Failure Modes

[Andy Boylett]

In my day job I used to get involved with looking at failure modes and mitigating them. Is there a list of large plane failures that I could look at? I am looking to try and design out as many possible failuires as I can. It would be great if you could all try and pick holes in the design and/or let me know of other possible ways that it could go wrong.....

For my half scale build I am opting for:
- 2 completely seperate Spektrum receivers (9 volt), each with two 7.4v batteries and kept totally separate with no interconnections.
- An SM services box on each pair of power supplies as these have diodes buit in that prevent one battery discharging the other if there was a fault.
- Two switches on each power supply to eleiminate a switch failure.
- Each receiver operates 5 Turnigy high power, high voltage servos running directly on the 7.4v, thus eliminating any regulator issues.
- At a maximum 5 amps through each receiver I will attach the battery supply through 2 wires onto spare channels, to spread the current.
- The ailerons are split so that there are 4 of them, each with a seperate servo, one to each receiver.
- Each elevator half has 2 servos and a mechanical mechanism on them so that each receiver controls one servo and can continue to control the surface if the other servo fails.
- The rudder has 2 servos ganged together, one servo on each receiver.

No comments re pilot failure modes please such as finger twitched the wrong way

Cheers
Andy

[Dave Hayfield]

Hi Andy, it always worries me when the printed circuit in a receiver is subjected to high current demands and 5 amps is considerable, instantaneous or stalled servo demand can be higher. I have always removed the receiver from servo power demand where several servos are involved by creating bus bar connections before the Rx to feed servo power and supplied the Rx with a couple of supply inputs which just power the RX. Always worked superbly and very easy to place rf filters into the Rx supply, probably not neccessary now with 2.4.

[John Evans]

Hi Andy
Like yourself and many others no doubt.Your method of installing redundancy in the model is beyond my comprenhesion The interpretation of failure modes is often discussed on this and other forums with trying to incorporate redundancy in the model itself. Whilst I am in favour of such provisions, for my part I have always had to keep it simple in the things I have done to incorporate such redundancy.In my opinion reducing the failure of 50% of the system as allways been a step in the right direction. Is it not time to consider the othe 50% with posibilty of building redundancy in to the Transmitter. Can it be done?. What would it take to make it possible ?. Is it time something was done about the possble failure of various parts especially the Rf module, Too expensive,or is it impossible ?.
The reason for this posting I hope will be to encourage the people with knowledge of electronics like yourself to put there views forward.
Happy Xmas
Regards
John Evans 1915
2x soc

[Andy Boylett]

John, Dave ,
Thanks for your suggestions, much appreciated.

Since myself and my son (Sam) moved to 2.4 we have not had a single glitch of a model in 2 years even though we fly HV electric models. We find that the new 2.4 mutli-aerial receivers are fantastic. Since we had one complete model loss of control we too have been thinking about how reliable the Tx end of things may be. I have been looking around at other forums and this does seem to be a topic of discussion now. So, is it possible to have 2 Tx's connected to a model with one controlling and one as back-up ready to takeover? I think the answer is yes and is worth looking into. Myself and Sam carry a spare Tx anyway (we have 3 Futaba 9c's with Spektrum 2.4 modules).

Companies such as PowerBox already use comparison electronics to decide whether to use the signal from Rx 1 or Rx 2 in their RRS models. Unfortunately, the way these are configured they would not be able to cope with deciding which Rx signals to use if the Rx's were connected to 2 different Tx's (a too complicated technical reason to explain). However, I think it it is not a very big change to configure for 2 Rx's using 2 Tx's (using a spare Tx switch channel as a 'flag' to say which Tx is the 'live' one) so I have contacted PowerBox to see if they would be willing to look at this. If they are not interested then I think I can find another way of setting this up.

Regards, Andy

[Andy Boylett]

Gents, I hae been talking with a specialist German electronics company and they now produce the piece of equipment that allows us to operate a large model with two transmitters. They had originally developed this unit to allow training. The unit has 2 receivers connected to it, each one controlled by a different transmitter. One of the transmitters is the master and a switched channel on it tells the unit which receiver to listen to.

As well as training this unit does of course mean that we could run a large model with 2 transmitters. The master transmitter would not not be the one used for flying. It would be held by the helper as the reserve unit and with its switch channel set such that the other transmitter is the flying one. If the pilot shouted a problem with his transmitter the helper could immediately flick his switch and he would have control.

The dual transmitter function was just a by-product of installing a trainer function. The rest of this unit is a 'powerbox' on steroids - it is way more sophisticated and offers far more options and monitoring functions.

http://shop.rc-electronic.com/e-vendo.php?shop=k_emcotec_e&SessionId=&a=article&ProdNr=A12075&t=6&c=705&p=705

Has anyone got any experience of this kit?

[Bob Thompson1894]

IF (and that is a big IF) anyone was to go down this road, then 35mhz was a simple way of doing it- two transmitters on the same crystal, any problems switch off and the other on. Talk about complicating things! I believe there was an experiment in the early 90s with a Tx with two aerials transmitting on 2 frequencies. Named after a gazelle or some other 'two-horned' animal. I would suggest that the German idea (whats wrong with a simple buddy lead?) is an answer looking for a problem, and with the excellent reliability record of radio gear these days, is more paranoia than redundancy. So can we all go back to 35mhz now? Please?

[Andy Boylett]

Bob,
in a previous discussion someone pointed out that the one remaining single, non backed up item we have is our transmitter and he asked if it was possible to have a back-up. This is why I was looking

I take your point re training but this does not add the security of a transmitter back-up. My son Sam had a total loss of one of our club trainers while he was in the middle of training someone - his transmitter failed!! In our local club we have had 3 transmitter failures last year - and in a club of 155 members that makes 1 in 50

However, I was not sugesting this unit is for training. I was suggesting it as a possible solution to the 'single transmitter' issue.

The German unit I have found has electronics that allows the use of 2 completely seperate transmitters. They do not have to be on the same frequency or even the same type. You could use a 35mhz Futaba and 2.4ghz JR together if you so wished! The more obvious way would be to use 2 transmitters the same though so that the set up could be copied from one to the other. In really big models with £10k or £20k invested this may well be an option to consider.

In an over 20kg plane which already has 2 of everything, receivers, batteries etc, it would be a relatively small additional cost to add a back-up transmitter.

[stuart cotgrove]

Named after a gazelle or some other 'two-horned' animal.

Sprengbok?

[Bob Thompson1894]

Named after a gazelle or some other 'two-horned' animal.

Sprengbok?

No, it may have been Impala. A one-off experiment, it had two separate aerials, one each side of the Tx and used two different channels. Was never seen again. Andy- 3 failures of transmitters in one club is staggering, I have had one in 25 years, when a soldered joint parted in a 5 year old transmitter. I have never heard of anyone else having a Tx go, except for one or two who had problems with the pins on the old FF8, caused by continually removing the module. Have you found out any reasons for the failures?

[John Evans]

Hi Bob
It was I that asked Andy to look in to the possibility of a back up system on the tranny. The reason for the request was that a number of years ago not long after I got my Futaba FF9, I lost a very good model due to the failure of the RF Module. It was relaced by Ripmax free of charge as they had the knowledge that a few were failing as another did in our club not long after. The RF module went intermittent on my zap last year. fortunatly prior to just taking off a expensive model. So if you take our club and probably many others out there that never worked out what the actual problem was and just dumped the whole set and went out and bought a different type. I do have a possible reason for failure as as we all know that the RF Module gets hot in the back of the tranny and that the rumour I heard somewhere is that it should not be left on without the aerial being extended. On many occasions whilst setting up a model, I have left the tranny switched on with the aerial down for long periods of time, this may have damaged the internal workings ?. My initial request was not to go down the two tranny system as you say it can be done with 35mh. But a automatic link of two RF modules, this way you have built in redundacy in all the ground system as well as the airborn system
John Evans 1915

[Bob Thompson1894]

Sounds like it should work, John, but its a bit daunting to have to switch the trannie off to switch the other on while the model is heading for Australia! Not sure how that could failsafe. On the other point, its not a rumour that the module gets hot, you should ALWAYS extend the aerial, otherwise damage will be caused. Shouldnt you be out flying? (its too bloody cold for me!)

[John Evans]

Hi bob
It was never my intention to have a back up system on the tranny that you used a switch to turn on another RF module. It would be a system that monitors the RF output and the case of a failure, switches over automatically ( I suppose it its got to be like a Battery backer system). May be just too much to ask for.
Anyway Bob, Today its too wet too windy too cold and I am too old and too soft to be out in this weather.
Will have to be out thursday, we are re roofing the club container
John 1915

[Denis Brown]

Hi bob
It was never my intention to have a back up system on the tranny that you used a switch to turn on another RF module. It would be a system that monitors the RF output and the case of a failure, switches over automatically ( I suppose it its got to be like a Battery backer system). May be just too much to ask for.
Anyway Bob, Today its too wet too windy too cold and I am too old and too soft to be out in this weather.
Will have to be out thursday, we are re roofing the club container
John 1915

That ( RF Module) sounds a brilliant idea bet it could be done quite easily. Get a patent on it

[Bob Thompson1894]

vulcan 015.jpg (62.19 KiB) Viewed 12806 times

This is what you want, John!

[Andy Boylett]

Does anyone know if any of the tranny manufactures are considering anything along the lines of 2 RF modules? or twin transmitting? or failsafe transmitter end?

Do we ever give them much feedback on how many times the tranny end fails us?

Nice shed, make a good club-house

[John Evans]

Hi Bob
We have one of those, but not as finished off as yours. If we had what you have we could not afford the weekly repairs caused by people who like to break/damage or steal other peoples property in our area.
To continue,we require a plug in RF module that in the event of RF failure it will take over the RF output and inform the user that this failure happened. From an old retired plumber as they say. Over to you wiz kids.

[Simon Willey]

With the advent of all this two way telemetry I would think it would not be long before something was available.
We seem to be getting new fancy things on a regular basis , maybe this system could be on the cards. Perhaps talking to some of the smaller Manufactures of 2.4 gear might be worth while.

Simon