Setting initial velocity

[osrf-migration]

Original report (archived issue) by Til Hoff (Bitbucket: turakar).

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I am trying to set the initial velocity of a model in the .sdf file. Therefore I defined a state according to the sdformat spec. This setting seems to be ignored by gazebo. Is there a different way of doing this? Or is there something wrong? The SDF file:

<?xml version="1.0" ?>

<sdf version="1.6">
  <world name="foobar">

    <physics name="1ms" type="ode">
      <max_step_size>0.001</max_step_size>
      <real_time_factor>1.0</real_time_factor>
    </physics>
    <plugin
            filename="libignition-gazebo-scene-broadcaster-system.so"
            name="ignition::gazebo::systems::SceneBroadcaster">
    </plugin>
    <plugin
      filename="libignition-gazebo-physics-system.so"
      name="ignition::gazebo::systems::Physics">
    </plugin>

    <gui fullscreen="0">

      <!-- 3D scene -->
      <plugin filename="GzScene3D" name="3D View">
        <ignition-gui>
          <title>3D View</title>
          <property type="bool" key="showTitleBar">false</property>
          <property type="string" key="state">docked</property>
        </ignition-gui>

        <engine>ogre2</engine>
        <scene>scene</scene>
        <ambient_light>0.4 0.4 0.4</ambient_light>
        <background_color>0.8 0.8 0.8</background_color>
        <camera_pose>-6 0 6 0 0.5 0</camera_pose>
      </plugin>

      <!-- World control -->
      <plugin filename="WorldControl" name="World control">
        <ignition-gui>
          <title>World control</title>
          <property type="bool" key="showTitleBar">false</property>
          <property type="bool" key="resizable">false</property>
          <property type="double" key="height">72</property>
          <property type="double" key="width">121</property>
          <property type="double" key="z">1</property>

          <property type="string" key="state">floating</property>
          <anchors target="3D View">
            <line own="left" target="left"/>
            <line own="bottom" target="bottom"/>
          </anchors>
        </ignition-gui>

        <play_pause>true</play_pause>
        <step>true</step>
        <start_paused>true</start_paused>
        <service>/world/foobar/control</service>
        <stats_topic>/world/foobar/stats</stats_topic>

      </plugin>

      <!-- World statistics -->
      <plugin filename="WorldStats" name="World stats">
        <ignition-gui>
          <title>World stats</title>
          <property type="bool" key="showTitleBar">false</property>
          <property type="bool" key="resizable">false</property>
          <property type="double" key="height">110</property>
          <property type="double" key="width">290</property>
          <property type="double" key="z">1</property>

          <property type="string" key="state">floating</property>
          <anchors target="3D View">
            <line own="right" target="right"/>
            <line own="bottom" target="bottom"/>
          </anchors>
        </ignition-gui>

        <sim_time>true</sim_time>
        <real_time>true</real_time>
        <real_time_factor>true</real_time_factor>
        <iterations>true</iterations>
        <topic>/world/foobar/stats</topic>
      </plugin>

    </gui>

    <light type="directional" name="sun">
      <cast_shadows>true</cast_shadows>
      <pose>0 0 10 0 0 0</pose>
      <diffuse>1 1 1 1</diffuse>
      <specular>0.5 0.5 0.5 1</specular>
      <attenuation>
        <range>1000</range>
        <constant>0.9</constant>
        <linear>0.01</linear>
        <quadratic>0.001</quadratic>
      </attenuation>
      <direction>-0.5 0.1 -0.9</direction>
    </light>

    <gravity>0 0 0</gravity>

    <model name="probe">
      <link name="link">
        <inertial>
          <mass>30</mass>
          <inertia>
            <ixx>12</ixx>
            <ixy>0</ixy>
            <ixz>0</ixz>
            <iyy>12</iyy>
            <iyz>0</iyz>
            <izz>12</izz>
          </inertia>
        </inertial>
        <visual name="visual">
          <geometry>
            <sphere>
              <radius>1</radius>
            </sphere>
          </geometry>
          <material>
            <ambient>0.5 0.5 1.0 1</ambient>
            <diffuse>0.5 0.5 1.0 1</diffuse>
            <specular>0.0 0.0 1.0 1</specular>
          </material>
        </visual>
        <collision name="collision">
          <geometry>
            <sphere>
              <radius>1</radius>
            </sphere>
          </geometry>
        </collision>
      </link>
    </model>

    <state world_name="foobar">
      <model name="probe">
        <pose>0 0 0 0 -0 0</pose>
        <link name="link">
          <pose>0 0 0 0 0 0</pose>
          <velocity>10 0 0 0 0 0</velocity>
        </link>
      </model>
    </state>

  </world>
</sdf>

‌

[osrf-migration]

Original comment by Diego Ferigo (Bitbucket: dgferigo).

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As far as I know, this is not yet supported by Ignition Gazebo. I recently needed to change the base velocity of a model, and I had to implement a new custom WorldVelocityCmd component and modify my vendored Physics system. Note that this is specific to the model base and not for generic links.

Maybe this could be a starting point to port a similar modification upstream and perhaps extending it to all model’s links.

[osrf-migration]

Original comment by Addisu Z. Taddese (Bitbucket: azeey, GitHub: azeey).

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The <state> tag is not yet supported in ign-gazebo. I've just created a PR adding that to the feature comparison page

[chapulina]

We most likely won't support the <state> tags in Ignition. See #137 for more context.

This feature could be implemented as a forward-port of gazebo::InitialVelocityPlugin, with an extension to support links as well as models.

[chapulina]

It's possible to set an initial velocity for models or joints since #693. Using the VelocityControl plugin or JointController plugin.