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PSU / Middle Schools Solar Racers Workshop

PSU / Middle Schools Solar Racers Workshop. Solar and Car Fundamentals Andy Lau, andylau@psu.edu Dale & Toby Short, SCASD. Overview. Maximize power produced Minimize power needed. Solar cells → motor → gears → wheels. Makes power. Friction Drag Acceleration. Uses power.

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PSU / Middle Schools Solar Racers Workshop

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  1. PSU / Middle SchoolsSolar Racers Workshop Solar and Car Fundamentals Andy Lau, andylau@psu.edu Dale & Toby Short, SCASD

  2. Overview • Maximize power produced • Minimize power needed Solar cells → motor → gears → wheels Makes power Friction Drag Acceleration Uses power

  3. Drive System Fundamentals Solar Cells Gears Motor Wheel

  4. Gear Ratio 1 Turn 2 Turns Axle Gear Teeth 20 = = = 2 Motor Gear Teeth 10 Gear Ratio = 2 Red gear spins twice as fast as blue

  5. 2 Turns Motor Speed Wheel Speed 1 Turn Motor Speed = Wheel Speed Gear Ratio 2 Turns = 1 Turn 2

  6. Circumference 2 π 6 = 38 cm Radius 6 cm 2π x Radius Radius 3 cm 2 π 3 = 19 cm

  7. How does wheel size affect the speed?

  8. Circumference Radius 6 cm Circumference = 2πr = 38 cm Radius 3 cm Circumference = 2πr = 19 cm • For each turn of the wheel your car travels the circumference of the drive wheel • Doubling wheel radius also doubles circumference which will make your car go twice as far in one rotation

  9. So why not use really big wheels?! Because the motor performs best at a certain speed! Suggestion: Pick a wheel size that you like. Experiment with different gears and gear ratios to find the best for your car. The best gear ratio will depend on the sun’s intensity and whether you’re running on batteries.

  10. Lessons learned at PSU • In full sun So if your wheel r = 6 cm, then the best GR is GR = 6 cm x 1.14/cm = 6.8 • In half sun • With batteries

  11. Getting the most power output from a PV panel Tilt towards sun Possibly increase solar input with reflectors

  12. Incidence angle

  13. Again

  14. Where is the sun?

  15. Where is the sun? On May 20 the sun will rise to around 70 degrees at solar noon (1 p.m.).

  16. Car Power Fundamentals Car Air Drag Friction Acceleration

  17. Reducing car power needs • Friction: • Low weight • Axle bearings • Skinny tires Air Drag: • Small frontal area • Smooth shape Acceleration: • Low weight Which body shape is fastest?

  18. What a fast car looks like Panel towards sun Small frontal area Straight light wheels Light

  19. What a slow car looks like Panel not towards sun Hot glue abuse Heavy crooked wheels Way too BIG and heavy

  20. So that’s all there is to it … Reflectors Make shape smooth Bearings Motor speed GR, r Reduce friction Face the sun Minimize weight Reduce frontal area

  21. Examples of JSS Cars

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  39. The End Any questions?

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