"URDF Model (New)" Have No Rigidbodies, New Links Have No Joints

[kneave]

• [X] I am at the right place and my issue is directly related to ROS#. General technical questions I would post e.g. at ROS Answers or Stack Overflow. For library-specific questions I would look for help in the corresponding library forums.
• [X] I have thoroughly read the Contributing Guideline and writing this issue is the right thing to do in my case.

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I have a question!

• [X] I searched the Wiki, open and closed issues for an answer. I tried my best to find the answer by myself without success. I believe that the discussion we will have in this issue, and the solutions we might find, will help me, and likely other community members who have a similar problem.

Here is my question:

Following the "create a new URDF" tutorial I found that none of the new links had joints created. In the video no extra steps were needed for this but I found I needed to manually add a rigidbody to the base_link in order for joints to be created in the manner shown in the video. I couldn't find reference to adding the rigidbody in the wiki or previous issues. Is this change by design or a regression of some kind?

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I found a bug!

• [X] I am using the latest ROS# version available here on the master branch.

• [X] I am adding all required information, code and data files, screenshots and log files so that you can reproduce the problem.

• My OS is: Windows 11, dev preview

• My Unity Version is: 2020.3.11f1

• My ROS Distribution is: N/A

• My Build Target Platform is: N/A

Here is my bug description:

Creating a new URDF doesn't include a rigidbody on the base_link, this prevents joints being created.

Perform the following steps reproduce the bug:

1. Create a new 3d object by selecting "urdf (new)" in the 3d objects menu
2. Click on the base_link and add a new link
3. Look at the newly created link, there will be no joint present

Observed results:

Base_link on a new model with no rigidbody

Newly created child link, no joint component

Expected results:

Base_link with rigidbody

New children have joints

[MartinBischoff]

Hi @kneave ! we didn't add a rigidbody by default, because links in URDF can also come without `inertial' tag. By adding a rigidbody manually, users can add the inerial tag. It is correct that joints require rigidbodies in both parent and child link.

[kneave]

Hi Martin, this is from creating a new model completely in Unity so no URDF imported in this case. If it's expected behaviour that the user adds a rigid body could I suggest the video demo be updated to show this please or it be included in a the documentation?

[MartinBischoff]

Hi @kneave , I digged a bit deeper into this issue. We changed the functionality in commit https://github.com/siemens/ros-sharp/commit/f15f3f9eeec0d46b7dbb3dfbc4364eeef8e7fbe8 to not automatically generate rigidbodies in this case.

The problem is that URDF does not require <inertial> tags (i.e. rigidbody data) whereas Unity requires rigidbodies to create joints between transforms (i.e. links). We had discussions whether to create a default rigidbody to a new/empty link or not since the beginning and didn't find a clear answer yet.

In pull request #405 I changed it back, such that creating a new link in Unity also creates a rigidbody / default inertial data. It seems like this is the more convenient / user friendly solution. Would you please test if it works for you?

[kneave]

I just pulled that branch and it looks like it works as I'd expect from the demo video, thanks for the quick update! Good call with the Newtonsoft.Json fix too. :)

[MartinBischoff]

Merged in https://github.com/siemens/ros-sharp/commit/6e91309b2447c0919d3dabaa0650bb71e3e490dd . Thank you @kneave .