Lesson 2: Using the [Wait until] Block

In this Lesson, you will create a project using the Bumper Sensor and [Wait until] block. In the mini-challenge, you will apply these skills to navigate from the beginning of the Wall Maze to the letter ‘A.’

Learning Outcomes

• Identify that non-waiting blocks have the stack continue even if the block's behavior is not yet complete.
• Identify that a waiting block pauses the stack until that block's behavior has been completed.
• Identify that the highlighting of the project's execution visualizes waiting vs non-waiting blocks.
• Identify that the [Wait until] block is a Control block that accepts Boolean values.
• Identify that the [Wait until] block will repeatedly check a Boolean condition and will not move to the next block until the condition reports TRUE.
• Identify that the [Wait until] block is used with a non-waiting block (e.g. Drive) in order to check the sensor condition.
• Identify that the <Pressing bumper> block reports a TRUE or FALSE value in a [Wait until] block.
• Identify how the [Drive for] and [Turn for] blocks are special blocks that can be either waiting or non-waiting.
• Describe how to create a project that has a VR Robot drive forward until the Bumper Sensor is pressed.

Name and Save the Project

• Start a new project in VEXcode VR and name the project Unit4Lesson2.

[Wait until] Blocks

The [Wait until] block is a Control block that accepts Boolean conditions. [Wait until] blocks repeatedly check a Boolean condition and control the project flow. A project will not move to the next block in the stack until the condition in the [Wait until] block reports as TRUE. The [Wait until] blocks are used in conjunction with non-waiting blocks such as [Drive] or [Turn].

For Your Information

Non-waiting and waiting blocks determine when the next block begins a behavior. Waiting blocks, like [Drive for] and [Turn for], complete their behaviors before moving onto the next block in the stack. Non-waiting blocks, such as [Drive] and [Turn], continue to move to the next block in the stack even if the behavior of the non-waiting block is not complete.

Certain blocks, like [Drive for] and [Turn for] can be waiting or non-waiting blocks. Selecting the arrow on the block will turn the block from waiting into a non-waiting block.

• Drag the [Drive] non-waiting block into the workspace.
  

  

• Attach a [Wait until] block beneath the [Drive] block.
  

  

• The [Wait until] block accepts Boolean conditions. This project will use the Bumper Sensor to drive through the Wall Maze Playground. Drag the <Pressing bumper> Boolean block into the [Wait until] block.
  

  

• Drag in a [Stop driving] block and add it to the project.
  

  

• Launch the Wall Maze Playground if it is not already open and run the project.
• Watch the VR Robot drive from the start of the Wall Maze and stop when the Bumper Sensor is pressed by the wall.
• The [Drive] block allows the VR Robot to keep driving forward while checking the condition of the Bumper Sensor with the <Pressing bumper> block. Once the <Pressing bumper> reports as TRUE, the VR Robot will move to the next block in the stack and stop driving.
  

  

  For Your Information

  To follow a visualization of waiting versus non-waiting blocks, watch the code execution highlighting function in VEXcode VR. At the beginning of this project, the green highlight will appear around the [Wait until] block until the condition is met. This is because the [Wait until] block is a waiting block. The green highlight will appear to skip the non-waiting blocks because these commands are quickly executed.