3GX went elevator reverse by itself---crash

[AlvaSpeed]

I asked this on the 700N forum but got no answers there.


Yesterday my friend`s 700N DFC 3GX which has been flying perfectly crashed.
He was taking off (about a feet or two of the ground) and all of the sudden when he gave rear elevator the heli reacted forward, then he over corrected not realizing what was happening and matters got worse, the heli flipped forward and crashed.
He did all the preflight checks and everything looked fine.(I was there)
He was lucky that damage was minimal.
I checked the heli afterwards and everything worked well except that the elevator was working backwards!
I just found a video from a guy (and some others) that had the the same problem.



Does this happen very often?
Is there a way to correct this problem (3GX)?

Luckily nobody was injured and now my friend is reluctant to fly this heli again thinking that it could happen again without notice.

[AlvaSpeed]

???????

[Taxus812]

I have only had the 3GX a few months but since no one has answered I will try.

Couple of things come to mind
He could just have a defective unit. how long has it been in operation?

Was he in the computer or in setup recently ? He also could have inadvertantly reversed the direction on the 3GX and didnt notice until he popped it off the ground and actually needed back elevator.

I am wondering if he had a total reset of the 3GX where the 3GX rebooted and reset to defaults. There are a few reorts of this happining when using a BEC that is insufficant to handle the power requirments. (6V and lots of current) and it reset in flight. (Look in the 3GX forum on this subject. )

couple of leads to run down.

[AlvaSpeed]

No he did not change any settings.
Preflight check showed everything working as it should.
Then the engine was started and proceeded for liftoff.
That is when everything went wrong.

[SteamEngine]

The ship described is a 700. I have a 550 (with 3GX), a 600 with 3G and a 700 with 3GX. All three have a separate 1900mah 2S battery for the radio/3G* and the servos. None of them run the 2S 7.4 volt battery down quickly and it usually lasts all day.

The 3GX has a power regulator right in the box and I am using that on the 550 3GX. The 7.4 volts goes into the 3GX plug marked 'battery'. The servos and the radio are supplied via the other servo and signal plugs. It is a very neat way to go. At the moment the ship has a pair of satellite Rxs straight into the 3GX. I may reinstate the original radio to get the Spektrum DSMX functionality back. You can't get that with just a pair of sat RXs into the 3GX

The 600 (3G) has an Align regulated power supply that is good for 6 amps - plenty! It is supplied by the same sized 7.4V lipo.

The 700 is in the middle of a re-wire to include the Align APS system which means it has to upgrade from a 3G to a 3GX. It did have the same arrangement as the 600 with an Align regulator unit. I am considering doing away with the separate regulator (as 550) and using the regulator in the 3GX. I have to check the 700 servo stall currents against the 3GX regulated current.

Why would you use a BEC on a 700? anyway. I strongly root for a safer separate 7.4v radio/servo battery, but with regulation, separate or 3GX built-in.

[AlvaSpeed]

This 700N has the Align B6T 2 in 1 voltage regulator to power the servos and glowplug.

[Taxus812]

I cant imagine that it is common or it would be posted everywhere. If it is new perhaps they can swap out for a new one.

Few more questions
Did he have other successful flights that day ? Were there any weird things occurring ?
Was it just the elevator servo that reversed or all three, so the swash movement was reversed?

[AlvaSpeed]

Originally Posted by Taxus812

I cant imagine that it is common or it would be posted everywhere. If it is new perhaps they can swap out for a new one.

Few more questions
Did he have other successful flights that day ? Were there any weird things occurring ?
Was it just the elevator servo that reversed or all three, so the swash movement was reversed?

I agree with you that maybe is not a common thing to happen. But also not all flights are recorded, and sometimes crashes happen so fast that you cant really tell what happened. (unless you are very experienced).

It was the first flight of the day.
Only the elevator was reversed.
In youtube there is a video I saw about a guy that had a 3GX related crash and when I read all the comments there was one from a guy that had the same thing happened (elevator reversed) to his 700N.

[Natewin]

I've had this happen on my 450 but I am 100% certain it was my fault. I had gone through the setup previous to flying and had incorrectly set the elevator gyro compensation to reverse of what it should have been. You would never have known it was wrong b/c stick movement on the ground pre-flight would appear correct. It wouldn't be until the heli left the ground and the FBL tries to maintain attitude and corrects in the wrong direction that you'd see it flip the wrong way.
I got extremely lucky with mine. It took off, got about 3ft up, and did a full backflip landing on the skids. I just got lucky and happened to pull the collective down at the right time in the flip to land it.
Sorry to hear about it. Check the gyro comp in DIR mode and see what color the LED is. Bumping the stick when goon through that part of DIR could have reversed it.

[AlvaSpeed]

The heli was setup once. (when it was built-new)
It flew well for 3 gallons.
The day of the crash the preflight check showed all stick movements and gyro compensation working correct.
The 3GX is covered by the canopy. So there is no chance of hitting the set button from the bench (preflight check) to the ground (where the engine is started). The battery was fully charged.
Domn`t know what else (info) to tell you guys.

[Taxus812]

yeah we are grabbing at straws here.

It is way out weird and not a normal occurance. my gut is if the direction changed permaninatly check the TX swash menu. If the compinsation is reversed replace the gyro (if you are absolutly sure you were not in setup between the last good flight and the mishap. )

it should not change on its own, if it did without any question of operator error, it is faulty and should be replaced. (same with drifting and other oddities)

[bad007]

Two times, first had a reset in flight. Loss of power or something. The 3GX was trying to reinitulize the crashed heli with stripped servo gears, smoke and all the god stuff.
The 3GX compensation had to be reversed from the way it was before. Green for elev and red for aile.
Second time, my fault, TH was on, moved throttle down but not the whole way at the same time I turned TH off, the motor started to spool and bumped my arm, wa la my compensation for both went backwards. Now red for elev and green for aile the way it way before the crash.
Running a cc bec at 6.0 v
Wierd.

[BlazinBones]

Same thing happen to my buddy on its maiden flight with 3gx. Pre flight inspection was performed and everything seemed right. 30 seconds into a hover, same exact thing. Drove itself tail in into the ground.

Replaced 3gx with a Beastx and never had an issue again. 3gx is plain garbage (its a hit or miss)..

[oliver1071]

I know this is an old post but I think I just had something similar.
No crash but I'm moving all my models to a new Radio from the Aurora 9 to 9x.
I moved all of my models over with exact settings all of them worked with the same exact settings with the exception of one my 550e 3gx the rudder and gyro is reversed.

I went over and over the settings and there is no way that my old memory is wrong or the settings were not copied over correctly. I even rebound the heli back to the original radio and it's still reversed.

Reversed the rudd and gyro in the radio and it fly's normally.

Hopefully it's just something I'm missing because random changes worry me.
With something this big I'd hate for something to reverse mid flight.