In the structure (a) (1) includes two beams with plates (2) at its ends.The mounting Plates (2) (3) that provide attachment points for the projections (4) (5) of a Cylinder (6) provided with a Shaft (7) Intern.The STEM (7) includes a Stop (8) at one end and the opposite is linked to a base (9) which is a column (10) and (11) two fins oriented Support plane.Between the fins (11) is provided with a Wheel provided with a Shaft (12) whose ends are fixed to the Rolling.The STEM (7) includes at least one limiter (13) located between the top of the Cylinder (6) and the CAP (8).The limiter (13) is a Clamp shaped Parts in two semi Cylindrical linkable to any suitable means that when they are United to form a Hollow central zone with a diameter of resultCoincident to or slightly greater than the diameter of the rod (7). In The Body of the Cylinder (6) are provided for Mouths (14) connected to ducts (15) connected to a Fluid Reservoir.The End of the rod (7) opposite to the stop (8) provides a Fork Nut (16) and (17),With the fork (16) connected to an anchor (18) which is fixed to the Supplement (19) of the column (10).The entry of Fluid into the mouths (14) Drives a piston (20) fixed to the Shaft (7).En la estructura (a) se incluyen dos travesaños (1) con placas (2) en sus extremos. Las placas (2) tienen soportes (3) que proveen puntos de fijación (4) para las proyecciones (5) de un cilindro (6) provisto con un vástago (7) pasante. Dicho vástago (7) incluye un tope (8) en un extremo y el opuesto se vincula a una base (9) de la que se proyecta una columna (10) y sendas aletas (11) orientadas hacia el plano de apoyo. Entre las aletas (11) se dispone una rueda (12) provista con un eje cuyos extremos se fijan rotatoriamente a aquellas. Cuyo vástago (7) incluye al menos un limitador (13) ubicado entre la parte superior del cilindro (6) y el tope (8). El limitador (13) es una abrazadera conformada en dos piezas semicilíndricas vinculables con cualquier medio idóneo que cuando están u
