Soil Slurry Churner
Team A5
24-441 Engineering Design II: Conceptualization and Realization
May 12, 2014
The Team
Miki Bassey: Miki Bassey is a robotics-loving Japanese-American mechanical
engineer. After seeing the aftermath of the Fukushima disaster, she wanted to work
on a project that would help. Miki worked on prototyping, making the Solidworks
models and doing some of the hands-on work in the machine shop.
Kathryn Davis: Kathryn acted as team leader and did her best to help out with a
little of everything. She worked on prototyping and CAD modeling, while taking charge
of the analyses, heavy machining, and welding.
Brenna Flatley: Brenna’s work on the team was as well-rounded as her interests.
She helped with woodworking, selected components, and worked on aesthetics. She
was also in charge of the slurry samples and testing the effectiveness of mixing.
Clair Hann: A quiet powerhouse with a thirst to create awesomeness, Clair
purchased and delivered large project materials. She also constructed the platform,
designed the tilt-assist mechanism, and made the expo poster.
Catherine Rudnick: With a clever eye for detail, Catherine completed the house
of quality, bill of materials, and cost analysis. She was in charge of electronic
components and wiring, and aided prototype building.
Problem Description
In the wake of the Fukushima nuclear disaster, farmland
surrounding the affected area was found to be
contaminated with dangerous levels of radioactive Cesium.
The government’s response to this was to completely
remove the topsoil layer in these areas, which is very costly
and wasteful.
Our project was inspired by research of Professor Masaru
Mizoguchi at the University of Tokyo, who found that the
radioactive Cesium particles had a tendency to attach to
clay particles in soil. From this, he developed a method of
systematically removing clay from farmland while retaining
nutrient density in soil. –To separate clay from soil, soil and
water must be churned into a homogenous mixture, then
left to sit for several hours so the clay will separate,
leaving the nutrient-rich silt. Mizoguchi’s method involves
sending several workers into the fields to painstakingly
agitate the soil using hand tools. This method removes
about 80-90% of cesium, falling into national safety
standards and allowing farms to begin producing quicker.
Opportunity Statement
Although Mizoguchi’s method is effective at removing clay, we felt it could be best accomplished
in self-contained system to be operated by fewer workers. Our opportunity lies in the ability to
create a clay extraction system that is smaller than expensive industrial machinery, but more
productive and less labor-intensive than hand-mixing methods.
Motivation
Creating a self-contained clay extraction system
for large-scale use has many benefits in nuclear
decontamination. Because we are designing a
system that can be operated by a single user with
many commonly available parts, we hope to solve
the problems of areas in need of decontamination
while using fewer resources and manpower.
Separating clay in a contained but small-scale
system reduces exposure to nuclear materials and
hopefully would quicken the Japanese farmer’s
return to production.
Market Research
Our market research focused on three specific groups that would find use in a system like ours.
This group included Japanese farmers as mentioned before, as well as local potters and gardeners
in the Pittsburgh area. From this, we approximated their priorities in a clay extraction system:
•Potters - interested in extracting indigenous clay for pottery use
-Wanted a safe, cheap, and portable system
-A system that could extract more clay in one iteration than by hand
•Gardeners in the Pittsburgh area - wished to reduce the acidity level from high clay
concentrations present in local soil, while still retaining nutrient density
-Wanted a system that leaves nutrients in the soil
-A safe system that easily extracts clay without requiring much heavy lifting or labor
•Japanese farmers - interested in removing contaminated clay from soil and reducing waste.
-Wanted a system that wastes less water than current methods
-A system that uses fewer resources than hand-mixing or heavy machinery
Design Requirements
At right is a selection of our
design requirements (in no
particular order). These have
progressed from our initial
stages in various ways
including the removal of
considerations for a selfmoving system (see “Concept
Generation and Evaluation”)
and the addition of specific
requirements that ensure the
system’s usability in isolated
or low-power conditions. Our
complete requirements are
described in full on the
following page.
Design Requirements
End-User/Stakeholder Requirements
System Requirements
• Ease of Use – The system should be easy to use and practical.
• Homogenous Mixing – It is of the utmost importance that the
• Portability – The system should be of an appropriate size and
• Engine Isolation – The engine should be separate from the wet
Operation should require less effort than current manual soilmixing methods. Unnecessarily complicated operation should be
avoided because it would deter users from adopting this new
system.
weight to be easily transferred from storage to field and between
containers.
• Compatibility with Existing Equipment – The mixer is
designed to fit a 5-gallon bucket, a standard bucket size many
have already in their garages or gardens.
• Safety – There should be little risk of bodily harm to the end
mixer is able to achieve a homogenous mixture of water and soil.
• Ruggedness – The system should be able to soils with various
compositions and perform consistently over extended use.
mixing portion of the system in order to prevent short circuits and
engine damage.
Functional Requirements
• Secures Bucket – Because of the rotational nature of our
user. As this mechanism will require a significant amount of torque
to operate, it is very important that the end user is prevented
from getting any part of their person caught in the moving parts.
To accomplish this, we will isolate the moving parts of the system
from the user with a lid.
mixing method, the system should be able hold the bucket in place
so that only the mixing tines and soil solution move.
• Low Maintenance – This system should not require frequent
• Prevents Spills – It is important that the water and soil stay
maintenance or supervision to operate.
• Stabilizes Tilted Bucket - After mixing, the slurry must be
poured in a controlled manner into a filtered reservoir for clay
extraction.
contained in the bucket.
• Marketability- The system should be easily marketable to
multiple types of consumers, including local farmers, industrial
users, and artists.
Environmental Requirements
• Long Life Cycle – The system should be durable, such that
it can sustain multiple uses and be used for a long time.
• Effective Clay Extraction – Clay should be sufficiently
removed from soil after cycling through the system.
Concept Generation and Evaluation
Our initial designs focused on mobile waterproof push-tillers. We quickly found that these designs were beyond the scope
and budgetary constraints of our design course.
We were later inspired by the design of common concrete mixers. From this we decided to design a self-contained system
and focus on the entire user interface, from mixing to settling and filtering. Shown below are examples of Pugh charts used
to evaluate our various concepts based on the design requirements. All concepts were rated on a scale of -2 to 2
(represented in the charts by + and –’s), and net performance was based on the weighted sum of ratings for each criterion.
We began by evaluating general concepts, as seen on the left. Once we decided to pursue a bucket based design, we
perfomed a secondary evaluation to decide on a specific mixing mechanism. This secondary evaluation was performed at the
same time as, and informed by, the activities of our first prototyping stage. This stage is explained on the following slide.
Prototype 1
To focus on developing a mixing attachment,
we made several small-scale replicas of
existing mixing tools using cardboard and wire.
To simulate the different layers present in the
material to be mixed, we tested the prototypes
in clear buckets with color-separated layers of
multicolored candies and judged each design by
its ability to disturb the layers. The prototype
mixers were each attached to a standard drill
and rotated in the candy layers. Although this
prototype was not an accurate portrayal of
realistic mixing conditions, it helped us decide
on the paddle-type mixing attachment because
other designs showed no added mixing benefit
for the additional manufacturing difficulty they
incurred.
Prototype 2
Our second prototype consisted of a steel paddle which was driven
directly from a rotational motor. The bucket was strapped into a tiltassist mechanism, which consisted of a long hinge attached to the
base. The motor and paddle were attached to a three-legged
platform, which would then be lowered over the bucket using the
attached handles.
It was in this prototype that we found our paddle design was overengineered for durability. For the purposes of our design task, we
found we did not need such a heavy paddle design, and decided that
user experience would improve with a lighter paddle. While this
prototype accomplished our main objective of mixing soil and water,
it failed to do so safely as it lacked vibration dampening and paddle
balancing. Because of the paddle’s weight, and because of the directdrive motor receiving full power on starting, a slight off-centering of
the mixing attachment led to violent jostling of the mechanism and
inconsistent performance.
Virtual Mock Model
The model shown on the far left is the
virtual mock model of what we initially
intended to construct for Prototype 2. Over
the course of the prototyping period, changes
to the paddle shape took place (as evidenced
by the image on the right), and the handle
design became more realistic. We abandoned
the dual bucket platform because we felt that
we could sufficiently demonstrate the highly
movable nature of the system without
explicitly showing the transition between two
buckets. Further, an individually scaled final
product would be unlikely to feature a dual
platform and a largescale use of the system
would have a more expansive setup with or
without the platform’s aid, so a dual bucket
prototype would not give an accurate
representation of the final product system.
Functional Decomposition
Visual signal that
system is not running
This flowchart details the desired functionality of our system.
Performance Metrics
We used the following metrics to judge our system’s performance:
• Homogenous consistency reached from operation
• No large clumps of clay or soil
• Clay extraction comparable to hand mixing
• Approximately 25% clay removed by volume
• Limited mixing time
• 30 seconds from powered experimentation
The first two metrics were informed by our first round of
experimentation. We wanted to compare the system to hand mixing,
which is extremely thorough (extracted the 25% clay cited above).
However, we also wanted mixing to occur much faster than by hand.
Using the faster end of durations that potential users expressed
interest in through market research, we developed our time goal.
Engineering Analysis
In the course of finalizing our design, several analyses were undertaken.
They will be addressed in the following order:
•
•
•
•
•
Basic Static Analysis
Optimization
Fluid Analysis
Full FEA Simulation
Electrical Analysis
Basic Static Analysis
Our basic static analysis was the basis of almost all subsequent analyses. The analysis was carried out to get an
approximation for the required shaft thickness and the thickness of the paddle components (since, based off of
successful mixing paddle designs, we were anticipating a mostly hollow design). Toward this end, however, we
looked at a worst case scenario of the paddle being completely clogged with debris, which was effectively a paddle
of solid cross-section. Additionally, a safety factor of 5 was enforced in all calculations. Both of these measures
were taken to ensure the system’s safety as users interact with it so closely.
We began calculations by finding the force that the paddle would feel from drag in the material. We work under
the assumption that this drag will be due to a uniform slurry because assuming a bucket full of soil would result in a
paddle that is so overbuilt that it is too heavy for a user to repeatedly move comfortably and because the densities
of soil and our particular slurry are similar enough that the difference is absorbed by our imposed safety factor.
The drag force was found using the following equations:
Here, φ represents the solid weight percent, 54.6% for the purposes of our system (given the 50% volume of soil).
CD is the drag coefficient due to the shape of the submerged body, 1.05 in this case. We agreed that a nominal
velocity of 120 rpm would be suitable as an approximation of the lowest end of the range of speeds for blending
mechanisms (low running speed for user safety).
Basic Static Analysis
To have a complete picture of the forces acting on the system, we must also consider the paddle’s inertia. This requires us to switch
gears. Using material properties from matweb.com to model our material options (303 stainless steel, 1045 carbon steel, and 6061
aluminum), we perform a bending analysis on an individual paddle tine (modeled as a uniformly loaded double cantilever beam, given its
welded connections to the paddle skeleton). Since the tines are angled in relation to the force from the material, this computational
model is not completely accurate, but assuming complete facial contact with the material at all times results in a more conservative
value than reality will require. We find the thickness by imposing an upper limit on the allowable deformation of the tine and solving the
following system of equations:
In these equations, L is the length of the tines (10 inches), E is the material’s modulus of elasticity, w is the width of the tine (1.25
inches) and P is the force per unit of length applied to the tine, the “force” being the drag force. With the thickness in hand, we can
easily find the mass of the paddle, followed by the paddle’s moment of inertia. Combining the inertial load with the drag force, we can
use the following deflection equations to find the dimensions of the shaft (the first being another safety-imposed limit).
G is the shear modulus of elasticity for the material, T is the applied torque (found above), and L is the length of the shaft (18 inches).
X is the length of the sides of the square cross-section portion of the shaft, and Δφ is the shaft’s angular deflection.
After all calculations are complete, we find that the aluminum requires more material to match the strength of either variation of
steel, as one would expect. However, the mass of aluminum is significantly lower, even in the increased quantities. This is an important
consideration given that the user will be lifting the system at times. With this in mind, it is apparent that aluminum is the ideal material
for our application. With aluminum, the resulting dimensions are as follows:
Shaft Side Length/Diameter: 0.794 inches
Tine Thickness: 0.214 inches
Optimization
One of the first steps in our design process was performing a
parametric optimization for the specific aspects of the paddle
design. Though this step included a stress analysis, these
results were used solely for comparison to a control shape, a
solid square paddle (shown right). The optimization was
performed to optimize the number of interior tines on the
paddle and their tilt angle with respect to the paddle’s mid
plane. We investigated numbers of tines ranging from one to
three and angles in the range of 5° to 60°. These variations
were judged by their maximum Von Mises stress and minimum
safety factor. At right is a table showing the results for each
case, where performance was based on Factor of Safety.
Cases are labeled such that the last number is the number of
tines represented, and the preceding numbers are the tilt
angle in degrees.
Optimization
All models involved a pin constraint around
the main shaft to simulate the bearing setup
that would be present, and the control paddle
felt pressures on its mixing surfaces that
simulated the resisting torque of the mixing
material. However, the parameterized paddles
were simulated with remote forces distributed
along all relevant sections of the paddle.
We found the optimal scenario to be one
interior tine per side (evenly spaced) tilted 60°
from the mid plane. After this was complete,
the results from the optimized configuration
were compared to those of the control paddle.
The former performed better than the latter,
and so was the design with which we
proceeded.
Fluid Analysis
We conducted a brief fluid analysis using FLUENT to confirm
that moving forward with our desired speed was reasonable. Our
performance metrics from early in the process stated that our
goal was to achieve a homogenous mixture within 30 seconds, so
in our model, we would be looking for an even distribution of soil
at that time. The analysis model involved a small impellor and
its angular velocity was set to match our given speed through a
polynomial expansion. The model was set up such that initially
the system contained a layer of soil (modeled with density values
courtesy of engineeringtoolbox.com) underneath a layer of
water. The mesh, shown top right, displays the soil in dark blue,
and the water in grey. When the simulation was run, the soil was
fairly well-distributed through the water at the end of one
minute (see bottom right). However, due to limitations of skill
and resources, and as one can see, this model is not entirely
representative of the system as it will exist in practice. This
simulation was used to inform the design process, but did not
serve as a specific foundation for any subsequent decisions.
Model was based off of “Using the Eulerian Multiphase Model for
Granular Flow” tutorial from FLUENT, Inc. documentation.
Electrical Analysis
We carried out a brief analysis for the purpose of finding the specifications required of our electrical components
to receive the results we’d been simulating. After determining the torque required to spin the paddle at the
desired speed, we used this information to find our power requirements. The minimum power was found via:
Here, P is power, T is resisting torque due to drag, and ω is the angular velocity of the paddle. After we found
that the optimized, non-solid paddle was the best design, an updated torque (due to the altered shape and
moment of inertia) was found. From this, we found that the system required approximately 230.36 Watts of power.
After the motor was chosen, batteries, a switch, and a controller were chosen such that the rated amperage is
not exceeded. The controller functionality allows the user to directly control the rate at which the motor
accelerates, ensuring that the nominal acceleration (associated with the magnitude of the inertial torque) is not
too high. Further, the ability to directly control the paddle acceleration drastically increases the user’s safety.
Full FEA Simulation
Once we had established the form and dimensions of the prototype, we
were prepared to move forward with the design. Via consultations with
machinists, we learned that our initial paddle design, seen on the second
Optimization slide, was not only impossible to fabricate with the means
available to us, but also extremely difficult to create in industry. The
complex form would drive up production time and costs for a product that
would mix only marginally better than a much simpler design. With this in
mind, we redesigned the paddle to a less curvaceous form. The redesign made
some of our previous simplifications more valid, but we still proceeded to do
a final FEA analysis.
This model is set up very similarly to the model used for the optimization:
The circular section of the shaft is constrained such that it can only rotate
about its long axis (simulating the conditions from the bearing and coupling
attachment, which constrain all other degrees of freedom). The surfaces that
are resisted by material as the paddle spins are loaded with uniform surface
pressures, simulating the drag (calculated previously). The simpler design
allows the pressures to be accurately applied along the surfaces, unlike the
previous model, which involved approximation via remote forces. By way of
the threaded connection between the paddle skeleton and shaft, and the
welded connections within the paddle itself, none of the other portions were
allowed to translate in the y-direction (constrains shown at right). The paddle
was modeled with built in properties for 6061-T6 Aluminum, with isotropic
elements. Strictly speaking, isotropic elements are not the best model for the
welded areas, but they are good for the vast majority of the model. Small
deflections were assumed because we imposed this condition when we
designed the structure (our limits on bending and angular deflection).
Full FEA Simulation
At the conclusion of the simulation, the Von Mises stress distribution was as seen on the left. The maximum stress
was 1046.68 psi in the shaft and 601.40 psi in the paddle itself. Both values are well below the yield strength of
6061 Aluminum (40000 psi), confirming that the paddle design is robust enough to be safe for users. Our final
paddle design has an overall footprint of 10x10 inches to fill up the majority of a standard five gallon bucket, while
still leaving space for mixing; a lightweight material for easy mobility; and a simple, robust geometry that all but
prohibits unsafe failure while in use.
Design Parts
The parts used in our design are as follows:
Purchased:
•
•
•
•
•
•
•
•
•
Bucket
Motor
Controller
Battery
Switch
Coupling
Bearing
Cheesecloth
Spring Hinge
Custom:
•
•
•
•
Cover with sealing tubing and supporting legs
Handles
Spacers between motor and lid
Aluminum Paddle
Purchased Parts
Bucket
-inexpensive and easily obtainable for any user
-standard size anywhere, strong and durable
Motor
-based on engineering analysis, need at least 400
Watt of power
-lowest cost for the power wattage necessary
Battery
-2 batteries that fit ratings of motor were acquired.
-not too heavy – user can somewhat easily lift
Spring Hinge
-allows user greater control over tipping of bucket by
resisting tipping
Controller
-Rated to at least 24V and 24A necessary
-easy control for user in form of dial
-inexpensive way of making design safer
Bearing
-sealed, able to work in muddy or wet conditions
-serves as one of two contact points for shaft
Coupling
-durably connect motor shaft to different diameter
paddle shaft
-withstand torque from motor and opposing from
paddle
Cheese Cloth
-inexpensive way of filtering clay from water
-easily obtainable
Custom-made Parts
Handles
-composed of 2”x1” wood blocks with wooden 1”
dowels connecting them. Glued together.
Motor Support Spacers
-made with ¼” diameter aluminum threaded rod
within ⅜” unthreaded aluminum spacer, each of
these cut down to length
-nuts on either end of threaded rod secure cover and
motor to spacer
Paddle
-welded aluminum stock together into paddle shape.
¾”x ¾” aluminum stock, after having part of length
being milled down to ¾” diameter cylinder, is bolted
into paddle shape. Washer included.
Platform
-⅝” thick plywood cut into 20” x 24” square
-supported by six 2” x 4” x 8” legs
-tilt-assist mechanism screwed onto platform
-trough for clay water can be placed next to platform
Cover
-⅝” plywood cut into 14¼” diameter circle with ¾”
hole for shaft drilled in center
-similar 8.88” circle centered and attached
-plastic tubing is cut once down its length and
encircles smaller plywood circle with epoxy
-three ¾”x ¾” x 15.5” legs are screwed onto cover
Bill of Materials
Wiring Diagram
The controller allows for two inputs from the motor and two from the battery. The switch is
inserted into the circuit by being connected between the controller and the battery. Thus, the
circuit can be completed just by flipping the switch, and once completed, the controller can
change the speed of the motor.
FMEA Applications
In order to prevent:
• a paddle tine from breaking, we designed the tines thicker while maintaining the optimized shape.
• a corner of paddle from breaking or bending, we designed it with thicker cross-sections.
• a motor stalling or burning out, we used a motor with a higher rated power than required.
• shaft failure by excessive angular deflection, we used a thick shaft (via application of high safety factor).
• the axle from slipping, we plan to glue the set screws on the motor axle in place.
• the bucket from cracking, we sized the paddle such that it had sufficient clearance space with respect to
the bucket wall and made the system self-centering.
• tilting mechanism from breaking, we will install a stronger spring hinge.
• the bucket spinning with paddle, we ensured the paddle had sufficient clearance and secured it to the
tilting mechanism.
• the handles breaking, we would strengthen handles by thickening or reinforcing them.
Manufacturing and Assembly for Mass
Production
Most of our design will be constructed from machined stock high-density polyethylene (HDPE) and acrylic,
chosen for their respective costs and strengths. We will purchase acrylic stock in the proper sizes for the lid, the
legs, and both parts of the handles for the lid. Acrylic was chosen over HDPE because this will undergo more
vibration and stress than the platform. The platform, the legs, and the bar for the tilt assist for the platform will
be made from HDPE to minimize cost. These will be machined to scale, as detailed in the Bill of Materials (BOM)
and appendix. We will machine grips for the handles and then we will adhere the rounded acrylic cylinders into
machined holes in handles. Assembly will include all fasteners and adhesive bonding, will all costs estimated in the
BOM.
The paddle is fabricated by cutting pieces of stock aluminum to length for each linear section of the
skeleton. The pieces for the top and bottom have square holes milled into them to house the shaft, which is then
inserted into the holes. The shaft stays in this position while the paddle is welded together to keep the final paddle
aligned.
In the lid, the bearing will be attached using a durable, strong adhesive, included in the lid price on the
BOM. The motor will be bolted on through the holes in the acrylic with threaded spacers giving room for the
coupler and axle. Finally, the gasket will be added on using an adhesive so that it is centered on the lid and can fit
the bucket diameter.
Design For Manufacture and Assembly
We wanted to make our design both easier to manufacture and assemble. The number of parts
we have is the least number we can have without compromising our structural elements. This
increases time for manufacture but is necessary to reduce the time for assembly, which is a boon
toward ease of use. We changed the material for many parts from wood to HDPE which increases
manufacture time but decreases assembly time drastically and benefits aesthetics. The original
paddle design made manufacture nearly impossible, and was redesigned. We have successfully
achieved a balance between short and easy manufacturing and assembly methods with our final
design.
Manufacturing and Assembling Final
Prototype
Our final prototype was largely constructed out of wood. Everything we used wood for we would
like to make out of acrylic or HDPE in the final product. We cut plywood for the platform and the lid. We
then cut legs for the platform out of 2x4 lumber. The wooden legs that support the lid when not in use
are made out of 2x2 stock wood. In the center of the lid, we drilled a hole for the axle and drilled a larger
radius hole halfway through the board to nest the bearing. We added a smaller circle of plywood to the
bottom of the lid and put tubing around it to create a gasket. The gasket insert is centered with respect
to the lid and includes a corresponding center hole for the shaft. We also drilled three specifically
positioned holes around the center for the motor attachment bolts. For the handles, we obtained 1x2
lumber and drilled clearance holes near the top. We then put a large wooden dowel through each pair of
drilled 1x2s to make the handles. We then attached the two handles to the lid. The platform we attached
the tilt assist which had a piece of 4x4 wood attached to a spring hinge. Then we added two wood stops
to further constrain the bucket. These were made from short 1x2s laid on their sides. We then painted
everything and waterproofed it. We made the paddle from aluminum and welded it together. We
attached the paddle to a rectangular axle, that was made cylindrical on one end. This fit into a coupler
that then fit onto the motor axle. We used nails to hold in the battery for the prototype but we will
bracket it on in the final product. The switch and speed dial are attached to the handles. And then we
had our prototype.
Final Product Model
House of Quality
Customer Requirements
Cost
Learning Curve
Ease of Use of Mixing Mechanism
Ease of Lifting
Risk of Broken Mixing Paddle
Safety of Use
Attention Required
Longevity of System
Mixing Efficiency
Comfort of Use
Ease of Cleaning Paddle
Ease of Adding Slurry
Time for Operation
Functional Requirements
Paddle Material Strength
Motor Strength
Thickness of axle
Power Input Required
Efficiency of Geometry of
Paddle
Weight
Volume of Soil Churned
Usability of User Interface
Vibration
Utility of Gearbox System
Waterproofing
System Volume
*Please zoom in for a better view.
Engineering Characteristics
The three most important engineering characteristics for our design were the motor strength, the volume of soil churned,
and the geometry of our paddle. These characteristics were the main constraints on how our system would operate and what
components and materials we chose. The worst case scenario of the paddle geometry, a solid rectangle of material, in an
estimated highest volume of soil mixed gave us our motor strength. With these values, the majority of other dominant
engineering characteristics are fully constrained, such as paddle material strength, thickness of the axle, power input
required, and weight.
Competition in HOQ
For our house of quality analysis, there are very few systems on the market with the same customer and design
requirements. Currently no system has been made for the precise purpose of mixing soil and water to aid sedimentary
transport.
A similar system in base functionality would be an electric drill attachment for mixing cement or plaster. This is composed
of a paddle similar to ours, but much thinner and smaller. It is used for mixing cement and plaster for construction. This
design is attached into the drill and then the user stands over a bucket with the paddle held in the mixture while the drill
runs. The paddle is not centered and can easily damage the bucket. The design has also been reviewed by users as prone to
breaking at the axle and paddle when under large loads. It is very light, cheap, and easy to clean, but lacks power and
requires constant user input.
Final Design HOQ
Our finalized design improved in many categories of user requirements. With the metal of the
paddle switched from steel to aluminum, the cost and weight of the system decreased. This
provided comfort of use, ease of lifting, and cost to have better scores. The motor was able to
turn at a faster rate due to the lighter material of the paddle, which increased the mixing
efficiency as well. This also allowed less attention to be required on the system as there were
much fewer vibrations at any speed. The speed controller increased the safety of the system,
giving the user the ability to quickly stop the system or ramp up the speed from a standstill. The
new gasket system allowed the entire system to self-center, so the entire mixing system could be
lifted off the bucket with minimal user input. Adding the soil and water is now easier than the
first iteration of the PT2 design due to the elimination of the need for a centering cone.
Overall, the final design ties or outranks the competition in every category besides cost, ease of
cleaning and ease of lifting, both due to the larger scale of slurry that can be mixed and the size
of the system itself.
Cost Analysis
For our cost analysis, we assumed that our design would be best manufactured in Japan, outside
the Greater Tokyo area. This is an ideal location due to the proximity to our potential primary
market of the Japanese farm workers and the ease of shipping to the United States for our
secondary markets of gardening and art enthusiasts. It is also a good location for shipping, factory
acquisition, and affordable labor.
Our estimated costs are determined through research in the retail prices of the components
through vendors like McMaster-Carr, so on the manufacturing scale these prices could potentially
be much lower due to bulk volume discount. All machining processes are performed by hand due
to the estimated low production volume. Fixed costs, shipping, and packaging are based off of
similarly sized industrial scales.
Variable Costs
Assumed Manufacture location: Japan, chosen for the demand for radiation
cleanup and prevalence of manufacturing locations.
Material cost estimated from standard vendors = $430, see BOM
Labor cost total = $42.44 per unit, see BOM:
Factory worker average salary in Japan = 800Y = $7.85 per hour
Mill and lathe work = $15 per hour
Welding = $20 per hour
1 cut = 2 minutes by hand, at average salary
1 screw = 0.5 min at average salary
1 inch on mill or lathe = 1 minute +5 minute set up
1 weld = 7 minutes
Shipping and Packaging:
Materials shipping = $200
Unit Shipping = $300
Packaging = $50
Total per unit=$1020
Fixed Costs
Assumed Production Volume: <10,000 units/year due to the niche demand for the system. Low
production volume therefore requires a smaller facility and less automated equipment.
Overhead Cost= Indirect Materials + Rent of facility + Utilities:
Assumed to be a 30,000 square foot factory space in Japan:
Rent= 150 Yen per square foot per month (equivalent to a factory in LA area) = 4.5M Yen per month = $440,000
Utilities= 6330 Yen per month = $62
Indirect Materials=Welding material, adhesives, maintenance= $1000 per month
Non-machining Labor cost = 200 workers, at approximately $7.85/hour, $358,100 per month
Equipment= Welding tools, Mills, Lathes, drill presses, band saws
Mills-$9,000
Lathes- $15,000
Drill Press- $3,400
Band Saw - $5,300
Total Fixed Costs Per Month= $800,000
Total Cost Analysis
Total cost per unit= $2,620 assuming 500 units produced each month.
Equivalent cost of a large-drum cement mixer of similar mixing volume- $3,320
Cost Analysis conclusions- This is an appropriate estimate for such a large scale industrial tool.
Testing
The soil slurry churner was tested multiple
times at the expo. It did its job beautifully by
silently but thoroughly mixing the soil and
water. No mud splashed out during the mixing
process, and the product was fully supported
by its legs when not in use. Despite the
constant use, there was no evidence of any
fatigue or failure. Onlookers were impressed.
Finding conclusive results about the clay
extraction required several hours of letting the
mixture sit, which we were unable to do at the
expo. However, after returning to the system
later on, complete separation was observed.
Success!
Dissemination of Technology
This product is easy to use, portable, and fits any standard 5 gallon bucket. It can be used for a
variety of purposes, from extracting local clay for pottery to decontaminating irradiated farmland.
It is silent, and takes mere minutes to accomplish its mixing. Clay can be extracted on a large
scale simply by setting up more buckets of soil and water.
References
1. Menon, E. Shashi. Piping Calculations Manual. New York: The McGraw-Hill Companies, 2005.
2. Steif, Paul S. Mechanics of Materials. Upper Saddle River: Pearson Higher Education, Inc., 2012.
3. http://www.linsgroup.com/MECHANICAL_DESIGN/Beam/beam_formula.htm
4. NHK World, “Decontaminating Fukushima: Cleaning Up Farms” Newsline. Dec 9, 2013
http://www3.nhk.or.jp/nhkworld/newsline/nuclearwatch/20131219.html
5. Aerospace Specification Metals, Inc. “Aluminum 6061-T6; 6061-T651”. MatWeb.
http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA6061t6
6. “Earth or Soil – Weight and Composition”. The Engineering Toolbox. http://www.engineeringtoolbox.com/earth-soil-weightd_1349.html
7. BOM- Custompart.net, McMaster-Carr,
8. Rent for factory and size in Japan- http://www.colliers.com/~/media/Files/MarketResearch/APAC/HongKong/Asia-Research/APIndustrial-May2012.PDF
9. Utilities- http://www.logansportutilities.com/stormwater.html
10. Price Comparison for Cost Analysis- http://www.toolfetch.com/toro-cm-958h-s-9-cu-ft-honda-gx240-2-1-2-3-bag-cement-mixerformerly-stone-equipment.html?cvsfa=2865&cvsfe=2&cvsfhu=434d2d393538482d53&gclid=CMKKnqeTp74CFdDm7AodXTEAmA
Assorted purchased part data courtesy of McMaster-Carr [mcmaster.com] and Home Depot [homedepot.com]
Appendix A:
Purchased Component Specifications
Motor Specifications
Appendix A:
Purchased Component Specifications
Battery Specifications
Appendix A:
Bucket Specs
Purchased Component Specifications
Appendix A:
Bearing Specs
Purchased Component Specifications
Coupling Specs
Appendix A:
Purchased Component Specifications
Controller Specs
Appendix A:
Cheesecloth
Purchased Component Specifications
Appendix A:
Rocker Switch
Purchased Component Specifications
Appendix A:
Spring Hinge
Purchased Component Specifications
Appendix B:
Platform
Custom Component Documentation
Appendix B:
Handle
Custom Component Documentation
Appendix B:
Paddle
Custom Component Documentation
Appendix B:
Cover
Custom Component Documentation
Appendix B:
Custom Component Documentation
Supporting Legs
Appendix B:
Custom Component Documentation
Cover, Tubing and Legs