RoMow Mk. II
A Project Proposal and Feasibility Study
Team 01
From the left: Se Ge Jung, Caleb Meindertsma, Emily Wheeler, and Aldo Daniel
ENGR 339
© 2015-2016 Team 01 and Calvin College
I
A Project Proposal and Feasibility Study
Team 01
Aldo Daniel, E.E.
Se Ge Jung, M.E.
Caleb Meindertsma, M.E.
© 2015-2016, Team 01 and Calvin College
ENGR 339
© 2015 Team 01 and Calvin College
Executive Summary
Team 01, comprised of two mechanical concentration students and two electrical concentration
students, will discuss the project feasibility and design of a remote controlled platform to be used
with a variety of lawn mowers. The objective for RoMow Mk. II is to design a remote controlled
lighter frame platform that is adjustable in xyz directions. An on-board camera will be added
with video streaming over Wi-Fi to make the user's experience more enjoyable. The team's
intensive research, analysis, and consultations confirmed the feasibility of the design project.
Prototype, design, testing, and optimization will begin in ENGR 340.
i
Table of Contents
1. Introduction ............................................................................................................................... 1
1.1. Course................................................................................................................................... 1
1.2 Team ...................................................................................................................................... 1
1.2.1 Aldo Daniel ..................................................................................................................... 1
1.2.2 Se Ge Jung ...................................................................................................................... 2
1.2.3 Caleb Meindertsma......................................................................................................... 2
1.2.4 Emily Wheeler................................................................................................................. 2
1.3 Chapter Overview ................................................................................................................. 3
Chapter 1: Introduction ........................................................................................................... 3
Chapter 2: Problem Definition ................................................................................................ 3
Chapter 3: Project Management ............................................................................................. 3
Chapter 4: Mechanical Design Process .................................................................................. 3
Chapter 5: Electrical Design Process ..................................................................................... 3
Chapter 6: Cost ....................................................................................................................... 3
Chapter 7: Conclusion............................................................................................................. 3
Chapter 8: Acknowledgements ................................................................................................ 3
Chapter 9: Appendices ............................................................................................................ 4
2. Problem Definition .................................................................................................................... 5
2.1 Need ...................................................................................................................................... 5
2.1.1 RC Lawn Mower Market ................................................................................................ 5
2.2 Customer ............................................................................................................................... 5
2.3 Reason for Selection.............................................................................................................. 6
2.4 Requirements ......................................................................................................................... 6
2.4.1 Customer Requirements .................................................................................................. 6
2.4.2 Previous Team Suggestions ............................................................................................ 6
2.4.3 Team Requirements ........................................................................................................ 6
2.5 Design Norms ........................................................................................................................ 7
2.5.1 Caring ............................................................................................................................. 7
2.5.2 Integrity .......................................................................................................................... 7
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2.5.3 Trust ................................................................................................................................ 7
3. Project Management ................................................................................................................. 8
3.1 Responsibilities ..................................................................................................................... 8
3.1.1 Design Assignments ........................................................................................................ 8
3.1.2 Administrative Assignments ............................................................................................ 8
3.2 Project Status ......................................................................................................................... 8
3.2.1 Key Milestones ................................................................................................................ 8
3.2.2 Time Tracking ................................................................................................................. 9
3.3 Course Deliverables .............................................................................................................. 9
3.4 Project Deliverables .............................................................................................................. 9
3.5 Team Meetings ...................................................................................................................... 9
4. Mechanical Design Process .................................................................................................... 10
4.1 Frame Material Selection .................................................................................................... 10
4.1.1 Steel .............................................................................................................................. 10
4.1.2 Aluminum ...................................................................................................................... 10
4.1.3 Extruded Aluminum ...................................................................................................... 11
4.1.4 Material Availability..................................................................................................... 11
4.2 Control Box Material Selection........................................................................................... 11
4.2.1 ABS Plastic ................................................................................................................... 11
4.2.2 Carbon Fiber ................................................................................................................ 11
4.2.3 Material Availability..................................................................................................... 12
4.3 Motor Power Specification.................................................................................................. 12
4.4 Control Box Electronics Dampening .................................................................................. 12
4.5 Frame Design ...................................................................................................................... 12
4.5.1 DIY RC Lawn Mowers .................................................................................................. 13
4.5.2 Mounting/Unloading .................................................................................................... 13
4.5.3 Height Adjustment ........................................................................................................ 14
4.5.4 Length & Width Adjustment ......................................................................................... 14
5. Electrical Design Process ........................................................................................................ 15
5.1 Hardware ............................................................................................................................. 15
5.1.1 Remote Controller ........................................................................................................ 15
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5.1.2 Motor Controller .......................................................................................................... 16
5.1.3 Motors ........................................................................................................................... 17
5.1.4 Power Supply ................................................................................................................ 17
5.1.5 Microcontroller ............................................................................................................ 18
5.1.6 Camera ......................................................................................................................... 19
5.1.7 Proximity Switch ........................................................................................................... 20
5.2 Software .............................................................................................................................. 20
5.2.1 Remote Controller Receiver ......................................................................................... 20
5.2.2 Main Movement Control ............................................................................................... 20
5.2.3 Video Streaming ........................................................................................................... 20
5.3 System Overview ................................................................................................................ 21
6. Cost ........................................................................................................................................... 22
6.1 Budget allocated and used ................................................................................................... 22
6.2 Mass Production Additional Costs ...................................................................................... 22
7. Conclusion ............................................................................................................................... 23
7.1 Design Decisions ................................................................................................................. 23
7.1.1 Mechanical Design Decisions ...................................................................................... 23
7.1.2 Electrical Design Decisions ......................................................................................... 23
7.2 Current Status ...................................................................................................................... 24
7.3 Risks .................................................................................................................................... 24
8. Acknowledgements ................................................................................................................. 25
9. Appendices ............................................................................................................................... 26
9.1 Motor Requirements ............................................................................................................ 26
iv
Table of Figures
Figure 1: Lawnbot400 by J D Warren ......................................................................................... 13
Figure 2: EvaTech RC Lawn Mower ........................................................................................... 14
Figure 3: Width Adjustment Mechanism ..................................................................................... 14
Figure 4: System Overview of RoMow Mk. II ............................................................................ 21
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Table of Tables
Table 1: Products in the Market ..................................................................................................... 5
Table 2: RoMow Mk. II Design Responsibilities .......................................................................... 8
Table 3: RoMow Mk. II Administrative Responsibilities .............................................................. 8
Table 4: General Properties of Alloy Steel .................................................................................. 10
Table 5: General Properties of Aluminum 6061-T6 .................................................................... 10
Table 6: ABS Properties ............................................................................................................... 11
Table 7: Remote Controller Specifications .................................................................................. 15
Table 8: Motor Controller Specifications..................................................................................... 16
Table 9: Development Board Specifications ................................................................................ 18
Table 10: Expected Component Costs ......................................................................................... 22
vi
1. Introduction
An electrical engineering professor at Calvin College, Yoon Kim, came to Team 01 and
proposed a design project that would improve and add on to RoMow, one of Calvin College
2014-15 senior design projects. RoMow is a remote controlled lawn mower platform which
would be beneficial for people with limited mobility. The first prototype of RoMow was a
platform with a control box and a metal frame on which an existing lawn mower could be added
without significant modifications. Team 01 will develop the next prototype that will address
mechanical and electrical improvements. Mechanically, the frame will be made adjustable so that
any size lawn mower can fit. Also the frame will be made lighter with other materials that can
withstand the weight, vibration, and throttle of the lawn mower. Electrically, more features such
as a collision sensor and remote camera.
1.1. Course
ENGR 339 and ENGR 340 are Calvin College’s engineering senior capstone courses designed to
prepare students to transition smoothly into their careers. Through team oriented coursework, a
year-long senior design project is executed. ENGR 339 focuses on team formation, project
selection, and a project plan feasibility study. ENGR 340 focuses on the development, testing,
and optimization of the prototype.
1.2 Team
1.2.1 Aldo Daniel
Aldo Daniel is an international electrical and computer engineering
student from Jakarta, Indonesia who expects to graduate in May
2016. He has had an electrical engineering consulting internship in
Jakarta, in which he worked on projects with companies such as
Grand Hyatt and Four Seasons. He also has had experience in
wireless video surveillance and programming which will benefit the
project. In his free time, he enjoys playing soccer, cooking, and
traveling.
1
1.2.2 Se Ge Jung
Se Ge is an international mechanical concentration engineering
student who expects to graduate in May 2016. He has manufacturing
internship experience with Innotec where he was involved in
monitoring and running Honda production lines. Always striving for
continuous improvement, he worked closely with the machine
processes and improving PFMEA and reducing RPN. He has gained
research experience in accelerated fatigue testing of a structure for
the past two semesters with Professor De Jong. After graduation, Se
Ge will join Innotec as a full-time manufacturing engineer. In his
free time, Se Ge likes to be updated with new gadgets and commerce
on ebay for electronics.
1.2.3 Caleb Meindertsma
Caleb Meindertsma is a mechanical concentration engineering and
mathematics student from Fairfax, VA expecting to graduate in May
2016. He has industry experience inspecting small-scale traffic
infrastructure integrity for Alpha Corporation, an Engineering firm.
He also has experience in the financial sector, interning at Wall
Street Emprises, LLC, and with construction, as an employee of
Smeda Design Build, LLC. After graduation, Caleb wants to move
back to the South and find work in the field of mechanical
engineering. He is also captain of the Calvin College Men’s Swim
and Dive team and is a member of the Calvin College StudentAthlete Advisory Committee.
1.2.4 Emily Wheeler
Emily Wheeler is an electrical and computer concentration
engineering student who expects to graduate in May 2016. She has
over 2 years of experience in the automotive industry at Burke E.
Porter Machinery Company in Grand Rapids, MI. After graduation
she plans to move to Arizona and find work as a controls engineer. In
her free time Emily savors spending time with her husband and one
year old son while enjoying the outdoors.
2
1.3 Chapter Overview
Chapter 1: Introduction
The first chapter introduces the project and the Calvin College senior design course. It also
introduces the team and gives a brief description of the design team.
Chapter 2: Problem Definition
The second chapter defines the design problem by outlining the requirements set by the
customer, Professor Yoon Kim, and the desire for the project, both in the community and the
team. It also breaks down the scope of the project, keeping in mind the chosen design norms.
Chapter 3: Project Management
The third chapter further breaks down the organization of the design process by dividing the
assignments and organizing them according to time. It also defines the deliverables of the
project.
Chapter 4: Mechanical Design Process
The fourth chapter organizes the mechanical design process according to the tasks associated
with the mechanical concentration students involved in this project.
Chapter 5: Electrical Design Process
The fifth chapter organizes the electrical design process according to the tasks associated with
the electrical concentration students involved in this project.
Chapter 6: Cost
The sixth chapter covers the cost of the project, including the budget allocated and budget used
in addition to extra costs associated with mass production.
Chapter 7: Conclusion
The seventh chapter concludes the project by justifying the decisions made for the design and the
risks associated with those designs. It also gives an update on the current status of the project.
Chapter 8: Acknowledgements
The eighth chapter acknowledges those who helped with the project.
3
Chapter 9: Appendices
The tenth and final chapter contains additional information and calculations pertinent to the
project.
4
2. Problem Definition
2.1 Need
RoMow would benefit those who have difficulty using a standard lawn mower. Instead of hiring
or physically being active, RoMow allows potential customers to control the lawn mower with
the touch of a button. Safety features include collision sensors, a mounted camera, and an
emergency deactivator.
The objective of the senior design project RoMow Mk. II is to improve the first prototype by
providing customers an improved platform which would be mechanically more versatile and
electrically more refined and upgraded with various safety features.
2.1.1 RC Lawn Mower Market
Currently, there are a handful of remote controlled lawn mowers for both residential and
commercial purposes. None of them feature a detachable lawn mower platform.
Table 1: Products in the Market
Company
EvaTech1
Summit Mowers2
Services3
Product
Hybrid RCLM B class
ZTR-34
Cost [$]
2,199
6,000
1000 annually
2.2 Customer
The project design has been governed and guided by the customer, Professor Yoon Kim. A clear
set of requirements and specifications have been laid out.
1
"EVATECH OFFICIAL WEBSITE." EVATECH OFFICIAL WEBSITE. Accessed November
15, 2015. http://www.evatech.net/.
2
"DIY or Hire: How Much Does Lawn Mowing Cost?" Angie's List. May 29, 2014. Accessed
November 16, 2015. http://www.angieslist.com/articles/diy-or-hire-how-much-does-lawnmowing-cost.htm.
3
"2015 Summit Mowers Remote Control Slope Mowers." 2015 Summit Mowers Remote
Control Slope Mowers. Accessed November 16, 2015. http://www.remotemowers.com/.
5
2.3 Reason for Selection
There are several reason for selecting the RoMow project. The RoMow Mk. II project offers a
balance appropriate for two electrical and two mechanical concentration students. In addition to
that, the first prototype left with a lot of opportunities for growth and improvement.
2.4 Requirements
2.4.1 Customer Requirements
A set of project specifications has been outlined by the client, Professor Yoon Kim.
 Lighter control box made of plastic with visible Calvin Engineering symbol
 Inexpensive motors with enough power specifications
 Mechanical touch sensor or electronic proximity sensor
 Modular design; easily retractable control box
 Adjustable frame (blade height and sizes)
 Camera with Wi-Fi streaming to personal device
2.4.2 Previous Team Suggestions






Aluminum control box
Fastened frame, instead being welded together
New, standard motors
Simplified electronics as the Arduino was overqualified for this project
Robust wiring and mounting
Automation
2.4.3 Team Requirements






Zero turn radius
Adjustable frame
Plastic control box
Electronic proximity sensor
Camera and display on personal device
Modular design
6
2.5 Design Norms
2.5.1 Caring
RoMow Mk. II will show genuine love and concern for people. The physical, social, and
psychological effects on the customers are one of our highest priorities.
2.5.2 Integrity
With an older generation making up most of the target market it is essential that the design is
pleasing and intuitive to use.
2.5.3 Trust
Lastly, the RoMow Mk. II must be dependable and reliable. It is important to establish a bond of
trust with the user.
7
3. Project Management
3.1 Responsibilities
3.1.1 Design Assignments
Each member strains on specific responsibility on the design of the prototype, even within the
electrical and mechanical division, which is shown in Table 2. This is done so that there is no
overlap between each member's work when the project is in progress.
Table 2: RoMow Mk. II Design Responsibilities
Member
Aldo
Se Ge
Caleb
Emily
Role
Camera, Wireless Communication
Frame Design
Control Box Design
Circuitry, Control
3.1.2 Administrative Assignments
To function well as a group, administrative responsibilities have also been assigned to each
member, which are detailed in Table 3.
Table 3: RoMow Mk. II Administrative Responsibilities
Member
Aldo
Se Ge
Role
Financial
Manager and
Webmaster
Professional
Description
In charge of maintaining financial expenditures and budget
status. He is also in charge of the website design and updates.
Manager
In charge of maintaining document formatting and
professionalism in all aspects of group work. This includes
document proofreading and communication developments.
Caleb
Marketing
Manager
In charge of all media and public aspects of the group work.
This includes posters, social media, and graphical diagrams.
Emily
Team Manager
In charge of keeping track of deadlines set by the faculty
advisor.
3.2 Project Status
3.2.1 Key Milestones
The group obtained an electric wheelchair in mid-October for free from Landon Potts, a
classmate at Calvin College. However, the group found that there is only one motor. The design
8
of Mk. II requires two motors and two batteries to perform adequately. The group obtained
another electric wheelchair in early November for $200 from craigslist. The group discovered
that the batteries, motors, and wheels meet the project design standards and are still in prime
condition.
The next week, the electrical team received a Raspberry Pi B for free from the customer,
Professor Yoon Kim. A Raspberry Pi is preferred instead of an Arduino Uno due to its video
processing capability.
3.2.2 Time Tracking
Each member tracks their own time in an online Excel spreadsheet to keep each other
accountable. So far, the team has accumulated up to 130 hours.
3.3 Course Deliverables
As detailed in the ENGR 339 course syllabus, each group has to complete project documents,
especially the Project Proposal and Feasibility Study, and two verbal presentations. Moreover,
each member has to complete quizzes and an individual journal that records the progress of the
project. The course also pushes each group to consider Christian values to be practiced in all
aspects of the project.
3.4 Project Deliverables
The group is committed to deliver a working prototype by the end of the Spring 2016. By the end
of Fall 2015, the group will complete the initial designs and create a bill of materials (BOM) that
will be needed to make the product by Spring 2016.
3.5 Team Meetings
All of the members meet Monday mornings to update each other on our progress from the week
and set our goal for the next. The group uses this time to work on course deliverables. By
October, the group decided that they needed another weekly meeting based on concentration.
Emily and Aldo meet Tuesday mornings to decide on electrical design alternatives and
occasionally meet with Professor Kim to discuss those decisions. Caleb and Se Ge meet
regularly every week to develop the mechanical design of the frame and control box.
9
4. Mechanical Design Process
4.1 Frame Material Selection
The platform has to withstand the weight of lawn mowers with the vibrations and throttle of the
diesel engine of the lawn mower. Two feasible options are steel and aluminum.
4.1.1 Steel
Steel is an alloy of iron and other materials that make up high durability and strength. It comes in
many forms and types including carbon steel, alloy steel, stainless steel, and tool steel. Because
of these reasons, steel is widely used for construction and railroad. Steel is generally cheaper
than aluminum. Material properties for common steel can be seen in Table 4.
Table 4: General Properties of Alloy Steel4
Property
Density
Tensile Strength
Yield Strength
Brinell Hardness
Value
7850
758-1882
366-1793
149-627
Units
kg/m3
MPa
MPa
-
4.1.2 Aluminum
Aluminum is ductile in nature, but strong when combined with other alloys. The major
advantage of aluminum is that the weight is about one-third of that of steel. Due to the lightness,
it is often used in aircrafts and high performance cars. Material properties for common aluminum
can be seen in Table 5.
Table 5: General Properties of Aluminum 6061-T65
Property
Density
Tensile Strength
Yield Strength
Brinell Hardness
Value
2700
310
276
95
4
Units
kg/m3
MPa
MPa
-
"EFunda: Typical Properties of Steels." EFunda: Typical Properties of Steels. Accessed
November 16, 2015. http://www.efunda.com/materials/alloys/alloy_home/steels_properties.cfm.
5
"ASM Material Data Sheet." ASM Material Data Sheet. Accessed November 16, 2015.
http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA6061t6.
10
One of the requirements from the client was to make a lighter frame. The team will do this by
utilizing aluminum’s lighter yet durable mechanical properties.
4.1.3 Extruded Aluminum
Extrusion is a process in which a material goes through a die to shape certain finished products6.
The team will be using extruded aluminum with T-slots. An advantage of extruded aluminum is
its high weight-to-strength ratio. Also, the slots make the assembly process easy. The team will
most likely use the aluminum 6000 series, which balances strength and material cost.
4.1.4 Material Availability
Extruded aluminum will be available from nearby companies around Michigan. Specifically,
Gentex has an inventory of materials that they are willing to donated. Phil Jasperse will organize
a trip to companies and gather the needed materials.
4.2 Control Box Material Selection
RoMow Mk. I used sheet metal for the control box which interfered with the antenna signals.
Mk. II hopes to improve better communication by making the control box out of plastic or
carbon fiber.
4.2.1 ABS Plastic
ABS plastic is an inexpensive plastic that is easy to fabricate and machine. It has a high strength,
is easy to paint, and has a very good impact resistance. Properties of ABS plastics are shown in
Table 6.
Table 6: ABS Properties7
Property
Density
Tensile Strength
Yield Strength
Value
1080
44
69
Units
kg/m3
MPa
MPa
4.2.2 Carbon Fiber
Carbon fiber is a material consisting of mostly carbon. It is strong, low weight, has high
temperature tolerance, and low thermal expansion. Carbon fiber is a better choice in many areas
than ABS plastic, however, typical carbon fiber costs $10-12 per pound8.
6
7
Wikipedia. Accessed November 16, 2015. https://en.wikipedia.org/wiki/Extrusion.
"ABS (Tecaran®)." ABS. Accessed November 16, 2015. http://www.plasticsintl.com/abs.htm.
11
4.2.3 Material Availability
Professor Kim mentioned that the team might get a hold of carbon fiber from Gentex.
4.3 Motor Power Specification
In order to push a certain amount of weight up and down, motors have to meet certain power
specifications. Assuming the team knows the weight of the frame and the lawn mower, and a
slope of 30°, motor power specifications were calculated in Section 10.1. Simple power
specifications will allow the team to know the power requirements and feasibility for RoMow
Mk II.
4.4 Control Box Electronics Dampening
Control box has electrical components that are sensitive to lawn mower vibrations. Dampening
mechanisms will be applied inside the control box. Also the camera should have image
stabilization.
4.5 Frame Design
RoMow is a unique product in that the platform is detachable from the lawn mower. Also, the
frame will be adjustable in x, y, and z direction. To make the frame adjustable, several existing
DIY remote controlled lawn mower designs are considered as well as new design alternatives.
8
"Top Stories." Price Keeping Carbon Fiber from Mass Adoption. Accessed November 16,
2015. http://www.plasticsnews.com/article/20140805/NEWS/140809971/price-keeping-carbonfiber-from-mass-adoption.
12
4.5.1 DIY RC Lawn Mowers9
Figure 1: Lawnbot400 by J D Warren
Figure 1 illustrates a DIY remote controlled lawn mower. The dimension of the lawn mower
was measured prior to building the mechanical frame. The frame's width matched the mower's
original wheelbase and the length had to let front caster wheels to turn 360°. The mechanical
frame is rectangular and is made from steel L-shaped brackets and steel tubing (1" x 1"). Much
of this design language is used for RoMow Mk. In fact, most of the other available DIY
projects10 have a rectangular frame made from steel. The motors, electronics, and batteries are on
the back and the caster wheels are on the front.
Mk. II will use extruded aluminum due to material availability and lightness, which will ease up
on the motors and result in longer battery life.
4.5.2 Mounting/Unloading
RoMow Mk. II will have the same mounting mechanism as that of Mk.I. It had 6" steel brackets
that folded down and made a ramp to mount the lawn mower from the back side.
9
"Lawnbot400 | Make: DIY Projects, How-Tos, Electronics, Crafts and Ideas for Makers." Make
DIY Projects HowTos Electronics Crafts and Ideas for Makers. Accessed November 16, 2015.
http://makezine.com/projects/lawnbot400/.
10
"Arduino R/C Lawnmower (painted)." Instructables.com. Accessed November 16, 2015.
http://www.instructables.com/id/Arduino-RC-Lawnmower/.
13
4.5.3 Height Adjustment
On the market, there are several products that have adjustable height of the lawn mower. Figure
2 shows how the height can be adjusted with a lever.
Figure 2: EvaTech RC Lawn Mower
A similar height adjusting mechanism may be implemented for RoMow Mk. II.
4.5.4 Length & Width Adjustment
Extruded aluminum has T-slots that the team will utilize. T-slots are great for attaching or
fastening. There will be extruded aluminum on each side of the frame. A sliding rack mechanism
will be inserted in the T-slots, which will control the length of the frame. The width will be
adjusted by L-brackets that will slide past each other.
Figure 3: Width Adjustment Mechanism
14
5. Electrical Design Process
5.1 Hardware
5.1.1 Remote Controller
The remote controller will be used to direct the system.
Requirements
The controller must be immune to interference from normal household signals. It must
also have a range long enough for a typical homeowner's lawn, which was determined to
be about 1000 feet. It must have four channels to control speed, steering, initiation of the
rotation movement, and an emergency stop of the mower blades.
Alternatives
Three alternatives were considered for the RC transmitter/receiver: Turnigy 6X, FlySky
FS-CT6B, and the Tactic TTX403.
Decision Criterion
Dependability, lead time, cost, and ease of modification were considered.
Decision
The FlySky FS-CT6B was chosen because it is dependable, has a lead time of only five
to seven days, and is only ten dollars more than the cheapest option at $40. Table 7
shows the specifications for each controller.
Table 7: Remote Controller Specifications
Dependability
Lead Time
Price ($)
Turnigy11
Previous Issues
2-4 weeks
$30
FlySky
No Issues
1 week
$40
Tactic12
Unknown
1 week
$40
Implementation
The FlySky receiver will be wired to the Raspberry Pi board so the signal can be used to
drive the electric motors.
11
Brandsen, Drew, Robert Hoff, Spencer Olson, and Jared Zoodsma. "Team 08 Final Design
Report." Calvin College Engineering Department. 2015. Accessed November 14, 2015.
http://www.calvin.edu/academic/engineering/2013-14-team8/Team08_Final_Design_Report.pdf,
82.
12
Tic Tac, . "Tactic TTX403 2.4GHz SLT 4-Ch Mini Transmitter." Amazon. Accessed
November 16, 2015. http://www.amazon.com/Tactic-TTX403-2-4GHz-4-ChTransmitter/dp/B00GKMX0B8.
15
Test
One useful test that will be done once the controller is purchased is to determine the pulse
widths of each channel. This will be beneficial to confirm the differentiation between the
channels.
5.1.2 Motor Controller
The motor controller will be used to move the motors based on the information from the
microcontroller.
Requirements
The controller must be able to handle load current of approximately 10A and have some
overload protection. It must be compatible with the power supply of 24V/31AH.
Alternatives
Three alternatives were considered: RTK Raspberry Pi Motor Controller Board Kit,
Sabertooth Dual 25A, and the Pololu High-Power Motor Driver.
Decision Criterion
Flexibility, ease of integration, and size were considered.
Decision
Table 8 shows all of the alternatives and their respective qualities. Each category has a
maximum value of 10 and was rated subjectively.
Table 8: Motor Controller Specifications
Flexibility
Integration
Size
RTK Kit13
3
5
5
Sabertooth14
9
7
5
Pololu15
5
5
3
The Sabertooth Motor Driver was chosen because it can communicate with analog
voltage, radio control, serial and packetized serial. Only one Sabertooth unit is needed to
control two DC motors which makes the part easier to integrate than the two units that
would need to be purchased with the alternatives.
13
Adafruit. "RTK Motor Controller Board Kit for Raspberry Pi." Accessed November 16, 2015.
https://www.adafruit.com/products/1687.
14
ebay. "Sabertooth Dual 25A 6V-24V Regenerative Motor Driver." Accessed November 16,
2015. http://www.ebay.com/itm/Sabertooth-Dual-25A-6V-24V-Regenerative-Motor-Driver/111736714458?_trksid=p2141725.m3641.l6368.
15
Pololu Robotics & Electronics. "Pololu High-Power Motor Driver 18v25." Accessed
November 16, 2015. https://www.pololu.com/product/758.
16
Implementation
The FlySky receiver will be wired to the Raspberry Pi board and the motors so it can act
as the translator between them.
5.1.3 Motors
Two motors will be used to drive the front wheels of the system.
Requirements
The motors must require 24VDC and they need to supply 0.6 hp as determined in section
10.1.
Alternatives
New motors like a Worldwide Electric PM DC Motor16 were considered along with
motors from a used electric wheelchair.
Decision Criterion
Cost was the most important criteria.
Decision
An electric wheelchair can carry loads over 300 pounds and can also be found at a very
low cost. It was the best option considering the $500 budget for the prototype. A Rumba
electric wheelchair was purchased and it has Motion Tech Motors model number
EC82M2446220L0B motors. Each motor is able to deliver 320 W which is equal to 0.57
hp. The two motors will deliver over 1 hp which meets the requirement of 0.6 hp.
Implementation
The motors will be removed from the chair and connected to the motor controller.
5.1.4 Power Supply
Batteries must be used to provide wireless power.
Requirements
With no load the motors are rated at 24V/31AH. With a range of 20 miles and max speed
of 4.4 miles per hour the loaded current requirement is about 10A.
Alternatives
New 12V batteries and the batteries from a used electric wheelchair were considered.
Decision Criterion
Cost and usage time were the two criterion.
Decision
The batteries with the wheelchair had a suitable battery life and were no additional cost
so they were the best option for this prototype. If this product was mass produced, a low
cost new battery would be selected.
16
WorldWide Electric Corporation. "Permanent Magnet DC." Accessed November 16, 2015.
http://www.worldwideelectric.net/product-category/permanent-magnet-dc/.
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Implementation
The batteries will be wired in series to provide the required 24V for the system.
Test
In order to check the viability of the batteries they will be visually inspected to make sure
no cells are completely empty. If the levels are low, water will be added according to the
manufacturer's directions.
5.1.5 Microcontroller
The microcontroller will collect and send data within the system.
Requirements
The microcontroller must be able to send a minimum 480p camera resolution. It must
also be able to communicate over Wi-Fi.
Alternatives
Three development boards were considered such as an Arduino, a Raspberry Pi, and a
BeagleBone.
Decision Criterion
Amount of RAM, quantity of I/O pins, and versatility of development environment were
considered.
Decision
Table 9 shows what each board has to offer. BeagleBone and Rapsberry Pi both use a
Linux type of development environment and meet the requirements. However, since the
camera that easily interfaces with the Raspberry Pi is much cheaper, it is the best choice
for our application.
Table 9: Development Board Specifications
Price ($)
RAM (MB)
Number of I/0
Price of Camera
Arduino17
$22
<1
20-60
-
BeagleBone18
$40
512
92
$88
17
Raspberry Pi19
$40
512
20
$30
Arduino. "Arduino UNO (USA ONLY) & Genuino UNO (OUTSIDE USA)." Accessed
November 16, 2015. https://www.arduino.cc/en/Main/ArduinoBoardUno.
18
Beagle Board. "BeagleBone Black." Accessed November 16, 2015.
http://beagleboard.org/BLACK.
19
Adafruit. "Raspberry Pi Model B 512MB RAM." Accessed November 16, 2015.
http://www.adafruit.com/products/998.
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Implementation
A Raspberry Pi model B board was donated to the project and will be used to control the
system. It will be placed in an anti-vibration casing within the control box.
Test
To ensure that this board works for this application it will be tested to make sure it can
stream data to the server.
5.1.6 Camera
The camera sends video data to the microcontroller.
Requirements
The camera should be able to deliver a minimum of 480p video quality at a good frame
rate.
Alternatives
One alternative is a Raspberry Pi Camera Board by Adafruit that attaches to the
Raspberry Pi by a small socket on the upper board surface. A Logitech Camera that is
connected to the Raspberry Pi through USB was also considered.
Decision Criterion
Video quality, cost, data process rates, and dependability were considered. Ease of
control was also considered because the camera might be shaking a lot when attached to
the lawn mower platform.
Decision
Adafruit's Raspberry Pi Camera Board was chosen for its dependability because it is
designed exclusively to carry pixel data. This ensures that the board will be able to
process higher data rates compared to USB20.
Implementation
The camera will be attached by a small socket on the upper board surface.
Test
The camera can be tested when it is connected to a computer. Different camera software
can be used to examine the video quality it delivers. More tests need to be done in order
to make sure that the wireless connection will be able to deliver the same quality as a
wired connection does.
20
Adafruit. "Raspberry Pi Camera Board." Accessed November 16, 2015.
http://www.adafruit.com/products/1367?gclid=CJDshtzEp74CFckWMgodO1QADQ.
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5.1.7 Proximity Switch
The proximity switch detects objects in the platform’s path.
Requirements
The sensor must be small enough to mount to the front of the control box and operate on
24VDC.
Alternatives
Alternatives have not been considered because the customer ensured the design team that
it will be something to purchase later in the design process.
Decision Criterion
Size and cost are the most important factors.
Decision
The proximity switch has not been decided yet for the same reason as explained in the
alternatives section.
Implementation
The switch will be mounted to the front of the frame and controlled by the
microcontroller.
Test
Ensure that the switch sends a toggle signal to the microcontroller.
5.2 Software
No code has been written or implemented at this point. Once the parts have been received,
software designs will be considered.
5.2.1 Remote Controller Receiver
5.2.2 Main Movement Control
5.2.3 Video Streaming
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5.3 System Overview
Figure 4 shows how the software and hardware are connected. The handheld remote controller
and video display will communicate wirelessly with the RC receiver and Raspberry Pi,
respectively. The camera is attached to the Raspberry Pi by a small socket on the board. The
motor control is connected to the Raspberry Pi as well. The motor control is connected to the
batteries and motors through wires.
Figure 4: System Overview of RoMow Mk. II
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6. Cost
6.1 Budget allocated and used
The team was allotted a budget of $500 for this project by the Calvin College Engineering
department. The cost of parts is split evenly between electrical components such as the camera,
microcontroller, batteries, motors and wheels salvaged from the electric wheelchair. The table
below shows an approximation of the expected component costs.
Table 10: Expected Component Costs
Component
Electric Wheelchair
Raspberry Pi
Project Use
Motors, Batteries, wheels
Microcontroller
Cost
$200
($40)*
Camera
Aluminum
ABS Plastic
Wi-Fi Dongle
Sabertooth Duel 25A
FlySky FS-CT6B
Visual Feedback
Frame Construction
Control Box
Wi-Fi Communication
Motor Driver
RC Transmitter/Receiver
$30
($3/ft)*
$0.78/kg
$6
$125
$40
Total Cost:
$406
*Note: Donated Component
6.2 Mass Production Additional Costs
Continuous production of the RoMow in a commercial setting would have a different set of
pricing guidelines. In addition to added financial burden and overhead costs from property and
employees, several component costs would change.
For instance, Gentex, a local engineering firm, is donating large amounts of salvaged metals,
including several long beams of extruded aluminum, to Calvin College for senior design project
use. In the future, the RoMow team will have to purchase extruded aluminum, which retails at $3
per foot. In addition, Professor Kim donated a Raspberry Pi board to the team nullifying that
expense.
The method of recycling a used wheelchair for its components would not be sustainable for mass
production. For this reason, new research into low-cost, high-performance batteries, motors, and
wheels to use would be needed, which would add to the total production costs of the RoMow.
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7. Conclusion
7.1 Design Decisions
This project is constrained primarily by price but also by the customer requirements. In some
instances such as material selection, the customer requirements take precedence over the
associated costs.
7.1.1 Mechanical Design Decisions
For frame material, the team will be constructing the frame out of extruded aluminum 6105 10
series. This material has a similar strength-to-weight ratio as steel and has slots making it easy to
use in a modular design. The control box housing all the electrical components as well as
batteries and motors will be made from ABS plastics for its durability and low cost.
The RoMow Mk. II also needs to be adjustable to accept most sizes of push lawn mowers. The
team decided that the sliding rack mechanism is the best option for this problem. This method
allows for a simple adjustment interface and will not make noise as a result of the lawn mower’s
vibrations.
The used electric wheelchair purchased for this project contained wheels, batteries, and motors
which will be used for this project. These components were tested and inspected to make sure
they still met the required specification.
7.1.2 Electrical Design Decisions
The team had to decide on an easy way to control the RoMow Mk. II. The FlySky FS-CT6B was
chosen because it is dependable and easy to use. In addition, it has a similar cost to comparable
controllers.
For the motor driver, the Sabertooth was chosen because it meets the electrical requirements. In
addition, it can communicate with two DC motors, allowing for an easier integration than
alternatives.
The Raspberry Pi microcontroller was chosen to send the video data over Wi-Fi because of the
amount of RAM and lower price of the associated camera. Adafruit's Raspberry Pi Camera
Board was chosen for its dependability because it is designed exclusively to carry pixel data.
This ensures that the board will be able to process higher data rates compared to USB.
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7.2 Current Status
This team concludes that the second iteration of the RoMow is a viable project and shall be
prototyped in the Spring of 2016 semester. Currently, the team is in the process of ordering all
the components to begin construction in ENGR 340.
7.3 Risks
The risks associated with moving forward with this project are that the scope of the project is too
broad or that some of the customer requirements are not feasible within the budget or level of
expertise of the team.
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8. Acknowledgements
The team would like to acknowledge the help of several key contacts. The first of which is the
customer and mentor, Calvin College electrical engineering Professor Yoon Kim. The next
contact is Phil Jasperse of the Calvin College machine shop for help in fabrication advice and
material acquisition. Lastly, Professor Ned Nielsen, the team’s advisor, has helped the team
greatly during the design process.
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9. Appendices
9.1 Motor Requirements
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