I am currently attempting to add an articulation velocity controller to my robot. The articulation root is set to the base_link, as shown in the second image below by filtering the stage window for articulation roots. There are four child joints that stem from it, the four wheels (whose joints take base_link as the parent body and /name/_wheel as the child. However, upon trying to add the controller to base_link, two error messages appear with the tags Parameter check failed and No valid joints found under the given articulation root prim, check if you need to give a different prim for robot root.
The only sticking point I can think of is the fact that as a URDF import, the mesh is under the base_link XForm and not part and parcel of it, but aside from that I lack ideas as to what the problem might be.
