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Catastrophe!

Model Air Crash Investigation Experts Sought...

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Nigel R25/01/2019 11:11:01
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3104 forum posts
479 photos

"Are the phone masts to blame?"

Simple test, did the failsafe fire? Answer, no, therefore not interference therefore squat to do with mobile phone masts.

"do the authorities/companys who erect these,test them for interference"

Oddly enough, large expensive monolithic pieces of radio frequency network infrastructure do actually get tested for RF emissions. I doubt very much if our toys are on their radar though.

kc25/01/2019 11:28:53
6056 forum posts
169 photos

Most of us have had a disastrous crash like that so we are sympathetic!

Damage looks bad but is repairable - see the excellent article by Peter Miller.

Many people would dump the model but keep the radio gear, but the opposite is the correct way to procede. Repair the model and keep the radio out of any new plane until the fault is found and eliminated. If not found then sideline the radio.

Edited By kc on 25/01/2019 11:31:22

Jonathan M25/01/2019 12:29:16
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670 forum posts
275 photos

I've learnt much from the experience, and from the responses to this thread (brow-beaters included), thanks.

Spoke to George at 4-Max, from whom I'm now ordering a new Wot4 plus the power-train, prop etc that he recommends.

Whilst nothing can be entirely certain, his view is that it could have been due to a bad connection somewhere, perhaps including a poor solder joint on a Deans plug or socket? As I'm effectively starting again, I'm going to remove the Deans from the three remaining LiPos and fit XT90s all round. Overkill maybe, but at least this should be more robust for 4s batts and eliminates the supply-side issue.

His other view was that the max draw of 54A with the 14x7 prop was too high for the 60A ESC.

Whilst it is theoretically possible, I don't have the time or inclination to attempt a re-build of the smashed-up model (too many other models in the line to build from new - 2m slope aerobatic, Gangster 63 for two-stroke, Mini Panic for EP, etc). Also, even if the RX wasn't at fault (it was a genuine Spektrum item from a well-known retailer), I'm not inclined to trust it any more and will replace with a new one - the least of my expenses!

George also recommends that - before re-using the existing servos - I check them with the Watt Meter attached.

Cheers

Jon

Don Fry25/01/2019 14:18:09
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4054 forum posts
47 photos

Sounds like a plan.

IanR25/01/2019 16:30:44
775 forum posts
4 photos

I don't understand how to check the servos with a Watt Meter. I thought the Watt Meter only told you what was going on with the drivetrain.

Ian

Denis Watkins25/01/2019 16:38:29
3913 forum posts
61 photos

The watt meter in your supply line Ian,

While you operate the sticks

A stalled or tight servo would show a sharp increase in the reading

Edited By Denis Watkins on 25/01/2019 16:39:51

Jonathan M25/01/2019 16:44:08
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670 forum posts
275 photos

On zero throttle, move one stick at a time and observe the readout for that servo on the Watt Meter (do each aileron servo separately by unplugging first one then the other), then repeat at 50% and 100% throttle - the difference in amps drawn for each servo should I assume be the same.

gangster25/01/2019 16:57:11
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965 forum posts
17 photos

I am not sure about why you think the control surfaces were in spin mode. The force or the crash could have left them anywhere. My money is also on power . We must not think for one minute that the ratings quoted on the power train components are safe. I allow at least 20% headroom. They are not necessarily describing the items wrong. But just not the way we expect them to mean. Also interference or make of radio should always be put very last as the possible cause of a crashing if you want to be getting near the real reason. As one who has been there I do feel for you it’s never nice to see it happen to anyone I hope you have not scrapped the model though you or someone else will get the inclination to repair it sometime

gangster25/01/2019 16:58:23
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965 forum posts
17 photos

Edited to remove duplicate post

Edited By gangster on 25/01/2019 17:00:47

Jonathan M25/01/2019 17:38:31
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670 forum posts
275 photos

Cheers Gangster - I agree, the power issue seem to be the most likely one... allowing for the fact that the loop problem took place at full-throttle and the spin problem at no throttle...?

The control surfaces were all in the same post-crash positions exactly as I'd first put them into to enter the spin: up elevator, left rudder and finally ailerons (see photos at top of first page of surviving surfaces and servo-arm positions). I agree that one would normally expect much more random deflections after such a hard impact, but - as I say - they were all exactly where I'd originally had them before loss of control.

Interestingly, I was just looking at my own Gangster 63 build-thread (started two years ago before I got distracted by other things but now thinking about making this year) and came across these contributions:

Posted by Phil Francis on 24/04/2017 19:37:45:

Don't use New power Servo's unless you want a world of hurt. Tried a couple a while ago they don't centre well, 1/4" either side of centre.

Posted by Percy Verance on 24/04/2017 20:48:13:

My experience of New Power servos isn't particularly good either. Those I bought were not good at centering well. I shan't buy anymore...........

Futaba 3001's or HiTec equivalents for me all the way....... More often than not, budget servos will eventually come back and bite you on the proverbial.

Not saying the NP servos were definitely connected to the Wot4's catastrophe. I won't know anything until I've run the tests, but the common denominator in the two instances of loss of response - the loop and the spin - both involved the elevator!

They were certainly very noisy and didn't seem particularly fast or responsive - I kept having to fiddle with rates and expo, trying to get the model to respond smoothly to stick movements, rather than too little and then suddenly too much that I kept experiencing!  They certainly didn't centre properly.  So I'm definitely going to fit one of the established brands on the new Wot4 (very happy with the Futubas on the Acrowot and the Hitecs on my Middle Phase).

Edited By Jonathan M on 25/01/2019 17:41:54

Don Fry25/01/2019 17:53:17
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4054 forum posts
47 photos

Jonathan. Quite right. A reassuringly expensive servo is not necessary. But you have to spend enough so the manufacturer can do it with some pride, and eat.

Peter Beeney25/01/2019 18:00:29
1557 forum posts
59 photos

Jon,

I think if this happened to me I would be trying to establish in the first instance why the throttle control behaved as it did. If I read this correctly you fully closed the throttle (stick) on two separate occasions from full throttle but the motor continued to run at full speed. I would now be thinking that for whatever reason, at least in the first instance anyway, the throttle stick is not working properly. I have to say that for me that would be a really major incident; from the safety angle just for a start...

It seems to me that the processor in the ESC will have to receive a valid pulse width signal on the throttle channel at all times to operate; if it did not it wouldn’t run the motor at all. This signal has to come from the receiver which in turn gets it from the transmitter, it’s difficult to see how any random component or any fault in this little power chain could create and maintain such a signal on it’s own. Also very significantly the transmitter’s throttle cut-off switch, which I consider just holds the throttle channel pulse chain at the fully closed position anyway, effectively closed the throttle. I don’t think it could have done that if the problem is not in the transmitter and related to the throttle stick.

And then almost simultaneously another separate fault appears to cause all the servos to stop working… …is that now perhaps stretching credibility to some extent, I don't know, but I think I’d certainly want to give the transmitter a very close coat of looking at to make sure it was 100% ok. In my experience, in a now long ago working life, I found that little occasional random faults and glitches on electrical kit generally, if every effort to crack them was not made at the time, 9 times out of 10 will sooner or later occur again.

Just another niggling thought, it seems as though the throttle channel doesn’t really like faithfully obeying full stick movements sometimes. When you initiate a flick roll where do the sticks go? I’d say generally in the corners at full stretch. So now you may be in front of me and saying perhaps the other sticks are also following suite… Sounds like an extreme long shot, bordering on the limits of visibility maybe, but pretty easy to prove one way or the other.

Good luck…

PB

eflightray25/01/2019 18:50:18
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584 forum posts
128 photos

Catastrophe ?

Many moons ago, the group I flew with had a trophy for the best (most stupid) crash.

It was made from cardboard, and depicted a 'cat's-ass' trophy. wink

Much cherished if won. All clubs should have one.

.

GrahamWh25/01/2019 21:15:13
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356 forum posts
53 photos

Jon regarding the throttle, have you tried looking at the "Monitor" screen on your Spektrum Tx and wiggled the sticks - slowly, fast, suddenly, any which way - just to check the sliders on the display continue to show the stick positions correctly and smoothly with no jumping? This will show if the sticks are behaving correctly without having to connect any servos etc.

A friend's Dx6i Tx was misbehaving (I cant remember which channel) and I solved it using electrical cleaning spray in the relevant potentiometer. A new pot may be better if a fault is found. As Peter says above the throttle cut just tells the Tx to send fully down (125%) to the Rx by-passing the stick. If the stick potentiometer was faulty this could explain the power problem and why it was initially cured using the cut button.

 

Edited By GrahamWh on 25/01/2019 21:17:11

Geoff Sleath25/01/2019 22:16:32
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3432 forum posts
297 photos
Posted by eflightray on 25/01/2019 18:50:18:

Catastrophe ?

Many moons ago, the group I flew with had a trophy for the best (most stupid) crash.

It was made from cardboard, and depicted a 'cat's-ass' trophy. wink

Much cherished if won. All clubs should have one.

.

My cycle club's award for the 'crash of the year' is 'The Flat Cat Award'. It was instigated in 1990 when I was downed (very seriously as it turned out) by a cat deciding that the shortest way across the road was through my front wheel. I think my wife and I are the only married couple to 'win' it (2 separate events).

Geoff

will -026/01/2019 08:55:26
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578 forum posts
19 photos
That's rotten luck, some years ago I managed to flatten my rx battery on entry to a spin. The plane spiralled down from on high and came to earth some distance downwind. Happily the earth was so wet and muddy that I got away with just a broken prop for my troubles. One question though, what's a three point spin?
Cuban826/01/2019 10:08:50
2763 forum posts
13 photos
Posted by eflightray on 25/01/2019 18:50:18:

Catastrophe ?

Many moons ago, the group I flew with had a trophy for the best (most stupid) crash.

It was made from cardboard, and depicted a 'cat's-ass' trophy. wink

Much cherished if won. All clubs should have one.

.

We've had one for years. A Merco 61 (I think) that looks like it's been run over by a tank, mounted on a tall wooden plinth. Very coveted trophy with many of our club's top flyers' (!) names on it. TBH, I think I can do without the accolade.wink

Don Fry26/01/2019 12:28:06
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4054 forum posts
47 photos

An old club had a bronze stick of rhubarb, plinth mounted. Very artistic.

leccyflyer26/01/2019 13:11:24
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1275 forum posts
302 photos

The fact that the control surfaces appear to be in the position required to enter the spin, and that the aeroplane wouldn;t come out of the spin, argues for a loss of power to the receiver, causing it to become non-responsive. I'd be looking at testing the current draw on those 4 servos all being run to their extremes at once and the stability of the current supplied to the Spektrum 6210 receiver under those conditions.

The model was described as being almost brand new - approximately how many flights on the board before the total loss?

Jonathan M26/01/2019 20:26:07
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670 forum posts
275 photos

Peter, Graham, Leccy, et al

Now back home from 24hrs away. Just checked the TX monitor which shows throttle (and other travels) all working fine. Also just checked the throttle-stick on my IC Acrowot's throttle-servo, which works fine. This leads me to conclude that I might provisionally rule out the TX end of things?

While Peter is right in what he observes about the throttle cutting via the switch when bringing the stick down didn't immediately work being related to a potential problem with the TX, it is also feasible - if it was indeed a poor connection disconnecting aloft at extreme-G or under other duress - that on both loop occasions it was the removal of such duress by the point that the model had entered the vertical dive part of the loop that coincided with my hitting the switch that reset the throttle connection, rather than the TX switch what did it? Conversely there would have been no removal of extreme conditions during the spin (thus none of the controls responded), so this also points to a problem in the air rather than on the ground.

Next up - tomorrow - is to remove the whole caboodle of servos, RX, ESC and motor from the box of wreckage parts and rearrange them statically on the bench powered by a fresh LiPo. The electronics all look physically fine and hopefully the motor isn't terminally damaged and will run mounted on a block of wood held by a vice. I'll do all this with the watt-meter connected up inline to carry out a full set of tests.

I won't be able to statically test for extreme or negative-G (vis the conditions at the top of the loop and in the spin), but will be able to wiggle each connection in turn, etc, and will report back afterwards.

The other thing - Leccy's question - is that the model had flown from new for a total of only four sessions (four Lipos per session so about sixteen flights in all) but most of these had been relatively sedate initial testing and trimming flights, and it was only on the fateful day itself that I was beginning to push the model harder.

Jon

PS: I'll reiterate this: I now fully recognise that it was an error to not ground the model immediately after the very first sign of trouble and this is a lesson I've fully taken on board for the future.

Edited By Jonathan M on 26/01/2019 20:46:14

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