In this text one can see the process of the preliminary design to achieve a solution for a high efficiency propelling system for the A boat competing in the Dong solar challenge. Specifically, this document reports the research made to achieve a solution for the mechanical design of this motor from some features given by the foregoing electric design. To achieve this goal, a methodical design will be performed. During this methodical design, 2 different concepts are considered. Almost every component in both concepts is the same, as they are the components which accomplish the main functions of the motor, which is turning electric power into movement. They differ in the bearing disposition and the shafts shape, which will be an important point of discussion. The aim of this report is then choosing between the two concepts according to some requirements, like the shape of the rotor determined by the electric design, and some wishes, like high efficiency, low weight and being easy to attach to the boat. The calculations are made to orientate the discussion about which concept is the best, but they are not definitive to set the final dimensions of the different components. Before being able to discuss which one is better, some calculations need to be made, as they make the difference within the two motors. The bearings’ life is considered a very important point of discussion. After calculating the forces applied on the bearings using the finite element software LISA 7.7, it is found that in both motors, there is at least one bearing which life is too short. For this reason, needle bearings are adopted to solve the problem in the motor 1. For the motor 2, this option cannot be adopted so this almost discards this concept as an option. Then the calculations for the connection between the shaft and the rims through the pins are made. The three possible failures of the connection considered are shearing forces on the pin, shaft tear and rim tear. The lowest safety factor found is the one concerning the shearing forces on the pin, so if this connection fails, it will be here. Nevertheless, as this safety factor is big enough, the connection is validated. After that, a first simulation to know the behaviour of the shafts is made. Both shafts are simulated under the same conditions of performance with the Solidworks Simulation Express extension. The two principal matter of discussion are the von Mises stress and the angular displacement of the nodes. The result of the simulation shows that the shaft in the motor 1 is better in both items of discussion, with a safety factor for the stress of 2,54 and a displacement of 0,2 mm. Other items considered during the design such as assembly, fabrication and weight don’t turn to be determinant because there is not a big difference between them in the two different concepts. After discussing each requirement and wish, one can see that the motor 1 is better, or at least equal, than the motor 2 in every item discussed. For this reason, the concept chosen for the motor is the motor 1.

Outgoing