Steerable concentric ring segment supported lift crane

Abstract From the Canadian patent

Front and rear pairs of crawler assemblies are provided for supporting concentric ring segments disposed forwardly under the boom and rearwardly under the counterweight so the crane can travel under load and swing through at least a partial horizontal arc. One and preferably both crawler assemblies are selectively and reversely powered to facilitate forward and reverse as well as turning movement during travel under loaded and unloaded conditions. The inner ring segment is at least partially surrounded by a rotatable cage structure which provides a connection point for a frame element extending to the forwardly disposed crawler assembly to permit independent steering of the rear crawler …