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Great Robot Race, The

Classroom Activity

Learning Objective | Materials | Background | Procedure | Activity Answer | Links & Books | Standards  Print this Teacher's Guide (PDF, 8 pages)

Activity Summary
Students will design, build, and test a rubber band-powered car.

Learning Objectives
Students will be able to:

• brainstorm solutions to design challenges.

• build, test, and evaluate a rubber band-powered car.

• communicate the design approach to others.

• distinguish between potential and kinetic energy.

• copy of the "Off to the Rubber Band Races" student handout (PDF or HTML)
• copy of the "Vehicle Construction" student handout (PDF or HTML)
• copy of the "Performance Expectations" student handout (PDF or HTML)
• rubber band (1/4-inch x 3-inch) (for energy source)
• bamboo skewers, pipe cleaners, drinking straws, dowels, and/or other material (for axles)
• CDs, plain and corrugated cardboard, milk cartons, and/or other material (for body and wheels)
• masking tape, small nails or screws, glue, staples, and/or other material (for assembling vehicle)
• compass (for drawing circles for wheels)
• scissors

• spring scale or appropriate balance for weighing the vehicles
• tape measure or meter stick
• several 250-gram masses or objects of equivalent mass (about 100 pennies)

Background
The purpose of this activity is for students to experience the process of designing and building a device to meet a set of design and performance criteria just as the teams competing in the DARPA challenge had to. The performance criteria have been specifically chosen to present students with sometimes competing requirements. Just as in real life, students may find that a winning solution to a problem must involve compromise—for example, while large wheels may mean more distance covered than smaller wheels, they also add mass to the vehicle.

The sample rubber band car shown in the student handout consists of two axles mounted with four wheels. The power source is the rubber band mounted around the axle. Winding up the wheels (in reverse so they will create a forward motion when released) winds the rubber band and stores potential energy. When released, the rubber band spins the axle and the wheels. How far the car travels depends upon how much potential energy is stored in the rubber band, how efficiently the potential energy is transferred, and how much friction the car encounters.

Key Terms

friction: The resistance of an object to the medium through which it is traveling, such as air or water, or that it is in contact with, such as a solid floor.

inertia: The tendency of a body at rest to stay at rest and a body in motion to remain in motion unless acted upon by an outside force.

kinetic energy: The energy due to the motion of an object.

potential energy: The energy an object has due to its position or internal condition rather than its motion.

1. Prior to vehicle construction:

   • Review the design rules and performance expectations.

   • Review each part of the model car with students.

   • Discuss the parts of the model car that might be changed to make it travel farther (wheels, power source, body design)

   • Explain that a front-wheel-drive car will have the rubber band winding around the front axle, a rear-wheel-drive car will have the rubber band around the rear axle, and an all-wheel-drive car will make use of both axles.

   • Discuss the materials that will be used to construct the vehicle. Students must all use the same-sized rubber band as their energy source, and all other materials must be made from everyday supplies, such as those listed in the materials list. Students cannot use store-bought wheels, axles, or car bodies.

   • Identify a relatively smooth surface where the vehicles will be tested.

2. Copy student handouts and gather and distribute the materials.

3. Require each team to draw three views of its proposed vehicle (side, top, and rear). This will help teams further think through their design prior to construction. Teams should use the example drawing in their handout for guidance in making this drawing. Have students design their vehicles.

4. Have students build, weigh, and test their vehicles. Decide on and tell students how much time they will have to work with their vehicles. Students can make as many changes to their vehicles as time allows, but must change and test only one variable at a time. Make sure to allow time for any glued parts to dry. Students should note on their three-view drawing any design changes they made when they built their vehicle.

5. Use the masking tape to mark the starting line and one-meter intervals down the course. As a class, decide on a consistent method for launching vehicles so that students do not add energy with a forward hand motion when the vehicles are launched.

6. Conduct the competition. Have each team carry out three or more trials of each of the last two performance expectations (farthest distance traveled and farthest distance traveled with load), and average the scores for each expectation. (If your class is large, have teams carry out two trials and choose the best trial for the final score.) You should act as scorekeeper, keeping each team's scores private.

7. Following the competition, have each team present its design approach. Have students consider the following questions:

   • What were the benefits of drawing your design before you built your vehicle?

   • What worked and what didn't work in each approach?

   • After each of your tests did your vehicle perform as expected? Explain.

   • What final modifications did you make to your vehicle? Why?

8. Announce the top three overall winners and the top three in each category. As a class, summarize the most successful characteristics of the overall winning designs and the most successful characteristics of those designs that were top in their performance expectation categories. What did the winning vehicles have in common? If students had another chance at design, what would they do for their next-generation vehicle? Have students support their reasoning.

9. As an extension, have students race their vehicles on a completely different terrain, such as grass or dirt. How did the vehicles perform? What changes would students make to the vehicles based on test results? Why?

Student Handout Questions

1. Where does the energy to move the vehicle come from? The potential energy stored in the rubber band, which received energy from the person who wound it.

2. What affects the distance the vehicle travels? Students should mention various types of friction (air resistance, resistance in the wheel bearings, etc.) as well as the circumference of the wheels, the strength of the rubber band, how much the rubber band was wound, and the mass of the vehicle.

3. Describe one type of energy transfer in this activity. Correct answers should make it clear that the energy still exists but in other forms. Three energy transfers that occurred were kinetic to potential energy when students wound the rubber band, potential into kinetic energy when the car was released, and kinetic into heat energy as friction slowed the car down.

4. What was the most difficult part of this activity? Any reasonable answer is acceptable here. The purpose of this question is to have students think about what they have done.

5. If you were going to make improvements to your vehicle, what would they be? Why would you make them? Many different answers are acceptable here, but more credit should be given for clear, detailed answers that are well thought out, well presented, and based on evidence.

Web Sites

NOVA—The Great Robot Race
www.pbs.org/nova/darpa
Learn more about 12 of the teams that raced, discover some real-world applications for autonomous vehicles, see video extras, and view a slide show that reveals what racing robots see.

DARPA Grand Challenge '05
www.darpa.mil/grandchallenge
Provides an explanation of the event and its importance to the U.S. Defense Department.

Rubber Band Vehicle Competition
driscoll.brookline.mec.edu/iMovieworkshop/rubberbandvehicles.html
Presents a video clip of middle school students testing their rubber band vehicles.

Books

Absolute Beginner's Guide to Building Robots
by Gareth Branwyn. Que Publishing, 2003.
Relates the history of robotics and provides detailed instructions on how to build three robots—from a simple one-motor walking machine to a programmable robot platform.

The New Way Things Work
by David Macauley. Houghton Mifflin, 1998.
Provides detailed explanations and illustrations of how things work, including a section on digital technologies.

Robots
by Clive Gifford. Smart Apple Media, 2006.
Describes what a robot is and looks at various ways that robots are used.

The "Off to the Rubber Band Races" activity aligns with the following National Science Education Standards (see books.nap.edu/html/nses).

Grades 5-8
Science Standard B
Physical Science
Motions and forces

Science Standard E
Science and Technology
Abilities of technological design

Grades 9-12
Science Standard B
Physical Science
Motions and forces

Science Standard E
Science and Technology
Abilities of technological design

Classroom Activity Author

Charles Low is a science teacher at Malden High School in Massachusetts and has participated in a Tufts University School of Engineering program.