Comment by Stone1295 on May 13, 2012 at 11:31pm

Sorry about the crash, but thanks for the detailed flight analysis.

The plane seems to have full down elevator in your pictures.  Do you think this is part of what caused the crash, or do you think the crash caused the elevator deflection?   I wonder if your elevator servo is stripped?

-Mike

Comment by Carl La France on May 14, 2012 at 1:46am

I can feel your pain . It is always the  the most expensive part that takes a hit . I was wondering how your roof top antenna mount turned out . Excellent story  and Google earth overlay  Did you figure wind correction angles for each of the pattern legs? If not the plane would be always hunting for the way point and be approaching  the way point from down wind  when it got there.  a set compass course would want it to go one way  direction to the way point that was constantly changing with the wind would want it to go another  in effect flying a erratic  semi circle

Comment by Mike Thorlin on May 14, 2012 at 5:25am

Mike,

I attributed the appearance of full elevator to be due to the tear between the vert and horiz stab. Ill fix that this week but your comment reminded me to validate that the servo isnt stripped. It never occurred to me that it would, but being a plastic gear servo its entirely possible, thanks!

Comment by John Stuart on May 14, 2012 at 5:39am

Just a question - did you consider enabling a RTL failsafe and in the event of the mission going awry, just switch off the transmitter to activate RTL?

Comment by Mike Thorlin on May 14, 2012 at 5:43am

Carl,
Thats a good point, it never occurred to me to consider wind effects in planning the mission. After analyzing the tlog further Ive established that only a very short period of autopilt flight was recorded, that is shown by the purple track in the google earth overlay.

For some reason the telemetry link terminated, with just a single data point recorded after that point. I need to figure out why. Perhaps the XBee failed priot to crash simply to to vibe or the steady state torque applied as a result of the slipstream against the antenna. Dont know, but next time I will either package the XBee in a project box or at least strain relieve it with a popsicle stick or similar to take the strain off the pcb/antenna connector.

Another possible contributor is the Turnigy TX. While searching for the plane, I carried the TX and periodically actuated the servos so that I might hear them "whirring", increasing the likelyhood of finding the plane in the brush. I noticed that as I gripped the TX, it would periodically power off if I applied too much pressure to the battery cover. This was repeatable, I could do it at will. I was very nervous during the whole flight, and I imagining I was "white knuckling" the TX. Perhaps I did this, shut the TX down for a moment. One serious failing of the Turnigy X9 is that the RX holds the last received input on loss of signal. If I was applying any control input at the time I squeezed the wrong spot on the Battery cover, the RX would just continue to move that surface, overriding the autopilot until I relaxed and the TX turned back on. Maybe, its thin, but maybe.

Comment by Mike Thorlin on May 14, 2012 at 5:50am

John,
Interesting that you should bring up failsafe as I was typing up my experience with the Turnigy losing power as I handled it. I tried to get fail safe to work, but the receiver based fail safe wont work on tn Turnigy in PPM. I have decided to rework the TX to eliminate any loose wires in the battery compartment, as well as swapping the module for the flysky module I see offered that is a direct swap replacement. With a good fail safe.... thanks.

Comment by John Stuart on May 14, 2012 at 6:13am

Hi Mike, no what I meant was the APM-based failsafe. This is independent of the receiver failsafe, if the APM ceases to receive transmitter input it activates either RTL or 'continue with mission', depending on how you configure it. You could also configure it to do nothing.

Sorry about your crash by the way, hope you get it flying again soon.

Comment by Richard on May 14, 2012 at 6:16am

great write up, It probably isn't a huge help, but i had a plastic servo strip on my skywaker elevator, I now use only Metal gear servos on the elevator.

Comment by Mike Thorlin on May 14, 2012 at 7:34am

John,

My understanding of fail-safe in the APM context is that the APM has to  detect no RX input before failsafe kicks in.  The problem is that the Turnigy RX will continue to send a valid PPM signal to the APM after it has lost TX input.  It just continues to send the last known "good" command.  That command might be nothing (neutral position for all sticks/switches)  or it might be extreme positions (full throt, full up elev, full left ail, full left rud...whatever).  The APM has no way of knowing that the RX is no longer receiving a signal and is just sending what it was last given before signal loss.

Either way, your point was a good one, I'm sending off for a new module with a reliable fail safe.

Comment by Mike Thorlin on May 14, 2012 at 7:35am

Richard,

I'm going to look at metal gear servos on the next build.  The servos in place now are all plastic, but I'd have to split the fuse to get them swapped out.  Next time. Thanks for the advice.

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