How i do sketch 3D in Autodesk Inventor?
A tubular chassis is a 3D lines structure which must be replaced by a profile of one or more kind, isn't it? Using Autodesk Inventor you can make this by using the Frame Generator. To start this, try to follow the tutorial from Autodesk: http://help.autodesk.com/view/INVNTOR/2014/ENU/?guid=GUID-D318C64F-776F-463C-BF6E-6313BAF8DD7C. Good luck!