Hello,

I am running ROS Noetic with Gazebo 11.11.0 (Ubuntu Focal) and trying to turn off gravity and self-collision on a few links. I tried both of these variations:

<!-- given upperarm_actuator_body_link is a <link> in URDF -->
<gazebo reference="upperarm_actuator_body_link">
    <gravity>false</gravity>
    <self_collide>false</self_collide>
</gazebo>

<!-- given upperarm_actuator_body_link is a <link> in URDF -->
<gazebo reference="upperarm_actuator_body_link">
    <turnGravityOff>true</turnGravityOff>
    <selfCollide>false</selfCollide>
</gazebo>

Also tried the same thing with 0 and 1 instead of True and False.

Gazebo doesn't recognize it. In the inspector pane selecting the link shows self collide "False" is unchecked, and gravity "True" is checked.

Full URDF: https://github.com/01binary/str1ker/blob/master/description/robot.urdf

If you want to clone & run "roslaunch str1ker gazebo.launch" and preview behavior, all the stuff is in "description" folder: https://github.com/01binary/str1ker/

This is all documented and there are examples of both variations on GitHub. Are you seeing the same thing or do I file a Gazebo bug and start trying to debug it?

[EDIT]

Found the source code, it appears to be correct at first glance, looks like I have to debug & create a pull request. If it looks correct but doesn't work, then it must be broken.

https://github.com/gazebosim/sdformat/blob/sdf13/src/parser_urdf.cc

// parser_urdf.cpp line 1382
else if (strcmp(childElem->Name(), "turnGravityOff") == 0)
  {
    std::string valueStr = GetKeyValueAsString(childElem);
    sdf->isGravity = true;

    // default of gravity is true
    if (lowerStr(valueStr) == "false" || lowerStr(valueStr) == "no" ||
        valueStr == "0")
    {
      sdf->gravity = true;
    }
    else
    {
      sdf->gravity = false;
    }
  }


  // parser_urdf.cc line 1437
  else if (strcmp(childElem->Name(), "selfCollide") == 0)
  {
    sdf->isSelfCollide = true;
    std::string valueStr = GetKeyValueAsString(childElem);

    // default of selfCollide is false
    if (lowerStr(valueStr) == "true" || lowerStr(valueStr) == "yes" ||
        valueStr == "1")
    {
      sdf->selfCollide = true;
    }
    else
    {
      sdf->selfCollide = false;
    }
  }