View Full Version : PiRobot at HBRC

01-30-2011, 07:47 PM
For anyone interested, the video of Patrick's presentation is now online:



Pi Robot
01-31-2011, 09:08 AM
Thanks Fergs! Also, here is an HTML version of the slides I used for the talk. Look for the "Continue" link at the top of each slide to advance. Click on the image on a video slide to go to the YouTube video, then click Back in your browser to go back to the slide show.



01-31-2011, 09:39 AM
Thanks for the great presentation Patrick and thanks to lnxfergy for posting the link.

02-04-2011, 05:41 PM
Really good talk, it was really good to highlight the most useful packages and what they do. I had a go a ROS over Christmas to see if it was easy to build a simulator for a robot. I found the system really cool, but got stuck on the getting the tf library working. I got very confused with robot publishers and joint state publishers and couldn't figure out how it was all meant to hang together.

After watching that talk I feel inspired to pickup ROS and apply it to an old project. The project was was to build a todo household tasks but which only got as far as a wireless rover with a webcam. Adding ROS to this would revitalise the old robot and be a good way to learn ROS as well.

Thank you once again for a great talk and cool robot :-)

Pi Robot
02-05-2011, 09:10 PM
Thanks for your kind remarks! Glad to hear I helped rekindled the ROS fire. Yeah, the tf library is powerful but can be confusing at first. You may have it sorted out by now, but the robot_state_publisher simply takes the URDF model of your robot, which includes the lengths of all the links and the types of joints connecting them, and maps the current joint angles into the positions and orientations of little coordinate systems attached to each link. I like the description from the robot_state_publisher page (http://www.ros.org/wiki/robot_state_publisher) on the ROS wiki:

"The package takes the joint angles of the robot as input and publishes the 3D poses of the robot links, using a kinematic tree model of the robot."

The kinematic tree model of the robot is typically provided by your URDF or Xacro file. As to how ROS knows the current joint angles of your robot--if you have a real robot then the node that talks to your joint controller (e.g. ArbotiX, USB2Dynamixel, etc) usually publishes the joint angles and you don't use the joint_state_publisher at all. However, if you just want to see how things hook together without involving the real robot, then you can use the joint_state_publisher with the "use_gui" parameter set to True, then use the slider controls to move the joints and view the result in RViz.


02-07-2011, 01:44 PM
Thanks for the explanation, that makes a lot more sense now.

I have ordered a new wireless adaptor as my current one dosen't play nice with my new router (was very flakey anyway). So with any luck I should have it this weekend and make a start integrating with ROS.