Unexplained crash

[AVC]

Posted by Gary Manuel on 18/06/2018 22:31:35:

Posted by alex nicol on 18/06/2018 22:27:41:

Hi Martin, separate channels, no y lead.

Further update, after plugging everything in on the bench, all worked fine. left it all switched on and did 5 minute interval quick stick wiggle checks, first couple went ok then the elevator servo was unresponsive, I picked the servo up and the base was absolutely roasting. hasty power off ensued servo in the bin. nothing's glitches remaining servos working fine, continuing to test

That servo that got hot, was probably putting a high load onto your receiver / battery which caused the receiver to brown out or the electronics to mis-behave.

I reckon you may have just found and fixed your problem.

This servo is probably part of the answer, specially if you are using NiMh batteries, as the discharge rate is relatively low so that servo was probably taking all the juice of the battery.

But I still think that you should double (or triple) check the F/S, because a loss or reduction of power in itself shouldn't result in full left ailerons, especially when using two separate channels. The 12z has two types of F/S, signal F/S (standard) and battery F/S. Check if the set up is different for the battery one, especially for channels 1 and 6

[Keith Berriman]

Hi again we're all the servos rated for 6 volt use ??

[AVC]

Are the servos Hitec by any chance?

[Neil (Itisme)]

Just a thought, i recently lost a plane in a similar way, take off as usual then suddenly rolled to the left. A friend watching said i stalled it (had that plane for about 18 months so i thought that unlikely). On inspection i found that all servos but the elevator servo worked correctly, the elevator would quickly go to full throw up (radio on low rates) then slowly return to centre in jittering steps.

[alex nicol]

all thoughts welcome.

the week prior it did a very similar thing and I thought id taken off prematurely and tip stalled. after repair a week later and being very mindful of last weekI kept it on the ground and got max speed before taking off and also kept the rate of climb at a low angle (about 20 degrees)

this time it came off the ground as if on rails, recommended engine is 40-45 2s, I had an Irvine 53 on an 11x6 so no lack of power. I was approaching the point where I was thinking about making a gentle 90 degree left turn. Before any control input was given model was on its back and contact was made with terra firma........it happened in a blink no time to react

[alex nicol]

Hi AVC

yes, rudder and elevator were HiTec servo's

[alex nicol]

Hi Don,

the bits will most likely have a future date with the bin........the only thing stopping me at the minute is the desire to get to the root cause.

[AVC]

Thanks Alex. I'm a great fan of Hitec servos but in my experience, when there have a electrical problem (and I have had a couple or three of them...) they tend to drain the battery very quickly, faster than other servos.

Have you checked the battery F/S in the radio?

[John Muir]

I once had some DYS servos which had a fault that caused electrical feedback to the receiver and made other servos connected to the receiver glitch. I replaced an aileron servo on an old plane with one and the rudder went mad. I thought the old rudder servo had gone defunct and replaced that with another DYS which only made all the servos start playing up. I figured it out on the ground luckily but if your rudder servo has developed an issue that causes something similar, maybe just when it gets hot or when vibration loosens a component, that could explain the left aileron command.

[Don Fry]

One thought that keeps coming back to me is a plane what has been range tested, tested mechanically, and has then done the same thing twice, at the (more or less), same range, and orientation to the pilot.

I struggle to see any other cause than a loss of signal issue

[AVC]

Posted by Don Fry on 19/06/2018 12:10:42:

I struggle to see any other cause than a loss of signal issue

I agree, although a loss of signal per se doesn't make the aileron servos to turn to the same position (i.e. banking) twice. The F/S would just hold the last position, unless is set.

That's why I keep thinking on the fail safe setup, specially in this transmitter with "dual" F/S (signal and battery)

[alex nicol]

the failsafe was not set, and on default. if I switch the tx off first the throttle closes, nothing else moves. I can't tell how the throttle servo was at impact........to the best of my knowledge it went in at full chat and the fuselage is mangled all the way back to the win t/e

the model has a 2 piece wing which attaches to the fuselage sides and a joining tube. The wings ripped two lumps out of the fuselage spilling the radio gear and the section from wing l/e to firewall is just mush

my initial feeling was to throw the whole lot in the bin bag, but as I was gathering the bits common sense kicked in. Admittedly I did look at the carb and the trottle was closed, but I suspect this was due to the crash as opposed to servo action

having found a servo meltdown post crash is a possible cause but I'm not 100% convinced, it could also be tx fault or external interference and it's how to eliminate these that's concerning me

[AVC]

I understand your concerns. I would make a simple test: discharge the battery down to 1 volt per element (assuming is NiMH), connect all servos, rx and battery, and switch it on, to see how the servos react to a low voltage. If there's no reaction, then the interference is more likely.

And sorry for being a pain, but I'm quite sure that the default position when failsafe is not set, is "hold" which means that the servos will remain in the last position. Have you tested that in your case, without setting the F/S, the throttle will close? If this is the case, then you have it set.

[alex nicol]

Hi AVC,

I've Just checked the flight pack voltage (Futaba battery checker) and its still showing 6.3v. with regard to the f/s if the throttle is open at all it closes on Tx power off all other servo's remain static. Upon power up they give a very quick & very small glitch, nothing that'd raise any concern.

I've got an old precedent fun-fly airframe which I'm thinking of kitting out with a known good flight set & see what happens......of there's any grief I'd need to consider looking at interference or Tx issue.

To All,

Thanks for all your contributions, certainly a lot to consider. If I find anything other than the "hot" servo I'll post it

On a separate note - how do I post a picture or create an album on here

[Allan Bennett]

Many years ago I had three unexplained crashes within a period of a few months. The second model used the same receiver as the first crashed model, so I blamed the receiver (having run out of any other ideas). But the third crash was using a different receiver, so I binned the transmitter, and have never had an unexplained crash since.

The original transmitter was a 35MHz Futaba, I think a 6-channel one, so I upgraded to a Futaba 10CP with a synthesised 35MHz module.

[alex nicol]

Quick Question,

In preparation for Sunday's test, I'm in the process of dotting i's and crossing the t's. I have an old and somewhat tatty precedent fun fly airframe. with a known good set of gear fitted plus new battery and switch. Everything has been checked out static several times. One question is what sort of range should I get with the arial removed from the tx ( futaba 12z on 35mhz)

[Denis Watkins]

Alex, you can definitely damage the innards of your TX, transmitting with no aerial

You have a load, with nowhere to go, so internal components will heat up

[alex nicol]

Thanks, I wasn't aware of that.

[Martin Harris - Moderator]

Not sure with the 12z but some Futaba transmitter aerials were connected via a screw tag at the bottom which could work loose, allowing the connector to drop off. If that was the case, it's quite conceivable that a range test could appear OK from the signal emanating from the connecting wire but erecting the aerial would effectively leave it in range test condition - fly a few yards further than the range test and ... splat!

[alex nicol]

I'm not sure of the physical arial connections, but I've tried aerial up and Arial down range checking. I checked aerial up at twice the distance of the crash with not a glitch......and that included the use of mobile phones for coms to ensure signal given and reaction were good......all performed perfectly. The only thing I haven't tried is range test aerial up with engine running.

At this stage my thinking is

1. the elevator servo that failed shortly after the incident

2. tx fault

3. interference

I've tried everything I can think of and can't get the fault to re occur or system failure. It's test time on Sunday afternoon so fingers crossed and praying for cause 1

but in the mean time happy to consider all suggestions

[Denis Watkins]

Clubs usually have a 35mhz frequency scanner that was used through the day to confirm and check frequency's switched on, and crystal accuracy.

You could do with the use of this simple scanner as you can test channels and your flight switch for on and off

And check that other unknown users are not switching on their sets uncontrolled outside your circle

[Peter Christy]

Clutching at straws a bit here, as there doesn't seem to have been a definitive answer yet, but have you checked the "buddy" switch?

I ask, because I used to take a spectrum analyzer down to my old club once a year, and check the transmitters of anyone who wanted a check. One transmitter showed an intermittent loss of modulation, which we traced to the buddy switch! The switch was noisy, and would occasionally try and take its input from the buddy lead, which, of course, wasn't connected! Result: total loss of signal!

You should be able to check it fairly easily. Just waggle a stick while flicking the switch. The servo should stop when in the "buddy" position and come back immediately in the normal position. Any jittering or erratic behavior here means a dodgy switch.

Probably not the fault, but simple to check and eliminate....

--

Pete

[Biggles' Elder Brother - Moderator]

Hi Alex,

sorry I'm a bit late with this I've only just spotted your question on inserting photos above.

For tutorials on this go here, you'll also find and area we call "The Sanbox" there where you can test out if you have it all working OK and it doesn't matter if it all screws up!

BEB

[alex nicol]

I'l try and answer all 3 in the one go

Dennis,

we're just a small club with about 20 members. I believe there is a club scanner about and am hoping we can use it this weekend. When the incidents happened there were only 2 of us at the site and the other members gear whilst not switched on is on 84, mine is 76

Peter

Haven't checked the buddy switch, but good call, will give it a try

BEB

Thanks for the info, I'll give it a go

[Denis Watkins]

Posted by alex nicol on 23/06/2018 12:09:17:

I'l try and answer all 3 in the one go

Dennis,

we're just a small club with about 20 members. I believe there is a club scanner about and am hoping we can use it this weekend. When the incidents happened there were only 2 of us at the site and the other members gear whilst not switched on is on 84, mine is 76

Peter

Haven't checked the buddy switch, but good call, will give it a try

BEB

Thanks for the info, I'll give it a go

Right Alex, have already posted that your even number crystals are usually apportioned to glider pilots on the hills

So glider guiders could be operating at your frequency, where you think you are alone, and your not!

For example, he should be on 85, and you on 75 to clear them from interference, power models on odd numbered crystals

And the scanner will give you a definitive on and off signal indicator, and that the frequency is well defined

All this is to reinforce the safe use of the equipment