Disclosure: This capstone project is not related to Nevada Dynamics, LLC’s flight management platform. To get information on Nevada Dynamics the company, please see www.nevadadynamics.com.
Nevada Dynamics aims to help grow the UAV industry by extending flight range capability for a variety of UAVs on the market. The team is comprised of five senior mechanical engineering students, who all have interests in UAVs and the industry arising from the problems that the systems are now able to solve. One such solution is using UAVs to deliver packages. The biggest limitation of these systems is the power intensive nature and the restrictions on battery size and weight. Because of these limitations, the use of delivery UAVs is currently restricted to a centralized local area. To help eliminate the greatest weakness of the UAVs, the team has proposed creating a charging station that will be easily adaptable for any UAV thus greatly increasing flight range.
Corporations, civilians, and governments are always in search of faster and cheaper ways to stay connected with society. One of the latest technologies that has entered the scene is the unmanned aerial vehicle (UAV). These vehicles meet societies demands for a faster and more cost efficient way of staying connected and completing tasks; however, they are still restricted by their short range and charging inefficiencies. In order for these UAVs to be cost efficient, they must complete their assigned task and return to the original launch area so that they may be reused. Though this can be accomplished over small areas, the UAVs are limited by their battery size requirements and the amount of time it takes to recharge the batteries between each flight. To extend the range of these UAVs, a durable charging station capable of adapting to various payload sizes is required.
The Design Concept is to ensure the battery on the on the UAV can be charged through contact points located on two of the six hexacopter arms. To accomplish charging, their must be a minimum amount of resistance through the copper wires and contact pressure applied to the contact points. The sloped sections of the charging station will add to the allowable error in landing as well as act as a funnel for the UAV arms into the charging station connections. The large open area at the middle of the charging station will allow for the UAV to land on the station with a sizable package. The battery charging circuitry will be housed in an enclosure that will be located off the main charging station chassis. The overall size and weight of the station will allow for easy relocation by a single trained person if relocation is required.
The Proof of Concept (PoC) was build to prove that battery charging is possible. In order to accomplish this, the design team constructed one sixth of the final designed station. The PoC comprised of eleven different parts: the ramp with a slot for the UAV arm, copper shimstock, carbon fiber arm, UAV battery, UAV battery charger, stepper motor, two clamps, clamp rod, Arduino UNO, Arduino stepper motor shield, and a batter for the stepper motor. The ramp simulated the station structure where the UAV will land. The copper shimstock acted as our contact points on the UAV arm and charging station. The stepper motor combined with the clamps and clamp rod help the UAV arm in place. The Arduino UNO was used to program the stepper motor and needed the stepper motor shield and stepper motor battery to function properly.
The Results obtained from the PoC testing revealed a lot about the over-engineered design of the testing platform. It was shown that there was a negligible amount of resistance through the copper contacts located on the arms and the recessed charging pads located on the base station. The measured resistance through the system without the copper contacts was about 3 Ohms. After the copper contacts were installed the overall resistance through the system only increased to 4 Ohms. Inspecting the contact points after a charging cycle showed negligible contact wear during operation. The stepper motor was also not able to apply a significant amount of force to the arm and therefore experimentally determined that the weight of the UAV would supply the necessary force to allow for positive charging. This will greatly reduce the amount of programming required to actuate the motor to apply a force.
The Charging Station will be hexagonal in shape with sloped arms that will align with a six-armed UAV upon landing to ensure a proper connection. The 3D printed hexagonal hoop easily accommodates for a package during the docking, charging, and undocking phases as it keeps the charging station components clear of the area under the UAV. With 3D printed parts, the design can be easily adapted to match any UAV without increasing production costs. The sloped arms will counteract slight errors during the landing sequence and allow for any unseen error. The Leg Supports will connect each component of the Hex Hoop so the structure is more stable. The legs will provide clearance distance for the package housed beneath the UAV and the length will be easily modified to accommodate many package sizes. The components that make up the hex hoop will be tabbed to allow for easy assembly.
Once the UAV has landed on the hoop, the arms will fit into the copper contact notches as seen in the image below. The copper notches will simultaneously fix the UAV in place while providing contact points for charging. A small copper contact placed on the UAV arm will connect with the corresponding contact on the charging station. This action will complete the circuit and allow the charging station the ability to provide power to the battery on the UAV. Switches will be placed on all notches missing a copper contact to ensure that the UAV is level and announce to the station that the UAV is connected.
The Detailed Design of the Hex Hoop platform is made up of six components. The individual parts are shown in an exploded view in the figure below. The Hex_Hoop Left and Hex_Hoop Right pieces notch together with tabs and are attached to the Legg_Support to form the Corner Assembly. Six of these Corner Assemblies are attached together to make up the Hex Hoop ring. The structural components are the two different sized plastic rods. The Station Support is added horizontally under each Corner Assembly and inserted into the holes of the Legg_Support on each side. The Station Leg is inserted into a hole in the bottom of each Legg_Support, and raises the Hex_Hoop off of the ground. This creates an open space for the payload that the UAV is carrying. The copper contacts for charging are located in the bottom of each notch between the Hex_Hoop Left and Hex_Hoop Right components. There are two contacts, one for each terminal of the battery, and they will be located on opposite sides of the platform. The components for the final prototype will be manufactured from a 3D printer and the structural supports are purchased from a hardware store. In the future, Nevada Dynamics has plans to manufacture all of the components with plastic injection molds.
ABS Plastic was chosen as the material for the Hex_Hoop Left, Hex_Hoop Right, and Leg_Support because of the high strength, low weight, and low cost to produce. These parts of the station were printed using a combination of 3D printers from the Edgington Engineering Garage and the office of our team advisor, Andy Smith . The pictures below show the 3D printed pieces before being assembled. Also prior to assembly, the Station Leg and Station Support parts were cut from wooden dowels and worked to fit into the slots in the Legg_Support. At this point in the build there is much to do, including fixing the parts of the station together, building the hexacopter frame, setting copper contacts in the proper orientation, and running wiring for the station and hexacopter.
The Station’s individual pieces were held in place with liberal use of Gorilla Glue, which became the adhesive of choice to hold the station parts together because of the wide variety of materials that it will adhere to and strength of the connection after the adhesive has set. The picture below shows the station legs being secured into place with the use of trigger claps.
The Electrical components of the station were then soldered and wired to the station. Nevada Dynamics took advantage of the easy to use and solder Molex connectors for the station many connections. The copper contacts were cut and rolled in the University machine shop with extended pins for easy soldering. After soldering, the copper contacts were fixed on station in the proper orientation and wires run down one of the station legs to a Molex connector. The electrical components for the positive landing indicator were also wired, and placed in a protective casing. The lights, wiring, and casing are all show in the picture below
The Hexacopter, though not a design of the charging station, is an integral part of the design for Nevada Dynamics and was a project in itself to design and fabricate. Nevada Dynamics manufactured the hexacopter system on a Tarot frame with an APM 2.6 autopilot. The first phase of the manufacturing process was to secure a motor and electronic speed controller to each of the six arms. Wire extensions were added to the ESCs and were soldered to the Tarot frame, which acts as a power distribution board. A power module, to monitor the current, was wired in between the PDB and the battery. Each ESC also has a UT15 servo wire that plugs into the APM autopilot. All of the wires from the ESCs run through the hollow arms. A Spektrum receiver was also wired to the APM using the same servo wires. Each wire controls the yaw, roll, pitch, and thrust commands that the DX7i transmitter relays for manual flight testing. A 3DR telemetry unit was attached to the APM and communicates wirelessly to the ground station Mission Planner software. This completed the base hexacopter platform.
The Charging Unit came from the manufacturer pre-programmed and ready to accept the use of a standalone balancing unit that stays connected to the battery on the UAV. To wire the charging output on the unit required the proper Molex connections to be installed.
FINAL PROTOTYPE AND TESTING
Final Prototype was assembled on a piece of Styrofoam insulation to simulate the station being fixed and the legs stationary. The Styrofoam board also gave a very secure base to transport the charging station and all of the components involved to operate the charging station.
Final Testing was done in the Applied Research Facility (ARF) High Bay because of the legal and safety factors that go into testing UAV’s. This location provided ample space for takeoff and landing of the UAV on the station. Testing was done in three phases to prove the validity of the project. For the first phase, the hexacopter was placed manually on the charging station, and the connection between the battery and charging station was tested. The landing light showed positive connection, the battery charger gave the current status of the battery and there was an acceptable amount of current passing to the battery. The stand alone battery balancing unit, located on the charging station, also displayed the proper light arrangement that corresponds with positive balancing. For the second phase, the UAV was hand launched, manually landed on the charging station, allowed to charge, and then flown off of the station. This was to test the ability of the autopilot to remain on while the battery charges. The last phase of testing was to test how quickly the battery could charge. The charging unit charged the battery from 22.9V at 2.17A to 25.2V ending in 69 minutes and 56 seconds.
Ultimately the complete final prototype, which includes the hex hoop charging station and the hexacopter, met the qualitative design objectives as well as the engineering specifications while staying within the bounds of the budget. The final design satisfies all qualitative design objectives as it safely includes space for a package, safe landing on the charging station, is easily adaptable to multiple designs, and does not require human monitoring for safe charging. Engineering specifications are also met as the design fully charges the battery under ninety minutes, allows for 6S/5500 mAH batteries, and can safely charge the battery without requiring constant supervision. Competitor research, market analysis, engineering calculations, PoC testing, and a structured revision process ensured that the final design was complete and operational.
The Nevada Dynamics engineering team feels that we have successfully gone through the complete design process, iterations of design and need identification, and came out at the end of the class with a successful product that has proven it works. Nevada Dynamics has gained a lot of experience with the engineering design process. This class has allowed this team a better appreciation for the complexities of the design process, as well as the need for extensive testing and prototyping.
MEET THE TEAM
From left to right: Harrison Gray, Daniel Ferguson, Amanda Nelson, Erik Edgington, Evan Autry
Harrison Gray is a senior Mechanical Engineering student with a minor in mathematics. He currently works at Gardner Engineering as an intern where he uses his skills to estimate budgets and design HVAC systems. Harrison plans to pursue a career in the aerospace defense industry after graduation.
Daniel Ferguson is a senior studying Mechanical Engineering and Unmanned Autonomous Systems. He currently works at Jensen MetalTech where he designs fixtures for the robotic welders. Daniel has a passion for designing small UAVs that can be used for completing various tasks. After graduation, he will pursue his Master of Engineering degree at Duke University. After that, he plans to pursue a career in the aeronautics industry.
Amanda Nelson is a senior Mechanical Engineering student that is expecting to graduate in the spring of 2015. Amanda has experience with test engineering from her internship at Click Bond and hopes to pursue a career in prosthetics upon graduating.
Erik Edgington is a senior Mechanical Engineering student with a minor in Entrepreneurship. He enjoys golf, riding his bike, and spending time with his family. Erik has experience in project management through his internship with NV Energy. Upon graduation in the Spring, Erik plans to pursue a career in engineering project management and would one day like to own his own company.
Evan Autry is a senior Mechanical Engineering student with a minor in mathematics. Evan enjoys flying single engine aircraft, and playing basketball. Evan has experience in leadership and team management from his role as President of Sigma Phi Epsilon fraternity. Upon graduation, Evan will pursue a career in aviation, as a military or commercial pilot.
Special thanks to Andy Smith, for taking on the role of team advisor, Dr. Geiger, for giving the team the ability and encouragement to take on this sizable project, and Tony Berendsen, for allowing time in the machine shop and always being available for questions about fabrication.