Assistance with potential cause of crash

Hey guys,

Had my XL Power 550 take a dirt nap on the weekend, it was the 4th flight of the day and everything felt normal, I was doing a simple transition from inverted to positive when the heli started pitching up and down violently about 4-5 times uncontrollably. When I saw this happening I hit throttle hold as I knew something was very wrong and tried to auto it.

Upon inspection of the heli, the only damage was a snapped servo arm (which at this stage I am suspecting was due to the crash) and broken blades. All other servo / pitch links were connected and the servo's were still receiving input and behaving as expected before I powered it off.

To me it seems like it wasnt a mechanical issue given the damage (only cause for mechanical fault would have been if the servo arm snapped in flight which looking at the snap I doubt and feel it was likely due to the impact when it hit the ground) having checked over the logs there were 3 events logged at the time the uncontrolled interactions happend (in bold below):

27.09.2020 11:00:10;VStabi Start -- XL550
27.09.2020 11:00:10 Good;Reset Reason: Power On
27.09.2020 11:00:12 Good;Hobbywing ESC detected
27.09.2020 11:00:13 Info;Bank 2 Loaded
27.09.2020 11:00:13 Warn;Init Failed, retrying...
27.09.2020 11:00:13 Good;Motorswitch Motor Off
27.09.2020 11:00:13 Warn;VBar Voltage: 7.06V
27.09.2020 11:00:14 Good;Motorswitch Idle Bailout
27.09.2020 11:00:17 Info;Calibration Finished
27.09.2020 11:00:23 Good;/battery/bt_26
27.09.2020 11:00:23 Good;Battery selected manually: Gens Ace - #4
27.09.2020 11:02:40 Info;Bank 3 Loaded
27.09.2020 11:02:55 Info;Governor Active
27.09.2020 11:02:55 Good;Motorswitch Motor On
27.09.2020 11:03:07 Warn;High Vibration Level
27.09.2020 11:03:17 Warn;High Vibration Level
27.09.2020 11:03:27 Error;Extreme Vibration Level
27.09.2020 11:03:37 Warn;High Vibration Level
27.09.2020 11:03:47 Warn;High Vibration Level
27.09.2020 11:03:57 Error;Extreme Vibration Level
27.09.2020 11:04:07 Error;Extreme Vibration Level
27.09.2020 11:04:17 Error;Extreme Vibration Level
27.09.2020 11:04:28 Warn;High Vibration Level
27.09.2020 11:04:38 Error;Extreme Vibration Level
27.09.2020 11:04:48 Error;Extreme Vibration Level
27.09.2020 11:04:58 Warn;High Vibration Level
27.09.2020 11:05:08 Warn;High Vibration Level
27.09.2020 11:05:18 Warn;High Vibration Level
27.09.2020 11:05:28 Error;Extreme Vibration Level
27.09.2020 11:05:34 Warn;The Cyclic Ring is active
27.09.2020 11:05:35 Error;Aileron Sensor Value out of Range
27.09.2020 11:05:35 Error;Aileron Sensor Value out of Range
27.09.2020 11:05:35 Info;Off - ESC - Umin:21.4V Imax:129.5A Temp:60°
27.09.2020 11:05:35 Error;Aileron Sensor Value out of Range
27.09.2020 11:05:35 Info;Governor Idle
27.09.2020 11:05:35 Good;Motorswitch Idle Bailout
27.09.2020 11:05:36 Info;Governor Stop
27.09.2020 11:05:36 Good;Motorswitch Motor Off
27.09.2020 11:05:36 Warn;The Cyclic Ring is active
27.09.2020 11:05:36 Warn;The Cyclic Ring is active
27.09.2020 11:05:36 Warn;The Cyclic Ring is active
27.09.2020 11:05:37 Warn;The Cyclic Ring is active
27.09.2020 11:05:37 Warn;The Cyclic Ring is active
27.09.2020 11:05:37 Error;Aileron Sensor Value out of Range
27.09.2020 11:05:37 Warn;The Cyclic Ring is active
27.09.2020 11:05:38 Error;Aileron Sensor Value out of Range
27.09.2020 11:05:38 Warn;The Cyclic Ring is active
27.09.2020 11:05:38 Error;Extreme Vibration Level
27.09.2020 11:08:38 Warn;The Cyclic Ring is active
27.09.2020 11:08:40 Warn;The Cyclic Ring is active
27.09.2020 11:08:40 Warn;The Cyclic Ring is active
27.09.2020 11:10:28 Warn;Hobbywing Undervoltage
27.09.2020 11:10:40;VBar Logfile End -- 27.09.2020 -- 11:10:40


These occured in the air prior to the crash, directly following this you can see where I switch into hold in mid-air and then again more of these logs when the heli hits the ground.

Things I have checked thus far:

* Mechanics - as above, only potential mechanical cause was the snapped servo arm if this did happen in flight (it was an aileron servo and if it happend in flight I would have expected the blades to hit the boom which they never did).
* Wires - I have gone over all the wires and checked for any chaffing and they all look fine. The wires connecting into the Neo were also firmly connected still (they are hot glued).

I am hoping you guys may be able to explain what the possible cause for this would have been? I did notice there were alot of extreme vibration warnings in the log, but I do fly relatively hard and going over my previous 45 flight logs those warnings are evident in all of them.

I am worried about fixing it and then having it occur again.



1 mal bearbeitet. Zuletzt am 28.09.2020 06:34 von emaryd.

Hi,

sensor out of range and cyclic ring happen if the sensors are driven to their mechanical limits, usually it needs a shock impact, but it can also be because of very quick direction changes (hardly ever happens in flight, though), and if the VBar electronically limits it's cyclic servo outputs because even with the max. deflection, it can not/no longer control the roll or flip rate.

So it's not an error message of the sensors, but a 'notification' that something is not operating within it's usual envelope.

Cyclic ring remains active until the end, so the VBar keeps doing something, and limiting itself from over-doing it at the same time.
Sensor out of range entries at the time the model hit terra firma (2 secs after motor off and 3 secs after the incident are also plausible.

So my best guess would be that either something went wrong in the model (servo arm) in flight, the VBar frantically trying to keep the model under control, or that the VBar itself maybe came loose, or it's top cover, and the additional oscillation/vibration took it's toll.

Best thing you can do without risking anything is, fix it, run it (on the ground, no blades, or carefully with only tail blades), check the log, tap and wiggle the VBar and the wires, apply pressure to the servos and move them all the way up and down at the same time, to see if they let go at some point, and check the vibration analysis (live graph) and the log for anything obvious.

I'd also be curious about the setup file of the model at the time this happened. Reason is, there are cases known where overdriven servos let go temporarily, I mean if servo throw (collective and cyclic) plus trim plus auto trim plus very high agility (combined high deflection) exceed the servo pulse accepted by the servo.

Kind regards

Eddi

Born to fly ...
forced to work.

Hi Eddi,

Thanks for your response, what you posted certainly makes sense and does have me wondering if perhaps it was the servo arm that let go mid-flight as I have very little trim in the servos (all less that 20), my agility is only 90 and I am only running 13 degrees of +/- pitch with 8 degrees of cyclic pitch so I dont feel like I would have hit the limits of the servos.

I will do as you suggested and see if I can trigger any odd interactions once its re-built on the bench by tapping on the case, wiggling wires and moving the servos full deflection. My vbar has a metal case on it and I have double checked it is all secure, so I am pretty confident it isnt an issue with that.

Will report back with my findings!