Lesson Plan Industry Sector
Engineering & Design

## Selecting Gears for VEX robots

### Lesson Plan Overview / Details

Students need to be able to choose appropriate gears to achieve desired speeds in their robots.  This lesson will introduce students to gear ratios and how they affect speed and torque.  Effects of different gear ratios will be demonstrated using small inexpensive robot kits.  Students will receive direct instruction on gear ratios and then use the information to choose the optimal gearing to complete a VEX robot.   Assessment will be on how well student robots perform in time trials (VEX is a specific brand of educational robot) This lesson can be modified to work with other educational robots by acquiring brand specific data.

One class period
90 Minutes

### Objectives and Goals

• Students will use mathematics to make appropriate choices of gears to power a robot
• Students will build a VEX robot using the selected gears
• Students will asses robot performance against predicted performance

### Activities in this Lesson

• Robot Race - Hooks / Set

Vex robot race video is cued up on the projector.  The following questions are on the board:  Why do these robots have different speeds?  What specific mechanical factors might cause differences in speed?

As students enter the room they pick up their notebooks from the book shelf.  As students sit and open their notebooks the video is started.  After watching the video students brainstorm answers in pairs and write their answers in their notebooks.

• The teacher leads a short discussion about the brainstorming.  Discussion may include replaying the video to look at specific student ideas.    Possible reasons students might list:  battery charge, friction, bearings, wheel sizes, construction quality, motor selection, programming issues, gears, gear ratios.

• Java Applets for mechanisms(animations) another great source of simple animations that illustrate different kinds of geared mechanisms
• Gear Ratios - Lecture

Once the students have ideas about possible causes of speed variation, I will validate all of the ideas and tell the students we are going to focus on gears and gear selection.  I will instruct students to take notes as I go over how to control speed using gears.  The attached power point covers changes in direction and gear ratios.  After the showing the power point I check for understanding.  Ask students to give examples of gear selections based on proposed outcomes.

For example:  I want the robot to go faster, but I want the wheels to rotate in the same direction as the motor.  How many gears do I need?  Which gear should be larger and which gear should be smaller, the input gear or output gear?

• Gear Calculation - Demo / Modeling

I will work through a sample calculation to demonstrate how to choose gears for specific outcomes.

The sample calculation will be based on using input data from last years USFIRST robot.  Students will be given a set of specifications for the motors, gears, and wheels for the VEX robots.  In the next activity they will use my example and the specifications to solve for a given speed on a VEX robot.

The sample calculation needs to be done based on lab materials and will up-loaded in the future.

• Students will be in groups of three.  Each group will be given a specification sheet and a copy of the rubric.  Each group will go through the calculation process to determine the optimal gear choices to achieve the specified speed.

Spec sheet needs to be developed and up loaded

• Students will build a VEX robot based on the criteria they have decided on as a result of their engineering calculations.  One set of VEX robots will needed for each team of students.

### Assessment

Assessment Types:
Rubrics, Demonstrations,

Students will demonstrate assembled VEX robots and the robots' ability to achieve the desired speed.

A Rubric will be used to grade the gear selection process and robot performance.  The rubric will be based on a visual inspection of the robot and the construction, the choice of gears used in the robot, the actual speed of the robot, the predicted speed of the robot, and the calculations used to predict the speed of the robot.

• Rubric [ Download ] Rubric for grading finished robot