Original Solar Racer
Our solar car has come from a kit including directions on how the original car is supposed to be built.
Our team took it upon ourselves to improve upon that design.
The original design for the car had a solid base of wood with another block glued to the middle in order to cause the solar panel to have a slight slant when it is attached. One large gear is to attach to the back axle along with two nylon spacers to connect the axle to the car and two wheels on each side. The axle in the back has a large gear that connects with a smaller gear that is attached to the motor on the car. The large gear is a 40 tooth gear and the smaller gear is a 10 tooth gear. The original racer has a gear ratio of 10:40 or 1:4. For every turn the small gear makes, the large gear turns 1/4 of a rotation. The front axle has no gear. An optional addition is the battery pack. The battery pack is to go right behind the middle wood block. Another optional addition is to screw in eyelets into the bottom of the racer and lead it on a fishing line to ensure a straight race.
If you would like to learn more on how to build your own solar racer, visit
https://c10645061.ssl.cf2.rackcdn.com/resources/userguide/ray_catcher_sprint_deluxe_student_ug_21211.pdf .
Building Process - Day 1
On the first day, we got our directions to build the solar car. Immediately my group starting thinking of ideas on how to change the design. The first change we came up with is to cut out the bottom and only leave a 1/4 in thick frame for the bottom of the car. We thought this would decrease weight and provide a more aerodynamic framework to the car.
We knew we needed some space along the outside in order to attach not only the nylon spacers for the axles, but also the motor, wooden block in the middle, and the battery pack.
During the first day of building, we cut out the frame and attached the two axles. The picture to the right is of the bottom of the racer after the first day. One set of the wheels are bigger than the other wheels because they are going to be directly attached to the power source in the back. We need them to be able to grip the ground better and not spin out.
The gear shown attached to the axle has 50 teeth. We chose this specific gear since it was closest in size to the wheels. If the gear was smaller, the rotations would have lost speed as they turned the wheels. A smaller gear would have had to tun more times than a same size gear in order to cause the wheels to complete one full rotation. The smaller gear on the motor has 10 teeth. We also had to go with these gears for space sake. We didn't want our gear to be too big and get in the way of the motor, or be too small and not have the two gears touch.
Building Process - Day 2
The second day of building was about putting the pieces together from the first day. We hot glued the nylon spacers in line with each other near the front and the back of the car on the bottom of the frame. In order to attach the axle with the gear, we had to cut a small slot so that the wood wouldn't obstruct the rotation of the gear. The side with the gear and bigger wheels is the back of the car. It is here where the motor and battery pack are to be attached.
Along with the axles, we glued on the wooden slab in the middle of the racer to the top of the frame. The point of this piece is to add a slight incline to the plastic that is going to be attached. That plastic is the platform for the solar panel that is going to power the car. We need a slight incline on the panel so that is catches the sunlight easier.
You can also see in the picture to the left that we screwed in eyelets. These eyelets are arranged directly in line with each other along the middle of the bottom of the frame. These are to aid in the racing portion of the project. A fishing line is to feed through the eyelets, pulling the car along in a straight line. This makes the racing a bit more fair since they are now both traveling the same distance.
During this day of building, we didn't stray too far from the original design other than a change in the measurements of the middle wooden slab. The original design had a steeper incline and taller middle wood slab for their car. We made ours smaller, thinking that the less of an incline for the solar panel would reveal more cells to the sunlight.
Building Process - Day 3
My team finished putting together our racer prior to testing on this day. The car is fully functional at this point even if it is not at its most proficient.
During the third day, we hot glued the motor and the battery pack onto the car. The motor had to line the gears up with each other in the back, but since the gears were a little too big to fit perfectly we had to glue on a small slab of wood under the motor in order to get the car running. Next, we took the option of adding on a battery pack to the car. The battery pack had to be glued across the cut out and right behind the middle wooden slab as to not get in the way of any of the other aspects of the car. You can see these two additions in the picture to the right.
The next important piece that was added on was the plastic sheet. This piece of plastic is the same size as the solar panel we needed to use for testing. The plastic acted as a platform for the solar panel and didn't interrupt any of the testing with the battery.
One change we made from the original design was wrapping rubber bands around the back tires. When we tested the car with the batteries a few times, we noticed that the wheels tended to spin out. In order to add more traction to the back wheels (the ones attached to the power source), we wrapped them in rubber bands. We saw how this increased the takeoff time and allowed the car to reach a higher speed faster than before. At this point, the car was completed and it was time for testing.
Adjustments Made During Testing
Adjustment #1 - Small Piece of Wood
When we started testing the car outside, we noticed one commonality. The wheels stopped spinning halfway through even thought the motor kept running. Turns out the gear sizes were off to the point where they barely even grazed each other. It caused the smaller motor to keep turning from the powered motor, but it didn't turn the larger motor since their teeth did not interlock.
In order to remedy this problem, we cut a small piece of wood off from the excess board we cut out of the base in the beginning. As you can see in the picture to the left, we attached the piece to the bottom of the plastic and to the top of the motor. The pressure the plastic forced down onto the piece from being jostled out of its incline pushed the motor down enough to interlock the gears fully. This fixed that problem.
Adjustment #2 - Tinfoil
After a few more tests with the battery pack and the solar panel, we realized that the car tended to move a lot slower when it was only powered by the solar panel. We wanted to change it so that the car was able to absorb and use as much energy as possible.
In order to increase the efficiency of the solar panel, we thought to put something reflexive onto one side of the panel. From where we were racing, the sun is always on our right side, so we needed to put something reflective on the left side so that the light would bounce off of that surface and back into the solar panel. We took the idea of using tin foil from those car windshield protectors. The metal sheets go into a car's windshield during the summer in order to prevent the light and heat from entering the car. We added a piece of plastic wrapped in tinfoil to the left side of the plastic platform.