In this work you could find the story of the RT system and the development of the new RTL system, whose purpose is to add a new movement to the current RT system without increasing so much the costs and making a more modern design. Finally I get to make this design more contemporary, changing those forms curves by straight and making a fairing that can change the form easily due to its process of manufacture. This project had as condition not overcome the price of the current system by more than 150€ and not make some investments higher to 25,000€. The two conditions are respected, having an increase of only €84 and investments have been met from as much € 14,000. The design is based on a central rotation system, which is fastened over the gas spring and on a vertical guide which is fixed in the outside shell, that at the same time it is welded on the base. On these, there is a part that I called bath, where is mounted the translation guide and on this is assembled the plate that subject the armchair. I could conclude this summary commenting the finite elements analysis that I did to check their deformations and know if the system could hold the 30 kg of the armchair more the 120 kg of a person. The analysis has been correctly, marking a peak deformation of 0.5 mm at the top of the system whose value is insignificant regarding the function that makes that part.