1. Solar Car Fundamentals

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

3. Drive System Fundamentals
Solar Cells
Gears
Motor
Wheel

4. Gear Ratio 1 Turn 2 Turns Axle Gear Teeth 20 = = = 2 Motor Gear Teeth10
Gear Ratio = 2
Red gear spins twice as fast as blue

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

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

7. How does wheel size affect the speed?

8. 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

9. 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.

10. 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

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

13. Incidence angle

15. Again
Again

16. Where is the sun?
Where is the sun?

17. 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.).

18. Car Power Fundamentals
Air Drag
Friction
Acceleration

19. Reducing car power needs
Friction:
Low weight
Axle bearings
Skinny tires
Air Drag:
Small frontal area
Smooth shape
Acceleration:
Which body shape is fastest?

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

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

23. 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

24. Examples of JSS Cars

25. Examples of JSS Cars

26. Examples of JSS Cars

27. Examples of JSS Cars

28. Examples of JSS Cars

29. Examples of JSS Cars

30. Examples of JSS Cars

31. Examples of JSS Cars

32. Examples of JSS Cars

33. Examples of JSS Cars

34. Examples of JSS Cars

35. Examples of JSS Cars

36. Examples of JSS Cars

37. Examples of JSS Cars

38. Examples of JSS Cars

39. Examples of JSS Cars

40. Examples of JSS Cars

41. Examples of JSS Cars

42. The End
Any questions?