Sudden control loss for a second - RC Groups
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Mar 07, 2018, 12:53 AM
Right on the Edge!
Help!

Sudden control loss for a second


Hi there,

Yesterday my plane suddenly stopped responding to my inputs for about a sec, then it went back to normal. No crash luckily.

I imagine this is going to be a bit of a guess work, but do you guys know what could cause a 1sec-long control loss over the airplane, other than:

1. Tx or module failure/reset which would trigger failsafe (the plane didn't act as if failsafe was being triggered - I know this because the failsafe setting is full elevator up, and it's not what was happening).
2. Rx brownout (I use a 20A BEC which is set to 5,5 V, so I'd tend to exclude such overload).

I've seen this happening before on a friend of mine's plane, but to me it was the first time. I don't know if he ever solved the problem. I've been using this setup for some 5 years and I never had a problem before. Here's what I'm using:

1. FrSky DJT module with standard antenna
2. D8R-II plus

I'm not really knowledgeable in electronics, so I have little clue what to look for...

Thank you!
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Mar 07, 2018, 01:11 AM
Bo Edstrom, Sweden
Hi,
Can You describe how You have transmitter antenna pointed while flyiing in general and if you can remember at this flight in particular?

How is the receiver antennas mounted in the plane, a photo of the plane internal where receiver and antennas can be seen would be valuable.

You say You have used this setup for 5 years. During 5 years there can be some wear and tear, but almost impossible to tell if that has any infuence on the short non responding in stearing of Your plane.

What radio do You use?

What ESC/BEC do You use?

I suppose most suggestions to You will be a guess at this point but one should not overlook a simple thing as the antennas and their location, how they are pointing (both TX and RX) while flying (that is why I ask how the antennas are pointing above).
If You fly a valuable plane to You with this setup I would maybe be little careful flying with this plane again with same equipment. I think I would mount at least the receiver in another cheap foam plane (that You can afford to loose) and fly for some time with that and see if problem is repeated.

/Bo
Last edited by bossee; Mar 07, 2018 at 03:55 AM.
Mar 07, 2018, 03:44 AM
No bounce, No play.
davidmc36's Avatar
5 years old? Could easily be some corrosion on connector or switch causing intermittent power loss.

Just pulling plugs and resetting could cure it but a cleaning would be a good idea.
Mar 07, 2018, 03:59 AM
most exalted one
The pins in the module bay on other makes have become loose causing intermittent results. Should not be, if you are not removing and replacing module often. But it did happen on another make perhaps because of rough treatment where no removal was ever done.
Mar 07, 2018, 06:24 AM
Right on the Edge!
The thing is, I'd tend to exclude issues from the Tx side because any Tx or module malfunction would have triggered failsafe, which didn't happen. That is, unless the signal were restored too shortly for the Rx to ever enter failsafe in the first place. So 1 sec signal lost, and then before failsafe would kick in, signal restored. Not impossible, I guess... it's difficult now to reconstruct in my mind the exact timing of that moment. But failsafe did not kick in, of this I am sure.

Anyway: the module is probably almost 5 years old, while the Rx must be around 2 or 3 years old. I firstly bought this module and receiver 5 years ago and then every time I needed a receiver I kept buying this particular one or the XP because I've liked it quite much and never had a problem until yesterday. Anyway a thorough cleaning of Tx, module and Rx with WD40 is surely easily done and can't cause any harm.

A fellow flyer at the field told me that a bad servo can disturb the Rx and cause it to freeze for a moment. To me this seems quite unlikely but I don't know. Does it sound true to you?

@bossee: I'd tend to exclude antennas issues as well. I can post a pic tomorrow when I will be back home but the antennas are roughly 90 in respect to each other, and when it happened the plane was very close to me, around 20 ft. I had reputedly sent it much farther away, some 300 ft, half an hour before, with no issues, not even the RSSI alarm.
Mar 07, 2018, 07:33 AM
No bounce, No play.
davidmc36's Avatar
WD 40? I would say more like contact cleaner and/or Stabilite on electronics.

And yes, a bad servo could easily draw excess current and drop the voltage down to re-boot level for a second.
Mar 07, 2018, 08:05 AM
Right on the Edge!
I see. So if it's a servo it's still a matter of browning out the Rx. I had interpret it as a bad servo itself causing some sort of "disturbance" to the Rx, making it freeze, but maybe this isn't a thing.

Through telemetry I can see the voltage supplied by the BEC to the Rx, so in theory I should see if it's dropping too much. So far it has stayed pretty regular: it stays at 5,6 and then it drops at around 5,4 when the servos are moving, but this is at the ground, without load. I'm not sure of those numbers once in flight. I think I'll set the BEC to 6 V anyway.
Mar 08, 2018, 07:09 PM
Right on the Edge!
Here's the pic I said I would take...
Mar 08, 2018, 07:24 PM
No bounce, No play.
davidmc36's Avatar
I see one antenna laying close to a bunch of electronics?

And they are not 90 to each other?

And not fastened down really? Moving around could give all sorts of random results.
Mar 08, 2018, 07:32 PM
Registered User
RCAddiction's Avatar
It appears the the antenna that goes up the vertical tube near the RX is actually bent forward. It appears to be lined up in the same direction as the forward-facing antenna. Slide the black lead down the black plastic tube so that the silver tip is located vertically.

Remember, the black part isn't actually the antenna. The roughly 1" silver tip of the black lead is the actual antenna portion and it's that silver tip that needs to be at 90 degrees from the other antenna.

The forward-facing antenna is also buried next to the servo. You might wish to raise it up a bit so it's not blocked by anything.

Net: from the photo, it would appear that if you were located with your radio facing the other side of the plane (right side in the photo), your radio might not have seen either of those antennas as they are presently located.
Mar 08, 2018, 07:38 PM
Right on the Edge!
Quote:
Originally Posted by davidmc36
I see one antenna laying close to a bunch of electronics?
Yes that's not*so* distant from the antenna, but I mean... I wouldn't know where to put them otherwise. The frame has the space that it has.

Quote:
Originally Posted by davidmc36
And they are not 90 to each other?
You mean not *exactly* 90? Because, I don't know from the picture, but looking at them they are very close to 90[/QUOTE]

Quote:
Originally Posted by davidmc36
And not fastened down really? Moving around could give all sorts of random results.
Again, I'm not sure from the picture, but the antennas have stayed exactly where they are despite all the vibrations coming from the engine (fourstroke) and despite the maneuvers. They are secured with cable ties and, unless somebody goes there and physically tear them out, they don't really move.

Anyway I'd tend to exclude issues of this nature, because that signal loss happened when the plane was very close to me, and like I said I had been flying much much further, without even the RSSI alarm beeping (which is even set above factory settings). I regularly perform range checks and again, everything has been fine so far.
Mar 08, 2018, 07:39 PM
Right on the Edge!
Quote:
Originally Posted by RCAddiction
It appears the the antenna that goes up the vertical tube near the RX is actually bent forward. It appears to be lined up in the same direction as the forward-facing antenna. Slide the black lead down the black plastic tube so that the silver tip is located vertically.

Remember, the black part isn't actually the antenna. The roughly 1" silver tip of the black lead is the actual antenna portion and it's that silver tip that needs to be at 90 degrees from the other antenna.

The forward-facing antenna is also buried next to the servo. You might wish to raise it up a bit so it's not blocked by anything.

Net: from the photo, it would appear that if you were located with your radio facing the other side of the plane (right side in the photo), your radio might not have seen either of those antennas as they are presently located.
Thanks for the suggestions. I'll certainly try to adjust the antennas for better signal, but please consider that the signal lost happened at a distance that normally would work even with the Tx in "range check" mode. I've been flying this frame much more distantly without a single RSSI alarm beep.
Mar 08, 2018, 07:51 PM
No bounce, No play.
davidmc36's Avatar
The antenna that close to the servo....and what else is that Yep item? You might be surprised what could happen.

I would move the vertical one right towards the back, far as it will go. Leave it parallel to fuse. The forward one I would put in the vertical position. Get them as far as possible ckear of wires servis etc.

I use straws to keep the silver portion on the end on position. Your ends are not in defined positions. The lead going to it is not so important.

The FWD antenna is lying right on some wires too.
Mar 08, 2018, 07:52 PM
No bounce, No play.
davidmc36's Avatar
But yes, I would check and clean connections also based on possible cause of the symptoms.
Mar 08, 2018, 08:00 PM
Right on the Edge!
Quote:
Originally Posted by davidmc36
The antenna that close to the servo....and what else is that Yep item? You might be surprised what could happen.
It's a BEC, now set to 5,5 V. But I will change to 6, to hopefully decrease chances of a Rx brownout. I've been using this particular BEC for a few years, I've got 4 of them and so far they've worked flawlessly.

Quote:
Originally Posted by davidmc36
I would move the vertical one right towards the back, far as it will go. Leave it parallel to fuse. The forward one I would put in the vertical position. Get them as far as possible ckear of wires servis etc.
This is a good idea. Moving it towards the back is going to involve some inconvenient hand work for big handed people like me but...

Quote:
Originally Posted by davidmc36
I use straws to keep the silver portion on the end on position. Your ends are not in defined positions. The lead going to it is not so important.
All of these is not going to be easy on a small frame like this (57"), but I'll have a try.

Anyway, what still makes me think that what's happened has little to do with signal strength is that, if the signal weakens, you don't experience a total control loss for an entire second or so. First you should have the servos jerking...

I had been flying pretty much the same way on another frame for at least one year, sending it much farther away and even close to cell phone towers. I'm not saying my antennas setup is the best in the world, but I suspect that this time something of an entire different nature is going on...

Would you think a bad component (including a servo) can "short" / freeze / block (?...) the Rx and make it reset for a second? Or it's really just about browning? 'Cause these are very different thing in my opinion...

This is tough... on the moment the signal went away, I was just gently rolling on the right, no maneuvers, no servo loading...


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