Lesson 2: Reading Code

In the previous Lesson, you learned about relative movement and how it compares to absolute movement. As you went through the Lesson, you were asked to make predictions about how the 6-Axis Robotic Arm would move when a project was run. This is an example of reading code.

In this Lesson, you will practice code reading to determine what will happen when a project is run.

A project is shown that will make the 6-Axis Arm draw a triangle on the Whiteboard Attachment, as an example of the kind of project that will be documented in this Lesson.

What is Code Reading?

Just like writing code, reading code is a fundamental skill for programmers. Programmers often need to read and understand code written by others, whether to fix problems in the code, review code, or learn from existing projects. You have read code each time you have looked at a project and made a prediction about what it will do in your engineering notebook. Now you are going to practice this skill more intentionally. In the projects in this Lesson, it will be important to look at whether the code is using absolute or relative movement and how this impacts what is drawn on the Whiteboard Attachment.

Organizing Your Code Reading

There are many tools that can be used to help you determine what will happen in a project. Using your engineering notebook to visualize the behaviors of the robot can be a helpful tool to get started reading code.

This Lesson will show one way to organize code reading in your engineering notebook. You can use the layout shown here as a starting point as you work through describing each part of your project. In the examples in this Lesson, the engineering notebook page has an image of the VEXcode project on the left, with the lines for adding text on the right. In each step, the blocks that are being focused on are highlighted with a red box, and the text describes the behavior(s) associated with those blocks.

Reading the Code in Project A

To practice code reading, we will walk though the documentation process as we read the code for Project A.

Document this project in your engineering notebook. This can be done by writing the steps out in sequence or by adding the image of the code directly to your notebook.

Before beginning the steps to read the code, make a prediction about what the 6-Axis Arm will do when the project is run. You will return to this prediction after completing this code reading process.

Project A begins with a When started block, and alternated between a Comment block and the associated Arm block. From top to bottom the project reads: Comment 1: Get set up to draw; set arm end effector to pen; Comment 2: Set up to draw a square; move arm to position 75, 125, 0. Then each side: Comment3: Draw side AB with relative movement; increment arm position by x 50; Comment 4: Draw side BC with relative movement; increment arm position by y 50; Comment 5: Draw side CD with relative movement; increment arm position by x -50; and finally, Comment 6: Draw side DA with relative movement; increment arm position by y -50.

To read code, start at the beginning of the project. Looking at the first block, write the behavior associated with that block in your engineering notebook, beside the project.

Here, the first blocks can be described as: 1. Set the end effector to the Pen.

Code reading notebook example, using Project A from above. The first comment and set arm end effector blocks are highlighted and described.

As you read the code, you will need to look closely at each block to determine if the 6-Axis Arm will be using absolute or relative movement.

In this project, the first movement block is a Move to position block. Note that the 6-Axis Arm will use absolute movement to move to the coordinates listed in the parameters of the block.

The beginning portion of Project A as described above, with the move arm to position x 75, y 125, z 0 mm block highlighted in a red box.

Record the behavior associated with the block in your engineering notebook. This comment and move to position block can be described as: 2. Use absolute movement to move to coordinates (75, 125, 0).

Code reading notebook example, showing the start of Project A from above. The second comment and the move to position block below it are highlighted and described. The block moves the arm to position x 75, y 125, z 0.

Look at the next movement block in the project. Is this an absolute or relative movement?

This is an Increment position block, so it indicates relative movement by the 6-Axis Arm.

The beginning portion of Project A as described above, with the block to increment position by x 50 mm highlighted in red.

Use the increment provided in the parameters of the block to determine the position where the 6-Axis Arm will be moving when this block is executed. Do this by adding the value of the relative movement (50mm) of the matching coordinate (x) from the absolute movement block.

Record this in your engineering notebook. This could be described as: 3. Relative move by adding 50 to the x-coordinate. The new coordinates are (125, 125, 0).

Code reading notebook example, showing a portion of Project A from above. The third comment and the increment position block below it are highlighted and described. The block increments the arm 50mm along the x axis.

Continue this process for the remaining blocks in the project. Document what each block will do when the project is run.

Remember to read Comment blocks and Notes for reference when reading the project.

The remaining steps of this project to draw the remaining three sides could be described as follows:

4. Relative move by adding 50 to the y-coordinate. The new coordinates are (125, 175, 0).

5. Relative move by subtracting 50 from the x-coordinate. The new coordinates are (75, 175, 0).

6. Relative move by subtracting 50 from the y-coordinate. The new coordinates are (75, 125, 0).

Code reading notebook example, showing the bottom portion of Project A from above. The final three comments and the increment position blocks below each are highlighted and described. The increment position blocks in this section read as follows: the first reads increment arm position by y 50; the second reads increment arm position by x - 50; and the final reads increment arm position by y - 50.

Sketch the path of the 6-Axis Arm when the project is run.

To help visualize the final product of the project, use the coordinates you determined to sketch the path in your engineering notebook.

An engineering notebook diagram showing a top down view of the 6-Axis Arm with the Whiteboard Attachment. An X and Y axis are overlaid, with the origin intersecting in the center of the base of the arm. A dotted line square is sketched to connect the four points plotted on the whiteboard, to match the coordinates described above in the code reading. The square is in the center right hand portion of the whiteboard.

Watch the project being executed. Answer the following questions in your engineering notebook.

How do the observed behaviors of the 6-Axis Arm compare to your list of behaviors in your engineering notebook?
How does your list of behaviors compare to the prediction you made at the start of the Lesson?
How does the prediction you made at the beginning of the Lesson compare to the behaviors shown in this video?
- In the video below, the 6-Axis Arm moves from the safe position to place the Pen at location (75, 125, 0). It then moves away from the base to draw the first side of the square, to the right to draw the second side, toward the base to draw the third side, and to the left to complete the square.

Congratulations! You have now read code and used that knowledge to determine what happens when a project is run. You will continue to practice this with two additional examples.

Reading the Code in Project B

In this example, you are going to practice reading code in order to find a mistake in a project. The intention of this project is to draw a square, just as in Project A. However, if Project B was run, the 6-Axis Arm would not draw a square as intended. You will read the code in this example by following the same steps you used in Project A in order to find the error. Then you will use the information from our code reading to identify how the problem can be fixed.

Document the project in your engineering notebook. This can be done by writing the steps out in sequence or by adding the image of the code directly to your notebook.

Make a prediction about what the 6-Axis Arm will do when the project is run. You will return to this prediction after completing this code reading process.

Project B begins with a When started block, and alternates between a Comment block and the associated Arm block. From top to bottom the project reads: Comment 1: Get set up to draw; set arm end effector to pen; Comment 2: Set up to draw a square; move arm to position 75, 125, 0. Then each side: Comment 3: Draw side AB with relative movement; increment arm position by x 50; Comment 4: Draw side BC with relative movement; increment arm position by y 50; Comment 5: Draw side CD with relative movement; increment arm position by x 50; and finally, Comment 6: Draw side DA with relative movement; increment arm position by y -50.

Start at the beginning of the project. Document the project setup blocks just as you did for the previous project.

The first comment and set end effector block could be described as:

1. Set the end effector to the Pen

Code reading example in the engineering notebook, with the first comment and set arm end effector block highlighted in a red box, and described.

Read the first movement block in the project, paying attention to whether the movement is absolute or relative. What behavior would the block cause the 6-Axis Arm to complete? Visualize this behavior.

The beginning portion of Project B, with a red highlight box around the move to position block beneath the comment Set up to draw a square. The block reads move arm to position x 75, y 125, z 0 mm.

Record the behavior you visualized for this block in your engineering notebook.

This behavior could be described as:

2. Use absolute movement to move to coordinates (75, 125, 0).

Code reading notebook example, showing the start of Project B from above. The second comment of Set up to draw a square and the move to position block below it are highlighted and described. The block reads move arm to position x 75, y 125, z 0 mm.

Now look at the second movement block. Is this an absolute or relative movement? This is an Increment position block, so it indicates relative movement by the 6-Axis Arm.

Visualize the behavior this block would cause the 6-Axis Arm to complete.

A portion of Project B is shown, with the red highlight box around the first increment arm block, beneath the comment Draw side AB with relative movement. The block reads increment arm position by x 50.

As you did for Project A, read the parameters of the block to determine where the 6-Axis Arm's position will be after the Increment position block is executed. Record this in your engineering notebook.

This comment and the increment position block could be described as:

3. Relative move by adding 50 to the x-coordinate. The new coordinates are (125, 125, 0).

Code reading notebook example, showing the start of Project B from above. The third comment of Draw side AB with relative movement, and the increment position block below it are highlighted and described. The block reads increment arm position by x 50 mm.

Continue this process for the remaining blocks in the project. Visualize then document what each block will do when the project is run.

The remaining steps in the project could be described as:

4. Relative move by adding 50 to the y-coordinate. The new coordinates are (125, 175, 0).

5. Relative move by adding 50 to the x-coordinate. The new coordinates are (175, 175, 0).

6. Relative move by subtracting 50 from the y-coordinate. The new coordinates are (175, 125, 0).

Code reading notebook example, showing the bottom portion of Project B from above. The final three comments and the increment position blocks below each are highlighted and described. The increment position blocks in this section read as follows: the first reads increment arm position by y 50; the second reads increment arm position by x 50; and the final reads increment arm position by y - 50.

Sketch the path of the 6-Axis Arm when the project is run.

To help visualize and document the final product of the project, use the coordinates you determined to sketch the path in your engineering notebook.

Engineering notebook diagram of the 6-Axis Arm with the Whiteboard Attachment, with an X and Y axis overlaid, and the origin intersecting in the center of the base of the arm. Five points are plotted, and connected with a dotted line, to reflect the coordinates described in the code reading above. The square is not drawn accurately, as the dotted lines are drawn downward, then to the right, then downward, then to the left.

Watch the project being executed. Answer the following questions in your engineering notebook.

How do the observed behaviors of the 6-Axis Arm compare with your list of behaviors in your engineering notebook?
How does your list of behaviors compare to the the prediction you made at the start of the Lesson?
How does the prediction you made at the beginning of the Lesson compare to the behaviors shown in this video?
- In the video clip below, the 6-Axis Arm moves from the safe position to coordinate (72, 125, 0). It then moves away from the base to draw the first side, to the right to draw the second side, further away from the base to draw the third side, and to the left to draw the fourth side.

Now return to your sketch. Identify the step at which point the project stopped drawing a square. As the 6-Axis Arm executes the first three movement blocks in the project, it seems as if the Pen will continue to draw a square.

However, on the fourth movement block, the 6-Axis Arm travels in the opposite direction than expected – along the positive x-axis rather than the negative x-axis. Locate this step in the project and mark it in your engineering notebook.

The same engineering notebook diagram from above with the dotted line of the third side drawn highlighted in a red box, to indicate movement in the wrong direction on the x axis.

Now identify the block in the project that corresponds with the step where the error occurred. Mark the block in your engineering notebook as well.

In this example, it is step 5 that aligns with the comment of “Draw side CD with relative movement” that is highlighted.

The engineering notebook code reading example from above, with step 5's text and blocks called out in a red box.

Apply what you know about movement along the axes to recommend a fix for this error.

In order to draw a square, the 6-Axis Arm needs to move along x-axis in the negative direction. This means that this Increment position block should have the x-parameter set to –50 rather than 50.

A portion of Project B with a red highlight box around the x parameter of the increment position block below the Draw side CD with relative movement comment. The x parameter is now set to negative 50.

Record the change that is needed to make the project run correctly in your engineering notebook.

This could be documented as a note below the project, as described as:

Step 5 should be changed to subtract 50 from the x-coordinate. The new coordinates should be (75, 175, 0) in order to draw a square.

Step 6 would then change because the movement is relative. The new coordinate after step 6 would be (75, 125, 0).

Watch the project run with the x-parameter of the Increment position block changed from 50 to –50. The 6-Axis Arm now moves from the safe position to coordinate (75, 125, 0_, and then moves to draw a square as intended.

Now you have finished reading code for two different projects – one to help you learn a process for reading and documenting code, and another to read code to identify an error in a project. You will continue to practice reading code, visualizing, and documenting projects each time you work with the 6-Axis Arm and VEXcode. You can return to this Lesson at any time to help you remember a process for reading and documenting code.

Activity

Now that you have practiced code reading using two different projects, you will practice again on your own.

Activity: Follow the procedure you learned to read the code in the project above.

Document the project above in your engineering notebook.
Predict what you think the 6-Axis Arm will do when the project is run. Document your prediction in your engineering notebook.
Read each block in the project, and visualize the behavior the 6-Axis Arm would perform when executing the block. Record this behavior in your engineering notebook.
Sketch the path the 6-Axis Arm would take when the project is run.
Check in with your teacher when you are finished. You will watch the project run as a class. Then you will discuss your prediction and documentation.

Check Your Understanding

Before beginning the next Lesson, ensure that you understand the concepts in this Lesson by answering the questions in the document below in your engineering notebook.

Check Your Understanding questions > (Google Doc / .docx / .pdf)

Select Next > to start your Mid-Unit Reflection.

< Back Return to Units Next >