Piled Up!

[Peter Beeney]

This post relates to an incident at the strip today, and again concerns battery problems, and I felt that because of it’s nature, and any subsequent actions, the new Incident Reports folder was the best place to post it in.

A regular pilot brought his large model, this has flown a number of times before without any problems; it’s a semi scale low wing very stable flying model. He took off, did a couple of circuits and was then shouting a warning that he had no control. The model then went in at full throttle, close enough to instantly grab everyone’s full attention! Fortunately there was no harm done, other than to wreck the model. When he’d investigated the remains he came over to me with the battery, saying that he thought the battery was completely naff, as it had been on charge all night and yet was totally flat.

The open circuit voltage was 5.2V, but that’s meaningless, it’s 4 cell Ni-MH, so I put on a discharge, and 2 mAh later, within a few seconds, it’s showing 4.3V, so, yes, his assumption is quite correct. He immediately wanted to throw the pack away but I rescued it, saying that we ought to check everything out. After all, the model had been ok previously. Later I put it on a (monitored) charge and it charged ok, so at the moment I’m giving it a test discharge, which so far also appears to be ok. If this is the case then we have to look further afield for the problem.

There was also a slight ‘knock on’ effect here, too. There was just three of us flying at the strip at that moment, I was flying with one of the younger members with his new Wot 4 foam-e on a buddy lead. Whilst the out-of-control model was suddenly occupying all my attention, the young man was also saying to me that his model was crashing out of control! By the time I managed to get back to him it was too late, and I was beginning to wonder what was going on. After briefly thinking about it, I realised that I must have inadvertently released the trainer switch, so that in effect neither of us had control. Or, at least, I didn’t have eyeball. So to some extent I would say that I was also getting it wrong, in relation to my pupil’s model.
Up until then the lad had been flying well, without any help. Now he’s also got some extensive repairs to make, but there are some really helpful members in the club so it shouldn’t be long before he’s up and running again.

I would refrain from making any comments about this particular incident, as always I wouldn’t want to make any pre-emptive guesses or criticisms, I’d sooner find out exactly what the problem is.

However, once again it has seemed to have highlighted with startling clarity the vital importance of being fully aware of the state of your battery. For me, it’s all about three things, Safety, Safety and more Safety! In the last couple of years a couple of models have been saved from a similar fate by an on-board battery monitor, in the most recent event the bottom red led was spotted by a sharp eyed observer, not the pilot. The battery was virtually flat before the model’s first flight! It was a 60” span Pitts.
All modern transmitters are provided with on-load voltage indicators and low volt alarms, I personally think that the same equal attention should be given to the receiver battery. If the power is lost to either the end result is the same. Plus the fact I think it’s a good idea to at least check out the health of the pack on a regular basis.

So, all the nickel charging problems aside, and there are a few, for starters could I suggest an accurate on-board voltage monitor, with an audio warning device activated when the voltage reaches the reds, it’s unlikely that it’s really necessary to fly with the monitor in the red. Also if the device goes faulty it needs to default to an all leds out or only red leds lit state. This is not always the case with the existing models, unfortunately, and this is a safety device.
I sometimes wonder at the modelling world’s use of the phrase ‘failsafe’.

The battery discharge is looking good, I think it will stroll though a standard test in terms of capacity.

PB

[Codename-John]

i had a similar thing occur to the first incident, turned out to be the standard charger that came with the radio kit that was goosed, lost a boomerang trainer when it happened, been flying about 2 mins then totally nothing, i checked the battery with a multimeter before flying and it showed 5 Volts no load, after the crash one of the lads tested the battery for me on load and it went down to less than 3 Volts, went home and plugged the batt into the charger to get a fizzing noise and some magic smoke

both were replaced under warantee, couldnt do anything about the boomerang tho but now i use my multi charger and ive got one of these now to check its condition while getting ready for a flight, it shows charge condition at a load of 1 to 3 Amps where i was testing with no load and getting an ok reading, if id have known at the time i coulda saved £70 odd quid, building new kit, loss of flying time etc

Edited By neil whilding on 20/06/2011 00:20:36

[Keiran Arnold]

Peter,

 

while in essence this thread is about batteries, it is worrying that you forgot the most important safety aspect in that you should fly the aircraft you have control of. I was not there and can't comment on how close the other aircraft was to you and your student but from your description it seems to have been a distraction rather than a immediate risk to life.

 

The point I am trying to make is that WE ALL must be aware of what we are doing as well as whats going on around us.

 

I do agree that we should be very aware of the the potential failure of the flightpack battery and monitoring thereof.

 

[Martin Harris - Moderator]

Peter's statement, "close enough to instantly grab everyone’s full attention!" sounds like a polite way of describing a situation likely to produce the odd expletive...in other words, I'd have read it as this being a very dangerous situation.

[Keiran Arnold]

Fair comment Martin as I said I wasn't there so can only reflect on what Peter has written, it came across as a little bit as - ' while I was looking at what had happened I forgot to pay attention to what I was doing with the Student ' . If however it was a dangerous situation then it's more than understandable to become distracted.

[Peter Beeney]

Keiran @ 09 :10 : 34, Yes, I entirely agree, this is exactly the same point I’m trying to make. Perhaps I’m not very clear. I’m trying to get across the fact that if we all were aware of what was going on, then I think this would not have occurred anyway. Had the pilot of the large model been aware of the state of his battery he would definitely not have even put the model together.
There is a adage which says that ‘The benefit of hindsight is a wonderful thing’, and I think that statement is certainly applicable here. So to capitalise on that I’m trying to establish exactly what went wrong and how we can try to prevent it happening again.

With regard to the accident, Martin is just about on the button, as always. I was on the point of grabbing the student and throwing us both to the ground but I didn’t have to. In the event I don’t think I would have had the time anyway. It was over in a flash; so in that sense I think I was well aware of what I was doing and what was going on around. Personal safety suddenly became very much the big issue here. I can say that over years of standing on busy flightlines with students I have got very used to ignoring the general hullabaloo of all the models going about all their respective journeys; and I can say that I did once have to throw us both to the ground to escape a crashing model but in that instance we managed to save our trainer!
Anyone who has experienced a model that suddenly has no control response will surely agree this is a situation they would not want to repeat! Ever! Closely seconded by the onlookers! Especially as in this case, the final strike was inches, rather than feet, from disaster!

Fortunately these events are rare, but crashes, for whatever reason, are not. Verbal recriminations are easy, as our old friend hindsight might say, again. Better to try and find the reason, and then do your best to rectify this in the first instance. An uphill struggle, I know, and I’m fast running out of puff anyway.

So with all this in mind I can say that the errant receiver pack, it’s labelled 2600 mAh, and it appears to well constructed, with a substantial quality silicone cable attached, returned a capacity of 2100 mAh. Not perfect, by any means, but I’m confident it would fly the model all weekend; there are no signs of any dodgy cells, the Achilles Heel of many of these packs; and from the sanguine way the pack accepted the charge I would bet money (but not a lot!) that it will easily cope with some higher rate discharges. That’s the next step.

Also I think that I’ve now got to dig out the old deerstalker, polish up the magnifying glass, send an email or two and start digging a bit deeper.

(Hopefully) it will be elementary, my dear Watson….

@ 13 :34 :46. I’m sorry about the vagueness, but yes, I’ve perhaps previously thought that I should be able to cope with a given situation. So I was very slightly disappointed that I’d broken the model. Which makes me determined to try and sort it; also I shall recommend that we take a good look at the voltage monitors.

In all seriousness though, I consider this a fairly strident wake up call………..

PB

[Keiran Arnold]

Thank you for your reply Peter, as I said above I was't there and can only go on your report. you abviously coped with what was a very dagerous situation to the best of your abiltiy, as you say its easy to be wise after the event. The frank and honest account of the event does give us all a chance to learn from your experience and ask ourselves "what would I do?"

 

Good luck with the investigation into the crash of the other aircraft, switch perhaps??

 

 

[andy watson]

The really interesting aspect for me is the "knock on" crash.

 

From the description this crash was "your fault" (read on before shouting at me!) in that you were (as I read it) on the master transmitter, inadvertantly took control of the plane by releasing the switch and not actually being in control of the plane.

 

In the circumstances I can see how this could happen in this instance, but I see instructors getting distracted by far less when on a buddy box. Really they should be concentrating on the flying just as hard as the trainee. The trainee has been let down in a number of ways here- he has a repair job to do despite making no errors of his own. Possibly the instructor should be taking responsibility for not being sufficiently aware? Perhaps the owner of the original crashing model should be taking responsibility for setting off a chain of events that led to a subsequent model crashing?

 

In truth in an incident as potentially serious as this it is all too easy and understandable why someone might stop looking at their own (or students) model, which could then cause a subsequent crash. But there is also a warning in here for instructors that they should have the same concentration as when flying themselves.

[nasa_steve]

interesting analagy there Andy BUT given the situation what would you have done??? i think Pete isn't saying it was'nt his fault what he is saying is something could be learned from the situation i don't think what he has written is actually blaming anyone for the situation

i can actually tell you that Pete was teaching people to fly RC probably before i was born so he is extremely qualified to make decisions. and beleive me if Pete says inches away it was probably nigh on ontop of them . given the situation i'd be surprised if YOU did'nt react the same way. i know it would be difficult to say how anyone react in a situation as that and all too easy to stand on ones orange box and preach what he should or should'nt have done in this particular situation.

nasa

[Peter Beeney]

The cause of the crash was simply that the battery was flat. This is beyond any doubt whatsoever. Or, perhaps in stark terms, in the beginning the pilot took off with a flat battery, and if you think about that very much, the implications are pretty indescribable; it doesn’t really bear thinking about. One result was very quickly in evidence. Also, I think, with even more certainty, he did not deliberately intend to do this; and as is obvious it can lead in turn to other events, but in the general scheme of things these were relatively harmless, any danger, and that’s at least 99.999%, was from the large model without any control.
So, simply because I’m only curious to know, can I ask why it seems that generally the secondary knock-on effect is the most interesting?

For me, the flat battery is the only interesting aspect. We need to crack this first. The BMFA handbook does give a small amount of information about checkers, but nothing specific.
Any responsibility that I have, as I see it, is trying to establish how this happened. Simply because I have some knowledge of the subject and some test kit to be able to do it. Straightaway I’ve shown that the battery is sound when it was thought to be faulty, so it now starts to point to the charging regime. This frequently happens, often batteries are suspected of causing problems when in fact this is not the case.

To all the pilots that have a system of accurately reading the battery capacity this is all perhaps a bit irreverent, but there are still many that don’t have such a system, so I’m now of the opinion this is worthy of some thought.

As far as the lad goes, if he wants any help with repairs I’m sure he’ll get it. Also I’m sure we will be talking, purely voluntarily, about any other matters; and I always fly on the basis that if anything goes wrong it’s not down to me. Whatever!

All that happened here, apart from the loss of a nice model, was that a foamy got bent, it happens everyday. However, this could indeed have become a great deal more personal, very quickly! This, surely, is what must be significant?

Perhaps, as a WEOAP, (Well Established Old Aged Pensioner), I’m beginning to slow down a bit anyway; and if we as a club ever even slightly start to go down the road of dishing out responsibility and making folks answerable for every questionable action I think that might be time for me to hang up the buddy lead and retire gracefully to the bar. Milky bar, that is, for a warm glass of low protein Horlicks……...

I will try and follow this up with any further developments.

PB

[flytilbroke]

From PB's comment or statements, one cannot fault him. His first concern is the safety of himself and secondary his pupil. The pupils' model while at risk or possibly being a risk, is of less import than the immediate risk from a model posing an direct dangerous threat.

 

I applaud all Peter's comment in this thread.

[Keiran Arnold]

Peter,

 

my interest in the second event is due to the effect of the first event, as you are well aware no accident has a sole cause there is usually a chain of events. Near misses can often be used to identify the chain and to 'break' the link. I for one am try ing to be objective and learn from your experience, and fault investigation thus helping me to

 

1. aviod the tequnical failure that caused the first crash

 

2. Try and work out how I would deal wih the event that caused the 2nd crash.

 

As I said above you frank and honest account of the events enables such analysis to be caried out and lessons to be learned

[Ian Jones]

Well done PB.

 

Some good points being raised.

 

Ian

[Peter Beeney]

Messrs FTB, Arnold and Jones - Thanks very much for the replies and comments. I’m pleased that it’s at least of some interest.

To briefly sum up for now, then, this is how I might consider the situation; and I stress it’s just my very simplistic personal view, certainly not necessarily what everyone would consider to be the case.

In the heat of the moment, total concentration on self preservation takes over, or, in a word, panic stations!

So any pre-arranged plan to cope with a similar situation would, I think, simply just fly out of the window! (Sorry!).

To prevent the secondary effect, the second crash, we need only to eliminate the primary cause, the first crash.

To eliminate the first crash, (as in this case), we need to ensure that we take off with at least enough power in the battery for the complete flight.

One positive way of doing this is to install an on-board voltage monitor for the battery, but, of course, the pilot has to check it from time to time!

So, with that in mind I’ve grabbed three OBMs, (On Board Monitors) with a view to doing a bit of calibrating, I think this might be important, a test instrument that gives you incorrect information is perhaps more dangerous than no test instrument at all. I’ll report back on this later, for anyone that's interested.
I’ll also try and have a little tinker with a piezo sounder, triggered by the red leds, for an audio as well as visual indicator.

A further thought, the model that takes off with a flat battery and then crashes 500 yds away is really no less dangerous than the one that comes down close to hand. From the examples that I’ve seen, one of the characteristics of a flyaway plane can be that when control is lost the model is in relatively straight and level flight, and it could fly for some considerable distance. Totally out of control, and with no possible chance of regaining it.
Also another view that I might have, as an average modeller, the loss of a big model could be expensive. If by buying a fairly cheap monitor I can avoid that expense, I think that may be a pretty good deal!

PB

[Martin Harris - Moderator]

I lost a smallish (.15 powered) combat model recently despite a pre-flight voltage check on a NiMH pack. The model glitched badly and while manoevering for a precautionary landing locked out in a turn, resulting in a large uncontrolled power on loop which terminated in a vertical dive into the ground out of sight.

 

I have a feeling that the (seemingly unconcerned) dogwalker who specified the exact position 30 feet from the edge of the field of linseed that it had landed in was not very far from the impact so I'd bear out Peter's statement above.

 

Unfortunately, I was on 35 MHz PPM - had it have been on my Jeti 2.4 equipped transmitter with telemetry I might have had sufficient warning - although NiMH do have a very steep final discharge curve so you'd need to act very quickly.

[Bob Cotsford]

Posted by Peter Beeney on 22/06/2011 10:35:21:


One positive way of doing this is to install an on-board voltage monitor for the battery, but, of course, the pilot has to check it from time to time!

So, with that in mind I’ve grabbed three OBMs, (On Board Monitors) with a view to doing a bit of calibrating, I think this might be important, a test instrument that gives you incorrect information is perhaps more dangerous than no test instrument at all. I’ll report back on this later, for anyone that's interested.
................
Also another view that I might have, as an average modeller, the loss of a big model could be expensive. If by buying a fairly cheap monitor I can avoid that expense, I think that may be a pretty good deal!

PB

yes please Peter, I use some of the TowerPro branded monitors and was wondering about their accuracy only yesterday afternoon. As a result I've left my Joker's 2100 pack on repeat discharge/charge cycle today to see what was really left in it when the monitor was starting to look dodgy (all the reds illuminating when moving two or more servos).

 

Bob

[Keiran Arnold]

Look forward to your reports

[andy watson]

I do hope I was clear that in view of the circumstances I didn't blame the instructor. However the incident of the second crash, from the perspective of the trainee, is worth looking at.

 

He was flying along, sensibly, with all the relevant safety precautions in place.

 

He makes no mistakes, no faults, no issues with his set up at all- he is in no trouble, when through no fault of his, control of his model is TAKEN FROM HIM by someone else.

 

As I said above, I don't blame the instructor for this in these circumstances, but I would suggest the pilot of crash #1 should be offering in some shape or form to be making reparations to the trainee.

 

The situation is obviously complicated by the instructor as a "middle man" here, and this is where insurance companies wheedle out of things, but if I had been the owner of plane #1, I would like to think I would be making some offer to help- even if it is just to repair the damage.

[Peter Beeney]

Andy, Yes, I can fully appreciate your concern, but I’m sure we will be talking amicably about this, probably along these sort of lines, when we all get together again; the pilot of the large model will be the first up to the oche, and, indeed, to some extent it’s supposition (on my part) that I actually let go of the trainer switch anyway. When I got back to the Wot as far as I was aware I’d still got the switch operated, but we’ll never know. It’s just that it conveniently explains the chain of events.

The lad has repaired his model, apart from the fact the motor shaft sheared off, Ripmax won’t supply spare motors apparently, so he’s asked me to talk to a couple of members, (good mates), that had volunteered help anyway, one with loan of a spare motor and the other with a repair to his. This will definitely be forthcoming and I’m particularly pleased he’s come back, unfazed, it could easily have put him off, I feel. He’s keen to get back.

With the best will in the world, these things happen, and no harm done, so there will be no recriminations. However, I like to think that I am trying to realise the full implications here, which is why I’m so concerned about the original problem, with the battery. Hence my comment about the out-of-control crash 500yds away. That’s just luck, it could just as easily be 5 inches; in every case. Battery problems, of all the different types, are far too frequent; in my opinion, anyway. Maybe this only happens to a modeller once in his model flying lifetime, but even that’s once too many. And judging from just the posts on the forum about batteries and other electrical devices it might well be more than one! Or five!

By going public here I thought that these experiences might serve to raise some awareness. It seems to me that sometimes incidents are not even circulated within clubs, let alone to a wider audience.

Anyway, All’s Well that Ends Well! As they say……

PB

[Bob Cotsford]

It looks as though that cheapo TowerPro on board battery monitor has paid for itself,oooh - 100 times over? The 12 month old 2100mAhr battery pack in the Joker gave out another 300mAHr on initial discharge (after resting for 6 hours), but further cycles rapidly dropped down to less than 150mAHr ! That pack is toast, and I would never have noticed until the model piled in if I hadn't been warned by the OBM. As confirmation I checked with a second charger which didn't want to put in more than 15mAHr before calling it a day!

So just replacing packs every two years is not enough with high capacity NiMh by the look of it.

[Peter Beeney]

This post is a little long, so to try and avoid any chance of zapping the thread, I’ve split it into two parts.

I now have a few figures concerning the OBMs, but in the first instance, for the benefit of anyone who is not really familiar with these, a little overview might be in order first.

An on board monitor is simply an expanded scale volt meter. We need to know the battery voltage in order to give us an indication of it’s remaining capacity and this is what it does. This needs to be relatively accurate, the discharge curve is fairly flat so there is not a lot of deviation. If we consider a 4 cell nickel pack, the voltage ranges from around 5.5V fully charged down to 4V, fully discharged; if we consider that we are not interested in the top end voltage too much, we won’t complain about it being too full, then the scale could be over 1 volt, from 5 volts down to 4 volts. So this is what we should have. If we have 10 leds, then each led will represent a fall of 100 mV, or 0.1V, or one tenth of a volt.

As our meter only measures a limited scale, naturally enough it will notice small movements within this range, and that is what is happening in Bob Cosford’s first post, above, when he says all the reds are illuminating when 2 or more servos move. This is actually measuring the volts drop across the wiring. This drop is caused when a current passes through a resistance the higher the resistance, the bigger the drop. We can say that the resistance of a piece of wire is directly proportional to it’s length and inversely proportional to it’s cross sectional area; which simply means that if we double it’s length we double it’s resistance, if we double it’s cross sectional area we halve it’s resistance. So we can see that short and fat is good, long and thin is bad. Model wiring tends to be long(ish) and thin, for a variety of reasons, but it’s adequate, at least in most cases.

The sudden drop is caused by the servo motors starting up, when the motor is at rest all that limits the current, called the ‘inrush current’, is it’s resistance, so it will be at a peak. As the motor runs up it will generate a back EMF and reduce this current. So there are lots of little spurts. In Bob’s case the drop would appear to be about one volt, that’s not good, but there are other factors which can also influence this.
The quality of a battery is judged on it’s internal resistance, this needs to be low, so if the battery is a bit iffy it will have a higher internal resistance and so this has to be added in series with the wires. Also the monitor itself, sometimes the manufactures seem to err on the side of caution, and raise the point at which the red leds are lit. Let’s say this might be at 4.5V, mid point on our the 1 volt scale, and so, whilst we are thinking that our volt drop is one volt, it is in fact only 0.5 of a volt! Again, this may be happening in Bob’s case; and, of course, a combination of these factors together, and we don’t know if we are on our head or our elbow!

These are some of the reasons why it’s a good idea to calibrate the monitor.

As it now transpires, in Bob’s case, it is the battery that is at fault, and this would seem an ideal time to discover this.

[Peter Beeney]

 

 

Part II.

The OBMs that I have are GWS types, GW/0BI05L/J. There is a H version , which ranges from 6V up to 9.6V. I think the J probably relates to the plug, which is a universal type. There are two switches to adjust the voltage range, thus giving us 4 ranges, 4.8V, 6V, 7.2V and 8.4V. There are 10 leds, 6 green, 1 orange, and 3 reds, they are nice and bright, the orange one particularly so.
I amassed quite a lot of figures in a short time, but I’ll just record the important ones.

I just wound the voltage down and noted the level at which each led became lit.

Monitor A, the last red led was lit at 4.090V, B = 4.089V, and C = 4.115V. Significantly, the orange led, and this is the level at which the operator is going to sit up and take notice, is the most important one.
So, for the orange led - A = 4.415V, B = 4.398V, and C = 4.457V. In general modelling terms we can call these figures simply 4.4V, and as my personal safety lower level for a test discharge is 4.4V, this looks about right. Spot on, in fact!

 

I ran through the 6V setting, with similar results, as follow:

Bottom Led, A = 5.045V, B = 5.091V, and C = 5.102V. Orange led, A =5.488V, B = 5.516V, and C = 5. 527V. So as before, the orange led is lit at the 5.5V level.

 

They all consumed a steady 14mA throughout; and they are also small and lightweight.

In my opinion, I reckon these are nice units. We have a 1 volt scale, and the leds are switching on and off at the right levels. In terms of operating levels, all three are all very close to each other; and at a LMS cost of £9, I think good value for money.

If you use one, I would say fly until the orange come up, and then consider the options; you can calibrate it against a test discharge on your charger; and if it runs up and down the scale when stick waggling, this is not necessary all bad, but if excessive, it needs a coat of looking at. As Bob has very aptly demonstrated! A good move!

Bob, I think I would definitely check out any new battery, and then on a regular basis. Some hydride batteries will go on for years, while others don’t even make a start.

PB