Chapter 7: Course Project description clarification


in the description about the robot arm is mentioned.

  • An origin frame called world
  • A separate robot stand, that connect the robot base with the ground floor
  • The connection between the robot base and the robot stand is a rigid joint.

Questions to me are.
Is the frame “world” and the seperate robot stand the same ? if not what is meant with world frame ?
The robot base is not shown in the graphic and the demensions are not in the text ?

If someone could clarify that ?


Hello @vkuehn,

the origin frame called world refers to a root link in the simulation. Sometimes this kind of link is called dummy link- Its only purpose is to determine the robot’s base coordinate frame in the simulation.
This link is special since it is the only link that does not has any physical properties such as inertia and others. All you have to do is add this line to create it:

<link name="world">

Then you can create a fixed joint between the robot_stand and the world link:

     <link name="world" />
        <joint name="world_to_root" type="fixed">
            <child link="robot_stand" />
            <parent link="world" />
            <origin xyz="0 0 0" rpy="0 0 0" />    

Finally, you link your robot base to the robot stand.

Hope this helps,


Hello @rzegers,

thanks for the clarification.


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