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Jan 10 2011

First Autonomous Flight w/ EasyStar

Today Nisarg and I went to a local field to test the Fly By Wire A, Fly By Wire B, Return to Launch and Auto modes. Our testing had started with the Fly By Wire mode. In this mode the airplane is supposed to maintain a 45 degree bank angle when the rudder is positioned to either side. Additionally, the airplane’s pitch is also maintained at a 45 degree angle when climbing or descending. When no input is detected the plane will maintain a straight and level flight. After recording the flight using the XBees we were able to verify that both the bank and pitch angles were maintained at 45 degrees when told to do so. In this mode the throttle was also controlled autonomously and a steady speed was maintained throughout the flight. Although this mode will probably not be used for data collection it serves as a test to make sure that all of the ArduPilot’s functions are operating as expected.

Next we decided to test the Return to Launch mode. In this mode all of the systems are controlled via the ArduPilot to position the plane above the location at which the first GPS data point was taken. Once the launch position has been reached the plane will attempt to circle above that position until manual mode is activated. The resulting flight path is illustrated below where “H” indicates the “home” location. Despite the plane's non-linear flight path the home location was eventually reached and a stable holding pattern was maintained overhead. It should be noted that the RTL mode was activated at the furthest point from home (located at the bottom of the following image).

After the above tests were completed the first fully autonomous waypoint flight was attempted. The following illustration shows the location of the waypoints used for the Auto mode test. During this flight the plane was only told to get within 60 feet of the waypoint before moving on to the next one. Future testing will require a less conservative waypoint radius (maybe 10-20 feet). Once all of the waypoints were reached the plane was told to return to the launch position indicated by the black and red waypoint marker labeled with an “H”.

The following illustrations show the first and second flight paths taken by the plane for the waypoints shown above. During both of these tests the plane had taken a non-linear path towards some of the waypoints. These curvy flight paths could be the result of a poor gain value in the code.

Ok, so the image above looks kinda messy but the important thing is that the plane made it within 60 feet of all three of the waypoints. Part of the overlapping in the plane’s flight path was due to the fact that I had flown over the waypoint area in manual mode in an attempt to replicate what the airplane would try to do in AUTO mode. After realizing that this was a mistake a second test was performed. This time I had made sure that no overlap was made within the area in which the plane would be flying in AUTO mode. In the following image it should be noted that the AUTO mode was activated at the furthest point from the home position (located at the top of the image) This flight path seems to indicate that a more direct path is taken when the plane is far away from the waypoint. As it gets closer to the waypoint it seems to experience significant overshoot resulting in a more winding flight path.  

Tomorrow I’m going to try getting the plane to fly to waypoints which are located at much greater distances from one another to see how it behaves. I’m also going to reduce the required waypoint radius to around 20 feet instead of the 60 feet used in the tests shown above. It seems as though the winding flight path may provide additional coverage which would otherwise be difficult to achieve with the slender and direct flight paths taken by the hexakopters. A downside to this is that flight repeatability will be extremely difficult if not impossible to achieve with this platform. The flight path’s repeatability however, is only being used now to create a constant from which a comparison can be made between the resulting synth quality of various flying heights and camera positions/arrangements.

After these tests it has become apparent that the EasyStar platform is capable of flight times of up to 25-30 minutes on an 11.1V 2200 mAh lipo battery. If we were to use a slightly larger battery pack I think that we could achieve flight times that exceed 30 minutes. I’ll begin to test more waypoint configurations tomorrow in order to determine the coverage capable with the EastStar platform. I would highly recommend that the Ecosynth team get a netbook to serve as a stand-in for the current field computer. I've been using an Asus netbook while in field and it's able to handle all of the programs required for the ArduPilot. In addition to it's easy to handle size the battery lasts for more than 10 hours when operating on high power and the screen is easy to read in the sunlight.   

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