PPFS - Calvin College

Treadstone
TEAM 17
David Exoo (ME)
Preston Phillips (ME)
Matthew Wever (ME)
Michael Vriezema (ME)
Project Proposal and Feasibility Study
ENGINEERING 339 SENIOR DESIGN
2012
Copyright
© 2012, Team 17 and Calvin College
Executive Summary
This report discusses the design and research regarding the creation of a two-tracked, all-terrain
vehicle. Treadstone, also known as Team 17, has chosen to build this utility vehicle for their
senior capstone project. Team 17 will design this vehicle in the cheapest way possible without
compromising its structural and operational integrity.
Upon completion of this report,
Treadstone has decided that the creation of their vehicle, the Treadnought, is, in fact, feasible.
And with the conclusion of this report, construction of the vehicle will commence at the start of
the next semester.
i
Table of Contents
Contents
Executive Summary ......................................................................................................................... i
1
2
Introduction ............................................................................................................................. 1
1.1
The Project ....................................................................................................................... 1
1.2
Design Norms ................................................................................................................... 1
1.2.1
Transparency ............................................................................................................. 1
1.2.2
Trust .......................................................................................................................... 1
1.2.3
Caring ........................................................................................................................ 1
1.3
The Team.......................................................................................................................... 2
1.4
The Class .......................................................................................................................... 2
Project Management ............................................................................................................... 3
2.1
3
Project Breakdown ........................................................................................................... 3
2.1.1
Engine & Drivetrain .................................................................................................. 3
2.1.2
Controls ..................................................................................................................... 3
2.1.3
Frame ........................................................................................................................ 3
2.1.4
Tread Assembly ........................................................................................................ 3
2.2
Schedule ........................................................................................................................... 4
2.3
Budget .............................................................................................................................. 5
2.4
Method of Approach ........................................................................................................ 5
2.5
Task List ........................................................................................................................... 5
Requirements .......................................................................................................................... 7
3.1
Safety................................................................................................................................ 7
3.2
Operating Conditions ....................................................................................................... 7
ii
3.3
4
Project Specifications.............................................................................................................. 8
4.1
5
Functionality..................................................................................................................... 7
Engine and Power Train ................................................................................................... 8
4.1.1
System Options ......................................................................................................... 8
4.1.2
Selected System ...................................................................................................... 10
4.1.3
Engine Selection ..................................................................................................... 11
4.1.4
Drive Train .............................................................................................................. 16
4.2
Tread Assembly.............................................................................................................. 20
4.3
Frame .............................................................................................................................. 21
Business Plan ........................................................................................................................ 22
5.1
Market Competition ....................................................................................................... 22
5.2
Break Even Calculations ................................................................................................ 23
6
Conclusion ............................................................................................................................ 25
7
Appendix A ........................................................................................................................... 26
8
Acknowledgements ............................................................................................................... 29
iii
Table of Figures
Figure 1: Gantt Chart ...................................................................................................................... 4
Figure 2: Electric Motor.................................................................................................................. 8
Figure 3: Hydraulic Engine ............................................................................................................. 9
Figure 4: Mechanical Engine ........................................................................................................ 10
Figure 5: Snowmobile Engine with CVT ..................................................................................... 12
Figure 6: Kawasaki 440 Snowmobile Engine Power Curve ......................................................... 13
Figure 7: Kohler Diesel Engine Power and Torque Curves ......................................................... 14
Figure 8: Briggs and Stratton Engine............................................................................................ 15
Figure 9: Model 40 Series Comet Clutch ..................................................................................... 16
Figure 10: Toro Hydrostatic Transmission ................................................................................... 17
Figure 11: Lawn Mower Transaxle............................................................................................... 18
Figure 12: Proposed Belt-Pulley System ...................................................................................... 19
Figure 13: Disc Brake ................................................................................................................... 20
Figure 14: DTV Shredder ............................................................................................................. 22
Table of Tables
Table 1: Proposed Design Budget................................................................................................... 5
Table 2: Task Breakdown by Hour ................................................................................................. 6
Table 3: Engine/Power Train Decision Matrix ............................................................................. 10
Table 4: Calculated Gear Ratios ................................................................................................... 12
Table 5: Production Costs ............................................................................................................. 23
Table 6: Break Even Calculations................................................................................................. 24
Table 7: Profit Analysis ................................................................................................................ 24
iv
1
Introduction
1.1 The Project
Team 17 (Treadstone) is setting out to design and construct an all-terrain utility vehicle. The
team’s vehicle, the Treadnought, will have two treads to allow it to traverse a wide variety of
terrains such as snow and gravel, and will have onboard storage for tools and equipment. Rider
safety is of particular importance to the team, so the Treadnought will be equipped with a 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 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. Similarly, reliability
is essential to ensuring driver safety beyond physical injury.
1
1.3 The Team
The team is composed of four mechanical engineering students: David Exoo, Preston Phillips,
Matt Wever, and Michael Vriezema. Matt has experience with manufacturing which will be
useful for production of the vehicle. He also has experience working with vehicles which will
help him lead the group in designing the drivetrain. Preston and Michael’s internship experiences
in quality divisions have provided them with a unique perspective in the design process, allowing
them to weigh the tradeoffs of the vehicle production. With an interest in controls design,
Preston’s will be in charge of creating the Treadnought’s control system. Michael’s project will
be the design of the tread assembly and suspension. David has an extensive knowledge of
materials and also has experience working with steel. He will lead the design, structure, and
assembly of the frame and roll cage. While each team member has individual leadership
responsibilities; most of the design and assembly of the vehicle will be 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.
2
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: engine/drivetrain, controls, frame, and tread assembly. Each member of
Treadstone was selected to lead one of the design groups. Other various tasks, such as
documentation and research, will not be assigned, but completed as a team.
2.1.1 Engine & Drivetrain
Matt will be in charge of the engine and drivetrain for the Treadnought. Responsibilities include
selecting an engine, clutch, and gearing system that will deliver the appropriate differential
power to the tracks.
2.1.2 Controls
Preston will be in charge designing the vehicle’s controls. The objective of this group is to create
a control system that will control the engine throttle, clutch engagement, differential power
distribution, and gear selection, providing reliable and intuitive control of the vehicle’s speed and
direction.
2.1.3 Frame
David will be responsible for designing and fabricating a frame that can withstand the weight of
the internal components, the driver, and any additional equipment. We will develop an optimal
frame design using finite element analysis to locate possible areas of weakness within the frame.
Research into potential welding materials and optimal frame structure designs will also be
conducted.
2.1.4 Tread Assembly
Michael will be responsible for fitting the tread assemblies from the old snowmobiles to the new
frame of the Treadnought. This group will also be responsible for designing the necessary
suspension system for the previously stated integration.
3
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 1, 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 1.
Figure 1: Gantt Chart
4
2.3 Budget
Treadstone is striving to create a safe, fun, and durable vehicle to traverse all-terrains at a
reasonable cost.
To do this, the team needs to weigh tradeoffs between building parts,
repurposing parts, and buying new parts. The senior design teams were originally given $500 for
their project, but were also asked to create a budget proposal for their project. Table 1 below
shows the budget proposal for Team 17’s all-terrain vehicle.
Table 1: Proposed Design Budget
Purchase
2 Snowmobiles
Steel Tubing
Sheet Metal
Seat
Wheel
Gears and Jackshafts
Brakes
Clutches and Pulleys
Suspension
Engine
Estimated Budget
Project Use
2 track systems, throttle control
Frame
Protective Shell
Seat
Stability
Gearing System
Braking
Differential Power Distribution
Suspension
Power
Cost
$400
$250
$100
$50
$100
$400
$100
$200
$100
-
Total Cost
$1,700
2.4 Method of Approach
Due the nature of this project, before any parts can be purchased, appropriate calculations must
be done to validate design decisions. For calculations, knowledge from thermodynamics,
machine design, and other mechanical engineering classes will be pivotal. This knowledge will
be applied to all aspects of the design: engine, controls, drivetrain, and frame. Once the
calculations and designs are complete, the assembly of the Treadnought may commence
according to the aforementioned schedule (Figure 1).
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.
5
Table 2: Task Breakdown by Hour
Task
Determine Budget
Req'd
Hours
Brief Description
3
Find out how much money is available and costs for the project
Establish Basic Vehicle
Structure
4
Determine basic shape and design
Preliminary Sketches
1.5
Visual representation of basic structure
1
Verbal with Vanderleest
10
Research necessary parts and components / tradeoffs (cost vs. performance) research donor vehicles
3
Prepare oral presentation for in class
6
Research parts and components fabrication feasibility for buying vs. creating
3
Verbal with Vanderleest
3
Progress report
2
Create rough outline and define key topics
3
Write-up on budget and projected costs
3
Analyze tasks to be completed and time remaining
3
Analyzing project in terms of engineering difficulty
4
Find acceptable donor vehicles
10
Design frame to accommodate motor, and track, as well as protect vehicle operator
6
Build part of frame to support the motor
6
Build part of frame to attach the track
6
Build part of frame to protect rider and attach other parts together
3
Design mechanism to control speed
5
Design mechanism to brake vehicle
4
Design mechanism to facilitate turning
10
Design gearing and linkages to transfer power to the tracks
8
Model our vehicle based on schematics
8
Use models to perform FEA analysis and design optimization
6
Put parts together
8
Donor vehicles likely will need engine maintenance
3
Attach crankshaft to transmission
6
Analyze tracks under projected load
4
Connect treads to frame and transmission
8
Combine calculations and summarize
8
Summarize design progress
8
Summarize construction process
8
Describe vehicle performance under testing
4
Put final report together and proofread
Communication 1
Determine Components
Presentation 1
Determine Purchasable vs.
Buildable Components
Communication 2
Presentation 2
PPFS - Rough Outline (Key
Topics)
PPFS - Budget Feasibility
PPFS - Schedule Feasibility
PPFS - Engineering
Feasibility
Buy Sleds
Design Frame
Build Frame - Engine Mount
Build Frame - Track Support
Build Frame - Chassis
Design Throttle
Design Braking
Design Steering
Design Power Train
Create AutoCAD Models
Frame Stress Analysis
Assemble Drive Mechanism
Get Motor Running
Attaching Drive Mechanism
To Motor
Track Stress Analysis
Attach Treads
Final Report - Calculation
Summary
Final Report- Design
Summary
Final Report - Fabrication
Summary
Final Report - Testing
Summary
Assemble Final Report
6
3
Requirements
3.1 Safety
The Treadnought will 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 will be secured in the vehicle with a safety
harness or restraint and surrounded by a roll cage capable of withstanding impact forces resulting
from crashes, rolls, and elevation drops. The design will incorporate the weights of the vehicle,
driver, and equipment to ensure maximum protection.
3.2 Operating Conditions
In order to achieve all-terrain capabilities, several terrains must be analyzed individually to
overcome the unique set of challenges associated with each one. These challenges, dependent on
the terrain, will 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 must 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 the storage must be easily accessible from a standing position outside of the
vehicle.
7
4
Project Specifications
4.1 Engine and Power Train
4.1.1 System Options
There are three options that were researched to supply power to the Treadnought: electric,
hydraulic, and mechanical. Each has its own set of pros and cons which were used to determine
the best option for our vehicle.
4.1.1.1 Electric
Because the design for the Treadnought originally started with a Segway-like body style, an
electric system was first analyzed. Two electric motors would provide easy control of the two
tracks. The electric option looked promising until the team decided to change the design of the
vehicle due to component size and price constraints. When the design changed to include larger
track assemblies, higher torque and power would be needed to operate the vehicle, and the larger
electric motors would be restrictively expensive. Additionally, the power demands from the
electric motors would require either a large, expensive battery system which would make our
vehicle difficult to build due to size, price, and material limitations, or vehicle performance and
range would have to be reduced, dramatically reducing the functionality and practicality of the
vehicle. The inclusion of an onboard generator or regenerative braking system would add to the
cost and weight of the system, and any benefits in vehicle range would be offset by increased
infeasibility in both budget and vehicle size.
Figure 2: Electric Motor1
1
http://www.walkeremd.com/CEM4106T-Baldor-20HP-3520RPM-3PH-60HZ-256TC-0940Mp/cem4106t.htm?gclid=CLeav6_22bMCFYs7Mgodz2UALw
8
4.1.1.2 Hydraulic
The next 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 needed for successful vehicle operation,
the cost of acquiring hydraulic components is restrictive. Hydraulic systems are also difficult to
work with and often have many complications. Figure 3 below shows what a typical hydraulic
engine looks like.
Figure 3: Hydraulic Engine2
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 zeroturn capabilities as simply as hydraulic systems can, it is less expensive. The mechanical system
will also provide a longer operating range than the electric system allowing the vehicle to reach
areas farther away. Figure 4 shows what a typical mechanical engine looks like. As you can see,
2
http://www.tradekorea.com/product-detail/P00078006/KJI_LK1R__HYDRAULIC_ENGINE_PUMP_.html
9
the hydraulic engines and mechanical look quite similar, as they typically are both combustion
engines, with hydraulic engines having hydraulic pumps incorporated into the engine design.
Figure 4: Mechanical Engine3
4.1.2 Selected System
To help select the appropriate drive train, Treadstone put together a decision matrix which
factored in multiple design considerations to figure out which system best meets the vehicle’s
requirements. In the end, the team’s cost restraints had the largest impact on which option to
implement. Table 3 shows the decision matrix used to choose a mechanical drive train.
Weight
Range of Use
Durability
Simplicity
Maintenance
Size
7
3
2
4
6
4
2
3
5
1
4
4
4
2
3
3
3
5
2
2
2
4
2
3
1
4
2
2
1-5 Scale
Importance
Electric
Hydraulic
Mechanical
3
http://www.briggsandstratton.com/engines/other-engines/
10
Total
Cost
Table 3: Engine/Power Train Decision Matrix
85
70
92
4.1.3 Engine Selection
Engine selection is an incredibly important aspect of this project, as no design, no matter how
sophisticated, can succeed if the power demanded cannot be generated. Many factors were taken
into consideration for engine selection including, but not limited to, power, torque, operating
RPM, size, weight, fuel type, and cost. As aforementioned, internal combustion engines will be
considered rather than electric motors, but there are still many different types of combustion
engines that need to be considered. One of the requirements for the vehicle is a small turning
radius and zero speed turning, which would place a large torque requirement on the system.
Equations 1 and 2 were used to calculate the torques associated with turning the vehicle around a
stationary track and rotating vehicle using the rear support wheel, respectively.
∫
(Eqn. 1)
(Eqn. 2)
Equation 1 calculates the torque based on the friction force exerted on the track due to one third
of the vehicle’s weight (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). Equation 2 calculates the torque from the rear
wheel, using the distance from the wheel to the axis of rotation (Lw) and the rolling resistance
force (FRR).
Another vehicle requirement is a top speed of 25 mph. Using these two requirements, engines
were assessed based on their power and torque capabilities, and the respective RPMs associated
with said capabilities, as well as the projected gearing requirements needed to convert and
transfer the power to the tracks. Equation s 3 and 4 are the general forms of the equation used to
calculate gear ratios.
(Eqn. 3)
(Eqn. 4)
11
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). Equation 4 calculates the
largest gear ratio for achieving the top speed of 25 mph using the RPMs associated with peak HP
(ωE) and the estimated rotational speed of the track driveshaft (ωT).
Table 4 shows the peak torque, peak power, and calculated gear ratios for a 12 HP riding mower
engine, 18.8 HP Kohler engine and 40 HP snowmobile engine. The complete calculations can be
found in Appendix A.
Table 4: Calculated Gear Ratios
Engine
Max Power
(HP)
Max Power
RPM
Peak Torque
(ft-lbs)
Zero-turn
Gear Ratio
Max Speed
Gear Ratio
Riding Mower
Engine
12
3600
19
42
13
Kohler Engine
18.8
3600
31
25
13
Snowmobile
Engine
40
6000
10
78
22
4.1.3.1 Engine and Transmission
An engine from a salvaged snowmobile was first considered for the power source for the
Treadnought. Adapting the snowmobile’s engine, clutch, and transmission would help keep costs
down, as buying individual components tends to be more expensive. Figure 5 shows an example
of a snowmobile engine.
Figure 5: Snowmobile Engine with CVT
12
Additionally, the components are already designed to work together, so interconnection of
components in the drivetrain becomes an easier task. However, upon further analysis of this
proposed system, the team determined that the snowmobile engine would not be a viable option.
Although the power and torque curves for engines vary from machine to machine, typical
snowmobile engines produce maximum power within a narrow RPM (revolutions per minute)
range somewhere within 4000-7000 RPM (Figure 6).
Figure 6: Kawasaki 440 Snowmobile Engine Power Curve4
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 transform it into a high torque, low RPM, would be difficult and expensive. Typical
vehicle transmissions do not exceed 30:1 gear reductions in the lowest gears, but the gear ratio
calculations reveal gear ratios of over 90:1. Also, many snowmobiles use belt style, continuously
variable transmissions. Although these are very efficient, for high torque applications they are
not ideal, as the belts can become subject to slipping. Therefore, it will not be a reliable option
for our vehicle.
4
http://www.homebuiltairplanes.com/forums/2-stroke-aircaft-engines/2571-proven-440-setups.html
13
4.1.3.2 Kohler Engines
The team considered a second option: purchasing an 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 7 shows the power curve for this engine.
Figure 7: Kohler Diesel Engine Power and Torque Curves
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 researched for its
similar performances specifications and lower price than that of its diesel counterpart. Using
these specs in combination with the torque demand calculations, a gear ratio of 22:1 was
computed for zero speed turning, and 13:1 ratio for max speed. The latter gear ratio can be
further reduced to decrease the operating RPM of the engine, as the calculation was performed at
the max power RPM of 3600 RPM. These gear ratios are much more reasonable and attainable
14
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 possible option.
4.1.3.3 Briggs and Stratton Engine
The third option the team considered is a 12 HP, Power Built, Briggs and Stratton engine.
Figure 8: Briggs and Stratton Engine5
This engine is significantly smaller than the Kohler engines mentioned earlier. However, vehicle
weight is proportional to the power supplied by and transferred in the drive train, as more
powerful components are generally heavier. Using a smaller engine can help reduce vehicle
weight, which will decrease torque demands from the engine. The gear ratios calculated for this
engine would be approximately 40:1 for zero-speed turning, and 13:1 for max speed. Again, this
second ratio can be reduced to decrease the operating RPM of the engine. This range of gear
ratios will be slightly more challenging to obtain than the range required by the Kohler engines,
but can be accomplished with proper gearing and transmission selection. The cost of this engine
is 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. The team will also look into the possibility of obtaining a more powerful engine either
by purchasing it used, or receiving it by donation.
5
http://www.northerntool.com/shop/tools/product_200514250_200514250
15
4.1.4 Drive Train
4.1.4.1 Clutch
Generating the power needed for the vehicle is worthless if the power isn’t transformed into a
useful form and delivered where it is needed. This is where the clutch and transmission come in.
The clutch engages the engine with the rest of the drive train. The team decided to use a
centrifugal clutch for simplicity of operation, as opposed to a belt tensioner clutch or a friction
clutch which involve user interaction to engage and disengage. Comet Clutches supplies a wide
variety of centrifugal clutches, including the Model 40 Series (Figure 9).
Figure 9: Model 40 Series Comet Clutch
The Model 40 engages at 1600 RPM and can handle engines up to 20 HP, which makes it a
perfect clutch for the Treadnought6.
4.1.4.2 Transmission
4.1.4.2.1 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 10 shows an example of a hydrostatic transmission.
6
http://www.hoffcocomet.com/EpiphanyWeb/flexpage.aspx?ID=75
16
Figure 10: Toro 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.
4.1.4.2.2 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
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 11 shows an example of a lawn mower transaxle.
7
http://www.toro.com/en-us/homeowner/mowers/zero-turn-mowers/pages/model.aspx?pid=timecutter-mx426074640
8
http://www.grainger.com/Grainger/HALDEX-BARNES-Hydraulic-Gear-Pump-1DBE2?Pid=search
9
http://www.ebay.com/sch/i.html?_trksid=p5197.m570.l1313&_nkw=hydraulic+transmission&_sacat=0&_from=R
40
17
Figure 11: Lawn Mower Transaxle
4.1.4.2.3 Belt and Chain Drive
Another option available to the Treadnought for power transmittance is a belt drive with an idler
pulley, connected to a chain drive. In this context, belts and chains serve the similar purposes.
Both can transmit the same power, however, a belt for example, 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 will be connected directly to the engine, so it will be
moving at very high speeds. The size of the pulleys can be used to turn down the speed of the
drive before the chain drive. The chain drive can 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 can then make the final reductions needed before the treads.
There will be two pulleys connected to the driveshaft of the engine. Each pulley will drive its
own belt that goes around two other pulleys. The pulley on the other end of the belt will power
the chain drive. To provide the belt with the tension it needs, an idler pulley will be used on each
belt. The driver will also be given control over these idler pulleys. When fully engaged, the
belts will 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 will start slipping. This decreases the power transference to
one of the treads, turning the vehicle. Figure 12 shows a diagram of the proposed belt and chain
drive assembly. The belt drive is in red, and the chain drive is in green.
18
Figure 12: Proposed Belt-Pulley System
4.1.4.3 Braking/Steering
Because a transaxle was selected in the drive train design, the braking system for the
Treadnought serves two purposes: braking and steering. Like any other vehicle, slowing and
stopping is achieved through braking. Unlike most other vehicles, the Treadnought will be
steered by braking or locking one of axles as the other axle is left to turn freely. For example, to
turn left, the brake on the left axle would be engaged, while the right axle would be left
uninhibited. Disc brakes were chosen over drum brakes because disc brakes have better cooling
and are therefore more apt to handle the additional braking demand presented by the proposed
steering strategy. Appendix A shows the calculations used to size the disk brakes. Two sets of
calculations were used: one for steering requirements, the other for stopping requirements. Both
sets yielded 10 inch diameter disk brakes. Figure 13 shows an example of a disc brake.
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Figure 13: Disc Brake
4.2 Tread Assembly
For the initial design and build of the Treadnought, the tracks will come from purchased
snowmobiles. Ideally, the Treadnought will have tracks that are more specialized towards its
purposes, but custom tracks like these can cost at least $1,000, and up to $5,000, making them
infeasible for this design. Purchasing used snowmobiles is not only cheaper, but also provides
additional parts that can be used. The entire track assembly, with minor modifications, will be
mounted onto the Treadnought. The frame will be designed in such a way that the treads will be
easily integrated onto the vehicle. There is suspension within snowmobile tracks so the shape of
the track assembly can change, but there is also suspension between the tracks and frame itself.
The frame will allow for this suspension from the snowmobiles to be used in the Treadnought as
well.
The tracks from these snowmobiles will be about 15" wide, and mounted on both sides towards
the front of the vehicle. There will be braces to support them on the outside of the vehicle so
they will not be cantilevered. There will also be fenders to cover them up, both to protect the
treads themselves, and to protect the operator from the moving parts and from any objects that
could get kicked up during operation.
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4.3 Frame
Because the Treadnought will be operating over rough terrain, and reliability is essential, the
design of the vehicle’s frame is very critical. While frame strength and integrity is important,
other aspects need to be considered as well, such as weight and cost. The frame can quickly
become the heaviest part of the vehicle and can easily slow it down if designed to be too bulky.
The Treadnought must be able to maneuver in rough terrains, and a heavy frame will not help.
Any unnecessary materials used in the frame are also a burden on the final price tag. The frame
should be a cheaper part of the overall design allowing for less of a budget constraint when
acquiring the engine and track assemblies.
The vehicle weight has been estimated to be roughly 800 lbs. It will be up to the frame to hold
the Treadnought together not only under static loading, but also under dynamic loading that will
be experienced during operation. In order to keep the frame strong yet light and inexpensive,
carbon steel will be the material of choice.
The next best choice would be aluminum.
Aluminum can be just as strong as steel. However, in this instance, strength refers to yield
strength. Aluminum's Modulus of Elasticity is much lower than that of steel, meaning it will
deflect much more than the steel will before failure, however, it is a great deal more expensive
than steel. The one redeeming feature of aluminum is being significantly lighter than steel.
Because of the strength issues addressed earlier, much more material would be needed,
effectively negating advantages in weight, and compounding the issues in cost. Because of these
tradeoffs, steel has been selected for the construction of the Treadnought.
For the actual design, carbon steel square tubing will be used. For the same amount of strength,
the hollowed-out tubing will be lighter. In comparison to round tubing, square tubing is much
easier to work with. The flat surfaces make welding and alignment for the whole frame much
simpler.
Initial calculations will assume 1 inch square tubing, with 11 gage walls. The assumption of 1
inch keeps the weight and size down, while maintaining high strength and a lower cost. 11ga
walls (0.120"), a standard thickness in industry, are used because it is so close to 1/8", making it
readily available.
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5
Business Plan
5.1 Market Competition
On today’s market, there is nothing like the Treadnought, however, there 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-$5,000.
The DTV Shredder, seen below in Figure 14 produced by BPG Werks is a product similar to an
off-road Segway designed for extreme sports’ use as well as for the military. 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 weighs only 200 lbs.
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 14: DTV Shredder10
10
https://bpgwerks.com/
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5.2 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 make up the fixed costs, whereas
variable costs per part can be found in Table 1 in Section 2.3. Below is a summary of total costs
as sums of both fixed costs and variable costs.
Table 5: Production Costs
Annual Fixed Cost
Rent
Salaries
Design Time
Insurance
Patent
Utilities
Tooling/Machinery
Cost per Vehicle
Raw Materials
Parts
Labor
Shipping/Handling
Marketing
Warranty
Production Cost Estimate
Cost
$187,500
25,000 sqft @ 7.5$/sqft
$250,000
5 people @ $50,000
$50,000
prototype design cost
$29,250
10% of building/equip cost per year
$25,000
vehicle design patent
$10,000
$30,000
Cost
$200
$1,100
$1,000
$100
$50
$150
Total Cost
$581,750
Total Cost
$2,600
By taking these costs into account a break-even analysis was calculated assuming an annual
vehicle production rate of 1,000 units, resulting in a break-even price of $3,182 (Table 6). Any
increase in production or markup in price would create further profits for the company. For
example, Table 7 shows a simple profit analysis assuming a market price of $4,000 and annual
production of 1,000 units.
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Table 6: Break Even Calculations
Break Even Analysis
Annual Production
1000
# of vehicles
Annual Fixed Costs
$581,750
Cost per Vehicle
$2,600
Total Annual Cost
$3,181,750
Break Even Sale Price
$3,182
Table 7: Profit Analysis
Profit Analysis
Sale Price
$4,000
Annual Sales
$4,000,000
Annual Costs
$3,181,750
Earnings
$818,250
Tax Rate
40%
Taxes
$327,300
Net Income
$490,950
Profit Margin
12.3%
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6
Conclusion
Now that the preliminary calculations and design research has been completed, the team has
come to the conclusion that the Treadnought is feasible. Obviously there is a lot more work to
be done but the calculations completed thus far have allowed the team to conclude that the
Treadnought will be constructed with a mechanical internal combustion engine, approximately
15-20 HP, with a belt and pulley system to transfer power to each tread. Gear reductions must be
completed to reach the ratios necessary for the optimal operation of the vehicle. In-depth finite
element analysis (FEA) will be used to determine the structural integrity of the framework.
Upcoming plans for next semester include purchasing of materials and components within our
budget to begin construction of the Treadnought.
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7
Appendix A
"!Zero-speed turning calcs"
"FBD"
W_vehicle= 1200[lbf] {tools, vehicle weight, passenger}
F_N_wheel=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
T_turn_wheel=L_CG_wheel*F_RR_wheel
L_CG_wheel=3[ft]
T_total=T_turn_track+T_turn_wheel
"Turning Speed"
V_turning=3[mph]
V_turning=omega_track*L_track*convert(in/min, mph)*convert(rev,rad)
omega_axle=omega_track*L_track/(pi*D_drivecog)
D_drivecog=6[in]
L_track=150[in]
"18.8 HP diesel engine analysis-Kohler"
T_max_18.8=31[ft-lbf]
RPM_maxT_18.8=2200[rev/min]
RPM_maxP_18.8=3600[rev/min]
m_18.8_T=T_total/T_max_18.8
"Snowmobile engine analysis"
HP_snow=40[HP]
RPM_maxP_snow=6000[rev/min]
T_max_snow=10[ft-lbf]
m_snow=T_total/T_max_snow
"12 HP lawn mower engine analysis"
P_12=12[HP]
RPM_maxP_12=3400[rev/min]
T_maxP_12=12[HP]/(3400[rev/min]*convert(rev/min,rad/s))*convert(HP, ft-lbf/s) {linear scaling}
m_12_T=T_total/T_maxP_12
"!MAX SPEED Calcs"
26
V_max=30[mph]
omega_track_max=V_max*convert(mph, ft/min)/(L_track*convert(in,ft))*convert(rad,rev)
omega_maxV=omega_track_max*(L_track/(pi*D_drivecog))
m_maxV_18.8=RPM_maxP_18.8/omega_maxV
m_maxV_12=RPM_maxP_12/omega_maxV
m_maxV_snow=RPM_maxP_snow/omega_maxV
"!BRAKING"
T_brake=P_max*convert(HP, ft-lbf/s)/(omega_maxV*convert(rev/min,rad/s)) {from Machine Design
Textbook}
P_max=18.8[HP]/2
0=(V_max*convert(mph, ft/s))^2+2*a_brake*delta_x
delta_x=45[ft] {braking distance @ 30 mph}
F_brake=m_vehicle*a_brake*convert(lbm-ft/s^2,lbf)
m_vehicle=W_vehicle/g*convert(lbf, lbm-ft/s^2)
g=32.2[ft/s^2]
"Disk Brake Sizing based on Engine Power"
theta=60[deg]
N=2
T_brake=N*theta*convert(deg,rad)/2*mu_brake*p_brake_max*(r_o^2-r_i^2)*r_i*convert(in,ft)
r_i^2=r_o^2/3
mu_brake=0.2 {wet brakes on iron}
p_brake_max=300[psi]
"Sizing based on braking force"
abs(F_brake)=N*theta*convert(deg,rad)/2*mu_brake*p_brake_max*(r_o2^2-r_i2^2)
r_i2^2=r_o2^2/3
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8
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
BPG Werks’ DTV Shredder – Design Inspiration
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