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:
It’s possible to generate a graphiz dot graph and a pdf from the urdf using following command:
after that open it e.g. by
looks like that: