**[Learning Unit-A Robot Analysis and Construction (*ROBOCON*)
Project]{.underline}**

Joseph S. Miles & Siva Thangam

New Jersey Space Grant, Stevens Institute of Technology\
Castle Point on Hudson, Hoboken, NJ 07030

***ROBOCON*** is a unit of lessons guiding students and teachers through
the process of building science, mathematics, and engineering concepts
utilizing LEGO materials and computer programming skills in the
framework of ROBOLAB software. The first learning module focuses on
providing a basic grasp of robotics from a historical and applications
perspective. The following two modules provide a brief introduction to
Lego Robot concepts and a step-by-step approach on construction and
programming of a commercially available Lego robot for a non-gripper (or
non-prehensile) competition based activity.

**Learning Unit approach**

The learning unit will help students develop engineering and ROBOLAB
programming skills. The three modules structure will guide students
through the process of robot design, construction, testing, revision,
and competition.

**Using this approach**

Although designed for self-study, the learning units can be used by
teachers to engage all learners in critical thinking throughout the
course of each lesson, optimizing classroom time. Teachers may be
flexible during lessons, spending more or less time with each lesson to
adapt the schedule for students' needs.

**Audience**

The target audience is high school students with a science background.
Each lesson is presented in steps along with vocabulary to help students
understand and develop scientific and technical terms.

**Prerequisite skills**

Previous experience with design briefs may prepare students for the
sequence of each lesson. ROBOLAB requires students to construct Gantt
Charts and flowcharts; therefore, it is also suited for teamwork.

**Materials**

Lego **MINDSTORM** Group Robot Kit and ROBOLAB software

**[Learning Unit Module 1: Introduction to Robotics]{.underline}**

**Summary**: Robots can be used in any industry providing work and
services, and can be adapted easily to numerous job functions with
uncanny skill and unmatched endurance. Over the past decade, highly
selective applications for robots resulted in so-called \"islands\" of
automation. Development of more sophisticated automation concepts have
lead to increased usage of robots for tasks ranging from home automation
to industrial robotics as well as for a wide range of space
applications.

Industrial operations are usually best automated through the integra­tion
of robots with machines into what is often referred to as a \"work
cell". In these configurations, the robots, along with machines that
they serve, are treated as a \"unified system". This integration, which
causes the need for knowledge about robotics, has become very important
in flexible automation today.

The module in this learning unit provides an introduction and a
preliminary application to learning the technical as­pects of common
robots. These modules are written for a reader in high school to provide
a practical approach, with simple examples, questions, and a practical
application associated with automation. It is designed to provide the
reader with a sense of relevancy, especially for space applications. An
overview of robot classification, the operation of robot systems,
grippers and manipulators, sensors and instrumentation, and safety are
given in this module and followed by an activity based robot
construction project.

**Objectives**: This module will help familiarize the reader with the:

-   history of robots

-   technology of robots

-   economic and social issues associated with robots

-   present and future applications of robots

In current usage, automation and robots are two closely related
technologies connected with the use and control of production
operations. In the context of applications involving aerospace industry
and space systems, we can define automation as a technology that is
concerned with the use of mechanical, electrical/electronic, and
computer-based systems to control production processes and complex
tasks. Examples of this technology include transfer lines, mechanized
assembly machines, feedback control systems, numerically controlled
machine tools, robots and human-assisted manipulators. Industrial
automation can be classified as fixed automation, programmable
automation, and flexible automation.

Fixed automation is used when the volume of production is very high and
it is, therefore, appropriate to design specialized equipment to process
products at high rates and low cost. A good example of fixed automation
can be found in the aircraft and automobile industry, where highly
integrated transfer lines are used to perform machining operations. The
economics of fixed automation is such that the cost of the special
equipment can be divided over a large number of units produced, so that
the resulting unit costs can be lower relative to alternative methods of
production. For products with short life cycles, fixed automation is not
economical.

![](media/image1.wmf){width="3.4097222222222223in"
height="2.8993055555555554in"}Programmable automation is used when the
volume of production is relatively low and there is a variety of
products to be made. In this case, the production equipment is designed
to be adaptable to variations in a product configuration. This
adaptability feature is accomplished by operating the equipment under
the control of a \"program\" of instructions that has been prepared
especially for the given product.

The third category between fixed automation and programmable automation
is call- **Figure 1: Types of Industrial Automation**

ed flexible automation. This type

of automation is most suitable for the mid-volume production range.
Flexible automation possesses some of the features of both fixed and
programmable automation. Other terms used for flexible automation
include Flexible Manufacturing Systems (FMS) and Computer-Integrated
Manufacturing (CIM). Flexible automation typically consists of a series
of workstations that are interconnected by material handling and storage
equipment to process different product configurations at the same time
on the same manufacturing system. The three types of industrial
automation and manual labor are illustrated in Figure 1. The definition
of an industrial robot is provided by the Robotics Industries
Association (RIA) as follows: "An industrial robot is a reprogrammable,
multifunctional manipulator designed to move materials, parts, tools, or
special devices through variable programmed motions for the performance
of a variety of tasks".

**A historical perspective on the evolution of robots**:

The word robot was introduced in 1921 by the Czechoslovakian playwright
Karel Capek, in his play P. U. R. (Possum\'s Universal Robots), and is
derived from the Czech word robota, meaning \"forced labor.\" Although
Capek introduced the word robot to the world, the term robotics was
coined by Isaac Asimov in his science fiction story \"Runaround,\" first
published in the March 1942 issue of Astounding, where he portrayed
robots not in a negative manner but built with safety measures in mind
to assist human beings. Asimov established in his story the three
fundamental laws of robotics as follows:

1\. A robot may not injure a human being or, through inaction, allow a
human being to come to harm.

2\. A robot must obey the orders given it by human beings, except where
such orders would conflict with the first law.

3\. A robot must protect its own existence as long as such protection
does not conflict with the first and second laws.

In a broader sense, Capek\'s term robot meant a manipulator that was
activated directly by an operator or other mechanical or electrical
means. More generally, an industrial robot has been described by the
International Standards Organization (ISO) as follows: A machine formed
by a mechanism, including several degrees of freedom, often having the
appearance of one or several arms ending in a wrist capable of holding a
tool, a workpiece, or an inspection device. In particular, its control
unit must use a memorizing device and it may sometimes use sensing or
adaptation appliances to take into account environment and
circumstances. These multipurpose machines are generally designed to
carry out a repetitive function and can be adapted to other functions.

According to Miller (1987), robots were introduced to industry in the
early 1960s. Initially, robots sold for an average of \$25,000 with a
life expectancy of about eight years, cost approximately \$4.00 per hour
to operate, and had to compete for jobs with human workers earning
slightly more per hour than the robot hourly operating cost. Robots,
originally, were used in hazardous operations, such as handling toxic
and radioactive materials, and loading and unloading hot workpieces from
furnaces and handling them in foundries. Some rule-of-thumb applications
for robots are the four d's (dirty, dangerous, difficult, and demeaning,
but necessary tasks) and the four h's (hot, heavy, hazardous, and
humble).

By 1970, approximately two hundred robots were in use in U.S.
manufacturing facilities. The jobs to which robots were assigned during
that decade were primarily hazardous, strenuous, or repetitious and
required the robot to respond only to simple input commands. Control and
feedback technology at this evolutionary point remained relatively
basic, limiting robots to jobs requiring a lot of \"brawn\" but very
little \"brain.\" During the 1970s, with nationally declining
productivity and increasing labor rates, a significant increase in robot
usage began. Many improvements in controls increased the flexibility and
capabilities of robots. The first robots had been introduced in the
automotive industry. Ten years later, the same industry was contributing
most to the growth of robotics by its widespread acceptance. The average
prices of robots increased to approximately \$45,000, life expectancy
remained at about eight years, operating costs rose to approximately
\$5.00 per hour, and the average direct labor cost in the automotive
industry was twice the hourly operating cost of an industrial robot.

In 1980, there were approximately 4,000 robots in the United States and
26,000 robots worldwide. By the mid-1980s, there were approximately
17,000 industrial robots in the United States. The average price was
approximately \$60,000, life expectancy increased to fifteen years,
operating costs were in the range of \$5.50 per hour, and---again using
the automotive industry as a compar­ative example---labor rates were
escalated to over \$14.50 per hour.

By the end of 1997, RIA estimates, some 84,000 robots were in operation
in U.S. factories, ranking the United States second in the world to
Japan. According to Dave Lavery, manager of the robotic program at NASA,
there are some 650,000 robots at work today worldwide, and the average
price is approximately \$72,000, life expectancy over seventeen years,
and operating costs in the range of \$7.00 per hour as compared to
average wages of over \$24.00 in the automotive industry.

**Aerospace and Industrial Automation**

Over the past decade, highly selective applications for robots resulted
in the development of more sophisticated automation concepts, such as
Computer-Integrated Manufacturing (CIM) and Flexible Manufacturing
Systems (FMS). Users learned that industrial operations are usually best
automated through the integration of robots with machines, which are
referred to as a workcell. This integration, which causes the need for
knowledge about robots, has become very important in automated
manufacturing today.

![](media/image2.wmf){width="3.540277777777778in"
height="3.4340277777777777in"}

These factors and many others, such as reducing production cost,
improving quality, and increasing productivity, to name just a few, have
contributed to the growth of robots and will continue to impact their
evolution, both in pace and direction. Robot application areas as a
percentage of total robot population for the year 1996 are shown in
Figure 2.

Two reasons are given for selecting a robot to operate in a production
line: (1) to reduce labor costs, and (2) to perform repetitive work that
is boring, unpleasant, or hazardous for human beings.
Computer-controlled robots were commercialized in the early 1970s, with
the first robot controlled by a minicomputer appearing in 1974. The
primary purpose of the robot as a machine is controlled motion: If it
does not move, it is not a robot. All robotic design endeavor has
controlled, sensitive, and intelligent motion as its
![](media/image3.wmf){width="3.3652777777777776in"
height="3.56875in"}collective goal. The variety of uses for robots is
increasing, although their main use still seems to reside in automotive
manufacturing. A decade ago the projection was that robots would begin
to grow in popularity about the year 1998 after the general public ---
as well as engineers and scientists --- had learned to routinely accept
them in their work environments, and that no robot would act or feel
like a human being in the foreseeable future. These projections are
still true. The primary driving force behind the renewed interest in
robots will be lower unit cost, greater reliability, and simpler
operation.

![](media/image4.wmf){width="3.459722222222222in"
height="2.676388888888889in"}

They are available in a wide range of shapes, sizes, speeds, load
capacities, and other characteristics. Care must be taken to select a
robot to match the requirements of the tasks to be done. One way to
classify them is by their intended application. In general, there are
industrial, laboratory, mobile, military, security, service, hobby,
home, and personal robots. The general configuration and operating
parameters of an industrial robot with a gripper or a *prehensile* robot
is also shown in Figure 3.

Robots without grippers or *non-prehensile* robots are also of wide
usage in various aerospace and industrial applications: such as
excavation, construction, and transportation as well as in communication
systems. Such robots could range from autonomous vehicles for performing
simple tasks to sophisticated satellites with sensors and
data-acquisition systems that are cable of terrain mapping, scouting and
surveillance.

**[Learning Unit Module 2: Introduction to Lego Robots]{.underline}**

The LEGO Mind Storms Kit contains most of the parts required to
construct a robot that can compete in an arena. Each robot is guided by
a navigation beacon from the friendly side of the arena (its home
territory) to the enemy side of the arena (the opponent's territory) by
a beacon light. Once on the enemy side of the arena, the robot is
required to extinguish a target light before the competing robot does
likewise.

![](media/image5.jpeg){width="4.4527777777777775in" height="3.0in"}

Figure 4: LEGO Robot

Building the robot requires the expertise of a project team of four or
five students. Throughout the project, the project team is expected to
learn a wide variety of skills such as the overall mechanics of building
a robot, project planning and management, time management and teamwork.
The team is introduced to the Project Design and Development environment
where they experience typical design problems and employ problem-solving
techniques.

**[Background Concepts:]{.underline}**

-   Mechanics

-   Scalars and Vectors

-   Distance, Velocity, Acceleration

-   Particles and Rigid Bodies

**[Activity Summary:]{.underline}**

-   Project Planning and Team Integration

-   Building the Competition Arena

-   Constructing the Robot Vehicle

-   Testing and Calibrating the Robot

-   Running the Competition

-   Post Project Enhancement Activities

**[Background Concepts:]{.underline}**

[Introduction to Mechanics:]{.underline}

Mechanics is the branch of the physical science concerned with the state
of rest or motion of bodies (or robots) that are subjected to the action
of forces. It deals with the motion of point masses (very small objects)
and rigid bodies (large objects that can rotate as a whole, but cannot
change their shape). Many practical objects can be approximately
considered either point masses or rigid bodies in most situations. While
the study of mechanics can encompass many subject areas, the initial
study is usually split into two areas; statics and dynamics. Statics is
concerned with bodies that either are at rest or move with a constant
speed in a fixed direction, whereas dynamics deals with the accelerated
motion of bodies. Statics can therefore be considered as a special case
of dynamics where the acceleration is zero.

While it is not necessary to sit down and draw free body diagrams or
figure out the static coefficient of friction between the LEGO tires and
the game board, it is helpful to keep certain mechanical concepts in
mind when constructing a robot. If a robot\'s tires are spinning because
they do not grip the floor, then something must be done to increase the
friction between the tires and the floor. One solution is to glue a
rubber band around the circumference of the tire. That problem/solution
did not require an in-depth study of physics. Simply considering the
different possibilities can lead to more mechanically creative robots.

Typical problems addressed in classical mechanics are:

-   Determining the amount of energy and time that is needed to
    accelerate a small point mass object to a given speed.

-   Predicting the motion of a spacecraft approaching some planet, if
    its initial position and velocity at a distance from the planet are
    known. Since the distances are great, the spacecraft can be
    considered a point mass.

-   Finding the trajectory of an object thrown into the air with a
    specific initial velocity, with the object being considered a point
    mass.

-   Finding the frequency of oscillations in a system of point masses
    connected by springs.

Before we address how mechanics affects the motion of a robot, let's
define a few other terms. The motion of objects can be described
specifically by the following terms - distance, speed, displacement,
velocity, acceleration, momentum and friction. Furthermore, these
mathematical quantities, which are used to describe the motion of the
robot, can be divided into two categories. The quantity is either a
vector or a scalar. These two categories can be distinguished from one
another by their distinct definitions:

-   Scalars are quantities of distance, which are fully described by a
    magnitude alone.

-   Vectors are quantities of distance, which are fully described by
    both a magnitude and a direction.

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-   Speed is a measure of how quickly a body is moving. It is defined as
    the distance traveled per unit time. Speed is a scalar quantity.

-   Displacement is a measure of distance in a particular direction.
    Displacement is a vector quantity.

-   Velocity is the rate of change of displacement with respect to time.
    Velocity is a vector quantity.

-   Acceleration is the rate of change of velocity with respect to time.
    Acceleration is a vector quantity.

-   Momentum is defined as the product of an object's mass and its
    velocity. This is a very important quantity in mechanics. It arises
    in many problems particularly those involving collisions. Momentum
    is a vector quantity.

-   Time is the measure of a succession of events and is a basic
    quantity in dynamics. Time is not involved in the analysis of
    statics problems. Time is a scalar quantity.

-   Length is needed to locate the position of a point in space and
    describes the size of a physical system. Once a standard unit of
    length has been defined, it is possible to define distances and
    geometric properties of a body as a multiple of the unit of length.
    Length is a scalar quantity.

-   Volume is a measurement of the physical size of an object. It refers
    to how much space an object takes up. Volume is a scalar quantity.

-   Mass is a different measurement of the size of an object. The mass,
    measured in kilograms, depends only on the amount of matter forming
    the body. Mass is a scalar quantity.

-   Density is related to mass and volume. It is defined as the mass per
    unit volume. This means that an object that has a large mass but a
    small volume will have a large density. Density is a scalar
    quantity.

-   Forces are influences on a body or system, which, acting alone would
    cause the motion of that body or system to change. A system or body
    at rest and then subjected to a force will start to move. To work
    with forces we need to know the magnitude (size), direction and the
    point of application of the force. Forces are vector quantities.

-   Friction - The robots to be built are wheeled vehicles, and without
    friction, those wheels would just spin in place without moving the
    robot anywhere. In order to increase the friction between the wheels
    and the arena one might use wheels made of a different material or
    add a rubber band around the wheel\'s circumference. Friction is not
    desirable in all cases. When it comes to axles spinning inside of
    holes in beams or gears rubbing up against beams or even gears
    pushing against each other, friction can cause two identically
    constructed gear trains to behave differently. Friction can even
    render the whole assembly ineffective.

[Idealizations:]{.underline}

In mechanics, we look at real life situations and try to predict what
will happen. The problem with real life situations is that they are
often quite complicated. When studying problems in mechanics we often
make idealizations of real life situations that simplify the problem.
There are many commonly used idealizations that we will introduce in
later sheets. Here follows a list of some common idealizations that are
used in mechanics.

Particles are bodies, which can be treated as a point mass in a given
context. For example, when modeling the motion of the planets around the
Sun, the planets and Sun can be treated as particles. Much of basic
mechanics study is concerned with objects that can be treated as
particles.

Connected particles arise in problems where two objects are attached in
some way and both objects can be treated as particles. For example, two
masses, connected by a string, which passes over a pulley, could be
modeled as connected particles.

Rigid bodies can be considered as combinations of particles in which all
the particles remain at a fixed distance from one another both before
and after applying a force i.e. there is no bending or stretching. For
example, a brick can in most circumstances be thought of as a rigid
body. Many real life objects can be considered rigid bodies to a good
approximation.

[Rigid Body Dynamics]{.underline}

Many of the things we come in contact with on a daily basis are rigid
for all practical purposes. Buildings, chairs, and sidewalks all flex
and vibrate, but these effects do not strongly affect us. You might ask,
\"So what?\" The answer is that we need to endow robots with the
\"knowledge\" and skill to manipulate autonomously things so that we can
send them into dangerous environments, like a battlefield, the surface
of the moon, at the bottom of an ocean, into a nuclear power plant, and
repair things rather than humans. The first step to building robots with
this knowledge and skill is the development of human scientific
knowledge of how bodies interact with each other on a grand scale.

The field of rigid body dynamics is all about designing mathematical
models and algorithms to predict the motions of bodies and the contact
forces, including friction, that arise between them. The two most
exciting applications of rigid body dynamics are robotics, and computer
games. In robotics, the goal is to build a robot with the capability to
plan, and autonomously carry out dexterous manipulation tasks - like
extinguishing lights. Computer games contain physics engines to improve
realism - for example, dropping a stone into the gears of a machine
could cause jamming, thus stopping the knife blades from swinging across
your path, and allowing you to escape the collapsing building.

These two applications differ in a critical way. The physics engine is
used to answer the question, \"Given the input (motor torques, gravity,
etc.), tell me how the robot will move and what contact forces will
arise. This is the forward rigid body dynamics problem. For example, if
a robot moves its bumper arm in a specified way that causes it to hit a
box on a table, the solution to the forward problem will allow us to
predict where the box will come to rest, among other things. Once it is
possible to predict the consequences of robot actions, it becomes
possible to plan the activities of a robot to achieve a goal. Given the
current state of the robot and its environment, and a task specified as
a goal state, of the robot and its environment, planning is equivalent
to finding the set of robot actions that transform the robot and
environment to the goal state. Solving this problem is an inverse rigid
body dynamics problem, known to be extremely challenging and often
counter-intuitive (other reasons I like rigid body dynamics). For this
class exercise, we will design a robot to compete in an arena by
navigating from one side of the arena to another and extinguish target
lights on the opposite side of the arena.

[Robots:]{.underline}

Robot project based learning courses entail teaching, logistic, and
project management challenges, since they typically use hardware and
software labs that have student teams that operate with a high degree of
autonomy. These courses use the building of robots and robot software to
motivate students to learn various aspects of engineering such as
mechanics, dynamics, electronics and information technology. We believe
that the lessons learned during creation of a robot will scale to the
broader engineering community envisaged in an industrial engineering
environment.

Good design does not just happen; it is planned and executed in a
systematic way, with random "Eureka" thoughts interspersed as catalysts
to the creation of the product. While students need a high degree of
autonomy, they nevertheless need both technical and time management
guidance in order to pass through the necessary milestones on schedule.
Ideally, courses also need to provide "apprenticeship" experience for
the student so that they can "see" how good designers function. In this
course, students are given a broad ill-defined task, such as "Design a
robot to compete in an arena competition," which encourages them to
explore different strategies and concepts using analytical, simulation
and hands-on experiments within a bounded design space.  While this
course has a single goal, it is organized into a series of knowledge
checkpoints that must be attained in order to reach the final goal. 
Each milestone represents an integrated, but limited, piece of knowledge
that must be grasped and understood and then utilized to make a design
decision.  A key need in project courses is to keep the student on track
and take action when the student falls behind the planned trajectory.

**[Learning Unit Module 3: Lego Robot Project]{.underline}**

**[Activities:]{.underline}**

**[Project Planning and Team Dynamics]{.underline}**

![](media/image6.wmf){width="5.740277777777778in"
height="2.5409722222222224in"}Project planning is the process of
breaking down a project into specific tasks and defining a sequence in
which those tasks can or must be performed. It is not just scheduling.
Once the major tasks are identified, they can be further broken down
into sub-tasks and the task duration estimated in number of days.
Ultimately, date ranges can be assigned to each of the sub-tasks.
Finally, resources, identified by a particular student's name, can be
assigned to each of the sub tasks. Microsoft Project is a useful
planning and scheduling tool, which can be utilized for the planning and
management activity. Gantt Charts and work break down schedules can be
easily created. A sample Gantt Chart is shown below:

Team dynamics goes to the heart of a well functioning group. It is the
unseen forces that operate in a team between different people or groups
that can strongly influence how a team reacts, behaves or performs, with
the effects being very complex. Meanwhile a significant shift is taking
place in our modern organizations, which increases the emphasis on the
group or the team. Technology is the driving force behind this shift as
currant tasks have grown too difficult for individuals to tackle alone.
Harnessing the potential power of the team can have a dramatic effect on
productivity and job satisfaction leading to the group or team becoming
the core unit in many organizations. Research has shown that groups are
more effective in solving problems and learn more rapidly than
individuals.

Activity #1: Identify students to be part of groups playing to the
strength of the student's background. Assuring that every group has one
student with their strength in either the electrical, mechanical or
software disciplines, will put the project in the best possible position
to succeed.

Activity #2: Monitor the group's progress throughout the development
life cycle taking corrective action as required, especially when a task
falls behind a pre-determined task timeline.

**[The Robot Arena:]{.underline}**

Activity #1: Building the Robot Arena

![](media/image7.wmf){width="3.8256944444444443in"
height="2.848611111111111in"}

The robot competition should be held in a 4 ft. x 8 ft. arena made of
plywood. One--half of the arena is painted black and the other half of
the arena is painted white to differentiate friendly and enemy
territory. There should be 4-inch walls surrounding the perimeter. Home
and enemy territories are determined at the beginning of the competition
when one of the first actions of the robot is to use its floor light
sensor to read and store the home court color. There are also two types
of lights: one navigation light located 30 inches above the direct
center of the arena, and four target lights (two friendly target lights
and two enemy target lights) located along the perimeter wall of the
arena. A light sensor on the robot is angled upward to determine the
location of the navigation light, and another light sensor to determine
the location of the target lights. Placed within the arena are
"obstacles" comprised of 3-inch high wooden shapes, which the robots
have to navigate around. The bumpers of the robot, when coming in
contact with an obstacle, are used to make course corrections. Two
robots compete simultaneously in the arena. The robot to first locate,
approach, and 'knock out' the enemy's target lights without knocking out
their own target lights, is determined as the winning robot.

**[The Robot Vehicle:]{.underline}**

Activity #2 -- Building the Robot: This is by far the largest part of
the robot project and is broken down into sub-activities 2.1 to 2.5.

The material provided to each team of the class should be a LEGO Mind
Storms Logo Kit -- Part \# 9733 as shown below.

![](media/image8.png){width="5.839583333333334in"
height="3.953472222222222in"}

Figure 7: LEGO Mind Storms Kit

[The kit contains:]{.underline}

Lego blocks for construction of the robot body and chassis

2 motors for wheel control

1 NiCad battery to power the motors

2 switches for bumper control

[Supplemental materials include:]{.underline}

3 photo sensitive resistors to be used for beacon, target and floor
modules

1 LED to be used in a floor sensor module

A typical robot that might be built could look like the model shown
below:

![](media/image9.png){width="3.25625in" height="2.654861111111111in"}

Figure 8: A Sample Robot

[Overall Robot Win Strategy:]{.underline}

The overall robot competition strategy should be for the robot to locate
the navigation beacon and move toward it while continually checking the
floor color. Once it crosses into enemy territory, the robot would
detect each of its target lights in sequence while again continually
checking the floor color to make sure it did not cross back into
friendly territory. If one or both of the robot's bumpers are hit it
might need to back up, turn and reverse course slightly before
continuing. Once both target lights are extinguished, the robot's task
is completed. The competition should take 3 to 5 minutes.

[Robot Design and Assembly (Activity #2.1):]{.underline}

A low profile chassis seems to work best keeping the robot's center of
gravity close to the ground. Rather than introduce gears, it is
advisable to drive the robot directly off the motors to avoid any
complications. Two rear wheels and a front roller to glide on the
surface of the arena should suffice. The chassis is built from the LEGO
pieces provide in the kit. It should be constructed about one-half inch
above the surface to allow room for the floor sensor module to be placed
beneath it. A second level was built to hold the battery pack, and above
that the RCX programmable brick.

[Bumper Sensor Module (Activity #2.2):]{.underline}

The robot should be equipped with two bumpers, from the LEGO kit,
mounted across the front of the robot. No matter what angle from which
an obstacle was hit by the robot, one of the two switches behind the
bumpers would be triggered and the robot advised to take evasive action.
The two bumper arms should directly come in contact with each of the two
contact switches.

[Navigation Sensors (Activity #2.3):]{.underline}

A light sensor for the navigation light and a light sensor for the
target lights were placed on the robot. The light sensor for the
navigation light was placed on the front of the robot facing upwards at
about a 45-degree angle to try to detect a more direct light. Shielding
was used to isolate the different light angles in respect to the
navigation light and its associated light sensor. The target light
sensor should be placed directly in front of the robot, to be in the
line of sight with the target lights. Shielding can also be used to
improve its directionality.

[Floor Sensor Module (Activity #2.4):]{.underline}

Create a floor Sensor module to read the floor color (black or white) to
determine if the robot is in friendly (home) or enemy territory. Utilize
a high currant LED to illuminate the floor powered by the on board
battery pack. A light sensor can then determine the floor color by
converting light reflected back from the floor into voltage. Additional
circuitry may be needed to control the operation of the LED. A
transistor can act as a high currant switch, powering the LED directly
from the 5 volt on board voltage source, turning on and off according to
programming instructions. An electrical schematic of such a circuit can
be seen below:

![](media/image10.png){width="5.941666666666666in"
height="2.279166666666667in"}

Floor Sensor Module Parts:

-   Printed circuit board for mounting the floor sensor circuitry --
    approximately 2 in. x 2 in.

-   White LED

-   Transistor -- 2N2222

-   220 ohm -- ¼ watt resistor

-   20,000 ohm -- ¼ watt resistor

-   Assorted color wire about 8 -- 15 inches

-   Round light sensor shield

[Assembly (Activity #2.5)]{.underline}

The materials used in the construction of the robot came from the LEGO
Mind storm Kit #9793. One must keep in mind the potential for the robot
to break apart upon impact. Therefore it is necessary to use redundant
pieces to help reinforce and maintain the stability of the robot and to
increase its strength. Special care should be taken on the construction
of the bumpers since they will be designed to come in contact with
obstacles.

**[Integration Testing and Calibrating the Robot:]{.underline}**

The team should test each component of the system individually since it
is easier to find and repair errors in small sections of the robot and
the associated code before attempting to integrate the entire project.

Initially test the **motors** and their control routines. Make sure they
can spin forward, in reverse, turn left, turn right. Also, determine the
correct speed you would want to have them operate at, depending on the
direction they are going in. Take care to note if both motors go at the
same rate given the same speed commands.

Next, test the **bumpers**. Make sure when the right bumper is hit it
can be detected by the RCX brick and likewise for the left bumper.
Integrate evasive action to the motors depending on which bumper hit was
detected.

The integration of the **light sensors** is the next step. Initially
each light sensor needed to be calibrated to determine the voltage
measured. A voltage as low as 0.1 volts indicated the brightest light
while a voltage as high as 5 volts indicated no light. Since each sensor
is unique and then again, its placement is different, measurements need
to be taken for the beacon sensor as well as the navigation sensor and
action taken based on the measurements.

Finally, test the **floor sensor module**. Initially turn on the LED by
program control. Next, take a light sensor reading, and then turn off
the LED. After the light sensor reading taken, it can be determined if
the robot was on the white or the black portion of the arena.

**[Running the Competition in the Arena:]{.underline}**

The competition is conducted by double elimination of each team's robot
against every other team's robot. The team with the highest total score
wins the completion. The toss of a coin can determine the team that
selects the side of the arena on which they want to place their robot,
while the opposing team determines the orientation of the robot (facing
the beacon, away from the beacon, or slightly skewed). A stopwatch is
started and the robots are turned on while a limit is set (3 minutes is
usually sufficient). The first robot to reach the enemy side and
extinguish both lights wins the match. Some individual matches may
result in re-matches if both robots get stuck on obstacles, while other
matches may result in draws with each team receiving ½ point. A typical
scoring matrix might look as follows, for six hypothetical teams:

**Figure 10: Robot Competition Scoring Matrix**

**[Post Project Enhancement Activities:]{.underline}**

Experience with numerous versions of robot construction lead us to
propose that the more light sensors, the better control of navigation
that occurs. For example, if there were a front and rear beacon
detection sensor, it could be more easily determined when the robot is
moving forward or in reverse. Likewise, if there are two navigation
light sensors, the robot could determine if the target light is to the
right or to the left, and move accordingly. However, the introduction of
additional light sensors makes the logic of the robot more complicated
while giving better control of the vehicle.