FF's Roam Notes

Initialize joint value in gazebo

1 min read

There’s two ways to initialize joint value of a give robot model:

  1. modify the origin attribute of <joint> in urdf file

  2. add -J JOINT_NAME JOINT_VALUE when spawn the robot

The first method will make default joints value wired, so I would suggest to use second method.

But there’s still a bug on gazebo when initializing joint value. Current workaround is:

<arg name="paused" default="true" doc="Starts gazebo in paused mode" />
 
<include file="$(find gazebo_ros)/launch/empty_world.launch">
  <arg name="world_name" default="worlds/empty.world"/>
  <arg name="paused" value="$(arg paused)"/>
  <arg name="gui" value="$(arg gui)"/>
</include>
 
<node name="spawn_gazebo_model" pkg="gazebo_ros" type="spawn_model" args="-urdf -param robot_description -model robot
            -z 0.0
            -J shoulder_lift_joint -1.57
            -J elbow_joint 1.001
            -unpause
            " respawn="false" output="screen" />

We need to launch the Gazebo simulation paused so that physics is off. Then use -unpause flag with the spawner to turn on the physics.

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