| dc.description.abstract | A gearing system is the mechanism used, by different types of transports, to modify the features of the transmission. This mechanism must adapt the speed, and torque, according to the road conditions and the requirements of the driver, in order to optimise the driving. In case of bicycles, the transmission mechanism adapts the energy produced by the muscular effort of the driver into rotational movement of the wheels. Nowadays, most of them include a derailleur gearing system, which uses a chain transmission and several chain rings to modify the speed ratio transmitted to the rear wheel. However, since the different context of use, and users, require different types of bicycles, the market also includes a large variety of designs and gearing proposals. The main goal of this project is to develop a design proposal based on a gear shifting system. From previous research, with focus on the state of the art and the actual market of bicycles, different ideas of designs arise. As objective, the proposals obtained must accomplish a functional improvement in relation to precedent models and the integration of the different systems studied during the research. Then, these are studied to verify the technical possibilities to carry out each one of them. The proposal finally selected is a redesign of the shifting system of the Sturmey-Archer gearing hub, which is known to be one of the first internal gearing systems. This mechanism was very popular when was launched but it presented problems in the cable shifting system, which failed in activating the correct speed. As a solution, the design focuses on incorporating the ratchet system of a motorcycle to replace the direct cable shifting. During the design process, the parts and the assembly are modelled by 3D software, and evaluated by mechanical calculations and simulations, which must guarantee the correct performance of the mechanism. In this process, the materials used are also compared and selected to achieve the safety condition. To conclude, the development of this project is considered to have followed correctly the process stablished. The results of the different design stages are satisfactory. Regarding the resulting proposal, it is considered to achieve the safety and functional goals, although some aspect might be modified to obtain a more complete solution. |
