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Teacher Toolbox icon Teacher Toolbox - The Purpose of this Activity

This activity will introduce students to using while and if statements to have the robot drive forward unless the screen is pressed.

  • This activity will introduce students to conditionals and the instructions that have the robot drive forward unless the screen is pressed.
  • For more information about if and if-else statements or others used in this activity, visit the help information within VEXcode V5. For more information about this built in help tool, check out the article about help in Python.

Teacher Toolbox icon Teacher Toolbox

For suggestions on teaching strategies for this section, review the Delivery column of the To Do or Not to Do Pacing Guide! (Google Doc / .docx / .pdf)

The Clawbot is ready to make decisions!

This exploration will give you the tools to be able to start creating some cool projects that use if-else statement.s

  • VEXcode V5 Python commands that will be used in this exploration: 
    • drivetrain.drive_for(FORWARD)
    • brain.screen.pressing()
    • drivetrain.stop()
    • if condition:
    • else:
    • while True:  
    • wait(5, SECONDS)

You can use the Help information inside of VEXcode V5 to learn about the Python commands.

Image of the Help in VEXcode V5 open in a Python project window

Make sure you have the hardware required, your engineering notebook, and VEXcode V5 ready.

Materials Required:
Quantity Materials Needed
1

VEX V5 Classroom Starter Kit (with up-to-date firmware)

1

VEXcode V5 (latest version, Windows, macOS)

1

Engineering Notebook

1

Clawbot (Drivetrain 2-motor, No Gyro) Template

Teacher Tips icon Teacher Tips

If this is the student’s first time using VEXcode V5, they can reference the Tutorials at any time during this exploration. The Tutorials are located in the toolbar.

2020-11-30_14-15-09.jpg

Step 1: Let's start with an understanding of conditional statements 

Before you begin programming with conditionals, read the article explaining if-else statements. The article can be found here (Google Doc / .docx / .pdf).
Image of the start of the Using if-else statements in VEXcode V5 Python article
For a list of operators to use in the if-else statements, read the article explaining Booleans. This article can be found here (Google Doc/.docx/.pdf).

Image of the start of the Using Booleans article

Step 2: Let's start programming with conditional statements.

  • Open the Clawbot (Drivetrain 2-motor, No Gyro) template example project.

     

  • Build the project below.

Image of a VEXcode V5 Python project with an if statement in it

Do the following in your engineering notebook:

  • Explain what the project has the Clawbot do. You will need to explain more than the fact that it creates a stop button. Explain which instructions make the Clawbot do what.

  • Write a one sentence summary that captures what the project does.

  • Test to see if your prediction of what the project has the Clawbot do is correct.

  • Name the project CreatingAStopButton. Download and run the project on the Clawbot.

  • Check your explanations of the project, and add notes to correct them as needed.

Teacher Toolbox icon Teacher Toolbox - Answers

This project has the robot continuously drive forward but stop if the screen is pressed. It does this by using a "forever" statement (while True) to drive and check continuously. If the screen is being pressed (True), then the Clawbot stops driving.Image of the project with the commands broken down with an explanation

Students are not expected to understand why the while brain.screen.pressing(): and wait(5, MSEC) commands are used. Explain that these commands are necessary because of the speed of the robot's program flow. If it was not there, the Clawbot's motors would behave as though the user is pressing the screen again and again as it loops through the project. Instead, these instructions stop the program flow and do not have the project start the loop again until the user stops pressing the screen.

The line of pseudocode could be as simple as: Drive forward until the screen is pressed.

Students' engineering notebooks can be maintained and scored individually (Google Doc / .docx / .pdf) or as a team (Google Doc / .docx / .pdf). The previous links provide a different rubric for each approach. Whenever a rubric is included in educational planning, it is good practice to explain the rubric or at least give copies to students before the activity begins.

Step 3: Understanding the while and wait() statements.

Notice that if the Brain's screen is pressed, the flow of the project moves quickly and the project will move to the next instruction, which is the drivetrain.stop() command.

Thus, the project needs the while and wait commands that tell the robot to remain stopped until the Brain's screen is released. Otherwise, the forever statement would cause the project to begin again.

Image of the the while brain screen is pressed command with a wait command in a VEXcode V5 Python project

The while and wait commands are necessary because of the speed of the project's flow. If they were not there, the project would move to the next instruction before the robot ever had time to respond.

Step 4: Change the project.

Our next step is changing the if statement to an if-else statement.

  • Start by saving CreatingAStopButton as the new project, StopOrDrive.

  • If you need help saving a project, view these articles.

  • Then build the StopOrDrive project shown below.

Image of the Stop or Drive example project in VEXcode V5 Python

  • Download StopOrDrive to Slot 2 on your Clawbot.

  • For help downloading and running a project, see this article.

  • Test CreatingAStopButton (Slot 1) and then test StopOrDrive (Slot 2) and compare them to see if there are any difference in the robot's behavior. Note any differences in your engineering notebook

Teacher Toolbox icon Teacher Toolbox - Answer

In regard to the robot's behavior, there should not be a difference between the CreatingAStopButton and StopOrDrive projects.

If the students need further assistance with understanding if-else statements, see this article (Google Doc / .docx / .pdf).

The two projects have the Clawbot behave the same way. The only difference is the use of the if-else statement in the StopOrDrive project.
Using the if-else statement will allow you to add additional buttons to the screen in upcoming activities.

Extend Your Learning icon Extend Your Learning

As this STEM Lab proceeds, students will develop projects that allow the Clawbot's screen to function as a user interface. In preparation for that, challenge students to figure out how to draw a colored rectangle on the screen that functions like a button. Because pressing anywhere on the screen is currently the condition, the button should take up the entire screen. Students should have the project broadcast an event to draw the button when started.

Direct students to first learn how the brain's screen is organized into a coordinate system. They will need to understand this in order to set parameters within the commands they will be using. The coordinates used correspond to the number of pixels not the number of the column or row. Here is the layout of the screen:Image of the coordinate system on the Brain screen

Students should plan, test, and refine these changes to the project while documenting it within their engineering notebooks. For the individual engineering notebook rubric, click one of the following links (Google Doc / .docx / .pdf), or click one of the following links for team notebooks (Google Doc / .docx / .pdf).

Here is an example solution: Image of an example solution in VEXcode V5 Python

As you can see, the button is drawn to take up the entire screen starting at the (0, 0) origin and filling all 480 horizontal (x-axis) pixels and 240 vertical (y-axis) pixels.