A mysterious incident

[Tim Mackey]

Ive had a few "mishaps" over the years Ive been flying Spektrum, but in all cases bar one ( The Sopwith camel ) an explanation was found.

Tonight I had another mystery one.

My favourite Ripmax Spitfire has hit the deck hard and fast, and needs some severe rebuilding of the entire front end. She has had many many trouble free flights on her AR500 and powertrain, and after binding her to my newly acquired DX8 last week, she was range checked, and has flown 7 times since, including some fairly long sessions up the Orme on Sunday, where she covered some huge distances.....all without a hint of trouble.

Today, I took 5 models to the field, 4 of which have just been bound and were due to get their first flights on the new Tx. Spitty went up first, and I enjoyed, as usual, a lovely 11 minute flight. The other 4 models were then "maidened" on the new Tx, and after trimming, all returned safely. I was happy.

As the evening progressed, the wind dropped right off and I decided to have another flight with the Spit. A freshly charged battery was fitted, and away she went to defend the nation against a sinking sun. All was fine, and I was enjoying my usual huge scale loops etc, when suddenly, around 5 minutes into the flight, and at a good old distance and height, she dived, and turned slightly...and I had NO CONTROL. It was obvious that she was heading straight down to the deck in a neighbouring field, so I closed the throttle ( due to the distance, I have no idea whether the motor was turning at that point )

I shut off the tx, and began the long walk across three fields to recover the remains.

I shall try to check whatever I can tomorrow, but at the moment, I am left bewildered as to what happened, and of course, more than a little unhappy, and more worryingly - somewhat unsure as to the reliabilty of my radio link.

Im off to bed now to sleep on it, and will investigate tomorrow.

Bah

[NigelH]

Does your chosen failsafe mode give any clues ?

 

I've been thinking that neither of the two options are particularly good. For example, why would you want to have Hold Last Command ? Banking and yanking, pulling a loop, etc, etc. I can'y see how holding any of those could be good

 

[Wiltshire Flyer]

Sorry to hear that Tim, from what i have read about Spektrum radios and glitches and software errors etc i have to say i have been put off them all together.

 

I know all TX's are not immune from issues but it seems Spektrum are the brand that seem to be discussed here with "issues" quite alot, i won't be buying a Spekky!

 

Hope you get to the bottom of it and that the spitty rises again mate

[Peter Jenkins]

Tim,

 

I had the self same experience with an AR 500 in my trainer that I was using to give a friend a taste of flying RC. I lost the link when I was around 800-900 yds away and luckily the aircraft was high enough to allow the system to re-cycle (or what ever it was doing) and regained control. I therefore brought it in closer and then lost control with the aircraft slowly rolling over and heading earthwards. Nothing I did had any effect and the aircraft crashed some 300 yds away. Having recovered all the bits, I reconnected everything and all the gear worked! I thought that the single Rx AR 500 might have been a bad idea and decided that I wouldn't fly my other AR 500 which is in my Bucker Jungmann.

 

However, two days later, I lost my Wind S 110 when it suddenly pitched nose down and headed earthwards with no sign of control being returned to me. This one had an AR 6200 Rx in it. I should mention that I was using a JR DSX9 Tx on both occasions. I should also say that I have never had a moments loss of link ever in the 2 years that I have been using the JR Tx with Spectrum Rxs.

 

I sent the Rxs back to Spectrum and received a note saying that both had no fault but that Horizon would replace both for my peace of mind. I sent the Tx back to MacGregor and they could find nothing wrong with the Tx but replaced the RF section as a precaution and for my peace of mind.

 

I am about to write back to both to say that my "peace of mind" has been shattered in the light of these two incidents and I would like a definitive statement from both that using a JR DSX9 Tx (which after all uses the Spectrum DSM 2 system) is fully compatible with Spectrum DSM2 Rxs. If that is the case, why was the radio link lost - what failure mode would result in this behaviour.

 

You have now suffered the same fate as me. We really must get to the bottom of this, although in your case you also have the DSM2/DSMX issue to resolve.

 

Be interested to hear your thoughts after you have had a think about what happened and, perhaps, linked up the system and checked its operation.

 

Peter Jenkins

[Ian Jones]

Sounds rather like your visit to the beach last Sunday Tim.

[Biggles' Elder Brother - Moderator]

Really sorry to hear this Tim - as I've said before, its always the ones we love that go in.

 

That feeling when you have no control is awful isn't it? And there is nothing worse than not having confidence in your radio link - it can undermine all your enjoyment of flying.

 

Look on the bright side - you haven't done the post-mortem yet, it might turn out to be something totally unrelated to the radio. This apparent run of very similar sounding incidents is worrying though.

 

BEB

[Hamish]

Disappointed at your loss, however am concerned that you "shut off the tx" and then went to recover model. Is this the correct proceedure?

[Romeo Whisky]

I bought a Spektrum DX7 (DSM2) over 2 years ago, because it was the "tried and tested" system with a huge uptake and userbase in the USA, with apparently universal acclaim. Since then my decision has been vindicated and I have never had so much as a glitch - whether using AR500, AR6011e AR6200, AR600 receivers - and I have several of each in a varied collection of models.

 

Last week I saw a fellow flyer using Futaba 2.4GHz lose a beloved model due to failure to change the model memory after previously flying a different model, and I don't believe anyone who says they have never done that using any system other than the Spektrum which makes this error impossible. So I ask how many disastrous crashes have been avoided by this one unique Spektrum feature alone?

 

The one item I never hear blamed in stories of crashes like this is the Speed Controller. Yet there are some very very cheap ESCs being flown these days and only yesterday I had a dead-stick in a model (thankfully got it down in one piece) and yet everything worked perfectly back on the ground before I disconnected anything. In many models the ESC is not only the power source to the motor, it also the power source to the receiver via the BEC. Yet all (?) ESC's incorporate thermal cut-out and LVC and can fail or over-react. I even have one ESC which appears to work perfectly yet smells strongly of having been burning internally at some point - needless to say, I don't fly it, yet it works fine for bench-testing.

 

I guess there are real issues with the move to DSMX, and I won't be upgrading until they are resolved, but there is just a bit too much unverified flak directed against Spektrum just now. How many models still flying happily today would have met their demise by now had it not been for Spektrum Model-Match, I wonder?

[Allan Bennett]

I'm a Futaba man myself, but doesn't the Spektrum receiver give you an indication of voltage loss or signal loss, presuming that it didn't become disconnected in the crash?

[Lee Smalley]

Oh mate gutted! Anyway your tale does scarily sound just like mine and it's why I never use an ar500 in anything I give 2 hoots about, whilst flying my pride and joy at the time I lost control and my pride dived and turned slightly to the left, my joy was thankfully at a good enough height for link to eventually be re made and I made a safe landing, now I have used many models of spekky rx and all but 500 has been faultless and indeed I have had a 500 in my blizzard at a stupid height that only I could see and my link was fine, that said there are many reports on the net and from club mates that recount almost exactly the same traits, it's not a brown out issue as the light is never flashing, I genuinely believe that the 500 can get it's knickers in a twist and it's takes some time for it to sort itself out, by the time it does however we have normally crashed, I don't know what the answer is but noone at our club uses 500s anymore in anything worth more that 20p

[Lee Smalley]

As for the spekky has more incidents than any other radio, well duh, that because there are more of them out there that any other radio, it's like the old argument that hurricanes shot more enemy aircraft down than the spitfire during the BoB well duh there were more than twice as many of them

[Tim Mackey]

Thanks for your response guys, will do a post mortem after brekky

[Ben B]

It's a good point re the ESC being a possible weak link in the chain, however the BEC output is likely to either work or not (permanently). It's unlikely to temporarily fade low enough to cause a brown out but then subsequently recover fully (when the post mortem is going on). Then again if all the loses were to be occuring in electric planes......? Or have there been incidents like this in IC planes?

 

Ultimately this might just be the downside of the 2.4Ghz system. A bit like analogue vs digital TV, with analogue TV the reception slowly gets worse, with digital it's either great or you get zero reception!?!?! IE my 35Mhz system might occasionally glitch but it rarely completely dies, the 2.4Ghz might glitch much less but when it does, it does it in a big way?!?! Just a thought!

[Chris Bott - Moderator]

That is really worrying to heat Tim, sorry for you loss.

 

Ben it is entirely possible for a voltage regulator in an ESC or in an external BEC to shut down when it gets too hot and to recover when cool, and this could be the case in one electric plane even if all the other losses were to I/C planes or gliders.

It's far too complicated an issue to say everything is down to one cause.

 

I know for sure that this won't be the case with Tim, but I believe that some of the issue with 2.4 is actually because it is so bullet proof, it is very easy to become blase about installation and use say a dodgy switch or a very old battery. I'm sure there are many models out there with no positive method of keeping servo plugs in receivers or extension leads etc.

 

Sorry Tim, getting off topic. Hope you find a cause, there's nothing worse than not knowing.

[Ben B]

If it's a switched regulator perhaps but the linear regulators I've used in my own projects will always (if you don't fit a heatsink) get hotter and hotter (whilst maintaining the voltage nicely) until they let out the magic smoke in a big way.

[Biggles' Elder Brother - Moderator]

Posted by Lee Smalley on 02/09/2011 08:40:11:
As for the spekky has more incidents than any other radio, well duh, that because there are more of them out there that any other radio, it's like the old argument that hurricanes shot more enemy aircraft down than the spitfire during the BoB well duh there were more than twice as many of them

Hi Lee,

 

actually not true mate - the biggest single radio use is almost certainly Futaba. I've heard that elsewhere and our own poll bears it out as well.

 

BEB

[Chris Bott - Moderator]

Hi Ben

 

I just looked up the first 5V regulator I could find at Maplin. The very common 7805.

The data sheet on the 2A version states pretty early on that it has thermal shutdown that makes it pretty much indestructable. see here

This is also my experience with variable regulators like the L200 etc.

And I've seen it happen on a number of ESC BEC's

 

Let's not make a big thing of it, but it is certainly a possibility.

[Ben B]

You know what Chris, you're absolutely right- even in SMD form they are stated as having thermal protection. I consider myself suitably re-educated! Oh well. Looks like voltage fade could be an option after all. It does beg the question what the heck am I doing to them to make the go poof though! Oh well. Looks like I was inferring from experience something which wasn't true- bit like the "models balloon when turning upwind" thing

[Peter Beeney]

Yes indeed, from much practical fiddling in the past with voltage regulators and many other such devious devices you will certainly not be able to destroy them. They simply shut down to prevent any self-destruction. They do get hot, a blistering 150 degrees C but they will certainly not start smoking, if the thermal cut-out operates they will shut down, cool down, restart, get hot, shut down, cool down, resta…………..ad infinitum. Well, at least for 24 hours, I’ve definitely proved that.
It is my experience that a regulator will always supply it’s stated voltage or shut down, i.e. no voltage. There is nothing in between.

However, I cannot speak for the components on ESC’s, because from observation of the performance of some ESC’s leads me to believe that the quality in some cases is very dubious indeed. I’ve seen examples of these catching fire, and one completely exploded, there was nothing left at all!

Also something that I’ve read, and I will try and find it again as proof, but I believe that the Hurricane was responsible for more wartime kills than actually all the other fighters put together!

PB

[Lee Smalley]

BEB does the poll differentiate between 2.4 and 35meg, i would have to bet that there are far more spekky 2.4 gig stuff out there that Fasst, if you take into account 35meg then yeah futabe is prob up there

[Lee Smalley]

oh i checked no it dont , so i stand by my post that spekky has the lions share of 2.4 gig radio sales therfore they seem to have more problems

[Tim Mackey]

OK chaps, lets not get too far off topic here

I have done usual, methodical post incident checks, and for those interested, here it is.

I have an Excel spreadsheet ( sad aint I ? ) with the following items listed, which I go through in chrono order, ticking off as I go.

 

1) Structural check - wing mount, bolts, tail feathers etc (obviously some allowance has to be made for crash damage) - in this case there was none in those areas.

2) Servo horns, linkages, C/S horns, and Clevis'

3) Tx Voltage

4) Flight Battery Voltage

5) Rx servo / BEC plug integrity

6) Aerial (s)

7) BEC output voltage

8) Signal and servo operation check

9) Range Check

10) Motor Check ( prop off )

 

All items from 1 - 9 were ticked off as good.

Now...interestingly, when it came to the motor check - it failed.

This was a fairly new motor with around 20 flights only on it.

Therefore, I firstly suspected the ESC and used a replacement spare unit - motor was still dead. I tried another motor, and it spun up fine.

I then tried the original ESC, ( EMax 60A 3A UBEC ) and all was fine, proving the motor was indeed dead.

 

I began a close visual inspection and wasnt too pleased to find evidence of poor soldering of the windings to the lead out wires, and what appears to be "solder spray" on the windings, general darkening of coils, and possible overheated/ failed enamel insulation on the windings. All magnets were intact.

A quick check with a DMM showed open circuit on all 3 windings.

 

Its my INITIAL conclusion that the motor "burnt up" in flight, presented effectively a dead short to the ESC, which in turn overheated causing the onboard BEC to also overheat and thermally shut down.

 

Now, as to why the motor overheated, thats a whole new question. It was not a real cheepy, ( £41 ) a JP ( Perkins ) EnErG 540Watt 1100 Kv from BRC in July 2011,

 

Its rated at 45A with 50A 10 second burst, and my wattmeter readings when first installed showed (static) 38A on folding 11 x 6 graupner cam prop.

I use either a 3700m/a flightpower battery ( fitted at the time of crash ) or a tipple 4000m/a.

Either of these held a consistent 10.5V or slightly more under WOT, and Wattage was registered at 385 Watts. At 3lb AUW the model performed well.

The website specs show that anything up to a 13 x 6 on a 3s is possible, producing 400+ Watts.

My combo was obviously therefore running well below maximum spec.

 

 

The motor cooling holes were aligned with the firewall holes, and the exhausted air exited through specially designed exit holes in the fuselage /wing area.

 

I took various pictures throughout the tests, and will upload few later on, but right now, I have removed the AR500 Rx ( which I have always had great success with TBH - and have in at least 6 models, and have never had a cause for concern ) and have fitted it to a Wildthing 46" wing, which I am now taking up the Orme and will do some "severe" range testing.

More later.

 

A few piccies for now.

 

Considering the speed and altitude she went in from ( vertical dive ) it was a very lucky "escape". I didnt see the actual impact due to treeline and distance

Basically, a new motor mounting and front end rebuild...and some cowl work.

Tx voltage and trim settings

Cooling hole alignment

Motor as removed, with heatshrink around wiring exit.

Edited By Tim Mackey on 02/09/2011 17:59:49

[Tim Mackey]

Continued.

 

Heatshrink peeled back to reveal poor workmanship

 

Stator windings showing distress and solder splats ?

[Chris Bott - Moderator]

I guess that's good news Tim, at least on the radio front.

Remarkably little to do to repair too. .

Not so good about the motor. Obviously it shouldn't have overheated in the first place, but is there any chance overheating could have melted solder?

I've had a motor go short before where the wire insulation had rubbed away between a wire from the inside of a winding and one on the outside. I guess the answer is, it doesn't matter what the cause was, the result was a dead motor.

 

[Romeo Whisky]

Now THAT is very interesting. Because in my post above I mentioned an ESC which smells as if it had burnt internally, yet seems to work OK (although it doesn't beep any more so I can't program it). Well that ESC was in my MPX Gemini when the EnErG motor failed in exactly the same way as Tim's did. Thankfully the thermal cut out must have worked in flight and reset in time for me to glide it down deadstick, but I'm pretty sure it was KO'd when bench testing the EnErG motor during the post-mortem.

 

I had noticed that the motor had always run hot, but had put it down to the poor cooling which is common in MPX front-mounts. As Tim says, EnErG motors are not cheap and such basic failures are unacceptable. I had already decided I won't be buying any more.