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T-REX 250 › Wag, Gyro and tail rotor issues..
12-28-2009 11:37 PM  7 years agoPost 1
NQNA

rrElite Veteran

USA

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I'm hovering my 250 in the garage (Snow and Cold outside) and I have a few questions..

I'm running a GY520 with a Align DS420 servo..

Maximum heading hold on the JR transmitter that I can get is 27% ... any higher and I get a tail wag. Is this a normal number or do I have something wrong? If anybody has some great insight to this little buggers tail would be appreciated...

GY520 settings:
Digital 1520 servo for DS420
Gyro Direction - Reverse
Servo limits set...
Flight Mode 3D Mode but I've tried it in F3C mode also.
Response - Fast but I've tried it in standard mode also.

I've tried the large and small tail blades..

JR X9303 Transmitter
Spektrum AR6100E Receiver
Scorpion HKII-2206-3900KV on a 15t pinion
Align 15A Brushless ESC RCE-BL15X
Normal Curve 90 75 90
Idle up 95 85 95
Head speed approx. 5000 rpm

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12-29-2009 01:12 AM  7 years agoPost 2
dkshema

rrMaster

Cedar Rapids, IA

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The 420 is not a great servo for the tail. Move your ball link inward on the servo arm. I'm at about 3 mm out from center. If you're out at 5mm or so, that's too far. Moving inward allows you to run a higher gain and makes the tail response less sensitive to small servo movements.

And make sure the tail rotor linkage, pitch slider, and grips are friction free and not binding anywhere.

-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz

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12-29-2009 05:38 AM  7 years agoPost 3
NQNA

rrElite Veteran

USA

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What servo would be the best for this bird. The Futaba 9257 is too big. The JR DS3500G is about the same size as the Futaba...

At first glance this looks like a servo issue.. You can always tell when a servo is not up to the job.

The linkage is as smooth as butter so I know it's not a linkage issue..

I will try moving in on the servo wheel..

Oh I am running 6 volts.

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12-29-2009 07:32 AM  7 years agoPost 4
NQNA

rrElite Veteran

USA

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Anybody try the JR DS290G servo?

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12-29-2009 01:07 PM  7 years agoPost 5
dizzymarkus

rrVeteran

Oswego, NY

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I run the 290 at a full 6v without issues -- check for excesive play in the tail grips ----

yes the gain is usually very very low number on these birds -- I got 27 myself witha 401

Markus

I reject your reality and substitute my own :0)

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12-29-2009 10:15 PM  7 years agoPost 6
NQNA

rrElite Veteran

USA

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Well I played with it some more today.

I reduced the servo wheel from 7.5mm to 4.5mm from center... With the small tail blades..

I went through the computer setup of the gyro. One thing that I noticed is the center changes from computer center to radio center. I rechecked this with a different GY520, a S9257 and AR6100... still a slightly different servo center. I didn't notice this change with my Trex 500 with a AR7000 DSM2 7-Channel Receiver, a GY520 and S9257...

Anyway... with the 4.5mm ball placement on the DS420, I now have 31% on the gyro gain. Three test flights with the last one with more than just forward flips from a hover, the gyro held well in fast sideways loops, backwards flight with rolls and backwards loops. Was a lot of fun.. but now my fingers are cold..

I do have a JR DS290G on order so it will be interesting to make a comparison...

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T-REX 250 › Wag, Gyro and tail rotor issues..
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