I would like to thank all of our sponsors that have helped us get to this point, and will help us finish strong. Our current list of sponsors includes IEEE, AESS, Boeing, Procerus, and Garmin. We’re still a little short on funding for the year, but we’re almost there. If you or your compnay may be interested in sponsoring our team in anyway (financially, with equipment, with publicity, etc.) please contact David Erdos at sponsors@aessuav.org for more information. Also, check back next week for another update (we plan on doing some more testing early next week).
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.
And now for some video of the flight and the telemetry from the navigation flights:
Sorry about the lack of updates, there are many new updates coming shortly so bear with us. 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 this picture 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 slower 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 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.
We began construction of the new wing on Friday (January 25th) after all the ribs were waterjet. The new wing is build out of plywood and balsa and hardwood rib caps. So far it seems to be significantly stronger than our previous wing. Building a wing from scratch can be a rather tedious and time consuming process, in the last two days we have put in 20+ hours building the wing, and it’s now nearing completion. The control surfaces are the last major component left to build. Below are some pictures of the wing (for more pictures visit our flickr).
The left wing panel.
The complete three panel wing.
By having a three panel wing, transportation is greatly simplified.
I recently started assembling a test rig to integrate all of the electronics that will be going in the UAV. By performing all of this integration on test bench, the final installation and configuration will be performed much faster. This will also allow us do our HIL (Hardware In the Loop) simulation with all of the 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 the autopilot and the it’s simulator, this part has been a bit finicky but it 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 on the ground from an altitude of 400 feet. We have since decided it would be best to use a much higher resolution still camera taking images at set intervals and tagging them with the GPS coordinates and the orientation of the UAV.
Starting January 1st, 2008, the University of Missouri-Rolla will be officially known as the Missouri University of Science and Technology (Missouri S&T), more about that here. As a result of this we will also be changing our name to MS&T AESS UAV Team.
Since our crash several months ago we have been developing a new wing specifically designed to meet our requirements for our mission. Since speed is high priority in our mission we have designed a wing that is smaller and more aerodynamic allowing us to fly faster in order to cover the search area in less time. Two of our excellent Aerospace Engineers have been working on the design of our wing, performing various calculations and CFD (Computational Fluid Dynamics) analysis. Unfortunately due to everybody’s busy schedules we have been slightly behind schedule in the construction of the new wing, but we plan to be back in the air by late January or early February. Below are a few images of our current design and a screenshot of our UAV flying in the X-Plane flight simulator.
We are also currently in the process of evaluating our strategy for acquiring and processing the images, we are working to decide what approach would be best suited and the most efficient for our mission. Our second revision of the power distribution board for the UAV is also nearing completion (see below).
We went out flying a few weeks ago (September 8th) with the intent of tuning the autopilot control loops better, since in their current state they were not tuned well enough for autonomous landing. We headed out to the RC field around 3 and shortly got everything together. We had also installed a camera on the vertical stabilizer to finally get some in flight video. For the most part everything was going smoothly until the third flight.
During the third flight shortly after takeoff we began a descent and then both wings suddenly tore off from the fuselage. It is important to note that this occurred under the manual control of the pilot, it should also be noted that the UAV was carrying more weight than we have had in any other flights. We had also previously suspected that the wings might be too weak to handle the weight, and it turns out they were. After the wings tore off, the airplane was still several hundred feet in the air and it quickly went into a dive and plummeted into an open field, thankfully no cows were harmed in the crash. Below are pictures of the carnage…
As you can see from the pictures above the fuselage is completely ruined, as are the wings, but thankfully all of the electronics and the engine survived. We have already begun to search for a new airframe, currently we have not been able to find an aircraft that is more suited for our purpose so we will most likely be purchasing another Sig Kadet and building our own wings in order to make them much stronger and more efficient (by using a different airfoil).
Here is some in-flight video before the airplane crashed…
Over the summer we have come to the conclusion that we will not be ready to compete in this years UAV Challenge due to a lack of progress, which is understandable considering we only had about 2 months together as a team before the summer break to build the UAV. Instead we plan on competing in next year’s competition, by then we should have a mature platform that will be tested and ready to perform the mission.
Currently our next goal is to get the UAV put back together since all of the electronics were removed over the summer to do some testing. The current goals are to have onboard video installed within the next few weeks, and get the control loops tuned better for autonomous landing.
We had our first few autonomous flights two weeks ago, and the UAV didn’t crash, unlike another airplane that day. We got out to the RC field in the early afternoon and it started to rain, it rained on and off all afternoon, so we were only able to fly for short periods of time in between the rain. There were also several other planes out at the field that day, including one of the senior project airplanes built entirely out of carbon fiber.
Unfortunately that airplane was extremely hard to control and on it’s first flight it crashed shortly after takeoff, shearing some nylon bolts. After replacements arrived, it took off again and the second flight lasted much longer, approximately five minutes, before the pilot lost control and it plummeted into the ground. Just as a note, the pilot was a quite experienced, and still had quite a bit of trouble controlling it. Now for the carnage…
As you can see, not much was left of that…
Thankfully our flights did not end like that. Once the runways were clear we prepared for our first autonomous navigation with the autopilot. I created a simple path in the shape of a rectangle for the UAV to fly over the RC field. The UAV took off under manual control and once it was in the air control was handed over to the autopilot. The first time it flew in autonomous navigation mode, the path that the UAV took was rather sloppy, and not very close to the waypoints that were specified. After giving a quick call to Procerus and adjusting a few parameters it flew much better and closer to the path designated. It was quite the sight seeing the UAV fly itself, a little scary at times, but also very impressive.
After flying a few simple paths and loiters, we attempted to use the autonomous landing mode of the Kestrel autopilot. The UAV began to circle down to the proper altitude and once it reached the altitude where it was supposed to come in for the landing approach, for lack of better words, it simply wandered off into the distance and we were forced to take manual control and bring it back. After a few attempts at it, all resulting in the same behavior, we decided to give up and just send the telemtry log back to Procerus to see if they can diagnose the problem.
In this picture you can see the pitot tube to measure airspeed on the wing.
That weekend we went out flying again on Sunday and attempted our first autonomous takeoff, which worked quite well the first time. Once again we attempted some autonomous navigation, this time going farther from the home location (over 1.5 kilometers or ~1 mile). Several times during those flights we had to bring the UAV back under manual control since there was real air traffic to the nearby airport and we did not want to interfere. I will be posting video of our first autonomous flight soon, as well as an update on our electrical system soon.
