Tag Archives: urdf

ROS is about: simulation, simulation and simulation …

ROS needs to know everything about the physics of a robot. It starts with dimension to avoid collusions – both with the outside world and the robot itself (e.g. if it is using two robot arms at once).  Further it is relevant where the sensors are – or in my case where the [amazon &title=Asus Xtion&text=Asus Xtion] is located in relation to the robots base. Another interesting information are the robots joints. Its needed to drive the wheels and to rotate the camera. For all that, a detailed description and representation of the robot in a format that a computer understands is essential.

Today I’ve made a hugh step in the simulation field, so struggeling with the motors in the real world for the last few days doesn’t feel too bad – at least I can generate some nice pictures now:

For me an interesting journey started, with a lot ups and downs – currently I am really excited where we will be in 18 weeks – because 2 weeks of my thesis already passed.

First experiences with the ROS Unified Robot Description Format

The Unified Robot Description Format is a nice way to describe robots in ROS. It is a xml formatted file which contains robot related information like links – geometry figures such as boxes, cylinders or sketch-up models(!), Joints – the information how the links are connected to each other, e.g. if they are fixed or continuous and in which state they are (using tf, the ROS transformation package)  – and a lot of more stuff I didn’t figure out after a day with .urdf.
There also is some macro language called xacro, which seams to be pretty amazing, reducing xml code length, enable the usage of variables in it (like for scaling a whole bot) and much more.

it may look simple, but this little robot took a complete evening. He has 2 movable wheels in the front, custom colors and hopefully will drive around in simulation soon:

ScreenshotAmosero_1 ScreenshotAmosero

It’s possible to generate a graphiz dot graph and a pdf from the urdf using following command:

urdf_to_graphiz path/to/file.urdf

after that open it e.g. by

evince file.urdf

looks like that:ScreenshotAmosero_2