©2015 Heather Kloet, Monica Limback, Kaitlyn Weinstein, and Calvin College
Executive Summary
Finding lost objects in marshes or shallow black-water can be a frustrating, unpleasant, and time
consuming task for humans. Sometimes, it can even be dangerous. In battlefields and war-torn areas,
improvised explosive devices (IEDs) and land mines may be placed underwater or in swamps and
marshes. An amphibious robot would alleviate the stress or danger of locating metallic objects by using a
combination of metal detection, GPS, and cameras to give a more defined location of the object. Using a
wirelessly controlled robot allows a person to look for objects from the comfort of a boat or on shore. In
this paper, the design and prototype of an amphibious robot for this purpose is determined. The robot
consists of a central body, tracks for locomotion, and electronics for communication. The body uses two
motors for driving the tracks in forward and reverse directions, a front mounted camera to aid in steering,
and a dry box that houses a Raspberry Pi, battery, and sensors. The belt is to be driven by a pressure
wheel and have long aluminum paddles that will provide traction on land and act as paddles in water. The
estimated cost to prototype the robot is $500. The robot will weigh no more than 50 pounds and the
structure will be a maximum of 3 feet in diameter. This will allow the robot to be easily transported. The
robot will be able to travel and communicate a distance of a quarter mile on land. The robot will
communicate over a Wi-Fi network. Video feed from the robot and GPS coordinates will allow the user to
determine the location of the robot and maneuver it using controls on a laptop or phone application.
Table of Contents
1
2
Introduction ........................................................................................................................................... 1
1.1
Calvin College and the Engineering Department.......................................................................... 1
1.2
Calvin College Senior Design Project .......................................................................................... 1
1.3
Project Specification ..................................................................................................................... 1
1.4
Team Member Bios....................................................................................................................... 1
1.4.1
Heather Kloet ........................................................................................................................ 2
1.4.2
Monica Limback ................................................................................................................... 2
1.4.3
Kaitlyn Weinstein ................................................................................................................ 2
Project Management ............................................................................................................................. 3
2.1
2.1.1
Heather Kloet ........................................................................................................................ 3
2.1.2
Monica Limback ................................................................................................................... 3
2.1.3
Kaitlyn Weinstein ................................................................................................................. 3
2.1.4
Other Management Tasks ..................................................................................................... 3
2.2
Schedule ................................................................................................................................ 4
2.2.2
Budget ................................................................................................................................... 5
Project Milestones ......................................................................................................................... 5
2.3.1
Fall Semester Milestones ...................................................................................................... 6
2.3.2
Spring Semester Milestones .................................................................................................. 7
Project Clarification .............................................................................................................................. 9
3.1
Customer ....................................................................................................................................... 9
3.2
Requirements and Prototype Outcomes ........................................................................................ 9
3.2.1
Performance Requirements ................................................................................................... 9
3.2.2
Physical Requirements ........................................................................................................ 10
3.2.3
Electronic Requirements ..................................................................................................... 10
3.2.4
Interface Requirements ....................................................................................................... 11
3.2.5
Cost Requirements .............................................................................................................. 11
3.3
4
Methodology ................................................................................................................................. 4
2.2.1
2.3
3
Team Member Responsibilities .................................................................................................... 3
Deliverables ................................................................................................................................ 12
3.3.1
Fall Semester Deliverables.................................................................................................. 12
3.3.2
Spring Semester Deliverables ............................................................................................. 12
Design ................................................................................................................................................. 13
ii
4.1
Design Criteria ............................................................................................................................ 13
4.1.1
Critical Considerations ........................................................................................................ 13
4.1.2
Design Norms ..................................................................................................................... 14
4.2
Design Alternatives and Decisions ............................................................................................. 14
4.2.1
Propulsion System............................................................................................................... 14
4.2.2
Motors ................................................................................................................................. 19
4.2.3
Materials ............................................................................................................................. 20
4.2.4
Motor Controls .................................................................................................................... 21
4.2.5
On-board Computer ............................................................................................................ 22
4.2.6
Wireless Communication .................................................................................................... 24
4.2.7
User Interface ...................................................................................................................... 25
4.2.8
Metal Detector..................................................................................................................... 26
4.2.9
GPS ..................................................................................................................................... 27
4.2.10
Webcam .............................................................................................................................. 28
4.3
Design Specifications.................................................................................................................. 30
4.3.1
Tracks .................................................................................................................................. 31
4.3.2
Body .................................................................................................................................... 36
4.3.3
Motor and Drive System ..................................................................................................... 40
4.3.4
Motor Controls .................................................................................................................... 41
4.3.5
User Interface ...................................................................................................................... 42
4.3.6
Metal Detector..................................................................................................................... 43
4.4
5
Prototype ..................................................................................................................................... 43
4.4.1
Track System ...................................................................................................................... 44
4.4.2
Metal Detector..................................................................................................................... 46
4.4.3
User Interface ...................................................................................................................... 46
4.4.4
Propulsion ........................................................................................................................... 47
4.4.5
Motor Control ..................................................................................................................... 47
4.4.6
Design Norm Analysis ........................................................................................................ 48
4.4.7
Amphibot Final Test Plan ................................................................................................... 48
Business Plan ...................................................................................................................................... 52
5.1
Marketing .................................................................................................................................... 52
5.1.1
Competition......................................................................................................................... 52
5.1.2
Differentiation ..................................................................................................................... 52
iii
5.1.3
5.2
6
Distribution ......................................................................................................................... 52
Final Product Cost Estimate........................................................................................................ 52
Conclusion .......................................................................................................................................... 55
6.1
Future Plans ................................................................................................................................ 55
7
Final Summary .................................................................................................................................... 56
8
Acknowledgements ............................................................................................................................. 57
Appendix ..................................................................................................................................................... 58
References ................................................................................................................................................... 66
iv
Table of Figures
Figure 1: Team 11 Monica Limback, Kaitlyn Weinstein, Heather Kloet ..................................................... 2
Figure 2: Screw Propulsion ......................................................................................................................... 15
Figure 3: Foldable Paddles.......................................................................................................................... 15
Figure 4: Foam Treads ................................................................................................................................ 16
Figure 5: Paddled Wheels ........................................................................................................................... 16
Figure 6: Propeller ...................................................................................................................................... 17
Figure 7: NASA Crawler ............................................................................................................................ 17
Figure 8: Duck Boat .................................................................................................................................... 18
Figure 9: Tracks .......................................................................................................................................... 18
Figure 10: Preliminary Track Conceptual Drawing .................................................................................... 19
Figure 11: Liquid Foam .............................................................................................................................. 21
Figure 12: Used Tires.................................................................................................................................. 21
Figure 13: Joystick ...................................................................................................................................... 22
Figure 14: The Rapsberry Pi B+ ................................................................................................................. 23
Figure 15: The BeagleBone Black .............................................................................................................. 24
Figure 16: Wifi............................................................................................................................................ 24
Figure 17: Bluetooth ................................................................................................................................... 25
Figure 18: Zigbee ........................................................................................................................................ 25
Figure 19: Visual Studio ............................................................................................................................. 26
Figure 20: Surf PI 1.2 Metal Detector......................................................................................................... 27
Figure 21: Adafruit Ultimate GPS .............................................................................................................. 28
Figure 22: Creative Webcam ...................................................................................................................... 29
Figure 23: GoPro Hero................................................................................................................................ 30
Figure 24: Model of Final Design ............................................................................................................... 30
Figure 25: Model of Single Paddle ............................................................................................................. 31
Figure 26: Diagram of Water Force ............................................................................................................ 32
Figure 27: Diagram of Water Drag ............................................................................................................. 32
Figure 28: Optimization Curve of Number of Paddles ............................................................................... 33
Figure 29: Optimization Curve of Length of Paddles ................................................................................. 33
Figure 30: Interior Track Frame.................................................................................................................. 34
Figure 31: Exterior Track Support .............................................................................................................. 35
Figure 32: Detail of Bolt through Track ..................................................................................................... 36
Figure 33: Motor Mounting ........................................................................................................................ 37
Figure 34: Body Casing .............................................................................................................................. 37
Figure 35: Buoyancy Calculations .............................................................................................................. 38
Figure 36: Casing Dimensions .................................................................................................................... 39
Figure 37: Dry Box ..................................................................................................................................... 39
Figure 38: Drive System Diagram .............................................................................................................. 41
Figure 39: Relay Schematic ........................................................................................................................ 41
Figure 40: Electrical Block Diagram .......................................................................................................... 42
Figure 41: Metal Detector Schematic ......................................................................................................... 43
Figure 42: Preliminary Prototype................................................................................................................ 44
Figure 43: Final Prototype .......................................................................................................................... 44
v
Figure 44: Tread Guide Design................................................................................................................... 45
Figure 45: Prototype Track ......................................................................................................................... 45
Figure 46: Prototype Metal Detector .......................................................................................................... 46
Figure 47: User Interface ............................................................................................................................ 47
Figure 48: Paddle Drawings........................................................................................................................ 62
Figure 49: Paddle Pattern ............................................................................................................................ 63
Figure 50: Hole and Member Placement .................................................................................................... 64
Figure 51: Track Structure Inner Frame ..................................................................................................... 64
Figure 52: Track Structure Outer Casing .................................................................................................... 65
Table of Tables
Table 1: Individual Hours Breakdown - Fall ................................................................................................ 4
Table 2: Individual Hours Breakdown - Spring ............................................................................................ 4
Table 3: Cost of Parts.................................................................................................................................... 5
Table 4: Motor Electrical Performance ....................................................................................................... 40
Table 5: Parts' Cost Estimate ...................................................................................................................... 53
Table 6: Break Even Analysis..................................................................................................................... 54
vi
1
Introduction
Team Amphibot consists of Heather Kloet, Monica Limback, and Kaitlyn Weinstein. The team has
created a prototype amphibious robot capable of driving on land and propelling through water in order to
find small metallic objects in marshes, swamps, and shallow black-water. This project meets requirements
for Calvin College Department of Engineering’s Senior Design Project.
1.1
Calvin College and the Engineering Department
Calvin College is a well-renowned college with academic excellence. It is a liberal arts college based in
the Christian Reformed faith. The engineering program is one of Calvin’s top programs for its
combination of liberal arts and technical aspects. Its courses enable students to learn both hands-on and
theoretical methods. Calvin works to prepare students for real-world situations and enables them to apply
a Christian perspective.
1.2
Calvin College Senior Design Project
The Senior Design Project is the two-semester capstone of Calvin’s Engineering program. The goal of the
senior design project is to test and develop engineering students’ understanding of the process of
engineering design, the ability to work in a team, and basic engineering skills learned over the past three
years.
1.3
Project Specification
This senior design project involved designing and building an amphibious, remote-controlled vehicle. The
vehicle, named Amphibot, is equipped with a number of sensory devices, including GPS, a metal
detector, and webcam, for the purpose of finding small metal objects lost in black water, mud, and
marshes. Amphibot could be useful for military application as a remote detector for improvised explosive
devices (IEDs) and land mines. Whether IEDs in rivers threatening soldiers in war zones, or land mines
forgotten in swamps after wars are over, Amphibot’s remote capabilities and all-terrain movement would
help provide safe detection procedures. Amphibot is also designed to be useful for fishermen, boating
enthusiasts, and other water hobbyists who might need to find items lost in shallow water, as well as
treasure hunting enthusiasts.
1.4
Team Member Bios
The team consists of Heather Kloet, Monica Limback, and Kaitlyn Weinstein, pictured below in Figure 1.
1
Figure 1: Team 11 Monica Limback, Kaitlyn Weinstein, Heather Kloet
1.4.1
Heather Kloet
Heather is an electrical and computer engineering student. She was born and raised in
Grand Rapids, MI. In her spare time, she volunteers at Frederik Meijer Gardens Gift
Shop. After graduation, she will be working as a Field Service Engineer at Burke E.
Porter Machinery Company, located in Grand Rapids, MI. She enjoys reading,
shopping, and listening to music. She is excited to work on the electrical and software
components of the project and help further develop underwater exploration.
1.4.2
Monica Limback
Monica is an electrical and computer engineering student. As the daughter of an Air
Force officer, she moved a lot throughout her childhood, attending three different
high schools and living in 7 different states. She is a cadet in the Army ROTC
program of Western Michigan University, and will be commissioning as an Active
Duty Signal Corps officer in May 2015. In February 2015 she married her best
friend, Cody Limback, and they will be moving to Korea together in October. She
enjoys reading, writing, and playing video games with her husband. She is excited to
use her knowledge of electrical engineering to build a robot that has both civilian and
military possible applications.
1.4.3
Kaitlyn Weinstein
Kaitlyn is a mechanical engineering student. She grew up on a farm in Leslie,
Michigan, which sparked her interest in mechanical engineering. She will be working
at K-Line Industries as a Mechanical Design Engineer. In her spare time she enjoys
reading, drawing, and making stuff. She also has a minor in architecture, which she is
hoping to use to build her dream home. She is excited to work with the structure and
propulsion of the robot on land and in water.
2
2
Project Management
2.1
Team Member Responsibilities
The team is made of a total of three members. Each team member has a set of responsibilities for which
she is ultimately responsible.
2.1.1
Heather Kloet
Heather is primarily responsible for the software and motor controls of Amphibot. She has overseen
communicating with Amphibot wirelessly, writing software to integrate the sensors and motor system
into a graphical user interface. She will also work with Kaitlyn to connect the motors to the electronic
systems to power Amphibot.
2.1.2
Monica Limback
Monica’s primary responsibility is for the hardware and sensors Amphibot will use to find objects and
track its location. She assisted with the purchase and implementation of the sensors. The most critical of
these sensors, the metal detector, has been Monica’s most time-consuming task throughout the semester.
2.1.3
Kaitlyn Weinstein
Kaitlyn is responsible for all aspects of Amphibot’s mechanical body and movement. She determined the
design of Amphibot’s body, chose and implemented necessary motors, and designed and built the
propulsion system. She was in charge of determining material needs and costs, as well as size, weight and
other physical limitations. Kaitlyn worked with Heather and Monica to implement the electrical to
mechanical connections and controls.
2.1.4
Other Management Tasks
As part of the team’s success, other management tasks were assigned to team members to ensure smooth
operation and allow the team to meet deadlines.
2.1.4.1
Team Webmaster
Heather served as the team Webmaster. The senior design team was tasked with developing a team
webpage that details the progress of the project, shares documentation, and serves to promote Calvin
College and the Senior Design project. Heather agreed to take on the task because of her familiarity with
Dreamweaver software and prior work in creating websites.
2.1.4.2
Weekly Project Leader
The team assigned a project leader, who was responsible for ensuring weekly goals were met, providing
weekly summaries to the team’s faculty advisor, and overseeing the work schedule for the week. To better
balance that responsibility, the leadership position is rotated on a weekly basis between all members of
the team. The weekly leader provided structure to the team, and reduced confusion over goals and tasks. It
also served to balance the load of day to day work evenly amongst the team members. This also
facilitated thorough communication, as each new team leader was responsible for understanding the entire
team’s progress that week, and ensured the team members were communicating their personal updates
and statuses.
3
2.2
Methodology
In order to maintain good relationships, effectively utilize time, and produce a quality product, the team
developed a method of weekly, all-team meetings combined with individual time and work. Time spent
on the project was tracked by an Excel sheet. Communication and document sharing was accomplished
via a combination of verbal conversations, email, Google Drive folders, Microsoft OneDrive, and the
Calvin College network shared drive.
2.2.1
Schedule
The team scheduled regular meetings throughout the year. This time was spent on updating one another
on individual progress, as well as to set short-term goals and discuss overall progress. In addition to this
group time, each team member was responsible for spending time on the project each week, and for
logging this time in a scheduling table.
2.2.1.1
Fall Semester Work Breakdown Schedule
During the fall semester, each team member was asked to spend at least 30 minutes a work day putting
effort into the project in order to see it through to completion. Individual times net at a total of 139 total
hours of individual work, broken down in Table 1.
Table 1: Individual Hours Breakdown - Fall
Name Number of Hours Worked
Heather
48
Monica
44
Kaitlyn
47
Total:
139
The team spent two hours per week in regularly scheduled team meeting times, as well as spending extra
time at key points along the project, particularly when deliverables were due. This time nets to 24
regularly scheduled hours over the course of the twelve weeks of the semester. Additional time spent
working together summed to a total of 50 hours, which together makes a total of 74 hours of combined
effort. With the three team members working during this time, the individual work hours amount to 225
hours. Overall, the project took 364 hours of labor during the fall semester.
2.2.1.2
Spring Semester Work Breakdown Schedule
During the spring semester, the team continued to institute a policy of semiweekly team meetings.
However, because the spring semester focused primarily on building, group work time was spent mostly
on individual tasks and duties. The combined work time allowed any projects that required two or more
members of the team to have easy access to one another’s help, input, and advice. The team collectively
spent a total of 502 hours on the project, broken down by team member as shown in the table below.
Table 2: Individual Hours Breakdown - Spring
Name Number of Hours Worked
Heather
191
Monica
116
Kaitlyn
195
Total:
502
4
2.2.2
Budget
In order to take charge of the budget, each desired component, sensor, tool, or piece of material for
Amphibot was researched for the best deal. Once a specific item was chosen, the team member who
requested it entered the item into a spreadsheet with the item’s cost. As a team, these components are
discussed and approved depending on their cost and level of necessity. Because many of the parts needed
for Amphibot can be quite expensive, the team was careful to find cost effective components to help stay
within budget. The final purchasing cost list is shown below in Table 3. In addition to the final subtotal of
$472.12, additional money was spent on taxes and shipping costs.
Table 3: Cost of Parts
Date
9/2/14
11/20/14
11/20/14
11/20/14
11/20/14
11/20/14
12/8/14
12/8/14
12/8/14
12/8/14
12/8/14
12/8/14
2/9/15
2/9/15
2/9/15
2/9/15
2/9/15
2/9/15
2/9/15
3/5/15
3/25/15
3/25/15
4/11/15
4/10/15
4/11/15
4/12/15
4/18/15
4/20/15
4/20/15
4/28/2015
5/9/2015
2.3
Description
Beginning Balance
Temp-Humidity Sensor
Raspberry Pi
Adafruit GPS Breakout
USB to TTL Cable
Creative Live! Cam Webcam
Adafruit Cobbler Breakout
Breadboard
SMA to UFL Adpater Cable
GPS Antenna
MicroSD card
Brushless Motor
Metal Detector Kit
DSD 18650 CR123A Charger Black
TrustFire Protected 18650 Lithium Battery
3-Slot 3.7V 18650 Batter Holder Case Box
RCA AH100R 100ft 24-Gauge Speaker wire
MTM Survivor Dry Box with O-ring Seal, Large
Kootek Raspberry Pi Wifi Dongle Adaptor
Wheels (8)
Urethane Foam
Plastic Roller Chain Sprockets
Plastic Wheels (2)
Brushless Motor
Roller Chain
Lithium Polymer Battery
Relay DPDT
Relay DPDT
Plastic Roller Chain Sprockets
1/2 bolts 5 in long (8)
Caulk and Waterproof Foam
Debit Credit
500.00
9.95
35.00
39.95
9.95
17.99
6.50
5.00
3.95
12.95
11.99
24.09
44.14
7.89
16.42
2.36
7.92
14.70
7.49
58.43
22.50
11.72
7.30
24.09
14.95
21.98
3.00
3.00
18.50
12.97
13.43
Balance
$500.00
$490.05
$455.05
$415.10
$405.15
$387.16
$398.65
$393.65
$389.70
$376.75
$364.76
$340.67
$296.53
$288.64
$272.22
$269.86
$261.94
$247.24
$239.75
$181.32
$158.82
$147.10
$139.80
$115.71
$100.76
$78.78
$75.78
$72.78
$54.28
$41.31
$27.88
Project Milestones
The team used a list of specific tasks throughout the year as milestones to judge completed progress and
future goals. The milestones completed in the spring semester, as well as key milestones from the fall, are
laid out in this section.
5
2.3.1
Fall Semester Milestones
The fall semester milestones consisted predominantly of planning the project and determining feasibility.
Those milestones which most contributed to the project’s success, as well as to the overall schedule, are
described below.
2.3.1.1
Form the Team and Select Project
The first step in the senior design project was finalizing the teams. Monica, Heather, and Kaitlyn
developed their team based on similar work ethics and personalities, as well as mutual desires for an
interesting, multi-discipline project. The project was then chosen by consensus based on interest and
perceived feasibility. The team was fascinated by robotics and the implementation of electronics into a
mechanical system. An amphibious robot was chosen for its unique challenge and level of interest.
2.3.1.2
Create a Work Breakdown Schedule
The team created a schedule of work based on deliverable due dates, expected difficulty of each task, and
additional considerations such as school breaks and test schedules.
2.3.1.3
Meet with Industrial Consultant and Mentor
Team 11 was assigned an industrial consultant who acted as a guide and mentor in helping determine key
tasks, points of research, and feasibility. During the meetings with industrial consultant, Eric Walstra of
Gentex Corporation, the team was able to form a more narrowed scope with a specific set of
requirements, as well as develop a timeline and research needs.
Professor Renard Tubergen of the Mechanical concentration at Calvin College was recommended to
Team 11 due to his knowledge of underwater operations as a hobbyist diver. In meeting with Professor
Tubergen, the team was able to narrow the scope of its project even further, allowing for a project feasible
for senior design.
2.3.1.4
Provide Weekly Status Reports to Faculty Consultant
Mark Michmerhuizen of the Electrical and Computer concentration served as faculty consultant and
guided the team through the senior design project. In order to better help judge team progress and provide
advice and recommendations, Professor Michmerhuizen requested weekly status reports summarizing
completed tasks, goals for the following week, and any struggles perceived.
2.3.1.5
Complete Presentations and Posters for Senior Design
Because the senior design project is a capstone class at Calvin College, certain requirements like team
presentations and team posters had to be fulfilled. The team incorporated these deadlines into its work
breakdown schedule, and made sure to complete them in time.
2.3.1.6
Complete the Project Proposal and Feasibility Study
The PPFS was the major milestone of the fall semester. A draft of the PPFS was submitted for approval
from the faculty advisor in November. The final PPFS marks the end of the fall semester, and was due at
the end of the fall semester in December.
2.3.1.7
Acquire Parts and Begin Testing
With the time remaining in the fall semester, the team began the process of acquiring parts and
performing preliminary testing on those parts. The team purchased its Raspberry Pi, GPS, webcam, and
humidity and temperature sensor, and acquired tread from the campus fitness center's treadmill. Heather
6
and Monica were able to program the Raspberry Pi to run the webcam, and then to view the webcam feed
on another computer via the wireless network. They also began the process of implementing the GPS with
the Raspberry Pi.
2.3.2
Spring Semester Milestones
The spring semester of senior design was when the research and project planning culminated in a working
prototype of the project. Throughout this testing and building phase, the team was able to track its
progress by completing the following milestones throughout the semester.
2.3.2.1
Set up Wi-Fi Network
A secure WLAN provides the means of communication between the user and Amphibot. A router gives
added strength and reliability to the network. The Raspberry Pi is equipped with a Wi-Fi dongle, which
allows for wireless connection to this network so that information can be passed between robot and user.
2.3.2.2
Test GPS
The GPS allows a user to monitor their own position, as well as the position of any detected item found
by Amphibot. The GPS easily interfaces with the Raspberry Pi which converts the data to GPS latitude
and longitude coordinates for the user interface.
2.3.2.3
Create Tracks
The tracks propel the robot on land and in the water. The tracks were constructed early to allow motor
testing. Track size, tension, and material were considered during design and construction.
2.3.2.4
Build and Test Metal Detector
Choosing a metal detector meant researching the types, sizes, and accuracy of the various types of
detectors on the market, factoring in cost and performance to choose the best option. In order to maximize
performance while minimizing costs, the detector was built from a kit, and thus required innovation to
implement. Once the components had been acquired and compiled, the metal detector could be tuned to
its maximum range and functionality.
2.3.2.5
Create Frame and Mount Treads
A frame to mount the treads to and hold the motors and electronics was constructed. The size of the frame
was affected by the size of the metal detector. The mounting of the metal detector also affected the form
of the frame. In order to complete this step, the size and shape of the metal detector had to be known.
2.3.2.6
Test Motors and Drive Control System
Two brushless DC motors drive the robot. A relay circuit was designed and tested which would allow the
robot to drive in both forward and reverse directions, as well as to turn. Incremental testing was done to
each part of the circuit worked properly before testing on final design.
2.3.2.7
Create GUI Framework
A layout of the GUI was designed to provide placeholders for sensor data and control buttons. This was
important in deciding how the user would interact with the features of Amphibot, and made it easy to add
the sensors once ready.
7
2.3.2.8
Combine and Test Components
The sensor data and motor controls were implemented into an aesthetically pleasing and easy-to-use GUI
for the user. Basic functioning was first tested, then addition security features and visual enhancements
were added later.
2.3.2.9
Complete Robot Assembly
The plastic cover was constructed and attached to the robot. Its ability to keep out water was tested by
slowly lowering the robot into a tub of water and checking whether water had penetrated the plastic
casing to pool on the inside. If the case was not waterproof, it would be removed, dried, and resealed.
2.3.2.10 Final Testing and Alterations
The robot was to go through its final testing phase to determine if the requirements had been met. It was
to be driven on a track to determine the distance it could travel. It was to be placed in a pool to determine
its maneuverability and whether it could sense objects. It was to be driven into a pond to see if it could
make the transition between land and water. It was also to be driven through tall grass and mud to test its
ability to traverse multiple terrains.
2.3.2.11 Prepare Senior Design Night Presentation
Calvin College hosts a Senior Design Night in May to display each senior design team and their
accomplishments. At this event, Team 11 demonstrated the design and capabilities of Amphibot as well
as gave a presentation summarizing the work done throughout the year to family and friends.
2.3.2.12 Complete All Senior Design Deliverables
The Senior Design capstone includes a number of deliverables, such as a Final Design Report, weekly
summary reports, and in-class presentations. The team made sure these deliverables were completed by
their respective due dates.
8
3
Project Clarification
In order to design Amphibot, Team 11 had to clarify the scope and requirements of the project. The team
developed a problem specification and target customer that helped narrow down the necessary features of
Amphibot.
3.1
Customer
For the purposes of building a working prototype, the team decided to limit the customer considerations
to a boater, fisherman, or hobbyist. Outdoorsmen and women who spend time on the water know that
nothing is as frustrating as losing a pair of expensive sunglasses, a beloved piece of jewelry, or the car
keys. Sometimes these items can be found, but often it is impossible to find the items once they have gone
beneath the water into the mud. Such customers will find Amphibot makes their lives easier, allowing
them to easily scoop up lost items without sifting through mud, wading through dirty water, or dealing
with any local wildlife. Military customers, on the other hand, would have very exacting requirements and
specifications that the team did not feel it could confidently identify or accomplish within the scope of a
senior design project. The option to market for defense application is left as a possible future plan.
3.2
Requirements and Prototype Outcomes
Team 11 developed a list of requirements that allow Amphibot to perform its specified function in a way
that is easy, useful, and helpful to its end user. These requirements are divided into categories of
performance, physical, electronics, interface, and cost. These requirements are further analyzed in terms
of how well the prototype meets the specification in its current state.
3.2.1
Performance Requirements
Amphibot’s performance requirements determine how well it should function. Amphibot’s functionality
is designed to balance being useful to a user by having adequate performance with being low cost, simple,
and easy to replicate.
3.2.1.1
Driving Requirements
REQ3.2.1.1.a The robot shall be able to traverse 0.25 miles on a single battery charge.
PROTO3.2.1.1.a The robot has not been tested for maximum range on a single charge.
REQ3.2.1.1.b The robot shall be able to travel on dry surfaces, wet, marshy surfaces, and on the surface
of still water.
PROTO3.2.1.1.b The robot has not been tested on differing terrain types.
3.2.1.2
Sensing Depth Requirements
REQ3.2.1.2 The robot shall be equipped with sensors which produce valid data to a depth of at least 3
feet.
PROTO3.2.1.2 The robot’s metal detector has a range of only eight inches, which is average for its price
range. More expensive metal detectors would be able to achieve greater range.
9
3.2.2
Physical Requirements
Physical requirements for Amphibot are based primarily on what the end user of the target demographic
would want in a personal sized robot in terms of size and maneuverability. In general, size limitations
represent maximums, as the robot’s size is to be as small as the components will allow.
3.2.2.1
Size Requirements
REQ3.2.2.1 The robot shall be constrained to fit within a 3 foot diameter sphere in order to allow for ease
of transport and to provide the most flexibility to the user.
PROTO3.2.2.1 The robot is smaller than required, fitting within a 2 foot diameter sphere.
3.2.2.2
Weight Requirements
REQ3.2.2.2 The robot shall weigh no more than 50 pounds since this is a manageable weight for a human
to transport for short durations.
PROTO3.2.2.2 The robot weighs approximately 30 pounds.
3.2.2.3
Speed Requirements
REQ3.2.2.3 The robot shall be able to travel at least 2 mph. This is a pace that is reasonable for travel
while being slow enough for sensors to work and the user to steer.
PROTO3.2.2.3 The robot has not been tested for maximum speed.
3.2.2.4
Maneuverability Requirements
REQ3.2.2.4.a The robot shall be able to go in forward and reverse directions.
PROTO3.2.2.4.a The robot is equipped with forward and reverse capability
REQ3.2.2.4.b It shall be able to turn within a 3 foot radius in order to be able to maneuver through the
tight spaces that it will encounter.
PROTO3.2.2.4.b The turn radius has not been tested.
3.2.3
Electronic Requirements
Amphibot’s electrical systems need to be robust enough to stand up to motion, transport, and wet
environments without breaking or needing replacement. The system needs to be able to properly interface
with the mechanical system via motor servos and to interface with the user via the wireless area network.
Each sensor must behave according to specifications determined by how Amphibot is designed to be
used.
3.2.3.1
Sensor Requirements
REQ3.2.3.1.a The robot shall provide metal detection that is accurate to identify metallic objects as small
as a quarter up to 3 feet away.
PROTO3.2.3.1a The metal detector is capable of identifying metallic objects only 8 inches away. Its
overall accuracy has not been confirmed in outdoor testing.
10
REQ3.2.3.1.b The robot shall be able to communicate its GPS coordinates to a user when it has identified
an object.
PROTO3.2.3.1.b The robot communicates live GPS information to the user.
REQ3.2.3.1.c The robot shall provide live video feed to allow for steering without direct line of sight.
PROTO3.2.3.1.c The robot provides live video feed.
3.2.3.2
Communication Requirements
REQ3.2.3.2 The robot shall communicate over a local area network provided by a router with the user.
The network will connect to the user via Wi-Fi, and shall operate within a range 100 feet.
PROTO3.2.3.2 The robot connects to the local area network wirelessly. Range untested.
3.2.4
Interface Requirements
Once the robot is connected to a user’s laptop, the user interface shall be intuitive to use, made with a
clean design, and easy to understand.
3.2.4.1
Control Requirements
REQ3.2.4.1.a The interface shall allow for moving in the X and Y plane, control speed, and store
necessary data.
PROTO3.2.4.1.a The interface allows for movement in X and Y plane at predetermined speeds and
allows for logging and clearing of GPS coordinates. Additional speed adjustments are not implemented.
REQ3.2.4.1.b The data provided by the sensors shall provide simple information to the user without
requiring tuning or calculations.
PROTO3.2.4.1.b The data provided is simple and accurate, and requires no calculations.
3.2.4.2
Graphics Requirements
REQ3.2.4.2 The graphical user interface shall be clean and easily understandable for a lay-person to use.
PROTO3.2.4.2 The user interface is clean and understandable.
3.2.5
Cost Requirements
In determining cost, a consideration of the customer demographic and resources determined the upper
limit of what could be charged for the end product. In determining prototype costs, parts could cost no
more than allowed by the senior design budget.
3.2.5.1
End User Cost
REQ3.2.5.1 The completed Amphibot must be cheap enough for an amateur hobbyist’s budget. It shall
cost an end user no more than $1000.
PROTO3.2.5.1 The end user cost is estimated to be $750, within the allowed range.
3.2.5.2
Prototype Cost
REQ3.2.5.2 The Amphibot prototype shall cost no more than $500.
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PROTO3.2.5.2 The prototype was built for less than $500.
3.3
Deliverables
Because the senior design project represents a capstone class in the Calvin College Engineering
department, there are a number of project deliverables that are due to the faculty advisors for grading.
These are outlined below.
3.3.1
Fall Semester Deliverables
The following deliverables represent the critical graded tasks of the senior design project during the fall
semester.
3.3.1.1
PPFS
Team Amphibot submitted a Project Proposal and Feasibility Study describing the proposed project and
determining its feasibility at the end of the fall semester of 2014.
3.3.1.2
Team Website
Team Amphibot created and published a team website during the fall semester of 2014 describing the
team, project, and important documents. This website was updated throughout the span of the project.
3.3.1.3
Team Poster
Team Amphibot created a preliminary poster in the fall semester of 2014 and completed a final poster to
be displayed in the spring semester of 2015.
3.3.2
Spring Semester Deliverables
The following deliverables represent the critical tasks due to the senior design class for the spring
semester.
3.3.2.1
Final Report
Team Amphibot submitted a final report specifying the final design specifications at the end of the spring
semester of 2015.
3.3.2.2
Working Prototype
Team Amphibot presented a final prototype at Senior Design Night on May 9, 2015.
3.3.2.3
Weekly Summaries
Team Amphibot submitted a weekly summary to the project faculty advisor each Friday, summarizing the
weekly accomplishments, goals for the following week, any issues being dealt with, and any additional
notes for the advisor.
3.3.2.4
Final Presentation
Team Amphibot presented the results of their project at Senior Design Night on May 9, 2015.
3.3.2.5
Reviews
Team Amphibot presented its project and status for review by CEAC and by faculty advisors.
12
4
Design
With a specific problem to solve and a list of requirements, Team 11 researched necessary components
and their specifications in order to settle on a final design for Amphibot. This design was then
implemented into a working prototype which provides proof of concept of the overall design. In the
sections following, the team spells out driving design criteria, explains the three design norms most
relevant to the design, summarizes design options and describes the steps of implementing the design
choices.
4.1
Design Criteria
The design decisions were made based on key criteria that were deemed important to the team as the
designer and important to the customer as the end user. These criteria are explained here.
4.1.1
Critical Considerations
Critical considerations are the variety of factors that the team needed to take into consideration when
determining its final design choices. These factors were based on user operation, operating conditions,
and design limitations.
4.1.1.1
Weight
In order to maintain battery life and buoyancy, the materials and components used must be as light as
possible. As the weight of Amphibot increases, more power must be utilized to propel it forward.
Additionally, a heavier product would be less desirable to an end user for transportation purposes.
4.1.1.2
Durability
The robot will be travelling through harsh conditions. In order to maintain the life span of Amphibot, the
components must be able to withstand jarring impacts, moisture, and dirt. Electronics should be
waterproof where needed and water resistant where possible.
4.1.1.3
Simplicity
In order to prevent breakage and make Amphibot easier to fix and customize, the systems must be as
simple as possible while still performing required functions.
4.1.1.4
Transportability
Since Amphibot will be used while boating, it should be small enough to fit in an average small boat
without trouble. It should also be compact and light enough that it can be carried by a single person to
transport between a boat and a vehicle, dock, or garage.
4.1.1.5
Reliability
Amphibot will be travelling in hard-to-reach areas with only wireless control. This runs the risk of losing
the robot in difficult areas to navigate. This risk should be minimized, so each component must be as
reliable as possible. Electronic components need to be able to function quickly and well regardless of
situation and location. Mechanical components must not break when performing intended functions.
Software must have checks to ensure proper communication and fail-safes incase communication is lost.
13
4.1.1.6
Maneuverability
Amphibot must be easy to maneuver. This is important because the user will be steering by control
buttons based on video feed and will not be able to physically make corrections to the robot’s path. It will
also need to be capable of travelling through tight spaces and go around large obstacles.
4.1.1.7
Versatility
Amphibot will be required to traverse a broad range of environments from land to water, including rocky
and marshy areas. The robot’s propulsion system must be able to travel through each of these. Amphibot
must also be versatile with regard to the customer’s needs from sensors and other performance related
requirements.
4.1.2
Design Norms
The three design norms emphasized in our project are delightful harmony, trust, and caring.
4.1.2.1
Delightful Harmony
Amphibot is designed to lighten stress and provide other sources of enjoyment. Amphibot will be
aesthetically pleasing and easy to use.
4.1.2.2
Caring
Amphibot makes the task of searching for lost items easy and harmless. Amphibot is designed to
minimize or eliminate dangerous human tasks.
4.1.2.3
Trust
The end user is considered in every aspect of Amphibot’s design. This will be visible in the durability and
usefulness of the final prototype.
4.2
Design Alternatives and Decisions
In determining the prototype design, a number of options were researched and considered. These options
are described below, as well as the end decision.
4.2.1
Propulsion System
Various methods of propulsion were considered for Amphibot. The challenges of propulsion came from
Amphibot’s amphibious nature, which required a method of propulsion for both land movement and
movement along the surface of the water. Additionally, the land around the waterways that Amphibot is
likely to be traversing will be both muddy and full of debris like rocks, marsh grass, leaves, sticks, and
other plant life.
4.2.1.1
Screw-Propulsion
In this system the robot would be propelled by two large power screws located on either side of the body.
If the interiors are hollow, it would provide the buoyancy needed to float on water and stay on top of mud.
This system would allow the robot to travel through marshy environments. Screw-propulsion is a more
recent development that is not commonly used. It is hard to maneuver and has problems with slippage.1
The parts needed are also more expensive and harder to obtain. An example of screw-propulsion is shown
in Figure 2.
14
Figure 2: Screw Propulsion2
4.2.1.2
Tracks
Tracks are an ideal way to travel across rough terrain. Modifications must be made in order to make them
suitable to drive on water. Small paddles are mounted on the treads. These can be in the form of paddles
that fold down when on land and open when in water, shown in Figure 3, rubber paddles that are small
enough to allow land travel but large enough to have significant traction when in the water, or foam
paddles that provide buoyancy and propel the robot forward, as shown in Figure 4.
Figure 3: Foldable Paddles3
15
Figure 4: Foam Treads4
Having paddles that fold down would provide a way to travel more efficiently on land and on water. The
drawbacks to this system are that it would require the switching of two levers - one for each track - and
the joints for the paddles could easily become jammed with mud. If the paddles are jammed, it would
throw the robot off balance and possibly cause the paddle to break. The rubber paddles would not be as
efficient as the foldable paddles but would still provide suitable motion for land and water. The rubber
would be durable and able to grip, while the deep tread would be well suited for muddy areas and
paddling through water. The foam paddles would allow travel on land and solve the problem of buoyancy
in the water, but they would not be very durable or provide much traction on land or in the water because
of the thickness required to make them sturdy. The foam is also light and could result in the robot being
top heavy.
4.2.1.3
Paddled Wheels
A final option for an integrated propulsion system would be to use paddled wheels, as demonstrated in
Figure 5. The paddles would be similar to the rubber paddles mentioned in the section above. The benefits
to this would be easy maneuverability. The negative is that the wheels are more likely to get stuck in the
mud or not be able to overcome obstacles.
Figure 5: Paddled Wheels5
16
4.2.1.4
Separate Systems
Propelling Amphibot by separate systems means finding a system that works well for land, a system that
works well for water, and combining the two systems into a single design.
4.2.1.5
Propeller
Each of these systems uses a propeller and some other method of travelling on land. Using a propeller like
the one in Figure 6 is the most efficient way to propel the robot through water. A single propeller could be
mounted on the back of the robot. A rudder would then be used to steer. Having a propeller would require
another motor, adding weight, and another control system, adding complexity. Transitioning between land
and water would also be more problematic.
Figure 6: Propeller6
4.2.1.6
Crawler and Propeller
A crawling system would make use of legs. There are many possibilities for leg structures and
positioning. All are driven by rotational motion. In one system multiple sets of legs are moved by rocker
arm mechanisms. In another, designed by NASA and shown in Figure 7, two beams are connected, one
long and one short, using a gearing mechanism so that as the first leg rotates, the second, shorter leg helps
to propel the robot forward.7 The motion resulting from this is complicated and jarring. The benefit of
legs is that in mud, they will not spin out. Drawbacks are that this system is unstable and maneuvering is
complicated.
Figure 7: NASA Crawler8
17
4.2.1.7
Wheels and Propeller
In a wheel and propeller system, the wheels would provide high maneuverability and allow higher speeds,
especially when there are no paddles attached. They still have the problem of being easily stuck in mud
and having a more difficult time in overcoming obstacles. The Duck Boat, shown in Figure 8, is an
example of such a system.
Figure 8: Duck Boat9
4.2.1.8
Tracks and Propeller
The tracks would allow for decent speeds on land and do well in overcoming obstacles. This in
combination with the propeller would provide reliable and efficient motion both on land and in the water.
Figure 9 shows an example of this system. One negative is that the tracks would create strong drag when
being pushed through the water and hinder maneuverability.
Figure 9: Tracks10
18
4.2.1.9
Decision
The robot is propelled by tracks on land and on the water. They are be constructed using treadmill belt
material with aluminum attached. The paddles are long enough and spaced far enough apart that they will
produce sufficient motion both when in the water and on land. The front and back of the tracks are angled
upward in order to better overcome obstacles on land whether going forward or backward. This
configuration also gives more flexibility when considering the buoyancy of the robot. The water level
must not be higher than the top of the tracks, but the body of the robot must still be high enough to clear
obstacles when travelling on land. The tracks are propelled using an electric motor that drives a pressure
wheel that will turn the tracks. This allows the belt to be taken off easily and prevent slippage. The length
of the tracks is 1.6 times the width of the body in order to optimize traction and maneuverability. See
Figure 10 below for the preliminary concept.
Figure 10: Preliminary Track Conceptual Drawing
There are two electric motors located on each side of the robot to drive the tracks. Each is reversible and
controlled separately. This allows the robot’s position to be easily controlled by determining the speed
and direction of each of the tracks separately. These motors must be able to provide a minimum of 25
Watts in order to be able to propel the robot at reasonable speeds and power it over obstacles.
4.2.2
Motors
Amphibot’s treads must be powered by small but powerful motors. The best options for these motors are
outlined below.
4.2.2.1
Brushed DC
Brushed motors were the first commercial electric motor. They are variable speed and reversible.
However, the brushes tend to wear down and need to be replaced. Brushed are able to be controlled with
an H-bridge Driver IC that lets the motor spin in either the clockwise or counter-clockwise direction. This
would be easy to work into the electrical signals from the Raspberry Pi, requiring only high and low
signals. The two leads from the brushed motor provide on/off and forward/reverse inputs. However, an
expensive motor controller would be required to handle the high current draw from the tread system.
19
4.2.2.2
Brushless DC
Brushed motors are more modern and have the same capabilities as brushed motors, but are controlled
differently. Since they do not require brushes to be replaced, they last longer and are more common in
electronics. RC cars usually use brushless motors. This offers a large variety of small sized motors that
are meant to consistently change velocity. Brushless motors must be controlled using ESCs. The
orientation of the three leads from a brushless motor determine the rotation of the motor. In order to rotate
in the opposite direction any two of the three leads must be swapped. Control from the Raspberry Pi
requires simulating certain pulse waves with varying duty cycle. The ESCs have high enough current
ratings to manage the current draw required to move the treads.
4.2.2.3
Decision
Brushless DC motor were chosen to drive Amphibot. They were chosen because they last longer than
brushed motors and are more common for RC cars, making them easy to find information about for
trouble-shooting.
4.2.3
Materials
An important decision was the materials that would be used for the different components of the robot.
4.2.3.1
Aluminum
Aluminum as a structural material would be ideal because it is light-weight. A drawback is that it is not as
strong as steel. It would, however, be strong enough to withstand the forces the robot will be
experiencing.
4.2.3.2
Steel
Steel is stronger than aluminum and is also denser. As a structural material it would add significant
weight while adding strength that isn’t required.
4.2.3.3
Plastic
Plastic is a light-weight, easily molded material that is ideal for the robot casing. It can absorb shock and
keep out particles. As a structural material, it would be light, but would require more volume to meet the
required strength.
4.2.3.4
PVC
PVC piping as a structural component would add buoyancy. It would, however, be bulky and harder to
attach components to. It also would not allow much flexibility when adjusting the height the robot sits at
in the water.
4.2.3.5
Foam
Foam to make the robot float is light-weight and easy to apply. Liquid foam, like that shown in Figure 11,
is easily moldable and can fit into crevices. Foam sheets can easily be cut into geometric forms and
removed from the robot. Both types come in a variety of densities. The foam could easily be scraped off
or added to in order to adjust buoyancy. A negative is that foam may chip off during use of the robot.
20
Figure 11: Liquid Foam11
4.2.3.6
Rubber
Rubber is a heavy material, but ideal for the tracks because it is flexible and has strong gripping
capabilities. This is important on land because there will not be as much contacting surface area because
of the elongated treads. Recycling tires is difficult and rubber needed by the team can be cheaply obtained
by collecting used tires, see Figure 12, and reusing them. This would be helpful to the environment by
reducing waste.
Figure 12: Used Tires12
4.2.3.7
Decision
Aluminum is used for the structure because it is low density and sufficiently strong to withstand the
forces that Amphibot will experience. Plastic is used for the casing because it is light and easily moldable.
It is also able to withstand moderate impacts that Amphibot may experience. Foam will be used for
buoyancy in the bottom of the body of the robot. If water seeps into the body of the robot, it will not be
able to penetrate the foam and the robot will continue to float. Aluminum paddles are used on the treads
to provide movement, due to their light weight and strength.
4.2.4
Motor Controls
The decision of motor control was carefully considered based on what would be ideal and natural for a
user to drive a robot with. The major modes of control were determined to be joystick, keyboard, and
graphical interface commands.
21
4.2.4.1
Joystick
A joystick, see Figure 13, is ideal for Amphibot in that it does not limit the range of movement available
to the user. They are cheap and widely used in driving and gaming purposes. A joystick with buttons
would allow the implementation of additional features for the user. The user would be able to manually
mark areas of interest.
Figure 13: Joystick13
4.2.4.2
Keyboard
The keyboard control would be a simple way for users to control the motors. Arrow buttons would be
used to direct the desired movement of Amphibot. The user would be able to use a variety of button
combinations to move Amphibot in the required direction.
4.2.4.3
Graphical Interface Buttons
Graphical interface buttons on a laptop would provide buttons that would be clicked with a mouse to
control the motors. This would give the user simple, easy to understand instructions about how to control
Amphibot.
4.2.4.4
Decision
The final decision was chosen as graphical interface buttons. The button commands allow easy interaction
with the motor signal needed to control the motor. It also does not require the user to have any additional
equipment on hand.
4.2.5
On-board Computer
In order to run the sensors, control the motors, and interact with the end user, Amphibot needs an onboard
computer to serve as its processing unit and manage these interactions. Because of size limitations, a
single-board computer is the perfect embedded system for Amphibot.
4.2.5.1
Raspberry Pi
The Raspberry Pi single-board computer is the most popular on the market. It has one of the cheapest
prices for single-board computers with adequate memory and processing power. In addition to its low
price, Raspberry Pi has the largest support forum of any single-board computer on the market due to its
open-source coding and wide fan base in the do-it-yourself market. This contributes to a great deal of
support to troubleshooting and coding. The Raspberry Pi comes in 4 models: A, A+, B, and B+, pictured
22
in Figure 14 below. All use a 700MHz ARM11 family CPU and a 250MHz Broadcom VideoCore IV
GPU. A models have 256MB of SDRAM memory while the B models have 512MB. The plus models
have a greater number of GPIO ports. All models have between 1 and 4 USB ports. They range in price
from 20 to 35 dollars.14
Figure 14: The Rapsberry Pi B+15
4.2.5.2
Arduino Mega
Arduino is a family of microcontrollers that come in many, many varieties for a number of uses. The
Arduino Mega2560 and the Arduino Uno are two of the more popular boards. Arduino makes
microprocessors, which differ from single-board computers by their lack of GPUs and graphical user
interfaces. They also tend to be weaker in general functionality, as they specialize in performing specific
tasks. The Arduino Mega2560 has a 16MHz processor, 256 GPIO pins, and sells for 43 dollars.16
4.2.5.3
BeagleBone
The BeagleBoard single-board computer is produced by Texas Instruments. BeagleBoard has some of the
best functionality for open-source, low power, single-board computers, but it is also one of the more
expensive. The BeagleBone and the BeagleBone Black, pictured in Figure 15, are two recently launched
BeagleBoard computers. They have a 720MHz processor and 256 and 512MB RAM, respectively. It is
priced at 55 dollars. 17
23
Figure 15: The BeagleBone Black18
4.2.5.4
Decision
The Raspberry Pi B+ was chosen for use in Amphibot. This decision was made for its price, size and
community. It was cheap and small which are some of our constraint concerns. The Raspberry Pi was
easy to acquire on short notice and start working with immediately due to the number of Raspberry Pis
owned by Calvin College. Additionally, as beginners in embedded systems, the vast amount of online
forums and assistance played a large role in the ultimate decision.
4.2.6
Wireless Communication
In order to communicate with Amphibot, the user needs to use remote communication. The
communication needs to be able to allow the user to control Amphibot from a distance. Some challenges
for communication were allowing for a large enough range and having a reliable connection.
4.2.6.1
Wi-Fi
Wi-Fi, see Figure 16, is the most commonly used local area wireless technology.19 It allows for data
transmission via an electronic device such as a router or switch. It is usually used within a home to
connect and allow portable devices to connect to the Internet. Out of all the wireless communications
protocols, it has the largest range, able to connect up to 20 m on its own and can be amplified to 30 m or
more with an added router.
Figure 16: Wifi20
24
4.2.6.2
Ethernet
Ethernet would be ideal for Amphibot because it is the most secure and reliable. Since it is a wired LAN
connection, there is no question whether the data is being transmitted. The wired connection, however,
poses problems for Amphibot and its proximity to water. The range of motion for Amphibot would be
limited by the length of the Ethernet cable. The Raspberry Pi has Ethernet readily available making it
more ideal for use.
4.2.6.3
Bluetooth
Bluetooth, see Figure 17, is another common form of wireless communication. It follows certain
standards set by IEEE and devices must meet these in order to be certified Bluetooth capable. Bluetooth
has low power consumption but can only connect in short distances, approximately 10 m. 21 Since it is
radio communication, it does not require line-of-sight to exchange data. This would be ideal if there are
obstacles between the user and Amphibot.
Figure 17: Bluetooth22
4.2.6.4
Zigbee
Zigbee, see Figure 18, is similar to Wi-Fi and Bluetooth in that it is a wireless personal area network. It is
the only wireless protocol to be open, global and provide the Internet of Things.23 Like Bluetooth, it has
low-power consumption and a shorter range. It is designed for applications requiring security and long
battery life. Like Bluetooth, Zigbee only has a range of 10m to 100m with line-of-slight.
Figure 18: Zigbee24
4.2.6.5
Decision
It was decided for Amphibot that Wi-Fi would be used as the mode of data exchange. It is implemented
using a router to create a WLAN (wireless local area network) between the Wi-Fi dongle in the Raspberry
Pi USB port and user. Wi-Fi will allow Amphibot to meet the required range of motion. It is also widely
used, making it easy to implement and reliable. Wi-Fi will allow us to secure the network and prevent
unwanted hacking of Amphibot.
4.2.7
User Interface
A graphical user interface (GUI) allows a user to easily interact with the robot. The GUI takes
information from the various sensors and provides that data to the user in a neat and orderly manner,
without requiring the user to do any extra work or calculations. It also gives the user options to send
commands back to the robot, specifically regarding motor controls.
25
4.2.7.1
Visual Studio
Visual Studio is a programming platform that is powerful and easy to work with. It is a commonly used
tool and has an extensive supply of tutorials and support for do-it-yourself projects. It allows for
programming in a number of languages and has built in features for applications making graphical user
interfaces easy to create.
Figure 19: Visual Studio25
4.2.7.2
Python
Python is a one of the most commonly used, high-level programming languages. It supports objectoriented programming and is less strict than other languages such as Ada or C++. Since it is dynamically
typed, it does not require the programmer to explicitly say what type the variable is, the compiler will
figure it out on its own. Because the programmer does not need to specify variable types, it aides in the
readability and writability of the language since a program can be written with significantly less words.
4.2.7.3
Decision
Amphibot’s GUI was written using Python. This was chosen mainly due to the ease with which the
sensors can be added to the GUI since all of the sensors are compatible with Python. Python’s design is
based around importing and making use of other libraries. This proved to be crucial in the implementing
of the sensors and making use of their ready to use libraries. Lastly, Python was chosen for its appeal as a
fundamental high-level language.
4.2.8
Metal Detector
The metal detector represents the key sensor on Amphibot. It is what ultimately is used to solve the
problem statement of finding lost items in black-water. Therefore, it is very important that the metal
detector function well. Aside from the basic ability to detect metal, the most important requirement for the
metal detector is that it be able to penetrate water.
There are two main types of metal detectors that work in water. These are Pulse Induction (PI) metal
detectors and Very Low Frequency (VLF) metal detectors.26
4.2.8.1
Pulse Induction Metal Detector
Pulse induction metal detectors use a single coil of wire for transmitting and receiving signal. The
transmit frequency of a PI is around 100 pulses per second, with lower frequencies achieving greater
depth and experiencing greater sensitivities to silver and higher frequencies achieving more sensitivity to
gold and nickel alloys. PI is not capable of great discrimination. That is, PI metal detectors cannot easily
be programmed to not respond to specific metals. However, they are good for detecting metal through
deeper salt water, and for searching mineralized ground.27
4.2.8.2
Very Low Frequency Metal Detector
Very Low Frequency is the most common metal detector technology at present. It uses two coils, a
transmitter coil and a receiver coil, to detect metal based on interference with the electric fields generated
and received. VLF can be adapted to discriminate between different types of metals, like silver and
26
aluminum, which is useful for treasure hunters seeking precious metal from areas with metallic debris in
the area. When combined with a microprocessor, VLF can be easily programmed to search for certain
types of metal, like silver, iron, or steel.28
4.2.8.3
Decision
The difficulty of implementing a metal detector begins with the difficulty of implementing the required
range. Small, 10-12 inch depth sensitive metal detectors are simple to implement,29 but finding a way to
balance the sensitivity and the depth was difficult to accomplish while still balancing our size, cost, and
power requirements.
Because of its ability to ignore ferrous sand, earth, and mud, as well as salt water, without losing its
sensitivity to metallic objects, a PI detector was a better choice to attempt to implement in Amphibot. The
Surf PI 1.2 proved to be the most workable choice of PI metal detector kits on the market. It provides
sufficient detection capabilities to demonstrate proof of concept while being affordable and simple
enough to fit within the scope of the senior design project.
Figure 20: Surf PI 1.2 Metal Detector30
4.2.9
GPS
.A GPS is used on Amphibot to relay back to the user the position of any discovered items. It also helps
the user know where Amphibot is as the GPS coordinates are relayed back to the user continuously.
4.2.9.1
Handheld GPS Unit
A handheld GPS Unit would be a portable device that would attach to Amphibot and then report the
results back to the user via an application. These devices, being built for a user to hold, are equipped with
features, like an LCD screen, that are of no use in Amphibot. These devices use satellites and would have
high accuracy.31 Most devices cost a few hundred dollars.
4.2.9.2
USB GPS Receiver
A USB GPS Receiver would be able to connect directly to a USB port on the Raspberry Pi.32 Since these
devices are mainly an antenna, it reduces the cost drastically to be in the range of 10 to 30 dollars. The
27
receiver would not be able to function with the Raspberry Pi, so conversion of raw data to coordinates
would need to be taken care of by the user device.
4.2.9.3
GPS Receiver Circuit
Adafruit sells a circuit board able to connect with single-board computers and micro controllers like
Arduino and Raspberry Pi. The Adafruit Ultimate GPS, pictured in Figure 21, has battery power
capability and an output for an antenna extension.33 Adafruit provides easy-to-use setup instructions and
tutorials for basic usage. It sells for a moderate price of 40 dollars for the circuitry and 13 dollars for the
external antenna.
Figure 21: Adafruit Ultimate GPS34
4.2.9.4
Decision
The Adafruit Ultimate GPS with antenna extension was determined to be the best GPS unit for Amphibot.
It was chosen mainly for its ability to be supported by the Raspberry Pi. Rather than have the data
conversion be handled by the user’s device, all conversions are handled by the Raspberry Pi so as to make
the process not dependent on user device.
4.2.10
Webcam
Amphibot uses an on-board camera mounted on the front of the bot to give the user a proper field of
vision for steering Amphibot remotely. Implementing such a camera gives the user the freedom to drive
Amphibot around corners or into areas the user cannot see directly.
4.2.10.1 USB Webcam
The market is full of various types, sizes, and quality of webcams. Typically, webcams connect to a
computer via USB and are used to stream live video over a network. The benefit of a webcam for use in
Amphibot is its small size, cheap price, and variability available in resolution, lens angle, and frame rate.
Webcams can be used on almost any computer platform, so there were very few compatibility issues.
However, a webcam is not usually waterproof, as their primary function is for video chatting and web
28
conferencing. Therefore, some method of sealing or waterproofing would have to be utilized in case of
submersion or splashing.35
The webcam determined to be the best option for Amphibot was the Creative Live! Cam Sync HD,
pictured in Figure 22. This is a good balance of good image quality, good lens angle, small size, and
affordable price. It was also determined to be well-compatible with Raspberry Pi and other single-board
computers.36
Figure 22: Creative Webcam37
4.2.10.2 Security System Camera
Many people choose to incorporate their own home monitoring systems, whether for security, for
personal interest, or for keeping an eye on elderly or special needs family members living alone. There is
a sizeable market of high-quality security system cameras, many of which are water resistant for use outof-doors. These cameras are also often equipped with infrared LEDs to allow for night monitoring as
well. The downside of implementing a security system camera on Amphibot is its relatively large size, as
well as its fairly expensive cost. Additionally, there was concern with easy compatibility with the onboard computer.38
4.2.10.3 GoPro
GoPro cameras have become a sensation because of their extreme waterproofing, high quality images,
and durability. They are often used in extreme sports as point-of-view cameras, and are often installed on
robots due to their small size, easy use, and difficulty to break. A GoPro camera would be the ideal
camera for our use as well. However, the cameras are expensive, costing over one hundred dollars for the
cheapest version, pictured in Figure 23. 39
29
Figure 23: GoPro Hero40
4.2.10.4 Decision
A USB webcam was determined to be the best option for use on Amphibot. It is easy to implement and
simple to use, and costs and weighs little. In order to waterproof the webcam, a clear panel in the robot
body provides for functionality without worrying about water damage.
4.3
Design Specifications
Once the robot had been researched and designed in theory, the spring semester was devoted to
implementing and building the design for each aspect of Amphibot.
Figure 24: Model of Final Design
30
4.3.1
Tracks
The tracks were designed to maximize propulsion through water while maintaining traction on land.
Dependability was essential because of the remote locations Amphibot will be travelling in. Focus was
placed on strength, outside material penetration, and steadiness of moving parts.
4.3.1.1
Paddles
In order to be as light as possible while still rigid, the basic form of the paddle is a rectangle bent in half.
It is connected to the belt by four 1/8 in rivets. The area between the holes is cut out so that the belt will
ride more smoothly over the wheels. The curved portion allows the belt to flex over the wheels. This
allows for smoother turning and more surface contact with the drive wheel. When force is applied, the
curved portion rests on the wheels and bears the load uniformly.
Figure 25: Model of Single Paddle
In order to determine the optimal dimensions for the paddles, Engineering Equation Solver (EES) was
used to model them. This project is capable of solving equations simultaneously and graphing them.
Because of the complexity involved in water movement, the flow of the wake was simplified to make the
calculations manageable. The force on the paddle was calculated by assuming that the velocity of the
water striking the paddle was a vector coming from the point of the preceding paddle. The drag on the flat
portion of the belt between the paddles was assumed to be a portion of the water that struck the
intersection of the paddle and the belt and was deflected. A diagram of these assumptions is shown below.
31
Figure 26: Diagram of Water Force
The drag force was calculated by assuming that the preceding paddle was a flat plate as seen below.
Figure 27: Diagram of Water Drag
32
The forces generated by these components were added to determine the required thrust force of the robot
to move. The following graph shows the resulting force of the paddles on the water as a function of the
number of paddles.
Figure 28: Optimization Curve of Number of Paddles
From this graph it was determined that each track should have 12 equally spaced paddles. Next, the
dimensions of the paddles was determined. They need to be long enough to push large quantities of water,
but small enough to maintain stability on land. Width was set as the width of the belt. The best angle
between the belt and the interior walls of the panels was found by varying the value in EES and solving.
The angle was set at 80 degrees. Finally, the length of the paddle was calculated. A longer paddle allows
more contact area with the water, exerting greater force, but it also increases the drag. An optimization
curve of the length is below.
Figure 29: Optimization Curve of Length of Paddles
33
Using this, the length of the paddles was set to be 3.75 inches.
4.3.1.2
Belt
The belt is 4 inches wide and 60.5 inches long with holes punched at intervals of 5 inches for the rivets
that hold the paddles in place. It is made from tread mill belt material with the textured side facing inward
toward the wheels. This textured surface provides the friction that pulls the belt forward on the drive
wheel. The ends are attached by two 1/8 in rivets that also go through the paddle. Multiple holes will
allow for the belt to be tensioned. This material was chose for its durability, traction, and resistance to
stretching while still being flexible. It is also readily available at low prices. The drive wheel is also
wrapped with it to increase the friction with the belt allowing it to turn at higher loads.
4.3.1.3
Guides
Aluminum guides bend over the outside edges of the track off of the paddle will keep the belt in place.
These guides will be located on every other rivet and face away from the center of the track. They will
slide along the plastic panels on either side of the track when the belt gets pushed off track. Otherwise, the
curved cutout of the paddles keeps the belt in line.
4.3.1.4
Casing
The track will be protected by two polycarbonate panels. One will be located on the outside surface of the
track and the other on the interior over the track frame. Their contour will follow the path of the belt
around the wheels. These panels will serve as a plane for the guides to slide along, sandwiching the belt
between them. They will also prevent weeds, mud, and other objects that could jam the wheels or drive
mechanism from entering the track system. The casing will be clear which will allow for easier
troubleshooting if the robot malfunctions.
4.3.1.5
Frame
The frame of the tracks will support the wheels, plastic panels, and attach to the body of the robot. Each
member is composed of 1 in by 1/8 in Aluminum bars.
Figure 30: Interior Track Frame
34
An angle bar with legs of 1 in and thickness of 1/32 in on the exterior will be connected through the
wheel bolts and riveted to the plastic panel with the bend facing inward. This will prevent the drive wheel
shaft from being forced inward by the force of the chain and belt tension.
Figure 31: Exterior Track Support
Bolts 6 inches long and 0.5 inches in diameter will be used to mount the wheels and hold the members
together. A 1 inch long bolt with a diameter of 0.25 inches will be used at the intersection without a
wheel. The bolts will also hold the plastic panels and wheel spacers as seen below.
35
Outer Polycarbonate Panel
Inner Polycarbonate Panel
Wheel
Member
Washer
Washer
Bolt
Nut
Nut
Spacer
Spacer
Figure 32: Detail of Bolt through Track
4.3.1.6
Wheels
The wheels are 2.5 in in diameter and 1.5 in wide with a 0.5 in bore and 3 inch hub. Plastic allows them to
be light yet durable. They are based on generic push mower glide wheels. Each track will have five
wheels as demonstrated in the previous figures. They support the belt and help distribute the force of the
robot. The drive wheel will be the front, upper wheel. A sprocket will be mounted to its hub by drilling
three holes and using screws to permanently attach it. This will provide the torque that will turn the belt.
4.3.2
Body
The body of the robot will house the motors and electronics. The metal detector will be mounted in the
bottom. A plastic casing filled with foam will provide the buoyance required to make the robot float.
4.3.2.1
Structure
Three angle beams will attach the tracks to each other and form the body of the robot. Cross members will
be used to add stability and provide surfaces to mount to. The bars are 1 inch by 1/8 inch aluminum and
mount at the smaller holes seen in the Figure 33. Two bent bars mounted to the top angle bar and the
bottom front angle bar will support the motors. Two holes are cut in each so that a hose clamp can firmly
hold the motors as seen below.
36
Figure 33: Motor Mounting
4.3.2.2
Casing
The casing of the body will be composed of a polycarbonate panel that will surround the body of the
robot as seen below.
Figure 34: Body Casing
37
This panels will be fused with the interior track panels to create a water proof shell using epoxy and
caulk. The panel on the top will be removable by removing six screws so that the user can access the
batteries to charge them and make any other changes necessary. The bottom of the casing will hold the
metal detector. The bottom volume of the casing will be filled with 2 lb Urethane foam. This foam was
chosen because of its water resistance, fluid form, and durability. A volume of 3456 cubic inches is
required to create enough buoyant force to keep the water level at the center of the tracks. This is
equivalent to about a 6 inch depth of foam beneath the robot. The calculations used to determine these
values is below.
Figure 35: Buoyancy Calculations
The bottom face is flat and sized for the metal detector. It will be even with the bottom of the belt. The
two longer angled faces allow for extra flotation if the robot jerks or gets caught on something. The top
angled portions allow the camera a clear view and make the top opening smaller. The top panel allows
access to the body and seals when tightened down.
38
Figure 36: Casing Dimensions
4.3.2.3
Mounting
A dry box such as in Figure 37 will be used to hold the electrical components. This box is small, light,
and designed specifically to protect items from moisture. There is a set of latches that allow access to it,
which will be ideal for prototyping and maintenance. This will also allow access to the batteries, which
will need periodic charging. Holes will have to be drilled into the side of the box in order to connect wires
to the motors, webcam, sonar, and metal detector. These holes will be caulked shut in order to maintain
the waterproof qualities of the box. The box can be seen in the figure below.
Figure 37: Dry Box41
The box will be mounted using metal straps to the body of the robot. It fits between the two bottom
structure bars. The motors will be mounted on either side of it through the polycarbonate casing with
wires going into holes on either side of the dry box. The webcam will be mounted to the top of the dry
box. Its wires will be fed through the same holes as the motors. The casing is clear, so the webcam will be
able to use its full range.
39
4.3.3
Motor and Drive System
Theoretical calculations found in the appendix suggest that 195 Watts are required to paddle the robot
through the water. These calculations do not take into account the resistance of the wheels and belt. These
could double or triple the required power. In order to make sure that the robot has enough power, two
brushless DC motors rated at 900 Watts were selected to run the tracks. A table indicating the energy
requirements for the batteries of a motor is below.
Table 4: Motor Electrical Performance
Motor Performance
v (in/s) v (mph)
1 0.05682
6.211 0.3529
11.42 0.6489
16.63
0.945
21.84
1.241
27.05
1.537
32.26
1.833
37.47
2.129
42.68
2.425
47.89
2.721
53.11
3.017
58.32
3.313
63.53
3.609
68.74
3.906
73.95
4.202
79.16
4.498
84.37
4.794
89.58
5.09
94.79
5.386
100
5.682
Battery Voltage
v (m/s)
P (W)
I (A)
0.0254 0.0002863 2.4681E-05
0.1577
0.06847 0.00590259
0.2901
0.4257 0.03669828
0.4224
1.314 0.11327586
0.5548
2.977 0.25663793
0.6871
5.656 0.48758621
0.8195
9.593 0.82698276
0.9518
15.03 1.29568966
1.084
22.21 1.91465517
1.217
31.38 2.70517241
1.349
42.78 3.68793103
1.481
56.64 4.88275862
1.614
73.22 6.31206897
1.746
92.75 7.99568966
1.878
115.5 9.95689655
2.011
141.7 12.2155172
2.143
171.5 14.7844828
2.275
205.3 17.6982759
2.408
243.2 20.9655172
2.54
285.6 24.6206897
11.6
Run Time (min)
Time
(min)
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
40
Energy
Time (s)
(J)
120 0.034356
120
8.2164
120
51.084
120
157.68
120
357.24
120
678.72
120 1151.16
120
1803.6
120
2665.2
120
3765.6
120
5133.6
120
6796.8
120
8786.4
120
11130
120
13860
120
17004
120
20580
120
24636
120
29184
120
34272
Energy (J) 182021.3
The motor is most efficient at high speeds. In order to maintain this efficiency, sprockets were used to
translate this speed into higher torque. A 9 tooth sprocket with a pitch of 0.1475 is mounted to the shaft of
the motor. A 52 tooth sprocket is mounted to the drive wheel and connected to the motor by a roller chain.
This will reduce the speed by a factor of 5.7. A 9 tooth sprocket is attached to the 52 tooth sprocket and
attached to the 52 tooth sprocket mounted to the drive wheel. This will reduce the rotational rate from the
motor by a factor of 33.
40
Drive Wheel
52 Teeth
52 Teeth
Motor
9 Teeth
9 Teeth
Figure 38: Drive System Diagram
4.3.4
Motor Controls
Brushless motors do not typically allow movement in both clockwise and counter-clockwise directions
from remote controlling. In order to spin the motor in the opposite direction, any two of the three leads
need to be flipped. Since the user needed to be able to do this from a distance, modifications were made to
the motor control circuit. A relay was added between the ESC’s (Electronic Speed Controllers) three leads
and the three leads of the motor as seen Figure 39.
Figure 39: Relay Schematic
The relay can be turned on or off remotely using signals from the general output pins of the Raspberry Pi
and the Pi.GPIO library. Depending on the state of the two relays, the motors can move the robot in the
41
forward, left, right, or reverse direction based on which way the motors are spinning. The speed of
Brushless DC motors are commonly controlled with ESCs. These take power from a battery and a signal
from a micro-controller to drive the motors and can optionally power a micro-controller through its 5V
output pin. The battery used to power the ESCs and relays is a 3-cell lithium-polymer, also known as lipo, battery. It has high energy density, is lightweight and is rechargeable.
The signal coming to the ESC from the Raspberry Pi is a pulse wave driven by one of the general output
pins using a library called pigpio.42 This tool provides an easy way to code pulse waves in Python. It
allows easy initialization and modification of the frequency and duty cycle. The variation in duty cycle is
what makes the motor spin faster or slower; it was crucial to be able to control these easily.
4.3.5
User Interface
The user interacts with Amphibot and its sensors as shown in the block diagram below. The user is able to
access Amphibot’s on-board computer using a PuTTY43 terminal from a laptop while both the laptop and
Amphibot’s Raspberry Pi are on a common WLAN. The WLAN is secure and reliable due to the added
layer of a router in the path between user and Raspberry Pi. From the PuTTY terminal, the user can run
the Python GUI in a command prompt terminal window.
Figure 40: Electrical Block Diagram
The graphical user interface of Amphibot was designed in Python using a library called Tkinter.44 Using a
grid layout implementation, frames, canvases, buttons and text boxes were added where sensor data could
be viewed or interacted with from the user.
42
The GPS has a set of buttons and text windows that let the user view and log GPS latitude and longitude
coordinates. One text window shows the current location of Amphibot, while a second shows GPS
location the user has saved. Buttons let the user add or reset saved locations. The GPS Breakout Board
uses the gpsd library. The GPS sends out reports when active that include information such as latitude,
longitude, speed, and altitude. For this design, only latitude and longitude were extracted from the reports.
They were then saved in text files that could then be displayed in the text windows on the GUI.
The motor controls are implemented using buttons. When the buttons are clicked it activates the different
signals to be sent to the ESCs and relays. The motors need to be initialized before being ready to use, so
an initialize button is included as well as forward, reverse, right, left, and stop buttons.
The webcam is controlled on a separate thread than the main thread of the GUI. This allows the webcam
to be run continuously independent of is happening with the other sensors. Python Imaging Library
(PIL)45 and OpenCV46 are used to convert the live webcam stream to a series of images able to be
displayed in the Tkinter GUI.
4.3.6
Metal Detector
The metal detector was built from the Silver Dog Surf PI 1.2 kit. This kit came with a circuit board and all
components necessary to complete the metal detector. The components were soldered to the circuit board,
and a detecting coil was made using 12 gauge speaker wire.
Figure 41: Metal Detector Schematic47
4.4
Prototype
In order to test the design, a prototype was built as seen below. This prototype indicated where problems
in the design were and confirmed that the design was feasible.
43
Figure 42: Preliminary Prototype
The prototype was built by the team at Calvin College with Calvin resources during the Spring semester
of 2015.
Figure 43: Final Prototype
4.4.1
Track System
This took the longest to construct because of the many small pieces. Initially, the guides faced the wheels.
When the drive wheel was turned, the wheels had a tendency to go up over the guides.
44
Figure 44: Tread Guide Design
The wheels were also crooked due to the tension of the belt. In order to remedy this, a supporting member
was placed on the other side of the track and the guides were turned around and cut down as seen in the
final design. The design already called for a plastic casing, so this casing was then used to further support
the wheels and provide a surface for the guides to follow. When turning the drive wheel, there was also a
significant increase in force when one of the paddle fins went over the upper wheels. Instead of leaving
the entire bent section flat on the belt, the space between the holes was cut and bent up. The design was
changed to call for this material to be removed. Now when the drive wheel is turned, the belt runs
smoothly on track. At larger speeds on land, the drive wheel slipped on the belt and the robot did not
move. To fix this the wheel was covered in treadmill belt material.
A large problem occurred when the belts were driven with more load. The chain began to break. The
forces had not been calculated on the chain and the maximum capacity of the chain had not been taken
into account. This limited the amount of testing that was able to be completed. There was not enough time
to switch to a metal chain and sprockets, but this was taken into account in the final design. The added
weight should not significantly change the robots performance.
Figure 45: Prototype Track
45
4.4.2
Metal Detector
Once the metal detector was built, it was powered by a power supply to ensure it maintained a steady
current and no components malfunctioned. When the metal detector did not malfunction, each component
was tested to ensure proper placement and component value. Next, the circuit was analyzed to determine
where the output was not as expected. A faulty chip was identified and replaced. Once the system was
operational, it was tuned by adjusting the potentiometers while running various sizes and types of metal
across the coil at different heights until the preferred specification was found. The coil was able to detect
a gold ring or a steel washer at a maximum of eight inches away. In order to allow remote detection, an
optocoupler was used to take the output audio signal from the piezoelectric buzzer and connect the
voltage to an input pin on the Raspberry Pi. The optocoupler allowed the two systems to be connected
while still protecting each respective device from the other. The input pin was set as active low, meaning
that whenever metal was detected and an audible response heard from the buzzer, the input pin was pulled
to ground, allowing the user interface to alert the user remotely that metal was found.
Figure 46: Prototype Metal Detector
4.4.3
User Interface
The first step to building the GUI was to visualize what it needed to encompass. Once a drawing was
made for the GUI including a layout of the design and what each component needed to do, it was easy to
begin coding. Python programs were written for each of the individual components and were able to run
and function as needed for the final design. However, it proved to be more difficult than anticipated to
implement these individual Python programs into the GUI. For the GPS module, it was possible to view
the needed information in the Python terminal window, but having them display in the GUI required
learning how to read and write to text files in Python. A problem also occurred in implementing the
webcam live video stream in that it was possible to run the individual program and view in a stand-alone
window but difficult to incorporate with Tkinter. Tkinter and OpenCV require an additional conversion
between them. PIL was added to convert the picture into a useable form for Tkinter. Additionally, since
the webcam needed to be run constantly separate from the GPS and motor controls, research needed to be
done on how to make this happen. Originally the solution was thought to have the whole GUI
continuously loop with a new video frame; however, a technique called threading was discovered that
allows an application to run two separate processes at once. Having the webcam run on a separate thread
from the main thread of the GUI proved to solve this problem.
46
A second thread was added for the GPS. This lets the user see the GPS coordinates continuously without
having to take any additional actions such as clicking a button. The GPS latitude and longitude are
reported in +/- format rather than N, S, E, and W. Additional code was added to convert the sign of the
coordinate to its appropriate compass direction.
Using selection and repetition, it was possible to create loops in the GUI that would check the Wi-Fi
connection and metal detector signal continuously. Should the wireless connection between Amphibot
and the user be lost, the GUI will register this and shut off the motors. Text was used to notify the user of
metal being detected. If the signal sent to the Raspberry Pi indicated metal has been found, green words
appear saying “Metal Detected” otherwise black words say “No metal detected.” The final GUI design is
shown in Figure 42.
Figure 47: User Interface
4.4.4
Propulsion
Once Amphibot had been assembled, it was necessary to test that it would move. First, the treads were
pulled by hand to estimate the force required to move them. This was compared to the motor control tests
as an indication of whether the motors might be expected to perform to requirements. Then the drive
system and motors will be installed, allowing Amphibot’s propulsion to be tested fully. First the motors
will be tested turning the drive wheel without the belt. If that works as planned, the treads can be added
and the motors tested with the robot suspended off the ground. From there, the robot can be placed on
various surfaces to ensure all aspects of the propulsion system work on solid ground, mud, grass, and
water. Finally, the limits of the system will be tested, including maximum speed, battery life, and range.
4.4.5
Motor Control
The motor controls and motors were tested incrementally. First, the ESCs were tested to ensure they
would drive the motors to turn on and off and hold speeds. Meanwhile, the relay circuit was tested to see
if it could turn on and off an LED. Once these disparate systems were tested, they could be combined to
ensure that the motors could be turned on, turned off, and reversed in direction, all done from the user
interface.
47
4.4.6
Design Norm Analysis
When considering the design norms chosen to influence the design of the prototype, delightful harmony,
caring and trust are evidenced throughout the many aspects of Amphibot.
4.4.6.1
Delightful Harmony
A number of design decisions were made to make Amphibot aesthetically pleasing and easy to use. The
GUI was designed around what would make sense for a person to intuitively use. Color text was added to
emphasize good and bad conditions of the Wi-Fi and detection of metal. As an additional step to make
Amphibot more pleasing to the eye, the Amphibot logo was spray painted on the side to add color and
artistic appeal.
4.4.6.2
Caring
Amphibot is designed with the purpose of eliminating harmful tasks to humans. One such way it does this
is by making it possible to safely detect landmines with no risk to the user. The body was designed to
optimize for the conditions under which Amphibot would be used. The body was designed to weigh no
more than easy to transport for short distances and to be small enough to transport in a car or boat.
4.4.6.3
Trust
A trust-worthy design was crucial to the prototype as the risks if failure occurs is great due to the
dangerous aspects such as LiPo battery and aggressive paddles. If water infiltrates the compartment where
the electrical components are kept, an explosion could occur were the LiPo to get wet. To protect against
this, double encasing was used for the electrical parts. They are first encased in a water-resistant dry box
and then in a water-tight polycarbonate case. In addition, code was implemented to shut off motors if
connection is lost, giving the user complete driving control of Amphibot. Furthermore, an extensive test
plan was developed to prove out the requirements of the design.
4.4.7
Amphibot Final Test Plan
Once each separate aspect of Amphibot had been tested individually, they were assembled together so
that the robot could be tested as a unit. This requires Amphibot to maneuver over land, mud, and water
successfully by a user. At the same time, the webcam must provide life video feed, the GPS record the
location as the robot moves, and any metal placed in Amphibot’s path must be detected as expected.
4.4.7.1
Testing Elevated
The robot was placed on a stand so that the treads were free to move without contacting anything.
Initially, the motor was unable to turn because the gear ratio was too low. After the gear ratio was
increased the motor was capable of barely moving the belt. The paddles were then altered to make the belt
move smoothly. This allowed the motor to turn the tracks. There was not enough power, however to turn
the belt consistently. This was due to errors in controlling the motor. Once the proper frequency was
found, the motors were able to turn both tracks smoothly and quickly. Forward and reverse were both
obtained.
4.4.7.2
Testing on Land
Once it had been confirmed that the motors were capable of driving the treads, Amphibot was placed on
the ground on carpet squares to provide traction. The motors were turned on with a slight increase in
power from the elevated test in order overcome additional friction. The treads were able to turn smoothly
initially. However, after moving more than a foot, the robot’s plastic chain was unable to withstand the
48
torque and snapped. In order to preserve chain for future tests, the team ended land testing after having
proven movement possible and progressed to water testing.
4.4.7.3
Testing in Water
The first test done in water was to make sure the casing around the electrical components of Amphibot
was water-tight. This required filling the tank in the engineering building with water until Amphibot was
able to float without touching the bottom of the tank. This test was done with the electronics removed for
safety. Amphibot was left in the tank until it was evident that there was no water leaking into the main
body.
Once it was clear that it was safe to place Amphibot in the water with no risk to the electronics getting
wet from water leaking in, it was tested whether Amphibot could move in the water. This was done by
placing Amphibot in the water and having the motors run at a slower speed than that used for testing on
land. Hands were at the ready should anything go wrong during this test. When the motors were started,
Amphibot started to tip backwards, meaning it was back heavy. However, this proved that with balanced
weights, Amphibot would indeed be able to move in the water. Unfortunately, this was the last test able to
be performed as the chain broke and was not able to be replaced.
4.4.7.4
Tests Unable to Be Performed
Due to these complications with parts and timing, many of the tests that would have clarified project
requirements and confirmed Amphibot’s ultimate success were unable to be performed. However, the test
plan the team would have proceeded to implement is outlined below.
4.4.7.4.1 Maximum Speed Test
First, the team would have tested for maximum speed in both land and water. In order to do so, Amphibot
would be placed on a long flat surface such as a track or road. The team would have increased the power,
and therefore the speed, provided to the motors. Because the motors are capable of producing more torque
than the treads would be capable of sustaining, the speed would be increased only until such a point that
the robot continues to drive stably and consistently, and that speed would be labeled as maximum.
The same test would be conducted in the indoor pool, where Amphibot would have enough distance in
water to attain maximum speed.
4.4.7.4.2 Obstacle Test
The team would then have tested Amphibot’s ability to overcome obstacles in land and water such as
bumps, grass and weeds, and sticks. Amphibot would first be placed along a track. Rocks or sticks of
various sizes would be placed in its path until it was no longer able to overcome them. Additionally, the
team would construct a crude ramp and increase the angle of its incline to determine the steepness the
robot could traverse both upwards and downwards.
In the water, a similar test to the sticks would be implemented, determining the ability of Amphibot to
handle solid objects in the water. Additionally, using the water tank to preserve the cleanliness of the
pool, the team would have placed leaves and water plants in Amphibot’s way to test for plant
maneuverability.
49
4.4.7.4.3 Control Test
The controls would have been tested by checking turn radius and motion response. Right and left turn
capability were provided to the user as control options, but due to an inability to thoroughly test the
controls it was unclear the turn radius Amphibot would have been able to achieve. In theory, the robot
should have been able to perform a zero-point turn with one tread moving forward and the other
backwards. However, this maneuverability is uncertain, and controls could not be maximized to provide
the most efficient maneuverability possible.
4.4.7.4.4 Communication Range Test
The communication range would have been confirmed, both inside and outside. The user with the router
would establish a position, and drive Amphibot as far away as possible while still maintaining a
connection with the Raspberry Pi. Another team member would follow the robot to measure the distance
away from the user the robot had moved. This would be done outside as well as within the Fieldhouse,
which is a large enough building to provide the opportunity for indoor range to be tested.
4.4.7.4.5 Battery Tests
The battery would be tested for speed of recharge, and the team would have tested distance the robot can
travel, on land and water, on a single charge, as well as the time it takes for the battery to reach the
minimum allowable voltage for a lithium polymer battery. The LiPo battery would be fully charged and
placed immediately into Amphibot. The robot would then be driven around a track until the battery
reached the minimum, and the number of laps recorded. The battery would then be recharged from the
minimum voltage to full and the charge time recorded. The test would take place again, this time with
Amphibot driving through laps in the indoor pool to test its drive time and distance on water.
4.4.7.4.6 Sensor Tests
The accuracy of the GPS would have been confirmed both indoors and outside, on both sunny and cloudy
days. The metal detection depth would be confirmed through earth and through both salt and fresh waters.
In order to test the GPS, the robot would be placed in various locations both indoors and outdoors, near
windows and in basements, on cloudy days and sunny days. The given GPS coordinates, if any, would be
entered into Google Maps to verify accuracy of locations. Any inability or time delay to receive signal
would be noted as well as any significant differences between actual and measured location.
In order to test the metal detector depth in various elements, a small steel washer would be used as a
control measure. The metal detector would first detect the washer in air and its range recorded as the
control group. The washer would then be buried under increasing amounts of sand, by the half inch, until
the metal detector can no longer sense the washer. The same procedure would be completed with a bucket
full of fresh water, adding half inches until the washer cannot be sensed. This process would also be
completed in salt water. This would provide the range of the detector in each likely medium.
4.4.7.4.7 Production Tests
In addition to these tests for the prototype, some tests were considered for a product in active production.
The robot would be tested for extreme temperature operating ranges, asking the robot to move, sense, and
communicate with a user in increasingly hot and increasingly cold conditions until failure. The robot body
would be subjected to a hit test which would confirm its structural endurance. The test would check both
that the robot could withstand impacts of particular strengths on various points of its structure, as well as
its ability to withstand falls from various heights. A test would determine whether water splashing the
50
robot would cause water leakage, and another would test the internal electronics at high humidity levels
for any sign of failures.
51
5
Business Plan
The team developed a business plan for their Amphibot product. This plan focused on marketing the robot
to the specified customer base and on determining appropriate prices for that product based on cost of
parts and labor.
5.1
Marketing
Team 11 is focusing its marketing efforts on the areas where the customer is most likely to shop. Outdoor
sporting goods stores like Cabela’s and Bass Pro Shop will market Amphibot through their magazines as
well as independent water activity websites. In order to support the low quantities expected and provide
for customization, Amphibot will be produced using small companies. The target customer for Amphibot
includes water enthusiasts and treasure hunters with possible military contracts.
5.1.1
Competition
In the realm of amphibious robots, most products on the market that serve the same remote controlled
function as a small vehicle with a land and over-water driving are either products in research in colleges
and universities or small toys like remote controlled cars and boats. Products like Aquapod,48 from the
University of Minnesota, make up the bulk of the amphibious robotic industry. Most of these research
robots are designed to explore different modes of transportation. Aquapod moves by tumbling; ACM-R5
moves like a snake in water.49
In the realm of metal detectors, alternatively, competition is mostly from handheld units that require the
user to walk along with the product in order to use it. Some of the more common units of PI metal
detection include the $700 Tesoro Sand Shark,50 the $900 Surfmaster PI Pro,51 and the $2000 Lorenz
LPX2.52
5.1.2
Differentiation
Amphibot will be a versatile robot that can be easily purchased. It will be small and simple to meet
functional needs. It will be low enough in cost to be accessible to a dedicated hobbyist and functional
enough to be of interest to a wide range of amateurs and professionals. It is user-friendly and can be
operated without training by adults and children alike.
5.1.3
Distribution
Because the customer base for Amphibot has as its unifying factor people who enjoy outdoor pastimes
and hobbies and because our company is small and focused, the team chose to distribute its product
through larger outdoors sporting goods stores’ magazines like Cabela’s and Bass Pro Shop and water
activity websites. These larger companies, with a firm customer base and an established marketing and
sales team, would advertise Amphibot on a commission and eliminate Amphibot’s need to market itself
or hire a sales team of its own.53
5.2
Final Product Cost Estimate
The cost of parts per unit in the final implementation of Amphibot is projected to be $295.50, based on
the breakdown in Table 5.
52
Table 5: Parts' Cost Estimate
Item
Aluminum
Plastic
Rubber
Treadmill Belt Material
Nuts and Bolts
Wheels
Motors
Sonar
Dry Box
Raspberry Pi
Webcam
Metal Detector
Batteries
GPS
Total
Cost [$]
15
4
1
5
0.50
40
30
20
10
35
30
60
15
30
295.5
These cost values were determined by slightly reducing the costs of buying these products individually
under the assumption that they would be bought in bulk for a cheaper cost. The final price of the product
was determined to be $750. This value was determined by considering cost of parts, labor, and other fixed
costs and performing a break-even calculation. This analysis was performed as part of the Engineering
Business class. The break-even analysis is reproduced in Table 6.
53
Table 6: Break Even Analysis
Amphibot
Break - Even Analysis
Year 2
Year 1
Sales revenue
Less: Variable Costs:
Variable Cost of Goods Sold
Variable Operating Costs
Total Variable Costs
Contribution Margin
Less: Fixed Costs
Fixed Cost of Goods Sold
Fixed Operating Costs
Depreciation
Interest Expense
Total Fixed Costs
Income Before Tax
7,500,000
4,000,000
585,000
9,000,000
4,160,000
672,750
4,585,000
2,915,000
670,000
95,000
214,350
262,500
4,326,400
773,663
737,000
95,000
375,924
492,606
Year 2
Year 3
1,241,850 1,700,530 1,621,994
39%
46%
53%
Break Even Sales Volume
3,195,154
3,672,631 3,073,285
Equipment
Purchases
Year 1
Depreciation
Year 2
Year 3
Equipment Purchases Year 1
1,500,000
214,350
367,350
262,350
Equipment Purchases Year 2
60,000
8,574
14,694
Equipment Purchases Year 3
80,000
11,432
214,350
375,924
0.2449
0.1749
7%
Year 1
Year 2
3,750,000 7,037,229
262,500
492,606
Year 3
6,111,686
427,818
0.1429
Interest Expense:
Annual interest rate on debt
Average debt balance
Interest expense
54
5,100,063
5,699,938
810,700
95,000
288,476
427,818
1,700,530
2,466,720
Total Fixed Costs
Contribution Margin %
MACRS Rates (7-year recovery
period)
10,800,000
4,832,750
4,167,250
1,241,850
1,673,150
Year 1
Year 3
288,476
1,621,994
4,077,944
6
Conclusion
For the given scope and time constraints of the senior design project, Amphibot fulfills the requirements
and goal set by the team.
6.1
Future Plans
If the team had the opportunity to do the project over with unlimited time, cost, and scope constraints, the
team would add a number of additional features to Amphibot. Amphibot’s metal detector is a low-end,
affordable metal detector with limited range. Given additional resources, Amphibot would be equipped
with a more powerful metal detector as well as a sonar to let the user visualize the object found. Ideally,
Amphibot would eliminate all possible harm to humans by removing them from the retrieval process
entirely. Amphibot would have a retractable claw or magnet to gather objects once found. It would also
have a stronger wireless communication system for practical applications where the user might not be
able to be close to Amphibot. Additional software features implemented would obstacle sensing
capabilities, advanced motor controls including gradient speed control, and a mobile application.
55
7
Final Summary
Team Amphibot has produced a prototype which we hope will be an ultimate success by Senior Design
night. We were able to operate within the financial and physical constraints of the project and met all
requirements of a Calvin College Senior Design Project. We are very proud of our work and our
accomplishments, and feel Amphibot is an interesting idea with a decent number of possible applications
within both the civilian and military markets. During our work on Senior Design, Team Amphibot learned
a number of important lessons about engineering as a discipline, about planning, time management,
budgeting, and team work. This has been a worthwhile and informative year, and the team is pleased to
conclude the semester successfully.
56
8
Acknowledgements
We would like to thank all those who have contributed to our project. These people include Professor
Mark Michmerhuizen who has taken the role of the team’s primary faculty advisor, Professor Renard
Tubergen who gave the team guidance when it came to interacting with watery environments, Professor
Ned Nielsen who helped the team find an appropriate project that was feasible and challenging, Professor
Yoon Kim who provided much assistance with the electrical components of the project, Phil Jasperse who
provided design suggestions and guided the manufacturing of the prototype, Chuck Holwarda who
provided parts and advice for electrical issues, Robert DeKraker who facilitated purchasing and parts
acquisition, Professor David Wunder and Professor Jeremy VanAntwerp who are instructors in our senior
design class, Ross Tenney and Tyler DeVries who helped form our business plan, and, finally, Eric
Walstra who served as our industrial consultant. Additional thanks is given to the members of the Calvin
Engineering Department who have all shaped our engineering education.
We would also like to thank those who have supported us throughout our endeavors. The support and
guidance of our families and friends has been invaluable.
57
Appendix
A1. Paddle Calculations
A2. Paddle Drawings
A3. Track Structure Drawings
58
A1. Paddle Calculations
59
60
61
A2. Paddle Drawings
All units in inches
Figure 48: Paddle Drawings
62
Figure 49: Paddle Pattern
63
A3. Track Structure Drawings
Figure 50: Hole and Member Placement
Figure 51: Track Structure Inner Frame
64
Figure 52: Track Structure Outer Casing
65
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