Hi all,

Just wanted to fill you in on a small UAV altitude record that was just set (still unofficial at the moment) using an autopilot similar to the ones discussed here. Here's a story about it: http://news.stanford.edu/news/2009/september14/airplane-self-pilot-091809.html

The record attempt was made by a group of graduate students who took a course this spring in the Aero/Astro Department at Stanford University. I was the teaching assistant for the course. This year the goal for the course was to design a small UAV to beat the remote control altitude record (~11, 000 ft). There were four teams of 4-5 students that had 10 weeks to go from a blank sheet of paper to a successful vehicle. The autopilot and propulsion system were provided, but the teams had to write their own control software and design/build the vehicles. The only sensor allowed was GPS (+ an barometric pressure sensor for the record attempt).

At the end of the class in June we had a flyoff where the teams had to demonstrate their vehicles by repeatedly climbing between 50 ft and 400 ft (to stay within FAA regulations). All four team succeed in demonstrating greater than 10,000 ft of cumulative altitude gain. A few students continued working on the project over the summer, culminating in a world record altitude attempt a couple weeks ago at the NASA Dryden Flight Research Center.

The altitude record attempt was for an autonomously controlled electrically powered UAV weighing less than 5kg, FAI Category U.2a Group 2. The news article gives a good account of the record attempt flights. The record altitude was 2177 m (7142 ft), which ended up being limited by winds aloft, not battery energy. Only about 40% of the charge was used getting to the record altitude.

Here are some pictures of the airplanes and the autopilot/GPS boards.


I designed and prototyped the autopilot for the course early this year. It uses the dsPIC30F4011 microcontroller and the uBlox LEA-5H + sarantel helical GPS antenna (basically the same as is being sold now, but in a slightly larger footprint). The xBeePro or xBeeProXSC is used for commands/telemetry. RC controller commands are read by the custom ground station software using a transmitter-to-USB cable and sent over the xBee to the airplane. This software based failsafe was not ideal, but it was the lightest option. The autopilot has inputs available for other sensors (thermopile, IMU), they just weren't integrated for the class and there isn't any software written to handle them.

If anyone is interested I should be able to post a BOM, the board files and the autopilot/ground station software, but it likely won't be supported at all since we are working on a smaller/lighter design to replace this one.

-Geoff

Views: 3157

Comment by Craig Palmer on September 19, 2009 at 5:19pm
Great Job !!

CraigP

3D Robotics
Comment by Chris Anderson on September 19, 2009 at 5:31pm
So this is a GPS-only autopilot? What aircraft did you fly it in?
Comment by Geoff on September 19, 2009 at 9:34pm
As used for the class it was a GPS only autopilot. It was flown in both of the airplanes shown above, plus about 6 others the team's built throughout the quarter. Since it was an aircraft design course, part of the challenge was designing a dynamically stable airplane, in addition to the maximizing the altitude. There are some other pictures from the class fly-off showing some of the other designs here: http://picasaweb.google.com/AlexStoll/AA241X2009#

3D Robotics
Comment by Chris Anderson on September 19, 2009 at 9:40pm
Is all that cracked clay Dryden AFB?
Comment by Roberto Hawkowski on September 19, 2009 at 10:16pm
Congratulations to all. Nice photos. Great work.
* You mentioned that barometric sensor used to record the altitude.
Can you comment about how much variation you have observed between GPS and barometric sensor based altitude information?
* I assume you have used IR sensors for attitude control? Did you also use IMU for attitude stabilization?
* What was the farthest linear distance between your ground station and your UAV? (i.e. how well the xBeeProXSC performed?)

3D Robotics
Comment by Chris Anderson on September 19, 2009 at 10:50pm
Roberto,

As he mentioned above, there was no attitude stabilization, neither with IR sensors or an IMU. They used an inherently stable (free flight style) airframe.
Comment by Jack Crossfire on September 20, 2009 at 12:45am
How did the XBee PRO reach 7,000 ft? I could only get 300ft out of the 2.4Ghz one.
Comment by tycinis on September 20, 2009 at 2:59am
Jack Crossfire : the Xbee pro 900mhz can go up to 6 mile and the XSc 15 mile .

Check sparkfun :

http://www.sparkfun.com/commerce/product_info.php?products_id=9099
http://www.sparkfun.com/commerce/product_info.php?products_id=9086

Moderator
Comment by Gary Mortimer on September 20, 2009 at 3:05am
Lovely airframes, really lovely well done. I keep saying those 1950's free flight designs are hard to beat! With a modern twist, obviously.
Comment by Geoff on September 20, 2009 at 8:09am
The cracked clay is on Rosamond Dry Lake down at Edwards AFB.

The barometric pressure and GPS altitude tracked each other very well, but the absolute numbers are usually offset a little due to local weather conditions. On the 7000 ft flight the difference was about 100 ft (which is very reasonable for a difference between geometric and pressure altitude).

The radio range is really dependent on the RF environment, the antennas used and their orientation with respect to each other. With the 2.4 GHz xBeePro radios (with whip antennas) we were only able to get reliable links out to about 1/4 mile around Stanford. Using the whip antenna on the aircraft and a dipole antenna on the ground station with the XSC radios we able to get a link out to about 3 miles at NASA Dryden, but it was starting to get intermittent at that range. Never tested it any further. On the list of things to do is to build a tracking mount for a higher gain ground station antenna (yagi or parabolic dish).

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