Solar Car Fundamentals
Overview Maximize power produced Minimize power needed Solar cells → motor → gears → wheels Makes power Friction Drag Acceleration Uses power
Drive System Fundamentals Solar Cells Gears Motor Wheel
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
Motor Speed 2 Turns Wheel Speed 1 Turn Motor Speed = Wheel Speed Gear Ratio 2 Turns = 1 Turn 2
Circumference 2 π 6 = 38 cm Radius 6 cm 2π x Radius 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 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: 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.
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 Again
Where is the sun? Where is the sun?
On May 20 the sun will rise to around 70 degrees 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 Air Drag Friction Acceleration
Reducing car power needs Friction: Low weight Axle bearings Skinny tires Air Drag: Small frontal area Smooth shape Acceleration: 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
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
Examples of JSS Cars
Examples of JSS Cars
Examples of JSS Cars
Examples of JSS Cars
Examples of JSS Cars
Examples of JSS Cars
Examples of JSS Cars
Examples of JSS Cars
Examples of JSS Cars
Examples of JSS Cars
Examples of JSS Cars
Examples of JSS Cars
Examples of JSS Cars
Examples of JSS Cars
Examples of JSS Cars
Examples of JSS Cars
Examples of JSS Cars
Examples of JSS Cars
The End Any questions?