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Add adhesion actuators.

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- Adhesion actuators using contact normals as force transmission mechanism.
- Related video: https://youtu.be/HdBue4MUZys

Closes #229

PiperOrigin-RevId: 464389367
Change-Id: I9f69b3cd152d957e8f65870d208788463c036a6d
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Yuval Tassa
2022-07-31 08:53:29 -07:00
committed by Copybara-Service
parent 5c5449bf82
commit 3d77eb1ef4
17 changed files with 475 additions and 63 deletions
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doc/modeling.rst
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@@ -492,9 +492,10 @@ addition, the user can specify the maximum number of iterations, and tolerance l
There is also a second Noslip solver, which is a post-processing step enabled by specifying a positive number of
noslip iterations. All these algorithm settings can be specified in the :ref:`option <option>` element.
The default settings work well for most models, but in some cases it is necessary to tune the algorithm. The best way
to do this is to experiment with the relevant settings and use the visual profiler in `simulate.cc`_, which shows the timing of different computations as
well as solver statistics per iteration. We can offer the following general guidelines and observations:
The default settings work well for most models, but in some cases it is necessary to tune the algorithm. The best way to
do this is to experiment with the relevant settings and use the visual profiler in `simulate.cc`_, which shows the
timing of different computations as well as solver statistics per iteration. We can offer the following general
guidelines and observations:
- The constraint Jacobian should be dense for small models and sparse for large models. The default setting is 'auto';
it resolves to dense when the number of degrees of freedom is up to 60, and sparse over 60. Note however that the
@@ -545,9 +546,18 @@ Actuator shortcuts
~~~~~~~~~~~~~~~~~~
As explained in the :ref:`Actuation model <geActuation>` section of the Computation chapter, MuJoCo offers a flexible
actuator model with transmission, activation dynamics and force generation components that can be specified independently. The full functionality can be accessed via the XML element :ref:`general <general>` which allows the user
actuator model with transmission, activation dynamics and force generation components that can be specified
independently. The full functionality can be accessed via the XML element :ref:`general <general>` which allows the user
to create a variety of custom actuators. In addition, MJCF provides shortcuts for configuring common actuators. This is
done via the XML elements :ref:`motor <motor>`, :ref:`position <position>`, :ref:`velocity <velocity>`, :ref:`intvelocity <intvelocity>`, :ref:`damper<damper>`, :ref:`cylinder<cylinder>`, and :ref:`muscle <muscle>`. These are *not* separate model elements. Internally MuJoCo supports only one actuator type - which is why when an MJCF model is saved all actuators are written as :el:`general`. Shortcuts create general actuators implicitly, set their attributes to suitable values, and expose a subset of attributes with possibly different names. For example, :el:`position` creates a position servo with attribute :at:`kp` which is the servo gain. However :el:`general` does not have an attribute :at:`kp`. Instead the parser adjusts the gain and bias parameters of the general actuator in a coordinated way so as to mimic a position servo. The same effect could have been achieved by using :el:`general` directly, and setting its attributes to certain values as described below.
done via the XML elements :ref:`motor <motor>`, :ref:`position <position>`, :ref:`velocity <velocity>`,
:ref:`intvelocity <intvelocity>`, :ref:`damper<damper>`, :ref:`cylinder<cylinder>`, :ref:`muscle <muscle>`, and
:ref:`adhesion <adhesion>`. These are *not* separate model elements. Internally MuJoCo supports only one actuator type -
which is why when an MJCF model is saved all actuators are written as :el:`general`. Shortcuts create general actuators
implicitly, set their attributes to suitable values, and expose a subset of attributes with possibly different names.
For example, :el:`position` creates a position servo with attribute :at:`kp` which is the servo gain. However
:el:`general` does not have an attribute :at:`kp`. Instead the parser adjusts the gain and bias parameters of the
general actuator in a coordinated way so as to mimic a position servo. The same effect could have been achieved by using
:el:`general` directly, and setting its attributes to certain values as described below.
Actuator shortcuts also interact with defaults. Recall that the :ref:`default setting <CDefault>` mechanism involves
classes, each of which has a complete collection of dummy elements (one of each element type) used to initialize the