The invention discloses a variable-
diameter positioning pin structure and a multiple-vehicle-type rail trolley. The variable-
diameter positioning pin structure comprises a mounting seat, a
rotating disc, a
servo motor, a protective cover and a plurality of pin claws. The
servo motor is mounted on the mounting seat, a shaft hole is formed in the mounting seat, and an output shaft of the
servo motorpenetrates through the shaft hole to be connected with the
rotating disc. The protective cover is mounted on the outer side of the
rotating disc in a sleeving mode and connected with the mounting seat. A plurality of radial notches are formed in the upper surface of the protective cover. The pin claws are mounted on pin claw seats, and the pin claw seats are mounted in the radial notches correspondingly. A rotating disc thread is arranged on the upper surface of the rotating disc. Pin seat threads are arranged at the bottoms of the pin claw seats. The multiple pin claws are evenly distributedto form a positioning column in a surrounding mode. The servo motor makes action to adjust the outer
diameter of the positioning column. According to the variable-diameter positioning pin structure and the multiple-vehicle-type rail trolley, the diameter of the positioning column can be adjusted specific to vehicle
body positioning holes of different vehicle types, and the step that the differentvehicle types are equipped with different positioning pins of the rail trolley is not needed, so that the structure is simple, operation is convenient, the cost is saved, resource waste is reduced, and storage of the rail trolley is facilitated.