What The? Catastrophic failure under Spektrum DX9 Control
 

First and foremost, I want to emphasize this is NOT to bash Spektrum in any way. In fact, I am a true advocate of Spektrum systems, as I have been flying them since I got into 2.4ghz 5 years ago. Started with the DX6i, then DX7, now DX9, all with AR7000 DSM2/AR7010DSMX receivers. I have never had an issue until now, and since the crash was severe, I have no way of telling what actually happened. So I am reaching out to you, my fellow pilots, to see if anyone has experienced something similar, maybe you could shed some light on it.


The plane is a typical wood built up plane, no carbon fiber parts or anything. Gas, DLE55. IGNIT master switch way up front, with an electronic cutoff. RX and smoke switches in back by the turtle deck. Spektrum AR7000 DSM2 RX. 6v RX battery, brand new. I fly 3D, and quite aggressively, so all of my planes are the same--absolutely NOTHING is allowed to move, swing, etc. Everything is securely strapped in, tied down, safety clips on ALL connections, all that. When I first started flying the plane after I finished it, I was using the DX7. Flew beautifully for the entire time, about 7 flights. Not even a hiccup or burp. Got a brand new DX9. Binded the TX to the AR7000 no problems. Went through the TX thoroughly, made sure everything was good. Now the engine being new, I still had to break it in, so I wasn't doing any wild maneuvers, just normal easy circuits, circles, figure 8s. Never had a hard landing.

With the DX9, the first flight was routine, nothing stuck out, no anomalies. Plane flew beautifully. Landed, no problems, greased. On the second flight, when I turned on the TX, then turned on the RX, I noticed that I had no response from the aircraft. No blinking lights on the RX or satellite, just no response. I figured maybe I just was too close, or something. So I shut everything down. Turn on the TX, held it as far away as my arm could reach, then turned on the RX. I had response then. It seemed odd, but I chalked it up as a hiccup. To be safe, I did range checks, one with the engine off, the other with the engine running. Everything seemed good. So I took off, just doing normal circuits, no tricks. About two minutes into the flight, I was making a lazy wide bank, and the engine died, and I suddenly had no control. It appeared to have gone into failsafe. The plane nosedived to the ground, totalled. All my leads pulled clean from the RX, due to the force of the crash (hit a tree before the ground).

The only other anomoly, is that there was a guy in a truck with a CB radio setup. I don't know if he caused an interruption (seems highly unlikely). For the last 5 years at the same field, guys pull in and do the CB thing all the time. The only difference is that this time, he was in the pilots' parking lot which is right behind the pits. Usually the CB guys are in the main FPD parking lot, alot further away. There were two other guys there flying as well, and they were not affected.

My fellow club members swear that something became disconnected. I don't see how given that everything was clipped. The only time I've had a problem with reception is ONCE when I had an RX battery go bad, and I moved the control surfaces to extremes. But the RX reconnected after a few seconds, and I still had control of the plane. That battery, when I charged it, would shoot up to high voltages immediately and would not hold a charge very long at all. Nothing like when I checked this battery. That seems to be the only explanation though. I checked the battery, and it was still registering 6+ volts under load, and it discharges/charges normally. So not a bad battery pack. I checked the RX on all channels, no jitters, just normal operation.

I'm wondering if there is a problem with the DX9 communicating with the RX? The TX has never been dropped or anything, I just got it Wednesday. I had the DX9 in DSM2 mode.

I know it's probably impossible to find out exactly what happened, but, anyone else experience failure like this with this setup?

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If the failsafe and trim was setup properly, the model should not have nosed over into the ground. Beyond that, I don't have enough info to even hazard a guess.
Back when I was using a DX-8, I had a couple of almost disastrous flights. The curious thing about them was that partial control was still sort of present, and allowed
recovery with no or minimal damage. In both cases, the ESC's built in BEC was providing power to the RX and Servos. Adding external BECs with 5A continuous
current capability seemed to solve the problems. They did not occur again! We could not see how partial control should have been available. You would thing that all or nothing
would be the case. (From the spec sheets, anyway!) One of the models did have a 7000 RX.

The failsafe was setup properly, i'd tested it before taking off. Thats why the plane nosed over. If the plane is in a turn, and the engine shut off and theres no rx control, thered be no way to maintain air speed or level the plane so there would be notthing for the plane do BUT nose over.

And remember, this is a gas plane, not electric, so theres no esc or bec in the equation. that is one luxury of electrics that you dont have with a gas plane. If you lose your rx, your engine goes to idle or quits depending on how you have failsafe set up. Either way, unless it reconnects, you have no way to control the plane.

Doubt its a CB, unless the guy is into jammers. Switch problem? If it went to failsafe, either the transmitter or the receiver rebooted. If power turned off then back on it might not locked back.

If you set your fail safe to idle, that means it was the electronic ignition switch that cut off power to the ignition and that means that it was a loss of power to the receiver rather than a loss of signal. The most likely reason is the flight switch unless dual switches were involved. If the Rx was powered by a single battery source wire, it could have pulled out. Redundant switches and taking power to the RX via two different connectors is prudent. There has been a move toward one battery but many if not most who make that move, still do two switches and supply the RX at both the battery port and one of the servo ports. Even if every channel is used, a Y can be used to import voltage from the second switch..

These things are impossible to track down on a forum without more data/clues.
There are several possibilities and possibly a combination of events. This kind of thing can happen way too often in something with higher than average servo load and tons of vibration. Helis or 3D planes. First most common is remote connector cables. You said it was Stubborn to Connect and then it Connected fine.That may be a clue.A big clue. Rx must have a remote to connect. If the cable connection is marginal it might be stubborn but finally connect.
Then normally if you get a momentary brownout or even a forced reboot from static or even possibly vibration and the cable is also in a marginal state it may refuse to reboot quickly if at all.
The remote cable may be marignal on the ground but in the air with high vibration it may not be working at all and your running on the main Rx alone without even knowing until the one Rx is shadowed and you go into Hold.
A couple questions though.
You said the AR7000 was new. Recently purchased new? Or been sitting around new? They have been out of production for awhile.We know it had a hard crash. If nothing else I would send it in to HH service and have them check it out.
How are you mounting your Rxs? Are you taking reasonable steps to isolate them from vibration?
Do you take extra care of your remote connector cables? I silicone or plasti dip where the wires go into the connectors.Not the socket but just where the wires go into the connector that plugs into the Rx. Tie them down to the fuse so they cant flop back and forth with g-loading. If you dont do that I found with 3D helis they are going to fail at some point likely sooner than later.

And the big one. Run telemetry. Log the data. Your radio is capable. Make use of it. I mostly run it on everything now. Set an alarm for low Rx voltage and 1 Hold on FL data. If a problem is developing you get warning before catastrophic failure. If you have a remote problem inflight you will generally get a momentary Hold with no noticable control loss long before you get in a place where you might get an extended Hold. Monitoring and graphing Rx voltage at the Rx(where its needed) will give a good idea of the heath of the whole power delivery system. Battery,switch,leads,connectors,reg/bec,smartfly/external bus,etc. There are alot of potential points of failure.Ive found that most components dont simply fail out of the blue.Ive seen Rxs just quit but the few I have seen were tied down tight straight to the fuse without foam or anything to isolate vibes.Sometimes it can be a combination of things. Problems generally develop until theres a failure. Like temperature. Motors dont just fry instantly.If you lean out for some reason (or you just miss your tuning) you generally dont know its going nuclear until it quits and likely the damage is done. If you monitor critical parameters and set limit alarms you can land before a failure. Without it your just fat and happy until something quits.
If you have those parameters logged in a file then many times a quick look at the graph and you can see exactly what happened with little guesswork if there a major failure. In demanding setups I cant see not using it both as a setup tool and a way to just keep tabs on the health of everything over time.
Without it everything is basically a huge guess.

You all bring up good points and ask great questions. I know that it is near impossible to find out what happened. I am ruling out a power failure mostly because of the first time there was no response when I powered up for the second flight. That never happened with the DX7. And again, after I powered down and started over, everything seemed normal, even after a second range check. The battery was brand new and it charged normally, and still does. All of my leads were safety clipped, even after the crash. The AR7000 was not new, I meant the battery was. The satellite RX was securely plugged into the main RX, and the lead, like all the other leads, was run thru conduit that was then secured to the fuse to restrict movement. The 7000 was checked at the "factory" before it was put in the plane, and has already been sent in to be checked since the crash. All my receivers are mounted wrapped in foam, then velcroed down, and finally strapped over securely so they cannot move, but are quite dampened from vibration. I make sure any leads that are connected to the ignition or ignition battery are well away from RX leads. I too use a spot of silicone on my connectors (cool that someone else mentioned this!).Trust me, because of the way I fly, I am very familiar with plane setups. This is the first time something like this has ever happened to me in my 20+ years of flying.

I really do appreciate all the feedback, especially about telemetry which is something I've been wanting to get into, but am even more so compelled to do now. Again, I know that trying to find out what happened is virtually impossible. Really, I was just wondering if anyone else had reception or binding issues with the DX9 and older RX's. I know they say it's supposed to work, but the DX9 being still relatively new, I wanted to see if it has happened to anyone else and what they experienced, tried, found out (if anything).

The only other thing that I am wondering is if my understanding of failsafe is wrong. As far as I know, when I set failsafe up, I have it set to kill the engine. The last thing I want if a plane gets away is for the prop to be spinning if it hits someone. From AA5's explanation, it sounds like if signal is lost, then the engine would keep running regardless of cutoff switch setting for failsafe. But if there is loss of power to the RX, then the engine would cut. Tech support explained it differently, more along the lines that I know. I will be testing this when it warms up again. BUT, if anyone else has any experience with this kind of situation, I would love to hear what you found out.

Once again I really do appreciate all the feedback and advice, Thanks y'all!

Thanks for clarifying the fail safe setting. That it was set to kill the engine, rules out determining that voltage was lost due to the engine dying. The engine then could have died do to fail safe (loss of signal) or loss of RX power.

I've read many others say they set fail safe to kill the engine, but I favor an idle setting for the reason that if signal is lost and then regained, the engine is still running to bring the plane back. For the same reason, I don't set a fail safe condition on the electronic ignition switch. Of course, if power is lost to the RX, the electronic ignition switch will kill the engine but for loss of signal, it will only kill if fail safe is set to do so. Again, I favor letting throttle fail safe handle the chore of taking the engine to idle to await a hopeful return of signal.

It might be that during the early days of 2.4 when a reboot sometimes took several seconds after a loss of signal, that killing the engine on loss of signal was prudent... but rebooting is instant now for many if not most receivers and having the engine still running seems more reasonable.

Last, you didn't say if you were using dual switches but if only one was being used, the failure to fire up you described might have been a precursor of a switch failure and many switch failures start by becoming balky and not readily evident during the after crash investigation.

I have lost several planes with the DX9 under similar circumstances. ( Plane flying well after multiple flights and suddenly it just loses control and noses over and crashes without ever regaining control). I finally sent it back to Horizon and it came back with a new RF section, new gimbals, and several other internal changes but no explanation. Seemed to work OK for a while then it happened again with same results. I should point out that these were at different locations, different planes, different Rx's, different batteries and switches, ect. 4 were gas and 1 was glow powered. Nothing was common other than the DX-9.

Last near crash (#6) was different. Gas plane with many, many flights (CAP 232 - 30cc) flew one flight with no problem. Second flight of the morning plane became sluggish and erratic in responses. I landed promptly and taxied back to pit area with some difficulty. Sitting in pit with engine idling still I noticed the rudder wiggling back and forth on it's own, then other controls started randomly flopping around with no input from me. Suddenly engine started reving up and down. I tried to shut it down with the optical cut off but had no control. Now I'm chasing this plane around the taxiway and adjacent area trying to grab it with engine and flight controls reving up and down. Finally caught it and shut it down with plane mounted switches. I checked everything on bench with nothing wrong. Then controls again started flopping around with no control at all from the DX9. I later noted that at the time there were two individuals nearby with a very old plane and very old looking transmitter trying to get the plane working. The conversation was the elderly owner had this plane/xmitter in his garage for many years (10 - 15) and younger friend was trying to get him back in the hobby and things working again. they were having trouble getting the servos working and had the thing on and off many times. This was at the same time I was having control trouble. I believe they had an old transmitter with the older banned freq. and jacked up power that was able to interfere and blank out my DX9. I know that 2.4gHz isn't supposed to be victim to interference but coincidence and no other explanation makes me very suspicious. Point is: I wouldn't completely discount the CB user nearby. A lot of these guys have jacked up power boost and pretty wide band transmitters so they can overpower everybody on the road and interference problems may not be as dead as we want to believe.

Just my story and the saga of the DX9 goes on.

hawkerone,
I'm very glad you saved your plane but I must confess I was laughing hard as I envision you trying to catch your plane. I bet you had a though of "this thing has a life of it's own"! I can see it speeding up just as you reached for and then it would let you catch up and it does it's thing all over again! I am very happy you managed to capture this wayward plane. Sorry for all your trouble but very happy you saved your plane!
Leo

I really would have made and entertaining spot on one of the TV shows. Like it had a mind of it's own with me in hot pursuit. I'd just about have it and a quick blip of the throttle and we're off again. Steering inputs at the same time. How we didn't hit someone or something I'll never know. DX9 was locked out with no functions working. Back at bench a few minutes later and everything checked perfectly.

Nothing is going to be bulletproof. I dont see any mention of monitoring your signal performance. With the ability to monitor and track the connection integrity Im still surprised so few take advantage of its merits. Plug and Pray may be ok for small foamies. There is definitely a proliferation of illegal radio equipment being sold right now. There is more of it out there than many realize. It may very well be a contributing factor to problems with certified equip.
Knowing this it only makes sense to me to attempt to mitigate the possibility as best as possible using all the tools that are reasonably available.Telemetry is a powerful tool. Logging the data for later interpretation is a big extension of it.

Very well said. It's ALWAYS a good idea to monitor your equipment, especially when the means to do so has been made so readily available. It has also been said that hindsight is 20/20. Going forward, sure, it's a great idea. But if it hasn't been done up to a point, the only thing that you have to go on is experience, or other similar incidents. Before black boxes, it was the same thing, it was a different type of forensics. And I'm sure even telemetry has its issues. Like you said, nothing is going to be bulletproof.

In example, I found a video of a guy that crashed, and he described the SAME exact thing that happened in my case. He was using a DX9 and an AR8000 RX. The only difference is that in the video, he still had power to his receiver and remotes. His receiver lights were still on. So I can ALMOST 100% rule out that it was a power failure in my case (given how my setup was, and that the same thing happened to him and it wasn't a power issue).

And guess what? I didn't need telemetry to tell me that. For sure now, I'm going to start using it though, because you're right, it's a great tool for narrowing down the issue. But everyone has a point where they learned about something new. There is always a point where someone learns that there is a better way to do something. If one has not gotten to that level yet, there is nothing wrong with doing some good old fashioned investigating. There is nothing wrong with learning.

Just remember the five ways in life to do something. Your way, my way, the right way, the wrong way, and whatever way tradition says to do it...

Yep. Forensics can be tricky. Ive led myself down the wrong path more than once by making assumptions. Remember with DSMX you wont get a reboot indication so just because the orange led is solid after an incident doesnt mean there wasnt a loss of power/reboot scenario involved. About the only way to be anything near definite is to have hard data.Even then it can be tricky to interpret what your seeing. Otherwise its a best guess. Sometimes data only leads you to a more educated guess. Sometimes it makes everything very clear.
Theres definitely always something to learn for me. Some traditional actions will keep you in line.Some others can keep you stuck in the same old rut.Wisdom is knowing when to break with tradition and head down a different path.Always keep an open mind.

Just read through this thread. Regarding interference from an old transmitter, it would be virtually impossible! You can rule that cause out for sure. The frequencies and transmitted protocol are so vastly different that your 2.4 GHz. radio would not know the 72 MHz radio even existed. So in this case, don't blame the FOG's for you problem.