The rotor complex of the bacterial-type flagellum consists of a membrane-anchored ring and the motor switch complex, which participates in the conversion of proton/Na+ energy into the mechanical work of rotation and controls the direction of flagellar rotation. [ http://www.ncbi.nlm.nih.gov/pubmed/10572114 http://www.ncbi.nlm.nih.gov/pubmed/12624192 http://www.ncbi.nlm.nih.gov/pubmed/25251856 ]