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

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

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Drive System Fundamentals Wheel Motor Solar Cells Gears

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

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

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

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How does wheel size affect the speed?

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Circumference Radius 3 cm Circumference = 2 π r = 19 cm Circumference = 2 π r = 38 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 Radius 6 cm

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So why not use really big wheels?! Because the motor performs best at a certain speed! Suggestion: 1.Pick a wheel size that you like. 2.Experiment with different gears and gear ratios to find the best for your car. The best gear ratio will depend on the suns intensity and whether youre running on batteries.

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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

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

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Incidence angle

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Again

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Where is the sun?

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

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Car Car Power Fundamentals Air Drag Friction Acceleration

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Reducing car power needs Friction: RLow weight RAxle bearings RSkinny tires Air Drag: RSmall frontal area RSmooth shape Acceleration: RLow weight Which body shape is fastest?

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

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

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So thats all there is to it …

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Examples of JSS Cars

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The End Any questions?

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