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Old Aug 05, 2003, 05:44 AM
Gentleman, scholar and acrobat
United Kingdom, England, Poole
Joined Mar 2001
431 Posts
Corona – how twitchy is your rudder servo?

Corona
HS81 MG
GY240

While my tail is rock steady, my tail servo is constantly twitching back and forth at about 2 or 3 times a second though about 15 degrees. This happens in the hover even when there are no throttle changes. Running up on the ground with it strapped down the servo is steady. If I turn the gain down the twitching reduces, but I lose the rock steady tail.

The servo itself seems fine with no missing teeth and it centres properly.

My guess is that is that this is caused by vibration moving the gyro around and giving false yaw signals that cancel each other out. My heli appears to be a smooth as a very smooth thing and any vibes must be of small amplitude, as I can’t see anything actually shaking.

I’m not really worried about this, other than wearing out the servo prematurely. As I fly alone I’ve never seen another R/C heli fly close up so have nothing to compare with. Is this twitching normal?

Thanks

Cush
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Old Aug 05, 2003, 12:16 PM
bps
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Indianapolis, IN
Joined Apr 2001
847 Posts
I have the same problem. My quess is the gyro moves (vibrates) and the hs81mg servo that I am using (non-digital) moves at a slower rate than a digital would and creates this. Just my quess. Does not bother the flying though.
JEB
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Old Aug 05, 2003, 02:50 PM
Registered User
Chicago
Joined May 2002
349 Posts
I found it's the vibrations of the heli shaking the gyro. It will eat your servo to the point where it will cause glitchy tail movements, then you'll have to buy another HS81. If you dismount the gyro and let it hang in a way that it's level and still works, the twichyness goes away.

I had an HS81 on the Logo 10 do the same thing, I think the pot gets dirty or wears in one spot. The first servos lasted pretty long, and they are inexpensive anyway. I look at them as spare gearsets now.

Greg
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Old Aug 05, 2003, 06:23 PM
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United States, NY, Mechanicville
Joined Mar 2003
1,203 Posts
We started calling it "stroking" the servo... Seems the servo is going so fast, the tail never really has a chance to repsond to the pitch changes.

Yup, it will cook the servo..

Yup, it is probably from vibrations.

I also reduced my vibrations to where I could not see the tail or the skids moving in flight, but I still had the "stroking".

I wrapped the gyro in receiver foam, to try and dampen the vibes. It worked pretty good, I was able to get up to 80 - 90% gain with no stroking.

If you are mounting with zip ties, etc., remember the zip ties can transmit the vibes as well. You would want to make sure nothing that touches the heli also touches the gyro (except for the foam).
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Old Aug 06, 2003, 03:47 AM
Gentleman, scholar and acrobat
United Kingdom, England, Poole
Joined Mar 2001
431 Posts
Thanks for confirming my thoughts – “stroking” I love it.

My gyro is mounted using the foam tape that Futaba supplied with it. I’ll try mounting the gyro in a different place to see if I can find a less vibe prone spot. In the UK HS81 MGs cost around $30 – not a disposable item.

Ta again.
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Old Aug 06, 2003, 01:24 PM
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Chicago
Joined May 2002
349 Posts
I do not like metal gears on the tail servo. There is much more slop in the gear train, they're more expensive, and it's not a servo that gets stripped all that easily anyway (like the cyclic servos).

Greg
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