EG1004 Lab 3: Reverse Engineering

1 OBJECTIVES

The experimental objective of this lab is to use the principles of reverse engineering to discover a robot’s function. To do this, you will take apart a robot, measure its gear and velocity ratios, and describe its gear trains.

We will learn the importance of reverse engineering and develop the ability to take a mechanism apart, analyze its parts, and then describe how they work.

2 OVERVIEW

Adapted from http://www.whatis.com.¹

Reverse engineering is taking apart an object to see how it works in order to improve or reproduce it. The practice, taken from older industries, is now used frequently in computer hardware and software development.

Automobile manufacturers often reverse engineer competitor's vehicles. They buy them, disassemble them, and examine the components and manufacturing elements of the vehicles in order to improve their own products. Sometimes, engineers will reverse engineer a part by producing a 3D image of the manufactured part when a blueprint isn't available. The part is measured, and a 3D wireframe image is generated and dimensioned. This image serves as a blueprint for manufacturing. Almost any part can be recreated by reverse engineering it this way.

Reverse engineering software involves reversing a program's machine code to obtain the original source code. This needs to be done when source code is lost. For example, when an older company is taken over by new ownership, or when an unfinished project is reassigned to a different team. Sometimes, this process is also undertaken as a way to improve the performance of a program, to fix a bug, or to find a virus. When the source code is obtained in this way for any of these reasons it is legal and necessary. Reverse engineering software in order to copy it constitutes a copyright violation and is illegal.

Hardware reverse engineering involves taking apart a device to see how it works. If a processor manufacturer wants to see how a competitor's processor works, the company can purchase the processor, disassemble it, and then make a new processor similar to it. In some countries, this process is illegal. Hardware reverse engineering is quite expensive and requires an expert in the field.

When you begin the process of reverse engineering your robot, identifying the gear trains and the individual gears used in the original design is critical to your understanding of the robot's operation.

There are two types of gear trains: simple and compound. A simple gear train has its gears arranged in a line (see Figure 1).

Figure 1: Simple gear train

Compound gear trains use axles to connect the component gears (see Figure 2).

Figure 2: Compound gear train

Gear trains have measurable characteristics known as gear ratio and gear velocity. These characteristics are inversely proportional. Gear ratio equals output over input, while velocity ratio equals input over output. To determine input and output values, measure the gear’s radius.

For example, to compute the gear ratio of the gear trains above, use these formulas:


Simple gear train	Compound gear train

For example, to compute the velocity ratio of the gear trains above, use these formulas:


Simple gear train	Compound gear train

It is important to note that the input is the source of rotation in a system, like a motor, and the output is the final gear of rotation in a system, like a wheel.

Figure 3: Types of Gears


Figure 3a: Rack gear. Its purpose is to change the direction of rotation perpendicularly, and to change the motion from.	Figure 3b: Crown gear. Its purpose is to change the direction of rotation perpendicularly rotation to linear translation.

Figure 3c: Spur gear. Its purpose is to transmit torque through the gear train.	Figure 3d: Worm gear. Its purpose is to change the direction of rotation perpendicularly

Figure 3e: Idler gear. Its purpose is to transfer force while not affecting the gear or velocity ratios.	Figure 3f: Pulley gear. Its purpose is to transmit rotation from one point to one or more other points.

Figures 3a-d courtesy of www.howthingswork.com
Figure 3f courtesy of Honda Motor Company, Inc.

Gears are used in product design to increase or decrease speed and torque. Torque is a turning force. Gear trains are designed to transmit a turning force, or torque, from one point to another. The force, F, produced by any mass is equal to the product of mass, m, and acceleration, a:

F = m *a

The torque produced by that force is equal to the product of force, F, and distance, D, from the rotational axis:

T = F * D

Your objective as you reverse engineer your robot is to understand how it works and to calculate the gear and velocity ratios for its gear trains. Remember, engineers reverse engineer products to reproduce or improve them. As you disassemble your device, consider how you would improve your robot's design.

3 YOUR ASSIGNMENT

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

The following discussion points must be addressed in the appropriate section of your lab report and in your PowerPoint presentation:

What is the robot’s function?
Describe how the components fit together and how the device was constructed.
Describe how you calculated the gear and velocity ratios, and discuss their importance in the overall robot design.
Isthe design adequate for its function?
Suggest design improvements.

4 MATERIALS AND EQUIPMENT

Previously Built Robot
Graph Paper
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 hand in a copy of your lab notes to the WC. Keeping careful notes is an essential component of all scientific practice.

5 PROCEDURE

Visually assess the robot's design. Consider how it works. Form a hypothesis based on your observations.
Sketch the front, top, and most detailed side of the robot. Be sure to include dimensions in your sketch.
Also sketch the most detailed view of the gear train.
Before disassembling your robot, ask your TA to take a picture of it.
Disassemble the robot. Analyze its inner workings and sketch the gear train(s). Note: All sketches in EG must be done in pencil.
Label major components and describe their functions.
Compute the velocity and gear ratios.
Have all sketches and original data signed by your TA.

Your lab work is now complete. Please clean up your workstation. Return all unused materials to your TA. Refer to Section 3 "Your Assignment" for the instructions you need to prepare your lab report.

Footnotes

¹ What Is website. TechTarget Network. Retrieved July 29th, 2003. http://whatis.techtarget.com/definition/0,sid9_gci507015,00.html

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