As Unmanned Aerial Vehicle (UAV) technology matures, and the practicality of its application in commercial and industrial markets grows, the need for effective infrastructure to support these craft in an efficient manner becomes apparent. This necessity inspired the Engineering International team to work toward developing a system which would work within, and indeed be part of, such infrastructure. Currently one of the main limiting factors for UAVs is the relatively limited battery life, and by extension, the limited range of these craft. To resolve this, Engineering International has conceived of a station which would allow a compatible UAV to land and exchange its battery, effectively refueling the aircraft in route to a goal. This design will operate autonomously while requiring very little calibration or technician work, as well as incorporating a modular build, so that components can be easily replaced. It is the vision of Engineering International that such battery stations would act as outposts for a centralized hub. These stations would provide an economical, and small footprint, method of drastically increasing the effective range of UAV operations for large scale applications.
Proof of Concept
The Proof of Concept of Engineering International is a battery charging system which consists of a battery housing and an interface. The battery charging system is an aspect of the design that drives all other parts of the concept. The battery housing is going to contain the battery itself which is going to connect to the interface via Molex connector. The case design testing determines the dexterity and force required to be implemented by the robotics of the project. Additionally, an implemented circuit design will be used, and by the help of an Arduino, LEDs, and a voltage sensor, the team is going to detect the charge of the battery. The charging circuit that is going to be used, must support the method of connection, and the effects that the connection has on the efficiency of power transmission, with respect to resistance, and other key factors. Given the fact that the team consists of mechanical engineers, validating a key component that members are not very familiar with, in the case of the charging circuit, is a very important step. Proving the best design for the battery interface is also important given the number of other components of the final design it informs, as mentioned above.
The Drone Docking Station is specifically intended for uses where autonomy is desired. It will work as an autonomous, centralized, battery charging station with the capability to change batteries on UAVs quickly and efficiently. The purpose of the product design specifications is to define the specifications for the Drone Docking Station and to outline the cost, usability, intended use, intended environment, and intended user. It also describes the product, usability, material, software, and packaging requirements. Some key product design specifications are that the Drone Docking Station should cost less than $800, be autonomous, and not be damaging to the UAV. In addition, the Drone Docking Station should clearly indicate all safety warnings and safety risks that are identified in the hazard identification process. The Drone Docking Station is to be modular so that components can individually be replaced during maintenance to lengthen the lifespan of the product. A trained technician will carry out any maintenance, set-up, and calibration work, so the end customer will not be obligated to cover costs related to training, or stocking replacement parts.
The Drone Docking Station was fabricated in the Mechanical Engineering manufacturing shop. Phase 1 of the manufacturing was the construction of the crown and landing station. Six PCV pipes were cut using an electric saw to equal lengths of 900mm. From there, the holes and notches for the crown pieces, which were 120 degrees apart were cut out of the pipes using the CNC machine. Using a big 3/8’’ inch thick piece of acrylic, six pieces of the crown were milled in the CNC machine. Tiny holes for screws to connect the crown to the pipes were drilled in using a manual milling machine and tapped.
During Phase 2, the battery case and charging interface were CNC milled from different sizes and thicknesses of acrylic. The battery case consisted of four components. One component was 3D printed and the other three made using the CNC machine and vertical saw. Since the Drone Docking Station has as the capacity to store three batteries, three battery case were manufactured.
The battery charging interface consisted of three panels. The left and right panel that will receive the battery case were CNC milled simultaneously to speed up the process. The back panel was CNC milled using three operations, the other shape, front and back holes for the Molex connector. Then holes were drilled in the sides of the panels so it can be screwed together.
Phase 3 consisted of the five remaining parts for the elevator mechanism which were manually milled. There was difficulty in during this procedure manually due to human error and some slight errors in tolerances. However, since these five pieces were relatively small, the error was minimized.
After all the parts had been finished, the team assembled the landing platform fixed to a wooden base. The battery cases, charging interface and elevator mechanisms were hot glued together.
Testing and Results
The Drone Docking Station was tested over the span of a week. The team’s objective for building the Drone Docking Station is to solve the problem of the limited fight range of many drones and UAVs. The Drone Docking Station allows the swapping and charging of drone batteries. As a result, the range of many drones and UAVs is expanded.
The main testing components were testing independently before everything was connected. The structure of the Drone Docking Station was assembled with slight ease. Most of the manufactured parts and pieces fit accordingly to the team’s design specifications. The team obtained a drone which had a landing gear too short for the width of the crown. So, small pipes were used to extend the arms of the drone. During the assembling phase, pieces were cut out from the base on the front side to receive the motor and elevator mechanism. Additionally, a hole was drilled into the base so all the wiring could be hidden. A fan was used to cool down the voltage sensors and drivers once it was determined that they were becoming hot and smoking during operations.
Battery Charging Testing
The first step of the electronic testing was validating that the battery chargers could charge three batteries simultaneously. From the Proof of Concept, we understood that one battery charger can only charge one LiPo battery at a time so three battery chargers were used in the testing and each had to be connected to a portable power source and that power source was plugged to an external output. This testing allowed the team to determine that the three LiPo batteries are better charged from a portable power source. Before the battery swapping operation could happen, the DDS must be plugged to an external output.
The second step of the electronic testing was verifying that the code using an Arduino can detect a drone with the push of a button. This included testing and understanding where the pins and wires from the button to the Arduino had to be plugged in. Initially, the button once pressed, didn’t work properly unless it was pressed and held down. This problem was determined using the LED on the Arduino. If the button is pressed, the led had to turn on and stay on. However, the LED turned on and stayed on only when the button was pressed and held down. The code was modified and the LED stayed on even after the release of the button. The team now concluded that the with a simple push of the button, the DDS can determine whether a drone was on top or not. If a drone was there, the process of grabbing its battery would begin.
Additionally, if the button was pushed and there wasn’t a battery connected to the charger then the battery chargers beep to indicate that nothing was plugged in, a modification in the code made to alert the user.
The external pieces of the elevator mechanism included a top, middle and bottom plate, a motor, bearing, elevator, a gear and two rods and gripper. The top and bottom plates kept the elevator in place. The motor sits on the bottom and the objective is to drive the elevator up and down using the two rods. Problems arose in this interface because the two rods weren’t perfectly straight so the elevator was slanted at an angle. This was because the rods weren’t grounded properly on the bottom plate and the motor. The team fixed this imbalance in the elevator adding small weights on the end of the elevator to balance out and using epoxy to hold the rods down firmly.
For the elevator, the objective was to move horizontally in and out, grabbing/inserting the battery of the drone. During this testing, the gear and motor stuttered on the track and didn’t move properly as intended until the team discovered that the problem came from the dead drivers and new drivers were had to be wired in.
The gripper, the part that grabs and inserts the battery was 3D printed. During testing, the gripper didn’t have enough of a hook to grab the battery so the team made some adjustments to it. Initially, the hook was mounted in the middle and would pull the battery out at an angle. For proper operation, the battery had to be pulled out straight so two makeshift hooks were added to plug and pull the battery out straightly which worked well.
Charging Station Testing
The charging station was assembled using epoxy but due to human error, its parts were slighted bent at an angle. As a result, the battery case didn’t slide in smoothly unless by forcing it. To make it easier for the Drone Docking Station to insert the battery smoother, the outside grooves and edges of the charging station were sanded. This makes it much easier to insert the battery cases with little necessary force.
After aligning the charging station with the elevator mechanism, the team discovered that the charging station was too low to the ground to be reached by the elevator. So the station was mounted on top of two thick pieces of wood. This gave the necessary elevation for the elevator to reach the charging station below.
Drone Interface Testing
For the drone that was obtained, an external battery case was 3D printed for its battery to sit. The case was mounted to a piece of wood using hot glue right underneath the drone. When the gripper came upwards to grab its battery, this external case moved around but it had to be fixed. So, the team used two L-shaped hinge brackets and bolts to fixed it on the piece of would. For more stability, plastic zip-ties were used to hold the piece onto the drone firmly in place.
After all the components were connected and assembled together, the full testing of the Drone Docking Station was performed. The operation includes, once the button is pressed, the elevator rises from bottom to top, grabs the battery from the drone and inserts it into an empty battery slot. Then it grabs a fully charged battery and places it into the drone. During testing, the operation failed to return to the drone after a fresh battery was chosen. This testing was performed with empty battery cases so the team is unsure if a fresh battery would’ve been chosen. Additionally, a burning smell was perceived coming from underneath the base and the operation was suspended.
After reviewing the code once more, the team concluded that the source of the problem of the elevator failing to return the charged battery is unknown and wasn’t a problem with the code.
On of the visible factors that lead to failure in operation is a misalignment in the elevator mechanism. There is a noticeable wobble as the elevator moves up and down. Additionally, the Drone Docking Station has to know where the elevator is positioned at all time. Measurements of the position from the base to the drones battery compartment and for each battery cases must be accounted for in the coding.
The Drone Docking Station is designed to be completely autonomous. However, our product required some manual input from the user such as a button press. Additionally, there is no visible output that tells the user which battery is fully charged or not and communication to the drone when the swapping process is completed and ready for takeoff. However, these are minor issues that can be resolved with more time.
Meet the Team
Seun Animashaun is a graduating senior studying Mechanical Engineering with a minor in Mathematics. He is the corresponding secretary of Tau Beta Pi Nevada chapter. Born in Nigeria, Seun moved to Iowa at the age of eight and to Reno before high school. After graduation, he plans to pursue a Master’s degree in Aeronautical Engineering and someday work for NASA or Boeing.
Born and raised in Reno, Nevada, Shane Lawson is a senior Mechanical Engineering student with minors in Computer Science and Unmanned Autonomous Systems. In addition to being placed on the Dean’s list multiple times, he is Vice President, of the UNR student chapter of Tau Beta Pi, Vice President of the UNR student chapter of The American Institute of Aeronautics and Astronautics (AIAA), and an active member of the UNR robotics club. Upon graduation in Spring 2017, Shane plans to pursue a Master’s degree in Aerospace Engineering.
Teresa Baerens is from Munich, Germany. She got the opportunity to join the swimming team of the University of Nevada, Reno in fall 2013 and decided to major in Mechanical Engineering. She participated in some projects connected with her academic career, amongst others building a hovercraft and a small-scale bridge out of balsa wood. She gained experience in using software like Excel, SolidWorks and MATLAB. After graduating in Spring 2017 she is planning on going back to Germany and pursue her Master’s degree in Munich.
John Hladky is a senior Mechanical Engineering undergraduate student originally from Kentucky. He continues to be involved in the leadership of numerous extracurricular engineering clubs and was previously awarded the General Undergraduate Research Award for work on developing a rocket deployed unmanned aerial vehicle. Additionally, he has a diverse educational background, with two bachelor’s degrees held in Anthropology, and Speech Communication. He hopes to utilize his education to pursue a career leading teams in aerospace, alternative energy, or applied robotics.
Wadih Zaklit was born in Lebanon where he spent most of his life. He moved to the U.S.A. to pursue his B.S. in Mechanical Engineering while minoring in Math. He has been placed on the Dean’s list for the past six semesters and is working hard to maintain that spot. His plan is to graduate in Spring 2017 and then continue his graduate studies to eventually get his PhD in Mechanical engineering.
The team thanks Tony Berendsen for his help and assistance in the manufacturing lab. Dr. Ryan Tung for his advisement and guidance during the early phases of our project.