22-12-2012, 04:36 PM
Quadcopter
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Abstract:
The military use of unmanned aerial vehicles (UAVs) has grown because of their ability to operate in dangerous locations while keeping their human operators at a safe distance. The larger UAVs also provide a reliable long duration, cost effective, platform for reconnaissance as well as weapons. They have grown to become an indispensable tool for the military. The question we posed for our project was whether small UAVs also had utility in military and commercial/industrial applications. We postulated that smaller UAVs can serve more tactical operations such as searching a village or a building for enemy positions. Smaller UAVs, on the order of a couple feet to a meter in size, should be able to handle military tactical operations as well as the emerging commercial and industrial applications and our project is attempting to validate this assumption.
To validate this assumption, my team considered many different UAV designs before we settled on creating a Quadcopter. The payload of our Quadcopter design includes a camera and telemetry that will allow us to watch live video from the Quadcopter on a laptop that is located up to 2 miles away. We are presently in the final stages of building the Quadcopter but we still improving our design to allow us to have longer flight times and better maneuverability. We are currently experimenting with new software so that we will not have to control the Quadcopter with an RC controller but will instead operate by sending commands from a remote laptop.
Our project has verified that it is possible to build a small-scale Quadcopter that could be used for both military and commercial use. Our most significant problems to date have been an ambitious development schedule coupled with very limited funds. These constraints have forced compromise in components selected and methods used for prototype development. Our team’s Quadcopter prototype is a very limited version of what could be created in a production facility using more advanced technology. Currently our Quadcopter has achieved only tethered flight because it cannot maintain a stable position when flying. Our next step is to fix the software so that we can achieve controllable untethered flight. We are also working on integrating our own Graphical User Interface (GUI) which will allow us to have direct control over all systems. Although there are many enhancements that we could do to the design, we have proven that it is possible to produce a small scale UAV that performs functions of interest to the military as well as commercial/industrial applications.
Introduction
UAVs for military use were reduced to practice in the mid-1990s when the Global Hawk [1] and the Predator [2] were developed. These were very large fixed wing aircraft with wingspans in the 50 – 100 foot range. Payloads for these large UAVs included radar, laser designators, cameras, and missile systems. The introduction of these aircraft removed the pilots from harm’s way plus added the ability to remain in the target area for many hours at a time. These very successful UAVs represent a fundamental change in the way conflict is managed by the U.S. However, these UAVs are large and very expensive and they beg the question of whether smaller UAVs could also play a role in military applications. Likewise, on the other extreme, there is considerable work in micro UAVs some of which are bio-inspired designs. There are designs modeled after insects and birds, but just as the large military UAVs are too expensive, we felt that these micro-UAVs were too small to be practical and required technology that was not readily available to a senior design project group. It was therefore a vehicle in the one foot to one meter class size that caught our team’s interest and is the basis for our project. Specifically, our team is very interested in whether these smaller UAVs can be used not only for military applications but also for commercial and industrial use.
UAV Background and Project Motivation
UAVs for military use were reduced to practice in the mid-1990s with the High-Altitude Endurance Unmanned Aerial Vehicle Advanced Concept Technology Demonstrator (HAE UAV ACTD) program managed by the Defense Advanced Research Projects Agency (DARPA) and Defense Airborne Reconnaissance Office (DARO). [1] This ACTD laid the groundwork for the development of the Global Hawk shown in Figure (1). The Global Hawk flies at altitudes up to 65,000 feet for up to 35 hours at speeds approaching 340 knots while costing approximately 200 million dollars. The wingspan is 116 feet and it can fly 12,000 nautical miles which is considerably greater than the distance from the U.S. to Australia. Global Hawk is designed to meet domestic needs including homeland security and has been demonstrated in drug interdiction. Global Hawks are also approved by the FAA to fly in U.S. airspace.
Another very successful UAV is the Predator which was also created in the mid-1990s but has since been enhanced with Hellfire missiles. “Named by Smithsonian’s Air & Space magazine as one of the top ten aircraft that changed the world, Predator is the most combat-proven Unmanned Aircraft System (UAS) in the world”.
Concept exploration:
After deciding to create the Quadcopter, we had to decide what electronics to use and which sensors we would incorporate into it. After a lot of research on the web, we found a couple forums that discussed open source electronic and software components suitable for making a Quadcopter. Also, very basic but highly customizable Quadcopter bodies were available that were suitable for us to use to create our baseline system. The DIYdrones forum provided good information on what was being done in the amateur drone community and
provided important information on what would be possible for us to use for our project. Motivated by the UAVforge challenge, we believed that the Quadcopter would be a good design starting point since it could lift off vertically, travel some distance to a specific location, record video of an object, hover if necessary, and return home upon completion. This scenario led us to the conclusion that we would need sensors including gyroscope, accelerometer, compass, GPS, and a battery monitor. We would also need payload components including a camera and a telemetry system to send imagery back to the liftoff site. Furthermore, we would need a control mechanism that would allow flight beyond the line of sight since that was also a requirement. We thought of two approaches for control beyond the line of sight. One was to use the camera and video to allow us to view the flight path from the Quadcopter point of view while guiding it with an RC controller. Second, a more ambitious approach would be to use onboard GPS and guidance and a waypoint system to send commands to the Quadcopter via the telemetry link which the Quadcopter would execute autonomously.
Flight Platform:
At the start of the summer, Gerad and I began to build the Quadcopter. We started by researching many different types of Quadcopter platforms and looking at current frames in use. We decided that we would use a commercial frame and then build around it with the electronics that we wanted. With the frame, we also got the motors and propellers. These components determined how much room I had for the electronics as well as how much weight I could put on the helicopter and still have lift. The next thing we chose was the microcontroller which was an open source Arduino board which allowed us to put our own software on it. In addition to a microcontroller, we chose a sensor board called the IMU Shield. This board included all of the major sensors that we would need to achieve flight. On the IMU Shield board there is a gyroscope, barometer, compass, and accelerometer which all need to work together to make sure the Quadcopter maintains stable flight while moving or hovering. Finally we purchased a Lithium-ion polymer (Lipo) battery because they have the best ratio of weight to power. The particular battery we chose has been sufficient to complete the design, assembly, and testing of the Quadcopter systems and our experiments have shown that since we have plenty of thrust we can chose a larger battery for our mission flights to improve the flight time. Figure (3) shows the final product of our Quadcopter system.