Extensible mounting device and underwater robot

The extensible mounting device comprises a frame body and a plurality of limiting ropes, a driving mechanism is installed at the upper end of the frame body, each limiting rope is composed of a plurality of cylinders and a plurality of nylon ropes, a first groove is formed in one side face of each cylinder, a second groove is formed in the other side face of each cylinder, and the nylon ropes are arranged in the first grooves. Limiting rods are arranged in the first grooves, adjusting mechanisms for driving the limiting rods to stretch out and draw back are installed in the second grooves, a mounting plate is arranged among the multiple limiting ropes, sleeves are installed at the four corners of the mounting plate, the limiting pipes are sleeved with the sleeves, clamping mechanisms are installed on the bottom face of the mounting plate, and multiple floating plates are installed on the top face of the mounting plate. The device is simple in structure, the mounting plate can be limited through the limiting r