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Public waffleboard to track Robotics Nanodegree Issues
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Issue with Launch File for Write ROS Nodes 3-10 'Look away' #104

Closed adammalpass closed 7 years ago

adammalpass commented 7 years ago

I had an issue running the look_away code in the Write ROS nodes section 3-10. Finally I managed to trace the issue back to the way the launch file is set up in section 3-10. There can exist a race condition whereby the look_away node starts up before the arm_mover node is ready and hence the look_away node's look_away_callback function gets permanently stuck at the 'rospy.wait_for_service('/arm_mover/safe_move')' line.

This can be fixed by creating a safe_spawner type script (like we do for later modules) or more easily just leaving the original launch file untouched and then instructing students to start the look_away node manually.

This was really complicated to debug, so please let everyone know to save lots of hassle later! :)

adammalpass commented 7 years ago

Btw I created and tested a safe_spawner.sh script to fix this issue. Now the project runs with no issues. I created a pull request on the simple arm repo to add this script, so if you like please accept so other students can share it :)

kylesf commented 7 years ago

I will check this out. Thanks :)

adammalpass commented 7 years ago

Hi Kyle I had a email saying the pull request was good and accepted, but it doesn't seem to have made it into the repo yet for some reason. I'm not expert in pull requests, so please could you check? Thanks! :)

Deborah-Digges commented 7 years ago

I spent about an hour wondering why look_away wasn't working! this turned out to be the issue. Quite frustrating really. Please could the lessons be updated to at least reflect the explanation given by @adammalpass

adammalpass commented 7 years ago

@kylesf Thanks for accepting the pull request to add my safe spawner script. Perhaps you could also update the lesson notes to recommend using it to, to help other students avoid finding this issue? Thanks!

adammalpass commented 7 years ago

@Deborah-Digges Glad it fixed your issue! Hopefully it can get added to lesson notes soon :)

kylesf commented 7 years ago

Done!