Solar Car Fundamentals Overview Maximize power produced Solar

Overview • Maximize power produced Solar cells → motor • Minimize power needed Friction

Drive System Fundamentals Solar Cells Gears Motor Wheel

Gear Ratio 1 Turn 2 Turns Axle Gear Teeth = Motor Gear Teeth =

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

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

Circumference Radius 6 cm Circumference = 2πr = 38 cm Radius 3 cm Circumference

So why not use really big wheels? ! • Because the motor performs best

Lessons learned • In full sun So if your wheel r = 6 cm,

Getting the most power output from a PV panel • Tilt towards sun •

Where is the sun? On May 20 the sun will rise to around 70

Car Power Fundamentals Car Air Drag Friction Acceleration

Reducing car power needs Friction: ● Low weight ● Axle bearings ● Skinny tires

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

What a slow car looks like Panel not towards sun Hot glue abuse Heavy

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Solar Car Fundamentals

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

Drive System Fundamentals Solar Cells Gears Motor Wheel

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

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

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

How does wheel size affect the speed?

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

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 sun’s intensity and whether you’re running on batteries.

Lessons learned • 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

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

Incidence angle

Again A g a i

Where is the sun?

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

Car Power Fundamentals Car Air Drag Friction Acceleration

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?

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

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