MEEG 401: Senior Design
Final Report University of Delaware – Department of Mechanical Engineering
Team 3:
John Artes
LaMont Cannon
Mark Dilullo
John Gangloff
Joseph Walther
Advisor: Nate Cloud
Sponsor: Schiller – Pfeiffer Inc.
December 16, 2008
2 | P a g e
Introduction
Schiller – Pfeiffer Inc. (SPI) is a company that specializes in the production of lawn and
garden equipment for personal and commercial usage. SPI has contracted UDME’s Senior
Design Team 3 to assist with the improvement of their premier product – the Mantis tiller.
Figure 1 displays the Mantis tiller and how it is operated. The Mantis tiller is a low-cost, low-
weight, easy to use personal garden tiller that has been in production for 30+ years. It serves as
a leading personal lawn and garden tiller on the market and must be kept up-to-date with its
engineering to remain competitive.
Figure 1: Mantis Tiller
Problem Definition
SPI has a well-established consumer base within the US. It has expressed interest with
improving its Mantis tiller product line in Europe. Currently within Europe there are strict noise
regulations in place for power equipment operated outside. The regulations have required SPI
to remove the 2-stroke US motor from its product due to its high noise levels and replace it
with a quieter 4-stroke Euro motor. The Euro motor is consequently at lower power versus the
US motor. When the motor reselection was made, no other parts were changed over for the
Euro tiller from the US tiller. SPI has found that the Euro has poorer tilling when compared to
the US tiller. It is believed that this is in part due to the Euro motor being mismatched with the
adapted US transmission. Figure 2 displays the tiller transmission assembly.
3 | P a g e
Figure 2: Tiller Transmission Assembly
The US transmission is set at a gear ratio optimized for the US motor and it is believed
that this ratio is not optimized for the Euro motor. SPI would like the team to improve the
performance of its tiller line for Europe and/or the US through the redesign of its transmissions.
Project Needs, Wants, and Constraints
To ensure successful completion of the project, the project’s needs, wants, and
constraints are to be identified and understood by the team. After completing research into the
customer’s needs, wants, and constraints, they are to be ranked in a way that will facilitate
intelligent engineering decision-making. The team chose to adopt the Pairwise Comparison
matrix from Dym and Little’s Engineering Design book for its customer wants ranking system.
Table 1 and Table 2 show the results of the team’s technical and marketing wants and rankings.
Initial discussion with the sponsor was used as to quantify the relative rank of each item.
The Pairwise Comparison of wants chart is a clever tool that the team used to rank the
wants of the customer. In the table, an entry of “1” indicates that the objective in that row is
more important than that of the column in which it is entered. The score column represents the
sum of all of the “1’s” in each row, which allows you to easily rank the wants based on the
information that we were given from our customer. Our application of the chart allows for the
straightforward comparison of the technical and marketing wants of the customer. The chart
shows that having a reverse option is the customer’s most important technical goal while safety
is the most important marketing goal. This chart is very helpful because it allow the team to
focus on the wants that are most important during the design process.
Wants/
Metrics
(target
values)
Adjustabl
e/
Variable
Speed
Compatibl
e with
Different
Engines
Tine
Speed
Between
(230-
240)
Revers
e
Option
5-6k
RPM
on
Engin
e
Fits in
Existing
Space
Outpu
t
Torqu
e (31
ft-lbs) Score
4 | P a g e
Adjustable
/ Variable
Speed 0 0 0 0 1 0 1
Compatibl
e with
Different
Engines 1 0 0 1 1 0 3
Tine
Speed
Between
(230-240) 1 1 0 1 1 0 4
Reverse
Option 1 1 1 1 1 1 6
5-6k RPM
on Engine 1 0 0 0 1 0 2
Fits in
Existing
Space 0 0 0 0 0 0 0
Output
Torque
(31 ft-lbs) 1 1 1 0 1 1 5
Table 1: Pairwise Comparison of Technical Wants
Wants/Metrics
(target values)
Cost
Effective Weight Size Durability Safety Score
Cost Effective
($40) 1 1 0 0 2
Weight 0 0 0 0 0
Size 0 1 0 0 1
Durability 1 1 1 0 3
Safety 1 1 1 1 4
Table 2: Pairwise Comparison of Marketing Wants
Key Performance and Cost Metrics
The primary performance and cost metrics that will define the project’s success are if
the tiller transmission design can operate at different input speeds, operate in reverse, fit into
geometric constraints, and maintain a low cost of approximately $40 for the tiller transmission
system. Achievement of these metrics will be used as the baseline for meeting sponsor
expectations. If a successful tiller transmission design cannot be achieved, the sponsor has
specified multiple contingencies that can be pursued for a successful project. One contingency
is to prepare an Excel spreadsheet that can take an input motor and size and output the
5 | P a g e
required gearing data needed to retrofit current transmissions for optimum performance.
Another contingency is to create two different transmissions for the US and Europe engines and
uses them for testing purposes by the sponsor. A third contingency is to design a testing
apparatus to test tiller motors for reliability and engineering data. Ideally a “one-size-fits-all”
transmission design can be crafted, but contingencies exist for the “just-in-case” scenario.
Benchmarking
To facilitate initial concept designs, the team turned to a variety of benchmarking
resources. The team decided to research continuously-variable transmission (CVT) designs for
their ability to provide variable output speeds and torques, which adheres to the project wants.
One particularly useful resource was found on HowStuffWorks at the following web address:
http://auto.howstuffworks.com/cvt5.htm, which explains the basics of CVTs and their design.
The team was particularly intrigued at the various diagrams of the different CVT designs. For
example, Figure 2 displays the basic pulley – based CVT design. The system works by adjusting
pulley widths to adjust belt distances between two pulleys. The adjusting of belt distances
provides seamless changes in gear ratios, rather than the discrete amount of ratios found with
conventional manual transmissions. This design is very common amongst CVT systems;
however belt slippage issues and pulley distance issues may affect its implementation into the
tiller transmission project.
Figure 2: Pulley – Based CVT Design
Figure 3 shows another CVT design called the Toroidal CVT. The Toroidal CVT uses discs
and power rollers to provide seamless gear ratio changes. The transmission works by adjusting
the tilt of the power rollers, which affects the relatives speeds of the input and output discs
connected to driveshafts. This design allows for more compact geometries, but can lead to
potential material wear issues for the rollers.
6 | P a g e
Figure 3: Toroidal CVT
Another benchmark the team found was the NuVinci CVT design (Figure 4), licensed by
Fallbrook Technologies Inc. The design uses a set of ball bearings set similarly to a planetary
gear system with rockers that adjust to different torque/velocity inputs. The rockers adjust the
pitch of the ball, which affects the gearing ratio produced. The system is contained within a hub
that can be retrofitted to a variety of mechanical devices, including lawn and garden
equipment. Pricing of system implementation has yet to be determined.
Figure 4: NuVinci CVT
Benchmarking is critical to concept generation, because it provides a strong foundation
for the team to brainstorm and facilitate design. Also, a solution to the design problem may
exist in industry already for which benchmarking would reveal to the team. Much time and
money in R&D can be saved if a transmission solution is able to be purchased and retrofitted for
the tiller application rather than designing one from scratch. All possibilities will be considered
at this stage of the project.
7 | P a g e
Initial Sketches
Figure 5 highlights one concept for the transmission design using inverted cone-shaped
gears and a reinforced belt. The mechanism works by moving the reinforced belt up and down
the inverted cones during rotation to provide a changing set of gear ratios. The belt could be
moved using a screw-based mechanism or lever that is either user controlled or factory set. The
transmission has a reduced number of parts compared to a traditional transmission system
with finite gear ratios. The inverted cone-shaped gears provide a large amount of gear ratios for
smooth transitions, which is important for the low-end torque required for initial tilling. The
reverse mechanism involves a sliding set of gears that changes the direction of the driveshaft
for tine reversing. If the torque upon reversal is too high for the gear teeth, then additional
reverse assemblies can be added to reduce stresses on the teeth. The inverted cone + belt and
reverse assembly concepts would be placed below the motor and above the current
transmission assembly in a custom housing.
Figure 5: Inverted Cone + Belt and Reverse Assembly Concepts
Figure 6 and 7 shows a reverse planetary gear system design. This design aims to replace
the current worm gear with a planetary gear system, which will allow for a high torque reverse
drive. In forward drive mode the carrier ring will lock the center sun and outer ring gears
together creating a rigid hub. In reverse mode the carrier ring will disengage from the center
8 | P a g e
hub allowing the planet gears to reverse the directions of rotation of the outer ring. This
concept will fit in the current housing and requires only a small hole drilled for the shift rod. The
current center tine shaft threads will need to be replaced as shown to prevent the threads from
“backing out” when reverse is engaged.
Figure 6: Reverse Planetary Concept
Figure 7: Reverse Planetary Concept – Exploded View
Figure 8 shows an additional reverse gearbox concept. This concept is aimed to add a
reverse gear to the Mantis Tiller. To do this, this design will add a gearbox between the current
transmission and the motor mounted above. While the transmission is selected for forward,
the input shaft from the motor will be in line with the drive shaft of the transmission. There is a
9 | P a g e
lever that can be moved upward that will slide a shaft that connects the input shaft of the
motor with the output shaft in the transmission. Mounted on this moveable shaft will be a gear
that spins freely in forward, but when in reverse, it makes contact with another spur gear
mounted on a shaft to the side. Below this spur gear to the side is another gear that makes
contact with two more gears, the main drive shaft as the final contact that reverses the
direction of motion of the tines.
Figure 8: Reverse Gearbox Concept
Figure 9 depicts a compact reverse gearing design derived from ancient Egyptian style
mechanisms. The input drives a worm that drives the splined drive shaft. Forward and reverse
can be selected by driving the left of right plate, along with an option for variable speeds. Speed
1 or speed 2 for forward or reverse can be selected by engaging the inner or outer ring of the
plate with the output cog. The design is very compact and relatively simple to execute in tight
volume constraints.
10 | P a g e
Figure 9: Egyptian Reverse Concept
Figure 10 displays a CVT concept. The concept for this Continuously Variable
Transmission came from a video that the team found when we were benchmarking. The idea is
that if you vary the height of the input gear you the two shafts on the outside will rotate and
the gear ratio will change. The shafts are able to rotate due to the addition of a Universal Joint
that over the range of speeds of the shafts is 1:1. The CVT uses friction to operate but choosing
an appropriate spring constant can easily control that.
11 | P a g e
Figure 10: CVT Concept
Figure 11 shows another transmission design that uses a gearbox that can be placed on
the top of the existing transmission, just below the engine. The design uses a small belt driven
continuously variable transmission that would allow the user to adjust the speeds by changing
the distance between the belt gears. The user will also be able to shift to reverse by moving the
gear in the reverse section out which will then engage the two other gears and allow the tines
to change direction.
12 | P a g e
Figure 11: Transmission Concept
Project Scope
The initial project scope given to Team 3 from SPI was to design an improved tiller
transmission for production”. This scope left the team with many different options involving the
redesign of the transmission. The team brainstormed many ideas regarding variable
transmission designs and reversing feature mechanisms to improve the transmission.Essential
to identifying the project scope is isolating the design’s subsystems. Identification of
subsystems permits for the team to follow necessary design pathways that will ultimately lead
to successful project completion. The following is a description of the project’s subsystems as
concluded by the team:
Subsystem Identification
1) Reverse Feature: To provide the consumer with an easy method of switching the tiller
to operate in reverse for instances where the tiller gets stuck during use.
13 | P a g e
2) Variable Speed: To provide the consumer with the ability to adjust the output speed of
the drive shaft. This will allow for other attachments to be installed and used on the
tiller by the consumer. Proposed attachments include a sweeping assembly and a snow
sweeping assembly, though the attachments are not in the scope of this product.
3) Changeable Gearing Option with Excel: To provide the company with an Excel
spreadsheet that can be used to find the proper gearing configuration for different
engines while maintaining the desired tine speed. The subsystem will also include plans
for the construction of the transmission. This subsystem is a contingency plan in the
event that the other avenues do not produce the results we desire.
4) Multiple Transmissions: Should the other transmission subsystems all fail, we may
design two separate transmissions for the two engines that are currently used.
(European and American)
5) Engine Testing: We would gather information on the engines including torque and
power curves as well as temperature information and its effects on performance. These
may be found from the manufacturers or elsewhere, and can be tested by our team if
the data cannot be found anywhere.
Connections
Ideal Result: To include the reverse and CVT subsystems into a single transmission that supplies
a tine speed between 230 and 240 rpm + 31 lb-ft of torque.
Reverse Feature: This feature is optimally desired with subsystems 1-4.
Variable Speed: This feature is optimally desired with subsystems 1-4.
Changeable Gearing Option with Excel: This subsystem could involve 1 and 2, but will focus on
the calculations and programming in Excel.
Multiple Transmissions: This could also involve 1 and 2, though the focus will be on developing
two transmissions that will likely closely resemble the current transmission.
Engine Testing: This subsystem, alone, is the final fallback if all other subsystems fail. This can
also be done to supplement the work in other subsystems to provide us with more complete
information.
In addition, the team determined a series of “critical” and “non-critical” wants to drive
the decision making of the design. The “critical-wants” or wants that must be met by the design
to generate a profitable and functional tiller are the following: competitive cost, constant
power, and unchanged transmission housing geometry. The “non-critical wants” or wants that
14 | P a g e
are desired but not required for the design are the following: variable engine support and
reversing feature. These wants were tabulated and used to systematically compare the team’s
concepts and determine the best of those concepts. Table 1 displays the results of this
comparison.
Critical Wants
Satisfies
Want
Does Not
Satisfy
Want
Non-Critical
Wants x -
Concepts Cost Space
Constraint
Constant
Power
Variable
Engine
Support
Reversing
Feature
Satisfied
Critical
Want
Total
Satisfied
Non-
Critical
Want
Total
CVT+ Reverse
Mechanism in
Modified Housing
- x x x x 2 2
Reverse
Mechanism in
Current Housing
- x x - x 2 1
CVT + Reverse
Mechanism in
New External
Housing
- - x x x 1 2
Change Worm
and Worm Gear
Ratio
x x x - - 3 1
Ta
ble 1: Concept Selection
After the concept selection process, it was determined that most of the brainstorming
ideas the team generated would exceed cost constraints for production. The concept the team
generated that fit the cost and additional constraints was to simply changing the worm and
worm gear assembly within the current US transmission to a different gear ration optimized
for the Euro motor. This concept selection narrowed and focused the project scope. Instead of
designing an “all-in-one” transmission with many features, the team will focus on optimizing
the older US transmission for the Euro tiller. Although the Euro tiller will be of lower
performance versus the US tiller because of it having a lower power engine versus the US
version, the team would like to make the Euro tiller perform to its best capability with better
gearing. This leaves the primary objective of the team to be how to find the optimal gear
ratio.
Project Path Deleted: Concepts
15 | P a g e
At the end of Phase 1, the team and the sponsor isolated two project paths that would
be suitable in meeting requirements. The project paths address different aspects of the overall
problem, but provide concrete engineering solutions. The first project path is a reverse
planetary gear feature that would be designed for the direct tiller product. The second project
path is a variable speed transmission test setup that would be designed for research and
development purposes for future tillers and other Schiller – Pfeiffer products. Each project path
provides critical performance and/or engineering data to the sponsor that would ultimately
lead to the design and sales of high performing tillers. The team systematically analyzed both
project paths to determine which could be best executed by the team in the timing allotted for
Senior Design.
Reverse Planetary Gear Feature Project Path
After researching the options, we have concluded that designing a planetary gear reverse
feature for production-line tillers does not seem feasible given the restraints on cost. This original
concept is shown in Figures 13 and 14.
Figure 13: Reverse Planetary Concept
Figure 14: Reverse Planetary Concept – Exploded View
Deleted: concepts
Deleted: project
Deleted: concepts
Deleted: concept
Deleted: concept
Deleted: experiment
Deleted: concept
Deleted: concepts
Deleted: Concept
Deleted: 2
Deleted: 3
Deleted: 2
Deleted: 3
16 | P a g e
We have, instead, decided that building a test transmission featuring a variable speed
transmission is a more reasonable project, and will benefit the sponsor by finding optimal gearing
configurations for any compatible combination of engine and tines. The planetary reverse design,
chosen for further study due to its simplicity and compactness, would require the parts listed below. The
prices marked “R” indicate the retail cost from a supplier, and the prices marked “P” indicate the
estimated cost when purchased in quantity. To estimate the difference between these prices, we
considered the current worm gear used in the transmission. The cost for one unit was approximately
twice that of the part when purchased in quantity, providing a 50% price decrease when purchased in
quantity. The 3” brass gear used currently costs $7.84, and the planetary system seeks to replace it.
List of Parts Required for Planetary Reverse
1 4’’-6’’inch internal gear R $130 [4] P $65
4 1’’ to 2’’ planetary spur gears R $41.4 [1] P $20.7
1 2’’-3” center sun gear R $80* P $8 [2]
1 gear selector ring R $.87 [1] P $.43
1 gear selector rode R $.17 [1] P $.085
4 housing closing screws R $.75 [1] P $0.5
4 small roller bearing capable of 12000rpm R $46.28 [1] P $ 23
1 custom planet carrier, R $130 P $65
1 two piece custom housing R ? P $7 [3]
Retail total: $429 plus housing Production total:$189
These costs demonstrate that with current concepts, including a planetary gear reverse feature
dramatically exceeds our maximum cost of $14. As a result of the information listed above, we are
proposing the development of an experimental gear ratio testing unit as our main focus for the design
process.
CVT Experiment Setup Project Path
From our meeting on September 23, 2008 the project path of developing an experimental
transmission for testing the performance of different gear ratios was discussed. This variable speed-
testing box is not subject to the restrictive cost guidelines that prevented the reverse feature from being
a viable solution. What follows is a description of the plan for the continuously variable speed
transmission box.
We plan to design a CVT transmission that will mount between the engine and the transmission
of the Mantis Tiller. Figure 15 displays conceptual sketches for the experimental CVT and housing. The
setup will serve as a test instrument for Schiller-Pfeiffer and will help to find the optimum gear ratio for
Deleted: Concept
Deleted: concept
Deleted: 4
17 | P a g e
any model in the Mantis Tiller product line. Use of this device will improve the functionality of the
European model, which is severely restricted, and optimize the quality of the American model. In
addition, the experimental setup can be used to find the optimal gear ratios for a variety of attachments
to the tiller, such as a snowbrush or other similar add-ons. This adds developmental value to the
experimental setup because it will be useful in testing tiller add-ons and other engine applications that
can benefit from gear testing in the future. The fixture will be able used for test tilling so does not have
to be suitable for production. It will have an ideal maximum volume of 6”x6”x6”. It should feature a
wide enough selection of gears so that any reasonable gear ratio can be obtained. Figure 16 displays
conceptual sketches for the proposed CVT cones and a keyway plate for mounting the cones.
Figure 15: The original CVT concept envisioned by the team (left).Proposed housing (right).
Calculations find that a box with ratios varying from 1:2 to 2:1 will provide a suitable range of
output torque vs. tine rpm. These can vary from 71rpm, 62 ft-lb to 285rpm, 16 ft-lb on the 6000rpm
engine and 119rpm, 62ft-lb to 476rpm, 16ft-lb on the 10,000rpm engine. The high- and low-end values
for each engine are above and below, respectively, the ranges that would actually be feasible for the
tillers.
Deleted: 5
Deleted: 4
18 | P a g e
Figure 16: Close-up of CVT gear cone without gripping inserts (left).Bolt-on keyway plate to secure
gear to rotating shaft, 1 of 2 per gear (right).
Price Sources and Footnotes
[1] McMaster-Carr
[2] Planet gears
-Steel Plain Bore 14-1/2 Deg Spur Gear 32 Pitch, 18 Teeth, 0.562" Pitch Dia,
3/16".$10.35 Each.
-Ultra-Precision Mini SS Ball Bearing - ABEC-7 Open for .1875" Shaft Diameter, .5" OD,
.1562".$11.57 Each.
- Round Head Slotted Machine Screw with Nut Zinc-Plated Steel, 1/4"-20 Thread,
3" Length. $9.39 per Pack of 50, $.18 each
- Wide-Rim Plain Steel Shim .134" Thick, 2" ID, 3" OD. $8.75 per Pack of 10, $.87
each
[3] The price for this gear is assumed to be similar to the cost of the current drive gear based on its
similar dimensions and requirements.
[4] The current transmission housing costs $6, and we estimate that an additional housing would
cost approximately the same.
[5] This information was found through Boston Gear, a leading gear manufacturer.
[6] No sources used, price assumed from known real production price.
Deleted: 5
19 | P a g e
As a result of this analysis, the team’s project scope is to design a variable speed
transmission test setup to find the optimized gear ratio for tilling in terms of tine torque and
RPM. The ideal ratio will be used in the final project design concept by installation of a new
worm gear into the current transmission housing or by providing the modified drawing plans
needed to build the new parts. The team will provide an outline for the new worm gear design
and installation, based on data from the variable speed transmissiontest setup. Please refer to
Figure 1 for project scope clarification.
Figure 1: Project Scope Diagram
Concept Selection
In the design process, concept selection can often prove to be an arduous task. A
weighted benchmark chart is a very useful tool that can be implemented to aid in the selection
process. Figure 2 shows a concept design selection chart adopted from Dym and Little’s
Engineering Design, that was used to determine the type of transmission to implement within
the variable speed transmission test setup
Type of
Transmission
Gearing
Range Cost Weight
Ease of
Mounting Drivetrain Size Durability Safety Total
NuVinci CVT 4 3 1 2 2 3 4 4 23
Belt and Pulley CVT 2 1 4 1 1 4 1 3 17
Belt and Cone CVT 3 2 0 0 0 0 0 2 7
9 Speed 0 4 2 4 4 2 2 1 19
14 Speed 1 0 3 3 3 1 3 0 14
Figure 2: Transmission Selection Weighted Benchmark Chart
The structure of the chart is such that the top row consists of a list of constraints
pertinent to the application, and the column on the left contains possible design concepts. The
numbers in the chart are a ranking of each design concept relative to the constraint. The
Formatted: Font: Calibri, 12 pt, Not
Bold, Font color: Auto
Formatted: Font: Calibri, 12 pt, Not
Bold, Font color: Auto
Formatted: Font: Calibri, 12 pt, Not
Bold, Font color: Auto
Formatted: Font: Calibri, 12 pt, NotBold, Font color: Auto
Deleted: n experimental
Deleted: implemented
Deleted: experimental
Deleted: 1
Deleted: .
Deleted: 1
Deleted: Concept Design
20 | P a g e
concept that meets the constraint the best gets the highest score (4) and the concept that least
satisfies the constraint get the lowest score (0). Summing the numbers in each row
corresponding to the design concept will yield a total score. The total score is directly
proportional to how well each concept meets the concepts overall. The concept with the
highest total score is the one that meets all of the constraints the best. From the chart the
NuVinci CVT system is the concept is best suited for the tiller test feature application. Figure 3
displays a picture of the transmission hub with a cut away to display its interior.
Figure 3: NuVinci CVT Hub
The NuVinci CVT works through a mechanism described in Figure 4, which involves sets
of ball bearings that are attached to rockers and provide a mechanical connection between two
rotating input / output discs for torque and velocity. After correspondence with the
manufacturer, the team has learned that the NuVinci system has been tested with positive
results at an input power of 41 horsepower, which is far higher than our application requires.
The cost, size, and weight of the unit are also acceptable. It is uncertain at this point, if the
NuVinci transmission can handle the required rotational speed of the engine, 10,000rpm.
Action has been taken to retrieve this answer.
Design Overview
The team has determined with SPI that in order to execute the process of improving its
tiller transmissions for the European market, a systematic approach will be necessary to find
the optimal gear ratio. The team has decided to find the ratio by creating an experiment setup
that will vary the gearing of the current motor and transmission assemblies. Tiller performance
will be evaluated at various ratios and the best performing ratio will be utilized in the redesign
of the worm and worm gear assembly for future transmissions. Figure 3 displays a schematic
and a three-dimensional sketch of the purposed experimental setup design.A detailed view of
the experimental setup design is provided in Figure 4. The system works by taking power input
from the motor that sits on top of the setup and runs it into a continuously variable
Deleted: 2
Deleted: 2
Deleted: 3
21 | P a g e
transmission (CVT). The CVT permits the user to vary the gear ratio experienced by the system,
which will permit the user to select different gear ratios for optimal tilling. The power is
transmitted from the CVT to the setup output. From the output, power is transmitted to the
current transmission and ultimately the tines. The system is such that the power output from
the motor is assumed constant and equivalent to the power output of the tines. Efficiency
losses throughout the mechanism are negligible, based on sponsor discussion and motor &
transmission operation data.
Figure 3: Experimental Setup Schematic and Three-Dimensional Sketch
Figure4: Experimental Setup – Detailed View
Design Subsystems
22 | P a g e
The design can be broken up into six subsystems: Motor Input, Step Down Mechanism,
NuVinci CVT, Step Up Mechanism, Transmission Output, and Enclosure. Figure 5 displays a side
view of the experiment setup with labeled subsystems. Section views of the design can be
inspected in Appendix Afor shaft and bearing locations and types.
[insert correct picture here and rewrite subsystems]
Figure 5: Experiment Setup – Subsystems
Motor Input
The motor input is a custom machined part that is designed to conform to the motor
clutch assembly output of the motor. The motor input houses the driveshaft of the experiment
setup and contains a roller bearing to maintain gear and driveshaft alignment.
Step Down Mechanism
The step down mechanism is a series of two spur gears that reduces the power input to
the CVT by a 10:1 ratio. This mechanism is necessary for meeting the nominal input RPM
specifications of the purchased CVT. The pinion gear is at 14 teeth and the larger gear is at 144
teeth. The larger gear will be custom machined to mount properly to the CVT. Lubrication is
provided by initial gear greasing during design manufacturing and periodic greasing after
experiments via a grease gun.
NuVinci CVT
The NuVinci CVT, as viewed in Figure 6, is a purchased system from Fallbrook
Technologies designed for bicycles that will be adapted for the experimental setup. It is the
“critical” subsystem of the design, because it houses the mechanisms that provide the gearing
variability and thus the primary function of the experiment setup. The decision to use the
system was very important and was assisted through the use of a weighted benchmark chart
adopted from Dym and Little’s Engineering Design. Table 2 displays the weighted benchmark
chart with results.
Table 2: Weighted Benchmark Chart
23 | P a g e
The structure of the chart is such that the top row consists of a list of constraints
pertinent to the application, and the column on the left contains possible design concepts. The
numbers in the chart are a ranking of each design concept relative to the constraint. The
concept that meets the constraint the best gets the highest score (4) and the concept that least
satisfies the constraint get the lowest score (0). Summing the numbers in each row
corresponding to the design concept will yield a total score. The total score is directly
proportional to how well each concept meets the concepts overall. The concept with the
highest total score is the one that meets all of the constraints the best. From the chart the
NuVinci CVT system is the concept is best suited for the tiller test feature application.
The NuVinci CVT works through a mechanism described in Figure 7, which involves sets
of ball bearings that are attached to rockers and provide a mechanical connection between two
rotating input & output discs for torque and velocity. The system allows for continuously
variable gearing from ratios of 1:0.5 to 1:1.75, which is within the ideal experimental gear ratio
range for the project. In addition, the system provides a wide variety of velocity and torque
output at the tines, ranging from 280 RPM/18 ft-lb to 80 RPM/ 54 ft-lb. These values are also
within the ideal experimental ranges after sponsor discussion. Following correspondence with
the manufacturer, the team has learned that the NuVinci system has been tested with positive
results at an input of 41 horsepower, which is far higher than project requirements. The cost,
size, and weight of the unit are also acceptable.
Step Up Mechanism
The step up mechanism is a series of two spur gears that increases the power
outputfrom the CVT by a 10:1 ratio. It is of a similar design to the step down mechanism and is
necessary in providing the high RPM for input into the transmission output for tilling. The
pinion gear is at 14 teeth and the larger gear is at 144 teeth. The larger gear will be custom
machined to mount properly to the CVT.
Transmission Output
The transmission output is designed to conform to the geometry of the current
transmission housing and mate with the current transmission shaft. It is a part adapted from
the current motor geometry that contains a second driveshaft that turns the worm gear set
connected to the tines. The output contains two ball bearings to maintain gear alignment and
ensure reliability. Lubrication is provided by initial gear greasing during design manufacturing
and periodic greasing after experiments via a grease gun.
Enclosure
The enclosure subassembly contains a variety of parts designed to secure and protect
the other subassemblies. The enclosure top and bottom consist of two machined aluminum
24 | P a g e
alloy plates that hold the step down/up mechanism gear shafts, the NuVinci shafts, the motor
input, and the transmission output securely in place. One of the enclosure sides is a machined
aluminum alloy plate that is designed to hold two L-brackets in place. The plate also provides
structural support for the experiment setup. The L-brackets house the bearings and shafts
connected to the pinions of the step down and step up mechanisms. The remaining three sides
of the enclosure are made of fiberglass to safely contain the moving parts of the design. The
corners of the enclosure consist of two support struts on fiberglass side and four support corner
blocks on the machined aluminum plate side.
Design Performance
The primary design driver for the experiment setup was motor power management at
the tines. For this application, power is assumed to be the torque multiplied by the RPM either
at the input or output of the experiment setup. It is also assumed that the input power of the
motor is equal to the output power of the tines. Efficiency losses can be assumed to be
negligible at nominal tilling gear ratios. If it is assumed that there is a constant input torque and
RPM from the motor, there is a trade off between the output torque and RPM. The output
torque and RPM distribution are controlled by the gear ratio.
Calculations were performed to determine if the NuVinci hub would provide the desired
output range of tine RPM and torque. The generated numbers were important for design by
establishing performance limits for the design. Table 3 displays the calculations.In addition, a
Microsoft Excel spreadsheet was created to precisely predict specific output ratios for any given
input. Figure 8 displays a screenshot of the spreadsheet with generated data.
Table 3: Tine Output RPM and Torque Calculations
25 | P a g e
Figure 8: Design Spreadsheet Screenshot
Design Analysis
The following is a finite-element analysis of a plain carbon steel input pinion that drives
the experimental test setup. The inputpinion receives load from a driveshaft that is connected
to the input pinion with a roll pin. The input piniondrives an idler gear, which then drives a
larger gear fixed to the NuVinci CVT. A reverse geartrain at theoutput of the NuVinci is used to
transmit power to the output of the experimental test setup and ultimately thecurrent tiller
transmission. FEA was performed on the input pinion, because the team was concerned that
thepinion would possibly not withstand power transmission at the .74 lb-ft torque input.
Figure ???: Finite-Element Analysis – Plain Carbon Steel Drive Pinion
26 | P a g e
According to the FEA, the gear will endure the given loading. The von-Mises stress value
is approximately .5times lower than the yield strength of the material, which indicates that the
gear will be able to performnominally. Also, the results show that the pinion would withstand
the 0.74 lb-ft, 6000 RPM input with a theoretical factor of safety at 2.02. Further testing will be
performed to validate initial FEA results.
Drawing Package
A drawing package of the complete design has been provided in Appendix D. The
drawing package contains a 3D isometric view, 3D exploded view + bill of materials, and 2D
orthographic views of each part of each subsystem. The drawings are to scale and are ready for
use in design manufacturing. Note: Fasteners were not shown so to improve drawing clarity.
Design Assembly
The assembly process of the experiment setup can be broken down into a series of
instructions. The team and/or the sponsor to put the design together for testing will use these
instructions. Assembly instructions are provided in Appendix C.
Testing Methodology
Design testingis divided into two segments. Testing will be conducted to validate the
functionality of the experiment setup and then preliminary testing will be conducted to begin
the process of determining the ideal gear ratio for tilling. Future testing for recommendation to
SPI after the conclusion of Senior Design is provided.
FunctionalTesting
Rotational Power Transmission and Variability Output RPM Test
1) The test box will be installed on the Mantis tiller.
2) The tiller will be suspended above the ground and the engine started.
3) The transmission of power through the test box will be verified by rotation of the output
tines.
4) Variability of the output will be verified by changing the NuVinci ratio from low to high
and checking for observed variation in tine output RPM.
5) The engine will be stopped and the testing setup will be visually examined for any signs
of damage.
Unaltered and Low/High Ratio Test
1) The tiller will be suspended above the ground.
27 | P a g e
2) The engine will be started and the engine RPM will be measured using a tachometer.
3) The NuVinci will be adjusted to a 1:1 ratio.
4) The output tine RPM will be measured using an infrared tachometer. This value will be
compared to the known value of output RPM without the test box installed on the tiller.
5) The engine will be stopped and the testing setup will be visually examined for any signs
of damage.
6) The test will be repeated with the NuVinci set to high and low ratios.
In-Ground Function Test
1) The tiller with installed test box will be started.
2) The NuVinci will be placed in the 1:1 ratio setting.
3) Tilling a portion of untilled ground in SPI’s tiller testing bed will attempted.
4) If the top layer of soil is successful broken and turned over, exposing the dirt below, and
the tiller tines sink fully into the soil without becoming jammed the test will be
considered a success.
5) The engine will be stopped and the testing setup will be visually examined for any signs
of damage.
6) The test will be repeated for ratio gradually varied above and below 1:1 to verify
functionally.
Performance Testing
1) In the typical test soil located at SPI’s garden test bed, untilled ground will be tilled while
varying the gear ratio from high to low in 10 even increments.
2) The tiller will be tested at each increment for 1 minute.
3) Each ratio will be evaluated by ranking the following categories which may quantify the
subjective notion of “good tilling” on a 1 -10 scale with the score of 1
representing“strongly disagree” and the score of 10 representing “strongly agree”:
• The tines can break the soil.
• The tiller easily turns over the top layer of soil.
• The tiller tills without becoming clogged by debris.
28 | P a g e
• The tiller is controllable by the user.
• The tilled soil is of an approbated consistency for gardening.
• The tiller successfully handles small debris without stopping.
• The tiller tills better then without the test box.
4) The result will be tabulated and then tests will be repeated for narrower range of
increments to more precisely find the idea ratio range.
Suggested Future Testing
The team suggests the following tests be performed by SPI in the future:
• Repeating the abovementioned tests in different soils typical of different regions of the
world, practically representative of the European countries in which the new tiller is to
be marketed.
• Tilling soil with different ratios and taking samples of the tilled earth to be closely
examined for consistency and permeability to differentiate soils.
• Tilling different parts of a garden with different ratios and then planting crops in the
different regions. Then examining the any difference in plant growth between regions.
Cost Analysis
The cost analysis for the design is divided into three sections. The first section highlights
the estimated costs of engineering research and development. Note that the course does not
additionally charge SPI for engineering services, but rather engineering services are provided
for academic credit. Engineering costs are included as a reference for comparison to other real
design costs. The second section highlights the bill of materials for the design, which includes
part names, amount of parts, cost per part, source of part, and the total costs. The third section
highlights parts that were purchase and in hand with real costs after shipping.
Estimated Engineering Cost
As an estimated cost of the real engineering associated with the research and
development of the project, the team presents the following approximation (Assuming a rate of
$50/hours of R&D):
16 weeks * 5 team members * 20 hours/week * $50/hours of R&D = $80,000
Bill of Materials for Test Gear Box
29 | P a g e
Part Amount Cost/Part Source Total Cost
Mounted Bearing 2 $10.26 McMaster $20.52
Thrust Bearing 2 $16.50 McMaster $33.50
Nuts 2 $0.63 McMaster $5.00*
Washers 10 $0.60 McMaster $5.00*
Screws 20 $0.19 McMaster $5.00*
Aluminum Plates 1 $150.52 McMaster $150.52
Aluminum Square 3ft Stock 1 $35.70 McMaster $35.70
Spurs Gears (2 different sizes) 4 N/A SDP/SI $220.00
Threaded Shaft 2 $28.04 McMaster $56.08
Fallbrook NuVinci CVT 1 $409.00 Fallbrook Tech $409.00
Aluminum Round Stock 1 $20 McMaster $20
Aluminum Block 1 $40 McMaster $40
Machining Cost 4 $70/hr $280
Miscellaneous 20% $256.07
Total $1536.39
*Small costs such as nuts and bolts are rounded up to $5 because part availability is only in
quantity.
Purchased Parts
NuVinci CVT $284.00
Gears $145.00
Total $429.00
Proof of Concept
Figures ??? and ??? displays the completed design assembly and the assembly installed
onto the tiller. The system works by taking power form the motor on top of the experimental
setup and inputting it into the NuVinci CVT. The user varies the setup gear ratio at the gear
shifter mounted to the tiller handle in order to select the best ratio for tilling. The NuVinci
permits for variable gearing between the ratios of 1:0.5 to 1:1.75. Power is transferred from the
CVT to the output of the experimental setup, where it is ultimately transmitted to the current
transmission and the tines. The range of RPM and torque at the given gear ratio limits are from
30 | P a g e
280 RPM, 18 lb-ft of torque to 80 RPM, 54 lb-ft of torque at the tines. It is assumed that power
output from the motor is assumed constant and equivalent to the power output of the tines.
Figure ???: Completed design assembly
Figure ???: Design Assembly Installed to Tiller
31 | P a g e
The proof-of-concept testing is intended to demonstrate that the developed
continuously variable transmission will work as expected to aid Schiller-Pfeiffer in finding a
more optimal gear ratio for the European tiller model. Figure ??? displays in ground tiller
testing with the experimental setup.
Figure ???: In Ground Tiller Testing
Our first test will prove that the device is capable of engaging the tines and shifting
through the full range of gears while running at full power from the engine. This test proves
that the device is able to withstand the power load required during tilling at all possible RPM
and torques. The first trial of the experiment showed that a large percentage of the power
from the engine was dissipated in the transmission due to minor misalignments. After
correcting these, a second trial demonstrated that the tiller was indeed capable of tilling soil
across its gear range. The device was run continuously for 6 minutes without any failure or
visible wear. The shifting mechanism was also tested and proven to shift gears successfully in
both directions and while the tiller is on and off. It was also found that the weight of the added
test transmission impedes tilling, suggesting to the team that counter-balance measures will
have to be taken to provide accurate quantitative testing. The success of this test suggests that
the transmission can, in fact, prove to be a useful tool in simulating different gear ratios for the
tiller transmission.
A laboratory experiment in which we use a power drill capable of reaching 2400 rpm to
drive the transmission without any load on the tines will quantify the power losses in the
experimental transmission. Figure ??? displays the power drill bench testing setup.
32 | P a g e
Figure ???: Power Drill Bench Test Setup
The data recorded from this test has been used to plot a chart of power losses versus
rpm. The resulting chart is then extrapolated to just over the full speed of 6400 rpm to give an
estimate of the inherent power losses at each rpm. (Need real data to compare here) The
losses, mainly due to friction in the NuVinci, gears, and bearings, are converted into
percentages of total engine power, which is based on a supplied power curve for the engine.
This data is vital to relate the performance the tiller when equipped with the experimental
transmission to the production tiller, which does not have to overcome the friction of the
experimental box.
The final experiment is another in-ground test during which we will use the device in a
counterbalanced system to till soil at all possible gear combinations. The team will collect data
from each trial to objectively and subjectively find the area of the possible gear spectrum where
the optimal ratio seems to lie. While the concept of the experimental continuously variable
transmission has already been proven, this test serves as the first experiment towards finding
an optimal gear ratio for the European tiller model. (More once testing is completed)
Experimental Results
Upon complete assembly of the experimental box testing was conducted to verify the
completion of the original design metrics. Specifically these metric tested are the range of
output speeds predicted was physicallyachieved
Experiments conducted on to validated and quantify the performance of the test figure.
To quantify the mechanical loses induced by the test box the following experiment was
performed using a corded power drill, an induction amp meter
Testing
33 | P a g e
Bench top input/output test
A 2500rpm electric power drill was used to supply input to the box and two inferred
tachometers to measure input and output speeds. This test was performed in with the NuVinci
transmission in full under drive, 1:1, and full over drive. This test demonstrated that when
provided with an input the test box can successful deliver the target range of gear reduction. It
also demonstrates the physical ability of the fixture to handle high RPMwithout mechanical
failure. The results of the tests shown in the table below demonstrate the predicted range of
reduction is delivery by the fixture. Also the box was examined during and after the testing and
now signs of damage were seen.
ADD CHART OF INPUT OUTPUT RPM from drill)
Quantification of 10 discreet NuVinci ratios’ for the purpose of testing
While the strength of the NuVinci is its ability to provide and infinitely variable ratio with in its
allowable range in order to begin to quantify tiller performance certain discrete points of
reduction need to be measured. This was accomplished using by providing a constant input rpm
with the power drill and measuring the output rpm while the NuVinci was change in 10th
increments of it’s total range. The chart below shows these ranges as well as the reduced
reduction at each range
(Add chart-showingratios for 10 marks and reduced ration at each mark)
Tiller mounted unloaded input/output test
Once the ability of the fixture to successfully produce the desired range of output was
confirmed by the bench top test and 10 discrete positions on the NuVinci were mapped to
there appropriate ratio further testing was conduced using the fixture fully mounted to the
tiller and the gx25 engine. This was preformed using the engine tachometer was well as an
inferred tachometer to measure the tine output rpm. The engine was run a full throttle and the
tines were suspended above the ground to yield zero load output rpm values. At each of the 10
positions the output tine output RPM were tested. As can be seen below the achieve values of
compared to the predicted values. The results of this test show that the tiller performed
successfully up to the two highest rpm testing in which the load applied to the engine by the
box caused a drop in rpm and thus a drop in output
34 | P a g e
(Add charts showing engine rpm, tine output rpm, and predicted tine output rpm.
Dynamic frictional loss tests
Form the results of the tiller mounted input/output test was determined that for the
tiller to be used to yield accurate data the dynamic frictional losses from the box needed to be
measured. This was done thought the use of a drill and an electrical current meter. The drill
was run at various constant rpm levels from 0 to 2500 and the current drawn be the drill at
each point was measured. The drill was then connected to the NuVinci mounted to the tiller
transmission and the test was preformed at high, 1:1; and low range. The test was then
repeated with only the current transmission. As see in the table below the torque required to
turn the NuVinci determined by this method.
Preliminary performance test
Because of the losses produced at by the test box, direct testing of high RPM ranges will not
provide accurate data because the output torque at the tines is less then the torque would be
with out the NuVinci. However the minimal using the know losses the minimal torque required
for acceptable can be determined. With the minimal torque know then the optimal gear for
tilling can be found
Fill in tests
Plan for future testing at by SPI
The testing has shown the experimental transmission performs up to the predicted
target values. SPI cannot continue the process of testing different soils to determine which ratio
by provide the most ideal tilling conditions. One this ratio has been determined it will be
implemented into there line through replacements of the current worm gear with a new worm
gear which provides the new ratio.
Path Forward
35 | P a g e
Following the conclusion of Senior Design, SPI will continue more detailed performance
testing to determine the ideal gear ratio for the Mantis tiller. Once the ratio is determined,SPI
will order a new custom worm and/or worm gear with the ideal ratio and continue testing. By
2010,SPI will conclude testing and introduce the Mantis tiller with the new worm and/or worm
gear to the European market for sale.
When the team hands the project over to Schiller-Pfeiffer, the sponsor will continue to
run experiments using the test transmission in soil to pinpoint the gear ratio to be used on
European production models. The experiments will be carried out both in the testing garden
outdoors and in a testing box indoors at the sponsor’s location. Outdoor testing will mimic
actual use, where the tiller may encounter grass, twigs, stones, and other natural debris.
During indoor experiments, varying soil types will be used to attempt to replicate European
soils as well as many other common soils. To simulate the weight of a regular tiller, a
counterbalance system will be used for all tests with a weight equal to that of the experimental
transmission exerting an upward force on the tiller. In the same manner that existing tillers are
commonly tested already, trials will not exceed 10 minutes of constant operation.
When sufficient testing has been completed and overwhelmingly points to a specific
optimal gear ratio, the sponsor will consult a Microsoft Excel spreadsheet in which they can
enter the numerical reading from the gear shifter and receive the proper gear ratio for the
worm and spur gears in the standard transmission. This reading could potentially become
inaccurate if the cable operated shift mechanism loses tension in the operating cables. The
repair instructions can be found in the Transmission Manual, which is supplied to the
sponsor. To gain a failsafe measure of the true gear ratio, readings from the engine
tachometer can be compared to rpm readings found at the tines by an optical tachometer. This
must be done at the desired gear ratio without any load on the tines, to prevent any slippage
on the engine clutch, which would offset readings.
After positively identifying the desired gear ratio, a worm and spur gear must be
designed and built to order. The design and manufacture of these gears is outsourced to the
local company that produces the current gears used in the tiller transmission. To prevent
spending on an incorrect design, a small quantity of gears should first be ordered and tested in
the tiller. The gears produced in this step will be more expensive than the gears used in the
actual production run, because the quantity needed initially is much smaller than the
production quantity. When the gear is proven to work effectively to improve the operation of
the European tiller, and production quantities for the European model are established, a full
order can be placed with the gear vendor.
The assembly process for the European transmissions will be identical to the assembly
procedure for the existing transmission except that a worm and spur gear set with a different
36 | P a g e
pitch will be used in place of the old gears. This helps to make the shift on the assembly line
smoother because the workers do not need to change their work habits and no other parts
need to be changed. The ability of the new design to replace exactly and only the two gears
saves a substantial amount of money because the cast-molded housing is no different than the
regular housing and no other hardware needs to be used. Part ordering for future production is
also simplified because all part ordering, except for the gears, concerns the total number of
tillers produced and requires no differentiation between the European and American models.
37 | P a g e
Appendix A: Design Section Views
Design Section View – General
38 | P a g e
Design Section View – Motor Input
Design Section View – Transmission Output
39 | P a g e
Appendix B: Gantt Chart
Mantis Tiller TransmissionSchiller-Pfeiffer, Inc.
Project Lead: Lana Gendelman
Today's Date: 12/16/2008 (vertical red line)
Start Date: 9/3/2008
Tasks Start End Dur
atio
n (D
ays)
Phase 1 - Design Requirements and Project Scope 9/03/08 9/17/08 14Benchmarking 9/03/08 9/11/08 8Obtain Tiller and Transmissions 9/08/08 9/08/08 1Investigate CVT and Other Transmission Types 9/03/08 9/11/08 8Tiller Transmission Wants 9/08/08 9/11/08 3Tiller Transmission Metrics 9/08/08 9/11/08 3Project Subsystem Identification 9/11/08 9/17/08 6Transmission Ideas and Sketches for Reverse Gear 9/08/08 9/16/08 8Test Mantis Tiller 9/12/08 9/16/08 4Assemble Phase 1 Report and Prepare for Sponsor Meeting 9/16 9/11/08 9/15/08 4
Review Concepts and Sketches with Sponsor for Approval 9/16/08 9/16/08 1
Phase One Report Due 9/03/08 9/17/08 14Phase 1.5 - Concept Selection and Project Plan 9/18/08 9/23/08 5
Decision Made between Reverse Feature or Test Gear Box 9/18/08 9/18/08 1
Prepare Presentation Explaining Subsystem Choice 9/18/08 9/23/08 5
Continue to Benchmark CVTs for Test Gear Box 9/18/08 9/23/08 5
Meeting with Mrs. Gendelman and Phase 1.5 Report Presented 9/23/08 9/23/08 1Phase 2 - Concept Selection and Project Plan 9/23/08 10/07/08 14Decide between NuVinci Hub and 9 Speed Bike Hub 9/23/08 9/25/08 2Research Ways to Implement Bike Hub in Test Box 9/23/08 9/30/08 7
Create First Draft Drawing Package of Concept 9/25/08 9/30/08 5
Prepare Presentation for Ms. Gendelman 9/25/08 10/02/08 7
Research Parts and Lead Times for Bike Hub Concept 9/25/08 10/07/08 12Meeting with Ms. Gendelman at SPI to Review Test Box 10/07/08 10/07/08 1Phase 3 - Detailed Design 10/08/08 11/05/08 28Final Tiller Transmission Drawing Package 10/08/08 11/03/08 26Complete Power Point Presentation and Discuss with Mr. Cloud 10/20/08 10/24/08 4Formulate a Detailed Cost Analysis 10/20/08 11/03/08 15Order Necessary Parts 10/22/08 11/06/08 17Design a Testing Methodology 10/22/08 11/03/08 11Oral Presentation to Engineering Panel 10/30/08 10/30/08 1Meeting with Ms. Gendelman and Phase 3 Report Presented 11/11/08 11/11/08 1Phase 4 - Performance Validation 11/06/08 12/16/08 40First Draft of Poster 11/06/08 11/13/08 7Machining of Gears 11/06/08 11/06/08 1Machining of Frame Components and Brackets of Box 11/11/08 11/11/08 1Machining of Top & Bottom Plates for Shaft Locations 11/13/08 11/13/08 1Machining of Shafts 11/17/08 11/25/08 1Bearings Pressed and Parts Press Fit, Initial Assembly 11/17/08 12/02/08 15Carbon Fiber & Polycarbonate Side Panels Fabricated 11/20/08 12/02/08 12Final Assembly of Experimental Transmission Box 12/02/08 12/02/08 1Tiller Assembled with Experimental Box in Place 12/04/08 12/04/08 1Initial Testing with Experimental Transmission with Mr. Cloud 12/04/08 12/04/08 1Troubleshooting and Modifications to Transmission Box 12/04/08 12/06/08 2Second Round of Testing and Tiller Evaluation 12/08/08 12/08/08 1Final Poster Due 12/08/08 12/10/08 2Design Experiment Procedure for Tiller Testing at SPI 12/06/08 12/09/08 3Test Designed Tiller Experiment Before Final Testing at SPI 12/10/08 12/10/08 1Final In-Ground Testing at SPI & Reverse Feature Presentation 12/11/08 12/11/08 1Final Report and Presentation Due 12/09/08 12/13/08 4Final Presentation to Panel of Engineers 12/15/08 12/15/08 1Final Presentation Given to SPI 12/16/08 12/16/08 1
11 /
24 /
08
11 /
17 /
08
11 /
10 /
08
11 /
3 / 0
8
10 /
20 /
08
10 /
27 /
08
12 /
15 /
08
12 /
22 /
08
9 / 1
/ 08
9 / 8
/ 08
9 / 1
5 / 0
8
9 / 2
2 / 0
8
9 / 2
9 / 0
8
10 /
6 / 0
8
10 /
13 /
08
12 /
8 / 0
8
12 /
1 / 0
8
40 | P a g e
Appendix C: Design Assembly
[Insert new assembly instructions]
41 | P a g e
Appendix D: Drawing Package