Friday, December 18, 2009
After extensive material testing and comparison of weight and cost to Cromoly, it was determined that bamboo could be a viable frame material for this vehicle. The frame has a tub style truss design to provide more protection to the rider, easier integration of a roll over protection system, and more mounting points for the aerodynamic fairing.
Many options for the drivetrain system, gearing, brakes and frame integrations were evaluated. This vehicle will have a 20” front wheel with a 26” rear drive wheel. A chain drive system seemed to best suit this application, with its wide range of gears and readily available low cost parts. The layout of the drivetrain will consist of a 55 tooth front crank chain ring, that is lead to a 40 tooth drive chainring, where motion will be translated through the frame to a two driven chainrings of 34 and 50 teeth. The chain will then be run to a 10-speed cassette at the rear drive wheel. Using this gearing the vehicle will be able to travel at 43.5 mph at a cadence of 120rpm. The system used to stop the vehicle from these high speeds will be mechanical disc brakes. A front crank arm was designed to allow the vehicle to be adjusted to different riders.
Eight composite layups were tested for the aerodynamic fairing, consisting of fiberglass and carbon fiber and various core materials. It was determined that using 1/4” Diviny cell foam as the core would best fit this application. Fiberglass was chosen over carbon fiber due to it’s cheaper price and flexibility. Three full fairing designs were made to encompass the frame and rider.
Going forward with this senior project, the next step is to build the jig for the frame and begin construction. A method of integrating all drivetrain components with the frame must be devised. The best fairing design will be determined through wind tunnel testing and CFD analysis, and it will be constructed. Construction of the vehicle will be completed by the end of March, and testing and tuning of the vehicle will be ongoing until the HPVC in May. The team is confident they have designed a practical, reliable, and fast human powered vehicle, and feel they will be successful in their goal of winning the ASME East Human Powered Vehicle Challenge.