Oregon State University Solar Vehicle Team Solar Car Mechanical Design “How do you start the design of a new solar car?” Mechanical Design Maximize Power Input Maximize efficiency (tractive force) Minimize drag Slide 7 of 62 A variety of vehicle designs Michigan Bochum Honda MIT Principia Minnesota Taiwan OSU, First Car Queens OSU, Odyssey Design Tools • Solidworks 2012 – Computer Aided Drafting • Solidworks Simulation 2012 – Finite Element Analysis • Solidworks Flow Simulation 2012 – Computational Fluid Dynamics Initial Design • Maximum power with minimum drag: – Lowest drag with maximum solar cell surface area • Design process: – Start with 6ft driver with helmet – Fit driver with body with max. surface area for cells (6 m2) • Good rule of thumb is to go to maximum width and length allowed – Wrap wheels, frame and suspension around driver inside body – Optimize body Initial Design Process 1. Insert driver model 2. Design solar car body, draw in “dummy wheels” 1. Fit body to driver model, dummy wheels. Maximum low curvature array area 3. Run wind tunnel testing (Computational Fluid Dynamics, Flow Simulation 2012) 1. 2. Evaluate drag force, power Evaluate cross sectional area vs. coefficient of drag 4. Alter body shape 1. Can be “arbitrary” change 5. Repeat steps 3 and 4 www.xkcd.com/844 Design to Rule (Initial Design) • 6.5.B Forward Vision: – From the normal driving position, the driver must be able to see at all times, without artificial assistance, points at the following locations: • (1) A point on the ground 8 m in front of the solar car • (2) A minimum of 17° above the horizon on level ground • (3) A full 100° to either side of center • (4) The driver will be required to identify 40 mm high letters at a distance of 3 m through any of the required viewing angles. • 6.1 Solar Car Dimensions – The solar car (including solar array) may not exceed the following maximum dimensions when moving under its own power: • (1) Length = 5.0 m • (2) Height = 1.8 m • (3) Width = 1.8 m • 6.4.B Seating Position: – The driver must be seated at less than or at a 27° angle, as measured in Appendix B. The driver’s head must be above and behind the driver’s feet. The seat must be appropriately constructed with a solid base and back rest. Chassis/Body Reconciliation • Best “body” initially designed with only driver, dummy wheels • Must “reconcile” body with chassis, due to chassis, suspension members taking up space • Remember: – Aerodynamics most important – Handling performance secondary – Mass considerations secondary Chassis Design • Build smallest chassis necessary to hold driver, wheels and withstand structural requirements – 5G frontal, side, rear impact – 4G roll over impact • Verify chassis, suspension design with Finite Element Analysis (Solidworks Simulation 2012) Body Re-work • Chassis/suspension will “poke out” of body • Remake the body for least drag that will fit chassis tightly Things to Remember • Tips for a “smoother” design process: • All designs valid unless proven otherwise – – – • Burden of good design proof is upon designer Must meet all rules, or design is invalid Absolutely avoid qualitative assertions: quantitative discussions much more useful Offer constructive help, avoid criticism in general. – “You could perhaps enhance your design by X,Y,Z” and not “Your design is failing in X, Y, Z!” • Avoid stating absolutes, unless you can absolutely prove it! • Go offline to compute numbers. Don’t argue with qualitative arguments: doing so will often result in circular discussions. • Don’t be married to your own design if someone else’s design is better – we’re all in it together to make the best car possible! • No place in solar car team for ego contests. • Remember – you’re working with friends. Be friendly!!!