Missouri S&T AESS UAV Team

We had our first flight of the airplane with the autopilot installed last Tuesday (April 17th). We arrived at the RC airfield around 6PM, much to our dismay there was some light rain, which eventually stopped. Setting up the ground station was the first priority, then all of the control surfaces were tested to make sure they were functioning and deflecting the right amount, although for some reason the throttle servo was not moving, after a little bit of tweaking in the Virtual Cockpit, it worked fine. Shortly after the throttle servo was fixed, the autopilot stopped responding, it turned out that the ground connection of the battery to the autopilot had failed, since we did not have a soldering iron handy, the two wires were twisted together and wrapped securely in electrical tape, although as an interesting note, if this wire would have come lose in flight, all control of the aircraft would have been lost.

Abe and Jonathan starting the airplane

The moment of truth came and we fired up the engine and began the to takeoff (on manual control), the airplane was able to takeoff in a relatively short distance and was quickly in the air. The radio link between the autopilot and the ground station was quite strong and the Virtual Cockpit provided us with the airspeed, height above ground, and the attitude of the aircraft. The first order of business was to calibrate the dynamic and static air pressure sensors on the airplane. The next few flights consisted of tuning the control loops with the correct parameters, this was fairly straightforward, but rather time consuming. Once the roll and yaw loops were configured, it was interesting to see how the airplane quickly straightened itself when the pilot attempted to roll it. Although we were not able to finish tuning the control loops since it began getting dark.

Overall the first flight with the autopilot was a great success. We plan on flying the airplane again this Sunday, and will hopefully finish tunning the control loops and have our first autonomous flight.  For more pictures you can visit our flickr site.

This weekend we began installing the Kestrel autopilot in the airplane, which consisted of wiring up all of the servos and GPS, as well as configuring the servos in the Virtual Cockpit software. This took a surprisingly long time, although most of the time was spent on making the wiring harnesses and troubleshooting why the servos were not function properly. Once everything was powered up, the servos didn’t want to move, which it turns out was because I did not use the autopilot’s power rails since I had completely bypassed them and sent only the PWM signal wire from the autopilot to the servos, and powered the servos independent of the autopilot. Once that autopilot’s power rails were hooked up the servos started working, although they were quite jittery and very rough when on manual control, possibly from some kind of interference from the radio or other electronics. Below are some pictures of the autopilot installed in the airplane.

The autopilot

The GPS unit.

Now that the autopilot is installed, and as long as there is good weather this week, we should be able to have the first few flights with the autopilot. According to the manual, it will only take about four flights to tune the control loops for fully autonomous flight. We will also probably end up purchasing an embedded computer this week for the image processing, which will allow us to start developing the image processing algorithm.

Last week the the Kestrel Autopilot from Procerus arrived, and I have to admit, I was quite surprised by the size of it. It’s literally smaller than a deck of cards (slightly taler but less area). Reading over the documentation was first step in learning how to use this powerful little thing. Thankfully the documentation was quite good, and after 5 minutes of soldering a few wires together, it was ready to be powered on for the first time. The accompanying software was quite straightforward and surprisingly once both the autopilot and ground station unit were powered, they instantly acquired a wireless link, and began feeding data into the Virtual Cockpit software.

One really cool and amusing feature was that there was an artificial horizon with a 3D model of an airplane that rotated in whichever direction the autopilot was oriented. After everything was configured roughly how it should be, I began to setup the HIL (Hardware In the Loop) simulation. This allows the autopilot to fly an airplane in a simulator on the computer, allowing the simulation of an entire flight from takeoff to landing. The HIL simulation was quite easy to setup, and was running within minutes. Of course there were several minor details that were overlooked, due to the fact that I had not read the entire manual yet and did not understand the various modes of the autopilot, so the UAV kept crashing, but eventually after playing around with it, it all worked great.

Overall I was rather impressed with how straightforward and easy it was to start using the autopilot right out of the box. From my experience I’ve rarely had such complicated systems up and running in such a short amount of time. Now the next step is to install the autopilot in the airplane, which is quite a task in itself. Hopefully we will be able to have it installed by the end of this weekend, and maybe perform the first flight with the autopilot this weekend, or sometime next week, weather permitting.

And now for some pictures:

The autopilot itself.

The communications box.