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Turtlebot + PhantomX Arm

asked 2014-01-12 10:24:30 -0500

cdrwolfe gravatar image

updated 2014-01-14 20:39:29 -0500

tfoote gravatar image

Hi,

I've just been experimenting with attaching a model (xacro.urdf) of a phantomx arm pincher to the top of the current turtlebot2 model.

In this instance I thought I would just try and add:

 <!-- Phantomx Arm -->
  <xacro:include filename="$(find phantomx_arm_description)/urdf/phantomx.xacro"/>

To the turtlebot_library.urdf.xacro file within the turtlebot_description package found in opt/ros.......

I edited the phantomx arm urdf to include a joint which links the top plate of the turtlebot to the base plate of the phantomx arm:

 <!-- joints -->
  <joint name="${prefix}arm_base_joint" type="fixed">
     <origin xyz="${M_SCALE*0} ${M_SCALE*0} ${M_SCALE*0}" rpy="${0} ${0} ${0}" />
     <parent link="plate_top_link" />
     <child link="${prefix}arm_base_link"/>
     <axis xyz="0 1 0" />
     <limit lower="-2.617" upper="2.617" effort="0" velocity="0.785" />
  </joint>

The rest of the joints simply continue as normal with parents of the former links and children being the next link in the arm etc:

  <joint name="${prefix}joint_1" type="revolute">
         <origin xyz="${M_SCALE*0.125} ${M_SCALE*-3.25} ${M_SCALE*8.75}" rpy="${M_PI/2} ${M_PI*2} ${M_PI}" />
         <parent link="${prefix}arm_base_link" />
         <child link="${prefix}link_1" />
         <axis xyz="0 1 0" />
         <limit lower="-2.617" upper="2.617" effort="0" velocity="0.785" />
      </joint>
      <joint name="${prefix}joint_2" type="revolute">
         <origin xyz="${M_SCALE*0} ${M_SCALE*4.15} ${M_SCALE*0}" rpy="0 0 0" />
         <parent link="${prefix}link_1" />
         <child link="${prefix}link_2" />
         <axis xyz="0 0 1" />
         <limit lower="-2.617" upper="2.617" effort="0" velocity="1.571" />
      </joint>

However unfortunately it seems that this little attempt has failed, though the 'arm_base_joint' and 'arm_base_link' connect to the TF of the robot model when loading up in rviz, all the other links fail, with a:

"No transform from [link_1] to [base_footprint]" error etc.

To be honest I'm not sure why?, my guess is that anything from link_1 and above which is a chain in essence is failing to link to the arm_base_link/joint.

But looking over it all the parent links and child links look to be correct in terms of order and spelling. Maybe it is a namespace issue.

Eventually I'd like to get a moveit package going for the little mobile manipulator then move on to some mobile pick and place etc. But I'm currently stuck at the moment.

Any help is appreciated

Kind Regards

Wolfe

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answered 2014-01-14 10:52:21 -0500

cdrwolfe gravatar image

updated 2014-01-15 02:15:05 -0500

Right after logically going back and forth through the urdf and doing various things it turns out that the reason that the other joints / links are not showing up is that they are listed as 'revolute', and that changing them to 'fixed' results in there appearance.

The question I have now is why this is the case?

Is it related to the turtlebot model or its particular type?

The PR2 robot model I assume has revolute joints and is essentially a mobile manipulator, which in some ways this is meant to be.

Surely it must be possible to add a robotic arm to the turtlebot urdf model etc, as it has been done before with the turtlebotArm package.


Right the answer turns out to be simple, all it was, was the lack of a joint_state_publisher node as discussed in

http://answers.ros.org/question/9130/visualizing-continuous-and-revolute-joint-types-in-rviz/

Well don't I feel foolish :)

Cdr

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Comments

Hi Wolfe - apologies for the comment on an old (and solved) question but could you add a bit more detail to how you edited arm.xacro and/or arm.urdf.xacro to connect the turtlebot and turtlebot_arm for rviz? I keep getting "invalid tag" errors - think I'm placing the snippets wrong! Cheers

wjvh gravatar imagewjvh ( 2016-04-14 11:59:22 -0500 )edit

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Asked: 2014-01-12 10:24:30 -0500

Seen: 655 times

Last updated: Jan 15 '14