Inertias are attribute to links

Course Support URDF for Robot Creation in ROS2
1

This is a good answer for a question in Unit 4: Using URDF for Gazebo.

I am not a native English, so maybe I do not understand the sentece.
But attributes in XML are like this <ELEMENT attributeName="attributeValue">, so “inertial” is clearly not an attribute of a link element in URDF.

So probably here (because of the word “inertias” and not “inertials”) the “attribute” word has its general meaning and not related to XML attributes.

If it is true, I think, it is a bit misleading, at least it was for me.

Maybe you can make it more straightforward for future learners.
Péter

2

Hi Peter,

i am not sure, whether i understand your question 100 % correct but i try:

With interias, you can give a physical component to a link, how it behaves physically, if force is applied.

In URDF - attribute has a general meaning and the interials a defined as element.

So the sentence “interias are attributes to links” is grammatically correct, since it defines a property of an object. But it is also misleading, because in URDF you dont use it with

<ELEMENT attributeName="attributeValue">
but you apply them like

<link name="base_link">
     <inertial>
       <mass value="10"/>
       <inertia ixx="0.4" ixy="0.0" ixz="0.0" iyy="0.4" iyz="0.0" izz="0.2"/>
    </inertial>
</link>

I hope i could help you and please ask, if i misunderstood or you have further questions.
If I describe something wrong, im happy to improve my knowledge.

Best regards, Freddy

3

Hi Freddy,

Thanks for the answer.
So you think the same as me:

So the sentence “interias are attributes to links” is grammatically correct, since it defines a property of an object. But it is also misleading, because in URDF you dont use it with…

What I would like to ask from The Construct Team, that may rephrase that particular answer, because it is misleading.

Like this:
Inertial is a child element of links.

Thank you in advance
Péter

1 Like
4

Hi,

Its true that it might be misleading this detail.
Just to know where you had this issue, this happened in which unit exactly? Or in the miniquizzes?

5

Hi,
It was in the mini quiz, in “URDF for Robot Creation in ROS2”, in Unit 4.
This was the good answer and with this text exactly: " Inertias are attribute to links"
I can not remember for the question.

Thank you in advance
Péter

6

Ok we will correct that :wink:

7

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