FBL Gyro Align 3gx acting up?

[helicc16]

After taking the AR7200BX off my Blade 300, I threw a 3GX unit on it and went through a thorough set-up (including a upgrade to firmware 3.0). So far, I've crashed it at least thrice during testing. The first time, the heli was doing fine about 5 feet in the air until the end of the flight when all of a sudden, it started to pull hard to the right and crashed into a wall.

The second time, being more cautious from the last crash, I took it easy on the heli, hovering it no more than a couple feet off the ground. Again, it was rock steady well into the first half of the flight. Then again, it took a dive for the ground so fast I had little to react. The repair bill was more expensive this time, including 2 brand new Eflite servos.

Suspecting either a gyro or servo problem, I decided to be doubly careful on the third try, barely lifting heli off the ground. This time the heli was rock steady for the entire battery; however, barely a minute into the 2nd battery, it suddenly started to lurch toward the front right. Anticipating this happening, I cut the throttle just in time to prevent another crash.

In the following video, you'll see that the swash-plate starts tilting in the front right direction on its own as the main rotor speeds up. When I disable the motor without disconnecting the throttle signal, it works fine.

<iframe width="420" height="315" src="http://www.youtube.com/embed/r_u4mctGxmw" frameborder="0" allowfullscreen></iframe>

Additionally, when this happens, the heli keeps yawing left in HH mode, fighting against my rudder control inputs.

I'd like to hear your thoughts. This is particularly troubling because most of my FBL helis are powered by 3GX

 

[stokke]

No trim on the trim levers?

 

[coolgabsi]

You replaced a 7200bx with a 3gx??????? What? Ok ... Now that you have ...

Have you checked with your servo specs (on the cyclic) what frequency they are and if that is an acceptable frequency to the 3gx cause if I know correctly , the 300x had eflite servos...

Another.. Like Marius said, any trim ?


I don't mean to be rude brother ... But you just downgraded a porche to a Suzuki. ... If you just did it for fun that's awesome !! But what other reasoning did you have ? (If you don't mind me asking)

Also I moved it to the right forum ...

Fly safe!! have fun!

 

[helicc16]

No, guys. All trims are set to zero. As I said, the 3gx acts up ONLY when the motor is running.

As far as the servos, I am not sure about frequency mismatch. I'd never used Eflite digital servos with 3GX before. I tried to use analog servos with 3GX once and it did not like it a bit.

The only reason I bought the Blade 300 X is its hidden jewel: the AR7200BX. I swabbed it out so that I could use it on my Trex 700.

 

[coolgabsi]

yeah 7200bx is ok with analog servos.. but i dont know about the 3GX..

I understand.. thats a good strategy

check what the frequency is.. and then as u said it acts when motor is running... is it getting vibrations.. ?? Use zeal tape if there are too many vibrations getting to the gyro...

couple of things to be ware of with these birds... and FBL gyros... tip overs or hard right or left or something happens either by vibrations or static discharges caused by the belt...

Fixing static discharge is simple, ground your tail case to the motor via your boom .. to prevent that.. so look into those two things.

 

[Tony]

ONLY use digital servos with the 3GX. But this is not your issue. Your issue is the battery seems to be getting too low to power the 3GX. When you land (or crash), are all 5 lights blinking? If so, then it's losing power.

And Gaba, stop hating on the 3GX. Just because it's too advanced for you doesn't mean you need to pick on it.

 

[Westy]

heh he ... dig it in Tony .. Dig it in! haha

 

[helicc16]

Earlier today, I conducted a couple tests to isolate the problem. First, I removed the main gear, allowing the motor to free spin as I watched the swash-plate. The 3gx behaved normally. And that ruled out the motor.

On the second test, I re-installed the main gear, removed the main blades and spun up the motor as I watched the for abnormal behaviors. Two battery packs later, yet still no problem. You would think that if it was a static problem, that would have been enough time for drive belt to build up enough static to wreak havoc. But no. I couldn't replicate the failure that way.

Put the main blades back on and began hovering just a few inches above the ground until the battery dips below its 20 % capacity. Again, no problem.

Just a minute after I put a fresh battery on, I lost the rudder control and the helicopter started pirouetting wildly. Luckily, it landed on its own in one piece. At this point, the normal green STATUS LED was blink RED and GREEN and I did lose all of the controls !?! This was different from the previous failures where the LEDs were what they're supposed to be.

After re-powering the heli, I continue to the hover test. Merely a few seconds later, BAM! The bird took a violent dive for the ground.

Another servo and another main gear to the trash bin.

At this point, I highly suspect the 3gx unit. I've had a bad Align gyro before: a GY780.

I am hesitant to put more money into this thing and seriously consider selling it as is plus its battery packs to anyone who is willing to take a crack at it.

 

[Westy]

damn..... Ditch it .... get another one of another gyro type...... you are right not worth the risk.

 

[Lee]

Did you have training gear on it? Seems all of your crashes could have been avoided with training gear on. If i ever suspect that something could go wrong in a test flight, I always put training gear on for that extra security.
It does seem you have a random glitch. As stated above the three things to check are the Vibrations (use 3M mounting tape) the Grounding of the boom, and the battery low voltage (use a LV alarm set to 3.5V) If you have done all that and the bird still does the same thing, then as you said, send it back and get another one.

 

[coolgabsi]

ok .. .is this video recent.. ? I hear something on the main transmission .. like a stripped gear or a bearing .. and its circular periodic so .. wondering if its vibration from the gear.


If it was already there.. I was on my cell phone before.. so may have not chekced..

 

[Slobberdog]

There's defo a clicky noise that gains in frequency when it spins up,

 

[helicc16]

Yes, I did use training gear. In fact, I almost always use training gear on maiden flights. I don't think its the vibrations or low power issues. As far as grounding the boom, how exactly do I do this?

I agree with you on the randomness of the glitch. Despite my best efforts, I couldn't get it to fail in a controlled manner. It only showed up when I actual hovered it. And by that time, it was too late.

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You've got a good ear

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Good observation, man! The main gear was indeed chipped a bit in the previous failure. I don't think it is the problem, though.

 

[coolgabsi]

vibration has random effects.. but .. if you have changed it out.. Then i would say thats not it.. But if not.. check it also check gear mesh again. crashes can change that.