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trajectory error in simulation / controller parameters

asked 2011-02-14 16:25:54 -0500

Tully gravatar image

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!

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answered 2011-02-14 16:26:32 -0500

tfoote gravatar image

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.

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Asked: 2011-02-14 16:25:54 -0500

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Last updated: Feb 14 '11