https://www.cnblogs.com/flyingjun/p/8926824.html
1、urdf功能包:http://wiki.ros.org/urdf
2、urdf语法规范:http://wiki.ros.org/urdf/XML
3、urdf教程:http://wiki.ros.org/urdf/Tutorials
4、urdf示例:http://wiki.ros.org/urdf/Examples