Designing an Unmanned Aerial Vehicle (UAV) for Humanitarian Aid

Daniel Boehm Andy Chen

djbcollege203@gmail.com xinghao.chen@gmail.com

Nina Chung Rohan Malik Brian Model

ninachung1@yahoo.com mroho626@gmail.com brian.model@gmail.com

Priti Kantesaria*

priti.kantesaria@rutgers.edu

New Jersey Governor’s School of Engineering and Technology

21 July 2017

*Corresponding Author

ABSTRACT — The objective of this project is to create an unmanned aerial vehicle (UAV) capable of providing humanitarian aid by transporting critical supplies such as food and medicine to areas in crisis. UAVs can transport items quickly and inexpensively to locations that are difficult and time-consuming to reach by road. To achieve this goal, a heavy lift quadcopter was constructed with a servo-operated release mechanism that allowed it to drop packages. Research was done to determine the most compatible, efficient, and cost-effective parts needed for the quadcopter, all of which were sourced from online suppliers except the prop guards and the servo holder, which were designed on TinkerCAD and 3D-printed. The quadcopter was then assembled, wired, and programmed in preparation for flight using a PixHawk flight control board and the Mission Planner firmware. The quadcopter then flew, and the parachute deployed, confirming that the design would be effective for providing humanitarian aid.

I. INTRODUCTION: UAVS AND HUMANITARIAN ACTION This project’s goal is to create a UAV capable of providing

humanitarian aid by carrying supplies to locations in need. Such trips could otherwise be time consuming, dangerous, or difficult to reach through traditional means of transportation.

In regions struck by disasters, emergencies, or conflict, it is often difficult for first aid responders to arrive quickly, especially in areas with damaged or poor infrastructure. For example, land vehicles cannot reach their destinations quickly without well-maintained roads, while large manned aircraft are cumbersome to prepare for flight. Alternatively, UAVs can can take off within minutes of a crisis and supply swift aid.

One example of UAVs providing aid is their ability to map areas of disaster, thus informing responders about which roads are traversable to help them arrive quicker. UAVs can also

help rescuers by using thermal sensors to identify hazards and locate trapped victims. In addition, UAVs can serve as makeshift emergency communication networks when ground-based telecommunication lines are destroyed [1].

UAVs are also used for cargo delivery, the focus of this project. Although the main focus thus far has been on commercial deliveries, there has been rapid development in the field of humanitarian aid. Examples of deliverable aid supplies include chlorine tablets, life vests, medicine, blood, heart defibrillators, food, and water [2]. However, much of the technology is still in the prototype phase [3], and the goal of this project to improve upon it.

While UAVs for delivery have many potential benefits, they also pose many challenges. For instance, UAVs are fragile compared to larger aircraft and can be easily damaged during flight by weather, debris, or birds. UAVs can also be difficult to navigate in areas of armed conflict as they may be shot down in the process of sending relief to war victims or refugees. Lastly, UAVs may interfere with air traffic or government airspace regulations [4].

In order to address some of these limitations and better deliver humanitarian aid, the specific goal of this project was to design a UAV with the best possible performance in terms of weight lifted (up to 2 kg) and flight duration (up to 10 minutes). Furthermore, due to possible complications UAVs may encounter upon landing, such as mishandling by civilians or gunfire from combatants, the project demanded an efficient package drop mechanism that could release the package from mid-air. Subsequently, it was necessary to design a package that could land safely upon release. The stamina, lift capacity, supply packaging, durability. and package release were all

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optimized through careful planning, engineering, and programming.

A side benefit of the project is to reduce the stigma that is associated with UAVs. UAVs, more commonly referred to as drones, are generally associated with military and surveillance purposes. By designing a UAV that is specifically catered towards humanitarian purposes, the public can recognize that UAVs can have a positive impact on society rather than a negative one [5].

II. BACKGROUND A. Frame and Parts

There are four main types of UAVs: multicopter, fixed-wing, single-wing, and hybrid [6]. Multicopter UAVs use at least three propellers to fly, are typically used for short-distance flights, and are able to carry lightweight items. Multicopters are usually remote- or radio-controlled (RC) and are also the least expensive of the four types of UAVs; all these properties made them the best choice for this project. Fixed-wing UAVs have two wings, like commercial airliners, and are typically used for long distances and heavy loads. However, they require a large area for takeoff and landing, are unable to hover in place, are significantly harder to fly, and are much more costly than multicopters. Likewise, single-wing UAVs, or helicopters, are heavier, more dangerous, and more expensive than multicopters. Finally, hybrid UAVs seek to combine the attributes of both multicopters and fixed-wing UAVs, but they are currently still in development. This project, therefore, focuses specifically on multicopters as their versatility adheres well to the goals mentioned in the background.

Multicopters are characterized by the number of propellers they have: tricopters have three propellers, quadcopters have four, hexacopters have six, and octocopters have eight. The more propellers a multicopter has, the faster, stronger, and stabler it is. However, as the number of propellers increases, the price of the multicopter increases while the flight time decreases.

For multicopters with four or more motors, non-adjacent pairs of propellers are located at opposite ends of the frame, the central piece of the UAV. The frame acts as the skeleton, providing structure, strength, and a base for the other parts [7].

A multicopter’s propellers are powered by electric motors, one per propeller. Motors are made of a collection of magnets and wire coils that rotate a component of the motor, the rotor, about an axis. When the rotor is attached to the center of a propeller, it allows the propeller to spin. There are two types of motors: brushed and brushless. In a brushed motor, the magnets remain fixed while the coils rotate, whereas in a brushless motor, the magnets rotate and the coils remain fixed. An important consideration for motors is the KV rating, which is the ratio between a motor’s angular speed (measured in rotations per minute, or RPM) and the voltage (in volts, or V) that powers it, with units of RPM per volt. Higher KV motors

are recommended for UAVs that require more agility and maneuverability, while lower KV motors are recommended for performing heavy lift tasks [8].

Fig. 1 The four propellers and motors assembled together.

Attached to each motor is an electric speed controller (ESC) that takes information from the flight controller and adjusts the current that flows from the power source to the motor, thus controlling the speed and direction of the propellers. Similar to an ESC, a Battery Eliminator Circuit (BEC) limits the amount of power going to a receiver and servo [7]. Typically, UAVs use lithium polymer (LiPo) batteries as they are lightweight and give off substantial power. The voltage (measured in volts, or V) of a UAV’s battery should be as high as possible within the limits of the weight and size of the UAV and also the capability of the electronics.

Other important values to consider are the battery’s capacity (measured in milliamp-hours, or mAh) and discharge rate (measured in capacity C). Battery capacity measures how much charge a battery can store, while discharge rate is the maximum current the battery can output at once [7]. Battery capacity represents the total electric charge a battery holds when it is full. The lifetime of a battery discharging at its max current is equal to 60 minutes divided by its discharge; for example, a 4C battery discharging at maximum dies in 15 minutes. Alternatively, if this battery had a capacity of 10 mAh, it could supply a current of 40 mA.

A power distribution board (PDB) is necessary to appropriately divide the battery’s power supply between the parts of a UAV. The PDB is attached directly to the battery, and conducts set voltages through different output ports [7].

Additionally, to protect the sensitive electronics of a UAV, a shell, or covering, is used. A landing base is used to let the UAV safely land. Propeller guards, also known as prop guards, surround each propeller and absorb the impact if the UAV collides with an obstacle. Propeller savers, or prop savers, anchor propellers in place to prevent them from flying off the motors. These accessories, as well as the base and the propellers, can be made from a variety of materials, including plastic; carbon fiber, which are microfibers made out of carbon atoms; wood; printed circuit board, or PCB, which are

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copper sheets that support electronic components; G10, a fiberglass laminate; and aluminum [7].

B. Maneuvering the UAV

To counteract the gravitational force, a UAV generates lift with its propellers. On a quadcopter, adjacent motors spin in opposite directions, with two turning clockwise (CW) and two turning counterclockwise (CCW)[7]. The pairs of the CW and CCW motors are conventionally marked by the color of the tips holding them down, usually silver and black, as shown in Fig. 1.

As shown in Fig. 2.a below, when flying directly upwards or hovering in place, all motors must contribute equal amounts of thrust. However, to move horizontally, there must be a net force acting horizontally, which can be achieved by changing the speed of the motors, as shown in Fig. 2.b and 2.c. For a quadcopter to travel in the direction of a certain motor, that motor must decrease its RPM as the opposite motor increases its RPM, causing the motors to generate less and more upward thrust, respectively. Thus, while the net force on the UAV itself remains the same, a net torque—the force that causes an object to rotate about its axis—is exerted about the center of the frame, causing the UAV to roll around the x-axis or pitch around the y-axis. Once the UAV is slightly angled below the horizontal, the thrust created by the propellers is increased slightly so that it still counteracts gravity while also propelling the UAV horizontally [9].

Fig. 2 UAV movement in relation to differing rotor forces [10]

To rotate horizontally about the vertical axis, or yaw, the

motors spinning in the desired direction have their speeds reduced and the motors spinning the opposite direction have their speeds increased, while ensuring that the total upward thrust remains the same [11]. For example, as shown in Fig. 3.d, to make a quadcopter yaw counterclockwise, the CW motors spin faster and the CCW motors spin slower. This works because the force exerted by the air on the faster CW propellers is counterclockwise in opposition to the motion of the propellers and outweighs the corresponding force on the

CCW motors. On the side of the CW propellers farther from the UAV’s frame, the torque exerted by the air about the center of the UAV is counterclockwise, while on the closer side, the torque about the center of the UAV is clockwise. However, as torque is the cross product of distance and force, and the force of the air on all parts of the propellers is equal while the distance is not, the net torque on the entire UAV is counterclockwise.

The lift produced by a propeller is given by the following equation [12]:

(1)ρv ACL = 21 2

L

where L is lift, ρ is the density of the air (in kg/m3), v is the relative velocity of the propeller blade to the air (in m/s), A is the area of the propeller blade (in m2), and CL is the coefficient of lift, which is unitless and typically between 0.5 and 0.7 at small angles [13]. Since ρ and CL are constants that depend on the environment and the shape of the propellers respectively, lift is proportional to velocity squared times acceleration. As the tips of a UAV’s propellers spin extremely rapidly relative to the UAV’s lateral speed, the v component of the lift equation is roughly proportional to ωr, where ω represents angular speed and r represents the radius of the propeller. Also, assuming that the proportions of propellers remain approximately constant at all radii, their area A is proportional to r2. Thus, L ∝ v2A ∝ ω2r4. More practically, as the size of the propeller increases, so does the lift it provides, at an exponential rate. C. Electronics and Control

Fig. 3 The circuit diagram of a UAV [14]

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UAVs operate through commands, or practical orders that are translated by the firmware to motor values.

Each command starts on the machine running the command program, usually a desktop or laptop. The command program uses all available data about the UAV’s setup and surroundings to determine how the UAV should move, and by extension at what value each motor should run.

The command is broadcasted from the controlling program as a signal on the telemetry system, a pair of radio transmitters/receivers that connect the commander and the UAV. The telemetry system, with the receiver on the commanding machine and the transmitter on the UAV, transmits information between the two. In a UAV system, one of those units will be wired to a flight controller board (FCB). As seen in Fig. 3, the flight controller board communicates with every other data-oriented object on the UAV, most often using signal wires, which carries messages throughout the UAV. Examples of signal wires include Pulse Width Modulation (PWM), Pulse Position Modulation (PPM), and Inter Integrated Circuit (I2C) connections. The FCB acts as the brain of the UAV, reading sensor values and sending commands to the ESCs [14].

Additionally, a transmitter and receiver pair can be used to control the ESCs. Transmitters are most often built in to specialized remote controls. The remote control utilizes four axes — corresponding to lift, roll, pitch, and yaw — and a series of button values. Those values are sent to the receiver, which passes along the information via PWM to the ESCs, or to an FCB. This setup would be used alternatively to a command program, or as an option for using the program. This can used in place of, or in addition to a telemetry system [14].

To travel a significant distance, sensors must be attached to a UAV to gather information about its position and environment. With this information, the controller can change the flight of the UAV accordingly to plan its course, as well as to prevent collisions, overheating, or other malfunctions. Standards sensors include accelerometers, which measure the linear acceleration of a UAV; gyroscopes, which detect angular changes in position and auto stabilizes the UAV; compasses, which provide the direction of motion; barometers, which measure air pressure and by extension, altitude; and a Global Positioning Systems (GPS) devices, which measure the geographic coordinates of UAVs. Often a camera is attached to take pictures, record or stream videos, and/or map the landscape [7]. Additionally, any other sensor that can be wired to a three pin output may be used, such as an ultrasonic distance sensor or a thermal resistor. Thermal resistors, otherwise known as thermistors, alter their resistance as temperature increases and decreases. By measuring the altered current, the temperature of the thermistor can be known, as well as the area around it.

After the flight controller board reads all the data from the sensors, the FCB sends the information back to the commanding machine, which interprets and analyzes the

readings. This information processing can be done using the Mission Planner firmware which allows for easy control of the UAV. After using the information to make a decision, Mission Planner sends the next command to the FCB, which passes the signal along to the ESCs. The ESCs then output a certain percentage of their input power to their respective motors, and the adjusted motor speeds moves the UAV. The cycle repeats, until the UAV accomplishes a task, such as reaching its destination or beginning a new one.

D. Cargo Delivery with UAVs

UAVs are extremely useful for transporting items. From assessing damage by means of a camera, or delivering vital supplies, UAVs can certainly find their place in the standard toolkit of humanitarian aid workers.

UAVs are a very powerful tool due to their ease of use and flexibility when compared to traditional vehicles. It is far safer and more effective to send a UAV over a dangerous area than to send a person. However, due to their size, they are often unable to carry excessively heavy loads, or easily leave behind cargo.

In some cases, the designers choose to have the UAV land with the cargo, and either release the package before flying off or have a receiver remove the package from the UAV. In other cases, the UAV releases the supplies mid-flight.

Since the lifting capacity of UAVs is limited, the supplies delivered have to be lightweight and fit in small containers. Cargo for humanitarian UAVs often consists of medicine, water purifying tablets, syringes, bandages, and/or blood. Emergency response UAVs can also bring defibrillation attachments.

III. PROCEDURE A. Design

The first decision regarding the design of the UAV was the dimensions of the frame as well as the numbers of propellers. A tricopter was the cheapest option, but is very unstable, weak, and prone to problems. Hexacopters and octocopters are incredibly strong, agile, and can still fly if one of their propellers stop spinning. However, both are hard to navigate in tight spaces, and have very limited flight durations.

For navigation through tough environments, and significant distance flights, the project required certain properties for the quadcopter design: simplicity, maneuverability, durability, and stability. The quadcopter can last far longer than other multicopters while being powerful enough to accomplish the tasks provided.

Furthermore, the method of procuring parts had to be determined. Most parts were bought separately, including the motors, propellers, ESCs, frame pieces, and the sensors. Others needed to be customized, and were designed digitally and 3D printed.

The UAV would require several sensors in order to function. First and foremost, a GPS and compass module were needed, so that the UAV could navigate to far off distances,

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and be aware of its own location. Similarly, an accelerometer and gyroscope were both needed, so that the UAV could measure its relative movement.

Secondarily, the UAV needed to be able to record mapping data, and be aware of the environment in case of manual override. The most effective way by far to satisfy these requirements was to mount a camera, and set it up to stream to the commanding program.

Finally, to avoid overheating — which may result in fires or explosions — thermistors were added to the design to track that the motors and nearby areas do not overheat while the UAV is in flight. B. Choice of Parts

The UAV needed to be built around a frame that could support all of the project’s needs. The frame needed to be sizable and strong enough to lift a few pounds, without adding more load for the propellers than necessary. As a result, a large frame was necessary to create a large UAV that is powerful enough to carry bulky weight. Furthermore, to reduce unnecessary weight, the material of the frame needed to be lightweight and durable. To satisfy these requirements, the frame chosen had a carbon fiber skeleton with PCB for the rest of the frame and a wheelbase of 500 mm.

The propellers chosen were made out of carbon nylon — a material similar to carbon fiber — due to the material’s toughness and low weight, letting the UAV consume less energy and fly longer. In order to guarantee more thrust at lower RPM and more stability, the largest possible propellers were sought, as larger propellers creates bigger thrust. As shown in Fig. 3 below, the maximum possible propeller length allowed by the wheelbase was 353.6 mm; therefore, 12-inch propellers (304.8 mm) proved to be the longest propeller length available below this limit.

Fig. 4 The dimensions of the UAV’s wheelbase and propellers.

Furthermore, the prop guards need to match the size of the propellers. However, since the necessary prop guard size cannot be bought online and shipped in time for the project,

the prop guards were 3D printed instead. The prop guards were designed using TinkerCAD software and 3D printed with the material polylactic acid (PLA), a common and reliable material as it is stable, cheap, and rarely problematic when printing. The prop guards were too big to print on the 3D printer, so each prop guard was divided into thirds and printed separately. The prop guard consisted of a quarter of a circle that goes below the propeller, with rods on the curved edge as a form of protection. This design was chosen for its simplicity, light weight, the ability to attach the circular end under motors using screws, and for its comprehensive protection of the propellers while taking up little space [7].

Fig. 5 A 3D drawing of designed propeller guard on TinkerCAD.

While buying prop savers would have been prefered, they

were not bought because cost was a limiting factor in the project, and were less important than the other parts of the UAV.

The next priority was choosing the flight controller, as it must be connected to every other information handling unit on the UAV. To be able to safely reach supply drop points for humanitarian aid, a controller was needed that could interface with a radio communicator, as well as the necessary sensors. The Arducopter V2.8 was selected, as it has built-in ports for GPS, PWM, I2C and telemetry.

Three components in particular — the motors, the battery, and the ESCs — had to be selected in conjunction because their required specifications each depended heavily on those of the other devices. The motor was chosen first, as its properties must be correct to be able to lift the UAV and package for the required distance and duration.

The main specification manufacturers provide for motors is the KV. This measures the ratio between the maximum, no-load rotational speed of the motor and the peak voltage across its wires. However, the theoretical maximum rotational speed of a motor obtained by multiplying KV by battery voltage is unimportant to rotating a UAV’s propellers, as this calculated rotational speed assumes no load. Since the weight of the propeller puts a load onto the motor axle, it is more important for the motors to provide sufficient torque. This can be estimated with the motor torque constant, or KT, which has units of Newton-meters per amp. For a given current, which is limited by the durability of a motor’s wiring, a motor with higher KT provides more torque. In fact, after converting KV from RPM/volt to radians/second·volt by multiplying by

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2𝜋⁄60, KV and KT for any given DC motor are reciprocals [8], which can be confirmed by comparing their units:

(2)KV : Vrad·s −1

= 1V ·s = A

W ·s = JA = A

N ·m (3)KT : A

N ·m (4)KV = 1

K T

Therefore, in order to raise KT and generate more torque, KV must be lowered. Given the budget of this project, the lowest motor KV available was 920 RPM per volt.

The battery had to be chosen in accordance with specifications of the motor in order to ensure the maximum possible power delivery. The manufacturer’s recommendation was 2-4S LiPo, so a 4S LiPo battery was sought out. “S” stands for the number of cells, and in the case of LiPo batteries, each cell has a potential difference of 3.7 V. Thus, 4S means there are four 3.7 V cells in the battery, for 14.8 V in total.

Since a battery with a higher charge capacity given a chosen voltage stores more energy, the 4S LiPo battery with the highest possible capacity and a reasonable price range was obtained. This battery had a capacity of 5000 mAh and a continuous discharge rate of 20C. A lower continuous discharge rate corresponds with a longer flight, and the discharge rate of 20C was one of the lowest available, so the chosen battery was optimal in this regard as well.

The set was completed by the choice of the ESC, which needed to handle the voltage fed by the battery, and have a maximum current lower than the battery and larger than the motor. The model selected took in 3S-4S, the same voltage as the battery, and a rated continuous current of 30A, twice the battery’s standard output. C. Package and Release Mechanism

As the UAV needed to deliver supplies, a large part of the design was the release mechanism. Since the UAV is intended to provide aid to dangerous locations, the most effective method of delivery was to drop the package over the target area. In this way, the chances that the UAV (which is costly to repair and fix) is damaged by outside forces would be minimized. The UAV would reach its destination, find an ideal location nearby to hover, and release the payload, perhaps around 20 feet in the air. This method keeps the UAV in the air for the entirety of the delivery.

A plastic bottle was chosen for the package container. The bottle was inexpensive, durable, lightweight, and easy for the UAV to carry. It was also the perfect shape to hold supplies such as pills, vaccines, and blood. Furthermore, since bottles are watertight, victims could reuse the bottles to store water and other supplies.

Styrofoam was chosen to provide cushioning for the package as it is cheap and common, which would be necessary if the UAV needs to distribute many packages during an actual crisis. Furthermore, styrofoam is also effective in

absorbing vibrations that occur when the package hits the ground.

A parachute was attached to the package for extra security when the UAV drops the package from a certain height. Nylon fabric was used for the parachute as it is lightweight, strong, and inexpensive. The strings for the parachute were made out of fishing wire, which since it is extremely strong and lightweight.

Some calculations used in actual parachutes were necessary to decide the optimal size of the parachute. The equation for the force of drag generated by the parachute is as follows:

ρv ACD = 21 2

D (5)

[15]. This is nearly identical to the lift equation (Eq. 1), with the only difference being the presence of the drag coefficient CD in place of the lift coefficient CL. In this case, v is the speed at which the package falls. To find the required properties to nullify gravitational acceleration, mg can be substituted for D, where m is the mass (in kg) of the package and g is the acceleration due to gravity (in m/s2) at Earth’s surface, and equals the force of gravity. To simplify the equation and make it easier to conceptualize the speed, √2gh can be substituted for v, where h represents the height (in m) from which a projectile needs to be dropped to reach speed v as it hits the ground; this expression can be easily derived from energy conservation principles.

hACm = ρ D (6)

The density of air at standard temperature and pressure is 1.225 kg/m3 [16]. As circles are the most common and effective parachute design, it was decided that the package’s parachute would be circular; it would have area A = πr2, where r would be its radius (in m). For a fully inflated, low-porosity circular parachute, CD is approximately 0.81 [17]. Substituting these values,

..12hrm = 3 2 (7)

To maximize the payload mass without raising the speed at which the package hits the ground, the radius of the parachute must be maximized as well. However, since the largest sheet of fabric available was a rectangle with a width of 42 inches or 1.07 meters, the largest circle possible had a radius of 21 inches or 0.533 m. Substituting this value for r into the equation and rearranging,

.13mh = 1 (8)

This means that the speed at which a 2 kg package with the parachute would hit the ground would be the same as if it were dropped from a height of 2.26 m without the parachute. Substituting this height back into the projectile equation v = √2gh, the calculated speed is 6.66 m/s, which, given the small size of the package, is sufficiently low to ensure a secure delivery.

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The package was secured to the parachute with eight sections of 10 pound (4.5 kg) test fishing line, ranging in length from 50 to 56 cm. The eight sections of fishing line were tied to the parachute with fisherman’s knots, equally spaced around the circumference. The strings were then bundled together with electrical tape and then secured inside a plastic water bottle, which was the container for the package.

To assess the sturdiness of the container and the effectiveness of the parachute, test drops were conducted from various heights, with and without the parachute. When the package was dropped with the parachute from a height of two stories, or about 7 m, the parachute did successfully inflate and cushion the landing, as shown in Fig. 8. To further confirm the strength of the container, the package was dropped without the parachute from the previously calculated height of 2.26 m. Both trials were successfully repeated multiple times.

Fig. 6 A slow-motion capture of the parachute successfully inflating on a

two-story test drop. When creating the release mechanism for the package, two

main considerations had to be taken into account: it had to be power efficient and it had to be light in weight. As such, a servos motor was used because it is not power-consumptive, and it is very lightweight. To hold the servos, a casing was 3D printed out of polylactic acid (PLA), as shown in Fig. 5. The design of the servos holder was inspired from an existing design from the TinkerCAD drawing [18]. The casing was made in such a way as to let the servos drop the package only when desired. In order to grasp the package, wire and electrical tape was added as an extension from the rotating axis.

Fig. 7 The release mechanism for the payload with servos attached

D. Construction

Once the components were delivered, assembly of the UAV began. The first step was to assemble the bulk of the frame. The arms, landing gear, and the PDB were all attached to one another. Next, the propellers were connected to the motors. The motors were then attached to the arms. The clockwise and counterclockwise motors are distinguished by the tip color: the motors with the silver tip spins clockwise, while the motors with the black tip spins counterclockwise. The motors that turn in the same directions were placed on opposite ends of the frame.

The first challenge was attaching the battery to the UAV’s frame. The battery was relatively large, and no materials or items were available designed to mount batteries, so it did not initially fit in the UAV. The issue was solved by using parts of the camera mount along with zip ties and straps to secure the battery in place. This proved to be an effective solution as it did not interfere with the rest of the UAV construction or the wires and enabled the swapping of batteries for extended use.

Fig. 8 How the battery was attached to the frame

Connecting the ESCs to the motor proved to be challenging

since the motor wires were incompatible to the ESC wires. As a result the parts were soldered together with a strip of wire in between, as shown in Fig. 7.

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Fig. 9 Soldering the ESC onto the motor.

Once the motors and ESCs were soldered together, the next

step was to solder the ESCs and battery to the PDB. The motors were soldered so that the positive and negative wires matched up to the PDB. The next step was to attach connectors to the wires that attached to the battery and to the PDB. The connectors would have to work and be easy to detach as the batteries would be swappable. After soldering the necessary pieces the frame was reassembled. The base of the frame was reattached to the landing gear.

The prop guards that were 3D printed in three separate parts were attached together with hot glue and duct tape. After each prop guard was fully assembled, they were attached to the UAV with zip ties. The circular part of the prop guard was placed below the frame where the motors were located.

The final step was figuring out a way to combine the release mechanism with the UAV itself. Since there was no space on the frame, the release mechanism was attached to the bottom of the camera gimble through fishing wire and hot glue. The package was attached to the servos through the string of the parachute.

E. Flight Controller and Electronics

The Mission Planner firmware gives the user a great deal of control over the flight controller. Initially, all of the mandatory parts of the UAV needed be configured; this included inputting the UAV’s frame type and dimensions as well as calibrating various equipment such as the gyroscope, compass, ESCs, joystick and telemetry. Once the initial setup was complete, the additional components of the UAV could then be configured, which for this project included the servo release mechanism, input from the various thermistors located around the UAV, and navigation using the GPS.

The flight controller caused various problems when construction and programming the UAV. While the FCB is typically placed between the power distribution board and the top frame, it was placed on the top frame as it would not fit

inside. Furthermore, a shock absorber was attached to the FCB to reduce vibrations. It was then calibrated and connected to Flight Controller.

The original plan for the flight controller was the use of the ArduCopter V2.8 due to its reliability, cheap price, and simplicity. However, there were multiple critical errors that could not be solved, making it impossible to use the ArduCopter as the flight controller. These problems include the inability to calibrate the accelerometer due to a glitch in the product, a “Bad Barometer Health Error” - meaning that there was a hardware error that prevented the FCB to calculate the altitude at which the UAV was flying - that could not be resolved, and an error that made it impossible to connect a joystick to the flight controller, making the user unable to manually fly the UAV. There was no online or printed information on the issues, and as a result, they could not be troubleshooted. The PixHawk was selected as a replacement controller, as it had all the same built in ports and sensors of the Arducopter, but functioned without errors.

Configuration of the majority of the sensors was relatively simple. The GPS and compass simply had to be plugged into their respective ports on the PixHawk. To power the PixHawk, an XT60 power module was used, connecting the FCB to the PDB. Next, to connect the ESCs to the UAV, the ‘MAIN OUT’ ports on the PixHawk were used. From there, the ESCs were calibrated, allowing control of the motors through the FCB. In order to allow radio controller operation of the UAV, a PPM encoder plugged into the ‘RCIN’ port of the FCB.

Complications in wiring to the PixHawk came when attaching the servo and the telemetry system. A servo cannot simply be attached to the output pins on the PixHawk as the FCB cannot supply enough power to keep all the various systems running, and run a servo. As a result, a BEC must supply power to run the servo. This was done by attaching the BEC to the PDB, and plugging the BEC into the Serial Bus (SBUS) port. Once this was done, the servo was attached to one of the ‘MAIN OUT’ pins, and controlled via Mission Planner, and radio controller.

Difficulty in connecting the telemetry was a result of a different problem. To connect to the telemetry, a cable was required with 4 wires and a 4-pin connector, and a cable with six wires and pins were required to interface with the FCB. Furthermore, the order of the wires coming from the telemetry cable did not match up with the order of the input pins on the FCB. First, the function of each output wire was figured out, and soldered with its respective counterpart. Then, parts of a 4-pin cable were soldered to the individual wires of a 6-pin cable.Once the wires were properly soldered, the telemetry was compatible, and plugged into the FCB.

Once everything was wired to the FCB, all the electronic equipment had to be attached to the frame of the UAV. Using an adhesive that doubled as a shock-absorber, all of the electronic equipment was attached. First, the PixHawk was attached, being certain to orient it so that the front of the FCB corresponded to the front of the UAV. Similarly, the GPS and

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compass has to be attached so that they faced the front of the UAV. The rest of the electronic components were attached where they could fit, as their orientation does not matter.

Fig. 10 The electronic layout of the UAV

F. Resolving Issues

There were several issues with the UAV that were unsolvable, such as making the PixHawk work or preventing the battery from sending too much power to the motors, as the battery was sparking when connected to the PDB. The first problem addressed was that the wires connecting the ESCs to the motors were too tiny and thus would not be able to supply enough power necessary to take flight. As a result, the green wires were replaced with larger wires, and a proper connector using 5mm bullet connectors were used. To secure the wires to the connectors, heat shrink wrap was put over the wires and each side of the connector. Another issue was that the battery was attached to the PDB using alligator clips, as no proper connector was available. To solve the issue, a more traditional bullet wire connector was soldered onto the UAV and the battery. Most problematic, the battery was sparking when attached to the PDB, eventually found to be a result of the positive and negative sides of the PDB touching each other through remnants of solder, creating a short circuit. To resolve the issue, the PDB was cleaned with flux and insulated thoroughly. Afterwards, the PixHawk and the sensors were attached to the UAV using a double sided tape. Finally all the wires were attached together, and the wiring was attached to the frame using zip ties.

IV.RESULTS AND ANALYSIS A. Flight Test

The UAV was tested twice. The first flight took place on Rutgers Postal Plaza field on Livingston campus. The UAV achieved a max height of 30 meters and displayed characteristics of UAVs with a max height of approximately 120 meters. Although it was a windy day, the UAV was able to stabilize itself with the gyroscope, even when knocked severely off balance. This remote control and location based

autonomous commands s extremely useful for humanitarian crises as weather conditions might not always be ideal for flying. The UAV proved capable of autonomous as well as manual flight. Both rwere carried out perfectly. However, while attempting to fly the UAV a second time, the propellers got caught onto one of the wires, and stopped after going through the wire, causing a crash. As a result, the propellers broke, the landing base came apart, and a handful of radio controlled wires snapped.

Fig. 11 First UAV Flight Test

B. Drop Test

The UAV was fixed the next day. The landing base was repaired with Kraze-GlueTM, propellers were replaced, and the wires were soldered back together. The prop guards were also broken and required hot glue and duct tape The UAV then performed a secondary test, this time carrying and releasing a package and parachute.

This time, the UAV successfully flew with the package, and was able to release the package midflight. Unfortunately, the servo did not fully rotate, and as a result the package remained on the servo a few seconds after the parachute deployed, leading to a less than ideal landing. However, the package landed softly enough to not compromise the outer layer, as well as to not visibly affect the weights inside.

Additional testing of the package drop with weights, with a more perfect drop, had the parachute unfold in sync with the package beginning to drop, and a sufficiently soft landing.

Fig. 12 The fully assembled drone with package and parachute attached.

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D. Future Improvements In future designs, a protective shell should be attached to

the UAV, in order to protect against crashes, high impact landings, and other unforeseen problems. The parachute on the package should have an increased area by 50% or so, in order to have an even softer landing. Parts breaking was a problem. To account for this issue, more parts, such as the frame and propellers, may be made with stronger, lighter materials such as carbon fiber in place of plastic or metal. To increase the UAVs ability to help people in need and to survive dangerous conditions, more sensors can and should be added, such as thermal sensors that can detect heat from long distances, and high enough quality cameras for a program to analyze the image of the ground and other aerial objects.

For general better performance, batteries with higher charge can be added, as well as stronger motors. This would allow the UAV to go even farther and lift even more.

If mass producing a series of UAVs it would be in the produces best interest to also produce motors that could take in the same voltage but a higher current. It would also be ideal to design and produce a perfect fitting protective shell, and moving landing gear, so that the UAV moves smoother and suffers minimal injury.

V. CONCLUSIONS UAVs are effective for small package deliveries. which can

be used for providing humanitarian aid to places in need. They can travel long distances and can generate powerful lift. The half meter quadcopter proved to be a superb design due to its stability, low cost, easy maneuverability, and flight duration.

The UAV created in this project was fully capable of carrying and releasing a cargo of medicine, syringes, or other supplies between two to three kilograms. The UAV was also able to safely travel to a selected destination within a mile on a map, release the package, and return to its starting point. If a set of UAVs was mass produced and kept in dedicated bases, each base could provide aid to any GPS visible location within a radius of a few miles.

VII. ACKNOWLEDGEMENTS The authors of the foregoing paper gratefully acknowledge invaluable guidance from Priti Kantesaria, their mentor and residential teaching assistant of the New Jersey Governor’s School of Engineering and Technology; assistance from Madara Dias, residential teaching assistant of Governor’s School; assistance from Jaimie Swartz, research coordinator of the Governor’s School; supervision from Edmund Han, head counselor of the Governor’s School; support from Dean Jean Patrick Antoine, NJ Governor's School of Engineering & Technology Associate Director; support from Dean Ilene Rosen, NJ Governor's School of Engineering & Technology Directo; several pieces of equipment loaned from Samret Darisipudi and Kristian Wu of the Institute of Electrical and Electronics Engineering; helpful guidance and electrical equipment and parts from Qilong (Shawn) Sheng; assistance

to gain approval to fly the UAV under Rutgers and Section 366 of FAA regulations from Alejandro Ruiz and Michael O’Connell; assistance from Jonah Varughese of Rutgers Makerspace; Michelle MacPherson of Rutgers School of Engineering’s Office of Student Services; support and generous donations from Rutgers University, Rutgers School of Engineering, the State of New Jersey, Lockheed Martin, Silverline Windows, and NJ Governor's School of Engineering & Technology Alumni.

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