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Cartesian end-effector control using site transmission.

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- Added `refsite` attribute to actuators with `site` transmission.
- Such actuators now have a well defined length and can be used for e.g., Cartesian end-effector control.
- Added example models and documentation describing the new feature.

PiperOrigin-RevId: 471561218
Change-Id: I538f09af9600d5c53992c4a9fed325648aab4fa3
This commit is contained in:
Yuval Tassa
2022-09-01 10:06:11 -07:00
committed by Copybara-Service
parent 834e8dd506
commit 46da1285af
10 changed files with 283 additions and 55 deletions
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test/engine/testdata/refsite.xml
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<mujoco>
<!--
Adding a high fluid viscosity and using implicit integration for extra stabillity.
Extra stabillity is required because the abstract "arm" model is not very realistic.
(e.g. 4 consecutive ball joints is not a realistic kinematic design)
-->
<option viscosity="10" integrator="implicit">
<flag gravity="disable" contact="disable"/>
</option>
<statistic meansize=".05"/>
<default>
<default class="translation">
<position kp="100" ctrlrange="-.25 .25"/>
</default>
<default class="rotation">
<!--
Note that the rotational control range is purposefully limited to (-pi/2, pi/2) to avoid the
documented instabillity near pi, which is due to taking quaternion differences.
Increase this range to pi or bigger in order to see the instabillity.
See here for more details https://mujoco.readthedocs.io/en/latest/XMLreference.html#actuator
-->
<position kp=".2" ctrlrange="-1.571 1.571"/>
</default>
<joint damping=".01" stiffness=".0001"/>
<site type="box" size=".012 .012 .012" rgba=".7 .7 .8 1"/>
</default>
<worldbody>
<light pos="0 0 2"/>
<geom type="box" size=".25 .25 .01" pos="0 0 -.01"/>
<site name="reference" pos="0 0 .25"/>
<body name="arm" pos="-.25 .25 0">
<joint type="ball"/>
<geom type="box" size=".01" fromto="0 0 0 0 0 .25"/>
<body pos="0 0 .25">
<joint type="ball"/>
<geom type="box" size=".01" fromto="0 0 0 .25 0 0"/>
<body pos=".25 0 0">
<joint type="ball"/>
<geom type="box" size=".01" fromto="0 0 0 0 -.2 0"/>
<body pos="0 -.2 0">
<joint type="ball"/>
<geom type="box" size=".01" fromto="0 0 0 0 -.05 0"/>
<site name="end_effector" pos="0 -.05 0"/>
</body>
</body>
</body>
</body>
</worldbody>
<actuator>
<position name="x" site="end_effector" refsite="reference" gear="1 0 0 0 0 0" class="translation"/>
<position name="y" site="end_effector" refsite="reference" gear="0 1 0 0 0 0" class="translation"/>
<position name="z" site="end_effector" refsite="reference" gear="0 0 1 0 0 0" class="translation"/>
<position name="rx" site="end_effector" refsite="reference" gear="0 0 0 1 0 0" class="rotation"/>
<position name="ry" site="end_effector" refsite="reference" gear="0 0 0 0 1 0" class="rotation"/>
<position name="rz" site="end_effector" refsite="reference" gear="0 0 0 0 0 1" class="rotation"/>
</actuator>
</mujoco>