youBot is not attracted by gravity

[rastaxe]

I have a problem with the simulated youbot. If I move the robot against an object, it happens that the robot raises up on two wheels. Then it never goes down on the ground, it continues to move on two wheels, so it seems that it is not attracted by gravity. Do you have the same behavior?

[frederikhegger]

We observed the same issue. In our opinion is because the planar move plugin is used (last lines of this file: https://github.com/mas-group/youbot_description/blob/hydro-devel/urdf/youbot_base/base.gazebo.xacro) in order to move the robot.

[rastaxe]

I see. So, is there no gazebo plugin for omnidirectional drive? The pr2 base.gazebo.xacro file uses the P3D plugin:

<gazebo>
      <plugin name="p3d_base_controller" filename="libgazebo_ros_p3d.so">
        <alwaysOn>true</alwaysOn>
        <updateRate>100.0</updateRate>
        <bodyName>${name}_link</bodyName>
        <topicName>${name}_pose_ground_truth</topicName>
        <gaussianNoise>0.01</gaussianNoise>
        <frameName>map</frameName>
        <xyzOffsets>0 0 0</xyzOffsets>
        <rpyOffsets>0 0 0</rpyOffsets>
      </plugin>
    </gazebo>

Do you think it is possible to use for the youBot? I tried but I am not an expert so I was not able to make it work.

[frederikhegger]

This plugin only publishes the pose of the robot as Odometry message (see http://gazebosim.org/wiki/Tutorials/1.9/ROS_Motor_and_Sensor_Plugins#P3D_.283D_Position_Interface_for_Ground_Truth.29).

Maybe the controller of the Care-O-bot 3 can be adapted to the youBot: https://github.com/ipa320/cob_driver/tree/hydro_dev/cob_undercarriage_ctrl

[rastaxe]

Is there a way to tell Gazebo to repositioning the youbot at run time (with a script or something)? Because when this problem appears and the robot face a little bit down, the laser sees the ground and the navigation does not work properly. Resetting the position of the model in gazebo will avoid to restart everything.

[frederikhegger]

I do not no if there is something only for the robot, but you can reset the whole world either in the GUI (gzclient) under "Edit -> Reset World", by pressing STRG + R in the GUI or using the rosservice:

rosservice call /gazebo/reset_world

[rastaxe]

No, with the Reset World or Reset Model it does not work, because the orientation of the model remains the same. The only way is to publish the desired orientation of the robot on the /gazebo/set_model_state topic and it works.

[frederikhegger]

Perfect. This I did not know. Thanks

[frederikhegger]

We replaced the move_planar plugin (used as "base controller") with the steered_wheel_base_controller (http://wiki.ros.org/steered_wheel_base_controller). Now, the youbot behaves properly in simulation and does not go up in the air or starts tilting.

It has been tested under hydro and indigo.