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rqt_plot error from incomplete joint state data

asked 2018-02-09 09:53:57 -0500

KBradner gravatar image

I am trying to plot joint efforts from a Baxter robot in rqt_plot. I can subscribe to robot/joint_states and get the data just fine. The format for the effort portion of the data is like this (from a rostopic echo):

effort: [0.0, 0.0, -1.66, 0.0, -0.872, -4.472, -0.084, -0.168, -0.008, -0.2, -19.056, 0.216, -26.844, -0.288, 0.076, 0.056, -20.48]

However, when I try to plot individual components of this effort in rqt_plot, effort[0] is the only one that works. If I add effort[1] or higher, I get the following error:

PlotWidget.update_plot(): error in rosplot: [/robot/joint_states/effort[1]] index error for: header: ,   seq: 122200,   stamp: ,     secs: 1517944540,     nsecs: 889999872,   frame_id: '', name: [r_gripper_l_finger_joint], position: [0.0], velocity: [0.0], effort: [0.0]

My best theory for the cause is that sometimes the effort field has just one component, which seems to be what the error message above is complaining about. I don't know why this occurs, but is it possible to make rqt_plot ignore the occasional missing data and just display what shows up? Alternatively, is there a built in way to prune out this missing data before I pass it along?

I am running the latest versions of rqt_plot, Ros Kinetic, Ubuntu 16,

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On the real Baxter (not the simulator), messages published on the /robot/joint_states topic sometimes contain the arm data, and sometimes the gripper data. As a result there are definitely messages published with varying lengths for these arrays. One easy workaround is....

jarvisschultz gravatar image jarvisschultz  ( 2018-02-15 09:31:16 -0500 )edit

... to use the joint_state_publisher with it's source_list private parameter. For example rosrun joint_state_publisher joint_state_publisher _source_list:="['/robot/joint_states']"will publish a new topic "/joint_states" that always contains complete joint information. Hope that helps.

jarvisschultz gravatar image jarvisschultz  ( 2018-02-15 09:33:04 -0500 )edit

I am having a similar issue with several servo motors publishing in array format. Did you end up resolving this?

RobotRob gravatar image RobotRob  ( 2018-03-21 13:03:00 -0500 )edit

I have not really resolved it in away that would be generally useful. I believe jervisschultz's reasoning about the cause of the issue was correct, but I did not get his fix to work correctly. I ended up using a workaround that was particular to my application.

KBradner gravatar image KBradner  ( 2018-03-21 13:06:44 -0500 )edit

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answered 2018-05-14 12:45:48 -0500

Davide Faconti gravatar image

I am 90% sure that PlotJuggler is not affected by this issue; may be you want to use that instead of rqt_plot.

Can you try it yourself or share with me a small rosbag to check if it works?

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Asked: 2018-02-09 09:53:57 -0500

Seen: 446 times

Last updated: May 14 '18