My design process to building three model solar cars.

1. Solar Model Cars
By Bill Kuhl http://www.scienceguy.org

2. Background
Looking for more science projects on the Internet, I ran across ran across
the Junior Solar Sprint Competition. I have been interested in alternative
energy for a long time, so I decided I would build a solar powered model
car.
EverythingHobby had two Tamiya solar panels and one motor. I purchased
the motor and the ½ volt 1200 mah panel to start with thinking both panels
were the same. I later purchased the other panel which was 1.5 volts
400 mah, this would be good for experimenting with trade-offs between
voltage and amperage.

3. For my next car I purchased the panel and motor specified for the Junior Solar
Sprint Competition, in my first tests of running this car pictured above, the speed
is at a jogging speed. This car was also an experiment in using bamboo to
stiffen the thin plywood chassis.
I also purchased a 10-pack of kit cars from Pitsco because the price is below
$10 a car and I thought this would be good for a class this summer. The solar
cell is rather tiny so I used lower gearing to get the car to move, but it will work
fine in bright sun.
The model solar cars appear to be a good activity to learn about harnessing
sunlight, electricity, electric motors, gearing, and construction ideas.

4. The first car I built from Tamiya components I found in local
hobby shop.

5. The second car built using solar panel and motor specified in
Junior Solar Sprint rules.

6. Sun Zoon Lite car kit was the third car I built which is an
inexpensive kit.

7. Applications for Photovoltaic Solar Power
This large solar panel seen at the Minnesota State Fair was available
for rent.

8. Another smaller solar panel seen at Minnesota State Fair

9. Calculator powered by small solar panel.

10. Traffic signals sometimes use solar panel to charge battery power.

11. Small solar panel recharges battery in garden light.

12. Home with solar panels on the roof.

13. Demonstrating Small Electric Motors
This demonstration electric motor leaves everything exposed to show
how motor operates.

14. Close-up of brushes and commutator in demonstration motor.

15. Commutator and windings seen in Speed 400, a typical brushed electric
motor. Note: When looking for a motor for solar power, it helps to look at
the start-up current requirements as some motors require more electricity
to start than others.

16. Building First Solar Model Car

17. This panel is ½ volt but 1200 mah.

18. This Tamiya panel of the same physical size but is 1 ½ volts and 400
mah.

19. 1 ½ volt panel has more cells.

20. No load voltage of 1 ½ volt panels reads 1.71 volts in bright sun.

21. 1200 mah .5volt panel displayed .56 volt in bright sun.

22. Tamiya motor designed for solar panels.

23. Lightweight wheels used for indoor radio control model airplanes, I selected
the wheels on the left for my car.

24. Brass eyelets are sandwiched between balsa for bearings.

25. At this point motor was only sitting on top of the chassis, I will shim the
motor to get good mesh between gears.

26. View of chassis with car turned upside down, Popsicle sticks were
used to stiffen rear of car where motor is mounted.

27. Some of the craft beads used in bearing assembly.

28. I used a spur gear from a RC car. The gear is glued to the side
of the wheel.

29. Tamiya panel came with a swivel mount that gave me idea
to replicate this for larger panel on second solar car.

30. Using Velcro makes it easy to change PV panels.

31. Shimming the motor gave space between gears and it ran
smoother.

32. Building Second Solar Model Car
Junior Solar Sprint - specifies a certain solar panel and motor which I
purchased from Solar World.

34. Specified solar panel produces 3 volts @ 3 watts, dimensions are 4 ½” x 13”

35. Motor comes with solar panel and it is the only motor allowed. The
motor can not be modified in anyway either.

36. The Accessory bag from Solar World
includes 2 shafts, 4 wheels/tires, and 3
spur gear sizes.

37. Craft beads I used for spacers .

38. Bamboo skewers were used to strengthen the chassis of the car.

39. As with my first solar car, I used brass eyelets sandwiched between
balsa. These eyelets were the kind used with medium size radio
control servos.

40. Eyelet from RC servo used for bearing.

41. Chassis turned upside down before I put layer of balsa on top of eyelets
which completes the balsa sandwich.

42. Motor running, gears must mesh easily for good performance.
The correct gearing is a trade off between quick enough acceleration and
top speed. Small gear on motor shaft is the “pinion” and large gear is the
“spur” gear.

43. Solar panel in the horizontal position, adjusting the panel to match the
angle of the sun will make a big difference in performance.

44. Ping pong ball used for swivel. Straps were made plastic in a cottage
cheese container.

46. The underside of rear half of car shows reinforcement done with
plywood and bamboo.

47. After seeing the pivot on the Tamiya panel, I built my own swivel
joint using a ping pong ball.

48. Platform for panel made from Popsicle sticks and thin plywood. Velcro
fastens the panel to the platform, the panel could easily be switched to
another car. I like to design everything to be flexible if possible.

49. Pitsco SunZoon Lite
I ordered the 10 pack of solar cars from Pitsco which are very
reasonably priced. The car goes together easily but needs very bright
sun to move the car.

50. Pitsco SunZoon Lite kits are available in a 10-pack.

51. Top side of the small solar panel.

52. As seen from the back, the solar panel is only .45 volt 400 mah.

53. I measured the voltage of the panel at .47 volt in strong sun.

54. Screw eyelets are used for bearings that are very quick to install.

55. Side view of front axle and wheels

56. Gears

57. Gear font gave the specs of all the gears included, more gears than
needed are included but might be useful for another project.

58. Many gears are included but some are larger in diameter than the
wheels which is a problem.

59. I installed the 20-tooth pinion gear per the instructions but the car
would only move in really bright sunlight. With the PV panel putting out
less than ½ volt there is no power to spare. Spur gear 40-tooth.

61. I installed the smaller 10-tooth pinion gear on the motor
shaft but it does not match up with the spur gear, a
modification would be needed.

62. I flipped the car over and considered putting the motor in the rear
but the solar cell could not rest on the motor because the wheels
were in the way.

63. Moving the motor in front of the spur gear will prop up the
solar panel and gears mesh fine. The gear ratio is now 1:4
which gives the car more torque to move.

64. Completed car, some of the wood chassis could be cut off
making the car slightly lighter.