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Crash investigation - taken ages to find the cause

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PETER BRUCE - Eastchurch Gap16/10/2018 00:06:33
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Geoff Sleath16/10/2018 00:18:44
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2941 forum posts
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Interesting! 5 amps isn't a huge load. I'm also dubious about the current carrying capacity of receiver power supply busbars but they seem to work OK. Most of my models are relatively modest but on my 84" Maher's Thunderbird powered with Zenoah 26 petrol engine I took advice and fitted 2 toggle switches in parallel.

Geoff

Rich too16/10/2018 05:05:14
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I don’t use them anymore - good video.

Nigel R16/10/2018 09:30:19
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Nice detective work!

Stall current on a basic standard size analogue, about 3/4A. Stall current on a basic standard size digital, about double that, 1 1/2 A.

Ignoring the motor for now, ye olden days setup of three analogue servos, one on each control, you'd only have 2 1/4 A to contend with. Nowadays with probably four digitals, more like three times that at 6A.

Cheap slider switches are not worth it. Certainly not in any setup with any kind of load. Some cheap connectors can be pretty poor, as well.

Anything with digital servos ideally needs the heavy duty 20 gauge cable up to the RX, and a decent switch. Personally I'd be happy with the RX busbar at this kind of load. Much higher and a power distribution unit starts looking necessary...

It does raise the question, do we need that much torque from our servos?

Peter Christy16/10/2018 09:40:12
1091 forum posts

Those slide switches with the built-in charger socket have been known as problematic for years. I was warned off them around 15 / 20 years ago. I only have one, and its used solely as a bench test item!

I still have a small stock of Japanese Noble switches, which were always regarded as the "gold standard" of switches, though I've never had any problems with the heavy duty JR harnesses - the ones with a separate charge lead. (There! That's done it now! sad )

On a large model, there is a case for having two switch harnesses in parallel, and many of the helicopter boys use electronic switches - activated either by removing a magnet or pin before flight - on large, expensive models.

--

Pete

Nigel R16/10/2018 09:53:48
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1854 forum posts
357 photos

I think the really naff switches just have a PCB with tracks, and the slider presses against, and wipes, on those tracks. They are truly awful. Prone to dirt buildup and susceptible to vibration, as well as being low capacity.

Glenn Stevenson16/10/2018 10:59:10
12 forum posts

If we cant trust these slide switches, what reasonably priced alternative are people choosing?

Maplins have a huge range of toggle switches, are any of these worth trying?

Glenn

Nigel R16/10/2018 11:25:43
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1854 forum posts
357 photos

Branded slide switches are ok as far as I know, within their limitations. I think Futaba HD switches are rated 6A?

I simply wouldn't use the cheap and nasty ones with the built in charge sockets.

PETER BRUCE - Eastchurch Gap16/10/2018 11:52:36
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759 forum posts
106 photos

Thanks for all the replies to my video. I had thought finding out what caused the crash would make me feel better however I still feel guttedcrying.

Some very interesting points have been raised here for larger models which I fear wont get the publicity those comments made really need.

To be able to demonstrate what happens with a faulty slider switch was too good to miss out on and to be able to show others was the reason I made the video - to demonstrate what can go wrong - then end up with a mystery because everything tested after the crash works - just like magic -.

The only clue I had was that my petrol DLE 35cc engine cut after a sharp manoeuvre - which I had performed many times in the past...

It ts my intention to take apart the offending slide switch shortly and see how its made and if I can see where the problem is within its construction... I will post it here shortly.

Just as a though perhaps I should have posted this in the forums video section (where I usually post)

Perhaps it would have the effect of spreading the word more about this issue for larger planes.thinking

Edited By PETER BRUCE - Eastchurch Gap on 16/10/2018 11:55:15

Peter Christy16/10/2018 12:04:00
1091 forum posts

In days of yore - and I'm talking valve equipment here - the advice was always to use a toggle switch! However, in the intervening years, the quality of toggle switches seems to have deteriorated, and certainly they seem to be less tolerant of engine vibration than a *good quality* slide switch.

The Noble switches I referred to earlier were 4-pole change-over types, so it was perfectly practical to parallel up poles, even when using centre-tapped batteries, for improved reliability. Unfortunately, they are no longer made, and those of us who have a few left, guard them jealously!

Of the current crop of switches, the only ones I have personal experience with are the aforementioned JR heavy duty types, though I believe the Futaba heavy duty ones are just as good. The JR ones have a separate charge lead - not the ones with the charge socket built into the casing. They are, essentially, two switches in one, paralleled up for improved reliability.

Sadly, Maplins are no longer with us, though much of their stuff was cheap rubbish! I have used some of their smaller slide switches on tiny models without issue, though.

--

Pete

Peter Robinson 916/10/2018 12:28:21
5 forum posts

Hi Bruce, sorry to hear about the model you lost. I have just started to use the electronic switches (soft switch) which have no mechanical parts. They are similar to the powerbox switch you can get them from HK (rated at 5amps). Another one I am using comes from T9 hobbysport which are rated at 14 amps plus duel battery setup. These switches always default to on if there is a problem. The other method is to bypass the switch for a direct connection if practical in the model. I have used in the past making up a jumper lead which I plug in for each flight for power (3-4mm gold connectors) Just a thought.

Peter

PETER BRUCE - Eastchurch Gap16/10/2018 12:47:59
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759 forum posts
106 photos

Hi Peter R. I am looking at a soft switch with no mechanical parts for my next AcrowotXL - yes going to get another one again as its a great model (But DON'T use the kit supplied clevises).

On the test I did I was only pulling 5 Amps but I do wonder if anyone has measured in real flight how many Amps a large fully acrobatic model like the large beasts at the displays pull ? I've seen 4 digital servos ganged up for the rudders and elevators - the mind boggles. - Or what force is on a model jets control surfaces when its pulling out of a dive - must be pulling a lot of Amps.

Not looked at what these planes use as out of my experience and price range but bet its not the slider switches I have used on all my fleet of planes...

Peter Robinson 916/10/2018 13:01:41
5 forum posts

Hi Peter, I have one of these spare if you are interested, I can bring it up to the field for you to have a look at and test this weekend if you are interested.

Peter

Supply Voltage: 3V - 8.7V

  • Dropout voltage (Input vs output): 100mV @10.2A
  • Continuous Operating current: ~ 20A
  • Peak Output current: ~ 50A
  • Standby Current (Off State): - ~ 5μA
  • Operating temperature range: -40°C 80°C

**LINK**

PETER BRUCE - Eastchurch Gap16/10/2018 13:38:14
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759 forum posts
106 photos

Hi Peter R. Thanks for the offer and what Im going to do is take a look at yours which is the best way to go - then buy my own. Hard lesson I have learnt with my AcrowatXL

Peter Robinson 916/10/2018 14:08:04
5 forum posts

Hi

I will put an alert on the club what's app when I am at the field.

Frank Skilbeck16/10/2018 15:45:08
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4159 forum posts
98 photos

I had a lucky escape with a brand new HD slide switch that I bought at a show that I installed in a glider, fortunately I was using a telemetry receiver and during set up on the bench the low voltage alarm kept going off, don't know the actual amps but wiggling the sticks pulled enough current to cause a significant voltage drop at the Rx. Plugged the battery in direct and the voltage hardly wavered under load (Sub C cells).

PETER BRUCE - Eastchurch Gap16/10/2018 15:51:51
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759 forum posts
106 photos

hi Frank. You were very lucky indeed. With the switch in the video it worked 100% fine then only with a load a 100% off with no in-between which makes it all the more of a surprise I found it. I am taking the switch apart later on ad hope to get some clue as to why its failed after around a year of use...

PS. Glad you still have.your glider

Regards Peter

Nigel R16/10/2018 15:58:11
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1854 forum posts
357 photos

"I have used in the past making up a jumper lead which I plug in for each flight for power (3-4mm gold connectors)"

Just thought this was worth highlighting.

No reason the jumper cable must be restricted to arming our electric motors.

Equally valid for RX power in bigger models!

Very low cost and easily doubled up if you want redundancy.

Rich too16/10/2018 17:50:01
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2836 forum posts
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I use these, not cheap I know .....

**LINK**

PETER BRUCE - Eastchurch Gap16/10/2018 20:38:05
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759 forum posts
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UPDATE - Slider switch taken to bits ---

Edited By PETER BRUCE - Eastchurch Gap on 16/10/2018 20:38:42

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