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Lesson 2: Using the Front Eye Sensor with While Loops

In this Lesson, you will create a project using the Front Eye Sensor with a while loop and not condition to navigate the VR Robot through the Disk Maze Playground. Your project will instruct the VR Robot to turn right when a green disk is detected by the Front Eye Sensor, and left when a blue disk is detected. In the mini challenge, you will apply these skills to drive the VR Robot to each disk in the Disk Maze Playground, and finish at the red disk.

Lesson 2 Introduction

Learning Outcomes

  • Identify that the while loop can be used with the Eye Sensors.
  • Identify that in order to use Eye Sensor data to make the VR Robot make a decision in a project, a condition must be used.
  • Describe how identifying a pattern in a project can be used to simplify your code.

Navigating to the First Four Disks

The Front Eye Sensor can be used to make the VR Robot detect disks and their colors, and to make decisions based on that data. The VR Robot can then navigate the Disk Maze using sensor feedback related to the colors of the objects that are detected, to determine the robot's movement. Essentially, the Front Eye Sensor data will be used to 'color code' the VR Robot's turns, so when one color is detected it turns left, and when another is detected it turns right.

To begin, let's look at the path the VR Robot will travel to navigate the first portion of the Disk Maze. image of the Disk Maze Playground with the VR Robot's path plan drawn out

For Your Information

The Disk Maze Playground contains colored markings on the floor of the Playground at each of the raised colored disk locations.turn right at green disc 

We will use the Front Eye Sensor to detect the disks in this Unit, but the same logic and project could be used with the Down Eye Sensor as well. Instead of detecting the raised disks, the Down Eye Sensor would detect the colors on the floor of the Playground, and make decisions with that data. The Down Eye Sensor does not detect the floor of the Playground as an object, but it will detect the colored spaces. 

Using a While Loop with Eye Sensor Data

In previous Units, the while loop was used to make the VR Robot drive while a condition was met, or a while loop with a not condition to drive while a condition was not met. Data from the Eye Sensors can be used in the same way. Let's look at the first step in the Disk Maze path.

 Turn right at green

The VR Robot should drive forward while the Front Eye Sensor does not detect green. When the Front Eye Sensor does detect green, the VR Robot should turn right 90 degrees to face the next disk in the maze.

Name and Save the Project

Let's begin building the project to use the while loop to instruct the VR Robot to turn when the Front Eye Sensor detects the first (green) colored Disk on the Disk Maze Playground.

  • Start a new project in and name the project Unit7Lesson2.Unit7Lesson2


  • To begin, add a comment to describe the VR Robot's behavior. This project will use comments to remind the user what the intention is for the behaviors of the VR Robot during the following section of the project. Remember that comments in VEXcode VR Python start with a # (pound) symbol. 
    python comment
  • The VR Robot will need to drive toward the first disk on the Disk Maze Playground. Drag in or type a while loop with a not condition in the workspace. Remember to include the wait command as part of the while loop, to ensure that the VR Robot executes the project correctly.

    while not loop

  • Set the condition of the loop to the Front Eye Sensor's detect command, and set the parameter to "GREEN."
    front eye detect green condition
  • Inside the while loop, drag or type the non-waiting drive command.
    drive forward command in while not loop
  • Outside the while loop, drag or type a turn_for command to instruct the VR Robot to turn right 90 degrees when it detects a green disk.
    turn for 90 degrees command
  • Open the Disk Maze Playground if it is not already open, and run the project.
  • Watch the VR Robot drive forward to the first green disk then turn right.
    turn right at green disc
  • Notice that the VR Robot drives forward while the condition of the Front Eye Sensor color reports False. Once the green disk is detected, the Front Eye Sensor color reports True and exits the loop. Then, it executes the next command, which is to turn right for 90 degrees.

Select the Next button to continue with the rest of this Lesson.