**Grade Level: **

9-12

**Prerequisites: **

9^{th} grade general math and science

**Concepts Addressed: **

In this unit, students will learn about the different types of mechanical power transmission.

Topics include various gear types, and how to calculate gear ratios. These principles will then be applied to the types of motor - arm systems seen on competition robots (and described in Unit 7.)

**Learning Objectives:**

- The students will be able to demonstrate how mechanical power transmission systems are very important in the design and construction of competition robots.
- The students will be able to vary the gear ratio (and the mechanical advantage) in a system, which gives them the versatility necessary to accomplish whatever work needs to be done.
- The students will be able to determine gear inputs & outputs by calculating the difference between them, and determine their gear ratio accordingly.

**STEM Connections: **

Mathematical concepts will be featured in terms of how a transmission functions.

**Materials Needed:**

- Unit Guide
- Paper
- Pencils
- Rulers
- Internet Access
- Dictionaries
- VEX Robotics Kit
- Computers with Autodesk Inventor
- Storage containers
- Online Resources

**Key Terminology: **

- Gear
- Gear Ratio
- Mechanical Advantage
- Transmission
- Spur Gear
- Bevel Gear
- Crown Gear
- Worm Gear
- Helical Gear
- Idler Gear
- Epicyclical (Planetary) Gear
- Rack and Pinion Gear
- Gear Pitch
- Levers
- Compound Gear Reduction

__Day to Day Lesson Plan:__

*Day 1:*

Introduce the unit with an explanation of how the transmission process works, or by having the students conduct research and present the information to their small groups who can then hold a peer review of the material.

Include information from figures 8.1.1 through 8.3.

Student groups of three to four members will prepare a presentation that they will give to the class at the end of the unit that will include the different gear types and how they are used in the design process along with the math needed to support their choices.

*Day 2:*

Have the student groups conduct an experiment on carrying the 15 lbs of books in a backpack up the stairs to study power.

Students will need to follow the methodical process that engineers use to solve a problem.

Student groups will conduct their own research and design an experiment to test their hypothesis.

Student groups will record their data and conduct an analysis.

Student groups will draw a conclusion based upon their data.

*Day 3:*

Review the different types of gears through a presentation or by having the students investigate the uses of different types of gears in equipment used in construction, farming, and industry. Use figures 8.4.1 through 8.11.1

Provide students with a variety of gears, which can be set up on simple structures to they can see how they work.

*Day 4:*

Gears - Include information on Teeth and Pitch and gear ratios, including Figures 8.12.1 8.12.1

Have the student groups design the different types of gear structures in Autodesk Inventor and show the class. Have them provide an explanation of how the gear structures work and what their advantage in the design process would be.

Alternative assignment will have the students sketch the different types of gears in their Engineering Notebook and explain the advantage of each type in the design process.

*Day 5:*

Levers - Find out what the students already know about levers.

Show how gears function in levers.

Include information from Figures 8.15.1 through 8.16.1

Students can demonstrate their prior knowledge through a series of sketches with a written explanation of how they work.

*Day 6:*

Gear Reduction - Review how the process works and the math needed to completed the calculations.

Review the material that includes the Figures 8.17.1 through 8.30.1

Worksheet with problems

(Needs to be created with solution sheet for the teachers.)

*Day 7:*

Continue the review of the gear reduction process.

Check for understanding of math concepts

Application of gears to DC motor systems

*Day 8:*

Students will revisit the arm design problem from the end of Unit 7.

- The designers will create a single motor, gearbox, arm system that can lift the weight of a single game object, the manipulator from Unit 6.
- The designers must choose an arm length appropriate for the game, which fits within the 18” robot size requirement. The gear ratio should be calculated such that the motor should be loaded such that it draws no more than one amp of current.
- After calculating the necessary ratio, users must design a compound gearbox that achieves this ratio, and then calculate the final speed of the arm.

*Day 9:*

Assessment of vocabulary

Worksheet of calculations

Design ideas for their arm

Engineering Notebook

*Day 10:*

Review any concepts that were challenging for the students.

**Engineering Notebook “Seed Questions”: **

- How do the different types of gears provide an advantage in your arm design?
- How do the mathematical calculations help you to determine what type of gear ratio is needed in your design?