reverse engineering: an excellent opportunity for student team projects...

63rd Annual ASEE/EDGD Mid-Year Conference Proceedings, Berkeley, California – January 4-7, 2009

Reverse Engineering: An Excellent Opportunity for Student Team Projects in Engineering Graphics

R. Barr, T. Krueger, B. Wood, T. Aanstoos, and M. Pirnia

Department of Mechanical Engineering University of Texas, Austin, TX 78712

ABSTRACT - Our group at the University of Texas at

Austin has developed the current version of

Engineering Graphics based on the pedagogical triad

of: 1. engineering graphics fundamentals, 2. computer

graphics modeling fundamentals, and 3. computer

graphics applications. The engineering graphics

fundamentals part covers the traditional topics of

sketching, projection theory, orthographic drawing

layout, sectioning, and dimensioning. The computer

graphics modeling component teaches 2-D computer

sketching, 3-D solid modeling of parts, assembly

modeling, and the projection of an engineering drawing

directly from the 3-D model. The graphics application

part includes kinematics animation, finite element

analysis, and generation of a rapid prototype directly

from the 3-D data base. In order to motivate the

freshmen students, and to tie the three pedagogical

components into a unifying theme, we have instituted a

team project in the course based on the concept of

reverse engineering. Reverse engineering is the

dissection of a common mechanical assembly into its

individual parts, studying the geometry and design

function of each part, and then reconstructing the parts

into 3-D solid model data bases. The team activities in

the reverse engineering project have been carefully

scheduled by our group so that the teams systematically

accomplish various phases of the project over the

duration of the course, with intermediate due dates for

major tasks. The student teams select a mechanical

assembly, dissect it into individual parts, make

measurements and sketches, build 3-D solid models,

apply the solid models to various analyses, and make

rapid prototypes. The whole project is eventually

documented with sketches, 3-D model printouts,

analysis reports, prototypes, and final drawings. The

attached Appendix I outlines the various tasks for each

student team. This paper briefly discusses the current

version of our Engineering Graphics course at UT,

which has evolved significantly over the last two

decades, and then outlines in detail the reverse

engineering project using an example student team

project.

I. Introduction to Modern Engineering

Graphics Instruction

Within the past two decades, the teaching of 3-D solid

modeling has become the central theme in most

engineering graphics programs. This recent paradigm

shift to 3-D has been facilitated by the development and

low-cost availability of solid modeling software that

allows the student to focus on the “bigger-picture”

approach to engineering graphical communication. In

this Concurrent Engineering approach [Barr, et al.

1994], the 3-D geometric database serves as the hub for

all engineering communication activities (Figure 1).

These communications include engineering analysis,

simulation, assembly modeling, prototyping, and final

drafting and documentation.

In the Concurrent Engineering paradigm for

graphical communication, the student starts with a


sketch of an idea. The sketch can then be used to build

a solid model of the part. The solid model not only

serves as a visualization modality, but it also contains

the solid geometry data needed for engineering

analysis. Typical of these analyses are finite element

meshing, stress and thermal studies, mass properties

reports, and clearance-interference checking. After

analysis, the same geometric database can be used to

generate final communications like engineering

drawings, marketing brochures, and even rapid physical

prototypes that can be held in one’s hand. Indeed, an

entire Engineering Graphics curriculum could be

developed around three major aspects of instruction:

engineering graphics fundamentals, computer graphics

modeling fundamentals, and computer graphics

applications. This triad of modern engineering graphics

instruction is listed in Table 1.

Table 1: The Triad of Modern Engineering Graphics Instruction

A. Engineering Graphics Fundamentals Freehand Sketching Generation of Engineering Drawings Dimensioning Sectioning

B. Computer Graphics Modeling Fundamentals Creation of 2-D Computer Geometry Creation of 3-D Computer Models Building Computer Assembly Models

C. Computer Graphics Applications Digital Analysis Animation and Simulation Presentations Rapid Prototyping and Manufacturing Design Projects/Reverse Engineering Presentation Graphics

Figure 1: The Concurrent Engineering Design Paradigm.


II. What is Reverse Engineering?

Reverse engineering is a systematic methodology

for analyzing the design of an existing device or

system. It can be used as a means to study the design,

and is a prerequisite for re-designing the device or

system. Reverse engineering is used to gain

information about the functionality and sizes of existing

design components. It should be noted that, for student

projects, reverse engineering is a legitimate activity.

Determining “how something works” is not stealing

someone’s ideas, but rather is a beneficial way to

enhance the learning process of engineering design for

the novice.

Reverse engineering is sometimes called

mechanical dissection because it involves taking apart

or “dissecting” a mechanical system. Mechanical

dissection has been promoted for many years as an

acceptable activity for engineering students [Sheppard,

1992; Mickelson, et al. 1995; Lieu and Sorby, 2009].

When the student dissects the system, careful sketches

of the parts are made. These sketches convey the

geometry of the part, and show how the parts fit and

work together. This facilitates reassembling of the

whole system at a later date. The student needs to

carefully measure all of the features on each part during

the dissection process so that solid models can be

created. Since correct measurements are a significant

part of the reverse engineering process, the students

learn to use common measurement tools such as scales

and calipers.

III. Student Reverse Engineering Project

The reverse engineering project serves as a semester-

long, culminating experience for engineering graphics

students at the University of Texas at Austin.

Typically, these students are freshmen engineers who

have very little background in design or analysis.

Hence, the reverse engineering project does not serve as

a rigorous analytical challenge, but rather allows them

to apply all the tools that they have learned in the

graphics course to a real-world design problem. The

checklist in Appendix I outlines all the activities

expected for the student reverse engineering team

project. The following sections detail the chronological

events that occur during this reverse engineering

project.

III(a) Assigning Teams

At the start of the semester, the students are asked

to fill out a form that includes information like section

number, class level, gender, dormitory name, and other

scheduling data. They are also required to take the

Myers-Briggs Type Indicator (MBTI) on-line, and then

to indicate their four-letter MBTI personality rating on

the information form. These data are then used by the

instructor and teaching assistant (TA) to assign the

teams (nominally four students per team) in an

equitable fashion that balances team factors such as

gender, academic backgrounds, and MBTI types. The

team will then have an inaugural meeting in class to

exchange contact information, to pick a team leader,

and to then begin the project.

III(b) Selecting the Engineering Object to be Reverse

Engineered

The first team task is to pick the engineering object

to be reversed engineered. Some judgment is needed to

select an object that matches the task at hand. Usually,

the instructor will give some advice on what types of

objects work well and will interact with the teams so

that they can select a feasible object. Table 2 lists some

engineering objects that have been successfully used in

the past for this reverse engineering team project. For

purpose of illustrating the reverse engineering project, a

Trailer Winch student report has been selected for this

paper.


Table 2: Examples of Acceptable Reverse Engineering Objects

Baby Toy Differential Gear

Master Cylinder

Shower Massage Head

Bathroom Scale

Doorknob Assembly

Model Car Drive Train

Spinning Disk Launcher

Beer Faucet Flashlight Oil Pump Sprinkler

Head

Bicycle Pump Fuel Pump Oscillating

Sprinkler Stapler

Bolt Cutter Gate Valve Pencil Sharpener Toy Gun

Can Opener Hand Tool Pepper

Grinder Trailer Hitch

Corkscrew Hose Nozzle

Piston Assembly

Trailer Winch

Deadbolt Lock

Kitchen Timer Pipe Clamp Vise Grip

Desktop Clamp Lug Wrench Ratchet

Tie-Down

Water Faucet Valve

III(c) Charts and Diagrams

As part of the process to get started, the team

selects a product for the reverse engineering project and

then submits a proposal for approval of that product.

The students learn within the same week whether their

proposal was approved. The students have to quickly

plan how to utilize the remainder of the semester,

efficiently, to complete the project. To do this, students

prepare a Gantt chart for the team to follow. The

students first review the team activities that are to be

completed during the semester. Some of the

assignments have multiple activities. The due dates

specified in the course syllabus are the deadlines for

completion of each activity. Figure 2 shows the Gantt

chart that is used for the Trailer Winch design.

The initial step in the reverse engineering of a

product is to analyze the product in terms of inputs and

outputs. The exact analytical operation that converts an

input into an output is not important at this time. The

students are encouraged to not only look at the

operation of the product, but to expand the way they

consider the use of the product in terms of customer and

engineering specifications. A black box diagram is a

convenient technique to identify and organize inputs

and relate them to the corresponding outputs. Figure 3

shows the Black box diagram for the Trailer Winch. It

is recommended that the Black box diagram be

developed before the physical dissection takes place.

Subsystems of the product should be identified or

surmised before the physical dissection takes place.

The dissection process will allow for a better

understanding of the subsystems. Some subsystems

may have been misunderstood and other subsystems

may be found that could not be seen until the interior

was exposed. The dissection of the product can be

performed with simple tools. For those dissections that

require more than just screwdrivers and pliers, the

students may utilize the services of the ME

department’s machine shop. The students need to

document the dissection with notes, sketches, and

digital pictures. An exploded assembly of the product

will also be developed.

As the product is being dissected, the students

identify the subsystems first, then the individual

components are identified. Students assign a name and

number to each part of the product, and create a parts

list. From this information the subsystems and

individual parts can be organized into a fishbone

diagram. The fishbone diagram shows the relationship

between the subsystems and the parts. The head of the

fish is labeled the project name, Trailer Winch in this

case, and a spine is drawn. Ribs angle off of the spine

to represent each subsystem. Minor ribs come off of

each subsystem rib to represent every component part

of the subsystem. Figure 4 shows the Fishbone bone

diagram for the Trailer Winch.


Figure 2: Gantt Chart for Planning the Reverse Engineering Project.

Figure 3: Black Box Diagram Showing the Major Function of the Trailer Winch.

Figure 4: Fishbone Diagram for the Trailer Winch.


III(d) Sketching the Parts

Throughout the entire Reverse Engineering

process, much thought has been given to the possible

changes that could improve the efficiency and

durability of the whole system as well as individual

subsystems and parts. This starts with the students

taking apart the mechanical system, studying the

subsystems that allow it to function, and inspecting the

individual parts. Part of this process includes

measuring geometry and sketching isometric pictorials

of the individual parts, as well as sketching the parts

assembled together. The following preliminary

documents are then produced in order to better

understand and visualize each individual part as well as

the overall mechanical assembly:

1. Isometric sketches of all individual parts,

2. An exploded-assembly sketch that depicts all the

parts (see Figure 5), and

3. A parts list of all components of the assembly

(see Figure 6).

Figure 6: Parts List for the Assembly.

Figure 5: Exploded Assembly Sketch.


III(e) Building Solid Model Parts and Assemblies

The students will have a good understanding of the

parts after the exploded assembly sketches and the

individual isometric sketches of each part have been

made. The students generally have a team meeting

during the next lab session and request digital calipers

from the professor. The students utilize the calipers to

get the gross dimensions of the individual parts and the

size and location dimensions for the details. The

students sketch the dimensions onto the isometric

sketches until there is enough detail present to construct

an accurate computer model of each part. Figure 7

shows the computer model of the handle for the Trailer

Winch.

The students divide the dimensioned sketches

among the team members. Each team member is

responsible for modeling several component parts. The

students work together to model their individual parts

and make sure that the parts are oriented properly so an

assembly drawing can be made by compiling the part

files into a single assembly file. Care is taken to adhere

to the dimensions taken from the real parts to assure

accurately sized and constructed components. Properly

constructed parts will mate in the assembly as they

mate in the real product.

The course prepares the students to make intricate

computer models. The students have had concerted

practice in making difficult profiles into extruded and

revolved parts. The students are capable of making

accurate internal and external threads. Each part is

constructed and saved as a part (.SLDPRT) file. Each

part is also saved as a stereo-lithography (.STL) file to

be emailed to the teaching faculty member for later

printing.. Figure 8 shows the computer model of the

Trailer Winch pinion gear. Each part will be submitted

with the original sketch, the CAD model, the mass

properties report, and dimensioned orthographic views.

The students will use the individual part files to

reconstruct the product as an assembly. The parts can

be aligned and mated to resemble the finished product,

or they may be aligned but exploded. To construct the

assembly the students bring their files to one computer

and sequentially open them and insert them into an

assembly file. Parts are mated as necessary, with the

most common mate being cylindrical components and

the holes they fit into concentrically. Figure 9 shows

the Trailer Winch computer assembly model with all

the parts mated properly.

Figure 7: Computer Model of the Winch Handle.

Figure 8: Computer Model of the Winch Pinion Gear.


III(f) Mass Properties Report and Design Analysis

One objective of the project is to have the students

assess the overall suitability of a design from a

materials performance point of view. The starting point

for this assessment is the Mass Properties Report. After

a part model is complete, the students assign material

properties, including the material type and mass or

weight density, depending on system of units used.

Stock materials can be chosen from a library or custom

materials can be defined. The software then

automatically generates the Mass Properties Report,

which includes the calculated mass, volume, and

surface area of the part, as well as principal axes and

moments of inertia at various locations (center of mass,

output coordinate system). The mass properties report

can also be generated for an assembly, in which case

overall properties are given and the resulting density is

volume-averaged over all parts in the assembly. Figure

10 shows a Mass Properties report.

Some projects also include a finite element study

of key parts or on the assembly as a whole. In such

studies, student teams assign realistic boundary

constraints as well as fixed or distributed loads on the

part or assembly so as to mimic what the real assembly

might see in normal duty. Resulting stress, strain,

and/or deformation color 3-D plots are then studied to

reveal high stress areas. Alternately, design check

studies can also be run to show performance of the

assembly against a stated margin of safety criterion.

Students are asked to evaluate the efficiency of their

model, and to suggest ways in which the design of parts

could be modified to improve overall design efficiency

of their project (e. g. reduce peak stress concentrations,

reduce total mass, etc).

Figure 9: The Trailer Winch Computer Assembly Model.


III(g) Making Rapid 3-D Prototypes of the Object

Once the solid models are produced in a computer

modeling software package, the parts can be saved in

the stereolithography (.STL) format. There are various

ways to then produce physical models. Physical

models can be made using CAM, laser sintering, or by

means of a 3-D printer. In our program, we print the

students’ STL files on a Stratasys Dimension BST 3-D

printer. The students send their STL files to their

instructor, who load the printers and control what is

being printed. In some cases, more than one part can be

printed in a single run, so the instructor tries to optimize

the print output by nesting the files on a print board.

Figure 11 shows examples of 3-D parts from the Trailer

Winch assembly that were produced on our 3-D

Stratasys printer system. The footprint for printing a

part is about 8” x 8” x 8”.

III(h) Creating Dimensioned Orthographic Drawings

Another objective of the project is to familiarize

the student with the purpose and practice of engineering

orthographic drawings from solid models. The student

sets drawing preferences (e. g. ANSI or ISO style,

units, tolerance, precision) and converts the

part/assembly 3-D model into a set of orthographic

views in a 2-D drawing document. Then, the student

constructs consistent, complete, non-redundant

dimensions in the appropriate views following

conventional dimensioning practice. Shaded isometric,

auxiliary, and/or section views should be added to the

drawing for clarity if needed. To document assembly

properties, an overall annotated exploded assembly

drawing should be included, with a bill of materials

defining the individual parts of the assembly. Figure 12

shows the individual part drawing of the Crank Arm.

Mass properties of CRANK ARM (2) ( Part Configuration ‐ Default ) Output coordinate System: ‐‐ default ‐‐ Density = 0.2854 pounds per cubic inch Mass = 0.4896 pounds Volume = 1.7153 cubic inches Surface area = 18.9277 inches^2 Center of mass: ( inches ) X = ‐0.3781

Y = 0.1050 Z = ‐0.5578 Principal axes of inertia and principal moments of inertia: ( pounds * square inches ) Taken at the center of mass. Ix = (0.9603, 0.0001, 0.2789) Px = 0.1290 Iy = (0.2789, 0.0003, ‐0.9603) Py = 1.5414 Iz = (‐0.0002, 1.0000, 0.0003) Pz = 1.5879 Moments of inertia: ( pounds * square inches ) Taken at the center of mass and aligned with the output coordinate system. Lxx = 0.2388 Lxy = 0.0001 Lxz = 0.3782 Lyx = 0.0001 Lyy = 1.5879 Lyz = 0.0000 Lzx = 0.3782 Lzy = 0.0000 Lzz = 1.4316 Moments of inertia: ( pounds * square inches ) Taken at the output coordinate system. Ixx = 0.3966 Ixy = ‐0.0193 Ixz = 0.4815 Iyx = ‐0.0193 Iyy = 1.8102 Iyz = ‐0.0286 Izx = 0.4815 Izy = ‐0.0286 Izz = 1.5069

Figure 10: Mass Properties Report for the Crank Arm.

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III(i). Submission of the Final Team Report

At the end of the semester, the students compile all

of the interim reports along with their dimensioned

drawings and their redesign recommendations, and bind

them into a final report. The students are required to

find a suitable box that will hold the bound report and

the printed prototypes (Figure 13). We have found that

unless you have these items turned in together as a unit,

it is hard to keep all of the parts of the project in the

same place. The checklist in Appendix I helps the

students in this final submission requirement.

IV. Conclusions

Our current educational paradigm for Engineering

Design Graphics is a fulfillment of 20 years of work to

deliver a robust course based on the solid modeling

approach to engineering design. During this journey,

many obstacles were encountered. These obstacles

included incompatible software and hardware systems,

user-unfriendly analysis software that frequently

crashed, and high costs for prototyping equipment.

Nonetheless, these hurdles were overcome, and the

Concurrent Engineering Design paradigm (as originally

envisioned in earlier versions of Figure 1) is now fully

functional for graphics education [Krueger and Barr,

2007]. Even more noteworthy is that, while the

educational paradigm itself has been realized, achieving

it has now opened a rich opportunity for graphics

applications and projects for our engineering students

beyond the graphics fundamentals. In addition to

building solid models and assemblies, they can also

analyze the models, perform kinematic animations, and

print 3-D parts.

This paper illustrates a reverse engineering student

project that not only exercises the graphics and

modeling fundamentals, but also extends the student

activities to analysis and prototyping. In doing so, the

teaching environment for Engineering Graphics can

now be extended deeper into design practices that will

serve the students well in later engineering courses.

Figure 13: Submission of the Final Project Report.


V. References Barr, R., Juricic, D., and Krueger, T. (1994). The Role of Graphics and Modeling in the Concurrent Engineering Environment, Engineering Design Graphics Journal, 58(3):12-21. Krueger, T. and Barr, R. (2007). The Concurrent Engineering Design Paradigm is Now Fully Functional for Graphics Education, Engineering Design Graphics Journal, 71(1):22-28. Lieu, D.K. and Sorby, S. (2009). Visualization, Modeling, and Graphics for Engineering Design (Chapter 8: Design Analysis), Delmar Cenage Learning, New York.

Mickelson, S.K., Jenison, R.D., and Swanson, N. (1995). Teaching Engineering Design Through Product Dissection,” Proceedings of the 1995 ASEE Annual Conference, Anaheim. Sheppard, S.D. (1992). Dissection as a Learning Tool, Proceedings of the 1992 Frontiers in Education Conference, IEEE.

Appendix I

reverse engineering: an excellent opportunity for student team projects...

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