Unexplained crash

[gangster]

If you want to do a check for modulation failure as detailed above you probably won’t need anything as elaborate as a spectrum analyser. An ordinary fm broadcast receiver tuned to vhf broadcast band will hear the harmonic

[onetenor]

The hot servo was probably "arcing" internally.As we all know don't we ???? arcing creates radio/wireless signals and i'm sure that this was the cause of the problem and why the fault was exactly the same each time. Had you been on modern 2.4 gear it might not have happened. However the problem might have caused a fire or meltdown so it's a good job you found it

[alex nicol]

Hi Dennis,

no glider pilots anywhere near, the nearest suitable hills are miles away. I've flown on 76 for 15years plus without as much as a glitch.

Hi Onetenor

I'm fairly sure the root cause was down to the failing servo. I'm struggling to see how frequency could effect the outcome.....for the amount of heat and current generated could potentially cause random Rx function.

all of that said, it's test time this afternoon with a new switch, battery ( power cycled and timed a few times)and a known good flight pack in an old ( bit tatty but structurally sound) airframe,.........so fingers crossed

[Frank Skilbeck]

A couple of years ago we were setting up a friends electric model and every time we plugged it in the Rx wouldn't work and the ESC got hot, we tracked it down to a faulty (new) servo, it was pulling so much current it was overloading the BEC in the ESC. If you were using a high capacity AA pack there's a chance that a failing servo pulling a high current could cause the voltage to dip and cause the Rx to "brown" out.

[Piers Bowlan]

A servo 'meltdown' would suggest it has either shorted out for some reason or stalled. Either way the current drawn would become very large and the battery voltage drop rather rapidly. In the case of a straight short (which would create enough heat to melt plastic) not only would the servo in question fail to move but the subsequent drop in voltage would cause all of them to stop working (according to my schoolboy physics). The question is, would the very large current caused by a short, if that is what it was, damage your receiver? I know that you said that your receiver works without fault now - good.

If you still have any doubts about the reliability of your transmitter however you could always send it away to be checked.

ps you beat me to it Frank 

 

Edited By Piers Bowlan on 24/06/2018 08:16:24

[Former Member]

[This posting has been removed]

[alex nicol]

Thing is we may never know the exact cause. If today goes ok I'll probably continue to test until happy all's ok and bin the old flight set........I appreciate I could be throwing good kit out but for the sake of peace of mind I'll just need to live with it.

if I get a repeat, it's Tx off to get checked and if that doesn't solve it it's a load of 35 MHz stuff in the bin and move to 2.4

PS fail safe set to kill throttle only and freq changed to 75. I'll post the result

Thanks again to all for taking the time to respond

[Rich too]

How old is the trans? How much time on it? Ever had it serviced ? I would be very reluctant to use 35meg radios today. But I have a 2.4 meg Futaba that is over ten years old and although it’s not had much use it will get a service soon.

[Former Member]

[This posting has been removed]

[Rich too]

Personal preference I guess Percy, but also 35meg sets must be very old now, or are they still available new? I’ve got an old Futaba 35 meg set but I wouldn’t use it now.

[Paulo Peres]

Hi all,

I also use a Futaba Skysport 6 on 35 MHz (35.050 to be exact)) without an issue. As of yesterday, I've had about 40 minutes divided in two sessions of pleasurabe flights with my 18 yr old Multiplex Panda on that frequency. What got my down was my neck and the need for water as we were experiencing about 86F at 10AM

Until a very short while ago I was using on the model a 19 yr Sksysport 4. The problem with it is the NiCd battery . It sat for long without use and somehow I got it recovered. Nonetheless, it charges fast, but discharges even faster! The NimH on the former after yesterday's usage still shows about 100% charge!

PP

[Paulo Peres]

Adding up to my last post, I also use a JR on 2.4Ghz. Memories to have many models with all the nitty gritty details of trim, D/R and expos always set, is a true blessing.

[alex nicol]

Update Time,

3 flights not a glitch all worked fine, One I've had a few more outings I'll put it down to outgoing servo

[Gary Manuel]

Nice one Alex.

Always good for the confidence, to know what cause the problem. The more good flights you have, the more confident you'll feel.

[AVC]

That's good Alex. I also think that this faulty servo had a key role to play.

[Rich too]

Well done Alex, fingers crossed.

[Julian Thacker]

I have just spotted this thread. Hopefully you have had no more problems Alex. I have a 12Z and it has been solid for well over 10 years now. I bought a 2.4 TM14 module for it around 10 years ago and have slowly moved most of my existing models (and all new ones) over to 2.4 over that time. I am posting because I also experienced a problem with a Kyosho F16 EDF with the 14 channel PCM2048 rx supplied with the tx. This happened about 10 years back now and I never got to the root cause. It probably was nothing to do directly with the rx but I never felt comfortable with that rx after that and reverted to PCM1024 and PPM rxs and never had a problem again. Likewise I have never had a problem with the 2.4 module in the 12Z. As a matter of interest are you using the PCM2048 rx in your hack model? I still have that rx and it could be useful to have a 14 channel rx available.

If you do decide to get rid of the 12Z remember they still have some value, especially if they are clean and undamaged. Don't bin it!

Julian

[alex nicol]

Hi Julian,

I quarantined the 'suspect' flight set for now. I'm flying the old hack with a GWS ppm receiver and Futaba 3001's with no issues to date. I'm happy the tx is behaving it's self so far.......confidence in it is returning.

I'm torn between trying the suspect kit or just binning it. The only thing causing a bit of doubt is of the servo's failed and got very hot on bench test after the event. the receiver was a Futaba G3 2048

[alex nicol]

sorry that should read one of the servo's got very hot

[Denis Watkins]

Have scanned the 5 pages of posts Alex, so apologies if this is a repeat

The hot servo

Temporarily take off the servo disc or arm and push that control pushrod operating the surface by hand

There should be no resistance to surfaces operated by hand.

Any mechanical resistance can result in a stalled overheated servo

Edited By Denis Watkins on 25/07/2018 18:21:11

[alex nicol]

Hi Denis,

I dismantled the servo to check, the motor had siezed solid......don't know exactly why, but I binned the motor and pcb as it was pretty hot and giving off that horrible fried electrics aroma, but kept the gear train for future spares.

As things stand I'm putting the issue down to this servo

[Denis Watkins]

Ah but, push the push rod that the servo was attached too

Is that movement completely free through full deflection?

[Gary Manuel]

Denis has a good point.

I think you have traced cause of the crash to the faulty servo - but what caused the servo to fail?

If the push rod is free to move, it was probably just an isolated servo fault, but if it's sticky, you need to sort it to prevent the same thing happening again.

[alex nicol]

The servo failed after the crash.

Difficult to check pushrods as the fuselage was mangled. That said the servos were still in their tray but not connected to anything. They were on the bench being checked, poked, prodded etc when the elevator sero failed. One minute it worked the next it'd stopped and got very hot.......at this point it was hastily removed from power.

The question now is do I try the suspect kit in an airframe to see if it's ok or bin it, I'm leaning on the side of binning it and chalking it up to just bad luck.

For me the main things are, after several flights with the 'hack' deliberately overflying the crash site no more glitches so flying site and TX seem to be good......so far

[Denis Watkins]

The next time Alex, check the surfaces can be pushed and pulled freely by hand, no resistance

Connect servos, one by one and check full deflection that the servo is not pushing or pulling too far

This will stall the servo at full deflection

With servo travel on your TX, reduce the push and pull % travel to keep the movement free from stall

We are just about all certain that a stalled servo overheated and died, putting a strain on your power supply

And reducing power to your RX