualize contact forces in
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mechanism. The easiest way to diagnose such vibration is to visualize contact forces in
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:ref:`simulate<saSimulate>`. The solution is usually to reduce the :ref:`timestep<option-timestep>` and/or add
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some :ref:`armature<body-joint-armature>` to the relevant joints. Another reason for vibration is feedback from
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explicit damping. Use the implicit or implicitfast integrators, as documented in the
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