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Lesson 3: Using Reported Sensor Feedback to Place Disks in the Goal

In Lesson 2, the VR Robot drove in reverse back to the starting point to drop off the disk. This required the user to calculate the exact distance for the VR Robot to travel. This may not always be possible. Instead, the VR Robot can use reported sensor values to pick up and drop disks with consistent precision. 

Lesson 3 uses reported sensor feedback to determine where the VR Robot should stop driving when returning to the goal. In using the <Eye Sensor near object> block earlier in this lesson, there is no need to know the distance from the goal to each disk.

VR Robot on the Disk Mover Playground with the first blue Disk attached to the Electromagnet.

The VR Robot will drive back towards the blue goal using data from the Distance Sensor to determine where to stop driving. Once the VR Robot has stopped inside the blue goal, the VR Robot will drop the blue disk.

  • Continue working in the Unit8Lesson3 project.
  • The Distance Sensor measures the distance from the front of the VR Robot to the nearest object. For this reason, the VR Robot will need to turn around 180 degrees before driving back towards the blue goal.
  • The VR Robot will use the Distance Sensor with the back wall of the Playground in order to determine where to drop the disk. For this reason, the VR Robot will need to turn around 180 degrees before driving back towards the blue goal.

  • The [Turn to heading] block can be used to ensure the VR Robot turns to the correct heading.

    VEXcode VR Turn to heading block from the Toolbox. The block reads 'Turn to heading 90 degrees'.

Using Switch Blocks 

This is the Switch [turn to heading] block. You can modify the degree of the turn by changing the numerical value in the parentheses. Remember that the number must be written before the unit of measurement (DEGREES), separated by a comma. 

VEXcode VR Turn to heading Switch block, with the Python command that reads drivetrain dot turn_to_heading (90, DEGREES).

For Your Information

The [Turn to heading] block turns the VR Robot to a specific heading using the Gyro Sensor. The direction the VR Robot will turn (left or right) is determined based on the current heading of the Gyro sensor. The [Turn to heading] block is used to direct the VR Robot to a specific heading regardless of the VR Robot’s position. As you pick up or drop a disk, the VR Robot may be knocked off course. Using the [Turn to heading] block ensures that the VR Robot will turn to the absolute position rather than a position relative to the prior heading.

A diagram of the heading locations in degrees of the VR Robot. There is a circle with a top down view of the VR Robot in the center, with the front of the robot facing up towards the 0 degree heading. Clockwise, each subsequent 90 degree heading is marked as 90 degrees, 180 degrees, and 270 degrees.

  • Add a [Turn to heading] block beneath the third comment.

    The same VEXcode VR project as the previous page, with a turn to heading block added below the third comment. The project now reads When Started, comment Drive to the first blue disk, with a Repeat until down eye is near object, drive forward, then stop driving. Next is a comment to pick up the first blue disk with an energize electromagnet to boost block. The third comment reads drive to the blue goal and has a turn to heading 90 degrees block next.

  • Set the [Turn to heading] block to 180 degrees.

    The same VEXcode VR project with the parameter of the Turn to heading block changed to 180 degrees. Now, the third comment section of the project reads Drive to the blue goal, Turn to heading 180 degrees.

  • Now that the VR Robot is oriented towards the starting position, the VR Robot will need to drive back to the blue goal. Add a [Repeat until] block beneath the [Turn to heading] block.

    The same VEXcode VR project with a Repeat until block added after the Turn to heading block. The parameter of the Repeat until block is empty.

  • To drive back to the blue goal, the VR Robot will use data from the Distance Sensor to determine when the VR Robot is inside the blue goal. As discussed in the previous lesson, each grid square on the Disk Mover Playground measures 200 millimeters (mm) by 200 millimeters (mm).

    A close up, top down view of the lower left corner of the Disk Mover Playground with the dimensions of a grid square on the Playground shown as 200mm tall by 200mm wide.

  • Using those measurements, the center of the blue goal can be determined to be approximately 200 millimeters (mm) from the wall of the Playground.

    A close up, top down view of the blue goal in the lower left corner of the Disk Mover Playground, with the approximate dimension from the wall to the center of the goal labelled as 200mm.

  • The VR Robot should stop driving when the Distance Sensor reports that the VR Robot is less than 200 millimeters (mm) from the wall of the Playground. Add the following blocks to the [Repeat until] block.

    The same VEXcode VR project with a less than operator block with a nest Front distance in mm in the parameter of the Repeat until block. Now, the third comment section of the project reads Drive to the blue goal; turn to heading 180 degrees; Repeat until Front Distance in mm is less than 50.

  • Change the parameter in the <Less than> block to 200.

    The same project, with the parameter of the less than block changed to 200. Now the Repeat until block reads 'Repeat until Front Distance in mm is less than 200'.

  • Add a [Drive] block into this [Repeat until] block. This will instruct the VR Robot to drive forward until the Distance Sensor reports a distance of less than 200 millimeters (mm).

    The same project with a Drive block add inside the C of the Repeat until block. The third comment section of the project now reads Drive to the blue goal; Turn to heading 180 degrees, Repeat until Front distance in mm is less than 200, drive forward.

  • Once the VR Robot has reached the blue goal (200 mm from the wall), the VR Robot will need to stop driving. Add a [Stop driving] block beneath the [Repeat until] block.

    The same project with a Stop driving block added after the Repeat until block. The third comment section now reads Drive to the blue goal; Repeat until front distance in mm is less than 200, Drive forward; then stop driving.

  • Now that the VR Robot is stopped in the blue goal, it can drop the disk. Add an [Energize Electromagnet] block beneath the fourth comment and set the block to ‘drop.’

    The same project with an Energize Electromagnet block, with the parameter set to drop, added after the fourth comment. The fourth comment section now reads Drop the blue disk in the blue goal, Energize magnet to drop.

  • The VR Robot will need to drive in reverse a short distance to avoid knocking over or colliding with any disks. Colliding with a disk could potentially knock the VR Robot off course. Add the following blocks to instruct the VR Robot to drive in reverse for 100 millimeters (mm) and turn back to a heading of 0 degrees.

    The same project with a Drive for block and a Turn to heading block added to the bottom of the stack. Now, the fourth comment reads Drop the blue disk in the blue goal; Energize magnet to drop; Drive reverse for 100mm, turn to heading 0 degrees.
  • Open the Disk Mover Playground if it is not already open and run the project.

  • The VR Robot drives forward, picks up the first disk, then turns to a heading of 180 degrees to face the blue goal. The VR Robot then uses the values from the Distance Sensor to determine when to stop driving and drop the blue disk.

    A close up side view of the Disk Mover Playground with the Blue Disk placed in the blue goal, and the VR Robot facing the remaining disks on the Playground, at the edge of the blue goal.
  • Notice how the second [Repeat until] block functions in this part of the project.
    • When the Distance Sensor on the VR Robot detects the wall of the Playground is less than 200 millimeters (mm) away, the project will move to the next block in the stack below the [Repeat until] block.
    • In this project, that meant the VR Robot stops driving and drops the Electromagnet in the blue goal.

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

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