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Lesson: What Is a Motor and How Does a Rotation Sensor Work?

Quick Look

Grade Level: 5 (4-7)

Time Required: 45 minutes

Lesson Dependency:

Subject Areas: Computer Science, Life Science, Physics, Science and Technology

Two photographs: A woman in a suit sits in the front seat of a car, driving and shifting gears. A close-up of a LEGO MINDSTORMS EV3 robot with a servo motor attached to one of its wheels.
Electric motors convert electric energy to mechanical energy.
Copyright © (left) 2004 Microsoft Corporation, One Microsoft Way, Redmond, WA 98052-6399 USA. All rights reserved. (right) 2006 Eirik Refsdal, Wikimedia Commons http://commons.wikimedia.org/wiki/File:Lego_Mindstorms_Nxt-FLL.jpg


Students learn about electric motors and rotational sensors. They learn that motors convert electrical energy to mechanical energy and typically include rotational sensors to enable distance measuring. They also learn the basics about gear trains and gear ratios. Students create a basic program using the LEGO® MINDSTORMS® interface to control a motor to move a small robot. Then, through a 10-minute mini-activity, they make measurements and observations to test a LEGO rotation sensor's ability to measure distance in rotations. This prepares them for the associated activity during which they calculate how many wheel rotations are needed to travel a distance. A PowerPoint® presentation, worksheet and pre/post quizzes are provided.
This engineering curriculum aligns to Next Generation Science Standards (NGSS).

Engineering Connection

Electrical and mechanical engineers use motors to perform many tasks. Motors are used in a wide variety of machines, everything from pencil sharpeners to school buses. Knowing how motors work, including their internal components, such as rotational sensors and gears, helps students understand this fundamental, everyday device.

Learning Objectives

After this activity, students should be able to:

  • Explain how a LEGO robot uses a motor and gears to move.
  • Explain how motors rotate and enable motion by converting electrical energy to mechanical energy.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS Performance Expectation

MS-PS3-5. Construct, use, and present arguments to support the claim that when the kinetic energy of an object changes, energy is transferred to or from the object. (Grades 6 - 8)

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This lesson focuses on the following Three Dimensional Learning aspects of NGSS:
Science & Engineering Practices Disciplinary Core Ideas Crosscutting Concepts
Construct, use, and present oral and written arguments supported by empirical evidence and scientific reasoning to support or refute an explanation or a model for a phenomenon.

Alignment agreement:

Science knowledge is based upon logical and conceptual connections between evidence and explanations.

Alignment agreement:

When the motion energy of an object changes, there is inevitably some other change in energy at the same time.

Alignment agreement:

Energy may take different forms (e.g. energy in fields, thermal energy, energy of motion).

Alignment agreement:

  • Fluently add and subtract multi-digit whole numbers using the standard algorithm. (Grade 4) More Details

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  • Use proportional relationships to solve multistep ratio and percent problems. (Grade 7) More Details

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  • Various relationships exist between technology and other fields of study. (Grades 3 - 5) More Details

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  • A product, system, or environment developed for one setting may be applied to another setting. (Grades 6 - 8) More Details

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  • Describe how new technologies have helped scientists make better observations and measurements for investigations (e.g., telescopes, magnifiers, balances, microscopes, computers, stethoscopes, thermometers) (Grade 4) More Details

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  • Describe how new technologies have helped scientists make better observations and measurements for investigations (e.g., telescopes, electronic balances, electronic microscopes, x-ray technology, computers, ultrasounds, computer probes such as thermometers) (Grade 5) More Details

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Worksheets and Attachments

Visit [www.teachengineering.org/lessons/view/umo_sensorswork_lesson02] to print or download.

Pre-Req Knowledge

  • Familiarity with the LEGO MINDSTORMS EV3 robot and how to program its EV3 intelligent brick (computer).
  • An understanding of how the (electrically powered) windows move up and down in a car.
  • Completion of the Our Bodies Have Computers and Sensors (unit 2).


(Be ready to show students the 18-slide Motors and Rotational Sensors Presentation, a Microsoft® PowerPoint® file, to teach the lesson. In advance, make copies of the Electric Motors Pre-Quiz, How Does a Rotation Sensor Work? Mini-Activity Worksheet and Electric Motors Post-Quiz, provided as attachments and slides, including answers. For a mini-activity, student groups use LEGO robots.)

Have you ever wondered how your car windows move up and down when you press the window button? Any guesses? (Listen to student ideas.) They are controlled by electric motors that draw on energy from the car battery and move the glass of the window up or down.

Electric motors are all around us—in CD and cassette players, in electric cars, and in subway trains! Today we will learn about how electric motors work.

In addition, the LEGO MINDSTORMS EV3 motor comes with a rotation sensor inside its casing (you cannot see it from the outside). This sensor provides us with information about how much the motor moves, as you will see in today's lesson.

(Continue by showing the presentation and delivering the content in the Lesson Background section.)

Lesson Background and Concepts for Teachers

This second lesson of the unit reviews motors—the fundamental device that causes motion in LEGO robots, and a device that might be considered equivalent to "muscles" in the human body, as presented in Humans Are Like Robots (unit 1). In the associated activity, students calculate how many wheel rotations are needed to travel a distance, an illustration of the use of rotational sensors and mathematics in engineering. Present the lesson using the content provided in the slide presentation, as described below.

For this lesson and its associated activity Master Driver, student teams each require a LEGO taskbot, which is used throughout this unit. In advance, assemble each taskbot with materials from LEGO MINDSTORMS EV3 Core Set (5003400) for $389.95 at https://education.lego.com/en-us/products/lego-mindstorms-education-EV3-core-set-/5003400, using instructions provided at https://www.youtube.com/watch?v=Dhe2jXi3Fc4 or with the core set. Note: This activity can also be conducted with the older LEGO MINDSTORMS NXT set. You’ll need a computer loaded with the NXT 2.1 software.

What is an Electric Motor? How Does a Rotation Sensor Work? Presentation Outline (Slides 1-18)

  • Administer the pre-quiz by handing out paper copies; the quiz is also on slide 2. The answers are provided for the teacher on slide 3 for discussion after students have completed the quiz.
  • (slide 4) Discuss how an electric motor works, making sure to mention that electricity is converted to motion.
  • (slide 5) Explain that a LEGO MINDSTORMS EV3 motor has gears and a rotation sensor inside its casing.
  • (slide 6) Discuss some real-world applications of electric motors, such as electric pencil sharpeners, car windows, electric can openers, fans, refrigerators, washing machines, vacuum cleaners, etc.
  • (slide 7) Explain how the motors help the EV3 taskbot to move. Make the robot/human comparison by going through the movement process for each: computer brick > electrical signals through cables > motor > movement, compared to: the human brain > electrical signals through the nervous system > muscles > movement.
  • (slide 8) Divide the class into teams and challenge each to develop a program to make the EV3 taskbot move forward and then turn right. Have students implement the program on the robot to show that it works. If they are familiar with programming EV3 robots, this serves as a refresher task. If they are not familiar with programming EV3 robots, give them time to brainstorm and experiment to figure it out. The answer for this program is provided on slide 17. (Note that the What Is a Computer Program? unit has considerable additional information about EV3 programming basics.) Use slide 9 to explain the functionality options for how to program the motor to move.
  • (slide 10) Explain to students that the EV3 motor casing also includes a rotation sensor that senses the rotations of the hub where the wheel is attached. Then give students a few minutes to write down the components of the stimulus-sensor-coordinator-effector-response framework for this activity; the stimulus-to-response framework answer is provided on slide 18.
  • (slide 11) Introduce students to a mini-activity (10 minutes long) to develop their understanding of how rotation sensors work. The activity objective is to test the rotation sensor's ability to measure distance in rotations.
  • (slide 12) Begin by briefly explaining how gears transform rotations. Emphasize that gears do not mesh perfectly, which results in errors in readings of the number of rotations.
  • Hand out the worksheet paper copies. Proceed to the mini-activity instructions (slide 13). Have students collect data and make observations about sensor accuracy on the worksheet (also on slide 14).
  • Lead a class discussion so students can share their mini-activity experiences, results and conclusions. Expect students to report that their mathematical calculations do not always match up to actual measurements. This may be the result of calculation mistakes, imperfect meshing of gears, variation in wheel positioning, etc.
  • Next, conduct the associated activity.
  • After the associated activity is completed, administer the post-quiz by handing out paper copies; the quiz is also on slide 15. The answers are provided on slide 16. Slides 17-18 contain answers.

Associated Activities

  • Master Driver - Students learn how to use rotation sensors to measure how far robots move. After determining the ratio of rotation to distance, they use this information to program LEGO MINDSTORMS EV3 robots to move precise distances as part of a class competition. In the process, they practice their mathematical skills, learn about potential sources of error due to gearing when using rotation sensor readings for distance calculations, and engage in the steps of the engineering design process.


electric motor: A motor is an electrical machine used to create motion. The device converts electricity (electrical energy) into motion (mechanical energy). Typically performed by rotating an object.

rotational sensor: A sensor that measures the turning movement of a wheel for purposes of calculating distance traveled.


Pre-Lesson Assessment

Pre-Quiz: Administer the three-question Electric Motors Pre-Quiz, by handing out paper copies (also on slide 2). Students' answers reveal their base understanding of electric motors. Answers are provided on the Electric Motors Pre-Quiz Answer Key (and slide 3).

Post-Introduction Assessment

Mini-Activity: Have students use the How Does the Rotation Sensor Work? Mini-Activity Worksheet as they conduct a 10-minute activity to explore how the LEGO rotation sensor works (slides 11-14). They collect data and record their observations on the worksheet. Circulate through the room, observing students and checking their work. Once students are finished, lead a class discussion so students can share results and conclusions.

Lesson Summary Assessment

Post-Activity-Quiz: Note: Administer this post-assessment after students have conducted the associated Master Driver activity. Administer the three-question Electric Motors Post-Quiz by handing out paper copies (also on slide 15). Review students' answers to gauge how much they know about the topic at lesson/activity end. Answers are provided on the Electric Motors Post-Quiz Answer Key (and slide 16).


© 2013 by Regents of the University of Colorado; original © 2013 Curators of the University of Missouri


Nishant Sinha, Pranit Samarth, Satish S. Nair

Supporting Program

GK-12 Program, Computational Neurobiology Center, College of Engineering, University of Missouri


This curriculum was developed under National Science Foundation GK-12 grant no. DGE 0440524. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.

Last modified: July 3, 2019

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