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Failsafe.


john stones 1 - Moderator
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As i just posted, i had one when my rx got soaked in fuel. I also had a 35meg non fail safe rx die in flight once. These are the only radio issues i have had on my own models. 

 

i had 2 rx's click into failsafe when test flying another persons model. It came back and i landed right away in one case, and in the other it came back very shortly before impact and i was just able to minimise the crash. Shielded antenna's were deemed responsible in both cases. 

 

 

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Believe it has happened to me once, completely lost all radio. Setting at the time was to hold last surface position, with closed throttle.

Plane did exactly that, which meant that it performed a gentle barrel roll and into the ground vertically near the pits area, but was repairable. I know it failsafed because the throttle servo closed. The cause was at the time i was using a JR9XII with a plug in FrSky module, which was reasonably regularly removed to plug in other modules. Needless to say upon realizing this, i committed to FrSky and soldered the module guts in, and no probs since.

 

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Never happened to me in my four years of flying but it does happen all to often to others at my club. The pilot usually says 'what happened there' others blame their choice of Tx. I have noticed that the model is often banking, diving or climbing with the top of the model facing the pilot. There is talk of microwave dishes and mobile stations being the cause but it does not happen to everyone, just a select few.  Curios that.

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Happy to hold my hand up to show dumb thumbs and/or poor decision making as the main cause of crashing, but that doesn't stop those instances of genuine equipment failure. I haven't knowingly had a model go into failsafe, other than my Webbit, several years ago,  where I took off with the Frsky module in range check mode, which then rolled in at the edge of the field as it flew out of range - I suppose that might have gone into failsafe, but it hit the deck, with no control before I could tell. That was chalked down to pilot error, I wrongly assumed that the Frsky module came out of range check mode the same as my DX7. It didn't work like that.

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I can’t speak for sites other than I’ve flown at but failsafes are incredibly rare in my experience and I’m struggling to recall any cases other than one club mate using a cheap third party receiver.

In well over 20 years of regular flying with failsafe equipped radios, I’ve only managed one failsafe activation - and that was deliberate, using a reduced range “indoor” receiver with which I flew a small foam model as high and far upwind as possible on a windy day in order to test failsafe behaviour under real life conditions. 

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I've had two instances of failsafe operation. 

A spektrum ar620 lost contact for a fraction of a second then came back on again. This was confirmed via telemetry. Range check showed no problems and it's been fine ever since, no damage to the model. 

The other was a stabilised Lemon receiver in a Hobbyking Skipper, pulling out of a loop the motor cut and I had no control. Fortunately I had set up the failsafe to engage the stabiliser, the receiver pulled the model out of the loop, rolled it upright and by shear good fortune it performed a perfect downwind landing. Subsequent range check meant it was consigned to the bin! 

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I had 2 instances of Rx going into failsafe.  In both cases, I was using a JR DSX9 Tx and SpeKtrum Rx.  MacGregor's comment was to use only JR Rx as they were built to higher standards.  That's what I did after that and then changed to JR's own design with the JR XG11.  I only use JR Rxs with this system, although there are clones on Hobby King, and have never had a moments loss of signal.  So, just 2 events in the last 11 years and both with JR Tx and Spektrum Rx.

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numerous times.

 

I was plagued for a while with a particular FrSky firmware version in quads on the tiny R-XSR Rx - a failsafe is quite apparent on a quad when it disarms itself & falls out of the sky.

 

it's quite noticeable when flying FPV with a horizontal Tx antenna that if you get too far to one side (even within legal FPV range) that since you don't follow the model with your head/body you can get quite end-on to the antenna & go out of range *much* sooner that you would otherwise.

 

we went through a spate of failsafes at the club in certain parts of the field when buddy-box training a couple of robustly-built trainees until we twigged that they were obscuring line-of-sight for the RF.  ?

 

I almost always fly with telemetry & the Tx will audibly alert me when the RSSI is getting marginal, which is more often than you might think.

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I have had a fail-safe occur twice on the same model in 2 separate locations witnessed by other flyers.

 

I had the fail-safe set to shut the throttles (twin motored model) and a faint dive to stop fly away occurring.

 

2nd incident I did regain control but too close to the ground to do any good.

 

The model is a Beaufighter constructed from balsa from a plan.

 

Cause of the fail-safe was traced to the receiver. The antennae connections to the board were secured with a dollop of paint, one had very little paint which had cracked. The supposition of what occurred was that the antenna was making & breaking contact causing on board interference hence the fail-safe occurrence.

 

Replacement of the receiver cured the issue, faulty receiver is now used for setting up and testing in the workshop and is very clearly marked to prevent use at the field.

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I have had three models go into fail safe with varying degrees of recovery and certainty that its was fail safe that operated as the root cause.

 

Firstly my SG Hurricane that Jon was flying which was in a long gentle low bank at some good distance away. It went to idle and Jon announced that he did not have control, then after a second or 2 the engine picked up and control returned. Jon then carried out an immediate landing and we did not fly that model until I mounted an additional satellite receiver in the under wing air scoop. The RX location was quite congested with RX batteries, LED battery, fuel tank, servos and wires all over the bay. 

 

The other was a eFlite Habu that had been flown many times but on this occasion it was very close to raining (fine mist hanging in the air) and with a high pass I decided a half roll and half loop would bring the model back across the flight line. Half roll and quarter loop edf shutdown and no control resulting in a crop field lawn dart. New foam nose and a few battle scares, but flying again. When I searched the web some old posts detailed a number of problems with this RX and TX combination so changed out the RX.

 

Lastly was the the TN Ta154, which had a very congested fuselage with battery, UBEC, ESC's (twin) RX and servos squeezed in. Its was a bit over weight and displayed a vicious tip stall spin and having the "leopard camo colour scheme" was a very hard model to fly in winter skies. It fell out of the sky a few times and was rebuilt, some my fault for slowing up too much when landing and other times seem like loss of control (too slow, loss of one motor, failsafe etc but always inside the perimeter of the flying field). I gave up on the model until I wanted to use the Lemon RX for something else. I made a test rig up with RX battery, RX and a few servos and left them on a bench at the flying field (passed normal range check ok). Then with someone watching the servos I headed down the flying field with the TX on full power and found that the RX would go into fail safe repeatedly.....on the same arc as all of the distant crashes. The crashes could be due to an ESC shutting down however when the rudder was mixed with throttles it produced a horrible yaw effect so my money is on the RX going failsafe airspeed bleeding off and then the tip stall.

 

IMHO these are the leading contenders

  1. Installation
  2. Dumb thumbs
  3. Software/hardware compatibility 

 

 

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My own last personal failsafe was with my Digifleet 35mhz PCM set, I'd been away to a fly-in and had changed the crystals to avoid a clash at the fly-in, came back to the flying field and put my peg on my normal slot, then another modeller switched on (with his peg on his slot) and shot me down. My fault and I was just glad it wasn't me who'd shot him down through me forgetting to swap the crystals back.

 

On 2.4 I have an old Spektrum Dx6i and MPX Royal Pro and Profi, never had a failsafe, and on the Royal Pro/Profi the LQI reading with telemetry receivers rarely drops below 100% and never 80% in the air.

 

Did have a failsafe with a clubmates model, but that was tracked to a faulty RF board on a Futaba DX6e. Have also seen some failsafes on multi-protocol radios, but usually when used with clone receivers on drones with lots of carbon, so hard to pin down the actual cause.

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There seems to be a bit of a pattern emerging with third party receivers. I wonder how many counterfeit receivers might be to blame too?

 

Having used telemetry since 2009 I can be pretty certain that I’ve had no failsafes and have usually taken claims of failsafes causing accidents with a pinch of salt but the cases above seem to be quite credible. 

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I had a failsafe and destroyed a model in 2015. I made sure the receiver, a few flights from new, was known bad, as I jumped up and down on it until I had to sweep the debris up. 
When temper cooled, I often wondered if it was a fake.
I’ve been very cautious about the source of stuff since then.

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Yes, I have had this happen on three or four occasions. The first two were with the same TN 46" Spit fitted with retracts, on DSM2 and 4.8V. A cell failure caused f/s which tried to operate the gear, making things worse. Recovery of the pack a bit then a repeat but luckily the model was almost impossible to stall and just pancaked in. New pack of a similar type and it happened again with no damage. At least 5s NiMh from then on so that a cell loss could be sustained.

Another time was with an o/d Lanc. at a show when three models totally lost contact at the same time due to some sort of interference, all on different radios (JR, Futaba, FrSky). The u/c came down and the throttles closed so with the controls at neutral it slowly spiraled in. Now repaired and flying again.

Only other time was with a 180 powered 72" Spit. which appeared to suffer a total power failure despite twin packs and an electronic switch. Full bore from a great height, still unexplained despite everything in it having been flown again many times.

 

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No it was not, but the thick plottens. Turned out that a new DSX9 Tx, identical to my original, was faulty. I put most of my best models on it but realised eventually that there were problems with signal loss. With freshly charged 2x 5s Eneloops it took off and was turned 180 deg. then up for a stall turn. Throttled back and nothing happened other than to continue vertically then spiral down at full bore. A faulty Tx could explain that but not the fact that everything amongst the wreckage was still plugged in and of course worked fine except that both packs were very hot and only registered a 25% charge, later to recover to 75% as they cooled. No burnt wiring which I was expecting to find due to a none existent short. The switch was an electronic failsafe type. All servos and Rx stripped and closely examined with no faults found and each piece later test flown separately in a hack model.

If the Tx was to blame then it should have gone failsafe but did not, so I am at a loss as to knowing the cause.

I think that this is relative to the thread because it just goes to show that when things go wrong you cannot rely on failsafe operating.

 

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24 minutes ago, Martin McIntosh said:

No it was not, but the thick plottens. Turned out that a new DSX9 Tx, identical to my original, was faulty. I put most of my best models on it but realised eventually that there were problems with signal loss. With freshly charged 2x 5s Eneloops it took off and was turned 180 deg. then up for a stall turn. Throttled back and nothing happened other than to continue vertically then spiral down at full bore. A faulty Tx could explain that but not the fact that everything amongst the wreckage was still plugged in and of course worked fine except that both packs were very hot and only registered a 25% charge, later to recover to 75% as they cooled. No burnt wiring which I was expecting to find due to a none existent short. The switch was an electronic failsafe type. All servos and Rx stripped and closely examined with no faults found and each piece later test flown separately in a hack model.

If the Tx was to blame then it should have gone failsafe but did not, so I am at a loss as to knowing the cause.

I think that this is relative to the thread because it just goes to show that when things go wrong you cannot rely on failsafe operating.

 

Depends on what was faulty in the transmitter. The failsafe operates when signal is lost, if the transmitter is putting out a strong signal, but the output data does not match the input data (what your thumbs are doing) the receiver will simply assume that you want the model to dive headlong into the ground and the failsafe will not operate!

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