Mars UAV MAE 435. October 15 th, 2014

Transcription

1 Mars UAV MAE 435 October 15 th, 2014 Team Members: Bryce Yarbrough, Brendan Walsh, Parker Jones, Joseph Miller, Kenneth Nieman, Tilden Thomas, Patrick Kennedy Project Advisor: Dr. Robert Ash ECE Team Members: Alexander Glandon, Matthew Clark, Blaine Eley, Trevor Kennedy ECE Project Advisors: Dr. Khan Iftekharuddin, Jeff Flora, Chester Dolph

2 ii Table of Contents Table of Figures... iii Abstract... 1 Aerodynamics... 3 Catching Mechanism... 4 Analytics... 5 Testing... 6 Electronics... 8 ECE Integration and Autonomous Flight... 9

3 iii Table of Figures Figure 1 Efficiency at different airspeeds... 3 Figure 2 Cross-section of the 3-D printed catching mechanism... 4 Figure 3 Plot of Height vs. Pressure of helium... 7 Figure 4 Plot of volume of helium vs. temperature... Error! Bookmark not defined.

4 1 Abstract There is significant interest in Mars and understanding its composition, history, and the possibility of future colonization but currently employed technology lacks the ability to thoroughly study much of the planet. Recent technological advances have enabled the development of a high speed and wide range surface-to-air recovery systems. This would increase the current capability to study Mars in a safe and reliable manner. An unmanned aerial vehicle (UAV) is capable of fast travel and traveling almost anywhere in range. The UAV will be equipped with a retrieval mechanism to grab payload attached to a line while still in flight. This approach to gathering important payloads carries risks with its benefits, to minimize the risks the system will be tested and examined throughout the project. Starting from examining previous similar systems that prove the feasibility to each part of the system having methods to be tested and improved. This project is based around the terrestrial testing of the feasibility of an unmanned surface-to-air recovery system.

5 2 Introduction Current Mars exploration has been confined to either planetary orbit with the use of satellites or the Martian surface with the use of surface rovers [6]. The rovers provide a highresolution detailed view of the Martian landscape but lack the ability to explore large areas in short periods of time. Orbiting satellites are able to cover more ground but lack the close proximity needed for scientific missions [7]. To fill the gap left by the two existing technologies, an unmanned aerial vehicle (UAV) capable of performing scientific missions within the Martian atmosphere should be developed. During these scientific missions surface-to-air recovery of samples left on the surface of Mars by the rovers would provide another avenue for scientific data to be collected. A design modeled after the Fulton Skyhook [9] system will be mounted on a remotecontrolled aircraft, to allow for relatively inexpensive testing before being deployed on Mars. While significant differences do exist between terrestrial and Martian atmospheres, these differences can be temporarily overlooked in order to provide a proof of concept for the system. This will also allow for a testing platform for future automation of the flight systems. The purpose of this project was to test a design of an aerial recovery system, which would allow for surface-to-air package retrieval.

6 3 Aerodynamics The Mars UAV group has to go through the aerodynamics the plane will face during the test. We have recently started doing calculations on the motor we are using for the airplane. The calculations have shown that the efficiency at 25 mph will be around 26 percent as can be seen in Figure 1. The peak efficiency occurs at around 17.5 mph. The group has also found the static thrust to be about 85 N. Figure 1: Efficiency at different airspeeds The plane is critical to find other aerodynamic calculations. We need the plane to calculate center of gravity (with and without add-ons), lift and drag. We will try to keep the center of gravity as close to the original center of gravity spot before any add-ons. The way center of gravity will be calculated is by measuring the planes length and weight in detail. If we can move the center of gravity it will be back further from the original spot, and that is due to force we are expecting on the front of the plane on pickup. When we look at if the UAV will stay in the air after it picks up the payload, we have an extra couple of forces acting on the plane. The group has also acquired strain gauges that will be used to find the forces on the front of the airplane. Test Platform Dr. Landman recommended the Air Titan RC plane. We choose the Air Titan after seeing it can carry up six pounds of extra weight in vertical flight. This plane is also favorable because it is lightweight but has more than enough capacity to carry the extra components and is below our projected budget.

7 4 Catching Mechanism The catching mechanism was designed with the premise of having as few moving parts as possible. The design utilizes the energy of the line being captured to trigger catching plates, as can be seen in the cross-section view of Figure 1. The mechanism will be mounted in the nose of our test aircraft, with a V-opening to guide the string towards the center of the plane. Furthermore, the utilization of springs with passive energy stored in them will serve as a safeguard against the mechanism closing, by allowing the mechanism to expand outwards a small amount to prevent accidental triggering. A longitudinal axle grounded to the Figure 2: Cross-section of the 3-D printed catching mechanism front of the aircraft mounts the entire mechanism. This allows the entire mechanism to rotate at a speed of roughly revolutions per minute, thus effectively winding the string. This will in turn raise the payload to the aircraft, where it can be secured, and the aircraft can complete the mission and land safely. This mechanism is integral to the project, as this is a prototype with which to test whether our design will work. Integration will occur through testing, with both in-flight and ground tests. The mechanism will be tested against a static line first, then it will be mounted on a testing

8 5 payload. This mounted payload will be suspended from a static line, which will provide a simulated live test. This will provide the necessary tests required for integration into the aircraft for live flights. Analytics The analytical approach of the current project has modified since the projects initial inception and proposed deliverables. Questions and interpretations of the original theoretical analysis of proposed flight dynamics, mechanism stresses and strains, and the payload path of travel have been asked by the group as well as professional advisors Dr. Ash and Dr. Landman and have raised the concern of validity of their accuracy. New analytical test methods and procedures have been developed to provide more real-to-life data gathering and will provide a more accurate and intelligent design focus. Initial testing of the Mars UAV system involved a more broad approach that relied heavily on a theoretical application of knowledge. Issues such as line elongation caused by forces created during the retrieval process and retardation of the force transfer over a given length of line could not be theoretically calculated with the mathematical modeling abilities at hand. The initial component testing of the first iteration also revealed that not all flaws present themselves during the theoretical design and analysis phase. New testing methods and procedures are being created to overcome these known shortcomings, as well as identify others not previously known. The first step is to separate and componentize as much of the planned project as possible, allowing individual issues found during testing to be addressed as they arise without being compounded by others. Following this logic, the testing of the catching mechanism, payload

9 6 delivery system, and electronic control system have been broken down into smaller testing phases. The catching mechanism will have a total of three individual tests, to include static action testing, motor mounted speed testing, and a dynamic test, all to be completed before being mounted to the aerial testing platform. The payload delivery system will be split into two separate tests, the first a line strength analysis conducted in a lab and the second a fly-by-wire test that will evaluate the line tension, flight path, and forces transmitted to the flight vehicle at different payload masses and flight speeds. The electronic control system will be bench tested as programming takes place, and will also become an integral part of the testing processes for the catching mechanism and fly-by-wire test, where the system is still componentized, but also able to provide data feedback during and after these tests processes. The competition of these extra tests and analysis will have only a slight effect on the timeline of the project. A majority of these procedures can be integrated into the already existing timeline availabilities set aside for the integration and previously planned assessments, with any additional time required being taken from the System Flight Trials at the scheduled completion of the project. Testing The purpose of the project is to test the catching mechanism on an unmanned aerial vehicle (UAV). The UAV has to catch the payload using a balloon and line attached the payload. The helium-filled balloon is of a microfoil material. This microfoil material is being used because it is unable to stretch; this ensures that the balloon will hold a precise amount of helium that has been previously calculated. However, being heavier than latex, the balloon itself adds a noticeable amount of weight to the objects the balloon must carry. Ideally, to minimize

10 7 the weight of the balloon, there should be enough helium in the balloon to be close to equilibrium, but not to go over so that the lifting force of the helium is stronger than the weight and starts floating. The testing of the catching mechanism will involve at least six trials, and a different balloon will likely have to be used for each trial for if the balloon floats away, or if the varying pressures and temperatures cause the balloon floatation to compromise the experiment. To account for the density varying with pressure, temperature, and as a result, height, it must be determined if and how the variation in density could affect the volume to be put into the balloons. In order to determine this, it is tested on MATLAB using the barometric equation. Going to about 200 ft (61 m), there is a small variation in pressure, but may only show a small degree of variation for the volume; this can be seen in Figure 3: Plot of Height vs. Pressure of helium Figure 3. However, to confirm this, a function in MATLAB is made to determine the variation of density and specific weight. This function relies on given temperatures and pressures as well as height. However, showing codependence with three variables may be complicated, and to show it well would require a three-dimensional plot. Ideally, the pressure should be at a given height of 50 feet, while the pressure varies based on temperature. The temperature should account for anything theoretically possible for the semester, so the temperature will range from 10 F to 90 F. By the time of testing, these extremes are unlikely, but will help contain the likely densities and

11 8 volumes required to undergo the experiment. Volume of helium at different temperatures can be seen in the plot in Figure 4. Aside from the cold extreme, the ideal volumes given are too large to fit in the balloon. This may be good for preventing floating, but will add weight to the payload overall. Figure 4: Plot of volume of helium vs. temperature Electronics The civil engineering department will be loaning us data acquisition equipment for the testing phase. The equipment and sensors are made by a company called LORD Microstrain Sensing Systems and are able to gather data from multiple channels. The available sensors will allow us to determine force and acceleration in the x, y, and z planes for both the payload and the aircraft. Testing will also give us more insight into the flight path of the payload upon recovery. There is a problem with the data acquisition equipment. The system is able to gather data from 8 channels; however, the civil department is only able to get data from a single channel at a time. This will prevent us from gathering the necessary data to being flight-testing. To fix this problem we will work with the ECE team and the civil department to try to come up with a solution and gather the full range of data needed. Now that funding has been approved, we hope to have the additional electronic components needed for the testing phase within a few weeks. These components will allow for control of the DC motor during the recovery process. An arduino microcontroller along with

12 9 Xbee radio frequency modules will control the motor through the program LabVIEW. Once testing is complete, two accelerometers will be interfaced with the microcontroller to gather accelerations once the payload has been caught. This information will tell help us determine the aircraft will actually behave in flight upon payload recover. Code has been written in LabVIEW to perform the above-mentioned processes, all that is needed now is the electronic hardware. ECE Integration and Autonomous Flight The immediate future of the project is dedicated towards the pickup and retrieval of the payload using controllers with human interaction, but the long-term goal is make this prototype completely autonomous. The MAE Mars UAV team has been working with the ECE team to integrate a visions system that can locate, fly to, and recover the payload while remaining completely autonomous. This is achievable through use of the 3DRobotics Pixhawk Autopilot Controller. The ECE team has selected the Pixhawk because it pairs with the 3D Robotics Video/OSD system. These two components can be programmed to automate the surface-to-air recovery system. Once initial testing of the prototype has been completed, the two teams can fully integrate to begin assembling the 3D Robotics system.

13 10 References: [1] M. Usui, A. Simpson, S. Smith, J. Jacob, Development and Flight Testing of a UAV with Inflatable-Rigidizable Wings, presented at the 42 nd AIAA Aerospace Sciences Meeting and Exhibit, Reno, NV, January 5-8, 2004, Paper AIAA [2] N. Brown, A. Samuel, R. Colgren, J. Lookado, Mars Exploration Airplane: Design, Construction, and Flight Testing of a Stability, Control, and Performance Demonstrator, presented at the Infotech@Aerospace Conf. and Exhibit, Rohnert Park, CA, May 7-10, 2007, Paper AIAA [3] F. M. Highley and R. V. Parker, Aerial Recovery and Cargo Delivery Systems, presented at the Society of Automotive Engineers (SAE) Meeting, October 26-28, 1964, London, England, Paper SAE 915A