PAGE INDEX
  • PURPOSE
    		•
  • IDEAS
    		•
  • CONCEPTS
    		•
  • MATERIALS
    		•
  • INVESTIGATIONS
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    1. PURPOSE:
      [index] A design review is an opportunity for any organized team of developers to gather all the information together and review it - establishing a more refined approach to the problem. At this point you have learned some things, through study and investigation, that will help you narrow the options you have in producing your car. A design review is where you take establish a design (in the form of a drawing and maybe with some of the "prototypes" you have already made) and present it along with the reasoning behind the decisions you have made to others. The presentation is then followed by a question / answer and comments period where the audience gives you feed back. Your team can then take this input and finalize the design you are going to build.

    2. IDEAS: [index]
      Some ideas for this presentation.
      • A final sketch or drawing of the car (overhead)
      • Examples in the form of sketches or prototypes
      • Samples of the materials you plan on using
      • Samples of processes you plan on using
      • Experiences in trying things that you learned from

    3. CONCEPTS: [index]
      1. Presentation
        Hold a team meeting to review all of the information you have learned about chassis, wheels & bearings, transmissions, solar panels, motors and bodies. Decide as a group what your final approach will be in each of these areas (for example a pulley & belt transmission) and record them on paper with small sketches of what you want to build. You can also use prototype projects you have already completed. Also record the reasons why you are making these choices. You might also record any statements on strategy that are affecting your design decisions such as "we expect a cloudy day - so we will build a transmission that will make the car move with very little sunlight."

        If you plan on doing anything special with a material in producing your car include statements on how you plan on doing the work.

        The presentation for you Solar Sprint car should be about 5 minutes long. Make assignments in your group to produce a sketch (with critical dimensions) or drawing of your final concept. Have a transparency of the picture produced.

        Identify one of your team members to make the presentation and another to act as a recorder of the comments that you receive. These notes can be very helpfull in making final decisions after the design review with your peers.

        When making the presentation, remember that you are not only sharing your ideas but trying to sell your audience on them. Make the presentation fun and exciting. Showcase your ideas and see what kind of reactions you get.

        Remember that the commments and questions are not personal. It is just others trying to understand what you are saying or giving you ideas they have. In the end, you will, as a team, make the final decisions on what you are going to build. The Design Review is a tool to try and help you produce a better vehicle.

      2. The audience
        When a team is presenting their design you need to be attentive. Do not interrupt the presentation and only express an idea or ask a question when called upon. The audience members need to be supportive of ideas they think are good, but also ask questions to clarify what you do not understand. You should freely express concerns about ideas that might have problems such as something you learned in an investigation that had different results. You are responding to the presentation to help the presenting team produce a better more competitive car.
        You also need to listen intently because you can learn things from other presentations that might help your team do better. Take notes when you hear something that impresses you or is a good idea.

        Remember, the better all the cars are the better the race and the more fun for all - you, your team-mates, the other racers and the audience that comes to see the results of all your hard work.

      3. Considerations for a Solar Car
        A solar car, whether full sized or a smaller model, must perform with very little energy available from the solar panel. Since the energy is limited, the designer must do everything possible to make the car efficient so that the maximum amount of energy is used to make the car go. In a car like Sunraycer, we had to consider many things. With the solar panel area limited, we wanted to have the most efficient solar cells possible. The electrical load on the solar panel had to be continuously adjusted by electronic controls to maximize the power under any condition of sunlight. The motor for driving the wheels had to be very efficient, too. In the Junior Solar Sprint, everyone must use the same solar panel and motor so these are not a matter of design for this application. What are the design points which have the greatest impact? They are aerodynamic drag, rolling resistance, drive train efficiency and weight.

        Aerodynamic Drag is very non-linear with speed. At very slow speeds, below 10mph, it doesn't have too much effect, but as the speed increases to more than 30mph, aero drag gets important. The magnitude of drag depends on the frontal area of the car; (ie., maximum cross section looking at the car from the front, multiplied by the coefficient of aero drag, which depends on the car's shape, multiplied again by the velocity squared). It is this velocity squared term that makes the drag increase quickly with velocity or speed. So the designer should make the frontal area of the car as small as possible and make the body as streamlined as he or she can. A poorly designed shape might have a coefficient of 0.5 (drag), and a very good shape might be as low as .02 (drag). So you can see that the drag could range over four to one! Make a smooth tear-drop shape as well as you can considering that the solar panel has to be included. Use the wheels with disc structure, not spokes. If spokes are used, they should be covered on both sides. Be sure the underbody is smooth, too, not open like a regular car. Make openings for the wheels (if the body covers the wheels) as small as possible. If the wheels are not enclosed in the body, consider wheel pants.

        Rolling Resistance is another energy waster. It is the energy lost in the wheel bearings and in the tire deformation. The tires on the Junior Solar car are probably solid rubber so tire pressure is not a factor, but the rubber should not be very soft and the tires should be smooth (no tread) and very narrow. The bearings should be given careful attention. The Axles should be straight straight and the bearings (if they are sleeved bearings) should be made from low friction materials like Teflon, Nylong or oilite (bronze). The lubrication should be very light - no grease.

        The Drive Train can waste energy too. Gears can be particularly wasteful if they are not precision made. Some form of belt drive may be best but be sure the belt doesn't slip, and that it is not overly tight. The drive ratio is very critical. You will want to experiment to see which drive ratio gives the best results with your car. It may be that different ratios are best for different sun conditions. You may want to be able to quickly change ratios to do best on a cloudy dat from that ratio that is best on a sunny day.

        The weight of the Junior Solar car is a very important design consideration. Since the car is probably accelerating most of the run, the weight is more important than if the car was traveling at a constant speed. Also, the weight is a direct multiplier on rolling resistance. Twice the weight means twice the rolling resistance for the same wheels, tires, and bearings. So use light-weight materials, built-up construction, or other lightening techniques. Remember though, that there must be enough weight on the drive wheels so that they don't spin.

    4. MATERIALS: [index]
      • Take a look at each of the materials sections in handouts 1 through 8 for ideas.
    5. EXPERIMENTS & INVESTIGATIONS: [index]