Lab 1: Wall Following

ECSE211 Design Principles & Methods 
Lab 1: Wall Following
Submission instructions: Students are expected to work in their assigned lab groups.
The lab consists of three components: demonstration, lab report, and code submission.
Instructions on the demonstration can be found in this handout. Lab reports and code
submission must follow the guidelines established in this handout and for the course. For more
information, see the submission instructions on MyCourses.
Design objectives
1. Design and implement a wall following system that can navigate around a sequence of
blocks and obstacles that form a wall containing gaps, concave corners, and convex
corners.
2. Implement Bang-Bang and P-type controllers as part of the wall following system.
3. Evaluate the design and compare the behavior of the two controllers.
Design requirements
The following design requirements must be met by your robot:
● Robot
o Must be able to complete a lap around a series of blocks while maintaining a fixed
distance from the wall, i.e. a bandcenter.
o Must account for right-angle convex corners.
o Must account for right-angle concave corners.
o Must account for gaps in the wall.
o Note: gaps will be no larger than the shortest width of a block, i.e. 10 cm.
o Must be able to drive around an arbitrarily shaped wall, made up of at most 7 blocks.
● Controllers and sensors
o Must implement a Bang-Bang controller.
o Must implement a P-type controller.
o Must use the ultrasonic sensor for range finding.
o Must be able to perform the course using each controller type.
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ECSE211 Design Principles & Methods Updated: 14 January 2020
Demonstration (30 points)
The design must satisfy the requirements by completing the demonstration outlined below.
Design presentation (10 points)
Before demoing the design, your group will be asked some questions for less than 5 minutes.
You will present your design and answer questions to test your individual understanding of the
lab concepts. Each person will be graded individually.
You must also present your workflow, an overview of the hardware design, and an overview of
the software functionality. Visualizing software with graphics, such as flow charts, is valuable.
Bang-bang controller (10 points)
● Place the robot at one corner of a sequence
of blocks as shown in Figure 1.
● Start the robot with the Bang-Bang controller.
● The robot must follow the wall continuously
for 2 consecutive laps.
● The robot cannot touch the wall at any point,
including its wires.
P-type controller demo (10 points)
● Place the robot at one corner of a sequence
of blocks as shown in Figure 1.
● Start the robot with the P-type controller.
● The robot must follow the wall continuously
for 2 consecutive laps.
● The robot cannot touch the wall at any point,
including its wires
Figure 1. Course and robot placement.
© Instructor and Teaching Assistant generated course materials (e.g., handouts, notes,
summaries, assignments, exam questions, etc.) are protected by law and may not be copied
or distributed in any form or in any medium without explicit permission of the instructor. Note
that infringements of copyright can be subject to follow up by the University under the Code of
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ECSE211 Design Principles & Methods Updated: 14 January 2020
Provided materials
Physical material
In the lab, blocks that will be used to build the wall are provided. The blocks will be placed per
the setup specified in the requirements by a TA.
Sample code
A package of sample code is provided which contains the following:
● Main.java
o The main class that runs the robot.
o Provides a menu to select the controller types.
o Creates and runs the program threads.
● UltrasonicController.java
o Provides a polling method for the ultrasonic sensor.
o Drives the robot and takes in data from the ultrasonic sensor.
● Printer.java
o Outputs information to the LCD screen.
o Runs in a thread.
● Resources.java
o Class for static resources.
o Defines the static constants used in the program.
o Defines the ports used by motors and sensors.
Implementation instructions
Implement the bangBangController() and pTypeController() controller methods in the
UltrasonicController class.
© Instructor and Teaching Assistant generated course materials (e.g., handouts, notes,
summaries, assignments, exam questions, etc.) are protected by law and may not be copied
or distributed in any form or in any medium without explicit permission of the instructor. Note
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ECSE211 Design Principles & Methods Updated: 14 January 2020
Report Requirements
The following sections must be included in your report. For this lab, you will not collect any
quantitative results; all data is qualitative. Answer all questions in the lab report and copy them
into your report. For more information, refer to the submission instructions. Always provide
justifications and explanations for all your answers.
Section 1: Design Evaluation
You should concisely explain the overall design of your software and hardware. You must
present your workflow, an overview of the hardware design, and an overview of the software
functionality. You must briefly talk about your design choices before arriving at your final design.
Visualizing hardware and software with graphics (i.e. flowcharts, class diagrams) must be
shown. These diagrams are expected to be simple and concise, for example, the class diagram
should not include too many low-level details. Make sure to mention how you arrived at tuning
your Bang-Bang controller and P-type controller constants (i.e. bandcenter, bandwidth, P-type
constant). The design evaluation section is expected to be within half a page (the graphics
would not count towards the limit).
Section 2: Test Data
This section describes what data must be collected to evaluate your design requirements.
Collect the data using the methodology described below and present it in your report.
Testing the P-type controller constant
1. Choose 2 values above and below your P-type controller constant used in the demo.
2. Run the robot using the P-type controller.
3. Note its performance, i.e. band center and oscillation behavior, for the 2 cases.
Bang-Bang controller test (3 independent trials)
1. Place the robot at the starting corner of a wall.
2. Ensure the wall contains convex corners, concave corners, and gaps.
3. Run the robot using the Bang-Bang controller.
4. Check if it completes a lap without touching the wall.
5. Note its performance, i.e. band center and oscillation behavior for each trial.
P-type controller test (3 independent trials)
1. Place the robot at the starting corner of a wall.
2. Ensure the wall contains convex corners, concave corners, and gaps.
3. Run the robot using the P-type controller.
4. Check if it completes a lap without touching the wall.
© Instructor and Teaching Assistant generated course materials (e.g., handouts, notes,
summaries, assignments, exam questions, etc.) are protected by law and may not be copied
or distributed in any form or in any medium without explicit permission of the instructor. Note
that infringements of copyright can be subject to follow up by the University under the Code of
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ECSE211 Design Principles & Methods Updated: 14 January 2020
5. Note its performance, i.e. band center and oscillation behavior for each trial.
Section 3: Test Analysis
Compare the performance of both controllers. Make sure to refer to your test data.
● What happens when your P-type constant is different from the one used in the demo?
● How much does your robot oscillate around the band center?
● Did it ever exceed the bandwidth? If so, by how much?
● Describe how this occurs qualitatively for each controller.
Section 4: Observations and Conclusions
● Based on your analysis, which controller would you use and why?
● Does the ultrasonic sensor produce false positives (detection of non-existent objects) and/or
false negatives (failure to detect objects)? How frequent were they? Were they filtered?
Section 5: Further Improvements
● What software improvements could you make to address the ultrasonic sensor errors? Give
3 examples.
● What hardware improvements could you make to improve the controller performance? Give
3 examples.
● What other controller types could be used in place of the Bang-Bang or P-type?
© Instructor and Teaching Assistant generated course materials (e.g., handouts, notes,
summaries, assignments, exam questions, etc.) are protected by law and may not be copied
or distributed in any form or in any medium without explicit permission of the instructor. Note
that infringements of copyright can be subject to follow up by the University under the Code of
Student Conduct and Disciplinary Procedures.
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ECSE211 Design Principles & Methods Updated: 14 January 2020
Frequently Asked Questions (FAQ)
1. What is a “lap”?
A single lap is defined as a closed trajectory that the robot must follow and keep its
distance from the wall before arriving in its starting location. In Figure 1, one whole lap
would mean following the wall on the right side (the dotted line) and continuing around the
end to follow it along the left side until reaching the starting point.
2. What is meant by “design presentation”?
Before a lab demo, you and your partner will briefly present your design. This can include a
basic visualization of how your code functions, such as a flow chart. You will then be asked
a series of questions. These could be related to the lab tutorial, the initial lab code. For this
part, a grade of 10 signifies full understanding, 5 signifies satisfactory understanding, while 0
shows no understanding at all. Note that memorized answers are discouraged and both
partners should be responsible for understanding the design and their associated code,
even if one of them did not write all of it.
3. Are partial points awarded in this lab demo?
No partial points are awarded. Possible demo points: {0, 5, 10, 15, 20, 25, 30}.
4. Should my robot follow the wall in an anti-clockwise direction (like Figure 1)?
No, it may follow any direction as long as it remains consistent throughout the demo.
5. Are reverse wheel rotations allowed?
Yes, you may reverse your robot at any point in the demo.
6. Is there a time limit on the demo?
No, but your TA can conclude your demo if your robot is moving extremely slow.
7. Will the wall setup look exactly like Figure 1?
No, it could be different. However, all setups will include at least one gap, one convex corner
and one concave corner.
8. Can I make additional Java classes?
Yes, you can add any classes as necessary, as long as you respect the submission
structure.
© Instructor and Teaching Assistant generated course materials (e.g., handouts, notes,
summaries, assignments, exam questions, etc.) are protected by law and may not be copied
or distributed in any form or in any medium without explicit permission of the instructor. Note
that infringements of copyright can be subject to follow up by the University under the Code of
Student Conduct and Disciplinary Procedures.
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ECSE211 Design Principles & Methods Updated: 14 January 2020
9. Can the speed of each motor be varied?
Yes, the speed of each motor can be changed, provided it continues to implement the
correct controller type.
10. Why does the EV3 brick keep crashing after running our code?
Common problems include:
(1) no sensors or motors connected,
(2) motors and sensor ports do not match the ones used in your code,
(3) project is not an leJOS EV3 project.
11. Why does my Java code not upload or run on the EV3 brick?
Common problems include:
(1) no IP address selected from Preferences → leJOS EV3 → Connect to named brick
[Solution: set the same IP address as shown on your EV3 brick]
(2) not using the correct JRE which is JavaSE-1.7 [Solution: right-click on your project →
Properties → Java Compiler → is 1.7 selected? If not, create a new project]
(3) not using a leJOS project in the eclipse IDE [Solution: create a new leJOS EV3 Project],
(4) checking the box under Preferences → leJOS EV3 → Use ssh and scp [Solution:
uncheck that box]
(5) bad USB connectivity [Solution: try using other USB ports and uploading your code
multiple times].
© Instructor and Teaching Assistant generated course materials (e.g., handouts, notes,
summaries, assignments, exam questions, etc.) are protected by law and may not be copied
or distributed in any form or in any medium without explicit permission of the instructor. Note
that infringements of copyright can be subject to follow up by the University under the Code of
Student Conduct and Disciplinary Procedures.
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