Brief
The purpose of this project is to optimise the crank arm for the Human Powered Vehicle designed during the engineering course at London South Bank University. The project has been made using Fusion 360 with the aim to create a stiffer and lighter part. The final outcome has been design considering the manufacturing equipment of the workshops at London South Bank University.
Research phase
The existing crank arm, made of Aluminium 6061 and machined in the workshop, was tested at three different points during the 'power stroke'. A 2000N force offset by 50mm from the crank at 0°, 90° and 180° was applied on the pedal axle hole. The simulation results suggest that the part would be under the highest stress in Load case 2 and 3.
Shape optimisation
The results from the initial research phase could be used to guide the redistribution of excess mass to areas of high stress, but this process can be sped up by running a shape optimisation study. A large piece of metal is reduced down to a rough mesh which can then be used as a reference to build a solid model for further refinement.
Adjusting the target to find areas that are not subject to excessive stress
The outlined new sketched part is then redesigned from the old one to create an optimised version.
Evaluation
Static stress simulations were carried out, using the same boundary conditions and load cases as before. The optimised part offers better all-round performance with an adequate factor of safety for all load cases, and comes in at two thirds of the weight.
Other materials were explored for the crank arm but most failed under the load of 2000N. Chromoly steel would be a good alternative to the titanium alloy as long as the weight difference is of no concern.
Final Design
