Inconsistent behavior of Articulation Bodies when starting scene

[karthikm-0]

Hi,

I'm trying to launch my robot and subscribe to a joint states topic from ROS. I find that the robot is extremely unstable at times and does not reach the start state of the ROS robot. Other times, this works perfectly. I've uploaded a short gif of a few runs where the first few are fine (https://media.giphy.com/media/ePnzMhBtlsfA5d1pRy/giphy.gif). Sometimes the robot keeps moving to different positions in a rapid manner (https://media.giphy.com/media/Y7bQxNHlhBgVEBozZ0/giphy.gif). Could someone help me troubleshoot the issue?

Thanks!

[vidurvij-Unity]

Hi @karthikm-0.
Thanks for reaching out with the problem. Is it possible to get access to your repo or a zip file of the project. I would be able to help you if I know more about the project.
Vidur

[karthikm-0]

Thanks @vidurvij-Unity! I've added you to my private repo. You'll need to import the tcp connector package before running. Also you'll need to run the program a few times to see the weird behavior (sometimes the gripper joints are oddly positioned and other times it goes crazy). If you don't see the behavior, please let me know because I also have a ros package to control the robot through a joystick which might be the cause of the issue (since it needs to transition from the start joint state to the joint state that my joystick input requests). I could share that if necessary.

Also, on a side note, I've been trying to import a specific robot (Franka Panda) and keep running into the AA BB error (Unity-Technologies/URDF-Importer#11 but without any crashes, just that the robot disappears from the scene). This is with using the ignore collision tags on all links (currently commented out). You can find the urdf inside the same project.

[vidurvij-Unity]

@karthikm-0 I got your invitation. I don't see any instructions to replicate the issue. Can you update the project readme so I can replicate the issue. Also I would recommend using the package manager to use the ROS-TCP-Connector in the Unity Editor.
Thanks
Vidur

[karthikm-0]

Hi @vidurvij-Unity sorry for the late response. I've decided to abandon this approach for now and am trying to import the Franka Panda using this URDF https://github.com/justagist/franka_panda_description but I am seeing the aa bb issue yet again. Could you try to import this robot and see whether it works? The .urdf file is also included in the repo I shared last week. Thanks!

[karthikm-0]

@vidurvij-Unity I just realized I may have posted this in the wrong repo as it may be better suited in urdf-importer (Unity-Technologies/URDF-Importer#25). Should I close this and open a post there? Thanks!

[vidurvij-Unity]

@karthikm-0 Does this issue appear when you press "play" ?

[karthikm-0]

@vidurvij-Unity Yes, the issue appears when I hit play. Please see the attached video:

https://streamable.com/j25usw

This occurs despite ignoring collisions between all links and disabling physics for the robot through layers.

[karthikm-0]

@vidurvij-Unity Quick update - I've isolated the issue as belonging to a specific articulation body - panda_link8. I believe it is because this isn't actually a real joint and is only a fixed link that exists to house the two finger joints. Since its mass is 0, I assume there is a divide by zero error somewhere. Disabling this articulation body or adding an infinitesimal value fixes the errors!

[vidurvij-Unity]

@karthikm-0 Thank you bringing this to our attention. This is will be resolved in
Unity-Technologies/URDF-Importer#57