(Reordered for chronologic order)

>>> > On Wed, Jan 12, 2011 at 4:32 PM, Andy Somerville
>>> > <andy.somerville@resquared.com> wrote:
>>> >>
>>> >> Hi,
>>> >>
>>> >> Has anyone had previous success with GazeboRosF3D in cturtle? In
>>> >> attempting to use the GazeboRosF3D I've hit a bit of a wall. I believe
>>> >> that I'm using it correctly and the topic is even being published to,
>>> >> but I get all zeros back in situations that seem to clearly imply
>>> >> there should be some forces and torques.
>>> >>
>>> >> My urdf entry looks like:
>>> >>
>>> >> <gazebo>
>>> >>    <controller:gazebo_ros_f3d name="${side}_FTsensor"
>>> >> plugin="libgazebo_ros_f3d.so">
>>> >>        <alwaysOn>true</alwaysOn>
>>> >>        <updateRate>100.0</updateRate>
>>> >>        <bodyName>DarmSim/${side}Arm/WAM/LowerWristFTPalmLink</bodyName>
>>> >>        <topicName>DarmSim/${side}Arm/WAM/Wrist/FTSensor</topicName>
>>> >>
>>> >>  <frameName>DarmSim/${side}Arm/WAM/LowerWristFTPalmLink</frameName>
>>> >>        <interface:position name="${side}_FTsensor_force_iface" />
>>> >>    </controller:gazebo_ros_f3d>
>>> >> </gazebo>
>>> >>
>>> >>
>>> >> Where side is being filled in by "Left" and "Right", and
>>> >> "DarmSim/${side}Arm/WAM/LowerWristFTPalmLink" is the name of a link
>>> >> defined above the f3d entry in the xacro.
>>> >>
>>> >> Running the simulation produces the expected topics:
>>> >>
>>> >> /DarmSim/LeftArm/WAM/Wrist/FTSensor
>>> >> /DarmSim/RightArm/WAM/Wrist/FTSensor
>>> >>
>>> >> But echoing them while performing an action that should clearly
>>> >> produce a force and torque on that link consistently only produce 0s.
>>> >>
>>> >> I can find virtually no references to GazeboRosF3D being used in
>>> >> google searches or in the stacks I have checked out with the one
>>> >> exception being in
>>> >> "pr2_common/pr2_description/urdf/gripper_v0/gripper.gazebo.xacro" but
>>> >> that doesn't seem to be being subsequently used by anything. My next
>>> >> step is to dive into the code behind GazeboRosF3D.
>>> >>
>>> >> Is anyone aware of some obvious factors that could explain the
>>> >> behavior I'm seeing?
>>> >>
>>> >>     Andrew
>>> >>
>>> >>
>>> >>
>>> On Wed, Jan 12, 2011 at 9:11 PM, John Hsu <johnhsu@willowgarage.com>
>>> wrote:
>>> > Hi Andrew,
>>> > gazebo_ros_f3d returns applied forces and I just checked with
>>> > rosservice call gazebo/apply_body_wrench
>>> > and rxplotted the topic, and things look as expected for me.  Can you
>>> > describe more detail what your setup is?
>>> > thanks,
>>> > John
>>
>>
>> On Thu, Jan 13, 2011 at 9:12 AM, Andy Somerville
>> <andy.somerville@resquared.com> wrote:
>>>
>>> John,
>>>
>>> When you say it returns "applied forces" do you mean to say that it
>>> does not return forces that are the result of the physics simulation,
>>> and only returns forces that are the result of something like
>>> "rosservice call gazebo/apply_body_wrench"?
>>>
>>> My goal was to implement a force&torque sensor. In my setup, I applied
>>> the plugin to one of the links in a 7 dof manipulator. My expectation
>>> was that all of the forces and torques that occur in the simulation to
>>> that link would be reported. Perhaps I misunderstood the purpose of
>>> the plugin? If so, do you happen to know of a way to get the forces on
>>> a target link?
>>>
>>>     Andrew
>>>
>>>
>>>
>
> On Fri, Jan 14, 2011 at 1:25 AM, John Hsu <johnhsu@willowgarage.com> wrote:
>> Hi Andrew,
>> You are correct that applied forces are only "external user applied forces",
>> and does not include any reaction or constraint holding forces based on
>> physics (LCP result).  To implement what you have described (force&torque
>> sensor), I think you can obtain that information by summing up external
>> forces (gazebo_ros_f3d)
>> and the constraint forces provided by joints:
>> dJointFeedback *ODEJoint::GetFeedback().
>> does that sound about right?
>> John
>
>
> On Fri, Jan 14, 2011 at 11:20 AM, Andy Somerville <andy.somerville@resquared.com> wrote:
> John,
>
> After going through the code, I came to that conclusion as well and
> modified the gazebo_ros_f3d plugin to do as much. I'm using the
> GetBodyTorque, and GetBodyForce functions of course to get at the ODE
> feedback data, but it seems to be on the right track and looks like it
> will work out.
>
> Thanks for the advice : )
>
>     Andrew
>

I should add for anyone else solving the same problem that there is
some extra urdf that is necessary to get the feedback without which a
call to any feedback related function will segfault.

    <gazebo reference="DarmSim/${side}Arm/WAM/LowerWristYawJoint">
        <provideFeedback value="true"/>
    </gazebo>

The provideFeedback tag must be declared as demonstrated, and not
inside the joint declaration itself or it won't be registered.

I'll file a separate bug report regarding the segfault.

    Andrew