Hardware Analysis and Synthesis

EG1004 Lab 2: Hardware Analysis and Synthesis

2.1 OBJECTIVES

The experimental goal of this lab is for your team to determine if a robot kit meets minimum standards for accuracy and precision. To do this your team will build and program a robot, and test it against the provided EG standard. All your results must be tabulated accurately.

Together, we will define the concept of product evaluation, demonstrate the importance of accurate measurements, and show how they relate to both precision and accuracy. Once you have completed your lab work, you will be able to describe the method of troubleshooting you developed.

2.2 OVERVIEW

Your team has been hired by an engineering firm to evaluate a robotics kit. This Robotics kit has a manufacturer’s suggested retail price of $199.95. The firm has specified the robot design they would like you to build and test. Your assignment is to test the kit and the specified design, describe what works and list the improvements that should be made to both the kit and the robot design you built. The price of the kit should be factored into the overall product evaluation. What other factors do engineers consider when they evaluate products?

Product evaluation is a common task for an engineer. Sometimes the product you evaluate will be one your team built, and sometimes you will be analyzing a competitor's design. In either case, you will need to decide on a standard (an accepted value), determine an average, and calculate accuracy and precision.¹²

Professional engineers must be sure of standards. For the purpose of this lab, the EG Standard that you will be testing to is 80% precision and accuracy. This means that the product you will be testing has to pass 80% of the tests that it undergoes. Some projects may require a degree of accuracy to a tenth of an inch. Attempting to make the project accurate to the hundredth might be unnecessary and difficult to control. It is up to you to verify that your solutions are accurate based on the standard for your design project.¹²

When taking measurements, the first step is to determine an average.

In this equation, A_P is the average, P₁, P₂, P₃, … are the results of the tests and N is the total number of tests to be performed.

The average is then compared to the standard. Accuracy is a variable you must always consider. The degree of accuracy required will allow you to verify your results. Engineers often work on projects that affect people's safety. Therefore, it is critical that the solutions to the problems you will solve as technical professionals are accurate.

The comparison of the average to the standard is called accuracy.

Acc = P_S - A_P

In this equation, Ps is the standard value, and Ap is the value you measured.

Precision is the repeatability of a result, or how close the results are to each other.

Prec = P_high - P_low

In this equation, Prec is Precision, P_high is the highest data value and P_low is the lowest data value.

A product test can be accurate but imprecise, or precise but inaccurate. The goal is always the combination of accuracy and precision. In order for engineers to make a recommendation based on experimental test data, it is important to determine how a device measures against a standard. Engineers need these benchmarks to determine the quality of a product.

By determining the percent accuracy of an experiment, and comparing this percentage to a standard, you can determine, based on experimental evidence, whether the prototype has passed or failed. The equation for percent accuracy is:

In this equation, %Acc is the percent accuracy, P_S is the standard value, and A_P is the value you measured.

Percent accuracy allows an engineer to determine how precise a device is compared to the standard. The equation for percent precision is:

%prec = 100e^-BP

In this equation, %prec is the percent precision, B is the exponential decay factor, and P is the actual precision you measured.

Calculating percent accuracy and percent precision and then comparing your results to a standard will allow you to determine the quality of your prototype.

2.3 YOUR ASSIGNMENT

Team PowerPoint Presentation and Individual Lab Report (one report per student)

Follow the lab report guidelines laid out in the section called Specifications for Writing Your Lab Reports in the Technical Communication section of this manual chapter. As you write, the following discussion points should be addressed in the appropriate section of your lab report and in your PowerPoint presentation:

• Discuss product evaluation and the importance of testing.
• Explain the importance of designing to a standard.
• Discuss average, accuracy, and precision.
• Assess the techniques used in the testing process.
• Discuss better testing methods for the robot design.
• Make a final evaluation of the product. Describe its accuracy and precision.
• Discuss the importance of % precision and % accuracy in determining product quality.
• State your recommendations.
• Include information about the RoboLab kit and software. To do this, visit Lego's website. Your discussion must include market research data. Make sure any information you use is properly attributed to its source.

2.4 MATERIALS AND EQUIPMENT

• RoboLab Kit
• Computer with RoboLab Software
• Protractor and Ruler

Remember: You are required to take notes. Experimental details are easily forgotten unless written down. You should keep a laboratory notebook for this purpose. Use your lab notes to write the Procedure section of your lab report. You must attach a copy of your lab notes to the WC copy of your lab report. Keeping careful notes is an essential component of all scientific practice.

2.5 PROCEDURE

Problem Statement

You have been hired by an engineering firm to build and evaluate a robotics kit by building a specified robot design. You have been asked to test the robot design and the overall kit, and to make suggestions for design improvements.

1. Build a robot according to the lab handout provided by your TA.

Warning: Do not disassemble the robot when you finish. You will use it again in Lab 3.

2. 2. Create a program in RoboLab:
1. Start the RoboLab Program, and select Programmer.
2. In the Inventor section, double click on Inventor 4.

We will use RoboLab to perform three tests: a distance test, an angle of deviation test, and a rotation test. Before we start, take a few minutes to become familiar with the Tools palette. To access this palette, pull down the Window menu in the box that appears after you create a new program, and click Tools palette.

The Tools palette contains three tools you will use often:

1. File:Lab2 18.gifThe Arrow is used to select icons and wires, or to move them around.
2. File:Lab2 19.gifThe Spool is used to wire icons together.
3. File:Lab2 20.gifThe Text tool is used to insert new text boxes or to edit existing text boxes.

You will also need to become familiar with the Functions palette. Access this palette the same way you accessed the tools palette. From the Window menu, select Functions palette. There are several icons that you will use to write the programs for this lab. Each of the icons has several connections where wires can be attached (not all connections must be filled, as some have default settings). To find out what each of these connections does, hover the cursor over the icon and the software will describe the connection. To get a general description of the icon, pull down the Help menu and select Show Help. Click on the icon you would like explained and RoboLab will describe it.

Here are descriptions of some of the icons you will find on the Functions palette:

1. File:Lab2 22.gifEvery program must begin with a Green Light. The green light has only one connection.
2. File:Lab2 23.gifEvery program must end with a Red Light. Your program may contain more than one red light (e.g. program forks).
3. File:Lab2 24.gifThis is a Motor Forward icon. It has three connections: Begin, End, and Power Level.
4. File:Lab2 25.gifThis is a Motor Reverse icon. It has three connections: Begin, End, and Power Level.
5. File:Lab2 26.gifThe Port icon is found in the Modifier menu on the Functions palette. It indicates which output ports will be affected by the parent icon. The ports correspond with the letters and numbers on the RCX. The port icon has two connections, one to the parent icon, and the other to a second port modifier. Note that a port icon with a letter is for output and a port icon with a number is for input.
6. File:Lab2 27.gifThe Timer icon is found in the Wait For menu on the Functions palette. This icon delays the program for a set amount of time. The icon has three connections. Two of them indicate the program flow. The third connection is made to a numeric constant to set the number of seconds of the delay.
7. File:Lab2 28.gifThe Numeric Constant icon is found in the Modifier menu on the Functions palette. This icon is used as a modifier to other icons. In the case of motor control, this icon is attached to the power level connection and can be set to any integer between 0 and 7. In the case of a timer, this icon can be set to any value (including decimals).
8. File:Lab2 29.gifThe Stop icon has three connections. These connections indicate the program flow. Note that there is more than one Stop icon. Stop icons A, B, and C stop motors A, B, and C, respectively. Stop icon ABC stops all the motors, and the generic Stop icon pictured here can be customized with port modifiers.

Uploading the program to the RCX

Make sure the RCX is turned on, the USB Tower is plugged in, and the RCX is within range of the USB Tower.

When you have done this, pull down the Project menu, select COM Port, and choose USB1. Then click the checkmark button.

Note: Program and test your robot for each test specified. To do this, make a list of the tests in your lab notebook. Brainstorm what you want the robot to do in each test. Then, use your notes to write your program. Record the standard, average, accuracy, and precision. If your robot does not operate correctly, troubleshoot the problem. Your TA must initial your original data.

Distance Test

Note: Use the Metric system for this test

In this test, the robot will go forward a set distance in a specified time. You are to test the robot's accuracy and precision for this distance. Before testing begins the standard must be found. To find the standard, program the robot to go forward for 5 seconds and measure the distance it travels. Divide your result by 5, and then multiply by 4. This number is your standard. Once the standard has been obtained, the testing can begin.

Warning: Read the section on the Angle of Deviation Test before performing this test.

1. Upload a program that will set the robot to travel for 4 seconds
2. Measure the distance traveled.
3. Repeat this test 10 times.

Angle of Deviation Test

Note: This test can be performed at the same time as the Distance Test. Since the robot is expected totravel in a straight line, the standard is 360°.

In this test, the robot will move forward for four seconds and the angle of deviation will be recorded. The angle of deviation is the angle between a straight line and a line drawn from the starting point to where the robot finishes.

1. Use a protractor to draw a 0° line from the start point.
2. Mark the start point and place your robot there. Identify a reference point on the robot.
3. Run the Distance Test.
4. Make a mark at the point where the robot finished, and draw a line from the start point to this mark.
5. Measure the positive angle of deviation.
6. Repeat this procedure 10 times.

Rotation Test

In this test, the robot will rotate around an axis. Again, the standard must be obtained. By running the rotation test for 5 seconds and dividing the angle obtained by 5, you will determine how many degrees your robot rotates per second. This is the standard. With the standard in mind, project how many degrees your robot will rotate in 4 seconds.

1. Write the program in RoboLab to perform this test. Your TA will explain this process.
2. Upload your rotation program from the computer to the RCX.
3. Make a center point on a sheet of paper.
4. Run the program for 5 seconds.
5. Mark the reference point after rotation and measure the rotation angle.
6. Divide this value by 5 to determine the angle of rotation for 1 second.
7. Multiply the angle of rotation per second by 4 to obtain the standard.
8. Go back to the RoboLab program and change the time from 5 seconds to 4 seconds.
9. Upload the new program to the RCX.
10. Run the program 10 times. Make sure to measure the angle the robot rotated by each time.

You now have measurements for each test you have performed. You must analyze this data. Calculate the average, accuracy, and precision for each test. Compare your results to the standard in order to determine if your robot is accurate and precise. You must also calculate percent accuracy and percent precision. Use this formula to calculate percent accuracy:

In this equation, %Acc is the percent accuracy, P_S is the standard value, and A_P is the value you measured.

Examples:

1. If P_S was determined to be 5cm and A_P was found to be 7cm, then the percent accuracy (%Acc) is 60%. This test does not pass the 80% criterion.
2. If P_S was determined to be 5 feet and A_P was found to be 25 feet, then the result of the equation is -300%. Since a negative percentage has no meaning in engineering, it can be said that the product has a percent accuracy of zero. Any percent accuracy less than zero is considered to be equal to zero.
3. If P_S was determined to be 10 ft, and A_P was found to be 8 ft, then the result of the equation is exactly 80%, which is a passing result.

Use this formula to calculate % precision:

%Prec = 100e^-BP

In this equation, %Prec is the percent precision, B is the exponential decay factor, and P is the actual precision you measured. Each individual test requires the use of a different exponential decay factor (B):

Distance Test: B = 0.0972

Angle of Deviation Test: B = 0.0323

Rotation Test: B = 0.0093

Examples:

1. For the Distance Test, if the precision (P) was measured to be 0.5 cm, the percent precision (%Prec) is 95.3%. This robot passes the 80% criterion for this test.
2. For the Angle of Deviation Test, if the precision (P) was measured to be 10.25°, the percent precision (%Prec) is 71.8%. This robot does not pass the 80% criterion.

Tabulation of Results

To decide if the product is ready to manufacture, arrange your data in a table designed to calculate its precision and accuracy. Remember it must pass all the tests at a rate of at least 80%.

	Accuracy	%Acc	Pass/Fail	Precision	%Prec	Pass/Fail
Distance Test
Angle of Deviation Test
Rotational Test

Your lab work is now complete. Please clean up your workstation. Return all unused materials to your TA. Refer to section 2.3 Your Assignment for the instructions you need to prepare your lab report.


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