ROS Version: Humble

Gazebo Version: Fortress

I'm looking for suggested ways of spawning an object that is attached to a robot arm at run time. That is I'm spawning a URDF model of the arm at startup and then I want to spawn and attach an object to an arm link while running the simulation.

If I use the service interface with the following command: ign service -s /world/depot/create --reqtype ignition.msgs.EntityFactory --reptype ignition.msgs.Boolean --timeout 1000 --req 'sdf_filename: "/root/calibration_ws/cal_grid/model.sdf", name: "sdf_model"'

And here is my sdf defined model and joint to attach it to the robot:

<model name="charuco_default">
    <link name="charuco_link">      
      <inertial>
        <inertia>
         .......
        </inertia>
        <mass>1.0</mass>
      </inertial>
      <visual name="visual">
        .....
      </visual>
      <collision name="collision">
          .....
      </collision>
    </link>    
  </model>
  <joint name="cal_joint" type="fixed">
    <parent>upper_wrist_link</parent>
    <child>charuco_link</child>
    <pose>0 0 2 0 0 0</pose>
  </joint>

But when I spawn the object it is not attached to my robots link and appears at world 0,0,0

When I look in the UI I can see that the model sdf_model (which is the name I spawned with) lists the Parent Entry as 1 which is the same for my robot which I assume means world is the parent.

If I run: ign model -m sdf_model I get.

    Model: [66]
  - Name: sdf_model
  - Pose [ XYZ (m) ] [ RPY (rad) ]:
    [-0.000000 0.000000 -0.004950]
    [0.000001 0.000001 0.000065]
  - Link [67]
    - Name: charuco_link
    - Parent: sdf_model [66]
    - Mass (kg): 1.000000
    - Inertial Pose [ XYZ (m) ] [ RPY (rad) ]:
      [0.000000 0.000000 0.000000]
      [0.000000 -0.000000 0.000000]
    - Inertial Matrix (kg.m^2):
      [1.000000 0.000000 0.000000]
      [0.000000 1.000000 0.000000]
      [0.000000 0.000000 1.000000]
    - Pose [ XYZ (m) ] [ RPY (rad) ]:
      [0.000000 0.000000 0.000000]
      [0.000000 -0.000000 0.000000]

Any ideas to make it work as desired?

---

More testing...

So I tried to set my model name of my sdf to the robot's name but get a bunch of errors looking it up.

 [ign gazebo-4] [Err] [UserCommands.cc:1194] Error Code 19: Msg: Child frame with name[charuco_default] specified by joint with name[cal_joint] not found in model with name[kinova].
[ign gazebo-4] [Err] [UserCommands.cc:1194] Error Code 24: Msg: FrameAttachedToGraph error, Non-LINK vertex with name [kinova::cal_joint] is disconnected; it should have 1 outgoing edge in MODEL attached_to graph.
[ign gazebo-4] [Err] [UserCommands.cc:1194] Error Code 24: Msg: Graph has __model__ scope but sink vertex named [kinova::cal_joint] does not have FrameType LINK or STATIC_MODEL when starting from vertex with name [kinova::cal_joint].
[ign gazebo-4] [Err] [UserCommands.cc:1194] Error Code 25: Msg: relative_to name[charuco_default] specified by joint with name[cal_joint] does not match a nested model, link, joint, or frame name in model with name[kinova].
[ign gazebo-4] [Err] [UserCommands.cc:1194] Error Code 27: Msg: PoseRelativeToGraph error, Vertex with name [kinova::cal_joint] is disconnected; it should have 1 incoming edge in MODEL relative_to graph.
[ign gazebo-4] [Err] [UserCommands.cc:1194] Error Code 27: Msg: PoseRelativeToGraph unable to find path to source vertex when starting from vertex with id [4].
[ign gazebo-4] [Err] [UserCommands.cc:1194] Error Code 20: Msg: parent frame with name[upper_wrist_link] specified by joint with name[cal_joint] not found in model with name[kinova].
[ign gazebo-4] [Err] [UserCommands.cc:1194] Error Code 19: Msg: child frame with name[charuco_default] specified by joint with name[cal_joint] not found in model with name[kinova].
[ign gazebo-4] [Err] [UserCommands.cc:1194] Error Code 22: Msg: FrameAttachedToGraph unable to find unique frame with name [charuco_default] in graph.
[ign gazebo-4] [Err] [UserCommands.cc:1194] Error Code 22: Msg: FrameAttachedToGraph unable to find unique frame with name [upper_wrist_link] in graph.
[ign gazebo-4] [Err] [UserCommands.cc:1194] Error Code 21: Msg: joint with name[cal_joint] in model with name[kinova] specified parent frame [upper_wrist_link] and child frame [charuco_default] that both resolve to [], but they should resolve to different values.