David,

Further investigation found one more bug with gazebo.  The torque values are
continuously overwritten by zeros, ticketed here
https://code.ros.org/trac/ros-pkg/ticket/4051
The fix in boxturtle has been checked in as r29314, will make a bug patch
release later.

thanks,
John

On Mon, May 3, 2010 at 1:22 PM, John Hsu <johnhsu@willowgarage.com> wrote:

> Hi David,
> Thanks for the feedback, I see two (potential) issues here,
>
>    - gazebo requires an iface internally, which I ticketed here
>    https://code.ros.org/trac/ros-pkg/ticket/4049.  For now, if you add an
>    interface line to your controller, then things should work better
>
>        <gazebo>
>            <controller:gazebo_ros_force name="box_force_controller" plugin="libgazebo_ros_force.so">
>             <alwaysOn>true</alwaysOn>
>
>             <updateRate>15.0</updateRate>
>
>             <topicName>box_force</topicName>
>             <bodyName>object_link</bodyName>
>    *         <interface:audio name="dummy_iface"/>*
>
>            </controller:gazebo_ros_force>
>
>
>        </gazebo>
>
>    - another issue that might come up:  if the world update rate differs
>    from the force plugin update rate, force application will be skipped in the
>    intermediate time steps.  For example, if world is updating at 1kHz and your
>    controller has an updateRate of 100Hz, the desired force on the body is
>    applied only 1 out of 10 simulation updates, resulting in what looks like a
>    1/10th smaller force than desired.  So I recommend changing updateRate to
>    match (or be greater than) your world update rate for now.  (I also ticketed
>    this here: https://code.ros.org/trac/ros-pkg/ticket/4050).
>
> Thanks,
> John
>
> On Mon, May 3, 2010 at 12:53 PM, David Ferguson <dhf@andrew.cmu.edu>wrote:
>
>> Hi,
>>
>> I am trying to write create a gazebo simulation of a 4 wheeled vehicle
>> (think golf cart). I am having an issue with trying to create forces in the
>> simulation. I want to apply a torque the rear wheels (equivalent to pressing
>> the gas pedal). I can't figure out however how to use the gazebo plugin
>> which is supposed to apply the force. In the .h file for the plugin it says
>> to use it as such:
>>
>>   This is a controller that collects data from a ROS topic and applies
>> wrench to a body accordingly.
>>
>>   Example Usage:
>>   \verbatim
>>   <model:physical name="box_model">
>>     <body:empty name="box_body">
>>      ...
>>     </body:empty>
>>     <controller:gazebo_ros_force name="box_force_controller"
>> plugin="libgazebo_ros_force.so">
>>         <alwaysOn>true</alwaysOn>
>>         <updateRate>15.0</updateRate>
>>         <topicName>box_force</topicName>
>>         <bodyName>box_body</bodyName>
>>     </controller:gazebo_ros_force>
>>   </model:phyiscal>
>>   \endverbatim
>>
>> To test it I essentially copied the tutorial showing how to use the iface
>> plugin (sets a models position). My urdf file is below:
>>
>> <robot name="object_model"
>>        xmlns:controller="
>> http://playerstage.sourceforge.net/gazebo/xmlschema/#controller"
>>        xmlns:interface="
>> http://playerstage.sourceforge.net/gazebo/xmlschema/#interface" >
>>   <!-- urdf requires at least one joint and one link, so here's the joint
>> -->
>>   <joint name="my_mug_joint" type="floating" >
>>     <!-- axis is in the parent link frame coordintates -->
>>     <axis xyz="0 0 0" />
>>     <parent link="world" />
>>     <child link="object_link" />
>>     <!-- initial pose of my_mug joint/link in the parent frame coordiantes
>> -->
>>     <origin xyz="0 0 0" rpy="0 0 0" />
>>   </joint>
>>   <!-- one floating link -->
>>   <link name="object_link">
>>     <inertial>
>>       <mass value="1"/>
>>       <origin xyz="0 0 0.0"/>
>>       <inertia ixx="0.05" ixy="0" ixz="0" iyy="0.05" iyz="0" izz="0.05"/>
>>     </inertial>
>>     <visual>
>>       <origin rpy="0 0 0" xyz="0 0 0.0"/>
>>       <geometry>
>>         <box size="1.0 1.0 1.0"/>
>>       </geometry>
>>     </visual>
>>     <collision>
>>       <origin rpy="0 0 0" xyz="0 0 0.0"/>
>>       <geometry>
>>         <box size="1.0 1.0 1.0"/>
>>       </geometry>
>>     </collision>
>>
>>   </link>
>>   <gazebo reference="object_link">
>>     <material>Gazebo/Black</material>
>>     <mu1>10.0</mu1>
>>     <mu2>10.0</mu2>
>>     <kp>10</kp>
>>     <kd>1.0</kd>
>>     <turnGravityOff>false</turnGravityOff>
>>     <dampingFactor>0.01</dampingFactor>
>>   </gazebo>
>>     <gazebo>
>>         <controller:gazebo_ros_force name="box_force_controller"
>> plugin="libgazebo_ros_force.so">
>>          <alwaysOn>true</alwaysOn>
>>          <updateRate>15.0</updateRate>
>>          <topicName>box_force</topicName>
>>          <bodyName>object_link</bodyName>
>>         </controller:gazebo_ros_force>
>>     </gazebo>
>> </robot>
>>
>> I then have a python script publishing a wrench message to the box_force
>> topic however no matter what settings I use it never seems to actually
>> affect the box in the simulation. Am I going about this completely wrong? Is
>> there a flag I'm not setting?
>>
>> Thanks in advance for any help,
>>
>> David Ferguson
>>
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>>
>