The shaft (20) has a wheel (22) movably rotated around a rotational axis (Y22) with respect to a shaft (37). A structure element (12) defines a reference plane (P2) approximately parallel to ground when the wheel rests on the ground. A swiveling system (24) is pivoted with respect to the structure…

The system (11) has four pivot articulations (41-43, 45) defining four quadrilateral vertices (Q11) arranged in a plane (P11) perpendicular to an axis (X42). Extension and retraction units comprising rigid support arms (21-24) and a hydraulic cylinder (31) deform the vertices of quadrilateral by…