124 lines
3.0 KiB
Markdown
124 lines
3.0 KiB
Markdown
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# Preparing a robot for simulation in MuJoCo
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## If you designed your robot in OnShape
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### Make sure to design you robot according to onshape-to-robot constraints
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https://onshape-to-robot.readthedocs.io/en/latest/design.html
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The urdf will contain frames named `closing_<...>_1` and `closing_<...>_2` that you can use to close the loops in the mjcf file.
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### Get get robot urdf from onshape
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Run
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```bash
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$ onshape-to-robot robots/bd1/
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```
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#### (Optional) If you have closing loops, follow the instructions for handling them in the documentation of onshape-to-robotn then:
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In `robot.urdf`, add :
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```xml
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<robot name="...">
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<mujoco>
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<compiler fusestatic="false"/>
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</mujoco>
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...
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</robot>
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```
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# Convert URDF to MJCF (MuJoCo)
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## Get MuJoCo binaries
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Download mujoco binaries somewhere https://github.com/google-deepmind/mujoco/releases
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unpack and run
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```bash
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$ ./compile robot.urdf robot.xml
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```
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## In robot.xml, add actuators :
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Example :
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```xml
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<actuator>
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<position name="left_hip_yaw" joint="left_hip_yaw" inheritrange="1"/>
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<position name="left_hip_roll" joint="left_hip_roll" inheritrange="1"/>
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<position name="left_hip_pitch" joint="left_hip_pitch" inheritrange="1"/>
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<position name="left_knee" joint="left_knee" inheritrange="1"/>
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<position name="left_ankle" joint="left_ankle" inheritrange="1"/>
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<position name="right_hip_roll" joint="right_hip_roll" inheritrange="1"/>
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<position name="right_hip_yaw" joint="right_hip_yaw" inheritrange="1"/>
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<position name="right_hip_pitch" joint="right_hip_pitch" inheritrange="1"/>
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<position name="right_knee" joint="right_knee" inheritrange="1"/>
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<position name="right_ankle" joint="right_ankle" inheritrange="1"/>
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<position name="head_pitch1" joint="head_pitch1" inheritrange="1"/>
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<position name="head_pitch2" joint="head_pitch2" inheritrange="1"/>
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<position name="head_yaw" joint="head_yaw" inheritrange="1"/>
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</actuator>
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```
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## Add a freejoint
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encapsulate the body in a freejoint
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```xml
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<worldbody>
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<body>
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<freejoint />
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...
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...
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</body>
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</worldbody>
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```
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## (Optional) Constrain closing loop
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Add the following to the mjcf file
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```xml
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<equality>
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<connect body1="closing_<...>_1" body2="closing_<...>_2" anchor="x y z" />
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</equality>
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```
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the x, y, z values can be found in the .urdf
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```xml
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<joint name="closing_<...>_1_frame" type="fixed">
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<origin xyz="x y z" rpy="r p y" />
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...
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</joint>
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```
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## Setup collision groups, damping and friction
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/!\ remove actuatorfrcrange in joints
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Put that inside the <mujoco> bracket
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```xml
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<mujoco>
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<default>
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<geom contype="1" conaffinity="1" solref=".004 1" />
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<joint damping="0.09" frictionloss="0.1"/>
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<position kp="10" forcerange="-5.0 5.0"/>
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</default>
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...
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...
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</mujoco>
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```
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still need to add :
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- change frames to sites
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## Visualize
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```bash
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$ python3 -m mujoco.viewer --mjcf=<path>/scene.xml
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```
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or
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```bash
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$ <path_to_mujoco_bin>/bin/simulate <path>/scene.xml
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```
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