Well, chalk up another one to the limitations of sims. Today's return-to-launch (RTL) testing was a mixed bag. When the Superstar was heading off away from us and I enabled the autopilot, it nicely turned back, but when it got overhead it went into a death spiral and I had to disable the autopilot to recover. This happened multiple times, despite it working fine in the sim. Perhaps this was due to the wind (10-12 mph) or the airframe, but the software should be doing a better job regardless.

I think we need to work harder on our "circle overhead" algorithm and otherwise put a little more AI in our navigation routines. This is pretty normal for this stage of development and we'll get there. Meanwhile, it was nice to fly on another beautiful day in the Bay Area.

Views: 340

Comment by Nick Sargeant on January 19, 2009 at 11:29pm
Hey Chris, do you have any video of either this or the first test?

3D Robotics
Comment by Chris Anderson on January 19, 2009 at 11:35pm
Well, I have video today taken by an eight-year-old of my launching, which is exactly as good as it sounds. And we have loads of video of us and planes flying around from Friday, which is also pretty much what it sounds like. But happy to upload a minute or two of it if you'd want for entertainment purposes.

Our airborne video (FlyCamOne2) conked out right after launch today. It really is a POS.
Comment by simonl on January 20, 2009 at 2:22am
Hi Chris. Not sure if you've seen the "circle navigation" explanation at tom.pyke.be (I may even have come across it from a link on this site!), but here's the link anyway http://tom.pycke.be/mav/101/circle-navigation
Comment by Michal B on January 20, 2009 at 2:46am
I wonder what could go wrong when you have yaw control limit to +- 15 degrees.
Isn't this problem caused by controlling altitude by throttle? In normal flight I'd certainly use elevator while making sharp circle. Seems that FMA copilot didn't cooperate properly in circles-above-head task.

3D Robotics
Comment by Chris Anderson on January 20, 2009 at 8:41am
Michael: I think the problem is that we don't have a proper circle routine programmed yet. When it hits the waypoint it immediately sees the waypoint behind it and tries to do a 180. Repeat, with increasing throttle as it dips in turns, and you've got a spiral. I think implementing a proper circle routine as per Simoni's comment will fix it.
Comment by Curt Olson on January 20, 2009 at 10:53am
Just speculation here, but it sounds almost like the co-pilot (I assume that's what's being used) is holding the nose of the aircraft low enough so that it can't maintain level altitude at full throttle in maximum bank? This could be more an issue of specific aircraft setup and tuning and gains and less of a problem with algorithms. It's been a long time since I've played with the copilot, but if there's a way to trim the aircraft for a little slower flight speed (more nose up) it might also do better maintaining altitude in turns.
Comment by Curt Olson on January 20, 2009 at 12:03pm
Maybe it's as simple as reducing the max rudder throw?
Comment by Jhon on January 20, 2009 at 4:46pm
to do circlues, maybe the best way is create 4 virtual waypoint around "home", like an square, with a dimeter of 100 or 150 meters, so it keep doing circles without falling doing in a espiral,

Comment by crystal garris on January 20, 2009 at 7:51pm
what was the weather like? i never got reliable operation of my co-pilot in cold and wet conditions . the problem is that as the temp of sky and earth get closer the less sesitive the stabilze loop is , it is very much like turning the gain down .therefore what ever you did to determine your max bank angle is being thrown off by this .i bet it would do just fine on a sunny , clear day. my basic-x AP had the same problem . sunny day and it was a champ,gray cold and wet and if it had to "180" it would spiral.

3D Robotics
Comment by Chris Anderson on January 20, 2009 at 9:31pm
Wayne: I'm afraid it was a perfect sunny day. The problem isn't the FMA, it's our software routines. it's just not handling the "arrived at waypoint" transition well. I think there may be a bug that's throwing the rudder past its 15 degree limit at that transition, and we need to create a series of four or six "synthetic waypoints" around home for loitering so it doesn't just try to yo-yo around a single waypoint.

Pretty straightforward stuff, and won't take us but a few days. We should have this problem solved by next weekend, weather permitting.


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