In an interactive and game-like manner, students learn about the mechanical advantage that is offered by gears. By virtue of the activity's mechatronics presentation, students learn to study a mechanical system as a dynamic system under their control as opposed to a static image. The system presented is of two motorized racing cars built using the LEGO® MINDSTORMS® robotics platform. The altered variable between the two systems is the gear train; one is geared up for speed and the other is geared down for torque. Students collect and analyze data to reinforce particular aspects and effects of mechanical advantage.
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- Common Core State Standards for Mathematics: Math
- 2. Multiply or divide to solve word problems involving multiplicative comparison, e.g., by using drawings and equations with a symbol for the unknown number to represent the problem, distinguishing multiplicative comparison from additive comparison. (Grade 4)  ...show
- International Technology and Engineering Educators Association: Technology
- New York: Science
- Next Generation Science Standards: Science
- Make observations and/or measurements of an object's motion to provide evidence that a pattern can be used to predict future motion. (Grade 3)  ...show
- Collect, average and compare single variable datasets.
- Compute speed from distance and time measurements.
- Clearly and confidently explain that gears can be used together in different sizes.
- Predict what would occur if gears were added to a system in either gearing-up or gearing-down configurations.
- a constructed and pre-programmed racer set-up (2 cars); the specific pieces shown in the set-up instructions are available at https://www.teachengineering.org/lego/building_instructions_gears/building_instructions.html; purchase the necessary parts for the racer set-up through either of the two following options:
- LEGO MINDSTORMS Education NXT Base Set (for $280 available at https://shop.education.lego.com/legoed/education/NXT/NXT+Base+Set/5003402&isSimpleSearch=false)
- additional parts shown in the set-up instructions, for ~$40, available at https://education.lego.com/en-us/lesi
- 2 LEGO MINDSTORMS Education NXT Base Set (for $552 bulk price, available at https://shop.education.lego.com/legoed/education/NXT/NXT+Base+Set/5003402&isSimpleSearch=false)
- 1 LEGO MINDSTORMS Education Resource Set, for $100, available at https://shop.education.lego.com/legoed/education/NXT/LEGO%C2%AE+MINDSTORMS%C2%AE+Education+Resource+Set/9695&isSimpleSearch=false; includes all remaining pieces shown in the set-up instructions
- thin nylon twine, 2-3 ft (0.6-0.9 m) length ($3 per 200-300 ft roll)
- fender washers, 3/16" x 1-1/4" (0.48cm x 3.18cm) x 100-200 pcs ($10 per box of 100 pcs; these may be reused for other LEGO NXT based lessons that require small quantifiable weights that fit nicely onto axle pieces or nylon twine)
- Gears Pre-Assessment Survey, Gears Post-Assessment Survey and Pod Racer Activity Workbook, one each per student
|gear:||A wheel with teeth around its edge that mesh with the teeth of another wheel to transmit power (as in a bike) or change the direction of motion in a machine (as in a clock). Think of the clocks of Hugo Cabret. Fixed ratios of speed in various parts of a machine are often established by the arrangement of gears, like the fast movement of a minute hand and the slower movement an hour hand in a clock.|
|gear(ing) down:||(introductory description): Arrangement of gears that uses a larger gear at a wheel and a smaller gear with a motor to make the wheel spin slower than the motor, but with more twisting force. (thorough description): Arrangement of gears within a gear train that multiplies twisting force, accompanied by a sacrifice in speed.|
|gear(ing) up:||(introductory description): Arrangement of gears that uses a smaller gear at a wheel and a larger gear with a motor to make the wheel spin faster than the motor, but with less twisting force. (thorough description): Arrangement of gears within a gear train that converts twisting force into a gain in speed.|
- In this activity, students use two experimental set-ups that are distinct in their gear train arrangements. "Gear Up" set-ups and "Gear Down" set-ups are configured such that one runs faster (but with less torque) and the other runs with more torque (but slower), respectively, as shown in Figure 1.
- The program that is loaded onto each controlling NXT brick should be calibrated such that the rotation sensors within the motor accurately measure distance. After calibration, a single program is needed to conduct the series of experimental speed trials. Students begin time trials by placing the robot on the ground, ensuring that the touch sensor is depressed; only then will the robot begin to move after a three-second countdown. Traveling an arbitrary distance, the robot continuously logs the distance traveled and time until the robot is lifted off the ground, thereby ending the trial. The program allows for repetition of the experiment by pressing the Enter button.
- Students tabulate the data recorded by the robot at the end of each trial: distance traveled and travel time. Students calculate the average speed of the robot for each of its trials and average them. The robots can then be tested to carry cargo, in the form of fender washers, which can be grouped and tied to the robots' axles, as shown in Figure 2. Students can investigate the maximum amount of cargo (in the form of washers count) that the two types of robots can manage to carry.
- After students conclude their hypotheses based on their observations of the two robots' performance, begin the competition portion of the activity. In the competitions, students predict the outcomes based on what they learned in the previously performed experiments. Conduct speed trial and tug-of-war competitions to test "geared up" and "geared down" robot sets, respectively. Speed trials are arranged as simple races between two or more racers. Tug-of-war trials are conducted between two racers running in opposite directions, connected by string or LEGO components.
Before the Activity
- Assemble each robot racer. The primary difference between the two types of racers is their gear train assembly (see Figure 3). Refer to the attached building and programming instructions for exact, step-by-step instructions. Note that the wheels in the instructions should be replaced with LEGO "motor cycle" wheels (part #2903). The program is common to both types of racers and is contained within a single file, pod_racer.rbt, which refers to three additional MyBlocks. These MyBlocks need only be inserted into NXT-G's MyBlocks directory.
- Once assembled and programmed, calibrate the racers to measure distance using the gear train configurations. Calibration depends on the material on which the racers will be tested (for example, carpet, tile or wood). Calibration requires the comparison of the actual distance traveled by the robot, measured with a yardstick, with the computed distance. Higher or lower discrepancies from the actual value require the negative or positive (linear) adjustment of the calibration factor, indicated in the NXT-G program as a variable. As with all robotic set-ups, each racer must be inspected for structural integrity and tested for program reliability.
- Fully charge the NXT brick battery packs.
- Make copies of the Gears Pre-Assessment Survey, Gears Post-Assessment Survey, and Pod Racer Activity Workbook, one each per student.
With the Students
- Administer the pre- assessment survey prior to exposure to the activity set-up.
- As a class, briefly discuss gears and their usage in the "everyday world."
- Define "gearing up" and "gearing down" as simply defined in the Vocablary section, using LEGO demos or online media.
- Develop a group hypothesis regarding the effect of "gearing up" and "gearing down" configurations on the racers' speed and towing abilities.
- Briefly describe the operation of the racer robots and how they can be used to test the class' hypothesis. Four experiments will be conducted:
- Experiment #1: Gearing-down time trials
- Experiment #2: Gearing-up time trials
- Experiment #3a: Gearing-down tow trials
- Experiment #3b: Gearing-up tow trials
- Distribute the Pod Racer Activity Workbook to each student. This includes operation instructions and data tables for students to log data. If required, demonstrate execution of the instructions to carry out one trial with one racer set-up.
- Discuss the results with the class and, if time permits, conduct either racing competitions and/or tug-a-war competitions (Figure 4).
- Conclude by administering the Gears Post-Assessment Survey.
- NXT program: pod_racer (rbt)
- NXT (MyBlock) program: Main Subroutine (rbt)
- NXT (MyBlock) program: Race Start Routine (rbt)
- NXT (MyBlock) program: Instructions (rbt)
- Gears Pre-Assessment Survey (doc)
- Gears Pre-Assessment Survey (pdf)
- Gears Post-Assessment Survey (doc)
- Gears Post-Assessment Survey (pdf)
- Gears Assessment Survey Answer Key (doc)
- Gears Assessment Survey Answer Key (pdf)
- Pod Racer Activity Workbook (docx)
- Pod Racer Activity Workbook (pdf)
- Pod Racer Activity Workbook example (docx)
- Pod Racer Activity Workbook example (pdf)
© 2013 by Regents of the University of Colorado; original © 2010 Polytechnic Institute of New York University
AMPS GK-12 Program, Polytechnic Institute of New York University
Last modified: October 9, 2015