[ros-users] trajectory error in simulation / controller parameters

[Gil Jones]

Hi Jannik,

The path you are seeing is indeed the path that comes from the planner.  But
there's an extra step that move_arm goes through of filtering the trajectory
using a spline_shortcutting method that tries to find ways to make the path
shorter while also assigning reasonable velocities when it can.  This can
change the trajectory quite a bit.  If you want to see the path that
move_arm will actually be sending to be executed you'll need to change the
code a bit.  Overlay arm_navigation.  In whatever version of the code you
are running find the line:

visualizePlan(current_trajectory_);  //move_arm_simple_action.cpp:1361 in
unstable.

Comment this line out, and then copy it an add it after the line:

current_trajectory_ = filtered_trajectory; //move_arm_simple_action.cpp:1422
in unstable
visualizePlan(current_trajectory_); // copied from 1361

The trajectory you see in rviz will now be the actual one getting passed to
the controller.  I expect it will look much more like the executed
trajectory.

Let us know if you have other questions.

-Gil

--
E. Gil Jones (gjones at willowgarage.com)
Research Engineer
Willow Garage, Inc.
68 Willow Road
Menlo Park, CA 94025
650.475.9772 <+16504759772>


On Fri, Feb 11, 2011 at 10:18 AM, Jannik Kett <jannik.kett at googlemail.com>wrote:

> Hello everyone,
>
> I'm a student at University of Stuttgart and work at IPA Fraunhofer with
> the Care-O-bot.
> We have here some problems with the planned trajectory in simulation. The
> actual executed trajectory of the robot arm in rviz differs from the planned
> one (display_path (motion_planning_msgs/DisplayTrajectory)). We guess that
> it comes from the dynamic model and the chosen controller parameters in the
> arm_controller_cob3-1.yaml file
> (cob_simulation/cob_controller_configuration_gazebo/ros/controller).
> So we're looking for ideas, hints and rules how to choose these parameters
> or explanations where the trajectory error could come from.
>
> Thanks in advance for your help!
>
> -Jannik
>
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