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Save the Sea Birds
X-TRA CHALLENGES
You have designed and built a solar car for mass transportation and determined how much of a load your car can pull. However, engineers work within constraints and have additional specifications that their designs must meet. For the following three challenges, consider the specification of SPEED (it can’t take forever to move Cantaloupes from California—they will spoil along the way!), the constraint of COST (this has to be affordable for the average family), and the problem of HILLS (you must cross the Rockies!)
Watch some of the following videos to give you some ideas.
SOLAR CELLS AND TRANSPORTATION
- How To Build A Solar car --- http://www.youtube.com/watch?v=h3mv8MFVtYo
- How Solar car Works --- http://videos.howstuffworks.com/howstuffworks/178-how-
solar-cars-work-video.htm
- Solar Electric Powered Airplane --- http://www.youtube.com/watch?v=WcWSI03NKo
- Helios Solar Powered Airplane --- http://www.youtube.com/watch?v=1NCOPLEJOl
- Solar Powered Trains (in Belgium) ---
http://www.youtube.com/watch?v=UC8PogeGF_w
- Solar Powered Trains (in USA) --- http://www.youtube.com/watch?v=ddF3Aon_5Lk
- Solar Powered Boat (USA) --- http://www.youtube.com/watch?v=LY9_i_1lVnk
Challenge 1- SPEED
Students will use gear ratios and reduce the car weight and increase aerodynamics to build the fastest car. Calculate velocity (distance/time) for each vehicle along a 1 meter long track. The gear ratio will likely be reversed with the largest gear on the motor and the smallest gear on the wheel axle. Extraneous parts should be removed. Students can test their vehicle at any time along several tracks set up around the room with stopwatches at each station.
Here you see a simple car frame with two axles and four wheels, one motor, two gears, and some bushes to keep axles from moving.
Challenge 3- HILLS
It’s one thing to ride a bike along a flat sidewalk, but have you tried going up hills? You need a lot more force! You need a lot more energy! To maximize your hill potential, think about gearing down (small gear on the motor) and about wheel size and stability so you don’t flip backwards. Create a sturdy hill out of the kit lid. Prop the lid up on books and measure the angle of the hill. The angle can be measured with a compass, or with math.
http://www.rapidtables.com/calc/math/Arcsin_Calculator.htm
To increase torque, have a small gear drive a larger one. The large gear is on the same axle as the wheels. They will go slowly, but have more torque. Note here that I mounted the motor upside down to align the gears better. A gear train would provide even more torque.
The gear ratio here is 8 teeth to 40, reduced to 1:5. This means that the small gear turns 5 times for one rotation of the large gear. This decreases the speed 5 times and increases the torque 5 times.
A gear train uses several gears to increase the gear ratio even more.
Height = 30 centimeters Length of ramp = 100 centimeters Sine of angle = opposite/hypotenuse = 30/100 =. Angle = arcsine (.3) = 17.45 °
Follow the gears from the motor to the wheels. See here that the first ratio is 12: which reduces to 3:5. The second gear ratio is 8:40 which reduces to 1:
We multiply the two gear ratios to find out the final ratio. Will this gear train have a larger gear ratio than the original 1:5?
x =
Is 3:25 a larger ratio than 1:5? For every three turns of the black gear, the wheel turns 25 times. So, for every one turn of the black gear the wheel turns 25/3 times or 8.33 times. So, yes, this gear train increases the torque of the motor by over 8 times.
Black gear—12 teeth Yellow gear- 20 teeth Small gray gear- 8 teeth Large gray gear- 40 teeth
