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How does time influence moveit motion planning?

asked 2020-05-15 06:58:46 -0600

You RQT gravatar image

updated 2022-05-23 09:57:41 -0600

lucasw gravatar image

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!

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answered 2020-05-15 07:12:09 -0600

gvdhoorn gravatar image

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.

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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?

You RQT gravatar image You RQT  ( 2020-05-17 04:31:33 -0600 )edit

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).

gvdhoorn gravatar image gvdhoorn  ( 2020-05-17 08:17:11 -0600 )edit

Thanks a lot, it's much clearer now!

You RQT gravatar image You RQT  ( 2020-05-17 08:19:44 -0600 )edit

@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?

bob-ROS gravatar image bob-ROS  ( 2020-05-17 18:12:07 -0600 )edit

Please don't post questions in comments under questions with already accepted answers.

Post a new question.

gvdhoorn gravatar image gvdhoorn  ( 2020-05-18 01:26:49 -0600 )edit

@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: . 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:

funky_watermelon gravatar image funky_watermelon  ( 2020-05-28 05:53:57 -0600 )edit

@funky_watermelon I think that is a very valid point and I'm interested to hear what @gvdhoorn thinks!

You RQT gravatar image You RQT  ( 2020-05-28 06:05:37 -0600 )edit

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.

gvdhoorn gravatar image gvdhoorn  ( 2020-05-28 06:14:59 -0600 )edit

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Asked: 2020-05-15 06:58:46 -0600

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Last updated: May 17 '20