Topic: Battery/switch Redundacy

I am thinking about doubling up the batteries and switches on my next model, a Capiche 140 powered by a DLE 30.

The simplest way I can think of is to have two switches and two batteries plugged into the the RX. I am planing on using two HD switches and two 2300mAh A123 batteries. Is there any particular issues with plugging two batteries into the RX ?

This is the simplest way I can think of doing this. I have also seen purpose made battery backers like below

http://www.innovative-rc.com/smartfly-batshare-standard-p-50.html?osCsid=71bd099aba5fbda9d4a3b22b74edf657

http://www.smservices.net/acatalog/Large_Model_Units.html

But to me they seem like one more thing to fail, are they worth it ?

Your idea of a simple (less to go wrong) redundant battery and switch is good.  If you are good at soldering, also consider putting a diode in each feed line, to prevent one battery going short cct. pulling the other down.  Often folk that have used a diode also use five cells to compensate for the additional voltage lost across the diodes.  I personally do not use diodes, as in my experience batteries do not fail short cct. in use.

The more complex battery backer boxes are good, but as you say, introduce more things to go wrong.  On a model over 50cc or particularly complex I would usually use a backup box, and run them on LiPo x 2.  I use a Jeti backup box on a model with an 80cc motor, that also has telemetry built in to give me the LiPo voltages.  As standard Jeti 2.4 send back Rx voltage, but on a backup box this is usually regulated, so a constant 4.8 reading does not help.  The monitoring of the source cells is worth while on a model that might get anywhere near it's capacity limits.

This is a more detail view on this issue - http://www.scalesoaring.co.uk/TUGS/Hints&Tips/Redundancy/systems3a.htm

We do not have reliability data on the components we use, only the subjective info we have gathered from our observations.  If we had good data, we could produce a "Fault tree" and do the maths on the options. 

Your simple solution gets my vote.

Hobbyking failover regulator switch for about £10 will do the job and also regulates the batteries to 5v :  http://www.hobbyking.com/hobbyking/store/__16811__FRS_Failover_Regulator_Switch_5A-Plus.html


   Tom

I have used a Powerbox product similar to the unit above and found it very good.  Much more expensive that the one above though.  The one I have has a major advantage of failing short cct. rather than open cct. by design, and has electronic switches rather than mechanical sliders etc..  This gives it a much greater ability to withstand vibration.

http://www.energonsolutions.co.uk/ProductListDetail.asp?FileB2BArticleDetailID=2148142 is the same device that I have, and why it is so much more than the above unit (copy?) is unknown.  I wonder if it's less profit margins or less electronics//

The power box stuff is a bit out of my reach price wise, one of the reasons I was looking at the A123 battery packs as I can use them with out regulator.

I have one question if I may ...... why?

With every wire, every switch, every component on a printed circuit board you're introducing a point of failure. There's a real trend these day towards simplification and it makes a whole lot of sense in my opinion.

On the diodes , I am handy enough to do the soldering and that sounds like a good idea. I think that is what the SM services common power supply has built into it.

I have one question if I may ...... why?

With every wire, every switch, every component on a printed circuit board you're introducing a point of failure. There's a real trend these day towards simplification and it makes a whole lot of sense in my opinion.

With one switch if it fails you loose the model, with two switches if one fails you don't. At about £5 each it's a cheap way of eliminating a single point of failure. Two batteries is because I want to use A123 for the fast charge time , and being able to use them with out a regulator and its cheaper to buy two 2300mAh ones rather than a 4600mAh one  . It also gives me something to put at the back of the airframe to balance out the weight of the DLE.

I have one question if I may ...... why?

With every wire, every switch, every component on a printed circuit board you're introducing a point of failure. There's a real trend these day towards simplification and it makes a whole lot of sense in my opinion.

Of course simpler is less likely to have a point of failure.   But that is why Redundancy is in the thread title.  Although the end result is overall more likely to develop a fault (more connectors, switches, perhaps diodes etc..) the fault is MUCH less likely to be catastrophic.   Obviously it is important to test both power packs before launch, just like FS pilots test magnetos before take off, because one issue is that a fault might lie undetected, and there might be less redundancy than expected...

There are lots of formal methods to evaluate reliability.  Look up Fault Tree Analysis, Failure Mode Effects Analysis etc... but for model applications the best that's possible is a simplified FTA in my opinion.

With one switch if it fails you loose the model, with two switches if one fails you don't.

Most switches are paralleled double poles so each one is actually two switches in parallel.  A high quality switch is very, very unlikely to fail - they're self cleaning and have positive contact pressure at all times.
I agree with Wiz, there are so many single-point-of-failures in the entire link (thumb to control surface) that imho you're just introducing unnecessary complexities and dangers - remember that A123s can deliver well over a hundred amps and you're paralleling them through the pcb track in your receiver.  If anything shorts or is connected wrongly there will be fireworks!   I'd go with one reliable battery (as A123s are), one good quality switch harness, & protect the harness from vibration.  Its just an opinion   
Cheers
Phil

Some Good Points there, testing the switches is one I had not thought of  ie if one fails. I am really trying to find out if there is a particular reason not to use the two switch, to battery set up. I have had one futaba style HD switch fail in a model , luckily it failed on the ground. It just seems that for the price its a good bit of insurance. I lost the my 30cc Sbach to a RX failure, a rare event by all accounts but to have a proper redundant receiver set up would cost more than the airframe.

I had not thought about the current issue with the A123 cells, maybe two 5 cell 2100mAh AA battery packs would suffice ?

Look up Fault Tree Analysis, Failure Mode Effects Analysis etc

Graham, with the greatest respect, utter twaddle.  I don't need to look-up the terms or the processes as I am already quite familiar in terms of system failure conditions or more correctly, potential failure conditions and, I have to say, again with respect, we are talking model 'planes here and specifically a Capiche 140!  For a start, long before I started considering electrical failure, I would be much more concerned with the potential for mechanical failure vis-a-vis servo motors, actuator arms, control rods, clevises and hinges and, if we truly deployed FTA methodologies to our models, perhaps combined with some six sigma "zero defect" manufacturing processes our models would not make it into the air, ever! Oh and the potential for human error should not be left out of the equation either. 

Now let's be practical - the key is not redundancy because taken to it's ultimate conclusion, where do you stop?  The key is to know your equipment and be confident in its installation.  It's about knowing your batteries and how they perform, it's about employing a sensible regime of charging and pre-flight checks of potential mechanical failure points.

A Capiche 140 with a DLE 30cc engine?  I would use a 4000mAh 2S LiFe pack for both receiver and servos (yes even digital servos), a good quality single switch and, if you need it, a 1300mAh 2S LiFe pack for the electronic ignition.

  AA battery packs would suffice ?

AA packs............ eeeeeeaaaaghhhhhhhhhhhhhhhhhhhhhhhhhhhh

I think what Stuey means is, if you're going to do that then use C cells but why are you considering NiCd/NiMh cells anyway?

I think what Stuey means is, if you're going to do that then use C cells but why are you considering NiCd/NiMh cells anyway?

Indeed, I have has some AA packs fail, but never sub C cells....

I only mentioned the AA packs as I have some spare. As for the LIfe batteries these are the ones I was looking at because they have , balance plug, deans for fast charging and the normal RX connector.

http://www.electricwingman.com/product.aspx?product=990

Two would cost me £42 but 1 of these http://www.electricwingman.com/a123-4600mah-2s2p-lifepo4-battery-pack.aspx is £56.90 and does not have an RX connector. So I either connect them up in parallel or use two switches and we are back to my original question.

The ignition unit cant handle the voltage on the fully charged 2s LiFe.

When you mention quality switches which ones are you talking about  ?

Wiz -  twaddle is rather a strong reaction to proving a tiny taster of some of the basic reliability tools for those not familiar with them.  PM sent

I am in the process of changing over to A123 cells (LiFe) on as many of my models as possible, as I have found NiMh to be far less reliable than the NiCd cells of old.  As Wiz said, LiFe is better, but I would use two 2000mAhr packs and two switches.  I suspect Wiz is a far better modeller than me, and looks after his batteries better than I, chooses better switches than I, hence his reliance on a single switch in a petrol shaker.

For those of us that have seen several crashes, and the cause has been found, is the percentage due to power loss worth trying to fix?  In my experience, after finger trouble, loss of power is the next biggest cause in a wide selection of models and modellers.

Wont a 2S1P pack suffice?  just wondering why the need for a nearly 5 amp/hour battery for the receiver & servos?   
Re switches, Knitter-switch, Omron, Devlin, etc all do good quality slide switches but the OEM one should be fine if its a 'name' brand set - unless its a really high current setup in which case I'd prefer to make one with heavier guage wire bussed to the servos with a tap to the receiver.
Cheers
Phil

Over 4000mAhr might be overkill.  By measuring what is left after a normal flying session compared with the original capacity this could be reviewed... But, in a true redundant system, either battery should be able to power the model for the flight, up to (as an absolute minimum) the next battery and switch test.   If one battery or switch fails just after the test (or a connector falls out etc.) it defeats the object of having a redundant power supply if it goes flat before the next test.

With a 30cc model 4000mAhr (2 x 200mAhr) does not sound too much.  I would consider running the ignition from two 4.8v regulators running off both batteries.  I am assuming 2.4 radio and high resistance to conducted noise on the power supplies.  The low internal impedance of LiFe cells would tend to vastly reduce any noise from the regulators. See http://www.jperkinsdistribution.co.uk/detail.php?JPNO=5509888&activepage=1&Navmain=Batteries/Chargers&subcatname=EnErG%20and%20EnErG-Pro%20lipos%20and%20accs

I have one question if I may ...... why?

With every wire, every switch, every component on a printed circuit board you're introducing a point of failure. There's a real trend these day towards simplification and it makes a whole lot of sense in my opinion.

commercial aircraft have twin ignition systems - 2 x magneto's, 2 x plugs and 2 sets of leads, airliners have multiple redundant circuits for most mission critical systems for very good reason - redundancy. Yes theres a time and a place for KISS (Keep It Simple Stupid) and whilst I don't run twin setups, many do and I can see good reason for it. Whether I would in this case I'm not sure.

J

The simplest and cheapest option for redundancy is to place an extra switch from battery to Rx. Switches have always been a major cause of crashes, I have seen it myself, loads of times. Better switches, are, of course a good idea anyway, with the type sold by SM services being double pole and good quality. I have, however, seen one of those fail....
The KISS theory is a favourite of mine, but for an extra fiver, adding a switch is a no-brainer.

...twaddle is rather a strong reaction to proving a tiny taster of some of the basic reliability tools for those not familiar with them

My immediate reaction was to apologise but, and please don't take this personally Graham, I stand by my comments.  I believe that to even bring-up FTA principles relating to model aircraft is twaddle, overkill call it what you will.  The fact is that someone could read it and believe it.

John I have to say bringing up commercial aircraft in this discussion isn't really helpful.  Yes of course you would have, want and need multiple redundancy systems where commercial aircraft are concerned but we're talking model aeroplanes here.

John I have to say bringing up commercial aircraft in this discussion isn't really helpful.  Yes of course you would have, want and need multiple redundancy systems where commercial aircraft are concerned but we're talking model aeroplanes here.

With all due respect Wiz, you said "With every wire, every switch, every component on a printed circuit board you're introducing a point of failure. There's a real trend these day towards simplification and it makes a whole lot of sense in my opinion" If it makes real sense and the additional redundant circuits increase the chance of failure my point which I illustrate is that if it works on full size it's good for us.

Now if you start talking about intoducing additional items in series with critical items eg a voltage regulator for example then I agree with you, more components = greater chance of failure, in this case the systems are in fact in parallel so there are no additional components between battery and Rx only a duplicate set and this wiill enhance reliabilty due to the fact redundant circuits are built in.

I also said that I'm not sure that I would go to these lengths on this type of model so I'm also in agreement with you to a point.

J

Now if you start talking about intoducing additional items in series

The diodes as used in the SM Services box are in series, and as you dont want to use the receiver servo connector block to common the power systems, there will be some form of junction point in series, be it intellingent box or just a T joint...
I'm surprised at the rate of failure Bob sees in switches. Most switch failures I've seen in 40 years of repair & design is in the wiring to the switch rather than the switch itself, with one or two oil ingress (ie bad installation) failures. My worry is that yes these systems will benefit a meticulous, keen flyer but will cause more trouble to the casual flyer.  The more complex the setup the more you have to be on the ball and that might not suit everyone.
Cheers
Phil

Agreed, On my boomerang jet it does have dual batteries but thats into a spektrum rx that has dual battery input and a failsafe switch i.e. if the switch becomes open circuit it powers the rx up, the switch has to be closed to make it shutdown.

Regards - J

The nearest experience I have regarding the OP is an Extreme Flight YAK54 74". I had a YS140 fitted rather than a petrol however I used a single switch and battery and the plane went in due to a battery failure(A123 LiFE). I originally thought the battery had gone flat but subsequently found that it would not hold a charge, it is probable that a two battery installation would have saved the model.

For a model of this size I think two batterys and switches are a good compromise between redundancy and over complexity.

The diodes as used in the SM Services box are in series, and as you dont want to use the receiver servo connector block to common the power systems, there will be some form of junction point in series, be it intellingent box or just a T joint...
I'm surprised at the rate of failure Bob sees in switches. Most switch failures I've seen in 40 years of repair & design is in the wiring to the switch rather than the switch itself, with one or two oil ingress (ie bad installation) failures. My worry is that yes these systems will benefit a meticulous, keen flyer but will cause more trouble to the casual flyer.  The more complex the setup the more you have to be on the ball and that might not suit everyone.
Cheers
Phil

I believe that some model fliers in the North East (a friend of mines' club) actually dispensed with switches altogether, just hanging leads out of the fuz which they plugged together, they had so many failures! Have you looked inside a typical switch?    I have personally seen (over a number of years) over 7 crashes proven to be caused by faulty switches. As I said, for a fiver, its good insurance.

Yes I have looked inside the common or garden switches as supplied with most radio sets and they're an accident waiting to happen. I think good quality switches are a must for larger models and by good quality, I mean sourced from RS or similar as opposed to those for the hobby market.

I originally thought the battery had gone flat but subsequently found that it would not hold a charge, it is probable that a two battery installation

It's possible Brian but are you saying the battery stopped holding a charge suddenly, that it went flat in flight or were the charge levels not checked prior to the flight?

I'm sure that the larger the capacity of the cells we use, the more blasé we become about our charging regime. In the days when the best we had was 1600mAh nicads, we checked and charged after pretty much every flight whereas these days, I venture, we may not check and charge at all during a flying session and I think that's asking for trouble personally.

Have you looked inside a typical switch?

of course I have Bob.

I think good quality switches are a must for larger models and by good quality, I mean sourced from RS or similar as opposed to those for the hobby market.

Re switches, Knitter-switch, Omron, Devlin, etc all do good quality slide switches

Cheers
Phil

Thank's for the constructive advice guys. Your right in that 4600mAh is way overkill but a lot of the A123 packs I have seen lack either a balance connector or power leads capable of handling  a high charge current. The ones from electric wingman have both, otherwise I would go with some from vapex or overlander of about 1600mAh.

The switches I have ATM are rexel ones that look like all the other HD ones I have seen. http://www.innovative-rc.com/heavy-duty-onoff-switch-charging-jack-futaba-type-p-391.html?osCsid=71bd099aba5fbda9d4a3b22b74edf657

As regards the ignition, I am highly reluctant to have a common power supply and it will have its own separate 4.8v pack. My radio is  a Hitec Aurora 9 and they have issued a warning about using opto kill switches as seems even this supposedly isolated connection has caused "lock outs". My RX failed completely and was deemed defective and replaced when sent back , I not sure if this is what they meant by lock out.

As for the S&M  toggle switches, but I have been told the sliding switches are better for RC.

QUOTE
I originally thought the battery had gone flat but subsequently found that it would not hold a charge, it is probable that a two battery installation

It's possible Brian but are you saying the battery stopped holding a charge suddenly, that it went flat in flight or were the charge levels not checked prior to the flight?

UNQUOTE

Wiz

It was an A123 battery that had not seen a lot of use and though I periodically check my batteries for capacity I do not do so every time I go flying. I had charged as normal and gone flying.

It was a while later ( 2-3 weeks) when I checked out the pack and cycled it, it was a 2300 pack but was only giving 200 - 300 mah on discharge.

If anyone has a way of reliably testing A123s prior to each flight please let me know.

If anyone has a way of reliably testing A123s prior to each flight please let me know.

Obviously voltage is no real indication, unless it's way down but I always monitor the cells as they charge so I know how much they've taken, that's all I do.

Just read my BMFA news, and, as we thought, the top cause of accidents is pilot error (which encompasses poor maintenance, bad building and poor fitting out) but the number two cause of accidents is loss of electrical power. Which would seem to point towards redundancy with switches/batteries. Maybe that that is the only way to reduce the number of these sort of accidents? After all, with total loss of battery power, a failsafe will be of no use.

As for the S&M  toggle switches, but I have been told the sliding switches are better for RC.

There's no difference physically

The question of switch types was raised a few years ago and after making a general statement as above, I was taken to task about it.  Well, I 'dismantled' a (scrappped) toggle switch of the highest quality, (aircraft spec for use in a non-redundant circuit costing around $75), and would you believe it - the guts were the same style as you find in you JR/Foobar standard slide switch

The advantage that toggle switches have is the variety of toggle styles - plain toggle, locking toggle, spring loaded, 2 and 3 way versions and combinations of any option, as well as single/double/triple pole.


Mark

I use powersafe receivers with twin a123 batteries on my 50cc models.  Some people fit one battery connected to two HD switches on opposite ends of the receiver sockets.

Your current draw will probably be a lot less than you believe unless you set up all the servos to be stalled out at full deflection.

IIRC the savox 1256 servo has a stalled current of 5 amps for each servo.   pretty major when the servo plug is barely rated to 3 amps!!

There's no difference physically

Slide switches have the advantage of self cleaning contacts, having a wiping action as opposed to the touch & pressure action of a toggle switch contact.

The advantage that toggle switches have is the variety of toggle styles - plain toggle, locking toggle, spring loaded, 2 and 3 way versions and combinations of any option, as well as single/double/triple pole.

Slides are also available in single/double/triple pole and in a variety of styles.
Cheers
Phil

Well, from reading the above, it seems both types have advantages and disadvantages. Reinforces the idea of doubling up the switch, and possibly battery. Is there an alternative to a switch?

Well, from reading the above, it seems both types have advantages and disadvantages. Reinforces the idea of doubling up the switch, and possibly battery. Is there an alternative to a switch?

There are alternatives, but I doubt they are anymore secure.

  Tom

There are alternatives, but I doubt they are anymore secure.

  Tom

thats it then. Two switches, and, on large models, 2 batteries. Do the batteries have to be matched? Talking sub C 6 volt here.

There are alternatives, but I doubt they are anymore secure.

The electronic switches are a lot more secure, as they fail-safe to the on position

Mark