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URDF question: origin

asked 2014-04-18 02:27:54 -0500

Yantian_Zha gravatar image

updated 2014-04-18 04:02:03 -0500

gvdhoorn gravatar image

Can anyone tell me

<origin xyz="${x_loc} ${y_loc} ${z_loc}" ...>

means what? In my view it is number like 0,1 that should be after xyz=, but not the ${x_loc} thing.

Additionally, I'm trying to mount an arm on turtlebot in URDF, is it OK to add turtlebot pan's origin parameter to origin parameter of arm base link? Or there exist other ways?

Thanks so much!

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answered 2014-04-18 07:40:46 -0500

Tom Moore gravatar image

Re: your first question, you can do two things. First, you can put in actual values, e.g.,

<origin xyz="0.13 0.4 1.2">

Alternatively, you can use xacro. What you posted was URDF with xacro markup in it. With xacro, you can define values like this:

<xacro:property name="x_loc" value="0.13" />
<xacro:property name="y_loc" value="0.4" />
<xacro:property name="z_loc" value="1.2" />

...and then do

<origin xyz="${x_loc} ${y_loc} ${z_loc}">

See this tutorial:

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Thanks, Tom. But the second question is more confusing and important for me. Would you pls help me out of this? Any suggestions or ideas are welcomed!

Yantian_Zha gravatar image Yantian_Zha  ( 2014-04-19 04:41:21 -0500 )edit

I apologize, but I don't quite understand what your second question is asking. I'm afraid I haven't worked with the TurtleBot before. If you're trying you mount an arm on the robot, I'm guessing you'd define the link and then define the joint. Can you post some URDF code?

Tom Moore gravatar image Tom Moore  ( 2014-04-22 03:52:30 -0500 )edit

No sorry at all. The link between arm and turtlebot has been found. But I still cannot understand deeply of the tricks described in the Tutorial you provided. I haven't learnt XML before. I don't know whether this learning matters more? Or do you have other advices? Thanks!

Yantian_Zha gravatar image Yantian_Zha  ( 2014-04-22 04:41:48 -0500 )edit

I would: 1. Go through an XML tutorial. 2. Go through the regular URDF tutorials, but ignore anything to do with xacro. Perhaps put together some sample robot models. This will help you understand why xacro is so useful. 3. Go through the xacro/URDF tutorial.

Tom Moore gravatar image Tom Moore  ( 2014-04-22 05:47:50 -0500 )edit

Thanks for your help!

Yantian_Zha gravatar image Yantian_Zha  ( 2014-04-22 12:18:23 -0500 )edit

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Asked: 2014-04-18 02:27:54 -0500

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Last updated: Apr 18 '14