Week 5: Making Robots React

Learning purpose

This is the big programming week. Students take the sensors from Week 4 and the sequences from Week 3 and combine them with loops and conditions so a robot can react on its own. They learn that a loop repeats steps, a forever loop repeats until it is stopped, and a repeat-until loop runs until a condition becomes true. They meet conditions and boolean (true/false) decisions, then use if and if/else to choose actions. They program obstacle avoidance - loop, read the distance sensor, and if something is close, turn - and explore line following by checking a light or color sensor to steer and stay on a line.

Expected student outcomes

By the end of this week, students can:

• Explain how a loop, a forever loop, and a repeat-until loop each repeat steps
• Describe a condition as a check that is either true or false (boolean)
• Use if to run steps only when a condition is true, and if/else to choose between two actions
• Program obstacle avoidance by looping, reading a distance sensor, and turning when something is close
• Explain how line following keeps checking a light or color sensor to steer and stay on a line

Suggested pacing

About 70-85 minutes. Adjust to your group - these are guides, not limits.

Before you start

Materials

• Block program planning sheet (printable)(Kit, Simulator, Unplugged)
• If/else decision-card set (printable)(Kit, Simulator, Unplugged)
• Reaction test record (printable)(Kit, Simulator, Unplugged)
• A programmable robot kit with a distance sensor and a light or color sensor(Kit)
• Boxes or books to build a small obstacle course(Kit)
• Dark tape (or a printed line) on a light floor for line following(Kit)
• Computer or tablet with the browser simulator(Simulator)
• Program cards (forever, if, if/else, move, turn, read-sensor, stop) and a floor grid or taped line(Unplugged)
• A partner to act as the robot and follow the cards(Unplugged)

Safety

• cautionKeep fingers, hair, and loose clothing away from moving wheels while a reacting robot drives, since it changes direction on its own.(Kit)
• cautionTape lines and obstacle-course pieces down flat and clear the floor so no one trips during runs.(Kit, Unplugged)
• infoSave your block program often so a browser refresh doesn't lose your work.(Simulator)

Running the session

1. 1.Teach loops, forever vs repeat-until, and conditions (true/false) before any programming, using the sense-decide-act loop from Week 1.
2. 2.Build the obstacle-avoidance pattern together - forever, read sensor, if/else - then let pairs adapt it.
3. 3.Do the prediction and three-try reaction test so students see reacting is about reliability, not one lucky run.
4. 4.Explore line following as a keep-checking, keep-steering behavior; expect wiggling, not perfect straight lines.
5. 5.End with the knowledge check and reflection.

Common misconceptions

• 'The robot only needs to check once' - without a loop it reacts a single time and then stops responding.
• 'if/else runs both branches' - it runs only the true branch or only the false branch.
• 'A bigger turn follows the line better' - large corrections overshoot; small, frequent ones work.
• Mixing up the sensor number with the condition - the sensor gives a number, the condition turns it into true/false.

Questions to ask

• Where is the loop, and what makes it stop?
• What is the condition here, and when is it true?
• What does the robot do in the 'else' - and why does it need one?
• How does the robot know it has drifted off the line?

Classroom & group adaptations

Hardware and no-hardware notes

Every activity this week runs three ways - all three teach the same core idea, so pick whichever fits your room. No specific product is required.

Troubleshooting

Common problems from this week's activities and what to try.

• The robot drives straight into obstaclesKitTry: Check the if is really reading the sensor, and that your closeness value is larger than the reading when a wall is right in front.
• The robot spins in place foreverKitTry: Your closeness value may be too big so it always thinks something is close; lower it, or add a short forward move in the else.
• Robot drives off the grid or into a wallSimulatorTry: Make sure the read-sensor and if/else are inside the loop, not after it, so the check happens every step.
• Robot only turns and never moves forwardSimulatorTry: Put the move-forward in the else branch so it drives whenever the path ahead is clear.
• The robot 'cheats' and just walks around obstaclesUnpluggedTry: Remind them a robot can only follow the cards; they must actually check the condition and act on it.
• The robot forgets to keep checkingUnpluggedTry: The forever card means go back to the top every time; point to it after each action.
• The robot loses the line right awayKitTry: Re-check your on-line and off-line sensor readings and set the threshold between them; the two must be clearly different.
• The robot spins in circlesKitTry: Make the correction turns small; big turns overshoot the line every time.
• The loop never endsSimulatorTry: Check the repeat-until condition (reached the end tile) can actually become true along the path.
• The robot drifts off the lineSimulatorTry: Make sure the read-sensor and if/else are inside the loop so it checks and corrects every step.
• The robot just walks the whole line smoothly without checkingUnpluggedTry: That is a human planning ahead - make them pause and re-check the condition each single step, like a loop.
• The robot argues about which way to turnUnpluggedTry: Write the rule so 'off the line' always turns toward the line, removing the guesswork.

Knowledge-check answer key

Answers are shown here for the adult only - the student worksheet keeps them hidden.

1. 1. Decide whether this statement is true or false.

   Correct answer: False

   Why: False. A forever loop keeps repeating until something stops it - it does not end by itself.

2. 2. What does a loop do in a program?

   Correct answer: It repeats one or more steps instead of writing them out again and again

   Why: A loop repeats steps for you, so the robot can do or check something over and over without a long program.

3. 3. What is the difference between a forever loop and a repeat-until loop?

   Correct answer: A forever loop repeats until you stop the program; a repeat-until loop repeats until a condition becomes true

   Why: A forever loop only stops when you stop the program; a repeat-until loop stops itself once its condition becomes true.

4. 4. A condition like 'is the wall close?' can only be:

   Correct answer: True or false (a boolean)

   Why: A condition is a check that is always either true or false - and a true/false value is called a boolean.

5. 5. What does an if/else block do?

   Correct answer: It runs one set of steps when the condition is true and a different set when it is false

   Why: An if/else block chooses between two actions: the 'if' steps when the condition is true, the 'else' steps when it is false.

6. 6. How does obstacle avoidance work?

   Correct answer: A loop reads the distance sensor and, if something is close, the robot turns; else it drives forward

   Why: Obstacle avoidance is a loop that reads the distance sensor and uses if/else to turn when something is close and drive forward when the path is clear.