Design of a Human Powered Maize Mill
by
Melvin Gustavo Salinas
Submitted to the
Department of Mechanical Engineering
in partial fulfillment of the Requirements for the Degree of
Bachelor of Science in Mechanical Engineering
at the
MASSACHUSETTS INSTITUTE
OF TECHNOLOGY
Massachusetts Institute of Technology
JUL 3 1 2013
June 2013
LIBRARIES
@Massachusetts Institute of Technology. All rights reserved.
Signature redacted
Signature of Author:
Department of Mechanical Engineering
May 28, 2013
Signature redacted
Certified by:
Kmy Smith
6'
Senior Lecturer in Mechanical Engineering
Thesis Supervisor
Signature redacted
Accepted by:
Anette Hosoi
Professor of Mechanical Engineering
Undergraduate Officer
Design of a Human Powered Maize Mill
by
Melvin Gustavo Salinas
Submitted to the Department of Mechanical Engineering
on May 28, 2013 in Partial Fulfillment of the
Requirements for the Degree of
Bachelor of Science in Mechanical Engineering
Abstract
The process of milling corn into flour in many rural communities of East Africa
has remained a traditional mortar and pestle process for centuries. Milling machines
have failed in these communities largely due to poor performance, as well as high cost,
and as a result the incredibly labor intensive process continues. This study seeks to
design and manufacture a prototype mill that will address the needs of the communities
in question. Initial testing on existing milling equipment generated a quantitative
understanding of the strengths and shortfalls of the available machines, and informed
the design of a new mill. Once the design specifications were determined, a two stage,
"twinmill" incorporating a stock low cost mill performing an initial coarse grind and a
second identical mill that used modified grinding plates to produce finer flour was built.
As expected, the two stage solution outperformed the existing machines by a significant
margin: the acceptable flour yields rose from the 30-40 percent range, to consistently in
the mid 60s. After subsequent modifications to the fine pass machine grinding plates,
yields rose even higher, to an average of about 80 percent.
Thesis Supervisor: Amy Smith
Title: Senior Lecturer in Mechanical Engineering
2
Acknowledgements
The author would like to express his appreciation to everyone who has made this
project possible. First, a special thank you to Gwyndaf Jones, whose support, ideas,
and manufacturing knowledge were critical to the creation of the machine.
Gratitude is also extended to the D-Lab staff, whose maintenance of an
impeccable shop provided a work space that was a joy to use.
Tobecukwu Madu and Cem Onat Yilmaz of Johns Hopkins University were
consulted prior to the start of the project, and provided useful information on their own
work towards the development of a pedal powered mill. Their feedback throughout the
project has been quite valuable.
Candace Chen was an able and helpful partner in the first stage of testing,
design, and building. Her insights and feedback were crucial to the interpretation of the
early data.
Other important collaborators include the staff of Global Cycle Solutions, who
have worked with previous student teams, and allowed the use of their limited space
and resources in the initial phase of involvement. Their early help was invaluable to the
development of the project and they will continue to be involved as the project moves
further.
Finally, a sincere appreciation is offered to the MIT Mechanical Engineering
department, for providing the framework of study in which to learn the principles of
mechanical design.
3
Table of Contents
Abstract
2
Acknowledgements
3
Table of Contents
4
List of Figures
5
1.
Introduction
6
1.1.
Motivation
1.2.
Background
6
6
2. Initial Experiments
8
2.1.
CTI mill
8
2.2. Johns Hopkins Modifications
10
3. New Designs, Testing, and Results
13
3.1.
Design of Twinmill
3.2.
Design of Modified Twinmill
13
15
4. Conclusion
17
5. Appendix
19
5.1.
Appendix A: Data Tables
5.2.
Appendix B: Mill, Kingoro visits
19
23
6. Bibliography
25
4
List of Figures
Figures 1 & 2: Unmodified vs modified grinding plates
7
Figure 3: Results of CTI machine trials
9
Figure 4: Results of Unmodified hand-crank mill trials
10
Figure 5: Results of Modified-plates hand-crank mill trials
11
Figure 6: Results of paired unmodified-modified mill trials
11
Figure 7: Bicycle mounted single mill
12
Figure 9: Results of Twinmill trials
15
Figures 10 & 11, flour output of modified Twinmill (left), sorted by particle size
16
(right)
Figure 12: Results of Modified Twinmill Trials
5
17
1. Introduction
1.1. Motivation
In many rural, off-grid communities, flour is still produced by mortar and pestle,
an incredibly slow and labor-intensive process. In order to mill enough flour to feed their
families, milling work comes to dominate a large fraction of their time. Even in
communities that are near villages with large powered mills, the poor condition of the
infrastructure adds time and expense to what would otherwise be a low-cost and quick
process; accounting for travel time, milling can still take up one full day each week.
There is a clear need for a locally built and operated human powered mill that
would obviate the need for ancient manual processes. Currently there are no existing
designs that successfully address the needs of the communities in question. Many
manual hand-crank mills available are largely based off a design that is over 100 years
old, and manufactured according to casting processes that are highly imprecise. While
these mills are typically low-cost, the flour they output is unacceptably coarse, even
after multiple passes. Better performing machines are typically too expensive, and the
flour is still too coarse.
The ultimate goal of the project is to design and build a human powered maize
mill that will produce acceptably fine flour. The mill should be designed with an eye to
the available materials and processes of the communities in question, to ensure that
local operators will be able to build and maintain the machines.
1.2. Background
Work built upon the past efforts of a John Hopkins University team that travelled
to Arusha during the summer of 2012 to work with GCS, as well as an MIT D-Lab:
6
Design team that worked with a mill developed for rural use by Compatible Technology
International (CTI).
The JHU team focused on a simple addition to maize pre-processing and
modification to the grinding plates of a low-cost Estrella mill in order to boost the
performance of the mill to acceptable levels. The Estrella is a mill manufactured in
Mexico from an old American design. Estrella mills, as well as other mills sharing the
basic design, cannot produce fine particles due to the large feature size of their grinding
plates. Even after many passes, the maximum allowable particle size is too large. In
order to produce smaller particles, and thus finer flour, the plates were ground down in
order to lower the height of the channels. With smaller features the plates could produce
a finer flour. In addition to the plate modifications, the JHU team also experimented with
soaking maize to soften the outer shell. Finally, the modified machine was attached to
the rear cargo rack of a commonly used bicycle.
Figures 1 & 2: Unmodified vs modified grinding plates
The results of the JHU team were ultimately inconclusive. The experiments in
wetting the maize did not result in significant differences in the data, and the relatively
7
few number of experimental trials were insufficient to perform a proper analysis of all the
variables being tested (the plates, the wetting, the bicycle). Furthermore, the
modifications made to the Estrella machine were not able to be properly tested, as the
mounting bracket suffered structural issues that affected the experiments.
The MIT D-Lab team, focused on creating an entire new prototype mill after
initially gathering data on the performance of the rather expensive mill designed and
made by CTI. The Design team found some success with the CTI mill, but found that
upwards of 4 passes were required to get the performance desired. The team felt that
the multiple pass approach was unacceptably cumbersome and a redesign was
needed. The prototype was designed and built to address the performance issues, but
proved too costly to realistically move forward with.
2. Initial Experiments
The first experiments were performed in Arusha, Tanzania, and were used to
gain a better understanding of the available machinery. We tested the CTI mill first, as
well as the mill modified by the John Hopkins team, and a similar (though not identical)
mill to the modified one that had been left unmodified.
2.1. CTI
We ran a total of five tests on the CTI mill, with sample sizes of 200 grams each.
The results we found were disappointing. The first four trials were of a single-pass only.
While we had not yet defined a maximum particle size of what we would accept as flour,
or unga, later findings revealed this machine as having yielded an average of 30
percent unga across its first four trials. In addition to its poor yields, the machine
8
experienced some jamming - tougher pockets of corn that prevented the machine from
running smoothly, and after the second trial, the grinding plates were beginning to heat
up noticeably. After two trials, the machine could no longer function properly, as partially
ground corn had become stuck and forced the plates apart, allowing larger particles
through.
The final trial would be a double pass. The first attempt at this trial resulted in the
machine jamming to a point that the machine had to be disassembled. Upon inspection,
it was revealed that the auger had deformed under the pressure of pushing corn. An
effort was made to reshape the auger, but after reassembly and retrial the performance
of the two-pass trial was not above that of the single-pass trials, indicating that the
auger had suffered a critical, non-repairable failure.
CTI Machine
100%
75%
3%
30%
4
39%
50%
77
58%
25%
0%
1
3
2
7%1
4
5
Trial
<500p
>500p
Figure 3: Results of CTI machine trials
The ultimate failure of the CTI mill helped to reinforce a design goal of our own
machine: user-repairability. Additionally, the critical failure happened remarkably quickly
in our testing; such a quick failure rate is unacceptable in the field, our machine would
9
have to be more robust. The poor performance, paired with the high price (~200 USD)
of this mill led us to focus our redesign efforts on the Estrella-type mills.
2.2. Johns Hopkins Modifications
While the original intention of the JHU mill was to function as a bicycle
attachment, our tests were run by hand crank, and investigate the bicycle attachment
design separately. The modified-Estrella design developed by the Johns Hopkins team
fared much better in our tests than the CTI did, and further informed the design of a new
machine. Predictably, the modified plates performed much better than the unmodified
ones. Four double-pass tests were run on both the modified and unmodified machines,
with the modified outperforming by an average of 20 percent. However, it was noted that
the amount of effort needed to perform the first pass on the modified mill was excessive.
The difficulties encountered in the first pass reinforced the point that the mill has a high
torque requirement, which would prove to create further difficulties in designing and
building a bike attachment.
Unmodified Mill
100%
75%
50%
25%
0%
1
2
3
4 (Wet)
Trial
>5 0 0 p
U <500p
Figure 4: Results of Unmodified hand-crank mill trials
10
Modified Mill
100%
75%
-
50%*
25%
--
-
0%
4 (Wet)
3
2
1
6
Trial
0
>500p
<500p
Figure 5: Results of Modified-plates hand-crank mill trials
To investigate the effects of paired coarse and fine runs, we ran another four
trials with the first pass being performed on the unmodified mill, then the second on the
modified one. The paired trials provided some promising results. While the new setup
did not strictly outperform the JHU mill, its performance was comparable to the JHU mill,
and better than the CTI mill. Crucially, the milling process went much smoother.
Paired Trials
100%
50%
0%
3
2
1
4 (Wet)
Trial
U <500p
>500p
Figure 6: Results of paired unmodified-modified mill trials
11
The initial attempts at mounting a mill as an attachment to the Phoenix bicycles
popular in Arusha proved difficult, and eventually failed. Although we had access to a
bicycle that had been kept in good repair, the rack we were mounting was simply not
designed to bear such a heavy, off center load. Even after building a sturdier rack that
could support the mill, the high torque requirement made precise sprocket positioning
crucial, as any misalignment was liable to make the chain disengage. It quickly became
clear that the bike-mounted approach might not be the best option for the mill, as the
minor and major difficulties experienced would be magnified in the real world case of a
bicycle in poor repair. Eventually, a mill was mounted stably, and performed solidly.
Once built, attempts to simulate the paired two pass approach by replacing the plates
between passes proved unsatisfactory, as the plates were similar but not entirely
interchangeable.
Figure 7: Bicycle mounted single mill
All the data gathered informed the design of a new milling machine. The best
results came as a result of a paired trial that incorporated the unmodified mill as a
coarse first pass and the modified mill as a fine second pass. A coarse-fine approach
12
was also the working principle behind the design of the plates of the much more
expensive CTI mill, which despite not performing at expectation still held some
strengths. The bicycle attachment idea was abandoned, however; while pedal power
was a great thought to ease the power burden on a human powered machine, the idea
of the end user attaching the machine to his or her own bicycle could prove problematic,
as the demands of the machine would require the bicycle to be exceptionally well
maintained. Additionally, the work of milling maize in East Africa is mainly performed by
women, who do not customarily ride bicycle, especially in more traditionalist rural
communities.
In the process of testing the available machines, it was quickly realized that the
metric of success was unknown. For our own purposes, all of our results were stratified
according to a set of 6 sieves from 4000p to 63p but we did not know at what level the
flour could be considered acceptable. After analyzing samples generated by local large
electricity powered mills, and an interview, we chose 500p as our standard for "good
unga" quality. After all of the data was processed, the design of a new milling machine
was decided as a non-bicycle machine, but built using easily repairable bicycle
components, that could accommodate both a coarse and a fine stage of milling that
would produce a high level of unga quality flour.
3. New Designs, Testing, and Results
3.1.
Design of Twinmill
The observation of the double-pass trials of the Estrella machines informed the
design of a new mill concept that would run two mills simultaneously. The mills would
13
not be identical, but instead double-pass test that used both the unmodified and
modified mills, even though the data revealed that two passes on the modified mill
produced slightly higher unga yields. This was due to the difficulty of the first pass on
the modified mill; it was nearly impossible to get a smooth, constant run on the modified
mill during the first passes, which would constantly jam, and require a highly variable
degree of power.
The two mills would be mounted onto a bicimolino, a machine designed and built
in Guatemala for use by rural communities there to also mill maize. Since the first,
coarse, pass would have the higher torque requirements of the two mills, it received an
extra gear reduction, operating at a 2:1 ratio with the finer pass machine. The new
platform also helped with the alignment of the sprockets that had proved so difficult with
the bike mount attachment.
Once built, the performance of the twinmill was
tested. Across seven trials, the machine returned a fairly
consistent unga yield of about 66 percent, greatly
outperforming all of the previously tested machines.
Additionally, the trials each went very smoothly, with no
jamming, or failures. The effort required to run the mill
was quite modest, and did not vary much until close to
the very end of the tests when the load drops
considerably (the top mill is empty).
Figure 8: Twinmil
14
Twinmill
100%
50%
0%
1
2
4
3
5
6
7
Trial
<500p
>500p
Figure 9: Results of Twinmill trials
3.2. Design of Modified Twinmill
After the Twinmill was built and tested, it was observed that the feature size on
the outside edges of both the modified and unmodified plates was larger than the
targeted particle size of the flour, and that the undulating shape of the plates would
cause the effective distance between the plates to increase and decrease with the
rotation of the plates - leading to a periodic release of larger particles. To prevent that
release, the plates of the second mill were sanded down further, until there was a flat,
featureless rim around the grinding area. Modifications to the first mill were not deemed
necessary as its purpose was to provide a coarse grind, and the modification would
therefore be counterproductive. This modification ensured that the plates could spin flat
relative to each other, as well as reducing the average particle size that could be
produced.
15
Figures 10 & 11, flour output of modified Twinmill (left), sorted by particle size (right)
As no other modifications were made, the plates could be replaced into the
previous twinmill machine and tested. There were a few key differences between the
trials run on the modified twinmill and the original. It was now possible to force the
machine to fail; whereas the original twinmill could run even at very tight plate settings,
the modified twinmill needed the fine pass plates to be set at a minimum width apart,
otherwise the flat featureless plates would not allow any material through, and the
maize would be stuck. More importantly, however, the modifications worked as
expected. The flattened plates were no longer letting through large particles, and the
non-featured plate edges were as well. The load on the operator was slightly higher, but
not significantly so. The yield improved, this time averaging at about 80 percent.
16
Modified Twinmill
100%
75%
50%
25%
0%
1
3
2
4
5
Trial
<500p
>500p
Figure 12: Results of Modified Twinmill Trials
4. Conclusion
The final yields of 80 percent represented a great improvement over all of the
machines that were initially tested. Furthermore, the design does not employ any
advanced materials or manufacturing methods, and can be both built and serviced
virtually anywhere in the world. Crucially, it meets the performance specification producing an acceptable flour in a few minutes times with a tiny fraction of the effort and
time expended using traditional methods, and if available locally, without inconvenient
travel time.
Moving forward, there is still analysis to be done regarding the particulars of
manufacturing, as well as a cost analysis. Further testing can be done to optimize the
grinding settings such as the plate distance and gear ratios. While optimization may not
generate significantly higher yields at this point, it will certainly help in insuring the
machine is more robust, and operation smoother.
17
Another key performance metric for the mill is its reliability and durability. To that
end, it would be important to develop a mill that could reach the same target yields but
employing only one mill. A single mill design would have a simpler drivetrain, as well as
lower the amount of materials used, components purchased, and build time leading to a
lower cost machine. The design would likely focus on the grinding plates, using the
concept of a coarse then fine grind but using a different design from the CTI, which also
attempted to incorporate a two stage grind but did not fare well in the experiments. Also,
the twinmill design also allows the second mill to be run below capacity, mitigating the
troubles caused by the constant flow-rate auger. The modified twinmill machine serves
to provide strong baseline performance level, to which other machines can be
compared to. Future revisions will focus on novel grinding plate and input shaft designs.
18
5. Appendix
5.1. Appendix A: Data Tables
Trial
Machine
Passes
4000p
2000p
1000
500p
250p
125p
63p
>500p
Trial
Machine
Passes
4000p
2000p
1000I
500p
250p
125p
63p
>500p
<500p
Trial
Machine
Passes
4000p
2000p
1 OOOP
500p
250p
125j
63p
>5 0 0 p
<500p
21
1
CTI
CTI
Ot
1!
0/a
9.5%
0%
57.1 /
14.2%
14.2%
4.7%1
66.6%1
33.1%
CTI
0%
9.4%1
CTt
1
1.1%1
-44.2%- -----
0%
0%
31.5%
19.5%
3.4%1
0%
76.8%
22.9%1
48.4%
34.7%
7.3%'
0%'
57.8%
42%
1
41
CTI
0%
11.8% 1
0%'
57.8%1
28.6%
1.6%'
69.6%:
30.2% 1
3 4 (Wet)
Unmodified
Unmodified
Unmodified
Unmodified
2'
2
2'
2
0%
0%
0%
0%
19.3%1
10.6%
38.7%1
12.1% 1
41.9%1
54%
0%
0%
10.7%
_
12.2%
47.3% 1
62.5%
12.9%
14.7%
9.4%
19.1%
129%
8.1%
4.3%
6%
2.1%
0%
0%
0%
__71.9
76.8%
86%
74.6%
27.9%
22.8%
13.7%
25.1%
2
21
Modified
Modified
Modified
2,
0%1
0.7%
()%
67.6%
23.5%
5.8%
2.2%
68.3%1
31.5%
2
'9%
11.3%i
3 4 (Wet)
Modified
2
21
0%
O%
1.1%
0%
28.8%
0%1
19.9%
54%
41%I
32.9%I
12.8%1
03
54%
45.7%
0%
58.6%'
41%
19
8.8%
0.1%1
49.8%
49.9%
5
2
0%
14.1%
31.8%
14.8%
29.7/%
9.2%
0O
60.7%
38.9%1
Trial
Machine
Passes
40 0 0p
2000p
1
Paired
0%
0%
58.8%
19.9%
20.9%
0%
58.8%
40.8%
>500p
<5 0 0 p
Trial
Machine
Passes
4000p
2000p
0%
64.9%
34.7%
2
1
Bike Mount
Bike Mount
2'
0% 1
0%
0%
__
--56.8% j --------34.4%
8%
250p
125p
63p
>500p
--------
64.7%
28.4%!___
0%1
0%t
57.3%
-----_--_---------------
3
Bike Moun t
2
0% 1
0.5%
500p.
------_
-----
Paired
2
0%
0.9%
43.3%
20.7%
28.2%1
6.5%
2
63p_
1000.
Paired
0%
10010p
500p
250p
125p
------------3 4 (Wet)
Paired
-4
2 ----- --2
-0%
0%
----------0%
6.5%
35.8%
38.4%
19.1%
13.1%
34.9%
30.7%
9.9%
10.9%
0%
0.1%
54.9%
58%
44.8%
41.7%
2
42.4%
c,
0%
1____
65.2%
34.5%1
2
0%
0.5%
0%
59.4%
23.3%
16.6%
0%
59.9%
39.9%
Trial
1i'
2
3
5
6
Machine Twinmill
Twinmill
Twinmill
Twinmill
Twinmill
Twinmill
Twinmill
Passes
1
1
1
1
1
1
1
4000p
0%
0%
0%
0.%A
0%
0%
0%
2
000p
0%
0%
0%
0 %O
0%
0%
0%
1000p
0%
___
0%
0%
0%
0%
0%
0%
500p
57.1%
31.9%
35.3%
33.3 %A
34.6%
33.3%
34.3%
2
20.7%
50p
35.1%
44.4%
37.5 %
41.5%
40%
39.6%
125p
16.8%
29.7%
19.1%
25 %O
21.7%
24.4%
24.4%
63p
5.1%
3.1%
4.1 A
1%
1.9%
2.2%
1.5%
>500p
57.1%
31.9%
35.3%
33.3 A
34.6%
34.3%
33.3%
<500p
42.6%
67.9%
66.6 A
64.5%
65.1%
65.5%
66.6%
20
Trial
Machine
Passes
4000p
2000p
5
4
3
2
Modified Twinmill Modified Twinmill Modified Twinmill Modified Twinmill I Modified Twinmill
l OOOP
500p
250p
125p
63p
>500p
<500p
0%
0%1
0%
204%
55.9%;
21.5%1
2.1 %
20.4%
79.5%
0%
0%t
23.4%
37.2%
37.2%
2.1%:
23.4%
76.5%
0
0%
%
15.5%
64.3%
19.9%
0.2%
15.5%
84.4%
0%
0%
0%
0%
0%
0%
25%
43.9%1
29.5%
1.5%
_
25%
74.9%
0%
0%
20.4%
51%
26.5%
2%
20.4%
79.5%
j
Notes on data:
These tables represent all of the data we collected to form a comparison of each
machine. After milling, the flour was run through a set of sieves to separate out the finer
grades of flour. The results of each sieve was then massed and recorded. All of the
recorded data is shown here, though the key variable was total particles below 500p,
and that is what is shown in the charts above.
Not all tests were run with the same input mass: The CTI mill tests were mostly
200g, while the other machines usually had 150g or 125g. For percentages, the "total"
amount was measured after milling and sifting - we did not account for corn lost to the
machine or the sieve. Any amount spilled would likely skew our data towards a lower
yield, as the lighter and finer flour is most likely to spill, and spends the most time in the
sieve.
Wet tests - we also ran a single trial of each of these modes with wet corn. After
soaking in water for five minutes and being allowed to partially dry, none of the wet trials
produced significant or interesting results, ranging from no difference to slightly better
yields. Given the initial result, and our findings that the local people do not process their
21
maize by washing if they intend to mill flour - there is washing involved if they intend to
only shell the kernels for different dishes. The process of nixtamalization, in which the
corn is cooked in a solution of water and slaked lime or ash prior to the milling process,
is rare outside of its cultural origins on the American continent, and could conceivably
improve yields by softening the kernels. Anecdotally, we were told that in the case of
East Africa, the locals simply dislike the taste of nixtamalized corn, although some
families seem to have incorporated the process for certain dishes in order to benefit
from the nutritional boost it provides. The local resistance to preprocessing their corn
led us to decide against experimenting with the idea of preprocessing the corn at this
time.
22
5.2. Appendix B: Mill, Kingoro Visits
We were able to visit three electric powered milling sites. Samples collected were
analyzed and used to define our goal particle size of <500p. The setup of all the mills
we saw were almost the same: a the milling and shelling machines were located in a
small room, with washing stations located just outside. The people would spread out the
corn and wet it just prior to running it through the shelling machine, but not when milling:
all milling was done dry. It is worth noting that the shelling machine appears to be just
as important as the mill: while some people just mill for flour, many people also just shell
the kernel, or shell and mill for a less nutritious but tastier flour. Although an effort was
made to visit villages and interview potential users that currently mill by hand, we were
not successful. Even in towns with poor access to electricity, a local mill would be
operated with either an electric or diesel motor, obviating the need for a human powered
personal or community mill. There are, however, people who travel to visit these mills
who would benefit from a human powered mill in their own homes or smaller
communities. We interviewed one woman during a visit to Kingoro Village, and gathered
some interesting data. It was evident that milling is quite a burden to the residents of her
village - a two hour walk each way every three days adds up to almost an entire day
each week dedicated to milling, even thought the actually process lasted less than the
duration of the conversation. It is interesting to note that mill customers discriminate
based on quality of the mill; there are two competing mills in Kingoro, one diesel
powered and one electric, with the electric mill producing a markedly superior product at
a slightly lower price. The diesel mill, likely an older model that had been running before
electricity was available or reliable in Kingoro, recieved only customers that lived
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nearby, according to our subject, but those that had to travel (like herself) chose the
slightly more distant but better and cheaper electric mill. Relevantly, she judged the
sample (That sample had a maximum particle size of 10001p) to be passable, but of
diesel mill quality.
Kingoro Transcript:
How long does it take to get here(mill)?
About 2hrs walking, or 30mins on pikipiki [Local motorbike taxi]
How much does it cost?
The pikipiki is 3000 TSH, the electric mill is 200TSH and the diesel is 300TSH
What is the difference between the electric and diesel mills?
The electric mill flour is "softer." No one likes the diesel mill flour.
Translators Note: "Even I cant eat this (gestures to our sample) flour"
What do you think of our sample?
It looks like it came from the diesel mill.
The diesel mill is more expensive and produces inferior flour. Why do people go?
The people that go to the diesel mill live very close by.
How long does it take you to mill?
Not long at all. (completed in the time it took to perform this survey*)
How much corn do you mill at a time?
I mill enough corn for three days; I come back here every three days
Comments/Interpretations:
A two hour trip to the mill means that total time spent "milling" is about 4.5 hours.
This represents a significant fraction of her daylight (1/3 - 1/2); if she pays for a cab then
its much less time, but at a cost of over 1000% of the milling. The people nearby the
diesel mill are willing to pay 150% and receive a worse product for the convenience;
there is reason to believe that even at sub-1000p a local mill may see good business.
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6. Bibliography
- Aijazi, Arfa. Hand Powered Grain Mill. Tech. N.p.: n.p., n.d. Print.
- Madu, Tobecukwu, and Cem 0. Yilmaz. Maize Grinder Report Update. Tech. N.p.:
n.p., n.d. Print.
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