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Old 02-26-2018, 07:23 AM   #1 (permalink)
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Default unexpected fail safe

Hey guys,

I've posted this before in the goblin/vbar forums, but i think it would be better here

Short version:
It appears my goblin 700 with x8r/taranis x9d is sometimes going into fail safe. No idea why, as the signal strength is good


long version:

I could use some help with my Goblin 700. Recently I had 2 unexpected failures:

Case 1:
I was doing an inverted funnel when suddenly the pitch glitched (positive pitch and back, all in a split second) and the motor stopped. I was able to auto rotate and land it safely, and I had full control after the glitch (except for the motor not running, although I believe it was spooling up during the auto rotation)


Case 2:
I was in a tail in hoover when suddenly the heli rolls 180 degrees to the right, again the motor stopped. Again I was able to land it safely. The roll looked controlled and wasn't fast like the servo was stuck/failed

I've ruled some things out:
- Batteries: ~100 flights old, but the voltage of the pack was around 3.66 volts during the failure. Current didn't exceed 40A since I was in a hoover.
- Bec: Bec voltage was above 7.8V at all times
- servos seem to function well
- Vbar logs are clean and all i got was a 'governor off' which you would expect since the motor shut off
-static issues were debunked in the goblin forum
- no broken or damaged wires
- signal strength is good according to the taranis logs

It looks like the receiver is going to fail safe for a very short period. Fail safe is setup as servo to center and motor off


I really have no idea what might be causing this and I definitely don't want to fly it until this is solved. Next time i may not be able to land it safely


Specs:
Goblin 700C
BK 7001 servos
Keto bec @ 8V
Full size vbar 5.3
scorpion 4520 520 motor
Taranis x9d/ x8r receiver


Thanks!

Last edited by mr. mark; 02-26-2018 at 08:30 AM..
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Old 02-26-2018, 08:44 AM   #2 (permalink)
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A couple of things to look at

1 - Does the v-Bar log throttle input or output?
2 - Did you log throttle output in open-TX or maybe stick position?
3 - I've heard people recommend only running HV servos at 7.4V. I think it was something on the Scorpion forum about it.

The reason for my first two questions are to see if you have an issue with your output from the TX.

Other possible thoughts.
ESC issue? Maybe bad signal wire on it?
Bad wire from the RX to the FBL?

This kind of sounds like it might be the wire between the RX and FBL now that I think more on it. Just because nothing is showing up in the logs. This would explain the BEC voltage being fine as well as never losing connection between the RX and TX. I'm not familiar with vBar, but is there something that logs if it goes into failsafe?
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Old 02-26-2018, 09:04 AM   #3 (permalink)
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Thanks

V-bar doesn't log the throttle, my esc does. I will look into that.

Vbar gives a load of errors when i disconnect my sbus cable, so i assume that one is fine since i don't see those errors
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Old 02-26-2018, 03:43 PM   #4 (permalink)
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Shooting a little in the dark here, but it sounds like the a possible x8r firmware bug. I assume you are also using telemetry.

If the x8r went into failsafe from LOS, the x9d logs would show that (if you have them).

If the vbar had LOS from the x8r, the vbar logs would show that.

Th sBus signal from x8r to vBar is an inverted synchronous pulse of 25 bytes carrying 16 channels of information. If the vbar got a bad burst from the x8r it would report it.

Quote:
https://github.com/bolderflight/SBUS
The SBUS protocol uses inverted serial logic with a baud rate of 100000, 8 data bits, even parity bit, and 2 stop bits. The SBUS packet is 25 bytes long consisting of:
Byte[0]: SBUS Header, 0x0F
Byte[1-22]: 16 servo channels, 11 bits per servo channel
Byte[23]:
Bit 7: digital channel 17 (0x80)
Bit 6: digital channel 18 (0x40)
Bit 5: frame lost (0x20)
Bit 4: failsafe activated (0x10)
Bit 0 - 3: n/a
Byte[24]: SBUS End Byte, 0x00
So by elimination, if is is not LOS, then it must be signal corruption.

FrSky protocol is frequency hopping and fault tolerant (ie. if unable to receive, decipher or match packet, repeats last know signal to FC/FBL till good packet received or LOS determined and failsafe mode established). If no LOS, then enough un-corrupted packet headers are getting through.

To send corrupt data to the FBL, the only system handling that data is the RX. So either firmware or very targeted interference.

There is a firmware update to the x8r to:
Quote:
https://www.frsky-rc.com/x8r/ - Firmware section - 2017-03-07 - v170210

Enhance anti-interference capability.

Add the function of enable or disable the telemetry mode on X12S Horus radio side when binding.
I'd look at upgrading the x8r firmware as a first step.
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Old 02-26-2018, 03:48 PM   #5 (permalink)
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i would never have thought about that, Will do that. (and also for my other receivers. I don't have problems with them, but it's better to be safe than sorry)

Could upgrading from 2.1.9 to 2.2 have something to do with it? That's the only change i made recently. Before that i've been using it for hundreds of flights across 4 models without problems

i do indeed use telemetry. I can't find anything weird in the vbar logs nor in the taranis logs, so your story makes sense
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Old 02-26-2018, 04:07 PM   #6 (permalink)
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Quote:
Originally Posted by mr. mark View Post
i would never have thought about that, Will do that. (and also for my other receivers. I don't have problems with them, but it's better to be safe than sorry)

Could upgrading from 2.1.9 to 2.2 have something to do with it? That's the only change i made recently. Before that i've been using it for hundreds of flights across 4 models without problems
Possible. Cannot completely rule that out.

Although 2.1.9 to 2.2 should not update the internal FrSky TX module, it could feasibly introduce corruption in the packets to be encoded and sent. There is a LOT of change between 2.1.9 and 2.2.0 (and 2.2.1).

2.2.0 is May 2017 release - 2.2.1 is December 2017 release.

I run 2.2.1, but I need the advanced telemetry and LUA for FPV drones, so no choice. FPV drones can log just about everything in the black box (including all channel values received), but use tiny RX's (XM+, XSR, R-XSR).

If you do not need all the new features, should be no problem running 2.1.9 (as long as you restore the firmware and use an older version of Companion).

If you have enough logs to highlight the issue in the current version it may be worth raising a ticket on the github for OpenTX - https://github.com/opentx/opentx/issues (much more knowledgeable people there than me).
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Old 02-27-2018, 03:31 AM   #7 (permalink)
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something that came to mind:
on the goblin i have the new receiver with the pcb antenna. On my other models I have the old plastic antennas. Would that make any difference?

What would be the safest way to go? update the firmware, or revert to 2.1.9? Or both?
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Old 02-27-2018, 03:53 AM   #8 (permalink)
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Ive had the same issue with a logo 600...

After 2 crashes with minimal damage and many changes, inluding swapping out the mini vbar for a brain 2, and updating the reciever(x6r), the random failsafe problem still happenned...

I have come to the conclusion the problem stems from rf noise caused by my bk7001 servos....

now you have the same issues with the same servos....

Ive now swapped out the 7001's for some futabas, but am yet to fly it...

this thread put me on track....
https://www.rcgroups.com/forums/show...is-Rx-lock-out

Last edited by K-rash; 02-27-2018 at 04:07 AM..
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Old 02-27-2018, 04:18 AM   #9 (permalink)
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Ive had the failsafes present in both forms....

full lockout(cycle power to recover)
momentary lockout(motor stops and starts spooling up seconds later)
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Old 02-27-2018, 04:40 AM   #10 (permalink)
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Quote:
A couple of things to look at

1 - Does the v-Bar log throttle input or output?
this was instrumental in determining the issue was actually failsafe
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Old 02-27-2018, 05:56 AM   #11 (permalink)
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I prefer the whisker antenna. I found the pcb antenna gave me low signal sometimes. Never figured out why but after I switched never a problem again.


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Old 02-27-2018, 06:06 AM   #12 (permalink)
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Boy...

I'll dive into it. Quite some reading to do

In the meantime i could use my x4r-sb? It has the whisker antennas, and it's even smaller. That would be a simple solution
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Old 02-27-2018, 06:15 AM   #13 (permalink)
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That's what I use on everything.
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Old 02-27-2018, 01:27 PM   #14 (permalink)
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As said, i'll dive into it to really understand where the problems come from.
I've ordered a new x4r-sb, from china, so it will take a while before I can test it

Thanks for all the sugestions, and K-rash, let us know if the servo swap changed anything for you? Safe flights!
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Old 02-27-2018, 02:36 PM   #15 (permalink)
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Have you considered the possibility of a static hit to the FBL controller?
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Old 02-27-2018, 02:44 PM   #16 (permalink)
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Ive changed many things to the setup, I cant afford to try one thing at a time and risk crashing each time

1 cyclic servo swap
2 new x6r, with latest FW (apparently has a fix for full lockout failsafe)
3 rx relocated away from all other electronics
4 BEC wires extended to allow ferrite rings and for wires to be routed further away from motor
5 power guard added

If my problem persists after this, it has to be....

1 faulty BEC.. (was changed after my 1st crash, so unlikely)
2 faulty tail servo
3 faulty motor

your problem helped confirm my most probable suspect being the BK7001,s....remember these weren't in production long before they were modified to make them less power hungry and re-released as BK7002..
Is it possible there is more to it.... I read somewhere that Mikado originally recommended all HV servo's should have there own capacitors (was unable to confirm)

The 2 different ways failsafe can present had me confused for a log time, as it had me thinking maybe I had 2 separate issues

I am positive the issue is failsafe activation due to brain log showing thr output from rx signal going to zero (non-lockout failsafe).... without affecting any other controls.

I haven't read anything about the susceptibility of the x4r to rf interference... but remember the fw update to prevent full lockout failsafe only applies to x6r and x8r (I haven't investigated if there is an equivalent update for x4r)......

You dont want full lockout failsafes, trust me..
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Old 02-27-2018, 04:08 PM   #17 (permalink)
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Quote:
Originally Posted by teamdavey View Post
Have you considered the possibility of a static hit to the FBL controller?
Yes, that was my initial thought. I asked that in the goblin section but was quickly debunked. The roll i had in the second case was just too smooth and slow. With a static discharge you would expect a more violent movement
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Old 03-04-2018, 07:09 PM   #18 (permalink)
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Quote:
Originally Posted by mr. mark View Post
and K-rash, let us know if the servo swap changed anything for you? Safe flights!
failsafed on the 5th flight... minimal damage again....
Ive been studying the logs.... nothing significant
see thread....
https://www.helifreak.com/showthread.php?t=801692

will replace esc/bec , tail servo, redo earth fix damage and try again.
will be a month or so.
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Old 03-05-2018, 01:31 AM   #19 (permalink)
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I'm sorry to hear that.

I had my exo shut down mid flight during the 4th flight yesterday. No damage luckily. I was inverted at ~5meters so it could have ended worse
I'm contemplating to go back to my futaba 14sg. Has always been fine and I still have some receivers laying around
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Old 04-10-2018, 01:39 AM   #20 (permalink)
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So I bit the bullet and bought a futaba 14sg which I have used before. No problems ever since 🙂
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