Futaba 2.4 radio issue?

[Peter Beeney]

Tim,

There is one more little angle here. Charging the new rx battery for the first time. On the very odd occasion this can give rise to a serious problem. It doesn’t charge! I’ve seen this happen really close up, in similar circumstances to yours, although in this case the model circled around for what seemed like half an hour, but probably only half a minute, and although the brand new model was totally splintered the rest of the damage was not so great as in your case. It was a brand new battery, too. I do also know that on at least two other occasions to my certain knowledge it has happened. Of course, it may be very unlikely that this is the reason in your case, it must be pretty unusual, but I also would suspect a power loss of some sort in the first instance. As I’ve said in previous threads, I’ve campaigned for years for pilots to do a check on any radio power supply battery, before it’s committed to controlling a model, and I have written to the suppliers etc., explaining the conditions and problems but with no response.

 

Is it possible you can salvage anything from the damaged pack, one cell perhaps? You can do a discharge test on one cell, that will give you some indication of the state of charge when you started. An open circuit voltage check is of very little use. Even a virtually flat nickel cell will give a good open circuit voltage reading.

Also it’s not to say that the pack is necessarily faulty, once you’ve charged and discharged it it will be ok. Plus the fact you will have an indication of the actual capacity; and that’s not always what it says on the label.

Incidentally, I would think that the switch failing is unlikely. The Futaba ones are double pole devices, but only the positive leg is switched and both poles are connected in parallel to increase reliability. I think it would literally have to fall to pieces to break the circuit. Or perhaps switch itself off, which could happen, I suppose, although I’ve never heard of this.

Another reason for a total power loss is that the battery plug, for whatever reason, pulls out of the switch harness socket. It would certainly not be the first time that this wallet-buster has occurred, either!

This, together with Martin's post above, the crystal incident, is the reason, and I’ve said this many times, too, that for years I’ve insisted that youngsters always tie battery plugs together and wrap a piece of insulating tape around the crystal. In fact, I do the first one for them, as a demo. As a consequence, we’ve never had a battery or crystal problem. But, post 2.4, the xtal situation is fast disappearing anyway.

If you can reach a probable conclusion as to the cause, that does at least help to remove some of the uncertainty.

PB

[Tim Morton]

Peter

Excellent point - I checked the battery and it was reading 7.4v (6v pack – 99% on the battery checker) and this was a pack I'd charged a few times as I'd had the Stick out to run-in the engine a few times ( but no flights as the weather was not too good) so it's possible but I think unlikely the pack failed.

But your point about the battery plug coming loose is a possibility - the Rx and battery were wrapped in foam which was a reasonably snug fit - but not a very tight fit and I think with enough g’s it could have moved.
I don’t know for sure as it wouldn’t have moved with ease, but if the whole lot moved (and there's plenty of space there) then just maybe, just maybe that’s what happened.
Matt who was flying is a very good pilot and was throwing the plane around a bit (I’d asked him to compare it with his Wot4) so it's not beyond reason that this could have dislodged something. It would certainly explain it and is serious food for thought....

On a positive note – the new Stick, engine and flight pack arrive tomorrow. So Stick number 4 will soon be here

[Peter Beeney]

Tim,

Thanks for your reply. It certainly appears as though the battery charge state was ok. I think I’d be inclined to practically rule that out.

With regard to the battery moving about, I witnessed an interesting phenomenon once. Someone had an engine hiccup on his trainer and I was running it on the ground with the wing off. There was the usual foam rubber and conglomeration of wires in the fuz and as I slowly ran the engine up and down just at one particular rev it must have reached a resonant point and the interior of the fuz dissolved into a blur. Any loose wires were being shaken up into space, and certainly quite violently. I found that I could quite easily hit this spot, it was not flat out, just some mid point, and it soon occurred to me that if this happened in the air then here was a really good set of excuses for any suspect plugs and sockets to perhaps rapidly become parted from one another! It may well have been a ‘one off,’ but as battery leads joined to switch harnesses are invariably quite long I wondered just how far the battery actually has to move to pull the plug out. This is all speculative stuff, and maybe it couldn’t happen in the air anyway. But I think there is certainly no doubt that batteries can and do become disconnected; and maybe they don’t always have to go on a route march to do it.

Because my installations tend to stay put for a while, I sometimes tend to join mine with a soldered joint. I cut the plug and socket off, staggering the red and black cuts by about 5 mm, slide a 25 mm piece of clean fuel tubing over the wire, trim a couple of millimetres of insulation off the four ends, tin with solder, touch them together with the iron, finally slide the fuel tube over the bare bits, this will now be a nice cosy fit over the little lump. Takes all of a minute and will last forever! Or, at least, till the next crash! It will never fall apart, though. If I do use the plugs, I always tie them! Be just my luck for one of my young students to check my model!

You remarked that you wrapped the rx in foam. I’m not a 2.4 man myself, I’ve only just got used to 35, but haven't I read somewhere this is not a good thing to do! There is a heat problem. Electronic components can get a bit shirty if they are warmed up. From practical experience of tinkering with electronic components, testing above and beyond the normal call of duty, I do know that when you get a bit of a runaway situation it can happen very quickly, as in milliseconds. It’s an exponential thing; and if you’ve encouraged this by wrapping it up in a thermal blanket………………….

Again, highly speculative, but it may well be worth having a quick ganders here…

All the very best of luck with the new model!

PB

[Tim Morton]

Thanks Peter

I've heard and read about this with 2.4 receivers but I don't really understand it though - a receiver is a receiver regardless of what frequency it works at - is it not? Okay some have some “intelligent” features but these are in reality pretty small in terms of processing power and indeed many existed in the 35Mhz versions too.

Anyway I've tried to test this heat thing out and felt a 2.4 receiver after a normal flight (say 10-12 mins) and found it to be ice cold.
If a receiver was getting hot to the point of failure I'd be quite concerned. It's not really processing anything taking significant power - if it was then surely a heat sink should be built in. Just in case!! And there’d be a bold “WARNING” sign on the accompanying documenation.

It's not that I don’t believe the manufacturer (Futaba) as they know their product. But I do think they need to be a little clearer on why this is now a problem (and is it cars and aircraft – looks like the aircraft was added as an afterthought).
Also the receivers immediately preceding the 2.4 versions were constructed along much the same lines yet they weren’t required to be cooled down and were required to be wrapped in foam.

Methinks a little better explanation is required.

Edited By Tim Morton on 20/04/2011 08:53:48

[Tim Mackey]

I must say that I have never wrapped any of my 25+ Spektrum receivers in foam, or anything else for that matter - a small square of velcro sticks the rx in a suitable location and thats it. As all my models bar one are electric, grime and vibration are two things which I dont worry about, which are surely the prime reasons for protective padding.

In the event of a crash, I doubt the padding would protect against it, and if its a really bad crash, I always send the rx in for checking as a matter of course.

I think it is only Futaba that recommend leaving the 2.4G rx uncovered for cooling purposes.

[Klippy]

Page 8 of the 6EX manual says categorically, 'wrap the receiver in G foam'. I know that since there has been a modification to this instruction by Futaba. As an aside, Receivers today are so light that it's hard to see how they can be damaged by a sudden stop!

[Klippy]

This is where I read it. Hobbico

[Biggles' Elder Brother - Moderator]

The reason that FASST Rx's should not be wrapped in foam is that there is some very powerful processing chips on there. We use a number of high perfomance DSP chips in work and they run very hot. The more processing they do the hotter they get! Thats why higher performance processors on PC's have not just heat exchanger fins but actual individual fans fitted these days.

 

FASST is very complex - even by 2.4 standards - so it needs a lot of processing power - hence the temperature issue. It will be interesting so see if the new DSMx receivers when they emerge have similar temp related issues.

 

BEB

[Tony Smith 7]

How much current does a FASST receiver draw? I seem to remember that my whole model takes 85mA when powered up and idle, which would include idle current to the servos and ESC as well as the receiver. Even so that's only 1/2 a Watt.

[Tim Morton]

Thats exactly the point Tony - i agree

I don't quite understand the power requirement for a receiver either - yes its a small computer in it;s own right but it's hard wired logic stuff programmed in machine code or equivalent. These things are al around our lives - in watches and clocks, fridges, net radio's, etc. etc. Okay these may be a little more complex but cannot imagine that they''ll draw such a large amount of power - if it is so much that they need cooling it would imply that it would need a similar sized large capacity battery - just to power the Rx.

 

Afraid I'm not convinced - just doesnt feel right...

 

How about some of you electronic boffins out there replying - how much power is required to generate this sort of heat?

[Martin Harris - Moderator]

I'd guess it depends on the mass of the component being heated and iwhether this is the critical part i.e. you might get local 1/2 Watt heating in one part which is unaffected and unlikely to conduct to a critical component but if that heat is locally generated - especially by the same component - then 1/2 a Watt might be more than enough to overheat it.

 

All reports of overheating I've seen have occurred in very high ambient temperatures ( > 100F ) so it may have been the case that all design and testing work assumed a direct cooling path from the casing to the surrounding air in any temperatures found in service.

Edited By Martin Harris on 20/04/2011 13:51:56

[Tony Smith 7]

I just found the spec for my own (Frsky) receiver, and they claim 30mA which could be correct from my measurements. If it is, then that's less that 1/5 of a Watt dissipated in the actual receiver.

[flytilbroke]

The higher the frequency of use the more critical any expansion or contraction of the circuits become, so heat, both of the component and the surrounding environment could "just" possibly play a part. Not an likely cause of failure of operation though, unless your installation "cooks" the RX.

 

Just to be helpful, there are little plastic clips which are excellent at retaining the plug and socket of our battery and any extension leads.

 

To ensure retention of the leads into the RX, a little wrap of Self Amalgamating rubber tape can be very effective as it can on the other plug/sockets.

 

It is not unknown for the plug pins or sockets to be badly fitted or indeed the lead from/ of the batttery tabs not to be properly welded or soldered. I lost a brand new model with all new fittings to this battery problem.

[Biggles' Elder Brother - Moderator]

We have a cutting laser at work, its not particularly spectatcular but it will cut thin wood, paper, vinyl etc. It s just 400mW - i.e. less than half a Watt. The point being of course that it is concentrated in a very small spot.

 

Extremely high levels of integration - such as in the chips in a FASST Rx could easily generate elevated temperatures. Tim the processing circuity in a FASST rx is hundreds, probably thousands of times more complex that anything you will ever find in a clock, fridge, watch etc. And its doing literally 100's of millions of operations per second. So such domestic appliances are not really very appropriate comparators. Believe me I know from the high speed DSP's we have that even though their current draw is low they do generate significant temperature raises albeit highly localised.

 

Also, just to be accurate. No one has said that Futaba Rx's need cooling, the advice is simply not to actively insulate them that's all.

 

A while back we had one of the first SHARC multiprocessor systems in the UK in our lab. It had incredable computation rates for that time (probably slow compared to a current FASST Rx!) It was great. The only problem was we could only run it for about 30mins. After that the heat generated by the chips caused the circuit boards to twist and then they would ride out of the connectors and bingo - the whole thing "blue screened"! Just shows you what "crunching a few numbers" can do! £50,000 worth of the latest computer and we used to try to hold the boards in by clamping them down with elastic bands!

 

BEB

Edited By Biggles' Elder Brother - Moderator on 20/04/2011 21:07:38

[Tim Morton]

Guess this is one of those marmite issues - there's no definitive right or wrong. Which is worse - having vibration wobble the battery leads free or the Rx overheating (both in the extreme case here)?

I don't know but think this can go on like caster oil vs synthetic...

[andy watson]

The FASST receivers that suffered from overheating were in the states.

 

Some (lucky) guys were flying in Nevada or similarly hot place and had their receivers wrapped in foam. Their models had big canopies which acted as greenhouses, and raised the internal temperature of the plane far beyond the already high direct sunlight daytime temperatures. Because of the foam there was no cooling from airflow during flights, and they were damaged- presumeably causing a crash.

 

There have been no examples of it happening anywhere other than these extreme weather type situations (so fat chance in the UK then!). It was nothing to do with chipsets overheating as a result of their own actions.

 

Can't remember where I read this, but I am pretty certain it was a reliable source.

 

 

[Craig Spence]

I've brushed through this and it sounds interesting.

We had a near incident at our club last week, a guy getting taught at the club who was using a Futaba 6ex (or the correct model) turned on his TX to do a range check.
On doing so his surfaces moved out with his controls, his throttle and rudder were moving.

So the instructor called him in and asked him to try it again and it was not responding to his commands, however one of the guys was getting ready to take off with the Same TX and RX. It was quickly realised that the fella getting ready for take off was controlling the new guys plane and the new guys plane was not controlling nothing.

Very strange, they rebound but keept picking up the fellas receiver. They stopped until he had landed and turned off, then rebound and never had a problem again that day.

Can anyone explain that?.

[David Ashby - Moderator]

Yes, could that be the last dregs of Futaba's common coding manufacturing error from around 3 years ago Craig?

 

Well documented at the time, might be worth them both checking that the TX's were replaced under the swap scheme run by Ripmax/Futaba. Here's the news article link.

 

 

 

 

 

Edited By David Ashby - RCME Administrator on 21/04/2011 09:08:02

[Josip Vrandecic -Mes]

Hello Tim,this is my solution(RX 607 FS)....all the best Jo

[Craig Spence]

Hi David,

I'll pass this on to the club chief flying instructor, I never knew that these guys had a recall as well.
I have sent my TX back once for recall but they have been called back a few times from starting up.

Cheers.

[David Ashby - Moderator]

Yes, it was all 'the news' back then and seemed to quickly resolve itself but, with the best will in the world, I'm sure the odd TX is still out there?

 

 

[Craig Spence]

Trying to inform the instructor, I'll get him soon.
I think it's strange how these 2.4ghz systems get recalled (my own is spektrum) and that the manufactures do it so care free.

It's a very important piece of equipment as we all know along with the RX and yet I've never heard of a refund for someone loosing their model due to that fault.

Potentially a faulty TX could end some clubs with one incident.

Never mind, sour grapes here lol!.

Thanks David.

[Tim Morton]

See this in the 8FG Manual (Pg 34) on wrapping Rx with foam
Futaba 8FG Manual

 

[Barrie Dav 2]

As posted before, here is the method that I use. RX on it's side for max cooling.

The 'Skate board' held in place by glued-in elastic bands, leaving an airflow all around the RX

[Peter Beeney]

Tim,

Regarding your radio installation, why not compromise a little and simply glue, or Velcro perhaps, a small slab of foam rubber in a convenient place, then Velcro the rx to the foam, also definitely make sure that at least the battery plug and socket are securely held together by some means or other, plus any excess loose wiring is bundled up and is held down by some more strategically placed foam or other means.

Thus now the rx will have some protection from vibration, but will not be thermally insulated to trap any heat in, the battery supply will not be lost because of a broken connection, and the leads won’t be able to flap around in the breeze and possibly come adrift either.

Whilst you’re there, why not install a battery monitor, too? I know they are far from being the most accurate of indicators, but you can calibrate them reasonably well with a voltmeter, and if you don’t check your battery capacity they can, in some circumstances, definitely save your model from certain destruction.

Then if you still get some any grief later, you might have some small satisfaction of knowing at least what it is not that’s causing it!!

Like you, I think I would be very sceptical about any rx overheating situations. If this were the case, I think it would be getting some general press, and apart from Andy’s post I’ve seen very little else. In fact, I think I would need to be tolerably convinced somehow that it was indeed some sort of failure of the actual radio communications link in the first instance anyway.

I think I might be inclined to go somewhat along these lines if I had this sort of dilemma; it’s knowing what to do for the best is always the issue. I’m not sure that you actually said if the rx was working ok again afterwards, but if this was the case, and that’s happened a few times before, it all becomes even more confusing.

Oddly enough, relating to the power requirements for 2.4, when I had a little dabble with the low voltage conundrum that seems to exist with this gear I actually found I could get a slightly lower voltage reading than with a 35 rx before it decided to call it a day. Admittedly only a hundred millivolts or so, and it was with only one 2.4 rx, but because of this it seem to me there might not be too much of a problem; and even then it was because the servo didn’t have enough power to start moving, the rx was still ticking away. In a literal sense, that is!

This is a pretty simple procedure, with the right sort of kit anyone could do it.

I remember watching the test flight of a Galaxy Models Magician, a long time ago now. The power was an OS 40 FSR, and the test pilot was very capable. At one point it went round a lovely big loop. Trouble was, it was too big, and the ground rather got in the way at the bottom. We had to dig the model out, the engine had buried itself. A host of reasons were put forward to explain this, but after some careful discussions later with the builder and the test pilot, who was a commercial airline pilot, so he could at least speak with some knowledge, we decided that because the surfaces were operated by snakes, and they in turn were unsupported within the fuselage, the elevator had experienced ‘blow-back’ at the fairly high speed round the loop. The snakes bending under the strain, and so the explanation fitted all the symptoms.
My one point of this obscure ramble is just to say that in all of the previous lengthy ‘talk’ about why this happened, no one else had suggested it. So it pays to examine every possibility.

PB