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HelicopterRadio - Servo - Gyro - Gov - Batt › GY401 - anyone seen drift?
03-13-2003 08:19 AM  14 years agoPost 1
stardotstar

rrApprentice

Sydney Australia

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It seems that my 401 is drifting nose left (very slowly - like perhaps 90' in a minute). I have noticed it only recently and it is about 8 months old.

Anyone else experienced this with the 401 and furthermore any suggestions on what could be causing it or how to diagnose/rectify.

BTW new Webra engine (still running pretty rich) in the heli. Someone once said that too rich can cause gyro drift - how so?

cheers all.

strdot

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03-13-2003 12:45 PM  14 years agoPost 2
SteveH

rrProfessor

Texas

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I've got three of the 401s and none drift. If the engine is too rich, to the point of breaking between 2 and 4 stroke, it will change the torque on the heli at the same rate of the engine braking in and out of the 2 and 4 stroke and the gyro will have a much harder time of holding the heli, but don't know if it would actually cause drift.

If your engine is that rich, I'd lean it at least to the point of a steady 2 stroke with good smoke.

Also mine seem to work better if I make sure the mechanical trim is set hand off when the gyro is in non-heading hold mode. Don't adjust the trim on the radio, but the pushrod length. Hope this helps.

SteveH

The government cannot give you anything without first taking it from someone else.

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03-13-2003 01:01 PM  14 years agoPost 3
Will B

rrVeteran

Bicester, Near​Oxford, UK.

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I'd say what Steve H said is right.

As the engine breaks in an out between 2 and 4 stroke the tail will kick due to the sudden change in torque. The gyro will have to compensate for this but probably doesn't correct quite enough each time and so it appears to "drift". I would also say that its even more likeley to be the "rich running engine/gyro undercompensating" scenario due to the fact that the nose is drifting to the left. Does the gyro drift when the engine is not running? If it doesn't then I'd focus my attention on the engine.

Try leaning the engine a few clicks or if that doesn't help then check your fuel system to see if your getting any air bubbles in the fuel line which would cause your fuel flow to the carb to be inconsistant and thus causing inconsistant running.

Cheers, Will.

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03-13-2003 01:03 PM  14 years agoPost 4
z11355

rrMaster

New England

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verify that when you power up the gyro,
the gyro is set to HH mode. The LED
should ON SOLID.

Verify that after flying around a bit
that when you land and look at the
LED, it is still ON SOLID.

If its blinking, then you have some
offset in the transmitter somewhere,
perhaps trim, subtrim or a mix (revo mix?)

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03-14-2003 12:56 AM  14 years agoPost 5
stardotstar

rrApprentice

Sydney Australia

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Thanks guys this is great diagnostic info.

The engine may be too rich still since it is only just beyond running in and the concept appears sound. I will test the gyro without the engine running - just by watching the servo.

The gyro is initialising correctly as far as I can see and it is not going into error mode at any time that I can observe it... (LED seems normal)

There is no trim or revo mix and I will double check the sub-trim.

Other thing is that normal mode is NOT properly setup and I think that it is a nose left drift which may indicate that mechanical trim to get normal mode stable in the hover will assist.


I will also lean the engine though I don't think it is 2/4stroking but the theory does make sense to me.

Cheers all - I'll report back.

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03-14-2003 06:41 AM  14 years agoPost 6
FinnDave

rrElite Veteran

Kouvola, Finland

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My 401 seems pretty solid, but I have never tried hovering in one position for several minutes to see if it drifts, why would anyone want to?

David S., Kouvola, Finland

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03-14-2003 02:45 PM  14 years agoPost 7
vetrider

rrElite Veteran

Daleville, AL​(Ft.Rucker)

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If your mechanical setup of the servo to TR is off and you have to keep your trim adjusted over more than a few clicks the gyro will start to drift.
Ask me how I know?

In non-HH mode make sure your trim is centered and adjust the servo to TR links till you need very little trim to hold straight in the hover. Then all should be well. If not your servo may be getting long in the tooth.
Depending on your gain settings the servo will not hold as well after a couple hundred flights. More gain the less servo life.

Nolan

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03-14-2003 05:18 PM  14 years agoPost 8
sharam

rrElite Veteran

Northern California​- Fly at Morgan Hill​Field

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Make sure your normal mode (non-HH) is set up properly first.

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03-15-2003 06:32 AM  14 years agoPost 9
stardotstar

rrApprentice

Sydney Australia

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Progress!

Thanks guys! All this info helped.

I setup normal mode - it was way off - and I had taken to just leaving it in HH all the time. In the end I have Normal mode mechanically timmed to my current hover power and am using -10subtrim. I will leave final mech adj till I have the engine fully sorted.

I had had the gyro setup gain and ATVwise by a flyer at an event and only now do I really understand enough about all the systems to see that it was potentially a bad setup. Check this out...

I had asked for a higher rate of pirro and the guy gave me just that... 130ATV on Rudd but here's what's wierd - I had been fooling around with gain in the Gyro setup in the radio but the 401 remotegain is plugged into Gear and, upon investigation (thanks Jeff!) I found this to be set to 110 in HH and 100 in Normal! Once I began to really explore the pirro rate with the new engine in the heli the drift was the least of my concerns - the tail started hunting furiously (scary!) Today I have set gain to 58 in HH and 70 in Normal and the hunting has abated, the drift is gone and now I only have to sus out the engine mixture/throttle/pitch.

I don't understand why these symptoms didn't show with the TT36 engine - It had been flying fine for ages but as soon as the Webra started to develop real power (and it still is) the gyro problems set in - perhaps I am too rich or lean - I'm going to get someone to check it form me tomorrow.

Thanks for your help guys.

BTW it seems that the GY401 does not see subtrim as ratedemand so does it see trim input as such?

oh, Vetrider - how do you know?

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03-15-2003 01:19 PM  14 years agoPost 10
SteveH

rrProfessor

Texas

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Stardotstar,

The GY401 sees any input made AFTER the turn-on and iniation sequence as a ratedemand, or yaw demand. You would be better off eventually to set your subtrim at zero and again set the mechanical trim in nonheading hold so the heli holds steady in the hover.

Also, it sounds like your rotor head speed significantly increased with the new engine, as that will increase the effectiveness of the tail rotor which in turn can cause the tail to hunt rapidly at a given gyro setting.

I would suggest you get someone with a rotor tach to help as you get your carb mixture sorted out as a leaning in the mixture will usually increase rotor speed and you don't want to put that Raptor into the "Woof and Puff" syndrome. As the rotor speed comes up during carb leaning, you will have to decrease the throttle setting at hover to compensate. Hope this helps.

SteveH

The government cannot give you anything without first taking it from someone else.

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03-15-2003 01:26 PM  14 years agoPost 11
BladeStrike

rrApprentice

Shelby Twp, MI

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I had a GY401 that worked fine then when the weather got colder it started to drift. So I sent it back for warranty work and GP replaced it with a brand new one. Hey they sometime go bad.

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03-15-2003 04:34 PM  14 years agoPost 12
vetrider

rrElite Veteran

Daleville, AL​(Ft.Rucker)

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stardotstar, I had the Yaw trim (not sub trim) adjusted about half way because I was lazy in getting the mechanical adjustments correct first. The gyro started drifting in HH mode even after doing the realignment procedure several times. It could be that that gyro was more sensitive to it but I'm still flying that gyro on my Sceadu 50 and it performs great.

Nolan

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