The car's chassis is its frame. It holds all of the main componenets, or parts, together.
Some possible ideas for a solar car chassis are shown below. Try different ideas.Try different materials.
Figure 1: Examples of chassis |
- Weight and Stiffness
One thing you will discover when you build your solar car is that designing and building involves tradeoffs. There is no one ideal design. This is true with the chassis of your car.
One obvious consideration is that you don't want your car too heavy. It is easier for your motor to push a light car than a big, heavy one. In solar cars, efficiency is very important, and you don't want to waste energy.
Figure 2: Weight affects ease of movementBut something you must also keep in mind is that a light car can be pushed easily by wind, too. Even if the wind does not blow the car over, it may make it harder to go in a straight line. (This depends not only on the weight, but on where theweight is, and the shape of the body, too. We will talk more about the body and aerodynamics in a later section.)
- Materials
In most cases it is more difficult to make the car light enough (you can alwaysadd a little ballast, or weight, anyway) so in this section we will emphasize lightweight materials and construction. The first step to a lightweight chassisis in choosing the right materials. Balsa wood, for example, is a commonly chosen material because it is lightweight. But more importantly, is fairly stiff for its weight.
What is the difference between strong and stiff? Strong means it will not break easily. Stiff means it will not bend easily.
Figure 3: Stength verses StiffnessFor the solar car, stiffness is very important. Stiff, light materials include styrofoam, foam core, balsa wood, corrugated cardboard, and some plastics.
- Shape
Some heavier materials are also appropriate if they are constructed correctly. Try Investigation 3-1 below to investigate how the shape of a material can effect its stiffness.
Engineers can stiffen flexible materials using shapes as shown in Investigation 3-1 or use less of a heavier material with just a change of shape. Look at a cardboard box. Why is the inside corrugated?
Figure 4: Examples of stiffening by shapeOther materials are made stiffer or stronger by sandwiching them between other materials. Look at foam board and plywood.
Figure 5: Examples of stiffeining by Layering - Orientation
As you saw with the folded pieces of paper, orientation is also very important in determining stiffness. Try Investigation 3-2 below to see how the orientation of the material affects its stiffness.
Imagine you wish to stiffen your chassis by adding ribs. You glue two strips of material to the bottom of the chassis as shown in figure 6 trying to strengthen to the chassis.
Figure 6: Stiffening chassis by layeringUnfortunately, that didn't seem to do the trick - the chassis still sags. Your partner insists that adding strips of material will help, but you know that this is not necessary. You have a better idea! What is your idea?
Figure 7: Stiffening chassis by orientationWell, if you turn the strips sideways, as shown in figure 7, (remember whichway the ruler was stiffer in Investigation 3-2), you add the weight again and your chassis is much stiffer.. without adding much material!
So, as you can see, if you are smart about your material selection, and you remember the importance of shape and orientation of materials, you will have much more control over the weight of your solar car.
Any material that is light and stiff would be appropriate. Some hollow tubing is very stiff for its weight. Arts and crafts stores, hobby stores and hardware stores are good sources. Some stores have scrap materials like cardboard. Or, look around your house for scraps. Some materials we found are useful are:
- Stiff insulating foam board
- Foam core board
- Balsa wood
- Brass tubing
- Cardboard tubes
- Shoe box
- Soda bottle
- Rigid plastic
- Corrugated cardboard
- Plexiglass