Lab 2: Odometry

ECSE 211 Design Principles & Methods
Lab 2: Odometry
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 Lab Submission
Instructions on MyCourses.
Design objectives
1. Design and implement an Odometry system that provides a robot’s position and orientation,
allowing it to autonomously navigate a field.
2. Evaluate the design and determine the accuracy of the implemented Odometry system.
Design requirements
The following design requirements must be met by your robot:
Odometer:
● Must determine the robot's X, Y and θ orientation.
● Must display the X, Y and θ on the LCD display.
● X and Y must be in cm.
● X and Y can be negative.
● θ must be in degrees.
● θ must range from [0⁰, 359.9⁰]:
○ When the value increases past 360⁰, it should return to 0⁰.
○ When the value decreases past 0⁰, it should wrap to 359.9⁰
● The zero values for (X, Y), i.e. (0,0), must respect the convention shown in Figure 3.
© 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.
1
ECSE 211 Design Principles & Methods Updated: 21 January 2020
Demonstration (30 points)
The design must satisfy the requirements by completing the demonstration outlined below.
Note: For this lab, you will only have 3 chances to demonstrate your work to the TA.
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 designed to test your individual
understanding of the lab concepts. Each person will be graded individually.
You must 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.
Float Motors (10 points)
The TA will check whether the X, Y and θ values are updated correctly on the robot’s LCD
screen by floating the robot’s motors/wheels.
All three axes (X, Y, θ) are checked:
● X & Y values work → 5 points
● θ values work → 5 points
E.g. if the (X, Y, θ) convention is set as in Figure 1, then:
● Moving both wheels forward should increase Y.
● Moving both wheels backward should decrease Y.
● Moving the right wheel backward and the left
wheel forward simultaneously should increase
θ.
● Moving the right wheel forward and the left wheel
backward simultaneously should decrease θ.
Figure 1: Robot faces north at 0o
.
E.g. if the (X, Y, θ) convention is set as in Figure 2, then:
● Moving both wheels forward should increase X.
● Moving both wheels backward should decrease X.
● Moving the right wheel backward and the left
wheel forward simultaneously should increase θ.
● Moving the right wheel forward and the left wheel
backward simultaneously should decrease θ.
Figure 2: Robot faces east at 90o
.
© 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.
2
ECSE 211 Design Principles & Methods Updated: 21 January 2020
Odometry Check (10 points)
The TA will ask you to run your robot off the center of a tile, as shown by S in Figure 3. The
robot should then follow the 3-by-3 tile square trajectory using SquareDriver. The robot
should work using odometry. Throughout the demo, the TA will observe the reported (X, Y, θ)
values on the robot’s LCD screen. When the robot stops at the final position (XF,YF) near S, the
final readings on the LCD screen (X, Y, θ) are used to evaluate the odometer’s accuracy and
calculate the error distance ϵ as:
ϵ = √(X − X ) F
2 + (Y − Y ) F
2
Note that the error ϵ is calculated as the Euclidean distance between:
• The odometer’s readings (X,Y), which signifies where the robot thinks it is with respect to
the origin (0,0), and
• The final actual position (XF,YF), which ideally should be the point S where the robot started
the 3-by-3 tile square trajectory.
This means that it is not an issue if your robot does not return to the exact starting point S, as
long as the odometer reports a position that matches its real-world location.
Point grid based on error ϵ:
[0, 3] cm → 5 points
(3,6] cm → 2.5 points
(6,∞) cm → 0 points
Point grid based on the difference
between the displayed θ and actual θ:
[0, 15] ° → 5 points
(15, 30] ° → 2.5 points
(30, ∞) ° → 0 points
(0, 0)
Figure 3. 3-by-3 tile trajectory using
SquareDriver.
© 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.
3
ECSE 211 Design Principles & Methods Updated: 21 January 2020
Provided materials
Physical material
In the lab, tiles with black grid lines are provided. These make up the competition floor, where
the robot will operate. Grid lines are separated by a distance of 30.48cm.
Sample code
A package of sample code is provided that contains the following:
• Display.java
● Provides a display mechanism for the Odometer.
● Runs in a thread
• Main.java
● The main class that runs the robot.
● Starts Odometer thread and Odometer correction thread.
● Drives the robot using SquareDriver.java.
• Odometer.java
● A skeleton class for building an odometer.
● Runs in a thread.
● Provides methods for manipulation of volatile odometer variables, such as X and Y
position.
• Resources.java
● Defines the ports used by motors and sensors.
• SquareDriver.java
● Runs the robot in a 3-by-3 tile square, where one tile is 30.48cm.
© 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.
4
ECSE 211 Design Principles & Methods Updated: 21 January 2020
Implementation instructions
1. In Odometer.java, implement your odometer design in the run() method of the
Odometer class. This class is threaded and will run continuously when your robot is working.
2. In Resources.java, tweak the values of WHEEL_RAD and BASE_WIDTH so that your
robot drives in a square pattern when calling SquareDriver.drive().
Report Requirements
The following sections must be included in your report. Answer all questions in the lab report and
copy them into your report. For more information, refer to the Lab 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. The design
evaluation section is expected to be within half a page (excluding graphics).
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.
Odometer test (10 independent trials)
1. Note the starting position S of the robot’s center and consider it to be (0,0) for this trial.
2. Run the robot in a 3-by-3 square using SquareDriver.java.
3. Measure its resulting signed XF and YF position with respect to its starting position S.
4. Note the reported values of X and Y shown for the odometer.
Section 3: Test Analysis
Present the following analysis in a table in your report
1. Compute the Euclidean error distance ϵ of the position for each test.
2. Compute the mean and standard deviation for X, Y, and ϵ. That means, you need to perform
3 mean and 3 standard deviation calculations in total. Use the sample standard deviation
formula. Show one sample calculation for both mean and standard deviation formulas.
.
Answer the following questions in your report
1. What does the standard deviation of X, Y and ϵ tell you about the accuracy of the
odometer? What causes changes in standard deviation?
© 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.
5
ECSE 211 Design Principles & Methods Updated: 21 January 2020
2. What is the sampling frequency of your odometer (i.e. the frequency at which the tacho
count is measured)? What is the tradeoff of having a high sampling frequency versus a
low sampling frequency?
Section 4: Observations and Conclusions
• Is the error you observed in the odometer tolerable for larger distances? What happens if
the robot travels 5 times the 3-by-3 grid’s distance?
• Do you expect the odometer’s error to grow linearly with respect to travel distance? Why?
Section 5: Further Improvements
• Propose a means of reducing the slip of the robot’s wheels using software.
• Propose a means of improving the accuracy of the odometer using one or more light
sensors.
© 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.
6
ECSE 211 Design Principles & Methods Updated: 21 January 2020
Frequently asked questions (FAQ)
1. 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 and the initial lab code. For
this part, a grade of 10 signifies full understanding, 5 signifies partial 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.
2. Are partial points awarded for Float Motors?
No partial points are awarded. Possible demo points: {0, 5, 10}.
3. What is the length of each square tile?
Each tile is 30.48 cm (1 ft) long.
4. Do the displayed values of θ have to be in ° (degrees)?
Yes.
5. Do I have to follow the same (X, Y, θ) convention as in Figure 1 and Figure 2?
Yes.
6. In the Float Motors part, what will be the initial conditions of the robot?
The robot's initial condition is based on your (X, Y, θ) convention - you must inform the TA
about your initial orientation. Once the float motors option is selected on the robot, the TA
will place your robot on a table. Assuming the same convention as in Figure 1, the TA will
forcefully rotate both the wheels forward to test the Y values. Not that the robot will not move
automatically, but rather the TA will rotate both wheels using his/her hands. The TA wants to
notice whether the Y-value will increase or not, without affecting the X and θ values by much
(since they could be affected due to experimental error). Therefore, the odometer's accuracy
is irrelevant here. The main idea is to observe whether the odometer functions well using a
fixed convention. A similar wheel-rotation test is also performed for checking decreasing
values as well as for other variables.
7. How accurate should the (X, Y, θ) values be during the floating motor demo? Should
the values only increase and decrease properly without considering the errors?
Accuracy of (X, Y, θ) values in floating motor demo is irrelevant. However, let us consider an
example when a robot that is oriented along the +Y-axis and both wheels are moved
forward. If the reported Y-values are negative, this means that the Y-axis does not work.
© 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.
7