Senior Design Final Report2. Table of Contents
1. Introduction and Background 2
a. Problem Statement 2
b. Design Constraints 2
2. Design Choices and Justification 2
a. Why Quadcopter? 2
b. Competing Products 4
c. Justification for Portable Military Quadcopter Design 6
3. Final Design Improvements 6
a. Frame 6
i. Materials Selection 7
ii. Composite Quad Arms 8
iii. Body Panels 11
iv. Payload Adapters 12
v. Landing Legs 13
b. Parachute Implementation 16
c. Flight Modes 21
4. Testing and Analysis 26
a. Propeller Lift Testing 26
b. Frame/Load Testing 28
c. Battery Testing 32
d. Flight Testing 33
e. Parachute Testing 33
5. Bill of Materials 38
6. Budget 40
a. Cost Total 41
b. Hour Total 41
7. Conclusion 42
a. Design Evolution 42
b. Strengths of Portable Military Quadcopter Design 45
c. Recommendations 46
d. Implementation Plan 48
8. Appendix 49
a. Table of Contents 49
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3. 1. Introduction and Background: Preventing Communication Breakdown
During field operations, military personnel use radio devices to communicate when they
need assistance. However, mountainous terrain or urban structures can sometimes block these
radio signals, resulting in unheard distress calls. Northrop Grumman, a global aerospace and
military defense contractor, challenged our VUSE design team to formulate a solution to this
communication breakdown.
Problem Statement
Create a device that enables communication regardless of landscape by carrying a relay
to a height sufficient for lineofsight communication.
Design Constraints
The device must be…
Capable of lifting a payload of no less than 1 kg
Manportable
Capable of maintaining its position in space within a 10 meter radius error margin
Reusable and cost no more than $500
Capable of altitude adjustment
Capable of position control
Able to trigger a backup parachute in the case of system failure
Relatively quiet
Note: No official lifetime constraint was provided. The necessary lifetime will be a
function of how high the quadcopter must go and how long the communication takes.
Reasonable order of magnitude estimate: 510 minutes
2. Design Choices
Why Quadcopter?
After considering various altitudegaining methods, a quadcopter proved to be the most
effective device to use. It satisfied all the initial design constraints: it has the ability to maintain
its position in space, even in relatively strong winds, to the precision of the onboard GPS unit
(which is within the given 10m radius sphere), and it can reach and maintain altitudes in the
ranges necessary. It can be designed to fit the requirement of “manportable” as well as to carry
the necessary payload. With the implementation of a rechargeable battery, the device is reusable,
and with the use of GPS waypoints and semiautonomous control, the device can easily be
controlled. A quadcopter is also conducive to the creation of a custom frame that can fold into a
compact storage position small enough to fit into a standard militaryissue packpack.
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4. The other major alternatives we had been considering were a balloon, a rocket, and a
balloonquadcopter hybrid. The balloon idea was eliminated first, as it would have involved
floating a platform with the communication software under a helium balloon. This design would
require the operator to carry a bulky helium tank, and the balloon would need to be large in order
to remain buoyant in the atmosphere with its 1 kg payload. Initial estimates using a hightech
balloon with helium yielded balloon diameters exceeding 2 ft, which would likely be visible in
the sky given its associated volume. Most importantly, a balloon would not be able to maintain
its position within the given error margin. With the balloon tethered, only the distance to the user
would be fixed; any wind at all would cause drastic and unfixable deviation from the desired
location, both in horizontal position and altitude depending on the wind’s force compared to the
buoyancy.
The second vetoed alternative was a rocketpayload system in which the communication
relay hardware would slowly descend via parachute after the rocket reached a maximum design
height. This alternative was eliminated as a rocket has little active control after launch and would
therefore be at the whim of crosswinds. It would be loud and visible, and the exhaust could be
seen by the naked eye or by an infrared camera. It would not be able to maintain its location
within the error margin, as the whole system would be slowly falling the entire time, unable to
maintain its altitude. The rocket itself would be relatively heavy and difficult for a user to
transport, and its reusability would be low; not only would it be difficult to recover the rocket
body and communication software after landing (possibly in unscouted and/or dangerous
territory), but even if it were recovered, it would need to be refueled and repackaged after each
use.
The third eliminated alternative was a balloonquadcopter hybrid in which the buoyancy
of a balloon would provide most of the lift to hover, while a low power quadcopter would
provide the remaining lift to rise and hover. By using this design, the lifetime could be extended
by a large factor if the motors were not supplying the majority of the lifting power. Additionally,
if the system’s power was cut off, the terminal velocity of the system would be very low due to
the balloon’s buoyancy and drag. Furthermore, the ability to maintain position in space would be
similar to that of a standalone quadcopter, and it would be quieter, with less noise from
propeller speed. The disadvantages, however, still outweighed the benefits of the standalone
quadcopter. The problem of carrying around a helium tank remained, and adding a balloon to a
quadcopter would increase the complexity of the system and the number of possible failure
points to an unacceptable level; whereas, quadcopters are known to work reliably and
effectively.
Construction vs. Modification
Following the selection of a quadcopter, a decision had to be made between modifying an
existing quadcopter and building one from scratch. We decided to build our own quadcopter
based on existing ones known to be able to support the target payload and attain the appropriate
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5. altitude. Building allowed for the implementation of motors, propellers, and other parts of the
exact desired specifications, as well as the creation of a unique, foldable frame for storage.
Additionally, this choice allowed us to test different parts in certain areas of the design to
provide justification for the selection of those parts.
Competing Products
As is commonly known, the military has increasingly used unmanned technology to
allow more complex operations to be performed without putting a human in harm’s way. Despite
this trend, no portable, individuallydeployed product is currently used for the specific purpose
delineated in our given problem statement. However, quadcopters similar to our design are
commonly used for surveillance and reconnaissance purposes when a small, quiet device is
required that has the option to remain still in the air as well as maneuver around or above
potential obstacles. These quadcopters are also capable of being fitted with custom payloads.
1. Aeryon Scout™
The Aeryon Scout™ is produced, along with the larger and more robust Aeryon
SkyRanger™, by Aeryon Labs Inc. and features some incredible feats of design. From its data
sheet, it has an operational range of 3 km or up to 25 minutes, and can fly up to 450m above the
ground. It weighs, without a payload, 1.4 kg and is made from predominantly polycarbonate. It is
fully GPS waypoint programmable and features a smart touchpad interface as a transmitter,
which also displays realtime camera data. The camera may be swapped out for a custom
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8.
Materials Selection
Leading up to this final prototype, a comprehensive materials study was performed to
obtain strengthtoweight ratio data (see figure 2) for various potential materials. After some
further analysis and discussion, medium density fiberboard (MDF) was removed from the study.
Not only was it the weakest material observed in this study by a significant margin, it also has a
poor reputation for both moisture resistance and cracking. These negative aspects were proved
in more recent testing of the flight modes, when upon hard landing, the quad arms had a
tendency to allow very little deformation before cracking completely through. Therefore,,
although MDF is inexpensive, it was not suitable for this application.
Figure 2: StrengthtoWeight Ratio of Various Materials
The next study involved strengthtoweighttocost ratio data (see figure 3). This study
was standardized between materials by using the same vendor’s pricings for similar geometries
(in this case, the price of a 6x6x1/8” sample of the material). Although this method has some
flaws, it was determined to be a good representation of overall strength and cost trends.
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9.
Figure 3: StrengthtoWeighttoCost Ratio Data for Various Materials (note the logarithmic axis)
As seen in figure 3, Nylon (6/6), extruded Acrylic, and 6061 T6 Aluminum have the best
strength characteristics for their costs, with Aluminum winning by a slight margin. After some
discussion of how to implement these newlystudied materials, it was determined that the best
way to implement the aluminum was in very thin sheets for the quadcopter’s arms (see next
section for assembly and fabrication details). Unfortunately, there was not a practical way to
implement the same composition tactics on the body of the quadcopter. In the end, the choice
between using the Nylon and the Acrylic was dictated by which was more readily available and
which was more able to be cut using a laser cutter. After some research, it was determined that
Acrylic laser cuts well, while Nylon has the tendency to melt badly around the lasercut edges.
Increasing the ease of the choice, ⅛” Acrylic was a supplied item, available for immediate use.
Later design choices led to the use of aluminum in a few other frame considerations.
Aluminum was the primary material used for both the payload attachment connections and for
the landing legs.
Composite Quad Arms
In order to maximize the loadsupporting characteristics of the sheet aluminum for the
quad arm design, we decided to implement a composite arm comprising of two aluminum sheets
sandwiching a rigid, closedcell polystyrene foam (see figure 4). (Pink polystyrene foam is the
most readily available color.) With this setup, during flight, the whole assembly would act as a
homogenous piece of material, bending like a cantilevered beam. This type of deformation
would allow the top sheet of aluminum to be nearpurely in compression and would allow the
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Figure 5: Final Composite Arm Model
Fabrication of four of these arms required the individual cutting and then adhesion of
acrylic spacers, aluminum sheets, and foam, The Acrylic spacers were first laser cut with center
holes which were drilled out to the correct diameter. Three thicknesses of the ¼” Acrylic were
then glued with Acrylic glue and stacked into groups of three to make a ¾” spacer. From there,
since neither the foam nor the aluminum could safely be cut by the laser available for quick use,
a model of the outermost rectangular dimensions of the aluminum was laser cut from MDF as
well as a two copies of a similar model for the foam insert. The first model was used to trace out
lines on a large sheet of 0.016” aluminum, selected because it is the thinnest available sheet
before it becomes foil and easily tears with regular use. These lines were then used with a
hydraulic press to cut out the models (eight in total).
From there, the eight nearly identical aluminum models were stacked, Acrylic spacers
were lined up on top of them as they would be in the final product, and the whole assembly was
tightly clamped. The laser cut Acrylic was used to locate the holes that needed to be drilled into
the aluminum. After the holes were drilled through all eight models at once (to ensure each one
had the same geometry), the aluminum components were bolted tightly together and taken to a
belt sander to achieve the final, desired shape.
The two MDF models of the foam sample were sanded to have a smooth edge, and then a
slightly oversized piece of polystyrene foam was placed between them. The smoothed MDF
provided an accurate and precise form for a hot wire foam cutter to follow. After some careful
cutting, four nearlyidentical samples were produced in this way.
Finally, strong adhesive was applied to all surfaces while the correctly sized bolts and
pins held them in alignment. In this way, days of preparation and fabrication produced four
identical, tightlytoleranced composite arms (see figure 1).
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15. quadcopter through where the arms bolt to the body, which is the strongest point on the design.
The hinges would be high friction so the arms would either stay deployed or stay folded away,
and there would be a hard stop to ensure the legs would provide actual support for landing
procedures. In this way, the landing legs could fold up to a very compact position for storage,
promoting the portability of the design.
Figure 9: First Idea for Landing Leg Fabrication
This idea was tested first. Readily available galvanized steel wire was used as the pin,
and aluminum sheet metal, with a thickness of 0.032” for better strength characteristics, was
used as the leg and the inboard attachment plate by bending a small section of it around the steel
wire. Upon clamping down the portion of the aluminum bent over the wire to promote a friction
hinge, it was quickly determined that not only was the idea was not viable, but also that the
quadcopter’s vibration would likely cause the legs to sag down to vertical, rendering the entire
setup prone to collapse.
The second iteration of the idea involved a similar concept, but instead of a high friction
hinge, a springloaded pin joint would provide the resistance to sag. The same basic concept of
bending the aluminum around a pin was used; however, room was left in the center for a
lightduty torsional spring. Instead of the steel wire acting as the pin, a size 10 bolt was used
instead, since it better fit the center diameter of the torsional spring and therefore kept the
twisting forces from interfering with the action of the spring (see figure 10).
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16.
Figure 10: Landing Leg Hinge
This idea, when implemented properly, provided a surprisingly effective springloaded
hinge. However, when the setup was mounted to the body, it became clear that the hard stop
mechanism was not going to be able to function as well as designed. It was decided, instead, to
use a doublethreaded string on the other side of the hinge to act as a hard stop for tension. This
way, the resting angle of the deployed legs could be adjusted easily by changing the string length
before the final knot was tied.
This redesign worked well, and as long as the angle of the deployed legs was close
enough to vertical, but not so close that it would risk collapse, the stings don’t experience very
much force from supporting the assembly. Upon attempting to mount the design, it was found
that there was nowhere feasible on the body itself to mount the landing legs that would allow
them to fold up neatly without interfering with other parts of the assembly. Luckily, the strength
of the new composite arms was much higher than the old MDF arms, so the design team felt safe
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27.
Figure 22: The onboard radio telemetry device sends GPS and altitude data to the Radio
Telemetry Receiver connected to the cell phone.
4. Testing and Analysis
Propeller Lift Testing
For lift testing, the motor and propeller were fastened to the end of an aluminum extruded
bar, which was vertically attached to a wooden block and the motor using slightly modified
aluminum Lbrackets originally meant to attach two aluminum extruded bars perpendicularly.
The ESC, the battery, the battery wattmeter and voltage analyzer, and the receiver were placed
on top of the wooden block. We obtained a scale, attached the test assembly to the platform of
the scale, and then attached the scale securely to a workbench. We tested by turning on the
system and slowly increasing the throttle to speed up the motor using the transmitter. After each
small throttle increase, we used the wattmeter and voltage analyzer to read and record the current
the motor was drawing and used the scale to record the resulting lift, in grams. We continued this
process, collecting data until the motor was at full throttle.
The results of our lift testing showed a positive correlation between the current that the
motor was drawing and the lift of the assembly, and the 12” diameter, 6” pitch propellers had the
greatest lift:current ratio (see figure 23 below).
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30.
Figure 25: Composite quad arm simulation under ideal flight conditions
After simulation, the arm was assembled. In order to adhere the “plys”, a 5 minute epoxy
was mixed and spread on the aluminum arms before firmly sticking them to the foam. After a
day of curing, the arm was ready to test. At first, the same protocol was followed from when the
first quad arms were tested: it was bolted down and sandwiched between two stronger pieces of
plywood. Unfortunately, the foam rapidly gave way upon tightening the bolts. It was decided
that this design could only be feasible if a small, more rigid component was placed at the base
(and at the motor mounting point when flight testing occurs) to facilitate the ability to tighten the
assembly down. After this modification, the arm was ready to test.
A boltedin plywood insert was used to maintain rigidity at the mounting point, and the
insert was then clamped down firmly to a table. Small notches were cut into the aluminum on the
sides at the loading point so a string could be hung, with a basket containing known weights
suspended on the other end (see figure 26). Under the basket, after 4 inches of room to allow
deformation, was a stool to keep the weights from falling and potentially cracking. This was the
same testing protocol used for previous failure tests.
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31.
Figure 26: Failure Test Assembly for Composite Arm
Weights were then incrementally added to the basket, and the system was given time to
deform. We quickly noted that though this arm was lighter than the tested MDF arms, it
deformed less at the same weights and very quickly surpassed the MDF arms in terms of
maximum supported load. Finally, the arm failed after supporting 5.3 kg (see Figure 27), which
not only is nearly double the weight supported by the MDF arm, but nearly double the entire
weight of the quadcopter with payload!
Analysis of the quad arm yields interesting results. As seen in the same figure below, the
arm failed through thin “column” buckling of the bottom aluminum ply in compression. This is
where the simulation could not simulate properly. Since column buckling typically occurs at a
slight, potentially imperceptible inhomogeneity in the material, the simulation cannot simulate
the actual situation well enough to account for it. The real reason the arm failed, however, was
the foam. Ideally, if the foam were harder and more rigid, buckling failure would be postponed
to an even higher applied load, if not negated completely.
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32.
Figure 27: Failure Mode of the Composite Arm
As it stands, even though the arm failed in an easily remedied way, it supported a far
greater load than would ever be experienced (with the exception of a crash) in common usage.
Even so, it was recommended that a thin layer of crushed fiberglass and resin be applied to the
sides. This would only add a gram or two to the weight of the arm, but significantly increase the
rigidity of the arm, providing a better connection between the top and bottom aluminum sheets,
and possibly delaying buckling failure in a way similar to how using a more rigid foam would. It
was decided, however, that due to the overwhelming success of the arm as it was, it was not
necessary to make major alterations other than in increase in width and a smoother foam cut.
The overwhelming success of the failure test of the composite arm lessened the
importance of spending time to test other materials in a similar manner. Since the 6061 T6
aluminum had one of the best strengthtoweight ratios as well as the best
strengthtoweighttocost ratio, we deemed it unnecessary to test other quad arm concepts
through a similar process. As stated in the improvements section, ⅛” thick Acrylic was used for
the main body panels. Below in figure 28, the deformation of the body under loading conditions
is shown. After simulation, it was determined that operating conditions allow for a
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34. For our purposes, the quadcopter only needs to remain in the air long enough to reach the
desired altitude, allow the individual to broadcast a brief message, and return to the ground.
Because of these stipulations, our estimated maximum flight length of about five minutes
(without draining the battery to dangerous levels) can be considered successful.
Time (seconds) Charge Usage (% of overall charge)
100 40%
Table 2: Final Battery Testing Trial
For a final trial with the most recent frame, battery testing using the same protocol was
performed on the encumbered quadcopter (see table 2). With all the additions to the final
prototype, the battery life came out to be, using linear interpolation, approximately 4 minutes,
which is on the low end of what is considered reasonable for this application.
Flight Testing
Stability as well as the functionality of the Loiter and Auto flight modes were tested in a
large, open field. The quadcopter showed greatly improved stability with no notable oscillation
after tuning the PID parameters. In order to test the loiter mode, the quadcopter was piloted to a
comfortable location and altitude, then switched to the flight mode. After tweaking PID values
and shielding the flight controller from magnetic interference, the loiter mode worked exactly as
intended. The quadcopter did not waver or drift by any significant amount once it was switched
to loiter mode. To test the auto mode, a simple flight plan was created which directed the
quadcopter to start from a home position and fly to a specified waypoint. During testing, the
quadcopter was able to successfully complete this procedure.
Parachute Testing
The weight of our entire quadcopter, including the payload is about 2.6 kg. Our goal was
to have the quadcopter fall no faster than 5 m/s. Using the drag coefficient calculator we
calculated the theoretical size of our parachute.
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40. APM board 67.99 Hobby King 1 67.99
Transmitter and Receiver 59.99 Hobby King 1 59.99
Battery 33.92 Hobby King 1 33.92
XT60 Connector 0.81 Hobby King 1 0.81
Solenoid 5.27 Amazon 1 5.27
Parachute 7.44 Amazon 1 7.44
Servo 3.98 Amazon 1 3.98
Propellers 1.08 Hobby King 4 4.32
Tupperware container 1.00 CVS 1 1.00
Acrylic 12x12x1/8” 8.63 McMasterCarr 2 17.26
Aluminum 24x24x0.016” 29.59 McMasterCarr 1 29.59
Aluminum 12x12x0.032” 12.99 McMasterCarr 1 12.99
Polystyrene Foam 12x12x1” 19.19 McMasterCarr 1 19.19
440 Bolts, 1” length 5.40 McMasterCarr 1 5.40
440 Bolts, ⅜” length 8.07 McMasterCarr 1 8.07
632 Bolts, 1.25” length 5.00 McMasterCarr 1 5.00
1024 Bolts, 1.5” length 11.66 McMasterCarr 1 11.66
440 Locknuts 2.74 McMasterCarr 1 2.74
632 Locknuts 2.67 McMasterCarr 1 2.67
1024 Nuts 2.74 McMasterCarr 1 2.74
5/32” Dia. QuickRelease Pins 1.80 McMasterCarr 4 7.20
Total 492.23
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41. 5. Budget
Monetary Cost
Item Price Supplier Quantity Total
USB Adapter 3.99 Amazon 1 3.99
Telemetry 25.99 Amazon 1 25.99
Motor 15.42 Hobby King 6 92.52
Power Distribution Board 3.70 Hobby King 2 7.4
Prop Drive 1.80 Hobby King 4 7.20
GPS 19.98 Hobby King 1 19.98
Electronic Speed Controller 8.95 Hobby King 6 53.7
APM board 67.99 Hobby King 1 67.99
Transmitter and Receiver 59.99 Hobby King 1 59.99
Battery 33.92 Hobby King 2 67.84
XT60 Connector 0.81 Hobby King 1 0.81
Solenoid 5.27 Amazon 1 5.27
Parachute 7.44 Amazon 1 7.44
Servo 3.98 Amazon 1 3.98
Propellers (Wide Variety) N/A Hobby King N/A 80
Tupperware container 1.00 CVS 1 1.00
Acrylic 12x12x1/8” 8.63 McMasterCarr 2 17.26
Aluminum 24x24x0.016” 29.59 McMasterCarr 1 29.59
Aluminum 12x12x0.032” 12.99 McMasterCarr 1 12.99
40
42. Polystyrene Foam 12x12x1” 19.19 McMasterCarr 1 19.19
440 Bolts, 1” length 5.40 McMasterCarr 1 5.40
440 Bolts, ⅜” length 8.07 McMasterCarr 1 8.07
632 Bolts, 1.25” length 5.00 McMasterCarr 1 5.00
1024 Bolts, 1.5” length 11.66 McMasterCarr 1 11.66
440 Locknuts 2.74 McMasterCarr 1 2.74
632 Locknuts 2.67 McMasterCarr 1 2.67
1024 Nuts 2.74 McMasterCarr 1 2.74
5/32” Dia. QuickRelease Pins 1.80 McMasterCarr 4 7.20
Battery Charger 32 Hobby King 1 32
Current/Voltage Reader 19.70 Hobby King 1 19.70
Postal Scale 12 Office Depot 1 12
Payload box 8 Office Depot 1 8
Total 701.31
Time Cost
Week of: Hours Sum for Prototypes (hours) Sum for Prototypes ($)
92114 27
92814 32
10514 37.5 Prototype 1: 96.5 ~ $375
101914 61 Prototype 2: 61 ~ $15
102614 to 12614 90 Prototype 3: 90 ~ $10
1415 9
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43. 11115 and 11815 30.5
12515 and 2115 61 Prototype 4: 100.5 ~ $100
2515 to 21215 18
21615 to 31215 67
31715 33
32615 59 Prototype 5: 127 ~ $100
Through 4915 103 Prototype 6: 153 ~ $100
Total 628 628 ~ $700
Total labor cost (at
$8.00/hr)
$5024
6. Conclusion
Design Evolution
Evolution of Frame:
Figure 35: One arm frame Figure 36: First full frame
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46.
Figure 43: Used a smaller servo and repositioned the solenoid
Strengths of Portable Military Quadcopter Design
With our given design constraints, we can say that our quadcopter design successfully
performs to Northrop Grumman’s specifications. Compared to similar, prebuilt quadcopters
with comparable payload lifting, ours is significantly cheaper. Compared to similarly priced
quadcopters, none have the payload capabilities necessary to lift a communication device for
long enough. Testing shows that our quadcopter can easily lift a 1 kg payload and safely support
it for about five minutes, giving it more than enough time to reach necessary altitude and
transmit a radio signal. Another benefit of our design is that the battery is accessible and held in
place by velcro so a dead battery can be easily removed and replaced, compared to other designs
which require significant time to disassemble the body, replace the battery, and reassemble it.
The payload itself is attached to the quadcopter frame only by clips on the bottom, meaning that
different sized payloads can be accommodated, provided they can be attached with the same
clips. Additionally our design makes use of programmable GPS waypoints, allowing a soldier to
move it to a specified point without the need for manual flight. This is helpful under conditions
of low visibility. The quadcopter itself weighs about 1.6 kg, and when folded measures about
14” x 14”, making it light enough and small enough to easily be handled by a person.
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