There are links to facts sheets in the post below this one. Check those out on Tuesday, May 15
The 21st annual Solar Car Challenge is happening at Cal Young Middle School on June 9th from 9:30-1:30 ish. Our science classes will be sending the two fastest cars from each class to compete in this annual race.
Beginning Wednesday, May 16
- Each student will work on the bottom view of your car design. Each person in the group must complete an actual size drawing on the large graph paper. Make sure you read the tips provided in the post below about chassis, axles, bearings and wheels.
- Bring the drawings to the front counter and get them approved and initialed by Ms Hohenemser. You will keep these until all drawings are completed and then will self score and turn them in
- Trace the outline of your chassis (body shape) using the overhead projectors on the front counter near the door onto a blank piece of legal sized white paper. Cut out the shape with scissors and put all scraps in the recycling
- Fill out your Materials Request Form (green) with your names and select the parts you will need to make a rolling chassis; this includes thin or thick balsa wood or foam core for the chassis, axels (aluminum or steel), wheels (large or small) and driven gears, the one that goes on your axle (12, 20, 30 or 40).
- Bring the filled out Materials Request form to Ms. Hohenemser and receive your parts. You will need to bring this form any time you want to trade out parts or get new ones
- Attach the traced drawing to the wood/foam with tape and trace around it onto the wood/foam core BEFORE you CUT the wood, ….Use the triangle to make parallel lines on your wood to show EXACTLY where the axels will be attached. Make some extra parallel lines so that you can line other items up.
- Check out a knife at the front counter and get a cutting board from the bottom shelf of Ms. Hohenemser’s computer cart and cut out your balsa wood/foam core. Always cut towards yourself against a straight edge for safety and be sure to use a sharp knife that has a triangular point (Ms Hohenemser will do a demonstration in class)
- While one student is cutting the chassis, the other partners should prepare the other parts needed for the roll down test. If you are using brass bushings, follow teacher directions on how to cut them. Cut your axels to the right length (using the huge bolt cutter behind the front counter) and file the sharp ends by following the directions in this video.
- Use the metal triangle and hot glue to attach your bushings to the chassis. It is super important that they are on straight and parallel to one another. (Check out this video at 2:48 to see how to attach the bushings and axels.) Attach the gear and wheels to the axles.
- You are ready for the Roll Down test. Get the Yellow Roll Down sheet from the front counter file folder and make your measurements including finding the mass of your car. Record your Roll Down score on the bulletin board data table as well as the class spreadsheet on your teacher’s computer. A score of 20 or higher is generally good. You may need to make some adjustments to reduce friction or re-glue your bushings if the car does not role straight. You can use powdered graphite to reduce friction in the bushing.
After you are satisfied with your Roll Down Score, it’s time to get it is time to get your motor, wiring, mount and battery pack attached. . Make sure you have recorded your scores on the spreadsheet on your teacher’s computer,
12. But first you must complete the top view of your design. Decide where the motor will go, finalize which gears you will use and draw in your solar panel mounts and battery pack. Get your drawing approved by your teacher before going to step 13.
13. Bring your Green materials sheet to the front counter with the items listed above filled out. You can choose from a prewired motor or do your own wiring. You will attach your motor with hot glue and your battery pack with velcro (please do not glue it). If you plan to use a motor mount you can also ask for some tiny screws to attach the motor to the mount or just glue it directly to the chassis. Be careful not to get glue in the teeth of your gears.
14. The important thing about mounting your motor is to get the gear spacing perfect. Gears that are too tight will reduce the rotational force that comes from your motor and slow down your car, but gears that barely touch each other will also not move your car very fast. You have to find that perfect sweet spot where they make good contact but don’t exert too great a force on each other.
15. Once you have mounted your motor with a pinion/driver gear, attached your battery pack with velcro and inserted your used batteries, it is time to take your car “out for a spin”. ALWAYS MAKE SURE THERE IS SOMEONE AT THE OTHER END OF THE TRACK THAT YOU TRUST. YOU DO NOT WANT TO HAVE TO START OVER! Get a green speed sheet for your group from the file folder on the front counter. Your initial speed test will be completed on the track in the back off the classroom on the roofing paper. This track is marked at 8 meters in length. In order to calculate your speed you will divide 8m by your car’s time in seconds.Use your iPad or phone for timing. For example 8 meters in 4 seconds would be 8/4= 2 m/s. A fast speed on this track is about 3 m/s. Record your speed on the bulletin board chart as well as on the computer spreadsheet.
16. Once you are happy with your time trials on the 8 meter track, you are ready to set up the hallway track and get a 20 meter speed (this should be faster than your 8 meter speed because your car will likely not reach a terminal velocity on the 8 meter track). You may need to add some traction to your drive wheels (the ones that are connected to the motor) You can use rubber bands or part of an inner tube from a bike tire. You may also decide that you want to make some kind of bumper for your car if it always pulls to one side. Possible materials are aluminum axel material or zip ties or anything else you can think of.
17. Once you are happy with your hallway speed without a solar panel, record your top speed on the bulletin board data table and the computer spread sheet as well as on your green speed sheet. It is now time to attach your solar panel. A good time for the 20 meter track without a solar panel is 5- 6 seconds. So the speed would be 20 m/ 6 sec = 3.3 m/s 20m/5 seconds= 4 m/s.
18. Now it is time to attach your solar panel mounts. Use the scraps that you made cutting out your chassis or any of the balsa scraps from the scrap box near the table by the whiteboard. The solar panel mounts should be glued down, but your solar panel MUST BE ATTACHED WITH VELCRO. Your teacher may give you a broken solar panel to test unless there is an outdoor track set up. This is to avoid breaking working solar panels in crashes.
19. For you last required speed test, you must run your car in the hall with batteries and the solar panel. Record your speed in m/s on the bulletin board data table and computer spreadsheet. This speed will be slower than without the panel. Finish your green speed sheet and turn it into the basket. If we have time, we will set up an outdoor track.