Topic: Loss of radio control

I have  a MiraJ, FG Fuz, CF skinned wings. I've flown it for about 6 months with an FrSky module and 7 channel Rx without problems. Because the fuselage servos are mounted on a sheet of CF reinforced ply and the wing is CF skinned, I installed the Rx with the whiskers external mounted. One left to right on top of the fuz, in front of the wing and one fore to aft below the wing.

I completely lost control at 200 ftish, no response at all.

Here's my story...

Twas a miracle the way it came done. I'd set failsafe to full crow and some left rudder and it respond that way! It was heading away when control failed  and then a gentle descent in a sweeping left arc. I thought it was going into the huge forrest to the left but it arrived at the top of the slope 2-300 yards away almost in a gentle fashion.

But what caused loss of contact/control? That's the nasty bit. The Tx was switched off when I got to the model some 3 or 4 hundred yards away.

Did I turn it off en route or whilst I was flying it? I was holding the Tx much closer than usual and my fingers were cold and clumsy. I was trying to shelter them behind the Tx. Never had a glitch before with this set up.
I'll swap the Rx for another and put this one in a wing.

It had a newly charged 4 X AA Eneloop pack in it. It had sat in the cold on the ground for 30 minutes before I flew it. The battery checked still showed full green even when I waggled all the sticks at the crash site.


Well what should I do before I head to the slopes with it again?

I've given it a thorough range check with the Rx 6-10 inches above the ground and all was fine up to 38 paces.

I'm checking all the obvious stuff like broken wires and so on. But what next??

Any suggestions?

Thanks Guy

Firstly..get a transmitter muff.. Well worth the money..ask me how I know? Failsafe works though.  ...How cold was it? I suppose it could kill the battery if it was minus twelvty where you were stood, and got down to minus a hundred and eleventy at altitude? I try to keep batteries warm before using-unless of course they're already in the model. If everything else checks out, I don't know what else to suggest, unless it got blinded by the CF? 

Eneloop technology is supposed to work down to -10 and I believe that Eneloop v2 works down to -20. I use Eneloops a lot and find that at low temperatures the drain is much lower than standard Nimh's. We tried an experiment charging them up to roughly 94% and then left them unused in the back of the car where the night temps were around 1-3 deg. After a week we retested and they had dropped by around 5% that was all. I was quite surprised by that - I expected it to plummet.

It couldn't have been the RX battery if the failsafe worked. Looks to me it was the Tx switched off that caused the loss of control.

 Tom

It was 1 or 2 degrees C and the pack was charged warm and put in the warm car and left sitting on the slope for 30 minutes or so before the flight, which lasted 15 minutes or so before the problem.

I wish it was as simple as turning the Tx off but I have never done such a thing in twenty plus years. There is always a first time I suppose.

It would be nice to have a mental check list when ones model is free flighting but of course I didn't check if the Tx was on or off and was so flustered am not sure when or if I turned the Tx off on the long trudge to the model.

I'll swap the Rx. The flight pack seems fine but my knees will be knocking the next time I chuck it off. It will be all fixed up by tomorrow.

I have a Tx muff but can't find it! My digits have never been as cold as I'm finding it this year. Creeping old age and circulation maybe. Another search is in order.

If it was the battery the RX couldn't have told the servos to go to the failsafe positions. In order to failsafe the Rx has to still be working, but not recieiving a viable signal.
The problem has to be loss of signal or interference.

Tom

Any chance you could have launched it in range check mode? That would have the effect you describe - going out of range at about 200ft (60paces).

As it landed 2-300 yards away it may not have been back within range during the freeflight section of the flight. I know what you mean about not knowing whether or not you switched off the Tx. I had a range problem last time I flew off water, and could not remember whether or not I had extended the aerial. Might well have done and retracted it before collecting the model with the "row of shame" dinghy.

Jef

Too late now, but its worth remembering to take a look at the receiver LEDs before switching off.
I assume you cycled the rx power cos you mentioned a green on the tester as you waggled the sticks.
Or did the model burst into life as you approached with the tx?
Module failures tend to be permanent fails, so if your module works now, I'd say its fine, thats not the problem.  Once it went into failsafe did it remain there without the slightest blip of 'normal' servo neutrals?   If it was circling on a bit of rudder there would certainly have been a point at which the antennas were optimally aligned, and Frsky re-lock time is one of the quickest by far.  Frsky is happy at low voltages too, many of us run them from a single lipo cell, so I dont suspect the rx battery, and you can see from the display that the tx battery is ok. No sign of a return from failsafe whilst the model circles means a complete loss of signal - my guess would be that you either switched the tx off or launched in range check mode as suggested above, and that your module, receiver & batteries are fine. Rebuilding confidence with a foamy is a good plan 
Cheers
Phil

I had cut the range button on the Rx flush with the housing, so putting the Rx into range check mode is most unlikely. I actually need a match or similar to press the button.

The plane was heading away from me at 2-300 ft when control was lost. It seemed a long time before the rudder started to turn it and I don't recall it ballooning as crow was activated but I was in a slight state of panic! It kept turning left slowly. I'd set about half rudder and rudder is not to effective on a V tail plane. It landed majestically at the top of the slope several hundred yards away. If the land had been flat it would have been a greaser but it was sloping so the plane came to an abrupt halt on soft soil. It really does show the amazing value of fail safe. Not everyone uses it but if not the controls would sit at last command with loss of signal - definitely not a good thing.

I'm just about convinced I turned the Tx off but I'll never know for sure unless the same thing happens again.

The weather has warmed up today but it was just above freezing on Monday and I left the model and Tx, switched on, in the garden for an hour. Every worked fine after an hour but I realize the was no in flight wind chill effect. I don't suspect the battery.

I had cut the range button on the Rx (sic) flush with the housing, so putting the Rx into range check mode is most unlikely. I actually need a match or similar to press the button.

I think what was meant was that maybe you'd done a range check, then left the module in that mode Marcellus      But had it been caused by low tx power, I would expect at least a few brief relinks as the model moved around, rather than a complete permanent loss of link.  Hard as it seems to accept, I think its likely the switch was the culprit in this case!  Re the landing, would you mind picking me some lottery numbers please?   
Cheers
Phil

Tend to agree with phil, does sound like you some how managed to switch off the tranny, only done it once myself accidently that was back in the sixtys flying with my kraft set in a vertigo, transmitters often had a toggle switch in them days so was a lot easier to accidently switch off, not arf made a dent in the concrete at Ashbourne,
As a matter of interest i did an experiment to see just how far you can get in the air in range check mode, this was on a day i was at the patch on my own and i knew i could quickly switch the transmitter off and back on and regain control and it was in an old flying wing that i use for testing purposes, failsafe kicked in at around 100 yards, a quick tx power cycle immediately restored control.

I did the same thing, see this post from almost 2 years ago:
[LINK]

Phil my test was about a year ago, i remember reading your post from around two years ago i have a feeling your test was with an early module before frsky considerably reduced the range check power output, i remember one of the first transmitters i converted that would be about two years ago long since sold on, the ground range check was silly really two hundred yards and still going so i wasn't surprised when they reduced the range check power output, these days i think it's one hundreth of the normal output.

I had cut the range button on the Rx flush with the housing, so putting the Rx into range check mode is most unlikely. I actually need a match or similar to press the button.

Not wishing to sound offensive in any way, but I thought the Tx module button was pressed to enter range check mode (not the rx)? On the latest ones, I am pretty sure the rx button is purely for binding and adjusting the failsafe settings.

Jef

Not wishing to sound offensive in any way, but I thought the Tx module button was pressed to enter range check mode (not the rx)? On the latest ones, I am pretty sure the rx button is purely for binding and adjusting the failsafe settings.

Jef

I know Marcellus, and also without meaning to be offensive I expect he meant to say Tx in the first place 

Actually I can quite easily imagine the tx slide power switch being only half pushed by frozen fingers and clicking back to off halfway through the flight. They sometimes aren't even proper switches, just a few strips of copper and a clever plastic moulding.

I know Marcellus, and also without meaning to be offensive I expect he meant to say Tx in the first place 

Actually I can quite easily imagine the tx slide power switch being only half pushed by frozen fingers and clicking back to off halfway through the flight. They sometimes aren't even proper switches, just a few strips of copper and a clever plastic moulding.

i would think thats 99.999999999999 percent certain, after all r and t are next to each other on the key board.

Not wishing to sound offensive in any way, but I thought the Tx module button was pressed to enter range check mode (not the rx)? On the latest ones, I am pretty sure the rx button is purely for binding and adjusting the failsafe settings.

Jef

Yup Tx button...Not offensive at all.....

I wrote a long missive earlier but it seems to have vanished.

Summary:

Re made wiring loom after Mpx wing side connector was damaged in arrival.

One wing mounted aileron not working. Established servo is OK. Problem is between Mpx connector in the fuselage and Rx or wiring generally.

I will investigate tomorrow and see what I can find!

It's good to find a 'fault' but surely not contributary to total loss of control?

Sherlock...

I've replaced the wing mounted Mpx connector. This was difficult because the wire used in the loom (built by another) was a very stiff Teflon sheaved wire and the builder had done the loom with the minimum of slack.

One aileron refused to work. Again complicated by the fact that it was hard wired to the loom. I cut it free and hey presto it works fine, wired direct into the Rx.

I checked continuity across the loom right back to the Rx and it shows zero Ohms, as it should.

The Rx is outputting 5.33 volts to the servo at the receiver. At the servo end this has decayed to only 0.33 volts. I changed the Rx and all the results are the same. What could cause this? Is it shorting in the loom?

I have decided to redo the loom from scratch.

What wire size would you recommend? I want it as small a diameter as possible as things are crampted. I'd prefer a soft sheaving as the loom has to turn at right angles as it enters the wing. Where can I buy it?

I don't know whether one servo going duff  (or at least the loom to it) would pull the volts down through shorting to give me loss of control and why this would suddenly happen in the air.

I'm sorry to bore you with all my problems!

Guy

I've replaced the wing mounted Mpx connector. This was difficult because the wire used in the loom (built by another) was a very stiff Teflon sheaved wire and the builder had done the loom with the minimum of slack.

One aileron refused to work. Again complicated by the fact that it was hard wired to the loom. I cut it free and hey presto it works fine, wired direct into the Rx.

I checked continuity across the loom right back to the Rx and it shows zero Ohms, as it should.

The Rx is outputting 5.33 volts to the servo at the receiver. At the servo end this has decayed to only 0.33 volts. I changed the Rx and all the results are the same. What could cause this? Is it shorting in the loom?

I have decided to redo the loom from scratch.

What wire size would you recommend? I want it as small a diameter as possible as things are crampted. I'd prefer a soft sheaving as the loom has to turn at right angles as it enters the wing. Where can I buy it?

I don't know whether one servo going duff  (or at least the loom to it) would pull the volts down through shorting to give me loss of control and why this would suddenly happen in the air.

I'm sorry to bore you with all my problems!

There's a 'servo wire' thread going on somewhere, with links on.

Did you check the continuity to all the other wires on the connector to make sure it wasn't shorting to them, even when waggled?

I hadn't but the wires are encased with heat shink and daylight can be seen between the pins. I

BUT I looked though a magnifying glass and I can see the insulation on two or more wires has been scuffed by the razor sharp CF wing skin, exposing the wires. There is potential for shorts there for sure. A new loom is called for!

I can't find the link you referred to!

I can't find the link you referred to!

http://www.rcmf.co.uk/4um/index.php/topic,88072.msg1017492.html

I hadn't but the wires are encased with heat shink and daylight can be seen between the pins. I

BUT I looked though a magnifying glass and I can see the insulation on two or more wires has been scuffed by the razor sharp CF wing skin, exposing the wires. There is potential for shorts there for sure. A new loom is called for!

I can't find the link you referred to!

Also, carbon fibre is conductive in it's own right, so things really need protecting. I'll be potting the MPX Greenies in epoxy and covering them in heatshrink when I build my Sunbird.
 

Thanks Paul,

I tested things again. As before the continuity over the 3 wires was fine. A:A B:B C:C

By jiggling things about I had a flicker of continuity of A:B but could not repeat it to order. I am now certain I have a short somewhere. The edges of the hole in which the connector sits are razor sharp CF. They have chaffed the insulation on the cables.

I had a harsh landing at Frocester, breaking the front wing bolt, allowing the wing to swivel and breaking some of the plastic body of the connector a bit. It all went together OK and worked. I didn't realise the wires behind the connector were chaffed.

I've ordered some cable and will rewire it all and pot the connector in the wing with silicone, so it can't move.

What I don't understand is if I had a short, why did the plane flew fine for 15 minutes at Selsley two days later, before control was lost. It went off with a fully charged pack.

What I don't understand is if I had a short, why did the plane flew fine for 15 minutes at Selsley two days later, before control was lost. It went off with a fully charged pack.

Intermittent short circuits are like that - no connection at all for ages, then you pull a fast turn at just the right (wrong?) angle and there you are, gone. There's enough current available in most rx batteries these days to temporarily spot weld them too, so once they're connected they could stay connected until something physically knocks them apart.

Can't think why there would be an impact though 

 

The Rx is outputting 5.33 volts to the servo at the receiver. At the servo end this has decayed to only 0.33 volts. I changed the Rx and all the results are the same. What could cause this? Is it shorting in the loom?


Guy

If the voltage has decayed without having a load on the servo end, there must be a high resistance (almost open) connection somewhere in between.  Try measuring the voltage drop with a load on it, (maybe a small indicator lamp). If there is a high resistance in the line, the lamp will drop the voltage substantially, may not even light.

I'm awaiting some wire to make a new loom.

The voltage decay suggests a short and I can see exposed wires where the insulation has been chaffed with a magnifying glass. I've not removed the wires from the wing to see the extent of possible shorting because I want to use the old wires as a pull through for the new wiring. The razor sharp CF in the wing caused the chaffing and cut my fingure whilst fiddling!

I'm not an electrical person! If the voltage decays from 5.33 volts to 0.3 volts along the wiring to one wing mounted servo, can It be possible  that the overall voltage available to the receiver might have decayed to less than 3 ish volts and explain my loss of control? Did the volts 'hang on' for the 15 minutes the flight was OK and eventually drop to around 3 volts? (FrSky say things will be OK down to about 3.2 V)

When I got to the plane the servo in question had been physically diconnected and all worked well with the other servos and Rx, Perhaps the voltage had been restored to the Rx by disconnection of the servo with the short in it's wiring. But then why did the failsafe work? Perhaps it didn't and it just drifted down wind. I think it worked. The plane flies straight and true hands off and does not drift in an arc!

If you can read my mind - I want to know why I 'lost control'!

If you can read my mind - I want to know why I 'lost control'!

Well, unless something very odd has happened to your wires, the drop won't be gradual along them, it will be across some high resistance bit, which could be a bad joint but is far more likely to be something inside the servo or the rx.

Switches and dead shorts usually take the voltage to zero rather than 0.33.

it could be a poor connection on the servo wire for the voltage drop, it could still meter ok but under load breaking down, get that alot at work.
If it was a shorting out it could of "crashed" the rx with the spikes it could have caused, turning the rx off and then back on again would have reset it.

I've ordered some cable and will rewire it all and pot the connector in the wing with silicone, so it can't move.

Guy, if you're going to use silicone, just make sure it isn't the normal type used for sealing baths etc. This contains acetic acid which is corrosive. For electrical stuff, always use a non-corrosive silicone such as Dow Corning 744, as used on all the best F1 cars  . You can get it on-line from Farnell.

Gordon,

Will the fish tank stuff do the trick? It doesn't honk of acetic acid like some.

Guy

Gordon,

Will the fish tank stuff do the trick? It doesn't honk of acetic acid like some.

Guy

I honestly don't know! The only time I used the fish tank stuff was for making control surface hinges. All I know is that Dow Corning 744 is specifically designed for electrical purposes. We used to use it to support wires that were soldered to PCBs, and I recently used some to support the soldered joints on the flight pack of my Ascot. Maybe you could see if there is a manufacturer's spec for the stuff you are using online.

Well, unless something very odd has happened to your wires, the drop won't be gradual along them, it will be across some high resistance bit, which could be a bad joint but is far more likely to be something inside the servo or the rx.

Switches and dead shorts usually take the voltage to zero rather than 0.33.

The whole thing is a bit grey! I get the 5+ volts out put at the Rx and .3 volts at the servo end of the loom, without the servo being attached, so there is almost certainly a short or an 'almost complete break' in the loom.

I ordered the new servo wire on Thursday night from Als and it arrived on Saturday - Xmas Eve. Well done Al and Royal Mail.

However Xmas has got in the way of doing anything such as fiddling with a model.  I'll pull through the new wire with the old and may be able to see what went wrong with the old and keep my fingers crossed that somehow it contributed to my loss of control problem.

I know how the loom got chaffed and know how to avoid it happening again. What I don't know is if this is a red herring and my 'big problem' lies elsewhere!

The whole thing is a bit grey! I get the 5+ volts out put at the Rx and .3 volts at the servo end of the loom, without the servo being attached, so there is almost certainly a short or an 'almost complete break' in the loom.

That just doesn't feel 'right' for a wiring problem - without any components attached you should either get exactly the same at both ends, or nothing, or intermittent. IT would be really really unusual to get a steady 0.3V. Have you tried measuring the resistance with the wires disconnected from the rx as well as the servo, for continuity in a single wire and for shorts between them?

Replacing the wires definitely sounds like a good idea. I guess if you were actually trying to read a single servo PPM signal wire it might give 0.3V on a DC range?

That just doesn't feel 'right' for a wiring problem - without any components attached you should either get exactly the same at both ends, or nothing, or intermittent. IT would be really really unusual to get a steady 0.3V. Have you tried measuring the resistance with the wires disconnected from the rx as well as the servo, for continuity in a single wire and for shorts between them?

Replacing the wires definitely sounds like a good idea. I guess if you were actually trying to read a single servo PPM signal wire it might give 0.3V on a DC range?

That is exactly what I am thinking too.

 Tom

Yup, as I said GREY!

The continuity across each of the three wires is fine i.e. A:A B:B C:C but twice I managed to get the same accross two wires i.e. A:B suggesting a short.

I can sort the wiring out, no problem and I'll check every inch from Rx to servo but the big BUT is did this or how did this give me complete loss of control?

Rather like how long is a piece of string I suppose!

Yup, as I said GREY!

The continuity across each of the three wires is fine i.e. A:A B:B C:C but twice I managed to get the same accross two wires i.e. A:B suggesting a short.

I can sort the wiring out, no problem and I'll check every inch from Rx to servo but the big BUT is did this or how did this give me complete loss of control?

Rather like how long is a piece of string I suppose!

The centre wire carries a coded positive voltage. If you check across that and the negative wire, you could get a reading and it would be a lot less than the voltage across the two outside wires.


   Tom

The cetre wire carries a coded positive voltage. If you check across that and the negative wire, you could get a reading and it would be a lot less than the voltage across the two outside wires.

Having a PPM signal shorting to the ground could screw up everything, as the ground is paralleled to every servo via the receiver.

I had something similar with my Audi when I bought it - the power connector to the ABS control unit was broken so it was drawing it's power from the data bus. This caused the data read by the central CPU (which is in the dashboard) from each unit to be corrupted. It was reporting faults in the gearbox, the oil, the rev sensor, fuel, all sorts.

£100 for a remanufactured ABS controller later and it's been perfect. Audi wanted to 'try' a £1200 switch inside the gearbox 'to see if it sorted it out'...

The centre wire carries a coded positive voltage. If you check across that and the negative wire, you could get a reading and it would be a lot less than the voltage across the two outside wires.

The centre wire is battery positive and with the meter should read full battery volts between neg and centre.
Reading the signal lead (furthest from the neg) with a digital meter (which is carrying a very low duty cycle pwm pulse) may or may not indicate anything, depending on the sampling method of the meter. An old fashioned analogue meter would show a voltage which varies linearly with the stick position between 0.25 and 0.5v

Having a PPM signal shorting to the ground could screw up everything, as the ground is paralleled to every servo via the receiver.

Disagree Yoyo for that very reason  -  neg is the reference for everything in the model and it matters not a jot what absolute floating voltage its at, a typical port I/O self limits to 25ma or so which will have no effect at all on a rx battery or ESC power source, it wouldnt pull the supply down (or neg up, its all relative). The processor port pin may or may not survive an extended period of shorting to deck, but is extremely unlikely to blow anything more than that one I/O bit. The rest would carry on regardless. In this case the rx still performs ok so there was no port damage.  Being picky, there is no PPM coming out of the rx unless its a heli cppm setup, I take that as just a typo 
Cheers
Phil

The centre wire is battery positive and with the meter should read full battery volts between neg and centre.
Reading the signal lead (furthest from the neg) with a digital meter (which is carrying a very low duty cycle pwm pulse) may or may not indicate anything, depending on the sampling method of the meter. An old fashioned analogue meter would show a voltage which varies linearly with the stick position between 0.25 and 0.5v
Cheers
Phil

You are right of course, positive is always the centre pin. I don't know what I was thinking of. must have had too much Christmas spirit

  Tom