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• 1
  

  Here are some of the materials you can use

  • corrugated cardboard (6-in. [15 cm] square) (corrugated cardboard has grooves in the middle, like a cardboard shipping box)
  • 2 pieces corrugated cardboard (5-in. [13 cm] square)
  • 1 plastic drinking straw 
  • 2 round candies (hard ones with a hole in the middle) 
  • 1 round pencil (sharpened)
  • 2 rubber bands
  • ruler
  • scissors
  • tape
• 2
  

  Prepare ahead of time

  • Have paper and a pencil ready to write down ideas and sketches as you design.
  • The car you’re building is called a rover, which is a type of all terrain vehicle (ATV). ATVs can drive over land that’s rocky, dusty, sandy, or rough. Think about all the ATVs you know of and what type of terrain they travel over.
  • TIP: NASA is building a fleet of ATVs called rovers. They are designed to crawl along the moon’s dusty, rugged terrain. Astronauts will need rovers to drive across the moon’s surface, carry supplies, help build their outpost, and explore the area. 
  • TIP: Inventors’ and engineers’ initial ideas rarely solve a problem. Instead, they try different ideas, learn from mistakes, and try again. The series of steps they use to arrive at a solution is called the design process.
• 3
  

  Think about the challenge

  • What parts of the rover vehicle are similar to those of a car?
  • What makes ATVs good vehicles for exploring the moon and other rough terrain? 
  • How many wheels does your rover need?
  • What shape should your rover’s wheels be to make it move across the floor?
  • TIP: Inventors and engineers work to invent and solve problems to help make the world a better place to live.
• 4
  

  Think about and write down ideas

  • List Earth vehicles that are similar to the moon rovers. (Dune buggies, snowmobiles, tanks)
  • Will your rover’s front wheels and rear wheels be the same?
  • What shape will you make your wheels? How big will they be?
  • List different ways you can power your rover.
  • TIP: The more corners your wheel has, the faster it will crawl across soft surfaces. The points of the corners dig into the rug, sand, or grass. This improves traction, which is the ability to grip a surface, and helps prevent the wheels from spinning out. 
• 5
  

  Look at the materials

  • What material can you use for the body of the rover? 
  • How will you make the wheels rotate together?
  • What materials do you have to attach the wheels to the axle?
  • What can you use to power the rover and move it across the floor? 
  • How will you attach the power source to the car?
  • TIP: A rod passing through the center of a set of wheels and securely attached to each wheel is called an axle. An axle makes the wheels rotate together. 
• 6
  

  Design and build the body

  • Decide on the material you will use for your rover’s body.
  • Think about how you will attach the axle and wheels.
  • Measure and fold up equal sides if your body has sides. 
  • TIP: Measure twice, cut once! After you measure something, measure again before cutting.
  • TIP: Measure the length of your body along the corrugations (grooves) in the cardboard. It is easier to fold along the grooves than against them.
• 7
  

  Design and build the front wheels

  • Decide what size the front wheels will be.
  • Decide what shape the front wheels will be. 
  • Choose the wheel materials and build your wheels.
  • TIP: Make the front wheels the same size. If one wheel is smaller than the other, the rover will turn in the direction of the smaller wheel. 
  • TIP: For the rover to move, there needs to be lots of friction between the wheels and the ground. Friction is when one material rubs against another. The more circular the wheels, the less friction there will be between the wheels and the ground.
• 8
  

  Modify the rover’s body to hold the front axle and wheels

  • Decide what material you will use as the front axle. 
  • Think about how you will attach the front axle to the body.
  • Modify the body to hold the front axle.
  • TIP: Use the pointy end of the axle to poke through the cardboard. Make sure your hand is away from the spot you are poking so you don’t poke your hand when the axle goes through the cardboard.
  • TIP: If you have trouble making holes by poking the axle through the cardboard, you might want to ask an adult to do this step for you.
  • TIP: Check that your axle is in a straight line as it goes through your rover, so the rover will travel in a straight line.
• 9
  

  Attach and test the front wheels

  • Attach the front axle and wheels to the body.
  • Turn the wheels to be sure they are firmly attached to the axle.
  • TIP: If the wheels and axle are not rotating together, check that you have tightly attached both wheels to the axle.
  • TIP: If your wheels don’t move freely, make sure the axle holes in the cardboard body are directly across from one another. 
• 10
  

  Design and build the rear wheels

  • Decide what materials you will use for the rear wheels and axle.
  • Build the rear wheels and axle.
  • Attach them to the rear of the body.
• 11
  

  Design and attach the power source

  • Choose the rubber band(s) to use for your power source.
  • Make a rubber band chain if your rubber band is not long enough. 
  • Attach the power source to the rover.
  • TIP: Different lengths and widths of rubber bands will wind around the axle differently, store different amounts of energy, and release their energy differently. 
  • TIP: You can make a rubber band chain by looping two or more rubber bands together. A rubber band chain can reduce how quickly the rubber band releases its power. Or it can let you wind up the wheels more to give the rover more power.
• 12
  

  Power your rover

  • Hold the body tight.
  • Rotate the front wheels to wind up the rubber band.
  • TIP: When you turn the axle on the rover, you are giving the rubber band potential energy—which is stored energy. When the rubber band unwinds and the axle spins, it transforms the potential (stored) energy into kinetic energy—or motion energy.
  • TIP: The more you wind the rubber band around the axle, the more energy can go to your rover’s wheels—and the faster and farther it will go.
  • TIP: You can make your rover crawl forward or backward depending on what direction you rotate the wheel.
• 13
  

  Test your rover

  • Hold onto the body and wheels and place your rover on the floor.
  • Stand back and let it crawl!
  • TIP: If your rover doesn't travel far, you might try making bigger wheels. Bigger wheels have a larger perimeter (outer edge). As a result, one turn of a large wheel will move the rover farther than one turn of a small wheel.
  • TIP: If your rover won’t travel in a straight line, make sure the axles are straight and the front wheels are the same size.
  • TIP: You’ve just built a prototype, which is an early version of a product. Prototypes help engineers understand a product’s strengths and weaknesses and how the product might be improved. 
• 14
  

  Did you know?

  • Custom Wheels
    The moon doesn’t have an atmosphere—there’s no air on the moon! Air-filled tires like the ones on a bike or a car would explode on the moon. So, how do the rovers crawl around? Engineers designed a tire that works perfectly when it is used on the moon. It’s made of thin bands of springy metal. This keeps the rover lightweight, gives it good traction, and lets it work at any temperature on the moon. Plus, this material flexes when it hits a rock, and it doesn’t need to be pumped up. All these things make it dependable. And dependability is important because there’s no roadside service when you’re on the moon, 250,000 miles (400,000 km) from home! 
• 15
  

  Try this next!

  • Test how different wheel shapes affect the way your rover moves. Modify your rover by changing the wheel shape. Start with square wheels, and measure how far your rover travels. Then snip off the corners of their wheels and test again. Make sure you wind up the wheels the same number of turns. Then test octagonal wheels and round wheels.