Switch failure

[Mark Harrison 579]

I saw an expensine model belonging to one of the club instructors pile in at full throttle today, destroying the model.

Testing the electrics after retrieving the pieces showed that the switch had failed in flight.

Something to be aware of folks.

[David Ashby - Moderator]

Oh dear, poor chap.

Well at least he's identified the cause, what sort of switch was that Mark, model type etc.?

 

 

 

Edited By David Ashby - RCME on 02/12/2012 17:07:37

[Biggles' Elder Brother - Moderator]

Switches can be a real "weak link" - I think we are all sometimes guilty of skimping a bit on the switch harness.

BEB

[Chris Bott - Moderator]

A sadly neglected area of our radio gear I fear. Good warning Mark.

[Peter Beeney]

I must admit that I’ve always taken the slightly opposite view, it’s always seemed to me that the switches are relatively quite robust judged by the standards of some of the rest of the equipment. I have no idea what sort of switch the gentleman was using in Mark’s OP, of course, but certainly at least 99% of modellers use the standard unit that comes with the kit, and right from the beginning I’ve always thought these are up to spec, from all the manufacturers I’ve seen, at least. That includes my favourite, MPX. Do the radio manufacturers construct their own switches, or are they made as a standard item?
And for the larger models, there are also heavy duty types.

Taking the Futaba example, this must be used by many modellers as standard, this is a double pole, double throw, making it a changeover. As standard, only the positive pole is switched, the negative is common throughout. This means that the two poles of the switch are wired in parallel. If you take one apart these are really well made, in my lowly opinion for the switch to fail it would have to completely disintegrate. One set of contacts just going open circuit would be very unusual, two at the same time very difficult indeed to achieve. I suspect the switch, particularly with the parallel contacts, would easily maintain a constant current of say 10 amps indefinitely, the limiting factor might be the plugs and wiring. The only dodgy switches I’ve ever seen were those on the Spektrum 5e transmitter, and we’ve definitely proved this to be so.

I think there are many reasons for power failures, though, batteries, for a start, and for a multitude of reasons, too. Plus those connector plugs, they can and do come apart in flight. The fact that they are non-latching, in my view, is this time a serious failure by the manufacturer, but it’s also worth considering that perhaps it’s a another tiny obscure attempt at some slight built-in re-cycling aspect. But then I’ve always tended to be a bit cynical on these issues anyway.

I’ve seen many reasons for models crashing, but I don’t think it’s ever been the fault of the switch, although I’ve seen at least one knocked to the off position on a hand launch……

PB

[Paul Marsh]

I had a model go in at the Bury club do. The model switch turned off in flight, with obvious results. The Mutunuc 65 purred until it flew into a grassy brush, next to the golf course. It was a new high power switch, but tapping it lost power. Not very good.

Luckely, the grass was high and the model suffered some damage, but was repairable, mainly snapping the engine mount off and creasing the fin.

Engine is fine and the model is all repaired to fly again.

[Chris Bott - Moderator]

I've had quite a few switch harnesses in the past which were double pole slide switches, with both psoitive and negative switched. I always found it very curious that these were wired this way, doubling the potintial for an issue when it would be so easy to wire them as you suggest Peter.

Some were pretty poor examples of switches too, which I wouldn't dream of using these days. But it isn't beyond the realms of imagination to think that some people would. As I did, as a youngster, when the only consideration for anything was price.

[kiwi g]

sorry peter .. but i have been a long time supporter of switch failure..

There are many good switch products with some brands of radio gear ,but the more models one has the more switches he needs ..

have you ever seen the guy cleaning his model after the flying session with the spray bottle . then wipe it all down and pop it into the car.. ever wondered how he has managed to clean and dry around the exterior of the switch so moisture and dirt wont enter the slide .. . nine out of ten times I bet that it hasnt been thought of ..

often the switch itself will test good for cuircuit but the slide has been compromised meaning the slide is only just in the right position when ready for flight. the slightest vibration or knock and its power off .

I would recomend overall the recessed toggle style of switch that is becomming more common today and put it inside a canopy .

I do have to agree with peters comment about plugs .. they too are a great source of problems when not installed properly.. but we are taliking switches here ..

thanks

[Paul Marsh]

These are much better. A positive lock on and off. You have to pull the switch to get it to latch. I've got a few, mainly on larger models. From SM Services.

[Peter Beeney]

Well, there you go, then, I guess I’ve just been lucky with the switches. But I’d have thought that if they failed on a regular basis this would soon begin to show up. I’ve taken the covers off one or two in the past to have a look, and as far as I can see there is very little ingress of dirt etc., , or even none, perhaps, and the action is considered to be self-cleaning anyway.

With regard to someone using a new switch on each of many models you may well be right, but I’d personally not go to the trouble of buying a cheap and nasty version, and I’m not even sure where I’d get these from, and then having to solder on all the wiring and such on to suit when for a reasonable cost I can buy a good quality genuine item all ready to go.

I have one in a trainer that has done much service, so I shall now take it apart and give it a close up inspection. It’s certainly never had any attention before.

Incidentally, when I post an answer here the thread disappears from the forum, at least in my viewing area. I have to do a search, but it comes back when others post. I don’t think this has happened to me before, but thinking back it could be possible.

PB

[Mark Harrison 579]

I don't know what type of switch it was I'm afraid.

[Martin Harris - Moderator]

Was it an obvious mechanical failure, intermittent contact with no visible deterioration or wiring/soldering failure?

[GrahamC]

I purchased a brand new switch at the NATS this year which was faulty. It turned out to be badly soldered and shorted out the live and earth. Fortunately the RX battery wasn't tucked away inside the airframe when I plugged it in or I think a brand new airframe would have gone up in smoke!

I think I would check any new switch with a multimeter now!

[Trots]

I've actually fitted two switches wired in parallel on my TN Spitfire so if one fails the other keeps things going.

[David Ashby - Moderator]

Posted by Mark Harrison 579 on 02/12/2012 21:12:23:

I don't know what type of switch it was I'm afraid.

What sort of model Mark?

[YakMad]

I have had several switch failure including a heavy duty version switch. It was the heavy duty one which proved the most costly as it resulted in the total loss of the model (a Great Planes Super Stearman), the switch shorted and the resulting load melted the wiring from the battery to switch which allowed the wires to fuse together, the battery got so hot it melted the heat shrink covering. By the way this switch was in the cockpit and was never exposed to fuel, dirt or water.

[Paul Marsh]

It's like tyres on your car. Some people buy an expensive car, have mods fitted to it and fit cheap n' nasty tyres. I know someone who did that, and the tyre blow on the corner, sending his car and himself down a slope - inverted. It had blown and wrapped round the wheel, causing the accident.

Some people say why I use a £180 "W" Michelin tyre on my car, where I can get £40 budget which work. Same as a swich, some go for £1, but wouldn't trust them on a model larger than a .10, or something not worth much - even then I would check it over and as said before, found some cowboy soldering work.

I had a "Y" lead, plugged it in and blew my then expensive JR PCM RX. Turned out the signal and positive where shorted out. The model shop wouldn't even give my money back for the Y lead, let alone the £110 rx it destroyed.

[Mark Harrison 579]

I don't know exactly what make of model but I do know it was either a large Sukhoi or Yak aerobatic ARTF job. The switch showed no obvious signs of physical damage.

[bouncebounce crunch]

I'm on the same flight as Martin Harris here. (I'm the one with or is nuts) corrosion, wiring, solder failure?

[John Hickson]

I bought a fus set from Hobbyking which consisted of a filler plug, rx charge socket and rx switch all in a nice molding for £4.00.

Can you guess which part I will be swapping out first

[Peter Miller]

I had a switch recently that showed my battery was only half charged when I put a battery checker on it. When I put the checker on the battery it was fully charged.

The replacement switch showed a full charge.

[bouncebounce crunch]

So was it wiring or solder that was the weakest link?

[kc]

Perhaps they are wired that way to prevent Black Wire corrosion getting further in?

Black Wire can afect red wires too--I have an example where both are affected.

[Martin Harris - Moderator]

It can be a nuisance when it starts a new page - KC wrote:

Perhaps they are wired that way to prevent Black Wire corrosion getting further in?

What way, KC?

Another edit after a bit of thought:

...do you mean the black isn't switched to lessen the chance of corrosion problems in the switch?  If so, it could actually make a worse situation where the receiver PCB tracks could be affected before any problems became apparent - perhaps there's a good case for switching the negative instead?

Yet another edit after a bit more thought::

This assumes Peter's correct in it switching the positive - I think they're usually that way but haven't got one to hand to check...

Edited By Martin Harris on 03/12/2012 13:58:23

[Glenn Philbrick]

I've had a similar problem to Peter in that checking an RX battery through the switch showed it to be low, however directly onto the battery it was OK. I then checked all my switches and found quite a variation in voltage. The ones with a high voltage drop I threw away.