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DETAIL A
11/21/2014
MAGNETIC EGGCARRIAGEPARTS LIST
M. E. C. M. E. C.
NOTES:
1. ALL LINKAGES AND CONNECTORS SYMMETRICAL ON EACH SIDE OF DOCKING STATION.
2. APPLY LIQUID ADHESIVE (ITEM 12), FOR ALL INSTANCES OF INTERFACE BETWEEN- ITEM 6 AND ITEM 10- ITEM 7 AND ITEM 11- ITEM 4 AND ITEM 5- ITEM 1 AND ITEM 5.
3. ITEM 5 SHOULD BE AS FLUSH AS POSSIBLE TO ITEM 1 AND ITEM 4 RESPECTIVELY.
ITEM NO. PART NUMBER DESCRIPTION QTY.1 DOCKING STATION 3D PRINTED PLA, 9.7" x 4.0" x 6.25" 12 LINKAGE 1 3D PRINTED PLA, 0.125" THICK 2
3 LINKAGE 2 3D PRINTED PLA, 0.125" THICK, 0.250" BOSS ON ONE END 2
4 TRAY 3D PRINTED PLA, 10 EGG CAPACITY CONTAINER 1
5 NEODYMIUM MAGNET 0.250" DiAMETER, 0.125" THICK CYLINDRICAL NEODYMIUM MAGNET 12
6 OUTER CONNECTOR 1 3D PRINTED PLA, 0.200" LONG 2
7 OUTER CONNECTOR 2 3D PRINTED PLA, 0.250" LONG 2
8 OUTER CONNECTOR 3 3D PRINTED PLA, 0.450" LONG 2
9 OUTER CONNECTOR 4 3D PRINTED PLA, 0.700" LONG 2
10 INNER CONNECTOR 1 3D PRINTED PLA, 0.250" LONG 2
11 INNER CONNECTOR 2 3D PRINTED PLA, 0.200" LONG 2
12 LIQUID ADHESIVE PERMANENT ADHESIVE FOR PLA n/a
D
C
B
AA
B
C
D
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INTERPRET GEOMETRICTOLERANCING PER:
MATERIAL
FINISH
DRAWN
CHECKED
ENG APPR.
MFG APPR.
Q.A.
COMMENTS:
DATENAME
TITLE:
SIZE
BDWG. NO. REV
WEIGHT: SCALE: 1:2
UNLESS OTHERWISE SPECIFIED:
SHEET 1 OF 1DO NOT SCALE DRAWING
C. CHO
1A
CHRISTOPHER CHO
PROPRIETARY AND CONFIDENTIAL
APPLICATIONAPPLICATION
11/20/2014
MAGNETICEGG CARRIAGE
M. E. C.M. E. C.
3D-PRINTED PLA
D
C
B
AA
B
C
D
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INTERPRET GEOMETRICTOLERANCING PER:
MATERIAL
FINISH
DRAWN
CHECKED
ENG APPR.
MFG APPR.
Q.A.
COMMENTS:
DATENAME
TITLE:
SIZE
BDWG. NO. REV
WEIGHT: SCALE: 4:5
UNLESS OTHERWISE SPECIFIED:
SHEET 1 OF 7DO NOT SCALE DRAWING
C. CHO
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CHRISTOPHER CHO
PROPRIETARY AND CONFIDENTIAL
APPLICATIONAPPLICATION
(6.25)
.1252x
1.000
1.025
1.250 3.050
4.850 6.650
8.450
.2002x
.380
.0252x
1.150
B
9.70
4.00
2.50
.3752x
A
R.75
R.375±.010
R.15
5.500
.250
1.150 .175
1.925
1.500
.375
1.125
5.210
.125
4.00 3.650
R.1253x
.1252x
R.157 .385 R2.000
DETAIL A
11/20/2014
DOCKINGSTATION
M. E. C.M. E. C.
3D-PRINTED PLA
D
C
B
AA
B
C
D
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INTERPRET GEOMETRICTOLERANCING PER:
MATERIAL
FINISH
DRAWN
CHECKED
ENG APPR.
MFG APPR.
Q.A.
COMMENTS:
DATENAME
TITLE:
SIZE
BDWG. NO. REV
WEIGHT: SCALE: 4:5
UNLESS OTHERWISE SPECIFIED:
SHEET 2 OF 7DO NOT SCALE DRAWING
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CHRISTOPHER CHO
PROPRIETARY AND CONFIDENTIAL
APPLICATIONAPPLICATION
1.939TO CENTERPOINT
OF RADIUS
5.803TO CENTERPOINT
OF RADIUS
2.150
3.950
5.750
7.550
.170
3.843
.2508x
R.1578x
.125
.125
DETAIL BSCALE 2 : 1
11/20/2014
DOCKINGSTATION
M. E. C.M. E. C.
3D-PRINTED PLA
D
C
B
AA
B
C
D
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DRAWN
CHECKED
ENG APPR.
MFG APPR.
Q.A.
COMMENTS:
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TITLE:
SIZE
BDWG. NO. REV
WEIGHT: SCALE: 1:1
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CHRISTOPHER CHO
PROPRIETARY AND CONFIDENTIAL
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11/20/2014
TRAYM. E. C.M. E. C.
3D-PRINTED PLA
D
C
B
AA
B
C
D
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ENG APPR.
MFG APPR.
Q.A.
COMMENTS:
DATENAME
TITLE:
SIZE
BDWG. NO. REV
WEIGHT: SCALE: 2:3
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PROPRIETARY AND CONFIDENTIAL
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11/20/2014
LINKAGES
LINKAGE 2
M. E. C.M. E. C.
3D-PRINTED PLA
D
C
B
AA
B
C
D
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DRAWN
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ENG APPR.
MFG APPR.
Q.A.
COMMENTS:
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TITLE:
SIZE
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WEIGHT: SCALE: 2:1
UNLESS OTHERWISE SPECIFIED:
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.075TYP
.25
.050TYP
.200TYP
.20
11/20/2014
INNER CONNECTOR 1 INNER CONNECTOR 2
INNERCONNECTORS
M. E. C.M. E. C.
3D-PRINTED PLA
D
C
B
AA
B
C
D
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Q.A.
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Outer Connector 4 Outer Connector 2Outer Connector 3
.075TYP
.25 .20
.125TYP
.45
.05TYP
.20TYP
.70
11/20/2014
OUTERCONNECTORS
Outer Connector 1
M. E. C.M. E. C.
3D-PRINTED PLA
D
C
B
AA
B
C
D
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Magnetic Egg Carriage
Design and Engineering Analysis Report
Christopher Cho November 20, 2014 FirstBuild – Icebox Challenge
P a g e | 1
C. CHO, FirstBuild
11/20/2014
FirstBuild
Icebox Challenge
Applicant: Christopher Cho
Design Submission: Magnetic Egg Carriage
Date of Submission: November 20, 2014
Content: Design and Engineering Analysis Report
Requirements
Designs must be able to be printed in a MakerBot Replicator (5th
generation). The build
volume of the printer is 9.9L x 7.8W x 5.9H in
Guidelines
Ideas could range from purely 3D printed pieces to battery operated electromechanical
devices
Designs/solutions should serve their function inside of the refrigerator
We encourage entries also be submitted to the Thingiverse site with the tag
#IceboxChallenge for a chance to be featured on their site.
Deliverable Views
Front View
Side View
Top View
Optional Additional View (3x)
Additional Deliverables
A CAD file must be submitted, preferably STL.
P a g e | 2
C. CHO, FirstBuild
11/20/2014
Design Considerations
Function
The Egg Carriage is a carton-like tray that hangs under a shelf on the refrigerator door.
The tray is attached to a dock via linkages and magnets; the dock itself is secured to the shelf
above via rigid arms. Utilization is simple and intuitive:
In the “Away” position, the tray is magnetically secured directly under the dock, which, by
design, is neatly placed under the shelf. This placement allows storage and protection for the
eggs.
In the “Forward” position, the linkages swing out and the tray is magnetically secured to the
forward set of magnets. In this position, the tray presents itself for use.
Image 1: Away Position Image 2: Forward Position
Image 3: Away Position Image 4: Forward Position
P a g e | 3
C. CHO, FirstBuild
11/20/2014
Image 6: Forward Position
Image 5: Away Position
P a g e | 4
C. CHO, FirstBuild
11/20/2014
Fabrication
All the components of the Egg Carriage can be fabricated via 3D printer save the
neodymium magnets. These essential magnets cannot be fabricated in the same manner and
must be purchased from a third-party. Though not included, some of the components, such as
the hanging arm-hooks on the dock, may need support material to create.
It may be important to mention that this may require a minimum of 3 separate print runs, as
the dock and tray will likely require separate print runs. However, the final print run can
likely fabricate the remaining loose components (linkages/connectors) in one go.
Attached as well are CAD drawings in the case that injection molding or CNC machining is
preferred.
Design Justification
The intent of this design was to target and eliminate the large footprint of egg storage.
Given their fragile nature, the simplest way for refrigerator manufacturers to ensure security
was to dedicate an area specifically for eggs. Sadly, this usually resulted in a siphoned off and
dedicated “egg-only” zone that took up quite a bit of surface area. I saw this as a challenge to
get these eggs out of the way while still maintaining their integrity.
The result of my efforts was the Egg Carriage that you can visualize using the attached
models and drawings. I kept the tried-and-true egg carton design, but targeted the location
instead. The Egg Carriage allows a refrigerator owner to simply hang their eggs off of a shelf
on their refrigerator door and recover all the lost space that was once a dedicated “egg-only”
zone.
This concept may seem daunting at first; why would one risk such fragile cargo with a
dynamic container that hangs? After much design iteration, I was able to develop a secure
method to keep the eggs intact, but still easily accessible. The strength of neodymium
magnets has been undervalued and underused for quite some time, and I feel that their
incorporation here allows for a strong, yet aesthetically pleasing design. Their hidden
adhesive strength removes the need for awkwardly placed securing mechanisms like locks or
latches.
The question then remains of whether or not the structural integrity of the material can
withstand its own weight with cargo. These issues are addressed below in the Weight and
Stress Analysis portion of this report.
P a g e | 5
C. CHO, FirstBuild
11/20/2014
Cost Analysis
The total build volume of all the components that need to be 3D printed is 544.22 cm3, or
33.207 in3. Utilizing Makerbot’s proprietary PLA white filament at $48.00 per 0.9 kilograms,
the cost of the prints can be approximated (excludes support material).
Total Build Volume 544.23 cm3 (33.207 in
3)
3D Printed PLA Filament Density[1]
1.25 g/cm3 (0.045 lbs/in
3)
Filament Cost[2]
$48/0.9 kg ($48/1.984 lbs)
Neodymium Magnet Cost[3]
$0.34
Quantity of Magnets 8
Table 1: Cost Analysis of Components
[ ⁄ (
⁄ )
⁄ ] ( )
Note: Cost does not include shipping and other acquisition expenses.
Potential Improvements
Over the development of this idea, there were many improvements that could have been
made, many of which were stifled by cost or design size criteria. The simplest way to upgrade
the design would be to utilize an adhesive (i.e. command strips, Velcro strips, etc.) that would
adhere the bottom of the shelf to the top of the dock. This would negate the deflection in the
rigid arms and really solidify the unit to the door of the refrigerator. Unfortunately, this would
remove the possibility of sliding the Egg Carriage back and forth to dynamically adjust space
on demand.
The most glaring detail of this design is the capacity for only 10 eggs, rather than the standard
dozen. Due to the static sizes of most eggs, it was not possible to create a tray of this design
that held the remaining two without exceeding the length restriction (9.9 inches) of this
challenge. However, part of the design intent was to include the potential for unbridled
expandability along that length if one were to have access to a 3D printer with a larger
workable area.
One of the unofficial challenge guidelines was to make it fit my refrigerator. However, for
consumer product design, there is no such concept. That is where modularity and universality
come into play. The rigid arms that hang on to the Egg Carriage are a static height that allows
the Egg Carriage to be placed neatly underneath the shelf. However, with telescoping arms
and a locking mechanism, one could have a dynamic length that can be adjusted for any
consumer’s refrigerator.
P a g e | 6
C. CHO, FirstBuild
11/20/2014
Another possible, but minor, improvement would be to increase the size of the magnets.
Neodymium magnets are strong, but their pull-force is still proportionate to their size; a larger
diameter or thickness would allow for a better factor of safety. Because neodymium magnets
are graded, with the utilized N42 being of a lower end, a higher grade magnet will also yield a
larger pull-force.
My final suggestion for design improvements would be full incorporation onto a refrigerator
door. This means that the docking system is molded with the rest of the door at the
manufacturing stage for a flush, clean design; the tray would simply click onto the door itself.
The elimination of the hanging arms will allow a skeptical consumer to accept the “my eggs
are simply dangling there?” concept with much more relief. This static design does come with
downsides in terms of mobility, but a huge boost in rigidity and aesthetic.
At $39 per unit, this design is a little more on the pricy side. To allow it to be a little
more economical, some compromises can be made regarding material and design.
Seeing as the material is 93% of the cost, one can definitely make changes to where the
filament is supplied. However, the MakerBot Replicator (5th
Generation) is only designed to
spool proprietary filament without modifications. When comparing with prices from third
party suppliers, filament at 40-60% of the original cost will directly correlate with 40-60%
reduced cost when fabricating the Egg Carriage. For a volumetrically large print such as this,
it may be cost effective to make modifications for the MakerBot to accept non-proprietary
filament, or print on a less restrictive machine.
The other option to reduce overall cost is to cut corners on the design itself. Optimization of
material usage will trade structural rigidity for price, however, that degree of optimization
extends beyond the scope of this report.
P a g e | 7
C. CHO, FirstBuild
11/20/2014
Weight Analysis
Name Quantity Volume (cm3, in
3) Material Weight (g, lbs)
Tray 1 242.26 (14.78) ABS Plastic 302.83 (0.66763)
Dock 1 297.93 (18.18) ABS Plastic 372.41 (0.82102)
Linkage 1 2 2.045 (0.125) ABS Plastic 2.556 (0.00564)
Linkage 2 2 1.643 (0.100) ABS Plastic 2.054 (0.00453)
Outer Connector 1 2 0.049 (0.003) ABS Plastic 0.061 (0.00013)
Outer Connector 2 2 0.043 (0.003) ABS Plastic 0.054 (0.00012)
Outer Connector 3 2 0.075 (0.005) ABS Plastic 0.094 (0.00021)
Outer Connector 4 2 0.107 (0.007) ABS Plastic 0.134 (0.00030)
Inner Connector 1 2 0.035 (0.002) ABS Plastic 0.044 (0.00010)
Inner Connector 2 2 0.032 (0.002) ABS Plastic 0.040 (0.00009)
Neodymium Magnet 8 0.101 (0.006) NdFeB 0.752 (0.00166)
Eggs 10 - - 1380.00 (3.04200)
Total with Eggs - - - 2061.03 (4.5421)
Total without Eggs - 544.32 (33.216) - 681.03 (1.5014)
Table 2: Bill of Materials; refer to separate Parts List for component representation
Average Weight of Extra Large Egg[4]
63 ~ 69 g (0.139 ~ 0.152 lbs)
Maximum Egg Capacity 10 eggs
Factor of Safety 2
Table 3: Weight Analysis of Eggs
[ ]
( )
Average Volume of Neodymium Magnets 0.101 cm3 (0.006 in
3)
Density of Neodymium Magnets[5]
7.45 g/cm3 (0.269 lbs/in
3)
Number of Magnets in Tray 4 pieces
Factor of Safety 2
Table 4: Weight Analysis of Magnets
[ ⁄ ]
( )
P a g e | 8
C. CHO, FirstBuild
11/20/2014
Volume of Tray 242.26 cm3 (14.78 in
3)
Volume of Linkages 7.38 cm3
(0.44 in3)
Volume of Connectors 0.682 cm3
(0.044 in3)
3D Printed PLA Filament Density[1]
1.25 g/cm3 (0.045 lbs/in
3)
3D Printed ABS Filament Density[1]
1.04 g/cm3 (0.038 lbs/in
3)
Factor of Safety 2
Table 5: Weight Analysis of 3D Printed Components
[[ ] ⁄ ]
( )
( )
Design Strength 2011.83 g (4.435 lbs)
Magnetic Pull Force[6]
:
- Magnet to Magnet Contact
- Grade N42 Neodymium
- 0.250” Diameter
- 0.125” Thickness
1043.26 g (2.30 lbs)
Magnet Count 4 pieces
Table 6: Pull-Force Analysis of Magnets
( )
Conclusion
Based on the calculations above, the combined pull force of the Neodymium magnets
(9.2 pounds) far exceeds the weight of the tray, linkages, connectors, as well as a maximum
capacity of eggs combined (4.435 pounds), inclusive of the factor of safety. With these
calculations, this choice of magnets allows a safety factor of 4. If a factor of safety higher
than this is desired, a higher grade of Neodymium magnets may be considered, as well as an
increase in the size of the magnets used. It is also possible to further maximize the factor of
safety by optimizing the conservancy of material when printing the tray.
P a g e | 9
C. CHO, FirstBuild
11/20/2014
Stress Analysis
Connectors
The bulk of the forces that will be applied to the egg tray itself will be the downward
forces of gravity. Based on the rigidity and tighter tolerances in the axial direction of the
connectors, it can be assumed that the forces axial to the connectors can be neglected. When
in changing state between forward and backward positioning, the majority of the stress will lie
with the connectors that hold the linkages together, and hold the linkages to the tray and dock.
Due to the symmetrical nature of the connector, the stress can be modeled as unidirectional in
the transverse direction.
Image 7: 20 lbf of transverse load on Outer Connector 4
Image 8: 20 lbf of transverse load on Outer Connector 2
P a g e | 10
C. CHO, FirstBuild
11/20/2014
The deformation analyses were performed on the Outer Connector 4 and Outer Connector
2 components because they were the longest and shortest in length, respectively. This
characteristic, combined with the consistent diameters across all the connectors, allows us to
visualize the range of maximum deformations for different lengths of connectors. Not only
are the simulated deformations on the magnitude of 1/1000th
of an inch, but these are also
conservative estimates.
In practical application, some of these connectors would be reinforced by their
complementing Inner Connector components. These solid Inner Connectors would be
inserted into the recess of the Outer Connectors, effectively creating a solid cylinder. The
bending moment for a solid cylinder is much higher than that of a hollow cylinder, greatly
increasing their ability to withstand deformation. Utilizing a 20 pound-force load was quite
safe as well, considering the maximum weight of a full egg tray was calculated to be 3.721
pounds. Even if one were to accidentally bump or mishandle the egg carriage during use, the
magnets and tight tolerance of the linkage/connectors would keep the cargo intact, while the
strength of the connectors would not allow the rigidity of the system to collapse.
Analysis of the linkages themselves was deemed unnecessary, as their presence merely
represents a guide for the motions of the tray. The forces exerted on the system that maintains
the tray preside mainly with the connectors’ rigidity and the pull-force of the neodymium
magnets.
Arms
One of the design intents was to eliminate the need for an excessive footprint to store
eggs. Given their fragile nature, a secure environment must be enforced. As the entire
structure is hanging off of the shelf’s “fence”, the arms that secure the unit must be able to
withstand the maximum weight of the egg carriage with a factor of safety.
Image 9: Displacement from 20 lbf of downwards-facing load on the Tray
P a g e | 11
C. CHO, FirstBuild
11/20/2014
Image 10: Displacement from a 20 lbf of downwards-facing load on the Tray (view from other side)
Given that the weight of a full capacity Egg Carriage is projected to be 4.542 pounds, the
arms must be able to withstand that force with minimal deflection. Given the positioning of
the carriage, it is unlikely that any kind of accidental bumping or knocking will apply a
downwards force on the carriage itself; it is more likely for the hooks themselves to absorb
any such impacts. Thus, only the weight of the tray and its cargo was considered as
contributing factors in this simulation.
As seen in the displacement results from an applied 20 pound force (safety factor of 5), the
front and back of the arms receive minimal change in position, with the blue to light blue
color labels signifying a ranging displacement from 4.000 x 10-32
in to 0.200 in, respectively.
The displacements near the back of the unit are larger, but an expected phenomenon due to the
nature of the carriage’s shape. Potential solutions to resolve this minor issue was presented
previously under Design Considerations, Potential Improvements.
In the realm of permanent deformation or potential fracture, the theoretical maximum
deformation can be calculated.
Uniform gravitational force over the area can be summed into one
resultant vector at the center of gravity. The moment is uniform
along the beam in question because the distance from the force
vector and then centroid of the beam is constant.
Image 11: Force Vector Diagram
P a g e | 12
C. CHO, FirstBuild
11/20/2014
Image 12: Dimensions of Cross Section and Center of Gravity (inches) Image 13: Dimension to Pivot Point (inches)
Elastic Modulus of 3D Printed PLA[7] 3368 MPa (488487 psi)
Applied Force 20 lbs (9071.85 g)
Distance to Center of Gravity 2 in (50.80 mm)
Length of Assumed Cantilever 4 in (101.60 mm)
Cross-Sectional Base 0.375 in (9.53 mm)
Cross-Sectional Height 0.375 in (9.53 mm)
Table 7: Stress Analysis of “Cantilever” Arms
( )
(
)
( )( )
(
⁄ ) [
( )( )
]
The max deflection of the hanging arm will be almost 1/10th
of an inch at the point where the
arm meets the main body of the dock. However, this is for an extremely conservative 20
pound force analysis. Given that these equations are linear, the max weight of the entire
assembly is a little less than 5 pounds, so the practical maximum deflection at that point will be
a quarter of this value, or 0.025 inches.
P a g e | 13
C. CHO, FirstBuild
11/20/2014
From the simulated stress image below, the stress is maximum near the point previously
calculated, but is limited to only 2906 psi and at no risk of fracture due to the material’s high
rigidity[8]
.
Image 14: Stress from 20 lbf of downwards-facing load on the Tray
P a g e | 14
C. CHO, FirstBuild
11/20/2014
References
[1]http://www.toybuilderlabs.com/blogs/news/13053117-filament-volume-and-length
[2]http://store.makerbot.com/pla-filament#rep-truewhite
[3]
http://www.kjmagnetics.com/proddetail.asp?prod=D42E
[4]http://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-
safety-fact-sheets/egg-products-preparation/shell-eggs-from-farm-to-table/#17
[5]https://www.kjmagnetics.com/specs.asp
[6]https://www.kjmagnetics.com/calculator.asp
[7]https://www.academia.edu/6209168/Mechanical_properties_of_components_fabricated_with
_open-source_3-D_printers_under_realistic_environmental_conditions
[8]
http://bme.ucdavis.edu/team/equipment/3d-printer-comparison/