Post on 31-Mar-2015
transcript
PSU / Middle SchoolsSolar Racers Workshop
Solar and Car Fundamentals
Andy Lau, andylau@psu.eduDale & Toby Short, SCASD
Overview
• Maximize power produced
• Minimize power needed
Solar cells → motor
→ gears → wheels
Makes power
Friction
Drag
Acceleration
Uses power
Drive System Fundamentals
Wheel
Motor
Solar Cells
Gears
Gear Ratio
Axle Gear TeethMotor Gear
Teeth
=20
102= =
1 Turn2 Turns
Gear Ratio = 2Red gear spins twice as fast as blue
Motor Speed
Wheel Speed
2 Turns
1 Turn
Motor SpeedWheel Speed
Gear Ratio
=
2 Turns
2= 1 Turn
Circumference
Radius 6 cm
Radius 3 cm
2π x Radius
2 π 3 =
2 π 6 = 38 cm
19 cm
How does wheel size affect the speed?
Circumference
Radius 3 cm
Circumference = 2πr = 19 cm
Circumference = 2πr = 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
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 at PSU
• In full sun cmcmr
GR/14.1
75.1
0.2
So if your wheel r = 6 cm, then the best GR isGR = 6 cm x 1.14/cm = 6.8
• In half sun cmcmr
GR/86.0
75.1
5.1
• With batteries
cmcmr
GR/69.0
75.1
2.1
Getting the most power output from a PV panel
• Tilt towards sun
• Possibly increase solar input with reflectors
Incidence angle
Again
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
Car Power Fundamentals
Air Drag
Friction Acceleration
Reducing car power needsFriction: 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
Light
Panel towards sun
Straight light wheels
Small frontal area
What a slow car looks like
Panel not towards sun
Heavy crooked wheels
Way too BIG and heavy
Hot glue abuse
So that’s all there is to it …
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?