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Hello all,

I just got started with ROS and moveit! to make my robot arm plan some movements. Ultimately I would like to optimize the speed of the executed movements by tuning the actuator's PID parameters. However, I noticed that moveit also keeps track of the time it takes to execute a motion. Now I worry that moveit factors in time somehow when it decides what trajectory to follow for the motion plannning, which would lead to it planning different motion trajectories when I start optimizing my PID's/execution time. I looked around on the internet but couldn't find any information about this.

So my question is: Does the motion execution time influence the planned trajectory of moveit? What influence does time have here?

Thank you for answering in advance!


Originally posted by You RQT on ROS Answers with karma: 35 on 2020-05-15

Post score: 1

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Now I worry that moveit factors in time somehow when it decides what trajectory to follow for the motion plannning,

If you're using the default planner (ie: OMPL), then it doesn't.

OMPL finds paths, not trajectories.


Originally posted by gvdhoorn with karma: 86574 on 2020-05-15

This answer was ACCEPTED on the original site

Post score: 2


Original comments

Comment by You RQT on 2020-05-17:
Thank you for your reply! I'm using set_pose_target() function from MoveIt! and the FollowJointTrajectory control for all the actuators. Is it still a path if I use OMPL in that way?

Comment by gvdhoorn on 2020-05-17:
OMPL plans paths, not trajectories. It doesn't matter which way you ask Moveit to plan it, in the end it's OMPL (unless you've configured a different planner to be used).

Comment by You RQT on 2020-05-17:
Thanks a lot, it's much clearer now!

Comment by bob-ROS on 2020-05-17:
@gvdhoorn does any of the current planners in Moveit set velocities/accelerations for the joints or is this done in post-processing with e.g. Iterative Parabolic Time Parameterization or Iterative Spline Parameterization?

Comment by gvdhoorn on 2020-05-18:
Please don't post questions in comments under questions with already accepted answers.

Post a new question.

Comment by funky_watermelon on 2020-05-28:
@gvdhoorn I think it is still relevant for this question. But the path returned by .plan() of the moveit commander returns a message of the type: http://docs.ros.org/kinetic/api/trajectory_msgs/html/msg/JointTrajectoryPoint.html . How does the time_from_start get involved if ompl doesn't return it. This link also point to the time dependency of the moveit commander functions: https://books.google.nl/books?id=wY2RCwAAQBAJ&lpg=PA353&vq=trajectory&hl=nl&pg=PA8#v=onepage&q&f=false

Comment by You RQT on 2020-05-28:
@funky_watermelon I think that is a very valid point and I'm interested to hear what @gvdhoorn thinks!

Comment by gvdhoorn on 2020-05-28:
It may be relevant, but it's a different question (which I believe also has already been answered).

The OP's question was: "how does timing information influence path planning?"

Your question is: "where does the time info even come from?"

Those are two different questions, and accordingly, should be asked in different posts.

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