David Exoo (ME) Preston Phillips (ME) Matthew … Executive Summary This report discusses the design...
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1 2013 Design Report SENIOR DESIGN 2012-2013 Treadstone TEAM 17 David Exoo (ME) Preston Phillips (ME) Matthew Wever (ME) Michael Vriezema (ME) Copyright © 2013, Team 17 and Calvin College 2012
Transcript of David Exoo (ME) Preston Phillips (ME) Matthew … Executive Summary This report discusses the design...
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2013
Design Report
SENIOR DESIGN 2012-2013
Treadstone
TEAM 17
David Exoo (ME)
Preston Phillips (ME)
Matthew Wever (ME)
Michael Vriezema (ME)
Copyright
© 2013, Team 17 and Calvin College
2012
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Executive Summary
This report discusses the design and research regarding the creation of a two-tracked, all-terrain
vehicle. Team 17, also known as Treadstone, chose to build this utility vehicle for their senior
capstone project. Team 17 designed this vehicle in the most economical way possible without
compromising its structural and operational integrity. Completion of this report is also
accompanied by a prototype of our vehicle to demonstrate the proof of concept of our vehicle,
both theoretically and in actuality.
Treadnought Prototype. Photo courtesy of Matt Wever. 2013.
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Table of Contents Executive Summary ........................................................................................................................ 2
1 Introduction ............................................................................................................................. 8
1.1 The Project ....................................................................................................................... 8
1.2 Design Norms ................................................................................................................... 8
1.2.1 Transparency ............................................................................................................. 8
1.2.2 Trust .......................................................................................................................... 8
1.2.3 Caring ........................................................................................................................ 8
1.3 The Team.......................................................................................................................... 9
1.4 The Class .......................................................................................................................... 9
2 Project Management ............................................................................................................. 10
2.1 Project Breakdown ......................................................................................................... 10
2.1.1 Engine & Drivetrain ................................................................................................ 10
2.1.2 Controls ................................................................................................................... 10
2.1.3 Frame ...................................................................................................................... 10
2.1.4 Tread Assembly ...................................................................................................... 10
2.2 Schedule ......................................................................................................................... 11
2.3 Budget ............................................................................................................................ 12
2.4 Method of Approach ...................................................................................................... 13
2.5 Task List ......................................................................................................................... 14
3 Requirements ........................................................................................................................ 15
3.1 Safety .............................................................................................................................. 15
3.2 Operating Conditions ..................................................................................................... 15
3.3 Functionality................................................................................................................... 15
4 Project Specifications............................................................................................................ 16
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4.1 Engine and Power Train ................................................................................................. 16
4.1.1 System Options ....................................................................................................... 16
4.1.2 Selected System ...................................................................................................... 18
4.1.3 Engine Selection ..................................................................................................... 19
4.1.4 Clutch Selection ...................................................................................................... 24
4.1.5 Transmission ........................................................................................................... 25
4.1.6 Snowmobile Driveshaft Coupling........................................................................... 30
4.1.7 Final Powertrain ...................................................................................................... 33
4.2 Controls .......................................................................................................................... 33
4.2.1 Brakes ..................................................................................................................... 33
4.2.2 Throttle .................................................................................................................... 36
4.2.3 Frame Integration .................................................................................................... 36
4.3 Frame .............................................................................................................................. 37
4.3.1 Body ........................................................................................................................ 37
4.3.2 Powertrain Mount Plate .......................................................................................... 39
4.3.3 Rear Wheel Mount .................................................................................................. 40
4.4 Tread Assembly.............................................................................................................. 41
4.4.1 Tracks ...................................................................................................................... 41
4.4.2 Additional Suspension ............................................................................................ 42
5 Prototype Testing .................................................................................................................. 43
5.1 Initial Testing ................................................................................................................. 43
5.2 Additional Testing .......................................................................................................... 44
5.3 Quantifiable Results Testing .......................................................................................... 45
5.4 Potential Modifications .................................................................................................. 46
6 Business Plan ........................................................................................................................ 47
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6.1 Market Competition ....................................................................................................... 47
6.2 Break Even Calculations ................................................................................................ 48
7 Conclusion ............................................................................................................................ 50
8 Appendix A (include Business Plan sheets in Final) ............................................................ 53
8.1 Powertrain EES Calculations ......................................................................................... 53
8.2 Braking EES Calculations .............................................................................................. 56
8.2.1 EES Code ................................................................................................................ 56
8.2.2 EES Solutions ......................................................................................................... 57
9 Acknowledgements ............................................................................................................... 58
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Table of Figures Figure 1: Team Picture.................................................................................................................... 9
Figure 2: Gantt Chart .................................................................................................................... 11
Figure 3: Work Breakdown .......................................................................................................... 14
Figure 4: Electric Motor................................................................................................................ 16
Figure 5: Hydraulic Motor ............................................................................................................ 17
Figure 6: Briggs and Stratton Engine............................................................................................ 18
Figure 7: Snowmobile Engine and CVT ....................................................................................... 20
Figure 8: Power and Torque Curves ............................................................................................. 21
Figure 9: Kohler Diesel Power Curve ........................................................................................... 22
Figure 10: 12HP Briggs and Stratton Engine ............................................................................... 23
Figure 11: PowerHorse Engine ..................................................................................................... 24
Figure 12: Centrifugal Clutch ....................................................................................................... 25
Figure 13: Hydrostatic Transmission ............................................................................................ 26
Figure 14: Belt and Chain Drive Schematic ................................................................................. 27
Figure 15: Lawn Mower Transaxle ............................................................................................... 28
Figure 16: Peerless 9000 Transaxle .............................................................................................. 29
Figure 17: Cub Cadet Transaxle ................................................................................................... 30
Figure 18: Drivecog and Shaft ...................................................................................................... 30
Figure 19: LoveJoy Jaw Coupling ................................................................................................ 32
Figure 20: Pillow Block Bearing .................................................................................................. 33
Figure 21: Final Powertrain .......................................................................................................... 33
Figure 22: Hydraulic Brakes ......................................................................................................... 34
Figure 23: Disc Brakes.................................................................................................................. 35
Figure 24: Brakes and Throttle ..................................................................................................... 37
Figure 25: Frame FEA .................................................................................................................. 38
Figure 26: Frame Fabrication........................................................................................................ 39
Figure 27: Mount Plate FEA ......................................................................................................... 40
Figure 28: Rear Wheel .................................................................................................................. 41
Figure 29: Final Track Assembly ................................................................................................. 42
Figure 30: Suspended Test ............................................................................................................ 43
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Figure 31: First Road Test ............................................................................................................ 43
Figure 32: Dirt Test Drive ............................................................................................................. 44
Figure 33: Mud Test Run .............................................................................................................. 45
Figure 34: Towing Test ................................................................................................................. 46
Figure 35: Pulley Failure .............................................................................................................. 46
Figure 36: DTV Shredder ............................................................................................................. 47
Figure 37: Final Product ............................................................................................................... 52
Table of Tables Table 1: Estimated Budget ............................................................................................................ 12
Table 2: Actual Budget ................................................................................................................. 13
Table 3: Decision Matrix .............................................................................................................. 18
Table 4: Peerless Gear Ratios ....................................................................................................... 29
Table 5: Cub Cadet Gear Ratios ................................................................................................... 30
Table 6: Production Cost Estimate ............................................................................................... 48
Table 7: Break Even Analysis ....................................................................................................... 48
Table 8: Profit Analysis ................................................................................................................ 49
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1 Introduction
1.1 The Project
Team 17 (Treadstone) set out to design and construct an all-terrain utility vehicle. The team’s
vehicle, the Treadnought, has two treads to allow it to traverse a wide variety of terrains such as
snow, mud, grass, and gravel. The production model would also incorporate onboard storage for
tools and equipment, as well detachable seats for additional riders. Rider safety is of particular
importance to the team, so the Treadnought will be equipped with a covered, canopy-like roll
cage and safety harness. These additional safety features separate the Treadnought from other
single rider power vehicles.
1.2 Design Norms
Calvin Engineers are not only expected to design products, but are called as Christians to help
others and show Christ through their work. For these reasons, Treadstone believes the
Treadnought should exhibit the following values:
1.2.1 Transparency
In order for the team’s vehicle to serve the greatest number of people, it must have a design,
especially in terms of controls, that the average user can easily understand and use. Open
communication between the team and customer is an additional aspect of transparency, allowing
for a final product that is consistent with the customer’s desires.
1.2.2 Trust
Making a vehicle that simply functions is one matter; creating a reliable and durable vehicle that
performs as needed and when needed is a more demanding task. The customer needs to trust that
the vehicle will perform as described without worrying about shortcomings or failure.
1.2.3 Caring
Driver safety is a major requirement of the Treadnought’s design; therefore, careful and
comprehensive planning must go into every aspect of the vehicle’s design. This includes
accounting for worst-case scenarios and incorporating safety factors into the design of
Treadnought components. Similarly, reliability is essential to ensuring driver safety beyond
physical injury.
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1.3 The Team
The team is composed of four mechanical engineering students: David Exoo, Preston Phillips,
Matt Wever, and Michael Vriezema (from left to right).
Figure 1: Team Picture
Matt has experience with manufacturing which was useful for production of the vehicle. He also
has experience working with vehicles which helped him lead the group in designing the
Treadnought’s powertrain. Preston and Michael’s internship experiences in quality divisions
have provided them with a unique perspective of the design process, allowing them to weigh the
tradeoffs inherent in the vehicle’s production. With an interest in controls design, Preston was in
charge of creating the Treadnought’s control system, which consisted of brakes and throttle
design, as well as the ergonomics of the control layout. Michael had the most experience
working in the shop, and therefore was responsible for the design, structure, and assembly of the
frame and roll cage. David’s project was the design of the tread assembly and suspension, as well
as brake selection for integration with Preston’s control setup. While each team member had
individual leadership responsibilities, the majority of the design and assembly of the vehicle was
conducted as a team.
1.4 The Class
This project is the main component of the yearlong senior design class, Engineering 339/340. It
not only puts the students’ education and knowledge to the test, but it also tests their problem
solving skills, time management, and communication amongst teammates. Along with this
capstone project, Engineering 339/340 consists of a variety of lectures which provide tools for
the job hunt, as well as preparation for entering a professional workplace environment. This
class aims to teach the students how to incorporate their technical knowledge as well as their
Christian morals and beliefs into their work.
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2 Project Management
2.1 Project Breakdown
The project is divided into four groups, each of which is responsible for a considerable portion of
the final design: powertrain, controls, frame, and tread assembly. Each member of Treadstone
was selected to lead one of the design groups while another member was also involved to create
a system of checks and balances. Other various tasks, such as documentation and research, will
not be assigned, but completed as a team.
2.1.1 Engine & Drivetrain
Matt was in charge of the engine and drivetrain for the Treadnought. Responsibilities included
selecting an engine, clutch, and gearing system that will deliver the appropriate power to the
tracks.
2.1.2 Controls
Preston was put in charge of designing the vehicle’s controls. The objective of this group was to
create a control system that controlled the engine throttle, gear selection, and braking, providing
reliable and intuitive control of the vehicle’s speed and direction. David also assisted in tasks
related to this group.
2.1.3 Frame
Michael was responsible for designing and fabricating a frame that can withstand the weight of
the internal components, the driver, and any additional equipment. An optimal frame design was
developed using finite element analysis to locate possible areas of weakness within the frame.
Research into potential welding materials and optimal frame structure designs was also
conducted. Matt assisted with the FEA and fabrication of the frame.
2.1.4 Tread Assembly
David was assigned the responsibility for fitting the tread assemblies from the old snowmobiles
to the new frame of the Treadnought. This group also was responsible for designing the
necessary suspension system for the previously stated integration. Preston also assisted in tasks
related to this group.
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2.2 Schedule
A Gantt chart was created to layout all necessary tasks needed for The Treadnought to come to
fruition. This graphic neatly illustrates the breakdown of work from the design of our vehicle to
the final product, from beginning to end. Figure 2, which can be found at the top of the following
page, shows an updated schedule (as of December 5, 2012). Tasks associated with the Gantt
chart can be seen in Figure 2.
Figure 2: Gantt Chart
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2.3 Budget
While the primary goal of Treadstone was to create a safe, fun, and durable vehicle to traverse
all-terrains, our team sought to do so at a reasonable cost. To do this, the team needed to weigh
tradeoffs between building parts, repurposing parts, and buying new parts to accommodate both
our design and our budget. The senior design teams were originally given $500 for their project,
but were also asked to create a budget proposal for their project. Through thorough cost analysis
Treadstone estimated that our design would require $2,500 to account for all of the components.
To account for any variance in prices or overlooked components we included a contingency of
20% in our budget proposal, bringing our final estimate to $3,000. Table 1 below shows the
budget proposal for Team 17’s all-terrain vehicle, while Table 2 shows an actual breakdown of
purchases made for the vehicle.
Table 1: Estimated Budget
Purchase Project Use Cost
2 Snowmobiles 2 track systems, throttle $1,000
Steel Tubing Frame $250
Sheet Metal Protective Shell $100
Seat Seat $50 Total Cost
Wheel Stability $50 $2,500
Controls Navigation $150 |
Gears Gearing System $100 |
Engine Power $600 |
Brakes Braking $100 |
Suspension Suspension $100 V
20% $3,000
Estimated Budget
CONTINGENCY
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Table 2: Actual Budget
Upon reception of our actual budget of $2,000 we realized that costs must be cut. More
importantly, Treadstone had to strive to keep the quality the same despite the reduced budget.
This was effectively done within the first week upon receiving our final budget, especially from
large savings from the purchases of our tracks, engine, and frame material. The tracks were taken
from two 1970 Arctic Cat: Jag snowmobiles and were $450 less than expected. In addition, it
was crucial to find two sets of track assemblies from identical snowmobiles such that the
integration of the assemblies to the frame and overall track balance was as close as possible to
one another. Furthermore, we saved nearly $200 on the purchase of the Treadnought’s engine
and the square tubing for our frame was a quarter of what we expected to pay. With these
savings we were able to reduce the cost of our prototype to a point that also provided us with a
small amount for contingency, projecting us to finish senior design slightly within our allotted
budget, with $2.86 remaining to be exact.
2.4 Method of Approach
Due the nature of this project, before any parts could be purchased, appropriate calculations were
done to validate design decisions. For calculations, knowledge of thermodynamics, machine
design, and other mechanical engineering classes proved vital. This knowledge was applied to all
Purchase Project Use Cost
RECEIVED PAID
RECEIVED PAID
RECEIVED PAID Steel Tubing Frame $68.48
RECEIVED PAID 2 Rear Quad Shocks Additional Suspension for Chassis or Rear Wheel $30.00
RECEIVED PAID Transaxle Power Distribution $150.00
RECEIVED PAID 414cc Powerhorse Engine/Power $410.65
RECEIVED PAID Safety Harness Driver Protection $37.99
RECEIVED PAID Painting Supplies Presentation Quality $13.20
RECEIVED PAID Splined Couplings Drive Cog Connection to Transaxle $75.19
RECEIVED PAID Splined Coupling Applied Industrial Technologies $82.90
RECEIVED PAID Dune Buggy Seat Seat $75.00
RECEIVED PAID Brakes & Brake Lines Steering & Braking $21.16
RECEIVED PAID Clutch, Exhaust, Pulley Vehicle Operation $150.00
RECEIVED PAID Extra Paint and Assembly Parts Presentation Quality $99.71
RECEIVED PAID Extra Steel Frame $60.15
RECEIVED PAID Hytrel Spiders Coupling Spacers $72.74
RECEIVED PAID 4 Pi l low Block Bearings Drivetrain Motion $35.36
RECEIVED PAID Brake Handles Handlebars $26.50 Spent
RECEIVED PAID Belts & Pulleys Power Distribution $27.97 $1,997.14
RECEIVED PAID Steel Tubing Handlebars $10.14
$2.86
2 JAG Snowmobiles2 track systems (Possible use: brakes, steering
controls, other controls)$550.00
STATUS
WITHIN BUDGET!!
Actually Spent (Approved for $2000)
REMAINING BUDGET
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aspects of the design: engine, controls, drivetrain, tread assemblies, and frame. Once the
calculations and designs were complete, the assembly of the Treadnought commenced according
to the aforementioned schedule (Figure 2).
2.5 Task List
By combining the schedule laid out by the Gantt chart and following the method of approach, a
list was created with an estimate of hours required for each task. These tasks were then broken
down on a group-by-group basis.
Figure 3: Work Breakdown
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3 Requirements
3.1 Safety
The Treadnought is designed to transport and protect a single operator. Driver safety will be
ensured by keeping the driving compartment clear of moving parts during operation. Similarly,
no exterior parts of the vehicle may exceed a temperature of 140°F, and any parts that would
regularly contact the rider must not exceed 105°F. The rider can be secured in the vehicle with
the addition of a safety harness and surrounded by a roll cage capable of withstanding impact
forces resulting from crashes, rolls, and elevation drops. The design incorporated the weights of
the vehicle, driver, and equipment to ensure maximum protection. For our prototype, a safety
harness and roll cage were not included. However, space was left for safety harness mounts
along the frame as well as connection points to the seat.
3.2 Operating Conditions
In order to achieve all-terrain capabilities, several terrains were analyzed individually to
overcome the unique set of challenges associated with each one. These challenges, dependent on
the terrain, include corrosion and other external damage to the vehicle. The Treadnought shall be
able to function properly when exposed to these different environmental factors. Similarly, each
terrain is accompanied by a unique climate. The Treadnought shall be able to operate within a
temperature range of -10 to 120°F.
3.3 Functionality
As a utility vehicle, the Treadnought is expected to be able to provide reliable and practical
transportation for the operator. The vehicle controls for speed and maneuverability should be
practical and comfortable. The turning radius of the vehicle should be as small as possible to
maximize agility over rough terrain and around obstacles. In addition to a practical riding
experience, the vehicle shall also provide sufficient cargo capacity for tools and supplies. To
accommodate a wide variety of cargo demands, the vehicle must have at least 8 ft3 of storage
space capable of holding 100 lbs., and storage must be easily accessible from a standing position
outside of the vehicle. All of these expectations were kept in mind throughout the design process.
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4 Project Specifications
4.1 Engine and Power Train
4.1.1 System Options
Three different drive train types were considered in the development of the Treadnought:
electric, hydraulic, and mechanical.
4.1.1.1 Electric
Because the design for the Treadnought originally started with a Segway-like body style, a
similar electric powertrain was investigated. Two electric motors would provide simple and
complete control of the two tracks and the vehicles motion. Electric motors are also known for
having very high torque at low RPM. However, when the design changed to include larger,
repurposed track assemblies to cut costs, higher torque and power would be needed to operate
the vehicle, thereby increasing the size and cost of the associated electric motors and battery
system beyond the project’s budget. Including an onboard generator or regenerative braking
system to help boost the range of the battery pack would add to the cost and weight of the
system, and any benefits in vehicle range would be offset by increased infeasibility both
financially and physically.
Figure 4: Electric Motor1
1http://www.walkeremd.com/CEM4106T-Baldor-20HP-3520RPM-3PH-60HZ-256TC-0940M-
p/cem4106t.htm?gclid=CLeav6_22bMCFYs7Mgodz2UALw
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4.1.1.2 Hydraulic
The second design alternative was a hydraulic drive train. Hydraulic systems are used in
construction vehicles and tanks, both of which need high torque, power, and maneuverability.
This system allows for zero point turning by running one of the hydraulic motors in reverse
while running the other motor forward. Having this feature in the Treadnought would be
beneficial for traversing complex terrain. While the hydraulic engine and power train would
provide the necessary power and steering requirements desired for optimal vehicle operation, the
cost of acquiring hydraulic components is restrictive. Hydraulic systems are also difficult to
work with when compared with electric or purely mechanical systems. Figure 5 below shows an
example of a typical hydraulic engine.
Figure 5: Hydraulic Motor2
4.1.1.3 Mechanical
The third engine and power train option that was considered was a mechanical gearing system
powered by an internal combustion engine. While the mechanical system can’t provide the zero-
turn capabilities as simply as hydraulic or electric systems can, it is significantly less expensive,
and relatively simple to troubleshoot and repair. The mechanical system will also provide an
increased vehicle range, providing both increased travelling distance and heavy-duty operating
time when compared to the electric system. Figure 6 shows an example of an internal
combustion engine. The hydraulic and internal combustion engines look quite similar, as
2 http://www.tradekorea.com/product-detail/P00078006/KJI_LK1R__HYDRAULIC_ENGINE_PUMP_.html
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hydraulic engines are typically internal combustion engines that drive hydraulic pumps that have
been incorporated into the engine design.
Figure 6: Briggs and Stratton Engine3
4.1.2 Selected System
To select the appropriate drive train, Treadstone created a decision matrix that weighted and
quantified a variety of design considerations to determine the best powertrain. Table 3 shows the
decision matrix used to select the desired power train. As budget constraints were a major factor
in the vehicle’s design, the mechanical powertrain had a distinct advantage, although it fell short
in other categories.
Table 3: Decision Matrix
3 http://www.briggsandstratton.com/engines/other-engines/
1-5 Scale
Co
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Wei
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Ran
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Du
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Sim
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ity
Mai
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nan
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Size
Tota
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Importance 7 6 5 4 3 2 1
Electric 3 4 1 2 5 4 4 85
Hydraulic 2 2 4 3 2 2 2 70
Mechanical 4 3 4 3 2 3 2 92
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4.1.3 Engine Selection
No vehicle design, no matter how sophisticated, can succeed if the power demanded cannot be
generated. Therefore, engine selection was critical for this project. As mentioned previously,
internal combustion engines were considered rather than electric motors. Many different engine
factors were considered, including power, torque, operating RPM, size, weight, fuel type, and
cost. One of the requirements for the vehicle was a small turning radius and zero speed turning,
which would require a large amount of torque. Equation 1 was used to calculate the torque
associated with turning the vehicle around a stationary track.
∫
(Eqn. 1)
Equation 1 was created to estimate the torque requirements of the vehicle by using the friction
force experienced by a single track (µFN), the contact area of the track (A), the width of the track
(w), and the length of the track in contact with the ground (Lt).
Engines were assessed based on their power and torque capabilities as well as the projected
gearing requirements needed to convert and transfer the power to the tracks. Each engine’s price
was also evaluated alongside their performance. Equation 2 is the general form of the equation
used to calculate gear ratios.
(Eqn. 2)
Equation 3 calculates the gear ratio using the torque required to meet the zero-speed turning
requirement (Tt) and the peak torque supplied by the engine (TE). This is the overall gear
reduction of the system, which will be achieved through a series of 3 sub-reductions: clutch
reduction, transmission reduction, and coupling reduction.
Achieving high torque capabilities and high vehicle speeds simultaneously comes at a cost, and
with a limited budget, Treadstone determined that not getting stuck was more important than
moving quickly, and hence selected components that would provide extra torque at the cost of
reduced speed. Therefore, although there is no top speed requirement for the vehicle,
Treadstone’s design focuses on meeting the worst-case torque requirements, and then optimizing
that design scenario to maximize top speed while maintaining the high torque capabilities.
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Four engines were considered for the Treadnought, and are explored in greater detail below: a
snowmobile engine, a Kohler diesel engine, a Briggs and Stratton lawnmower engine, and a
PowerHorse engine.
4.1.3.1 Snowmobile Engine
The first engine Treadstone considered was the engine from one of the Arctic Cat snowmobiles.
Adapting the snowmobile’s engine, clutch, and transmission would help keep costs down as it
would prevent buying individual and additional components. Figure 7 shows an example of a
snowmobile engine.
Figure 7: Snowmobile Engine and CVT
Additionally, the components are already designed to work together, so interconnection of
components in the drivetrain becomes an easier task. However, upon further analysis, the team
determined that the snowmobile engine would not be a viable option. Although the power and
torque curves for engines vary between models, typical snowmobile engines produce maximum
power within a narrow and high RPM range (5000-9000 RPM) (Figure 8).
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Figure 8: Power and Torque Curves4
Maximum torque is produced at a lower RPM, which is often on the edge of the power curve
which declines steeply. Even though snowmobile engines can produce in excess of 50
horsepower, depending on the model, the gearing needed to take advantage of that power at high
RPM and reduce it to high torque, low RPM, would be difficult and expensive. The gear ratio
calculations reveal reductions of over 90:1, which would require considerable and expensive
reduction steps within the power train. Most snowmobiles use belt style, continuously variable
transmissions, and although these are very efficient, they are not ideal for high torque
applications as the belts are prone to slipping. For these reasons, repurposing the Arctic Cat
engines was eliminated.
4.1.3.2 Kohler Engine
Kohler produces many gas and diesel engines ranging in size and style. Two different Kohler
engines were considered for use in the Treadnought. The first engine, an 18.8 HP Kohler Diesel
Engine, is capable of producing 31.1 ft∙lbs of torque at 2200 RPM. Figure 9 shows the power
curve for this engine.
4http://www.homebuiltairplanes.com/forums/2-stroke-aircaft-engines/2571-proven-440-setups.html
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Figure 9: Kohler Diesel Power Curve
The second engine, an 18 HP Kohler Gas Engine, is capable of producing 32.2 ft∙lbs of torque.
Although the power curve for this engine could not be found, this engine was assessed for its
comparable performance specifications yet lower price when compared to its diesel colleague.
Using these specs in combination with the torque demand calculations, a gear ratio of 22:1 was
computed for zero speed turning. These gear ratios are much more reasonable and attainable than
those calculated for the snowmobile engine. However, both engines are very expensive, ranging
from $1,500-2,000 for the gas engine and $3,000-5,000 for the diesel engine. Purchasing a new
engine of this size is not a viable option.
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4.1.3.3 Briggs and Stratton Engine
The third option the team considered was a 12 HP, Power Built Briggs and Stratton engine.
Figure 10: 12HP Briggs and Stratton Engine5
This engine was significantly smaller than the Kohler engines mentioned earlier. However, using
a smaller engine helps reduce vehicle weight which will decrease the torque demands of the
system. The gear ratios calculated for this engine would be over 60:1 for zero-speed turning.
This range of gear ratios would be slightly more challenging to obtain than the range required by
the Kohler engines, but could have been accomplished with proper gearing and transmission
selection. The cost of this engine was the most attractive feature of this engine, as it is already
owned by Calvin’s engineering program; the only costs would be those involved with returning
the engine to proper operating condition. However, because it had a vertical shaft, which would
complicate the gear train when compared to a horizontal shaft engine, the engine was eliminated.
4.1.3.4 PowerHorse Engine
After eliminating the three previous options, Treadstone pursued acquiring a used horizontal
shaft engine from A1 Mowers in Holland. However, during this process, Phil Jasperse, the shop
manager, introduced the team to Northern Tool and Harbor Freight. Both websites offered
affordable engine options. After careful consideration of performance specifications and
associated price points, the team decided to purchase a 414cc PowerHorse engine that produced
5 http://www.northerntool.com/shop/tools/product_200514250_200514250
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18 ft-lb of torque. Although this engine was not free, it only cost $420, which fit Treadstone’s
budget perfectly. The gear ratio calculated to achieve zero-speed turning requirements was 35:1.
Figure 11: PowerHorse Engine6
4.1.4 Clutch Selection
The next component in the power train is the clutch, which provides a means of connecting and
disconnecting the engine from the rest of the powertrain. Reduction is also possible at this stage.
4.1.4.1 Continuously Variable Transmission
The first system considered was the CVT from one of the Arctic Cat snowmobiles. CVTs
eliminate the need for a clutch by shifting through large, essentially infinite, range of gear ratios
by adjusting shape at different RPM. At low RPM, the CVT disengages completely, eliminating
the need for a clutch altogether. Repurposing the CVT would require changing the springs and
shape response of the CVT, which was designed to operate at the higher RPM range of the
snowmobile engine. In addition, the size of the CVT was also a concern, as it measured nearly 11
inches in diameter, and 4 inches thick. The team concluded that this was not a viable option.
4.1.4.2 Centrifugal Clutch
Treadstone decided to acquire a centrifugal clutch for use in the Treadnought. Centrifugal
clutches engage at certain a certain RPM, which can be altered by changing the springs within
the device if necessary. However, for simplicity, the team purchased a clutch that would engage
6 http://www.northerntool.com/shop/tools/product_200480407_200480407
25
at just above the engine’s idle speed, which eliminated the need for clutch modification. The
clutch selected, although rated for 8 HP engines, was guaranteed to function properly by Rick
Harper, the owner of A1 Mowers in Holland, who has used the same clutch in his 20 HP
application for years without issue. The 3 inch pulley Comet clutch is also significantly smaller
than the snowmobile’s CVT, and by purchasing the 8 HP version from A1 Mowers for $90, the
team saved money, as the 12 HP version, available online, was nearly twice the price.
Figure 12: Centrifugal Clutch
4.1.5 Transmission
4.1.5.1 Hydraulic
Hydraulic drive components are common in industrial applications, such as farm and
construction machinery. They are also common in skid-steered and differential drive vehicles.
For this reason, hydraulic transmissions and motors were considered for the Treadnought’s drive
train. Figure 13 shows an example of a hydrostatic transmission.
26
Figure 13: Hydrostatic Transmission7
However, hydraulic components have many disadvantages. They are complex and present
additional complications not present in mechanical drives, such as fluid leaks. The larger
deterrent is price: hydraulic pumps and motors range from $300-1,0008, and used transmissions
range from $200-3009. For these reasons, Treadstone decided to pursue other options.
4.1.5.2 Belt and Chain Drive
Another option the team considered was a belt drive with an idler pulley, connected to a chain
drive. In this context, belts and chains serve similar purposes. Both can transmit the same
power. However, a belt is better suited to transmit this power with high speeds rather than
torque. The chain, then, is a better fit for transmitting the power through torque. The belt drive
would be connected directly to the engine, and would be moving at very high speeds. The size
of the pulleys could be used to turn down the speed of the drive before the chain drive. The
chain drive could then transfer more of the power through torque, and potentially turn down the
speed of the drive even more. A very basic gearbox after the chain drive could then make the
final reductions needed before the treads.
7http://www.toro.com/en-us/homeowner/mowers/zero-turn-mowers/pages/model.aspx?pid=timecutter-mx4260-
74640 8 http://www.grainger.com/Grainger/HALDEX-BARNES-Hydraulic-Gear-Pump-1DBE2?Pid=search
9http://www.ebay.com/sch/i.html?_trksid=p5197.m570.l1313&_nkw=hydraulic+transmission&_sacat=0&_from=R
40
27
To achieve differential steering, two pulley systems would be connected to the driveshaft of the
engine. Each pulley would drive its own belt. The pulley on the other end of the belt would
power the chain drive. To provide the belt with the tension it needs, an idler pulley would be
used on each belt, with the driver in control of said idler pulleys. When fully engaged, the belts
would deliver the power from the engine to the treads in equal amounts. If the driver lets off of
one of the idler pulleys, the belt would start slipping. This decreases the power transference to
one of the treads, turning the vehicle. Figure 14 shows a diagram of the proposed belt and chain
drive assembly. The belt drive is in red, and the chain drive is in green.
Figure 14: Belt and Chain Drive Schematic
After further review of the concept, the team determined that decreasing belt tension would not
provide a linear correlation with track speed. Rather, the drives would function as ON/OFF,
which would result in either a very jerky ride, or an inability to steer at all. The team decided to
pursue differential transmissions, or transaxles, instead.
4.1.5.3 Transaxle
Transaxles function as both transmissions and differentials, gearing down drive shaft revolutions
and allowing variable speed between two axles. The team decided to pursue lawn mower
transaxles due to the multiple gears provided and the ability to handle engines similar in size and
power to the one selected. Transaxles often come with a reverse gear as well, which is a very
28
important feature for any vehicle that requires any sort of agility or maneuverability. Actual gear
ratios vary from model to model, and therefore would be determined after the components have
been purchased. Figure 15 shows an example of a lawn mower transaxle.
Figure 15: Lawn Mower Transaxle
4.1.5.3.1 Peerless Riding Mower Transaxle
Two main transaxles were considered for the transmission and differential needed to achieve the
drive and steering envisioned for the vehicle. The first was found in Calvin’s storage closet: a
9000 series Peerless transaxle from a riding lawn mower. The gear ratios provided by the
transaxle were in the desirable range for our 12 HP engine (4 gears ranging from 20-60), but the
output shaft was only ¾ inch in diameter, which was cause for concern as all the other shafts of
the vehicle were 1 inch in diameter. Before calculations were conducted to assess the power and
torque capabilities of the transaxle, a fellow student, Lake Chen, forwarded information from
Peerless regarding the functional limits of the transaxle. The Peerless transaxle, though appealing
as it would be available at no additional cost to the team, was not an acceptable solution to our
demands as it was only rated for 220 ft-lbs of torque and an input speed of 2000 RPM, whereas
the demands for the transaxle were ~600 ft-lbs and an input speed of 3500 RPM.
29
Table 4: Peerless Gear Ratios
Figure 16: Peerless 9000 Transaxle
4.1.5.3.2 Cub Cadet Transaxle
The second option, a used lawn tractor transaxle from A1 Mowers, was considered. Rick assured
us the heavy-duty transaxle from the old Cub Cadet lawn tractor would be able to handle the
large torque projected by our calculations, as well as the input speed of 3500 RPM. The transaxle
cost $150 dollars, which was a reduced price as the transaxle had a broken brake. The broken
brake was non-essential for the Treadnought’s operation, as two additional brakes will be used
after the transaxle for both braking and steering operations. This transaxle also offered gear
ratios ranging from 20-60.
1st Gear 68:1
2nd Gear 34:1
3rd Gear 19:1
Reverse 42:1
Peerless 9000
30
Table 5: Cub Cadet Gear Ratios
Figure 17: Cub Cadet Transaxle
4.1.6 Snowmobile Driveshaft Coupling
The final part of the powertrain is the coupling between the transmission and the snowmobile
drive shafts. Figure 18 shows one of the drive shafts salvaged from the Arctic Cat snowmobiles.
Figure 18: Drivecog and Shaft
Four different coupling techniques were considered: belt drive, gearing, chain drive, and straight
coupling.
1st Gear 58:1
2nd Gear 28:1
3rd Gear 19:1
Reverse 24:1
Cub Cadet
31
4.1.6.1 Belt Drive
The incorporation of a belt drive would provide an inexpensive and simple method of coupling
the two shafts while also providing the opportunity for further reduction. However, with such
high torque being transmitted, the chance for belt slippage is high and therefore makes a belt
drive undesirable.
4.1.6.2 Gearing
Meshed gears were considered as they would provide further reduction and be able to handle the
high stresses of the high torque at the track end of the power train. However, issues of potential
misalignment and lubrication concerns quickly eliminated this as a viable option. The cost of
acquiring meshed gearing is also quite high.
4.1.6.3 Chain Drive
A sprocket and chain drive was a serious contender for the end-of-line coupling system.
Providing opportunity for variable reduction through the use of hubbed sprockets, the chain drive
would also be able to handle the stresses and forces associated with the high torque situation, all
without slipping. However, upon reviewing the calculations, the team determined further
reduction after the transaxle was unnecessary.
4.1.6.4 Straight Coupling
Because additional reduction was determined unnecessary, the team considered different
methods of directly coupling the two shafts.
4.1.6.4.1 Universal Joint
The first method of direct coupling that was considered was the insertion of a universal joint
between the two shafts. This joint would allow for any degree of misalignment, either resulting
from the manufacturing process or from strain experienced during operation. This would also
handle the torque without issue. However, universal joints are incredibly expensive, and were
thereby eliminated as a viable option.
4.1.6.4.2 Rigid Coupling
The second method that was considered was the purchasing of rigid couplings. These would
mate the two shafts together with a solid metal coupling capable of handling the torque required.
However, using these couplings would require near perfect alignment of the shafts, which would
32
be difficult to achieve in the manufacturing process, and nearly impossible to maintain during
high-stress operating conditions.
4.1.6.4.3 LoveJoy Jaw Coupling
The team eventually decided that Jaw-type couplings provided a good balance between strength,
flexibility, and price. LoveJoy, the industrial leader in couplings, provides a large and wide
selection of couplings. Calvin’s metal shop had 2 matching sets of L95 1 inch bore couplings.
However, the snowmobile drive shafts do not have straight bores, but rather 15T splined shafts.
To make the L95 couplings work, the shaft would have to be cut and machined to fit the bore
properly. To avoid machining the shaft in attempts to maintain the integrity of the snowmobile
parts, the team pursued acquiring jaw hubs that mated with the splined shafts. LoveJoy makes
hubs that mate to 15T 1 inch splined shafts in the L100 coupling, so the team purchased two
splined hubs and acquired one standard 1 inch bore hub from Calvin, and the second hub was
donated by Innotec. The L100 couplings are also thicker than the L95 couplings are therefore
better equipped for handling the torque at the tracks. L-100 couplings can also handle twice as
much torque (1134 in-lbs) as the L-95 couplings that Calvin has in stock already. The jaw hubs
also provide both linear and angular misalignment, which is an added benefit for both
manufacturing and operation.
Figure 19: LoveJoy Jaw Coupling
4.1.6.5 Bearings
Connecting the drive train to the rest of the frame is best accomplished through the use of
bearings, which provide accurate alignment and reduce the friction of the system. Treadstone
was able to acquire 4 heavy duty 1 inch bore bearings for mounting the snowmobile drive shafts.
These were selected instead of the bearings and mounts pulled from the snowmobiles, as the
snowmobile bearings were worn and the press fit mounts more complicated to use than the
pillow blocks on the heavy duty bearings.
33
Figure 20: Pillow Block Bearing10
4.1.7 Final Powertrain
A final image of our powertrain, excluding the PowerHorse engine, can be seen in Figure 21.
This picture shows the connections between the bearings, drivecogs, couplings, and brakes to the
transaxle shaft.
Figure 21: Final Powertrain
4.2 Controls
With all of the attention that the powertrain received, it would be a shame for the operator to not
be able to do anything with it. This is where the controls for the Treadnought come in. This
section is split into three main sections: brakes, throttle, and frame integration.
4.2.1 Brakes
Throughout the design process, several possible choices came to light for braking our vehicle.
The options boiled down to hydraulic versus disc brakes and hand versus foot operation.
10
http://www.thebigbearingstore.com/servlet/the-9/1%22-Pillow-Block-Bearing/Detail
34
4.2.1.1 Hydraulic Brakes
One braking option for the Treadnought was hydraulic brakes. Hydraulic brakes are widely used
in the ATV, motorcycle, and car industry. Their main features include a master cylinder, brake
lines and fluid, and calipers. The main advantage to using hydraulic brakes is that a very large
mechanical advantage can be obtained using the cylinders to create a pressure in the brake fluid
to transfer the force rather than a cable. The fluid pressure varies with the square of the applied
force rather than just linearly. A brake cable can also kink and have trouble transferring the
applied force, whereas a fluid line does a much better job at force transference. The main
drawback to hydraulic brakes is the price and maintenance. Hydraulic brakes are hard to come
by used, and are very expensive new, a large red flag for a project on a budget. There was a pair
of hydraulic brakes from an electric car available to the team from Calvin. They would do the
job, but it would take effort to get them into working condition. As they were also very
oversized, both physically and in braking capacity, the team decided to pursue other options.
Smaller hydraulic brakes would be optimal for a production version of the Treadnought, but
were deemed infeasible for the prototype design.
Figure 22: Hydraulic Brakes
4.2.1.2 Disc Brakes
Disc brakes were ultimately used in the design of the Treadnought because of their simplicity
and availability. Implementation of disc brakes also only requires a few parts: rotors, calipers,
and brake lines. For the Treadnought, the team used the rotors from the Arctic Cat snowmobiles
acquired earlier in the project. The calipers also came from the snowmobiles, although minor
35
machining was needed to separate the caliper system from the crankcase. The disc brakes are
much easier to maintain than hydraulic brakes, as they are simpler in design, and their price
made them an acceptable option for the Treadnought prototype.
Figure 23: Disc Brakes
4.2.1.3 Testing
The first thing done the team did was collect data to find braking forces that the design should
aim for. To find these, a vehicle was driven at 20 mph and stopped at both normal and fast rates.
Times were taken for the period of deceleration and plugged into equations to find values for
deceleration. The braking force values were then obtained from the deceleration values.
Dimensions were taken from the hydraulic brakes available to Treadstone in order to see how
they might work on the Treadnought. The solutions showed that the required applied forces
were very low, a max of just over 6 lbs. per foot, assuming hard braking and wet rotors. 6 lbs.
was an extremely small number for a max force.
The snowmobile disc brakes were then tested to see how much braking force they could
generate. This was achieved using a series of masses to hold the brake rotor and pad as rigid as
possible while pulling the other side with force gage until the pads could no longer clamp the
rotors. This test was then repeated for wet conditions yielding a braking force of 114 lbs for dry
conditions and 72 lbs for wet conditions. Because the lowest calculated force required for a
gradual stop from 20 mph is 45.8 lbs, and the fact that the Treadnought’s maximum velocity is
half of the velocity calculated for, our actual braking values for both wet and dry conditions
36
indicate that our brakes will function properly for both braking and turning operations for the
Treadnought prototype. The Treadnought would not be going as fast as a production vehicle
would. With dry rotors, the Treadnought would still have 80% of the production vehicle’s
approximate braking power. Even with wet rotors, the Treadnought can easily get the average
braking force the team deemed necessary. These calculations helped ensure that using
snowmobile brakes would provide the necessary braking capability for the prototype.
4.2.1.4 Operation
We originally imagined our vehicle operating with two separate brake pedals, one for each track,
which would also steer the Treadnought. However, a couple revelations changed this decision:
The first was that the operator was already going to have to have an input for throttle, and adding
two more inputs for brakes would be a bit much in addition to shifting. The second revelation
was that the force required to apply the brakes to the tracks could be attained from grip force. By
combining these two realizations, the idea to use handlebars for braking while incorporating the
throttle into the design of one of the handlebars was born.
4.2.2 Throttle
As previously discussed, the decision to shift into using handlebars for braking while using one
of them for throttle was determined to reduce the number of inputs that operator would have
during operation. In our case, one handlebar was mounted directly to the frame, and the other
was flattened at one end to be bolted down and serve as a throttle arm. Both tubes were bent to
make the controls more ergonomic. A cable connected to the throttle arm which then was set in
place by a screw on the engine’s throttle.
4.2.3 Frame Integration
When designing the Treadnought’s controls and their integration into the frame, the decision was
made to create a handlebar mount plate that would serve multiple purposes. First, the plate would
serve as a surface for our seat to bolt to. Because of this, the mount plate allowed the handlebars
to be on both sides of the driver in comfortable positions. The mount plate was cut to size and
had reinforced by angle iron. These also served as locations for the handlebars to be mounted.
Pictures of the contrast in integration of the handlebars can be seen in Figures 24.
37
.
Figure 24: Brakes and Throttle
4.3 Frame
4.3.1 Body
Using 3-D sketching tools in SolidWorks, a wireframe sketch was created that represented the
frame of the Treadnought. Dimensions were taken from the acquired track assemblies to locate
screw holes for attaching the treads to the frame, and were subsequently used to dimension the
wireframe. SolidWorks has a great feature for creating space frames. Once a wireframe sketch is
finished, the program can generate a steel tube around the sketch using the “weldment” feature.
Then, a cut list was generated, which gave the lengths and cut angles of each section of the
frame, which vastly simplified the fabrication process.
Upon completion of the general design, the structural frame was analyzed under rest conditions
and maximum torque conditions. These two scenarios provided areas of high stress and
deflection, which were used to further adjust the frame to reduce weight by eliminating members
in low stress areas, and increased strength/reduce deflection by adding members in other areas.
The maximum deflection measured under maximum torque loading was about 15 mm at the
tread assemblies, and 10 mm at the drive shaft mounts.
38
Figure 25: Frame FEA
Although not ideal, this was an acceptable amount, as the Lovejoy couplings provide a ½ degree
of angular misalignment. When multiplied by the shaft lengths on either side of the couplings,
the couplings are able to function properly with approximately 18 mm of mount deflection,
nearly twice the projected deflection. The maximum stress recorded under this worst-case
scenario was approximately 40 ksi. The yield strength of the metal is 50 ksi, and the tensile
strength is 60 ksi, giving a safety factor of 1.25 and 1.5 respectively. Under normal operating
conditions, when the tracks are not completely restricted, the safety factors are well above 2,
which proves the frame’s integrity.
The frame of the Treadnought was designed using 1 1/4” square tubing. The main difference
between the prototype frame design and the production model’s design is the absence of a roll
cage. Because the Treadnought is a proof of concept vehicle, the team decided to focus on the
performance and operation of the vehicle, rather than the integration of a roll cage. Time and
money constraints also played a factor into this decision.
39
Figure 26: Frame Fabrication
Treadstone spent a lot of time in the metal shop for frame fabrication and modification of parts.
One piece of additional fabrication was the redesign of the exhaust system. Because of the
orientation of the engine on the vehicle, the exhaust had to be modified to keep it from blowing
directly towards the operator. Because of this, a different muffler was purchased which allowed
alterations to be made to divert the exhaust away from the gas tank and the operator. The throttle
control and shifter needed to be altered as well. Proper support for the throttle cable and pedal is
important for constant control of the vehicle, so fabricating a sturdy throttle support was deemed
necessary. The transaxle that was purchased also needed alteration, as it had a shifter built into it
for changing gears, but was oriented poorly when mounted in the Treadnought’s frame.
Therefore, the shifter was cut and redirected to a more accessible location.
4.3.2 Powertrain Mount Plate
A mounting plate for the engine and transaxle was also needed. This plate would be attached to
the back section of the frame. Because weight is a big issue with the Treadnought, FEA analysis
was done to determine the thinnest plate that could be used without failure. Figure 27 shows the
FEA completed on the selected 1/8th
inch plate. The mount plate was also used to mount the
tensioner pulley. The tensioner is necessary for the belt to operate as effectively as possible.
Without it, the belt would slip during operating, or fail to drive the pulleys altogether.
40
Figure 27: Mount Plate FEA
4.3.3 Rear Wheel Mount
Initially, the Treadnought had been designed without a rear wheel in order to concentrate the
entire weight of the vehicle over the tracks in order to maximize traction. However, the vehicle
was prone to tipping backwards without an operator seated in the vehicle. Although the vehicle
was balanced with an operator, the tipping could still occur during hill climbs or complex terrain
maneuvers, which would cause the brake rotors to hit the ground. To prevent this issue, a large
caster was mounted on the back of the vehicle. This wheel provides additional support and
protection of the powertrain without taking away from turning ability and minimally affecting
vehicle traction. This design addition was reminiscent of one of the preliminary vehicle designs,
and therefore was easy to integrate as the idea had already been developed. This addition also
provided the opportunity to expand the functionality of the vehicle by integrating a hitch mount
into the caster support frame. Figure 28 shows the Treadnought’s caster and hitch additions.
41
Figure 28: Rear Wheel
4.4 Tread Assembly
4.4.1 Tracks
Perhaps the most crucial components for the Treadnought were the tracks. With a larger budget,
the team could have had tracks custom-made for the Treadnought. A similar option was to
purchase a set of tracks that would be used on another production ATV. This too would have
been extremely expensive. These tracks are very nicely built, which is a must for a production
vehicle, but because the Treadnought is more a proof-of-concept vehicle, a more inexpensive
route pursued. With some research, Treadstone determined that the best route was to obtain a
pair of older snowmobile, even though finding similar or identical snowmobiles could prove to
be very difficult. However, there were upsides to this method. The first was that because
Treadstone only needed the tracks and track assemblies, the snowmobiles could be in various
states of disrepair, as long as the tracks were intact. This was the main advantage of this option
as our budget was a huge driver in our decision making, and broken down snowmobiles would
be significantly less expensive. Another advantage was that other parts from the snowmobiles
could be salvaged, such as brakes and controls. The team ended up finding a Craigslist posting
for a couple older, identical snowmobiles. It turned out that the man who posted the ad collected
snowmobiles, motorcycles, and other similar vehicles. We told him our situation and he guided
42
us to different pair of snowmobiles than the ones he had posted about. We were able to walk
away with two identical Artic Cat snowmobiles from the late 1970’s for $550.
4.4.2 Additional Suspension
After assembling all of these components onto the frame, one of our fears was confirmed: the
Treadnought’s rear suspension was too weak; because we turned the tracks around to facilitate
the drive cog in the rear of the vehicle, the suspension that held up the majority of the
snowmobile’s weight was now situated in the front, leaving the weaker suspension in the back.
To alleviate this issue, an additional suspension coil was added to the rear suspension. Mounts
were fabricated by plasma cutting out some of the track assembly and replacing removed
sections with angle iron. The brackets were modeled after the brackets that held the
snowmobile’s original suspension components. Then, the springs were preloaded and bolted into
place. A picture of the final track assembly, with the added suspension can be seen below. The
existing dashpot and springs can be found on the left side while the additional spring is located in
the middle of the right side of the figure.
Figure 29: Final Track Assembly
43
5 Prototype Testing
5.1 Initial Testing
Testing began as soon as the powertrain was bolted into the finished frame. The initial testing
was with the vehicle suspended off the ground (Figure 30).
Figure 30: Suspended Test
This allowed the team to test the brakes and the variable speed turning for basic functionality,
and to assess potential misalignment from the manufacturing process. The vehicle functioned as
expected, and minor misalignment was corrected by adjusting the mount positions of the pillow
block bearings.
Figure 31: First Road Test
The second test was the first road test (Figure 31). Again, basic functionality was evident,
although it was noted that the turning and braking was unresponsive. The team remedied this by
44
adjusting the brake handles and tightening the controls. After this initial test of functionality was
complete, more tests were done, this time on rougher terrain. The team did not want to push the
vehicle too hard before the design night, so the tests were limited to loose woodchips and grass
rather than dirt piles, gravel, and mud. The Treadnought was driven up grassy slopes and
through softer ground near the baseball and lacrosse fields. The Treadnought handled well under
these conditions, although it was noted that the belt coming from the clutch was too loose. This
was adjusted by shortening the spring in the tensioner arm, which increased the belt tension,
resolving the issue.
5.2 Additional Testing
After Senior Design Night, the team wanted to put the vehicle through more rigorous tests.
Some additional tweaking had been done to the engine to open the throttle and maximize power.
The brakes and throttle controls had been tweaked and were working to the best of their ability,
so controlling the vehicle was much simpler, and turning response was noticeably quicker. The
Treadnought was driven through the roughest terrain available on Calvin’s campus: The first
test was conducted in the dirt construction zone in a section of the Gainey Athletic Complex
(Figure 32).
Figure 32: Dirt Test Drive
The dirt had been left very rough by bulldozer wheels, and also had an area with standing water
and mud that still had not dried out from the previous week’s rain. The vehicle was able to go
through the standing water easily, and went over the dirt mounds without issue. However, after
these tests, the belt and pulleys were very warm and were slipping due to the expansion of the
belt. For the second round of terrain testing, a smaller belt was used to improve tensioning.
45
The second round of testing was conducted back by the baseball field to see how much better it
performed with the optimizations and to further push the vehicle by driving through a deep mud
pit (Figure 33).
Figure 33: Mud Test Run
The mud in the swamp was deep to the point that the back wheel was completely submerged.
The wheel was also dragging a lot of reeds and other things with it. The Treadnought would get
stuck occasionally from the overload of dead grass and reeds, but switching to a lower gear
allowed it to get out under its own power every time. The same amount of torque and power was
also exhibited during a hill climb test in which the Treadnought was able to climb all tested hills,
up to a 40o incline.
5.3 Quantifiable Results Testing
To test the hitch and tow capacity, the Treadnought was strapped to a 1997 Mazda B2300. The
truck, which was put in neutral and has a curb weight of almost 3000 lbs, was towed easily. The
truck also put into gear for a bigger challenge, but the Treadnought did not have the weight it
needed to transfer the torque to the ground, as the tracks slipped easily on the grassy turf. The
team also tried towing the truck up a paved hill, but again, the lack of weight, and traction,
prevented success in this category.
46
Figure 34: Towing Test
5.4 Potential Modifications
On the way back to the Engineering Building, the vehicle stopped moving. With some
investigation, the tighter belt had worn right through the driven pulley and begun to shred itself
(Figure 35).
Figure 35: Pulley Failure
As nice as the extra grip had been, it was likely too much and had done in the belt drive. To
immediately remedy this problem, the team purchased a cast iron pulley to replace the cast
aluminum pulley that had been worn through. The belt drive has been one of the weak points of
the vehicle operation, and in a second iteration of the Treadnought, there would likely be a chain
drive. Chain drives are much more expensive, but easily beat out belt drives in performance and
transfer of power.
47
6 Business Plan
6.1 Market Competition
In today’s market, there is nothing like the Treadnought. However, there are some comparable
vehicles, such as the common all-terrain vehicle (ATV), snowmobile, and a relatively unknown
product called the DTV Shredder. These are the products which we will compare the
marketability of our product to.
ATV’s come in all sorts and sizes to cater to the individual needs of the customer. On average,
an ATV that would have similar capabilities as the Treadnought, in terms of traversable terrain
and carrying capacity, would cost approximately $4,000-$6,000.
The DTV Shredder, seen below in Figure 36 produced by BPG Werks is a product similar to an
off-road Segway designed for extreme sports’ use with some models specialized for military use.
Due to the innovative qualities of the DTV Shredder, the typical selling price is $5,000. The
DTV Shredder can be controlled remotely, reach speeds of up to 30 miles per hour, and weigh
only 200 lbs. Additionally, using a 196 CC, 4-stroke, 13 horsepower engine, the DTV Shredder
can get approximately 30 miles per tank and tow 300-500 lbs., depending on operational slope
and terrain.
Figure 36: DTV Shredder11
11
https://bpgwerks.com/
48
6.2 Break Even Calculations
To develop a production cost estimate, research was done to create approximate costs for
annually fixed costs and variable costs that vary according to production volumes. Things such
as rent, salaries, insurance, patents, tools, and design time made up the fixed costs, whereas
variable costs are approximated from our actual budget. Below is a summary of total costs as
sums of both fixed costs and variable costs.
Table 6: Production Cost Estimate
By taking these costs into account, break-even analyses were calculated assuming an annual
vehicle production rate of 500 and 1,000 units, resulting in a break-even price of $4,143 and
$3,561, respectively (Table 7). Table 8 builds upon the break even analyses and shows an
estimated profit analysis for each case, resulting in a profit margin of 4.8% for case A and 6.6%
for case B.
Table 7: Break Even Analysis
Annual Fixed Cost Cost NOTES
Rent $187,500 25,000 sq ft @ $7.5/sq ft
Salaries $200,000 5 people @ $50,000
Design Time $50,000 prototype design cost Total Cost
Insurance $28,250 10% of building/equip cost per year $510,750
Patent $25,000 vehicle design patent
Tooling/Machinery $20,000
Variable Cost Cost
Raw Materials $192 steel and paint
Parts $1,787 all other purchases
Labor $500 Total Cost
Shipping/Handling $200 $2,979
Marketing $100
Warranty $200
Production Cost Estimate
Annual Production 500 1000
Annual Fixed Costs $581,750 $581,750
Cost per Vehicle $2,979 $2,979
Total Annual Cost $2,071,250 $3,560,750
Break Even Sale Price $4,143 $3,561
Break Even Analysis
49
Table 8: Profit Analysis
A detailed Business Plan can be found Treadstone’s website12
, including a projected income
statement, cash flow analysis, balance sheet, and other financial documents.
12
http://www.calvin.edu/academic/engineering/2012-13-team17/home_page.html
Sale Price $4,500 $4,000
Annual Sales $2,250,000 $4,000,000
Annual Costs $2,071,250 $3,560,750
Earnings $178,750 $439,250
Tax Rate 40% 40%
Taxes $71,500 $175,700
Net Income $107,250 $263,550
Profit Margin 4.8% 6.6%
Profit Analysis
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7 Conclusion
This project was invaluable. In addition to expanding the team’s knowledge of motor vehicle
components and operation, a topic that hadn’t been explored in class as much as other topics,
building the Treadnought gave real, hands-on experience. Each team member acquired
fabrication skills such as welding and machining. The project also taught the importance of time
and time management, and the important truth that everything takes much longer to do than
predicted, especially for prototype fabrication. The impact of finances was another concept that,
although taught in the classroom, was not a truly acknowledged design factor until the team was
tasked with purchasing actual components for the Treadnought prototype. And finally, creating
the Treadnought reinforced the importance of teamwork, communication, and cooperation; four
people working independently could not have achieved what the members of Treadstone
achieved by working together.
As with any prototype, the Treadnought is not perfect. A few issues remaining in the prototype
are belt tensioning, belt and pulley burnout in high torque applications, and slipping of the
throttle cable. Tensioning can be resolved by using a smaller belt, or tightening the tensioner arm
as needed, which also helps remedy the problem of belt burnout. An unexpected result of the
swamp testing was the burnout of the transaxle drive pulley. To resolve this issue, the team
recommends upgrading from cast aluminum to cast iron pulleys. Although having problems is
not ideal, having the most probable failure modes concentrated in a low cost section of the
powertrain is preferred, as replacing a belt or pulley is easier and less expensive than replacing
an engine or transaxle. The throttle issue is also a minor problem, and can be fixed by attaching
the throttle cable to a longer throttle lever, thereby reducing the tension that was causing the
outer sheath to slip from its mount.
For the second prototype, Treadstone has a number of design alterations. The first change would
be to use a centrifugal clutch with a chain rather than a pulley. This would prevent slippage in
high torque applications, although the cost would be higher. The second change would be to use
a transaxle with different gear reduction. The powertrain calculations show the Treadnought
producing more torque in first gear than it needs. Changing the reduction of the system would
eliminate this excess torque and boost the top speed of the vehicle. A third change would be to
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increase the ride height of the vehicle. During swamp testing, the transaxle would drag sticks and
grass, bogging down the vehicle. Raising the ride height would prevent this issue, and would
allow for traversing of harsher terrains, such as boulder fields. Similarly, Treadstone
recommends eliminating the rear wheel. Although needed for the prototype, the team suggests
shifting vehicle weight over the tracks, either by increasing track length, or moving the power
train further forward in some other way. This would eliminate the need for a rear wheel, thereby
maximizing traction and eliminating another snag point for branches or foliage. A fourth change
would be to install body panels. These would both protect the operator from water and mud
thrown from the tracks, but also protect the brake pads from water and the entire power train
from direct impact with obstacles such as rocks or tree stumps. Some additional features that
could be added to a future prototype include headlights, interchangeable additional seating and
storage containers, a winch, a jerry can, and a detachable rain/sun visor to protect the rider from
the elements.
In terms of managing the project and the team, Treadstone has gathered a few insights over the
course of the year. The biggest change the team would make would be to frontload the design
process. Because the frame dimensions were determined from the dimensions of the acquired
track assemblies, and the powertrain elements were all dependent on each other, determining
budget and obtaining components early is crucial. Having the design started earlier gives more
time for overcoming potential hurdles and unexpected obstacles in both the design and the
fabrication of the prototype. Frontloading the design is very important for teams with physical
prototypes.
In terms of managing the actual team, the members of Treadstone suggest establishing a system
of accountability within the team, where each team member is accountable for and accountable
to another member. Task distribution is also very important, and can change rapidly throughout
the course of the project, either from design alterations, or the addition or completion of other
tasks. Additionally, the team would like to caution future teams about scheduling and time
management: because everything takes longer than originally anticipated, and unexpected
hurdles arise, it is very easy to fall behind schedule. Changing the Gantt chart or schedule to
accommodate falling behind is a simple solution to this problem, but the team strongly
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encourages future teams to resist this solution. Rather, Treadstone recommends determining the
root causes of the shortcomings and addressing those reasons, as simply changing the schedule
does not remedy the root problem, and will only lead to further time crunches later in the project.
Figure 37: Final Product
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8 Appendix A (include Business Plan sheets in Final)
8.1 Powertrain EES Calculations
"!Torque Estimates" "FBD" W_vehicle= W_total F_N_wheel= 0 {1/3*W_vehicle} F_N_wheel+2*F_N_track=W_vehicle "!Track" "Friction Force" F_F_track=mu_track*F_N_track mu_track=0.9 "Surface Contact" L_track_contact=4[ft] w_track=15[in] A_contact=L_track_contact*w_track*convert(in,ft) T_turn_track=1.5*(2*integral(F_F_track/A_contact*w_track*convert(in,ft)*x,x,0,L_Track_contact/2,0.1[ft])) "Wheel" F_RR_wheel=C_RR_wheel*F_N_wheel C_RR_wheel=0.2 {Rolling Resistance Coefficient} T_turn_wheel=L_CG_wheel*F_RR_wheel L_CG_wheel=3[ft] "Total Torque Estimate for Zero-Turn Scenario" T_total=T_turn_track+T_turn_wheel "!Design Modeling" "A = Engine Shaft B = Transaxle Input C = Transaxle Output D = Track Drive Cog 4th Gear = Reverse" "!Engine Specs" "PowerHorse 414cc 12 HP Horizontal Shaft Engine" omega_max = 3850 {+/- 150} [rev/min] omega_idle = 2150 {+/- 50} [rev/min] T_max = 18 [ft-lbf] P_max = 12 [HP] "Power Curve Assumption Calculations - Max Torque RPM" P_max*convert(HP,ft-lbf/s) = omega_maxtorque * T_max *convert(rev/min,rad/s) "Test RPM" omega_A = omega_maxtorque T_A = T_max "Belt Drive Reduction" m_belt = D_pulley/D_clutch D_pulley = 3 [in] {Original = 5.5 in} D_clutch = 3 [in] {typical 1in bore centrifugal clutch pulley} m_belt = omega_A/omega_B m_belt = T_B/T_A "Cub Cadet 3-Speed Transaxle Gearing"
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m[1]=58 m[2]=28 m[3]=19 m[4]=24 m[1] = omega_B/omega_C[1] m[2] = omega_B/omega_C[2] m[3] = omega_B/omega_C[3] m[4] = omega_B/omega_C[4] m[1] = T_C[1]/T_B m[2] = T_C[2]/T_B m[3] = T_C[3]/T_B m[4] = T_C[4]/T_B "Chain Drive Reduction" m_chain = N_tread/N_transaxle N_tread = 16 N_transaxle = 16 D_transaxlesprocket = 6[in] m_chain = omega_C[1]/omega_D[1] m_chain = omega_C[2]/omega_D[2] m_chain = omega_C[3]/omega_D[3] m_chain = omega_C[4]/omega_D[4] m_chain = T_D[1]/T_C[1] m_chain = T_D[2]/T_C[2] m_chain = T_D[3]/T_C[3] m_chain = T_D[4]/T_C[4] "Velocities" D_drivecog = 6.5 [in] + 1[in] {track width} v[1] = pi*D_drivecog*omega_D[1]*convert(rev/min,rad/s)*convert(in/s,mph)/(2*pi) v[2] = pi*D_drivecog*omega_D[2]*convert(rev/min,rad/s)*convert(in/s,mph)/(2*pi) v[3] = pi*D_drivecog*omega_D[3]*convert(rev/min,rad/s)*convert(in/s,mph)/(2*pi) v[4] = pi*D_drivecog*omega_D[4]*convert(rev/min,rad/s)*convert(in/s,mph)/(2*pi) v_max[1] = pi*D_drivecog*omega_max/(m_belt*m_chain*m[1])*convert(rev/min,rad/s)*convert(in/s,mph)/(2*pi) v_max[2] = pi*D_drivecog*omega_max/(m_belt*m_chain*m[2])*convert(rev/min,rad/s)*convert(in/s,mph)/(2*pi) v_max[3] = pi*D_drivecog*omega_max/(m_belt*m_chain*m[3])*convert(rev/min,rad/s)*convert(in/s,mph)/(2*pi) v_max[4] = pi*D_drivecog*omega_max/(m_belt*m_chain*m[4])*convert(rev/min,rad/s)*convert(in/s,mph)/(2*pi) "!Solving" {T_D[1] = T_total "1st gear torque requirement"} "!FORCE, STRESS, STRAIN" "Belt and Chain Forces" F_belt = T_A/(D_clutch/2) *convert (ft,in) F_chain = T_C[1]/(D_transaxlesprocket/2) *convert (ft,in) "!TRANSAXLE TORQUE" LOVEJOY_TORQUE = T_total *convert(ft-lbf,in-lbf) "Vehicle Mass Calculations" m_transaxle = 60[lbm] m_engine = 70[lbm] m_fuel = 1 [gal] * rho_87 rho_87 = 0.75 [kg/L] *convert(kg/L,lbm/gal) m_oil = 1 [quart] * rho_10W30
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rho_10W30 = 54.6 [lbm/ft^3] *convert(lbm/ft^3,lbm/quart) m_trackassembly = 85 [lbm] m_seat = 20 [lbm] m_controls = 50[lbm] m_operator = 250 [lbm] m_tools = 50 [lbm] m_frame= m_steeltube + m_steelplate m_steeltube = l_steel * 1.844 [lbm/ft] l_steel = 110 [ft] m_steelplate = 40 [lbm] W_total = (m_frame+m_tools+m_operator+m_controls+m_seat+m_trackassembly*2+m_oil+m_fuel+m_engine+m_transaxle) *g*convert(lbm-ft/s^2,lbf) g = 32.2 [ft/s^2]
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8.2 Braking EES Calculations
8.2.1 EES Code
mass = 1000 [lbm] Velocity = 20 [mph] * convert(miles, ft) * convert(s, hr) decel_rapid = 8.84 [ft/s^2] "From advanced vehicle performance testing" decel_normal = 2.95 [ft/s^2] "From advanced vehicle performance testing" R_track = (3.25 [in] + 0.75 [in]) * convert(in, ft) "Cog radius + Track thickness" R_brake_eff = 4 [in] * convert(in, ft) "Effective radius of pad & rotor interaction" Dia_cyl_master = 0.4 [in] Dia_cyl_slave = 1.872 [in] Area_cyl_master = pi# * (Dia_cyl_master / 2)^2 Area_cyl_slave = pi# * (Dia_cyl_slave / 2)^2 L_pedal = 12 [in] L_piston = 2.5 [in] mu_wet = 0.2 mu_dry = 0.4 Force_rapid = mass * decel_rapid * convert(lbm*ft/s^2, lbf) Force_normal = mass * decel_normal * convert(lbm*ft/s^2, lbf) "Ground to Rotor" Torque_ground_rapid = Force_rapid * R_track Torque_ground_normal = Force_normal * R_track Torque_brake_rapid = Torque_ground_rapid Torque_brake_normal = Torque_ground_normal Torque_brake_rapid = (Force_brake_rapid * 2) * R_brake_eff "x2 for brake assemblies" Torque_brake_normal = (Force_brake_normal * 2) * R_brake_eff "x2 for brake assemblies" "Rotor to Foot" "!Wet Conditions" Force_brake_rapid = Force_clamp_rapid_wet * mu_wet Force_brake_normal = Force_clamp_normal_wet * mu_wet "!Dry Conditions" Force_brake_rapid = Force_clamp_rapid_dry * mu_dry Force_brake_normal = Force_clamp_normal_dry * mu_dry "!Wet Conditions" Force_clamp_rapid_wet / Area_cyl_slave= Force_pedal_rapid_wet / Area_cyl_master Force_clamp_normal_wet / Area_cyl_slave = Force_pedal_normal_wet / Area_cyl_master "!Dry Conditions" Force_clamp_rapid_dry / Area_cyl_slave = Force_pedal_rapid_dry / Area_cyl_master Force_clamp_normal_dry / Area_cyl_slave = Force_pedal_normal_dry / Area_cyl_master "Wet Conditions / Rapid Deceleration" Force_foot_wet_rapid = Force_pedal_rapid_wet * L_piston * cos(20) / L_pedal "Wet Conditions / Normal Deceleration" Force_foot_wet_normal = Force_pedal_normal_wet * L_piston * cos(20) / L_pedal "Dry Conditions / Rapid Deceleration" Force_foot_dry_rapid = Force_pedal_rapid_dry * L_piston * cos(20) / L_pedal "Dry Conditions / Normal Deceleration" Force_foot_dry_normal = Force_pedal_normal_dry * L_piston * cos(20) / L_pedal
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8.2.2 EES Solutions
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9 Acknowledgements
Team 17 would like to thank the following people for their contribution to this project:
Ned Nielsen – Team Advisor
Ren Tubergen – Industrial Consultant
Phil Jasperse – Metal Shop Supervisor
Bob DeKracker – Part Ordering
BPG Werks’ DTV Shredder – Design Inspiration
Rick Harper – A1 Mowers
Transaxle and Clutch Supplier
Steve Grant – Innotec
Couplings Supplier
Bruce D. – Craigslist
Seat and Cover Supplier
Tom Bunker – Craigslist
Snowmobiles Supplier
