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Author Topic: BGL-6G-AP testing in the Black Widow  (Read 41 times)

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Online Deerslayer

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BGL-6G-AP testing in the Black Widow
« on: January 27, 2018, 10:14:12 AM »
This is a copy of the posting I made in another Forum, where the BGL-6G-AP GPS-capable stabilization system is discussed, Wilf and I have these units and have done a lot of experimentation with them.  Don't worry, there really is a video in here, at the end of the discussion.  :D


This may be of interest to others:

I have had the unit on a flying wing for a couple of months, as a test bed. Yesterday, we were flying in extreme winds - significant wind gradient plus high level of turbulence. (Don't worry, there is a Video link at the end of this).

I set the plane out a somewhat downwind and the selected RTH. It immediately oriented itself and then flew upwind toward the Home point, as expected. I had, let's say, 1/3 throttle to maintain good progress.

Aside: the BGL's Return To Home control strategy is to self-level if necessary, head straight back to its Home coordinate, then circle or sometimes follow a figure-8 pattern centered on Home. It will attempt to maintain a constant altitude, provided it can maintain airspeed; if you chop the throttle, or are a pure sailplane, it will gradually lose altitude and may even stall or perhaps snag a nasty tree or such before you may regain control.

The plane arrived in the vicinity of Home and began its circle. Now, as one would expect, there will be some drifting and the resultant path over the ground would be somewhat elliptical. However, to the airborne pilot, maintaining a constant bank and airspeed will still result in a circle within the air mass. Now, one would expect the RTH function to be trying to maintain a circle with respect to the ground, as it is using the fixed Home coordinates and its GPS to set up a fixed radius circular or figure-8 pattern w.r.t. that ground Home point. Therefore, I expected to see it altering its bank angle accordingly, within limits, to try to retain its circular orbit. Not so much!

With this strong wind, the plane made its first turn and flew WAY downwind before beginning to turn back to Home. For awhile, I could observe it making some control corrections, probably experiencing some turbulence even at its "3 trees" altitude. I really began to wonder if something had gone wrong, but it eventually managed to turn back and beat its way toward Home. I had been just about ready to switch off RTH and take over with full throttle in order to get back. Well, she did make it back without my interference, but I had to use a high throttle and I watched as it sort of zig-zagged along its path back.

I repeated this test, with exactly the same results.

Now, this was a bit disturbing, but it was a good learning experience.

The BGL limits its bank angle to something that would be a shallow to medium turn while in RTH, regardless of its reference to the Home coordinate.

So, if I have this unit installed in, say, a sailplane that may not have terrific penetration and if I were to lose sight of it, I better crank up the motor and hope! As we know, you normally thermal in a circle within the rising air mass which, in turn, is being shifted downwind. Think of a funnel that is tilted and you are keeping inside of it. As you go higher, the migration downwind is likely to increase, as will be the effort to beat back home once you leave said thermal, especially when you encounter the surrounding sinking air.

In considering using the RTH feature under Failsafe, the question is, does one kill the power or set it to something like, say, 1/2 throttle? Not an easy answer, as circumstances vary. Besides, you may have no choice anyway! Not all receivers handle a loss of signal the same way. and ESC's tend to shut off the throttle if no signal is seen for a very few seconds. So, all you can do is hope for the best! Also, you may want to bump up the throttle immediately upon activating RTH, if you cannot see the aircraft or if you suspect that it may have failed safe into that mode. If you in no-power soaring mode and go into RTH, the aircraft may not make it back, especially if it has to do much banking to achieve a straight line flight path and/or if it does a lot of the weaving back and forth that I observed. Of course, you want to know that your airframe, especially a large foam sailplane, can stand high airspeed and gust loading combined, or it may relocate itself in pieces!

I think about this stuff. It's all part of this weird hobby. We have so much terrific technology available, it is fun to learn what it can, and can't, do.

My purpose in Life is to serve as a Warning to others