The frame has driving wheels mounted on rods (15) sliding with respect to legs (9). An actuation system is mounted between a base (6) and bars (24, 25) of spiders (22). The legs are placed in contact with a ground when the frame is positioned on the legs. The actuation system is rested or pushed on the bars of the spiders. An upper extreme region of the bars is supported against the rods of the wheels when the frame is positioned on the wheels. The frame is rested on the wheels and the actuation system drawn over the bars so as to pull the legs.