I just posted a 60+ Mb movie to my web page. As with most of my movie
posts, it might not be completely worth the time to download. :-)
http://baron.flightgear.org/~curt/tmp/20080710.AVI
This isn't directly FlightGear related, but it does tie in a couple ways.
The flying wing UAS is running several code modules straight out of the
FlightGear/SimGear project ... (1) our xml parser (2) our property system
(3) the FlightGear autopilot system (4) an adaption of the FlightGear route
following system. This code has been ported to a small gumstix embedded
computer which runs Linux, and the *gear code is pretty much verbatim except
for a few small tweaks to remove unneeded dependencies. In order to
highlight it's heritage, the code running on the UAS is called "MicroGear".
It is very nice to be able to load and parse xml configurations files. The
property system is very convenient for exchanging data between modules and
for referencing configuration data parsed out of the xml files. And the
coolest thing (I think) is that the UAS is running a direct port of the
FlightGear autopilot system ... and it works quite well in the real world.
In fact, if you have a decent flightgear model of your aircraft you can do a
lot of gain tuning in the simulator and then just copy your autopilot.xml
file over to the UAS and it just might work out of the box ... I'm 1 for 2
on that.
The display in the movie is developed by John Wojnarowski (of LFS
Technologies and a contributor to the FlightGear project --
http://www.lfstech.com) You can probably figure this out, but there is a
live com link between the UAS and the ground station. The UAS is
continually blasting flight data, autopilot data, and other status and
health data down to the ground station, and the ground station can reply
with commands (i.e. to change the route, fly at a different altitude, come
home, etc.) The com link is a wireless serial connection (900mhz) so it
doesn't have enough bandwidth to send all the data at full rate. Thus you
can see the live display is not perfectly smooth. But the data is captured
at full rates onboard, so all this data can be replayed nice and smoothly
later, back at the shop.
I don't have time to write a book about the LFS glass display tonight, but
it's been a tremendously useful tool for tuning the autopilot, monitoring
live flights, and analyzing flight performance. For instance, the altitude
hold module is comprised of three stages ... Stage 1 outputs a target rate
of climb based on altitude error. Stage 2 outputs a target pitch angle
based on the rate of climb error. Stage 3 outputs an elevator deflection
based on the pitch angle error. So in the LFS glass display, you can see
current altitude, target altitude (drawn as a bug), current rate of climb,
target rate of climb (drawn as a bug), the PFD shows your pitch angle, and
an area on the right side shows all the control surface deflections. The
coolest part (I think) is the flight director vbars that show target pitch
angle (and also target roll.) So if the autopilot is doing it's job, the
yellow "bird" should sit right inside the green "vbars". It's fun to watch
all the different components interact. The bird is always chasing the vbars
at least a little bit ... especially on turbulent days. So being able to
see a nice real time graphical representation of the key inputs and outputs
for each stage of the autopilot is tremendously helpful for isolating which
stage might still need some tuning and with a little experience you can know
which parameter to tune and in what direction.
This has been a fun project ... a few cool toys have landed on my desk to
play with, this spring I ended up on a NOAA research ship 1000nm from the
nearest point of land to do test flights of this UAS. And it's really neat
to see how code that has been developed and tuned and refined in a pure
simulation environment can be moved over to an embedded computer on a real
aircraft and it works just as well over there too.
Curt.
--
Curtis Olson: http://baron.flightgear.org/~curt/
-------------------------------------------------------------------------
Sponsored by: SourceForge.net Community Choice Awards: VOTE NOW!
Studies have shown that voting for your favorite open source project,
along with a healthy diet, reduces your potential for chronic lameness
and boredom. Vote Now at http://www.sourceforge.net/community/cca08
_______________________________________________
Flightgear-devel mailing list
Flightgear-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/flightgear-devel
