Dirtcross BAJA 2015-16
SAE’s Baja India is an international competition for undergraduate engineering students in India with the objective of building an off-road buggy to participate in a 4 hour endurance race. The buggy has to meet strict specification and design, manufacture and test robust vehicle systems from scratch to participate in the final race. A team of 25 students was formed to compete in the competition and buggy was manufactured maintaining the rules in rulebook. As a result of sound engineering practices and manufacturing, team’s objective of completing the 4 hour endurance was achieved.
Through research it was clear that the buggy will be subjected to highly rough terrain including bumps, slush, steep inclinations, rocky fields. Suspension became an important part for such a vehicle which will be subjected to rough terrain and shocks. Further research was carried out to understand current systems that are implemented in off-road vehicles and on-road vehicles to understand advantages and disadvantages of each. Based on our requirements, a suspension system containing double wishbones was selected for implementation in the buggy. The design was divided into 2 parts- dynamics and kinematics. Kinematics deals with pure motion whereas dynamics deals with motion under the action of forces. Kinematics simulation was carried through msc Adams and dynamics through Ansys workbench.
Designing a suspension system also needs inputs from all other departments such as brakes, steering etc. Space frame design of chassis, position of transmission system, requirements of steering arm, diameters of disc from braking department, all the data from other department was considered for designing a system which achieves the requirements of suspension as well as other departments. In kinematics, msc Adams helped us visualise and measure the motion of double wishbones and suspension related parameters like camber, caster, toe and after multiple iterations on msc Adams, predetermined values for suspension parameters were achieved. The hard-points from msc Adams were plotted in CAD software to get the plotting points on chassis and engineering design points for other suspension components such as knuckle, wishbones etc.
Through research, possible impact loads were identified and were used for designing stiffness for shock absorbers. Suspension theories were used as front and rear suspensions both work together to keep the vehicle and driver safe from sudden shocks. Customized springs, suitable for our requirements were designed and manufactured. Ansys workbench was used to understand stress levels on wishbones during loading. Over the time, design of certain suspension components evolved to suit the manufacturing methods and feasibility of use. A high grade aluminium alloy was selected for its high strength and less weight for manufacturing some of the components.
Other parts of vehicle were also designed such as hubs for wheels, gearbox for engine, steering rack and pinion etc. using Ansys workbench. A DFMEA (Design Failure Mode and Effect Analysis table) was developed to understand failure impact on vehicle and eventually the driver. The attempts for changing the design for components having high SOD (Severity-Occurence-Detection) number were made to make the vehicle more reliable. In the end, the buggy was tested by professionals working in automobile industry and on the off road for 4 hours.
The buggy successfully completed the 4 hours endurance race and also showed the areas for improvements in next years.
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