Nasty incident

[Andy48]

Posted by Erfolg on 20/07/2013 17:48:27:

My biggest concern is with respect, what would I do if the motor stayed at the set power setting after switching the Tx back on, and the Rx did not respond. Again I set the throttle to half power with the view, if the motor cannot be shut down, I will need to disconnect the Lipo, although I have thought about disconnecting the ESC to Rx, but never tried it. This scenario has never occurred though, I do not like the idea of disconnecting a Lipo on load.

Its obvious really, you just simply remove the safety plug.

[leccyflyer]

Please bear in mind that if your model is fitted with a failsafe, the advice in the revised CAP 658 is that you should ensure that it is set correctly to, as a minimum, ensure throttle is set to off, or idle on loss of signal.

It is quite common for the throttle channel to be reversed on initial set up, and, as decribed above, it becomes critical to set the failsafe and rebind, after reversing the throttle, in those cases.

[Chris Bott - Moderator]

Posted by Erfolg on 20/07/2013 20:22:01:

For some there is a mantra, take the propeller off, no real logic.

Erfolg the logic to this perfectly sensible mantra is that with the propeller off, the model is not going to shoot accross the room or slash into somebodys arm, no matter what they do with incorrectly set failsafes or reversing of channels.

As I type, one of my smaller models (around a 250W setup) is sitting running with it's prop off at full throttle. It's drawing around 1A so is having to dissipate around 12-13W. It reaced a final rpm as soon as I opened the throttle, and has just sat there running at that speed for some minutes now.

The 13W is being turned into sound, rotation against all the different system losses and ineficiencies and a little warming of both ESC and motor.

Whatever is going on, it's a LOT SAFER than leaving the prop on.

[Andrew Russell 2]

I love how this thread is bubling onabout fail safe in 2.4 what about the majority who still fly 35mg?

[Pete B]

Good question, Andrew - I wonder if the majority are still flying on 35Mhz or has 2.4Ghz tipped the balance? Either way, if there's a failsafe option, it should be set.

Pete

[Andrew Russell 2]

Speaking for my club the majority still fly 35mhz. Some have a 2.4 but only use it for bnf models

[Chris Bott - Moderator]

From my (as limited as everyone elses) perspective, I hardly see anyone on 35Mhz any more.
That's at two clubs and a number of flyins/shows.

At the RCM&E fly in at Greenacres we had 2.4GHz transmitters outnumber 35Mhz about 10:1

[Andrew Russell 2]

But chris bear in mind that at most shows only 2.4 is permitted. I have no idea as to the mainland but from traveling around the flyins in ireland 35mhz is still the main player maybe were just slow to catch on over here. Anyway straying off topic here I support using fail safes when there available but when there not being careful should avoid incidents.

[leccyflyer]

Posted by Andrew Russell 2 on 21/07/2013 12:23:54:

I love how this thread is bubling onabout fail safe in 2.4 what about the majority who still fly 35mg?

If their transmitter has a failsafe then the situation is the same. If there is no failsafe on the transmitter then it is different.

In this case the issue was caused by an incorrectly set failsafe. That can happen with 35mhz just as it can with 2.4ghz.

[John Privett]

Certainly from my perspective, 35MHz is now a small minority - at least amongst those who fly at the weekend at my club. Some people do still use 35MHz, but they often have 2.4 as well. I'm just about to go out flying, I'd guess there will be 10 to 20 flyers over the course of the afternoon. I'd be surprised if I see more than 2 or 3 txs on 35.

[Peter Beeney]

Erfolg - With the greatest respect, but in relation to any electrical ‘limited knowledge’ I’m not quite sure if that always matters greatly. In general the gentlemen that fly electric planes at our site I’m sure would would cheerfully admit to having ‘very limited electrical knowledge’, but they seem to manage admirably. I’m sure that it’s simply the case of perhaps buying a suitable motor for an application, and coupling this with the appropriate battery and speed controller. Of course, the more familiar you are with the principles involved, the easier it probably becomes.

To that end, and perhaps as a sort of variance to my rather bald view there perhaps, I’ve always felt that to some extent aeromodellers seem to be quite capable of taking something and then trying to make it do something that it shouldn’t be doing! Also I’ve noticed for a long time, too, that occasionally the odd electrical principle seems to become somewhat ‘strained’, … if, indeed, not completely bent…

A good example of the former statement might be the humble but ubiquitous voltage regulator, or BEC, in modelling jargon. I think there is a story to be written in defence of the BEC; over time it does seem to have become rather misaligned, if not downright lambasted in some cases, although through no fault of it’s own.
Even the name is a bit of a contradiction in terms, the E being for Eliminator. I think Exchange would be more appropriate, because in the modellers case he is just Exchanging one battery for another. Indeed, he’s just exchanging a receiver pack, which is eminently suitable to power the receiver, for the motor power-pack, which is in turn totally unsuitable to power the receiver, A proper Battery Eliminator Circuit is the small transformer plugged in the wall socket, this transforms the AC mains to the correct low voltage DC to power a great variety of appliances. It Eliminates the Battery entirely…

In the second instance, the flexible electrical principle effect, one such example of this might be the quotes you copied into your post at 20/07/2013 20:22:01: - I have some difficulty in keeping up with parts of that gentleman’s narrative with regard to the volts, amps, watts and power; I feel a much more explicit explanation is called for on his part, but I’m not convinced it would ever be forthcoming!

Not really suitable for this thread, maybe, but a general discussion in a thread designated to these motor and other other similar queries might be an idea, at least; the topic can then wander sideways and up and down to some extent without coming under the moderator’s spotlight too closely. A closer grip on the very basic motor theory, although leaving out as much of any arithmetic as possible of course, I’m sure would lead to a better understanding why motors do what they do.

With regard to the unloaded speed, provided it’s run within spec., any permanent magnet motor should easily be capable of running indefinitely at full speed; and whilst some types of motor will run up to a theoretical unlimited top speed when unloaded; (that becomes a runaway), such as a car starter motor, for instance, again our permanent magnet motor is never going to do this, only in the most extreme of circumstances.

Happy Motoring……

PB

[Biggles' Elder Brother - Moderator]

I recently looked around my club to see if anyone would like to be the receipient of some 35MHz Rx's I had lying around. No takers. In the whole club - 61 members - I could only find 2 that fly 35MHz and both of them aready had a shed load of 35MHz recievers given to them and definitely weren't interested in anymore of them! And I should add that both of these flyers also have 2.4GHz gear - which they are migrating to anyway - but they do still fly some 35MHz.

A pegboard is a rare sight in our club now! And I don't think we are unusual in that.

But even saying all that, Leccyflyer is spot on - 35 or 2.4 it makes no difference, if you have a failsafe is should be set - set correctly - and tested!

BEB

PS Erf - I'm sorry, but think you've "lost it" mate on the prop issue - working on a live model with a prop attached in the workshop is absolutely asking for trouble! We spend a lot of time on here impressing on beginners this is not good practice!

[fly boy3]

I am still using 35meg, ppm, Futaba 6ex. As I am starting to get into electrics, is there any thing I can do regarding a fail safe system, as it can now only be set for PCM. Do I need a new Xc. Cheers

[Martin Harris - Moderator]

The sight of a silvery pole sticking out from the flight line is rare enough at our club to provoke comment!

[John Privett]

Posted by John Privett on 21/07/2013 14:07:43:

I'm just about to go out flying, I'd guess there will be 10 to 20 flyers over the course of the afternoon. I'd be surprised if I see more than 2 or 3 txs on 35.

Well, as expected whilst I was there we probably had about 15 or 20 people flying and 3 were on 35. Two of those were members who turn up once in a blue moon, so without them it would have been only 1.

[fly boy3]

Sorry Martin, didn't, mean to frighten you,but there are a few of us still about for various reasons. LoL. Always appreciated your help to us who need to ask such questions. Cheers

[fly boy3]

In a recent poll. 14percent still use 35 megs,and 28percent use it now and then. Off thread I know but relevant I think. Cheers

[Peter Beeney]

fb 3 @21/07/2013 20:45:40 - As it happens, by default your 35 ppm receiver will be failsafe on a straightforward loss of signal situation: a crystal failing, or losing the receiver power, say. The ESC will only operate on receipt of a valid signal from the rx, so if this is missing the ESC will not run the motor. Not so clever with i/c though, if the signal goes missing the throttle servo just stays where it is, and that might be at full throttle. There is a gadget that goes in the throttle line to close the throttle servo on loss of signal, I had one, which worked well in this case. However, if there is severe interference, such as another same-frequency tx turned on, the throttle signal/servo will be extremely erratic, but so will all the other servos. So it’s all a bit irrelevant perhaps, the model is going to inevitably crash in a few seconds anyway. The in-line servo failsafe device is supposed to shut the throttle here, too, but when checking it with severe interference in my case it opened*!? the throttle fully, every time in numerous tests.

You could also use a MPX Intelligent Pulse Decoding, (IPD) ppm receiver, fully compatible with your Futaba transmitter. This uses a microprocessor like a pcm receiver and you can set the throttle failsafe position to return to if there is an aberration on the normal signal. Also the Corona Digital Signal Processing (DSP) ppm receivers, again fully compatible, which will only accept the correct signal. Some of these don’t have a failsafe facility, although with an ESC it’s a default situation anyway, the motor won’t run, thus it only affects i/c; but some do support failsafe, such as the Corona RP8D1.

I’ve no idea on the availability on any of this 35 MHz stuff now, it could be a bit difficult. Just give your exiting kit a really good workout with regard to loss of signal etc. but I’d have thought that the fact that the motor will stop on loss of signal will be sufficient anyway. It’s a natural failsafe situation. If you ever try it for interference by switching on a same-frequency tx, slip the servo arms off the servos first, otherwise the linkages will tie themselves in knots!
But being shot down on 35 must be an ever decreasing risk, too, nowadays, so exactly how significant this risk is I’m not sure.

Hope this is of some use.

PB

[Erfolg]

Chris

Leaving a propeller on to do a test does not by definition mean that the operation is intrinsically unsafe. It is perfectly possible to do some test sensibly both safely and have a definitive answer to what is being tested with a propeller on.

I have witnessed two events where not using a propeller has resulted in an error. Both revolved around the checking with no propeller. Where the rotation of the shaft was observed, and the wrong decision reached as to correct rotation. At the field low and behold the error is found..

In my opinion it is better to do this test in controlled conditions at home, to verify correct operation, by operation, than turning up in the genuine believe that all is in order. Where the conditions are generally not as controlled as it can be, or indeed must be when testing at home.

I also feel that it is better to test the failsafe operation, in as near conditions as possible, that is under load. Of course it needs to be in controlled condition. Where the flying field flight line is not normally the safest conditions. How else can you be certain it will operate as required, if not under actual conditions.

The idea of testing systems which do not replicate operational conditions, were one of the issues cited when many years ago I trained, passed my certificate for "The Management ,Commissioning and Testing of Electrical Equipment". None duty tests were one of the issues where incidents had occurred, as a consequence of out operating specification operation.

Unfortunately it is a Mantra Chris," remove the propeller", no thought is being given to benefits and debits of the act. Modellers, just like anybody else should think, not blindly follow a mantra. I am sure that many other engineers will have had to deal the consequences of wrecked equipment, from just connecting up and turning on, because that is what we have always done.

The trouble with your test is that it is a one off, and does not mean that the results will always be as happy. To be honest, I have tended to take the advice from professional engineers, with respect to electrical and electronic systems. There are a few who contribute on this site and thread. Again one of the reasons, is one incident I can think of, where an operative disregarded the testing procedures, did what they thought was better, damaged equipment. When interviewed, the answer was "I have done it before and it was alright". Yes he knew better, than the engineers who had written the test procedures.

As with the weekend case, the paramedics certainly remained safe, although the process of saving live was not quite as successful. Many will applaud their Safety First ethic, although it appears that they could have been far more effective by accessing the risks, and behaving accordingly.

 

Edited By Erfolg on 22/07/2013 18:01:21

[Pete B]

TBH, Erfolg, I think you're arguing for argument's sake on this subject.

It doesn't take much searching here or on any other forum to find instances where a moment's thoughtlessness has resulted in a model setting off across the kitchen or through the flower bed.

You state: Leaving a propeller on to do a test does not by definition mean that the operation is intrinsically unsafe. It is perfectly possible to do some test sensibly both safely and have a definitive answer to what is being tested with a propeller on.

Of course leaving the prop on a model isn't inherently unsafe, provided the model is suitably restrained or in a cradle and you keep yourself away from the prop arc. In the real world, however, there will be more than a few who won't take any of these measures and the model will be sitting on the table, bed, floor or lap - an accident waiting to happen!

You might call advice to remove the prop a 'mantra' but if we are offering advice, often to a newbie, part of that advice has to be a consideration for safety - often gained by hard-won, bitter experience.

If repeatedly mentioning the possible dangers of working on a 'live' model with the prop attached results in just one person not having to make the dash to A & E, then the repetition is undoubtedly worth it. I, for one, will continue to mention it....

In respect of not noticing the direction of rotation, well, words fail me - folk here offer advice but they can't hold everyone's hand!

Pete

[Chris Bott - Moderator]

Erf my test is not a one off, I've been using brushless outrunners designed for model aeroplanes for just about as long as they have been available. Every one (a considerable number) has been run without a load. I'm still here, the world hasn't ended, and more importantly I have all my fingers.

You carry on with the way you do things, that's up to you.

But I for one will continue to advise that while testing an electric model, if the motor has to be "live" while servos, servo directions, failsafes and the like are set up, then is is MUCH safer with the prop off than with it on.

The fact that an accident happened where an industrial operative had something go wrong, on equipment that differs in many ways from the equipment we use, is in my opinion completely irrelevant.

[Erfolg]

Chris

You are either mis-understanding or misquoting what I do.

I set the failsafe without servos, just the Rx. I use my servo tester Nicad or it might be NMH (futaba Rx) battery.

I then set up my model with the servos in the model. No motor connection,

When I am satisfied that the only thing left to check, I secure my model, in a safe place, so whichever way the motor turns, it will remain secure, Connect my Lipo, in a safe way as at the field. That is from the rear. I verify correct rotation.

I disconnect the Lipo, then put my Watt meter in line, placing and securing it. Switch on my Tacho, again place in a safe location, which is handy.

Whilst restrained/secured (dependant on model type) I arm the Lipo. Advance the throttle. Then on a note pad record the watts, volts and revs/min. To do these tasks the workplace must be organised to have tools etc in safe and ergonomically arranged.

To my mind, you have to be certain that the propeller is rotating correctly. It is also important that the watts drawn are known, relative to the ESC, Lipo spec. The revs are useful in establishing potential speed and verification of the performance relative to the data sheet.

I have never had one accident, I know the systems performance.

More emphasis on not just safe working, as that is a given, however achieved, on overall safety. But without the propeller and the measured data, is the model as safe as it could be? If not I would argue there is some question on respect to overall safety.

I argue very strongly you need that propeller to undertake some tests to ensure safety.

[Biggles' Elder Brother - Moderator]

The only tests I ever do with the prop on are:

1. The power check
2. The final failsafe test - ie full power then turn Tx off.

Both of these I do outside, with the model restrained with a spike in the ground. I never install and connect a power battery to a model with the prop on in the workshop.

That's not quite true,... I did it once, a long time ago. As a result I found myself in a small room with a very excitable aeroplane doing a passable impersonation of a chain saw! Not good. Fortunately, no injuries; just a lot of inconvinience due to stuff being blown everywhere in the workshop and the model damaged in my wild efforts to grab it!

Since that day, never again! And no, I didn't inadvertantly move the throttle stick, I didn't even accidentally move the throttle stick, in fact the throttle stick didn't move at all! What I did was decide that I'd been a silly boy and set the model up as a "one-aileron" wing when it should have been "two aileron", so I switched it over.... doing that sets everything else back to default - including "unreversing" the throttle - the result was, as I say, exciting to say the least!

This is a very good example of the type of accident that happens. It isn't what you expect - very often it isn't an absent minded movement or even an accidental one like the OP describes. As Peter Beeney says above its something completely "out of left field". There I was, changing the wing type, its got zip to do with the motor; right? Wrong! And the penality for that very minor, and perfectly understandable oversight, could have been me losing my fingers!

And as TX's become ever more complex, with more mixes set up and more "interconnections" the likelihood of overlooking some obscure reason why the motor might start up when you don't expect it gets greater and greater.

No thanks - I'll stick with the "Mantra" as you describe it. Its kept me safe and whole upto now. And I know it will in future, because if the prop isn't attached it can't hurt me! And I have absolutely no indication whatsoever that any motor has ever suffered at my hands from occassionally being "whizzed up" without a prop on it.

In case you are wondering - how I set up servos? Easy, I unplug the ESC from the RX and supply power to it via a standard 6v NiMH pack. Even then I still usually remove the prop. In fact, truth be told, I simply avoid connecting the prop to a new model until I am about to do those final tests (outside and restrained) that I describe above.

If I'm doing maintaince on an existing model, then if that will involve installing and connecting the power battery there's no hesistation on my part - off comes the prop.

Oh, and I've never had any problem so far in telling which direction a motor is going even when it doesn't have a prop on it! Its really not hard to tell.

BEB

[WolstonFlyer]

I do exactly the same sort of thing BEB. Better to be safe than sorry and I have (so far) not had any problems.

To work out my motor rotation I find it sometimes helps to stick a flap of masking tape to the motor staft, then you can start the motor at a very low throttle and it is easy to see the rotation direction.

[PB]

As a relative newcomer to the hobby I've learned a great deal from the responses to my OP. Thanks to everyone who has contributed.

The only thing I can add to the prop or no prop debate is that I would never under any circumstances whatsoever attach the prop to an EP model in my house or any other confined space come to that. This is not a 'mantra' handed down from my club safety officer or instructor, it comes from my personal understanding of the massive amount of power contained in the average electric model power set up. The thought of accidentally unleashing 400 or 500 Watts of energy instantly and without warning in a living room/dining room/kitchen should be scary enough for anyone simply to remove the possibility of it happening. So no prop in the house for me.