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Mikado Modellhubschrauber . GrandRC . CanoMod

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Main Discussion > Miracle inverted landing, but what caused the gyro lockup?
 
 
rdalcanto
Key Veteran
Location: Salt Lake City, UT

3 minutes into my first flight with my EVO90 today, and I come out of a piro maneuver only to find the heli won't stop spinning. It wasn't spinning too fast, and I found that I was able to stop it from spinning by holding a certain amount of left rudder. I'm able to land and discover that the 601 gyro servo isn't centering anymore. The only way I'm able to get it to center is to shut the heli down and reboot. After that, everything checks out on the ground - no loose plugs or anything. So I take off again, do some backwards flying, and everything seems fine. Do another piro maneuver, and this time the heli is piroing FAST and won't stop. I'm inverted, and it is going too fast for me to stir/piro flip back over, so I hit throttle hold and auto it down while it is piroing FAST and manage a fairly soft, level landing inverted on the head button. I scraped the paddles a little, broke the head button, shaved a little plastic off the top of the main blade grips, and scraped my SABS a little.





After counting my blessings, I find that the rudder servo arm is stuck cranked all the way over. Reboot, and everything seems fine. However, I then play with the elevator servo and discover that everytime I flick the stick back and let it quickly recenter, the elevator servo starts oscillating rapidly around center. If I put my hand on it, I get it to stop.

The receiver is PCM.

Did the elevator servo get damaged in the inverted landing, or did it cause the gyro problem? Is the 601 bad? Is it the receiver (I would think that with PCM I would have total lock-out and not this)?

I'm thinking of sending everything to Futaba. What do you all think?

Thanks,
Rick

Team MRC & Magnum Fuels
04-16-2006 Over year old.
HOMEPAGE  
 
 
Sapca
Heliman
Location: belgium

Hi Rick,

I have just the same problem and crasht the Tornado Revolution twice.
I writh it on a German forum and the all told me it's the tailservo.
A futaba repaircenter here in Nederland told me the same.
I d'ont trust it anymore and I think to put a compleet new gyro (GY611)

When you have sent it to futaba,let me know what is they site of the story.

Regards

Sapca

Dyna-X, MA Stratus,mille3 pro ,Fury-extreme ,Heli-prof Revolution,T-Rex Heliup ,T-rex SE ++T14MZ++
04-16-2006 Over year old.
 
 
heliham
Senior Heliman
Location: San Jose, CA

Does the 601 have the "recenter" control that the 401 does?

In the 401, if you flick the Gyro Gain channel back and fourth a couple of times quickly, the HH "center" gets set at the "current rudder position". This is intended to allow you to trim out the heli in Normal mode and then center the HH mode.

The problem is that if you are running PPM mode and get a little glitch while you have the tail pushed way over, the gyro may decide that it has a new "center position".

(BTW, you can check it on the ground by holding the rudder stick off to the side and flicking the switch a couple of times (stopping in HH mode) and see where the center moves.)

This doesn't happen in PCM mode (except when you actually flick the switch), but it sounds like it might have happened to you. You may be getting some metal-to metal while inverted that causes just enough of glitch to tweak the gyro. Sometimes a stuck servo can cause power glitches that will do the same thing, EVEN in PCM. It's the short switches into the Gyro that causes it to "recenter".

Just a thought.
...paul
04-16-2006 Over year old.
 
 
rdalcanto
Key Veteran
Location: Salt Lake City, UT

Quote 
Sometimes a stuck servo can cause power glitches that will do the same thing, EVEN in PCM. It's the short switches into the Gyro that causes it to "recenter".


Perhaps the elevator servo, if it was doing that oscillating thing in flight, could have caused it....

I'm sending receiver, elevator servo, and gyro to Futaba. I'll let you know what they say.

Thanks,
Rick

Team MRC & Magnum Fuels
04-16-2006 Over year old.
HOMEPAGE  
 
 
rdalcanto
Key Veteran
Location: Salt Lake City, UT

According to Futaba, the motor in the 9252 servo was bad, and there was fuel damage in the servo for the 601 gyro. Neither is worth fixing, so I'm buying two new servos.

I don't know what to do about the fuel damage to the gyro servo. I will either have to find a way to seal it up better, or find a place for it inside the frames of my EVO 90.

Rick

Team MRC & Magnum Fuels
05-02-2006 Over year old.
HOMEPAGE  
 
 
racingstripe
Veteran
Location: Sacramento, CA

I put the T/R servo under the canopy after I soaked a 8700g & 9254. You can just catch the T/R servo mounted above the fore/aft servo in the 2nd pic.

andy-





Proofread carefully to see if you any words out.
05-02-2006 Over year old.
HOMEPAGE  
 
 
Eury
Elite Veteran
Location: Ankeny, IA, USA.

Any chance we can get a detail pic of the front tail servo with the canopy off?


Nick Crego
I'm not going to put my lot in with economists.
05-02-2006 Over year old.
 
 
Free Bird
Senior Heliman
Location: Somewhere in the USA

Also, how did you mount the bellcrank to the tailboom? Details please!!!

FB
05-03-2006 Over year old.
 
 
racingstripe
Veteran
Location: Sacramento, CA

The bellcrank is a Sceadu fore/aft "x-type" lever. The clamp around the boom is from the stock mount that was cut down.

I'll take a couple more pics when I get home on Thurs and maybe draw up a diagram on how to cut the T/R mount.

*EDIT*
additional pics here:
http://www.runryder.com/helicopter/t256028p1/

The servo mount concept is similar to this (from the Sceadu):



Note that if you do the mod, you'll end up nose heavy even with a full tank. A sub-C Rx pack is out of the question. I'm using a 1950mAh Ni-MH pack, 9602 throttle servo and moved the canopy back 3/8" from the stock location... still slightly nose heavy.

andy-
05-03-2006 Over year old.
HOMEPAGE  
 
 
w.pasman
Elite Veteran
Location: Netherlands

Quote 
the elevator servo starts oscillating rapidly around center


Sounds like a rotten potmeter? I have had three Futaba servos with this problem. I caught this problem very early and had the pots replaced. Solved the problem although we could hardly see any wear inside the pots.
05-03-2006 Over year old.
HOMEPAGE  
 
 
RICH.L
Veteran
Location: east springfield p.a.

man that is exactly the same problem i am having on my evo right now.
the tail went nuts and i managed to flip it back upright.
same thing i shut everything off and then reboot and the gyro centers o.k.
i did send in my gyro,servo and amp to futaba to have them look at it.(haven't heard anything yet)
i did strip the gears of my pitch servo(S9252)
i replaced the gears on it and it seems fine,but now i am wondering if it could be damaged and causing my gyro to go nuts?
all four of my s9252's have only four flights on them!
i wonder if he rdalcanto ever figured out which one was the problem?
and what did he mean about oscillating at center?
rich
09-27-2006 Over year old.
 
 
rdalcanto
Key Veteran
Location: Salt Lake City, UT

According to Futaba, the motor in the 9252 servo was bad, and there was fuel damage in the servo for the 601 gyro. Neither is worth fixing, so I'm buying two new servos.

Rick

Team MRC & Magnum Fuels
09-28-2006 Over year old.
HOMEPAGE  
 
 
ChristianM
Veteran
Location: Oslo, Norway

rdalcanto

Regarding the 9252 oscillating, it might be the servo motor but I doubt it even if the service guy said it. This will happen with the 9252 and probably other servos after the gears get a bit worn. I have had the same thing happen on two of my 9252s. The solution is to get a new gear set for about $10 and they are good as new. The elevator should not cause the gyro issue you had.

I have also had the same thing happen to my 502 gyro (now converted to a 601). It suddenly started spinning in flight but I managed to get it down safely. Afterwards it apparently worked on the bench but after hovering for a while the problem reappeared. It turned out that oil had penetrated the TR servo and causing the problem. After changing out the servo it has worked without a problem for more than a year.

Nice save by the way.

Christian

Burn fuel, be happy
09-28-2006 Over year old.
 
 
w.pasman
Elite Veteran
Location: Netherlands

..
09-28-2006 Over year old.
HOMEPAGE  
 
 
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Main Discussion > Miracle inverted landing, but what caused the gyro lockup?
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