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Human-Powered Peanut Thresher for Small
Scale Zambian Farmers
Alex Caine, Oscar Castro, Cody Lange, Ashley Wilkey
ME 491
Dr. Thompson
December 9, 2016
Executive Summary
Human-Powered Peanut Thresher
International Humanitarian Design
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Students enrolled in ME 491 International Humanitarian Engineering, taught by
Dr. Brian Thompson, assembled into teams of four in order to successfully complete a
semester-long design project.This project is continuing the development of a previous
ME 491 project by Adam Lyman. His team created a bean thresher that has been
successfully prototyped in Zambia. Our project description states “design and
manufacture a modular peanut threshing machine that can be used by small-scale
farmers in Zambia to de-shell and separate peanuts from their husks.”
On the current bean thresher design, four variables could be adjusted in order to
create a compression and shear force necessary to break open a peanut. An
experiment was created to test the effect of threshing when different rubber and sheet
metal surfaces were attached to the drum and concave. Also, different surface speeds
were tested, and distances between the concave and the drum.
Results from this experiment led to the selection of a material that was
manufactured to be fitted onto the existing bean thresher. Mechanization of the peanut
threshing process will allow small-scale zambian farmers to produce more output. In
turn this will give the women of Zambian more time to focus on education, health, and
family.
Table of Contents :
Project Introduction 3
Design Parameters 6
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Weighting Factors 7
Function & Performance 8
Product Cost 10
Delivery Date 10
Quantity 11
Safety 11
Quality 12
Energy Consumption 12
Reliability 13
Maintenance 13
Mechanical Loading 13
Size 14
Weight 14
Spatial Constraints 14
Aesthetics 15
Transportation & Packaging 15
Personnel and Human Factors 15
Service life and Shelf Life 16
Noise Radiation and Environmental Issues 16
Operating Instructions 16
Health Issues 17
Government Regulations 17
Operating Costs 18
Environmental Conditions 18
Introduction into Design Phase 18
Peanut Thresher Designs 19
Duplication Design 20
Combination of Belt and Drum Threshing 21
Swinging Rods Threshing 23
Empathy 25
Brainstorming 27
Checklists 28
Analogy 30
Biomimetics 31
Decision Matrix 32
Experiment 33
Setup 34
Procedure 36
Results 37
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Fin Design 37
Smooth Rubber Design 37
Scale Design 38
Metal Punch-Star Design 39
Metal Punch-Rows Design 39
Metal Punch-Star 40
Manufacturing 41
Conclusion 44
Bibliography 45
Appendices 46
Project Introduction
Zambia is a landlocked country located in the center of Africa as shown in figure
1. Currently, Zambia has a population of around 11.2 million people. Life expectancy in
Zambia is only 41 years old (National Geographic). Zambia is currently considered to be
the Least Developed Country by the United Nations. Countries present on the list of
Least Developed Countries, “comprise more than 880 million people (about 12 per cent
of world population), but account for less than 2 percent of world GDP and about 1
percent of global trade in goods.”
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Figure 1. A map of Zambia.
Currently there has been an increase in agricultural development to help lessen
the struggles with malnutrition and starvation in Zambia. Agricultural development is
done by primarily two methods. The first method is improving practices such as
increasing seed varieties. This has been the primary approach being implemented by
NGO’s. Although there is more yield being produced, they are now lacking the
machinery to process the crops.
This device will use the second method, which is introducing technical
equipment to reduce labor time. Most of the farm labor is performed by the women. If
mechanization can be introduced successfully, women would be able to spend saved
time to focus on education, health, family, and much more.
Our project will be contributing to current Michigan State University research
trying to introduce mechanization to small-scale farmers in Zambia. Right now there is a
threshing machine system being tested in Zambia which is powered by developing
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universal pedal power take-off. This machine can process common beans but not
peanuts. Peanuts are relatively soft compared to the beans. When the peanuts are ran
through the bean thresher they become broken, and are no longer acceptable to be sold
in the market.
As a team, we are to design a peanut thresher that can dehusk peanuts with no
defects for small scale farmers in Zambia. Peanuts are a popular crop in the northern
region of Zambia.Farmers in Zambia rely on these peanuts for a source of nutrition and
income. If there are defects in the peanuts they will not be accepted to sell in the
market. This can be detrimental to farmers considering that some people in Africa are
surviving on less than two U.S. dollars a day with seventy percent of Zambians living in
poverty.
Even though peanut threshers have been developed in Zambia, the people have
not adapted them into common farming practices. Our team needs to design a new
innovative peanut thresher. Along with the task of diffusing the innovation so that it can
be accepted by the farmers in Zambia. Cultural traditions will be taken into account
when attempting to introduce the peanut thresher device, and Adam Lyman will be
working on how to integrate these thresher into the lives of these women farmer.
Without the acceptance from the farmers, there is no functionally project. As seen with
other threshers, natives may be reluctant to accept the technology but it is a risk that is
necessary.
Design Parameters
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It is impossible to design anything without first knowing the design specification.
A design specification is a way of clearly defining the problem that needs to be solved.
Without this knowledge there would be no foundation for the purpose of the design, and
its possible that the device created won’t solve the problem presented.
To specify a design there must be defined design parameters. Design
parameters imposes constraints on the design. This is a very necessary step in the
designing process because if a problem is not properly defined it can not be properly
solved. Table 1 lists common design parameters that need to be taken into account
when designing our peanut thresher.
Table 1. Common design parameters taken into account for our device.
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Weighting Factors
Each design parameter needs to be evaluated on how essential it is to the
design. This can be done through assigning each parameter an importance factor
ranging from three to zero as shown in Graph 1.
Giving a design parameter a score of three would indicate that it is essential to
the design and if not satisfied completely would make the threshing device
unsuccessful. Assigning a design parameter a value of two would mean that its is highly
desirable and needs to also be met in the design. Design parameters given a one are
desirable, and should be taken into account when designing but does not need to be
present in the design. Parameters given a evaluation of zero are almost irrelevant when
creating our peanut thresher.
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Graph 1. Above shows each design parameters importance factor assigned
by the team.
Function & Performance
Currently, farmers are able to de-shell peanuts by hand at a rate of 10 kg
per hour. This is a very time consuming-process, and these women do not have time to
invest in their education, health, and socio-economic status. Adam made it clear that the
peanut thresher needs to output 100 kg of peanuts per hour within the tolerances of -5
kg of peanuts per hour.
Our thresher will need to be compatible with an already existing bicycle mount.
This mount was created only for the buffalo bicycle. Pedaling the buffalo bicycle should
input 100 W of power to our peanut thresher. An issue could arise with pedaling for
inputting power because farmers could be using this machine for eight or more hours at
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a time. To solve this issue another group is designing a platform to power our peanut
thresher. We need to callibratorate with this group to make sure their design can
properly run our peanut thresher.
The product of this machine needs to be a sellable peanut at the customer's local
market, meaning that the peanut gets separated from its shell and remains perfectly
intact.Figure 2 shows peanuts that would not be sold in the market. Out of 100 kg of
peanuts threshed per hour, the team is shooting to reduce the amount of unsellable
peanuts to less than three kg/hr. This parameter was given a 3 because creating a
functional and successful device is the whole point of the project.
Figure 2: Unacceptable groundnuts to be sold in the market place.
Product Cost
Our team was given a budget of $500 to develop a prototype for peanut
threshing. This parameter was given a 3 because Michigan State University and the
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Zambian farmers that we are building the device for do not have infinite funding to
develop this device.
Delivery Date
Design Day, or December 9th, 2016, is the deadline for this project. This
parameter was given a 3 because, otherwise, everyone in this team would likely fail ME
491 and our opportunity to change the world would be a waste. Adam Lyman also
wants to be able to use this prototype for the harvest season of 2017 which is another
reason why the delivery date is set as is.
Quantity
Ultimately, by the end of 2018, the final model of the peanut thresher will
be replicated 12 times by a company that is not yet known. For this class, however, the
team is only concerned with designing and developing the initial prototype, so this
parameter was only given a one.
Safety
Safety is always a priority, regardless of the fact that this is supposed to
be an economical machine. Hence, this parameter receives a 3. Safety is one of the
most important measurements in any project. We took into considerations the lives and
the well-being of the women farmers that will have to operate this peanut thresher. On
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average the operator will weigh any where from 130 to 180 lbs, and be 16-70 years of
age.
Quality
By the end of the fall 2016 semester, the team needs to have a visually
appealing, working, and economical prototype that can easily be tweaked into a
production model. Also, the peanut thresher needs to thresh peanuts into something
that can actually be sold. High quality is the goal, so this parameter gets a 3. Quality
can be defined as the peanut thresher outputting 100 kg of peanuts per hour for a
minimum of one harvest season. Zambians will most likely not understand the
importance of maintenance for the device. For this reason to maintain high quality of our
peanut thresher there needs to be little to no maintenance required.
In the words of Adam, “Imagine when you hand shell a peanut. As soon as you
uncrack the shell, there are two "whole nuts" inside, three if you get a special one. That
is what you need to aim for in the machine design.” In worst case scenarios, the broken
peanuts are deemed “bad” by the farmer are usually thrown away. Instead of throwing
away the broken peanuts the small-scale farmers of Zambia can benefit from starting a
business of making peanut butter with the “bad” peanuts.
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Energy Consumption
100 watts of power or less is required to run this machine. Right now there
is threshing machine system being tested in Zambia which is powered by developing
Universal Pedal Power Take-off. Our design should use this same powering method for
our device. This is a very important parameter, but because this does not yet seem like
a challenging goal, this parameter gets a 2.
Reliability
This specific peanut thresher must be able to last 10 harvest seasons. The
peanut thresher is expected to operate successfully and reliably, meaning that the
thresher will not need major maintenance from non-local fabricators. This parameter is
assigned a 2.
Maintenance
Local fabricators need to be able to repair the machine, should anything
happen to it during the harvest.Average tooling found in a toolbox should be enough to
repair any and all parts within the product. Maintenance must also be done on the bike
to retain its aesthetically pleasing design and display. This parameter is assigned a 1.
Mechanical Loading
Wood will be avoided for structural support in the final design. In the
prototyping phase, wood can be used for pulleys and other minor components.Standard
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stock material will be used, for the most part. Using acceptable materials is essential to
both the function and budget, so this parameter gets a 2.
Size
General dimensions are 3 ft wide, by 3 ft. deep, by 3 ft. tall, and the
machine needs to fit on the back end of the buffalo bicycle on a mounting system. If the
machine does not fit, the project can be considered a failure, so this parameter is
assigned a 3.
Weight
Zambian farmers need to be able to pick up the machine and need to be
able to use it, so 100 kg is the highest mass that the machine can be. Any weight higher
than that would not be beneficial to the farmers as they are responsible for the
transportation of the bike and thresher. This parameter is assigned a 3. The weight is
also a parameter that can be tied in with safety as well. Weight is a factor that must be
analyzed as the farmers do not have unlimited strength after a long day in the field.
Spatial Constraints
This parameter can somewhat be grouped together with size. As stated
before, the thresher must be 3 ft. wide, by 3 ft. deep, by 3 ft. tall. A wheat threshing
mount exists that the peanut thresher needs to be compatible with, and the machine
needs to be able to fit on the back of a bike, so this parameter is assigned a 3.
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Aesthetics
An understanding of tasteful design and Zambian culture is essential to
this project, because the machine needs to be something that the Zambian farmers
actually want to use. This parameter gets a 1. Adam Lyman will be diving deeper into
the understanding of Zambian culture and will be prototyping and collecting real data
from the farmers.
Transportation & Packaging
Zambian farmers will be transporting the bike from farm to farm via the
bike that the machine is mounted on. Due to this specific manner of transportation, the
team needs to be able to keep the weight of the thresher much below 100kg. This
parameter gets a 1. It is expected for the farmer to not travel in weather that may be
detrimental to the bike and its functionality.
Personnel and Human Factors
Our team will be dealing with customers that range from a 130 lb., 16 yr.
old male or female to a 180 lb., 70 yr. old male or female. Average heights of Zambians
are similar to the average heights of Americans, if not slightly shorter, and the machine
should be designed such that a person with a height of 5 ft. 2.5 inches can load the
machine. It is crucial that the Zambian farmers are actually able to use this machine, so
this parameter gets a 3. The human factors that are foreseen with this thresher are the
education level of the farmer, that only needs to know how to ride a bike. Dress code for
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the farmers, as most of the farmers will be women and they wear long dresses. Lastly,
due to the multiple kids that may be around while the thresher is in use, the team must
also take into the account the possibility of kids playing with or around the peanut
thresher.
Service life and Shelf Life
As mentioned before with reliability, this specific thresher must be able to
last 10 harvest seasons and must be able to maintenanced by local fabricators using
the contents of a regular toolbox. When not in use, five years is our initial goal.This
parameter gets a 1.
Noise Radiation and Environmental Issues
There are no parts of this specific thresher that will violate any EPA or
OSHA Regulations. The noise radiation from the thresher must not exceed 90 dB. The
team must also take into account the different environments the product will be placed
in, thus surfacing possible mouth and eye protection while the thresher is in use. This
parameter is assigned a 1.
Operating Instructions
Riding a bike that will automatically thresh the peanuts for the operator is
a task that is known by the farmer so there will not be a need to create operating
instructions for the bike, so this parameter gets a 1. Instructions for the loading and the
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collection of the peanuts will be created. Any instructions needed for the farmer will be
in English, as deemed by Adam.
Health Issues
With the exception of any potential safety hazards, the prototype is not
expected to pose any health issues. This parameter gets a 1. Adam also stated, “No
particular health issues outside the obvious emphasis on safety.” The team will take
into account the well being of the farmer and will take into account the work day, to
ensure the bike does not require any work that could potentially cause short term or
long term health issues for the farmer, such as wear and tear on the body and muscle.
The team, as stated before, will also take into account the need for eye and mouth
protection for the farmer using the thresher and the farmers that could possibly be
around the thresher while in use.
Government Regulations
After reviewing official documents and regulations, there are no government
regulations that will be violated in either the United States or in Zambia. This parameter
is assigned a 1.
Operating Costs
The bike must be able to generate 100 watts for the thresher to operate at
its maximum capacity. The farmer must be able to produce these watts solely from the
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bike itself. These 100 watts will help the operator produce 100 kg of peanuts rather than
the 40 kg that they are producing with other threshers. This parameter is assigned a 1.
Environmental Conditions
Although difficult to predict, dust storms and possibly rain at times are the
harshest conditions that the thresher needs to be able to operate in. Because this
parameter is related to its performance, this parameter gets an importance factor of 2.
The team will also consider the implications of the design, such as the possible
production dust storms and flying particles.
Introduction into Design Phase
The best kind of design phase of any project is one that produces multiple ideas
from the different minds available. As Linus Pauling once said, “The best way to have a
good idea is to have a lot of ideas”. After the creation and careful analysis of the design
parameters, the peanut threshing team was able to enter the design phase to create a
conceptual design.
There are 3 different types of conceptual designs, first suggested by Pahl and
Beitz, these three are named, Original Design, Variant Design, and Adaptive Design.
Original is where “a radically new product or concept is created”. Variant is when the
“size or configuration of a product is changed but the operating principle and the
function remain unchanged”. Adaptive design is defined as “a product is changed to
solve a different problem but the original operating principle remains unchanged”. The
project requires an adaptive design as the idea of threshing peanuts came from a
previous project based on threshing regular beans.
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Following a discussion with the team collaborator, Adam Lyman, the team was
set on the path to conceptualize and build a working drum for the thresher. Along with
the design of the actual drum, the team was also tasked with testing and optimizing the
speed necessary to thresh the peanuts correctly.
Each team member produced two different ideas each. All ideas were created
using different methodologies to maximize innovation and creativity. Methodologies
acted as guidelines to allow the team members to dive deeper in creativity. The different
methodologies used were Historical, Combination, Duplication, Biomimetic, Empathy,
Brainstorming, Analogy and Check List.
After all conceptual designs were created, the team members used a design
matrix to rank and find the “best” idea. Multiple tests and prototypes are in the
immediate future for the team. All prototypes will be created using the best designs
seen in this report.
Peanut Thresher Designs
Designs were generated by the team for different drums that will be evaluated for
the final peanut thresher design. A threshing drum is the cylinder in the center of a
thresher that rotates to break the shell away from the peanuts. The concave of the
thresher is the cover for the drum that traps the peanuts against the rotating drum. Both
of these components can be viewed in figure 4 below.
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Figure 4. Drum and Concave Locations on Thresher
Duplication Design
Figure 5: Duplication Design of a Drum
This drum design will have threaded holes along the whole body of the cylinder
to allow for exchangeable rubber attachments of different shapes to be tested as shown
in Figure 5. Each different type of attachment can be screwed into each threaded hole
of the thresher in order to obtain proper function. Individual attachments will be made of
rubber in order to create a less forceful process to keep the quality of the groundnuts up
Drum
Concave
Peanut Input
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the design specification. The drum will be made of sheet metal to support the screwed
in attachments during the threshing process.
An advantage of this design would be its versatility. The team will be able to
quickly produce, and exchange out different drum surfaces. This will allow the team to
evaluate the effectiveness of many ideas without putting all our energy into one single
design.
A strong disadvantage to this design is the amount of time it will take to load it
into the thresher, and attach all of the components. This design will also involve making
a lot of parts which in turn will increase the overall cost.
Combination of Belt and Drum Threshing
There are many different methods that currently exist for threshing a variety of
different crops. Each method has its advantages and disadvantages. This idea was
generated by combining two know threshing methods to try and reap the benefits from
both of them. These methods are belt and drum threshing.
Belt threshing is a process that incorporates two rubber belts that rotate at
different speeds. The top belt rotates in a counterclockwise direction and the bottom belt
rotates in a clockwise direction. This process is typically used on crops that require a
more delicate approach.
Drum threshing utilises a rotating cylinder with a rough surface that grinds the
shell of the crop against a curved wall to separate the seed from the shell. This process
is much more aggressive and can cause the seeds to break during the process.
Advantages of this method is that it has a compact and simplistic design.
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These two processes were combined by taking the rubber surfaces from the
belts and applying them to the drum and the concave walls of a standard drum thresher.
An image of this design can be seen in figure 4.
Figure 6: Drawing of the Combination Design
Rubber surfaces provide the desired delicate touch to extract the peanuts form their
shells without damaging the quality of the peanut. Figure 7 shows the rubber texture
that will be applied to the outer surface of the drum and the concave.
Figure 7: Rubber Applied in Design
Advantages to this design include the delicate threshing approach, the compact
design, and the manufacturability. Unlike most drum threshing designs, the combination
design creates a friction driven process that provides torque to the shell to twist it off. By
Front Side
Rubber Surface
Hollow Steel Cylinder
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twisting the shell off, the peanuts themselves are never under any pressure and have a
lower chance of cracking. By having the drum instead of the duel belts, the thresher can
function in a smaller space. In addition to these other advantages, this design have very
few parts in its design.
Disadvantages for this design include concave alterations and number of
materials used. By adding material to the inside of the concave, it is adding more
material and steps to the installation process. There will also have to be a design
feature that will temporarily connect the rubber to the concave. Also, there are two
different types of materials used in this design, so cost of this design will be higher.
Swinging Rods Threshing
Evolution of technology can cause tasks to become overly complicated. Looking
back on the history of threshing can provide insight to simple ways of accomplishing this
task. Early forms of threshing involve the beating of shelled seeds with sticks and rocks
in order to expose the seeds. This method is extremely simple and can be integrated
into the advanced drum threshing design.
In the swinging rod threshing design, the drum is attached to a number of beating
rods that can rotate about the connection point between the rods and the drum. By
allowing these rods to have this additional degree of freedom, the rods will be able to hit
the peanuts and recreate a miniature version of the old beating process. Figure 8 shows
the front and side view drawing of the swinging rod design.
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Figure 8: Drawing of Swinging Rod Design
Advantages of this design include that it threshes all peanut shell sizes and that it
will thresh the peanuts at a fast rate. One of the issues that the Zambian farmers are
running into is that threshing peanuts by hand takes far too much time, this is why the
parameter was ranked so high in the previous report. Also, having to change the drum
in the thresher to thresh different sized peanuts is a waste in time and materials.
Disadvantages of this design include aggressiveness, number of parts, and cost
to manufacture. Zambian farmers need the peanuts to be whole, so that they can be
sellable in the market. If the peanut threshing process breaks the peanuts, then the
farmers will be losing money and will not profit off of the improvements in the threshing
process. In addition, adding more parts to the design will make it more likely to fail and
will make it much more expensive to manufacture.
Installation of this drum will involve opening up the bean thresher, sliding the old
drum out, and sliding the new drum in its place. This drum requires no alterations to the
Front Side
Hinged Steel or Wood
Hollow Steel
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concave of the thresher making the exchange simple. Handling this drum design could
also have safety issues due to the fact that it has many moving parts and pinch points.
Empathy
Figure 9: A design for a hollow steel drum coated with rubber is depicted
Safety is a heavily prioritized design parameter, so using the design synthesis
method known as empathy, the concept of making a steel, cylindrical drum that is
coated with rubber and using rubber teeth on the concave was made. A sketch of this
design can be found in figure 9. Zambian operators using this device are at less risk of
suffering a major injury if something gets caught in the thresher, as rubber will do less
damage. A relatively soft surface also minimizes damage to the peanut during shelling,
and hard bristle at the end of the concave helps to complete the separation of the nut
from the shell, so the function and the performance of the machine are actually
improved.
T
Side
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Front Side
Top
Thic
However, the improvement of safety, performance, and quality are at the
expense of other important parameters. Coating the drum with rubber will make the
device more expensive and heavier. Also, the rubber on the device potentially lowers
the reliability of the machine, as the rubber will get worn down faster than steel would.
Maintaining the machine would be more routine and costly.
To build this design, sheet metal needs to be rolled and welded together. Circular
plates are welded to the drum to complete the shape. A strip of rubber teeth is screwed
down to the drum.
Brai
nsto
rmin
g
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Figure 10: A hollow sphere design with steel teeth and bristle fixtures is shown.
When designing an interchangeable drum, a cylindrical shape is often the first
shape that comes to mind. However, using the brainstorming synthesis method, a
hollow, spherical design made of steel was considered, as shown in figure 10. Thick
bristle fixtures are placed along the concave of the thresher so that there are no gaps
for peanuts to fall through, and as the spherical drum rotates around, peanuts of
different sizes are sorted to areas between the drum and the bristles where they fit the
best.
Currently, this design proposes the use of teeth that define the look of a
basketball, as aesthetics are important to customers. In theory, allowing different areas
between the drum and the concave for peanuts of different sizes to go through also
increase the quality of the finished product and bolsters the performance of the
machine.
Disadvantages to this design include that placing the bristle fixtures is an added
step with added costs, and they might not even help the peanuts find where they are
sorted best in the concave or adequately help separate the nut from the shell.
Additionally, manufacturing a spherical drum is more expensive than manufacturing a
cylindrical drum.
To build this design, steel needs to be kneaded between two dies, flash lines
need to be removed with cast iron plates, the drum needs to be heat treated, and a
fixture needs to be placed that connects the drum to the thresher’s main body. Steel
teeth are welded to the drum, and bristle fixtures are screwed to the concave.
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Checklists
Figure 11: Concept drawing of drum based on Checklist methodology
The idea and concept drawing displayed in Figure 11 was a creative idea that
had its roots based in the methodology of Checklist of Questions. A list of questions that
were first produced by A. F. Osborn, allowed the team member to tackle the open-
ended question of the drum design. This type of methodology can also be used in the
detailed design phase of the project, as that is when there is a focus geared towards
hardware considerations.
In this type of drum, the “teeth” would be fins that are straight across the drum,
as displayed in the front view of the figure. Fins would also be present on the inside of
the concave that wraps around the drum. Both sides of fins would minimize the amount
of “bouncing” the peanut does within the concave, which would reduce any damage to
the peanut within the shell. Another advantage of the fins is the ability of threshing
different sized peanuts. Since the fins within the thresher increase in height, any sized
Side Front
Rubbe
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peanut would be caught in the fins, thus reducing the number of peanuts left
unthreshed. Not only are there foreseeable advantages but there are also
disadvantages that can be predicted. Design of the fins could also create pockets where
the peanuts could be caught and could go through the process unthreshed.
Materials necessary for this idea would be sheet metal and rubber. The fins
would be entirely created from rubber. Another concept is having the fins be created out
of sheet metal and have rubber casings over the fins. The fins would be welded, if made
of metal, or the fins would be adhesively bonded or bolted into the sheet metal drum.
Lastly, another concept could be creating the fins using a rubber belt. Having
replaceable belts would allow for different types of teeth to be used with different
peanuts (wet, dry, big, small, etc.) and having replaceable belts would allow for quicker
maintenance of the thresher.
Analogy
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Side Front
Rub
Figure 12: Concept drawing based on Analogy Methodology
Direct Analogy was the methodology used in creating the design in Figure 12.
This type of methodology involves making a comparison of similar techniques,
technologies, or knowledge from different fields. The team member used prior
knowledge and experience with gears and the technique behind them to create a similar
symmetrical design. Just as with the teeth of two gears, the teeth of the drum will align
and fit perfectly with the teeth on the inside of the concave while leaving a pocket for the
whole peanut to exit the process.
With the reduction of pockets and free space within the concave, there will be a
reduction of “bouncing” the peanut goes through. There is also a reduction of peanuts
that go through the system unthreshed, since there will be minimal space between the
teeth of the concave and the drum, all sized peanuts will be caught by the drum.
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Based on the first conceptual design, the material required was metal. After
further review, the teeth could also be produced with rubber material which would
lessen the impact of drum on the peanuts. Fins would either be screwed into the drum
or welded onto the drum. The fins on the inside concave would go through the same
process the drum as the drum. Overall, this idea partially uses a concept used in a
different field and a hint of creativity to try to solve the major issue at hand.
Biomimetics
Figure 13:Biomimetic Drum design
This drum design was inspired by the operation of a raven using its beak to chip
away at the outer shelling of a peanut. As seen in the figure above the peanuts would
drop down into concave while the drum would be rotating and coming into contact with
the peanut imitating the peaking motion of a raven. This entire drum would be made of
metal in order to replicate the hardness of a raven’s beak.
Biomimetic Design
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An advantage of this drum design would the sharp point of the teeth. The point
will be able to catch more easily on the outer shelling of the peanut, and be able to roll
of the roundness of an already unshelled round peanut.
A disadvantage of this drum design would be the complexity of manufacturing the
needed shape for the teeth. Another major drawback would be the needed maintenance
when the teeth would become dull from the continued use of the thresher. Also this
drum design would be hard to load and unload into the peanut thresher because of its
heavy weight compared to other drum designs.
Decision Matrix
Table 2. The decision matrix used to select the top 3 designs is shown.
A decision matrix, as shown in Table 2, was used to determine the most effective
designs for threshing peanuts by assigning ratings for how each design addressed the
most highly weighted parameters described in Progress Report 1. This process resulted
in the top three designs being rubber-based designs. These designs were synthesized
by combining belt and drum threshing, making a checklist of questions, and empathy
best addressed the defined design parameters. Ratings of 1-3 were issued to each
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design for how they addressed each parameter. “1” meaning that the design did not
address the parameter relatively well and “3” meaning that the design met and
exceeded the goals defined by the parameter.
Glaring issues were present with the designs made by the biomimetics, swinging
rods, and duplication methods, especially with the parameters weighing to weight, size,
cost, and maintenance. Not too many issues were apparent with the analogy-based
design, but the combination, checklist, and empathy designs scored better and will be
focused on during the prototyping stage.
Experiment
In order to modify the current bean thresher there was four variables that could
be changed in order to create a more gentler process for threshing peanuts. The
combination of these four variables had to create a compression and shear force on the
peanut in order to get a good quality peanut. This good quality is defined as the
groundnut being whole, and the red film still being attached to the peanut.
First the variable of drum surface could be altered on the existing design. Our
team decided to test two types of surfaces rubber, and sheet metal. Rubber was chosen
because it is less forceful, and these surfaces could be repaired with materials available
to Zambian farmers like bike tires. Sheet metal was chosen as our second surface to be
tested because the team could easily manufacture a hole punch design with materials
available to Zambian farmers including a hammer and nail.
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Another variable to change was the concave surfaces. Both rubber and sheet
metal were also used to attach to the concave. The distances between the drum and
the concave could also be altered to adjust how many peanuts could run through the
thresher. Lastly the surface speed could be adjusted to change the rpm the drum was
rotating. Speeds were tested from 150-920 ft/min.
Setup
In order to test the threshing process the team was able to obtain a 10 year old
thresher from the Crop Barn shown in Figure 14. This thresher was originally created for
wheat threshing, and therefore was too violent for peanuts. In order to run our
experiment the team needed to change this spiked tooth thresher into a thresher that
could be modified to fit our different desired surfaces on both the drum and the concave.
Figure 14: Wheat Thresher obtained from Crop Barn.
First, the team was able to remove the teeth by hammering them off both the
drum and concave. Then it was time to get into the College of Engineering Machine
Shop in order to turn down the diameter of the drum using the lathe. This would allow
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the drum to have a smooth surface for applying our surfaces. To attach the surfaces we
drilled and threaded four holes into the drum. Surfaces on the drum were then able to
be screwed in, and surfaces for the concave were screwed in and bolted.
Figure 15. Attachment of surfaces on the concave and drum.
Originally the wheat thresher was attached to a motor that was not ideal for
testing, and was exchanged with a new motor. In order to get slower speeds a second
power system was implemented for testing. A new platform was also created to allow
for proper placement of the thresher, motor, and pulley system.
Procedure
1. Screw one of the six surfaces shown below into the concave and drum.
Food-Grade White
Styrene Butadiene
High-Strength
Zinc plated 26 gauge
Zinc plated 26 gauge
Zinc plated 26 gauge
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Incline Conveyor Belting Nitrile
Rubber
Multipurpose Neoprene
row design grid design star design
2. Adjust the speed dial, and use the Tachometer to find the desired speed of 150
ft/min. Tolerances are set to plus or minus 10 RPM.
3. Run two cups of raw,unsalted, and unthreshed peanuts through the thresher.
4. Sort the output into three categories: good quality, bad quality, and unthreshed.
5. Hand thresh the peanuts that were not threshed by the machine.
6. Weigh each category in grams.
7. Record the data.
8. Repeat steps 1-7 using surface speeds of 220, 460, 850, and 920 ft/min
Results
Fin Design
Data that was collected from the experiment was put into bar graphs to compare
how the surface types and surface speeds affect the percentage of good, bag, and not
threshed peanuts. Firstly, the fin rubber design had an exponential increase in percent
of bad quality peanuts as the the surface speed increases as seen in Graph 2. Good
quality also increases with surface speed, but peaks at 850ft/min then decreases.
Overall for this design, the optimal speed was 460 ft/min because it threshed
approximately 25% of the peanuts with good quality and only broke 3%.
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Graph 2: 4.5inch Diameter Drum Fin Design Results
Smooth Rubber Design
Next, the smooth rubber design also had an increase in percent of bad quality
peanuts as the the surface speed increases as seen in Graph 3. Good quality stays
10% and 15% for all of the speeds. Overall, this design’s bad quality to good quality
ratio was high and the surface didn’t thresh enough.
Graph 3: 4.5inch Diameter Drum Smooth Design Results
Scale Design
Lastly for the rubber surfaces, the scale rubber design also had an increase in
percent of bad quality peanuts as the the surface speed increases as seen in Graph 4.
Good quality increases steadily as the surface speed increases. Overall, this design’s
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bad quality to good quality ratio was high and it either didn’t thresh enough or it broke
too many peanuts.
Graph 4: 4.5inch Diameter Drum Scale Design Results
Metal Punch-Star Design
To start the metal surfaces, the star rubber design also had an exponential
increase in percent of bad quality peanuts as the the surface speed increases as seen
in Graph 5. Good quality also exponentially increases as the surface speed increases.
Overall, this design’s bad quality to good quality ratio was high and the ratio remained
the same as the surface speed increased.
Graph 5: 4.5inch Diameter Drum Star Design Results
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Metal Punch-Rows Design
Metal punch with the star pattern had a steady percentage of bad quality peanuts
as the the surface speed increased as seen in Graph 6. Good quality fluctuated
between 10% and 15% with all the surface speeds. Overall, there was not a definitive
best surface speed for this design and none of the results showed a reasonably good to
bad quality ratio.
Graph 6: 4.5inch Diameter Drum Row Design Results
Metal Punch-Star
Lastly for the metal surfaces, the grid design had a steady amount of bad quality
of peanuts as seen in Graph 7. Good quality increases steadily as the surface speed
increases until 460 ft/min then it decreases. Overall, this design’s bad quality is low
compared to the other surfaces. This surfaces best performance is at 220 ft/min.
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Graph 7: 4.5inch Diameter Drum Grid Design Results
After testing was completed on the wheat thresher from the crop barn it was time
to take our best design, and test on the current bean thresher design. First, the team
had to remove the spiked teeth from the bean thresher by taking our each individual
screw and bolt. Our fin design was then manufactured to fit the dimension of the current
bean thresher drum and concave. Surfaces were attached in the same manner as the
smaller thresher, and the testing procedure remained the same. Except to account for
the larger drum size 13” compared to 4” the team ran three cups of peanuts through the
thresher for testing.
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Graph 8: 14 inch Diameter Drum Fin Design Results
Manufacturing
Cost reduction and ease of manufacturing were all taken into consideration when designing and
making the drum surfaces. An emphasis was placed on allowing for simplified assembly and repairing
processes.
For the fin surface, a 6.5”x43.5” strip of food-grade white incline conveyor belting nitrile was
purchased from the McMaster website. Typically, a perfectly sized strip of rubber is not available for sale.
If this appears to be the case, a box cutter can be used to cut the surface down to size. Nine ¼”-20
threaded screw holes exist on the bean thresher already, so holes of the same diameter are drilled into the
fin surface. Locations of these screw holes are indicated in figure 16. A Phillips screwdriver is then used
to attach the surface to the drum with ¼”-20 flathead screws.
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Fig. 16 White dots indicate where the quarter inch holes need to be made.
Fin concave surfaces are also bought from McMaster and attached in the same manner to the
thresher concave, only the concave surfaces are 6.5”x12” and only six ¼” screws are needed to fasten
concave surfaces. Screw holes are still punched from the same relative distance to the ends of the surface,
as shown in figure 17.
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Figure 17. Dimensions and screw hole locations are shown for fin concave surfaces
Fig 18: Properly attached material to concave and drum
Fig. 18 provides a reference of what a properly assembled Thresher and Concave looks like. A concave
with the surface attached is shown on the left, and a drum with the fin surface attaches is shown on the
right.
Once the drum and concave surfaces are attached, the concave must be placed on the hooks that
hold it to the thresher frame, and it must be adjusted by moving the hex nut that constrains the concave’s
movement so that the clearance is 0.875 in. from the peak of a drum fin to the peak of concave fin. This
can be done by adjusting the location of the hex nut on the part of the thresher frame that restricts concave
movement.
It is predicted that fin surfaces will erode significantly over the course of the threshers intended
10 harvest period of use, so either replacement surfaces will need to be purchased and prepared. Another
solution is patch repairs which can be done using household materials. If a patch repair is opted for,
household materials, like the rubber on bicycle tires, can be used to repair the surfaces by cutting the
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desired piece of rubber and using an adhesive, such as various epoxies, to fill the worn away portion of
the surface.
Conclusion
Through experimental testing our team was able to create an interchangeable
drum and concave surface for peanut threshing. This material is known as food-grade
white incline conveyor belting nitrile. It was obtained through a supplier website called
Mcmaster. Compression and shear forces were best created with this surface, and
adequately produced a good to bad ratio of 7 to 1 peanuts.
Overall introducing this human-powered peanut thresher design to small-scale
farmers in the Northern Province of Zambia will make a profound impact on their lives.
Currently, the farmers are hand threshing at a rate of 1 kg/hr. With mechanization of this
design the farmers will be able to generate an output of 35kg/hr. That is an overall
improvement of 35 times more output.
If a typical Zambian farmer works 8 hours a day they can output 8kg/hr, and
when using this design that same output of 8 kg/hr can be created in 14 mins. This will
allow the farmers to save time with threshing peanuts, and allow for more product to be
sold in the market. Also, female farmers will have more time to dedicate to their
education, health, and family with all the time saved using this mechanization.
Bibliography
"About LDCsA Propos Des Pays Les Moins Avancés - UN-OHRLLS." UNOHRLLS. N.p., n.d.
Web. 22 Sept. 2016.
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Caine, Castro, Lange & Wilkey. (2016). Design Specification of a Human Powered Peanut
Thresher
National Geographic Atlas of the World, Eighth Edition. Web. 22 Sept. 2016.
Thompson, Brian S. Creative Engineering Design. Okemos, MI: Okemos, 1997. Print.
Appendices
Figure 12: Benchmarking different types of threshing drums 1) Peg 2)Loop 3) Angle Bar
Figure 13 : Possible design for a drum inside a human powered peanut thresher
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Figure 14: A design shown with a conical drum and shaker is depicted.
Figure 15: Gear System for Powering Thresher
Figure 16: Separation System for Belt Threshing Design
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