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06-18-2009 08:18 PM  11 years ago
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Hamo

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Ireland

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Experiment with a 401
I understand that Heading Hold Gyros such as the 401 are actually accelerometers. They do not have compasses so they don't know the actual heading. They simply produce a signal proportional to the rate of rotation. This means, the quicker the gyro rotates, the bigger the output signal, conversely, the slower it rotates, the smaller the signal. I figured that if a heli with a gyro in HH was to rotate very slowly (tail drift) the gyro would not be able to correct it. To prove it, I powered up the Tx in HH, then the heli, gyro initialized after 3 seconds, red light solid, 9254 servo steady. After a while I held the tail and slowly rotated the heli CCW a quarter turn in about 1 minute and guess what, the servo didn't move at all. Then I pushed the tail quickly and the gyro responded by moving the servo to counteract the rotation. Simply put, if an external force such as a gentle breeze was to slowly rotate a helicopter, a 401 would not be able to correct it. I believe this is why I can't get rid of the slow tail drift. I would appreciate other raeders' views or tests.
Hamo
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06-18-2009 08:25 PM  11 years ago
tadawson

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Lewisville, TX

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Where was the gain set when you did this? I think it will have a large effect on what the gyro will and will not correct for . . .

- Tim
Friends don't let friends become electrotarded . . . .
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06-18-2009 08:30 PM  11 years ago
TaleGunner

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Deer Park WA

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your over thinking the problem. I have several 401 gyros and all hold very well but yes in a very lite wind they will drift a little. the question is does it hold for you when your flying. you need to set the gain for your flying style or set it for hover. I have never been able to have both in one mode. if I get to correct for the small drift in a lite wind it shakes at high speed forward flight.CRASH! GLUE! REPEAT!
Spectra-G, Ion X-2
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06-18-2009 08:32 PM  11 years ago
Hamo

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Ireland

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The gyro gain was 70.
Hamo
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06-18-2009 08:37 PM  11 years ago
TaleGunner

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Deer Park WA

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what heli what the servo arm distance etc, these are all relevant

try moving the servo arm ball in and out 1 hole and readjust the gain until it hold & flies the way you want. just saying 70 is irrelevant because no 2 will set up exactly the same. hope this makes since.
CRASH! GLUE! REPEAT!
Spectra-G, Ion X-2
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06-18-2009 08:52 PM  11 years ago
Hamo

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Ireland

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Yes, I understand the relevance of the servo arm length and gain etc and I'm not faulting the 401, just trying to understand the reason for the small drift which the 401 can't get rid of. The tail actually holds very good during flight, rolls, flips, pirouettes etc. Thanks for your response.
Hamo
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06-18-2009 08:55 PM  11 years ago
TaleGunner

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Deer Park WA

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do you have another one or a friend with one? try it you may just need to send your in for repair. The other thing is that maybe with your setup that is just as good as it gets. I quit beating my head against the wall on the small suffCRASH! GLUE! REPEAT!
Spectra-G, Ion X-2
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06-18-2009 09:05 PM  11 years ago
jphilli

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Atlanta, Ga.

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What you saw was probably to result of a low I gain or too high of an I decay.

90 degrees in 30 seconds isn't very much at all though. If you notice a drift in flight, then it's more likely due to a vibration than anything. People have been using 401's for years and a fast drift in a hover is not normal.

Try some different mounting pads and make sure all of your shafts are running true.
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06-18-2009 09:09 PM  11 years ago
jschenck

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La Vista, NE.

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make sure there is no trim or sub-trim. Check every flight mode. Most radios have separate trim settings for each flight mode. I found that was the reason for a guys drift once with a 401. there must be no trim or sub-trim on the 401. Well, you can use sub-trim but why would you (with the 401).

Different for gyro's that have a fixed known center (JR 500 is an example)
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06-18-2009 09:10 PM  11 years ago
Hamo

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Ireland

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90 degrees in 30 seconds isn't very much at all
Actually it's 90 degrees in 60 seconds. In flight there's no drift.
Holds very well. Sub trim zero, rudder trim centered.
I had a CSM 310 HH gyro and it had the same slow drift.
Hamo
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06-18-2009 09:26 PM  11 years ago
jphilli

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Atlanta, Ga.

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Oops, sorry; I misread the OP. But yeah, if you have to rotate the heli 90 deg./min. in order for the gyro to not know that it's moving, then I wouldn't be too concerned. How fast is the heli. drifting in flight?
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06-18-2009 09:32 PM  11 years ago
Hamo

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Ireland

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if you have to rotate the heli 90 deg./min. in order for the gyro to not know that it's moving, then I wouldn't be too concerned. How fast is the heli. drifting in flight?
In flight I don't notice any drift, only while hovering, as my experiment, about 90 degrees in one minute. Thanks for all the responses.
Hamo
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06-18-2009 09:35 PM  11 years ago
jschenck

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La Vista, NE.

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I have seen a 401 do this before and could not find the reason. Possibly some high frequency vibration, say from the clutch stack?
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06-18-2009 10:52 PM  11 years ago
rotaryfalcon

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S.E. USA

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I have experienced this same thing in crosswinds. It is really a very slow drift. If you simply turn the heli into the wind the drift stops. Doesnt seem to improve with gain settings. It is so minor you soon just automatically correct for it.
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06-18-2009 11:04 PM  11 years ago
cfranks

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Adelaide South Australia

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Did you initially set it up mechanically for NO drift in Rate Mode (not HH). That is a requirement for a 401.
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06-18-2009 11:22 PM  11 years ago
rotaryfalcon

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S.E. USA

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Yes, I always set the mechanical set up in rate for as "hands off" as a heli can be. I try to use a "perfect set up" by swapping servo wheels so as to keep atv and sub trims at zero. my tails fly very solidly. But as I said in a stiff crosswind, with no corrections, the nose will weather vane into the crosswind very slowly. Once there it will HH very nicely. This is in extended hovering though not something I really do very much of. I noticed it one day while tracking blades.
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06-19-2009 12:08 AM  11 years ago
missle

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West Chester, Oh

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Not to be an ass, but the only way your gonna see a drift that slow is if your sitting still. Point being, fly her and stop concentrating on the tail.
BTW, your drift could be also due to changes in temp within the 401
WATCH OUT!!!!!!!!
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06-19-2009 04:21 AM  11 years ago
wkfg

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Michigan

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With a 9c, I set it down and toggle between Rate and HH mode three times and drift is gone.
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06-19-2009 06:20 AM  11 years ago
2LTime

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Walworth,NY

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Why would a lite breeze make any difference? The gyro is continually fighting the torque of the engine, which is a fairly significant force. In a lite breeze, it is fighting the lite breeze plus the torque. In your experiment how do you know it wasn't correcting? Are you expecting that when it reaches 90 degrees it will be at max deflection? In my experience the correction isn't necessarily cumulative to the amount of rotation, it is instead somewhat proportional to the rate of motion. Try putting a large arm on the servo to see if it is moving. At the rate your moving the tail, the correction would be very small.

The only time I have had 401's drift in a hover, it turned out to be a vibration issue.

Jeff
If you can't learn to do it well, learn to enjoy doing it badly.
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06-19-2009 01:15 PM  11 years ago
Skarn

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Pasadena, MD

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Did you initially set it up mechanically for NO drift in Rate Mode (not HH). That is a requirement for a 401.
LOL, no it's not! (unless you plan on flying in rate mode). Don't want to litter this thread up with a debate, but thousands have proven otherwise...

Skarn
It's better to burn out than to fade away...
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