Wait Program!

Engineers and scientists frequently write programs to assist them in solving problems. Often, these programs perform simulations or mathematical operations to help them analyze the results of many different inputs. As a result, computer programs must be flexible enough to deal with variable conditions, not just one specific case. For example, if programming a calculator, the program must be able to operate on any two numbers that might be entered.

In the first lesson in the unit, the programs were only good for navigating through a maze with precisely the given measurements. In the calculator example, this is analogous to being able to compute 1+2 correctly but not accounting for any other possible inputs. Using wait blocks, we can program robots to account for variable conditions, for instance, to move forward any distance until running into a wall. The skill of designing solutions that can handle a variety of conditions is incredibly useful in engineering and in life.

After this activity, students should be able to:

• Program the LEGO MINDSTORMS NXT robot using sensors to accomplish useful tasks.
• Explain how the wait block functions and provide reasons for using it in programming LEGO robots.

Completion of the associated lesson so that students are ready to create their own NXT programs using wait blocks.

It is very important in programming to know how to use a "conditional" statement. This means the program tells a computer or robot to do something IF a particular event happens.

In robots, sensors provide information about the environment around the robot, and this input helps robots decide what to do. For example, a robot might stop if an object is in front of it, or wait until it hears a clap and then move left. The ability to respond in this way makes the robots more useful. Today's activity will help you learn how to implement such "conditional" statements.

Before the Activity

• Gather materials and make copies of the Wait Program! Pre-Quiz (PDF) and Wait Program! Post-Quiz (PDF), one each per student. Also, make copies of the Wait Program! Worksheet (PDF), two each per student, for the two programming challenges. The quizzes and worksheet are provided as separate attachments, and also embedded in the presentation to make it easier to go through them as a class, if desired.
• Assemble a LEGO MINDSTORMS NXT taskbot for each group, following the instructions in the base set manual.
• In advance, perform the entire activity so as to be familiar with all details, especially the programming solutions on slides 5 and slides 7-8.
• Present the activity challenges and background information to students using the 11-slide Wait Program! Presentation (PPTX), a PowerPoint file. Set up a computer/projector to show the presentation to the class.
• Arrange for enough computers so you have one for each student group. Make sure each computer has the LEGO software loaded.

With the Students

1. Administer the pre-quiz by handing out paper copies (also on slide 2). Answers are provided for the teacher on slide 3.
2. Challenge 1: Introduce the first design challenge using slide 4: Program the robot to move forward until it hears a clap, then turn left.
3. Distribute one worksheet to each student for the challenge 1 activity.
4. Divide the class into student pairs. Direct them to work together to program their robots to complete the task using wait blocks, which they learned about in the associated lesson. This challenge uses a sound sensor.
5. Once student groups have designed their programs, give them the following instructions:

• Attach the sound sensor to the robot using instructions given in the base set manual. Then attach the sound sensor to port 2 of the LEGO brick.
• Make sure the battery is fully changed. Then press the orange button to turn on the LEGO brick and plug it into the computer.
• Download the program onto the LEGO brick by clicking the gray down arrow in the bottom right corner of the computer screen.
• Test the program to verify that it works as desired to meet the challenge. As necessary, troubleshoot and fix any problems and re-download the program until it is successful.
• Note: The programming solution is provided for the teacher on slide 5.

6. Challenge 2: Use slide 6 to introduce a more challenging task that uses wait blocks: Write a program so that your robot:

• Remains at rest until you press the touch sensor.
• Once you press the touch sensor, moves slowly forward until you press the touch sensor again.
• Once the touch sensor is pressed a second time, moves twice as fast.
• Once the touch sensor is pressed a third time, moves twice as fast as before.
• Once the touch sensor is pressed a fourth time, stops.

7. Distribute a second blank worksheet to each student.
8. Have student pairs write programs using wait blocks to accomplish this task. This challenge uses a touch sensor.
9. Have student groups download their programs onto LEGO bricks and test to see if they work.
10. Reinforce the engineering design process and how it is an iterative process. Like engineers, students typically must iterate their initial designs many times in order to get them just right and fix any problems in their programs. Learning to do this "iteration" is important to be a successful scientist or engineer, or anyone working to achieve the best solution to a problem.
11. Note: Refer to the programming solution on slides 7-8 to check student programs.
12. Administer the post-quiz by handing out paper copies (also on slide 9). Answers are on slide 10. Vocabulary are provided on slide 11.

Pre-Activity Assessment

Pre-Quiz: Administer the three-question Wait Program! Pre-Quiz (PDF)(also on slide 2) to assess students' retention of knowledge about conditional commands, wait blocks and move blocks from the associated lesson. Answers are provided on the Wait Program! Pre-Quiz Answer Key (PDF) (and slide 3).

Activity-Embedded Assessment

Worksheets & Iterations: For both programming challenges, have students first complete Wait Program! Worksheets (PDF) to ensure they have good ideas of what they want to program and to guide them through the program development design process. Like engineers, it is extremely rare for students to create programs that navigate the robots perfectly through the maze the first time, so do not be worried if students take some time and repeated efforts to do this. The teacher should, however, know the solution well (provided in the slides) and ask pertinent questions to guide students to successful solutions. Review students' worksheet answers to gauge their comprehension of the concepts covered.

Post-Activity Assessment

Post-Quiz: Have students complete the Wait Program! Post-Quiz (PDF) (also on slide 9), which presents two of the same questions as the pre-quiz, as well as a review of the concept of an algorithm. Expect students to be able to provide more informed responses to the post-quiz questions after completing the activity. Answers are provided for the teacher on the Wait Program! Post-Quiz Answer Key (PDF) (and slide 10).

NXT User's Guide. Accessed Jul 17, 2013 http://goo.gl/wuhSUA