Nullified's Posts

Missouri S&T UAV Team - More Autonomous Flying and Bottle Drop

Posted by Nullified on July 7, 2008 at 5:10pm

For those of you not familiar with the project we are a university team competing in the 2008 UAV Outback Rescue Challenge, for more information about our team visit our site: www.aessuav.org
On May 10th we attempted our first bottle drop from 400 feet. The bottle had an aluminum tab attached to it which was held by small servo at the center of gravity of the UAV. We took off under manual control and gained altitude, as the UAV flew it’s oval path autonomously, the bottle was released over the field. The first bottle we dropped was a 500mL Nalgene bottle, which failed miserably (see picture below). Missouri S&T UAV

With the water bottle attached, the flight characteristics were not affected, although takeoff distance was increased, the autopilot’s ability to control the UAV was not affected noticably. During these flights the winds were relatively high, ranging from 10 to 15 MPH, which made navigation for the UAV difficult, but the autopilot performed admirably. Though at times it was blown off the path, it returned quickly to the intended flight path. Several autonomous test flights were performed in the windy conditions, further demonstrating the robustness of our UAV platform. Missouri S&T UAV Team - Nalgen Bottle

Three more test flights were performed on May 15th, all of which included water bottle drops with different bottle designs that took into account lessons learned from the first test. Enclosures were developed for subsequent bottles that allowed them to survive the 400-foot drop. Data was also gathered about where the bottles landed and at what point they were released. With this data the theoretical and actual horizontal distance traveled were compared. After analysis it turned out that the horizontal distance traveled from two of the drops was consistent, this allowed a simple model to be developed for the trajectory of the bottle. During the final flight, aerial video of the bottle being released was also obtained from the onboard digital camera (see the video below).These test flights provided valuable data about how the bottle’s trajectory is affected by the wind resistance, as well as about how the UAV platform handles moderate winds. The next crucial step will be to integrate the onboard computer along with the camera into the aircraft to allow testing of the system as a whole.
For more visit: www.aessuav.org

Missouri S&T UAV Team - Autopilot Tuning

Posted by Nullified on April 8, 2008 at 9:00pm

On Saturday (April 5th) we flew the airplane for the first time with the autopilot since it got the new wing. But before we went out to the RC airfield we had to physically install the autopilot in the fuselage, which went well. We then performed all of the flights necessary to tune the autopilot in HIL (Hardware In the Loop) simulation mode.

Using HIL simulation allowed us to all to get a better of idea of what we had to do once we got out to the airfield. In the end performing the HIL simulation in the lab saved us a lot of time and allowed me to get more familiar with tuning the PID control loops for the autopilot. Previously we had not used the PID window in Virtual Cockpit, but after using it in the HIL simulation it proved to be invaluable for properly tuning the autopilot, it allows you to see the actual, desired, and effort of a certain control parameter (i.e. pitch, roll, yaw, altitude, etc.). Previously we had had issues seeing a change in the behavior from the ground after changing a certain PID gain.On the first flight soon after takeoff the aircraft became unstable and began to become uncontrollable and began oscillating wildly, fortunately our pilot Kyle was able to get it back on the ground without any damage. It turns out that our CG was too far aft, but after adjusting the CG we were able to continue with testing. Using the PID window and the having performed the same process of tuning the autopilot in HIL mode, the first few flights went quickly and we were able to quickly tune the level 1 control loops within two 15-minute flights. A graph of the autopilot’s roll performance is shown below, ideally the two lines should match, and they are in fact very close.

We then moved on to the level 2 control loops (i.e. pitch from airspeed, pitch from altitude, airspeed from throttle, etc.). These were slightly more difficult, and took several passes over the airfield to complete, but we were able to get them tuned to a reasonable level. The ability of the autopilot to maintain a constant altitude is shown below, there are slight oscillations in the altitude (+/- 3 meters), these are reasonable, but might be improved at a later time with more tuning.

Just as my laptop battery was about to give out we moved on to the final flight of the day. The purpose of the final flight was to verify that the autopilot is able to navigate accurately and safely. The first test was simply placing a loiter waypoint above the center of the RC airfield; although there were some oscillations in altitude, the overall performance was quite good (note the 4 m/s wind speed).

The final test was to create an oval over the airfield that the UAV would have to navigate. The first time around the circuit the UAV did not adhere to the waypoints too strictly, but after adjusting some of the navigation parameters the performance was significantly improved (see image below). After completing these flights the telemetry was reviewed and we were better able to analyze the performance of the autopilot and its navigation.

Overall the testing went well and we were able to tune the autopilot control loops better than we had previously been able to with the old wing, this is most likely due to our use the PID window and the HIL simulation which allowed our time at the airfield to be spent much more efficiently.For more information or past posts visit our site: www.aessuav.org

New Wing for Missouri S&T UAV Team

Posted by Nullified on March 30, 2008 at 8:38pm

Sorry about the lack of updates, we will be updating more frequently now. The first update being that we completed the new wing and completed the first flight with the new wing and it performed very well even in windy conditions. Unfortunately there are no pictures of the actual flight but here are some pictures of the new wing on the airplane. This new wing is significantly stronger allowing us to carry our large payload, it also has less drag allowing us to fly at greater speeds.Although you can’t see from the picture above the entire trailing edge consists of the control surfaces for the flaps and the ailerons, we plan on using the flaps during landing to allow us to land at slower speeds.We have also been working on the onboard computer for the airplane, below are some pictures of it and the new enclosure that we had rapid prototyped out of polycarbonate using the facilities on campus. The onboard computer is a single-board-computer (SBC) with a 1.8GHz Pentium M processor, 1GB of RAM, and 4GB of flash running Ubuntu Linux. This computer will handle all of the image acquisition and some or all of the image processing.

Since we have the UAV in flying condition again we will be slowly integrating the all of the electronics into the actual airframe and there should be more frequent updates now that we will be back in the testing/development phase.For older posts or information about the project please visit www.aessuav.org

UAV Electronics Integration

Posted by Nullified on January 5, 2008 at 8:30pm

For those of you who have not heard of this project, I am a member of the Missouri University of Science and Technology UAV Team (www.aessuav.org) and we are building a UAV to compete in the 2008 Australian UAV Outback Rescue Challenge. We are currently in the processes of integrating all of our electronics that will go into our UAV (you can find previous blog posts about our progress on our site). I'm not sure if our project would really fit into the average DIY Drone user's price range, but here it is anyways.

UAV Electronics Test Rig

I recently started assembling a test rig to integrate all of the electronics that will be going in the UAV. Byperforming all of this integration on test bench, the finalinstallation and configuration will be performed much faster. This willalso allow us do our HIL (Hardware In the Loop) simulation with all ofthe components connected.

You may have noticed that there are two large NiHM battery packs, these will soon be replaced by two (11.1V 3200mAh) Lithium Polymer battery packs, saving us about half a pound of weight and significantly increasing our power capacities. Although for bench testing all of the electronics will be powered of off a standard ATX computer power supply. The next step is the get the HIL simulation working with theautopilot and the it’s simulator, this part has been a bit finicky butit should be resolved now.

As a team we have also discussed possible strategies for image acquisition and processing. We had previously planned on simply acquiring VGA resolution video at 30 frames per second, but after reconsidering what altitudes we will be required to fly at to cover the search area in a reasonable time we quickly realized that VGA video would not provide the resolution we need to identify a human target onthe ground from an altitude of 400 feet. We have since decided it wouldbe best to use a much higher resolution still camera taking images atset intervals and tagging them with the GPS coordinates and theorientation of the UAV.