Motorized Toy Project - Learning about Gears (Lesson 6)

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SWBAT understand how gears work and be able to calculate gear ratios

Big Idea

The motorized toy requires gears - how do gears work?

The Need for the Lesson

Students need to develop an understanding of gears. They need to know how they work and how gear ratios are calculated. The gears are research needed to support the student motorized toy design choice. 

Investigation Preparation & Summary

5 minutes

This is lesson six of the Motorized Toy Project

Students will learn and use the vocabulary of engineers, defining problems, constraints and criteria for success. Students will experience the integration of skills across the curriculum as they delve into the project. (MS-ETS1.1 - Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment that may limit possible solutions.) Students will be asking the question and solving the problem - What toy design will best meet the marketing goals of MTI (Motorized Toy Company) and how will we develop it? (SP1 - Asking Questions and Defining Problems)

Students collaborate to design and implement a solution to the Request for Proposal letter sent from the fictitious toy company - MTI. (MS-ETS1.2 - Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem.) Students will examine various gear ratios to determine which best meets the criteria and constraints of the problem defending their choice using data collected. (SP7 - Engaging in Argument from Evidence)

Students will construct and test multiple gear ratios and use the data collected to make and informed decision about their final product. (MS-ETS1.3 - Analyze data from tests to determine similarities and differences among several design solutions to identify the best characteristics of each that can be combined into a new solution to better meet the criteria for success.) Students must analyze the data they have collected. Some student groups may not actually meet the performance requirements set forth by MTI (Motorized Toy, Inc.) and may have to justify their choice of a gear ratio for the toy based on their interpretation of the best fit according to their data. (SP4 - Analyzing and Interpreting Data)

An important understanding for students in that engineering is an iterative process. They will build and test multiple gear ratios models to determine the optimal performance of the motorized toy. (MS-ETS1.4 - Develop a model to generate data for iterative testing and modification of a proposed object, tool, or process such that an optimal design can be achieved.) (SP2 - Developing and Using Models)

In this lesson students will be multiplying fractions to find the gear ration for gear trains. (7.RP.A.2Use proportional relationships to solve multistep ratio and percent problems. Examples: simple interest, tax, markups and markdowns, gratuities and commissions, fees, percent increase and decrease, percent error.)

After implementing their successful solution, students will create a short video to promote their new product (WHST.6-8.2 - Write informative/explanatory texts, including the narration of historical events, scientific procedures/ experiments, or technical processes.)

The project models for students how scientific research, collecting data about gears and their performance, and societal desires in the form of the project request from Motorized Toy, Inc., the Crosscutting Concept of Influence of Science, Engineering, and Technology on Society and the Natural World.

This PBL is based on the curriculum developed by the SAE (Society of Automotive Engineers) AWIM (A World in Motion) Motorized Toy Project. The original curriculum has great lessons and takes about 8 weeks to complete. The program is outstanding. My modifications are designed to allow the project to be completed in about 3 weeks. The time line allows students to experience a taste of the entire engineering design process required to bring a new product to market.

Kits are available for purchase on the SAW AWIM website - here. If you can partner with an SAE member, the member can apply for one new kit each year for your school. The form to apply for a free kits is here. I have partnered with an SAE member for several years and have three kits that allow me to run this project with all my classes at once.

A complete materials list for this lesson can be found in the resources section.

The NGSS Evidence Statement publication for middle grade engineering was used as a guide for verifying that all engineering standards could be observed in the Motorized Toy Project series of lessons. This video briefly explains that process.

All NGSS Evidence Statements for middle school can be found here.

Students in Action

45 minutes

Before you can build and test the your motorized toy, MTI would like to know that you are trained to work with gears. You know how gears work and how to calculate the gear ratios. 

What does the term gear ratio mean? The gear ratio is the ratio of the number of rotations of the driver gear to the number of rotations of the driven gear.

What does a gear ratio of 5:1 mean? A 5:1 gear ratio means that the driver gear rotates 5 times to 1 turn of the driven gear 1 time. We can also say say that the driver gear rotates 5 times as fast as the driven gear. 

In this video, I share an easy way to help students determine the number of rotations for both the driver gear and the driven gear.

Next we will calculate the gear ratio for gear trains. Most of the gears you will be building and testing are gear trains.

It is important that the number of driven gear teeth appear in the numerator and the number of driver gear teeth appear in the denominator of the fraction.

Your sheet has great step-by-step instructions for your reference. We will complete the first two examples together and you and your team will then finish the rest of the calculations.

In this video I explain how to write and multiply the fractions to find the gear ratio for the gear train. 


I remind students to place both completed sheets into their corporate binder. These sheets are evidence of training completed to share with MTI (Motorized Toy, Inc.) to show that they are qualified to build and test motorized toy prototypes.