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?