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02-18-2014 05:09 PM  3 years agoPost 1
chris6414

rrApprentice

Sneads Ferry, NC USA

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OK, I am am at wits end with this issue I have been having. I recently rebuilt my tail rotor on my Century Predator gasser with all new bearings as the old ones were tight and corroded. All reasembled and grips are greased up and smooth. Re-installed and now my JR 770 3D gyro is wagging in HH mode. Rate seems to be fine. Rod, linkages to the tail are smooth. Tail servo is the JR 8900G digi servo with a Futaba 7C radio. I bought the helo used almost 2 years ago and it has been rock solid until I rebuilt the tail. I have taken it apart twice to see if the thrust bearings were installed correctly and all is well. I am stumped as to why it would wag now and not when the bearings were all bound up in the tail. You would think it would be the other way around. Changing the gain does nothing other than change the wag speed. It almost looks like a "hunt" vice a "wag". When I lift off in rate into a hover, then switch to HH, within a second or two the slow wag begins until I switch back to rate mode. When I reassembled I didn't change a setting on the radio. Same gain,expo and dual rate. I am thinking that the bird was set up to run smooth with a bound tail and now that it is smooth something is not mechanically right. I have about 10 mm out on the the jr horn on the servo. Arm/ball position to short? Servo gears still seem snug. Any insight or is this just a JR 770 thing that eventually happens? Thanks for any insight.

Chris

Century Hawk Sport, OS .32, Futaba 7C, GY-601 9251
Predator Gasser SE G-23, Fut 3010 servos, JR gyro/servo

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02-18-2014 06:00 PM  3 years agoPost 2
JEEPWORLD2002/2

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Blue Bell, Pa

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possibly to high of a gain try lowering the value to see if that helps

also make sure you set center in rate mode. only thing i can think of ??

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02-18-2014 06:51 PM  3 years agoPost 3
chris6414

rrApprentice

Sneads Ferry, NC USA

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Thanks. Yeah, I went from almost zero to 100 on the gain(in HH). Still there just at a different speed. Thats is why I am thinking to increase the ball out on the arm and see what happens. On my Hawk when I adjust to wag and then back off, the wag is usually much faster than what I am seeing here. It is a one second wag in either direction at 75% gain.

Century Hawk Sport, OS .32, Futaba 7C, GY-601 9251
Predator Gasser SE G-23, Fut 3010 servos, JR gyro/servo

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02-19-2014 01:12 AM  3 years agoPost 4
balsabasher

rrVeteran

Central Ohio, USA

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For that size of heli, I would think 10mm is too short. Try around 14mm.
Btw, how is your engine running? Is there a surge or vibe that is driving the gyro crazy. Maybe with the tail bound-up the servo could not react fast enough before but can now.

Blades; what goes around, comes around!

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02-19-2014 01:22 AM  3 years agoPost 5
Pistol Pete

rrProfessor

Seffner, FL

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I would try the servo from your Hawk.

Also double check Tx rudder trim as sometimes it gets bumped out of center when man-handling radio.

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02-19-2014 01:41 AM  3 years agoPost 6
Santiago P

rrProfessor

South West, Ohio

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Chris,

How old, or better put, how many flights old is the 8900G?

The 770 3D is a great little gyro with the 8900G but very suceptible to vibrations.

My best setup was using an isolator plate like in the Futaba GY601 and the 770 worked GREAT UNTIL, the servo reached about 90 flights.

Then it started doing EXACTLY what you described.

Simply put, the servo was worned out. Several JR reps/pilots confirmed my problem.

Added a new servo and problem went away.

hope that helps.

Santiago

Team Minicopter - PeakAircraft.com
bavarianDEMON- Team Kontronik - Scorpion Motors-

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02-19-2014 03:39 AM  3 years agoPost 7
chris6414

rrApprentice

Sneads Ferry, NC USA

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Thanks guys. I'll give the arm move a try. It really looks like a low gain hunt vice that quick over gain wag. I would say it has around 100 flights from me on it and no idea from the previous owner. Engine runs great with no surging. Could the servo be bad even if it flies well in rate mode? In did just double check the manual and for a vibe 90 it says 14mm out.

Century Hawk Sport, OS .32, Futaba 7C, GY-601 9251
Predator Gasser SE G-23, Fut 3010 servos, JR gyro/servo

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02-22-2014 08:01 PM  3 years agoPost 8
chris6414

rrApprentice

Sneads Ferry, NC USA

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Well I can't explain it but the HH mode in the gyro seems to be the culprit. Tried another servo and it cycles the same way in HH mode but works fine in Rate mode. Weird.

Century Hawk Sport, OS .32, Futaba 7C, GY-601 9251
Predator Gasser SE G-23, Fut 3010 servos, JR gyro/servo

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02-22-2014 08:37 PM  3 years agoPost 9
Dan Minick

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Columbus, WI

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if you want to try a different servo iv got an extra 8900 I would sell you. its about 20 flights old sitting in a box in my shop.

Team Synergy, Team FBL Rotors-------if its not broke...it will be!

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02-22-2014 08:42 PM  3 years agoPost 10
chris6414

rrApprentice

Sneads Ferry, NC USA

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Servo

I moved the ball position, adjusted the gain, tried a different servo and it still wont stop wagging. I usually do all my flying in rate but I like having heading hold as well. May try some new tape next and see if that helps.

Century Hawk Sport, OS .32, Futaba 7C, GY-601 9251
Predator Gasser SE G-23, Fut 3010 servos, JR gyro/servo

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02-23-2014 12:30 AM  3 years agoPost 11
JEEPWORLD2002/2

rrKey Veteran

Blue Bell, Pa

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I don't use tape on my 770 I use the zeal gel stuff. I think it loosens the vibe to the gyro ??? Think I had tape but was too sensitive I also use to use a strap which doubled my issue so I moved to the gel n lowered my gain and was good to go. I also suffered through a wag blow out issue on my qww sweetie ten but that was with a 601 n it turned out to b mechanical as my front Tt gear was oversized n over spinning the tail. Humm try the tape/ gel report back maybe the gyro let loose . Do u see any tail glitch ing on the table ??

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02-23-2014 12:55 AM  3 years agoPost 12
doorman

rrProfessor

Sherwood, Arkansas

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Hunt..

Just helped a friend having the same problem, but on a new heli..
Other then the servo going bad, check the attachment of the ball links on the tail slider... if you changed them the new ones might be too tight and causing a very slight bind which would cause your hunt..
Also, check for links being too loose on the tail pushrod at both ends...these get the heaviest usage on a heli and just a bit loose can also give you the hunt..
The servo is working in rate, so I would be hunting down a mechanical cause...
Pretty sure moving the ball further out will only make the hunt worse..

Hope this helps you out..

Stan

AMA 2918-Team JR, Spin Blades, East Coast Scale Helicopter,Castle Creations

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02-23-2014 01:11 PM  3 years agoPost 13
chris6414

rrApprentice

Sneads Ferry, NC USA

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Thanks doorman,
Found a link a little loose and a tail slider with a slight wobble when the whole linkage is moving. Checked against my Hawk Sport and it has 0 movement in it's linkage. I am thinking my binding tail was masking this issue as it worked great before I rebuilt the tail with new bearings and got the grips smooth.

Chris

Century Hawk Sport, OS .32, Futaba 7C, GY-601 9251
Predator Gasser SE G-23, Fut 3010 servos, JR gyro/servo

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02-23-2014 04:58 PM  3 years agoPost 14
doorman

rrProfessor

Sherwood, Arkansas

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Good News!!

Glad you were able to find the two possible "gremlins"!!!

Not sure how a stuck bearing would have not shown up before, but these machines consist of a 1000 pieces try to get away from each other, so not much surprises me any more on these things!!

Hope you will check back when you get a chance to test hop it, once you have the rest taken care of...

Good Luck,,
Stan

AMA 2918-Team JR, Spin Blades, East Coast Scale Helicopter,Castle Creations

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03-01-2014 10:55 PM  3 years agoPost 15
chris6414

rrApprentice

Sneads Ferry, NC USA

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Test flew today and the HH wag is still there. I took off the 770 3D and threw on an ole G-154 and even before it I turned it on the servo has uncontrolled chatters. Not a Digital hum but a noticeable intermittant chatter. None of the other servos do this. I can move the rod slightly and it will chatter much worse, Test flew and it would hold intermittently and just change trim un-commanded in a hover. Before you knock my 154, it worked solid with an analog 310G on my Hawk recently. Should the 8900 chatter or is this a sure sign she is on her way out?

Century Hawk Sport, OS .32, Futaba 7C, GY-601 9251
Predator Gasser SE G-23, Fut 3010 servos, JR gyro/servo

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03-02-2014 12:52 AM  3 years agoPost 16
JEEPWORLD2002/2

rrKey Veteran

Blue Bell, Pa

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154 ?? Is this a gyro ? Is it capable of 1520 relesolution ?

Sorry edit did a search don't think the rate gyro is capable of 8900 resolution possibly hurting the servo ?? Hate to say but might want to send the 8900 on for service n have them go though it with a fine tooth comb

Trex600n,Trex500,MR25,MikadoLoGo5003d/KDE,Goblin 380XNova,CastleCreations,Ys,JR XG8,Tags Mini XBus Dmss//FAA# FA3NYC9TAP

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03-02-2014 01:51 AM  3 years agoPost 17
chris6414

rrApprentice

Sneads Ferry, NC USA

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Gyro wasn't turned on. Just basic receiver signal going to the servo and it was chattering.

Century Hawk Sport, OS .32, Futaba 7C, GY-601 9251
Predator Gasser SE G-23, Fut 3010 servos, JR gyro/servo

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03-02-2014 04:22 AM  3 years agoPost 18
JEEPWORLD2002/2

rrKey Veteran

Blue Bell, Pa

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Don't think u can do that either ? Unless u have a fBL Rx ?

Trex600n,Trex500,MR25,MikadoLoGo5003d/KDE,Goblin 380XNova,CastleCreations,Ys,JR XG8,Tags Mini XBus Dmss//FAA# FA3NYC9TAP

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03-02-2014 03:05 PM  3 years agoPost 19
doorman

rrProfessor

Sherwood, Arkansas

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Got Me!!

These kinds of problems can be really tough to find, and cure!! But you already know that
If the 154 is what I think it is (an old mechanical unit) it will not work with new tech servos as suggested by others. It sounds like it is time to send your servo in for service...but while its out, why not try another servo..does not have to be a tail servo, but it should be a digital one with below .13 speed..or if you have an old analog servo (S148!!) Put that on with you 154 and give it a try!!!
Good luck and let us know how it is going!!!
Stan

AMA 2918-Team JR, Spin Blades, East Coast Scale Helicopter,Castle Creations

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03-02-2014 07:10 PM  3 years agoPost 20
rexxigpilot

rrProfessor

Florida

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I'm placing my money on vibration being the problem. I've had this happen on several helis. A slow wag is typically a vibration issue, not a gain issue. A worn main mast bearing can cause a slow wag, so can engine vibration or unbalanced blades (tail and main). Try using Zeal gel type mounting tape like Jeepworld recommended. Or get some 1 mm Parma servo mounting tape instead (less bouncing of the gyro compared to 5mm thick Zeal). If this solves the wag, don't stop there. You are only masking a vibration issue. Solve the vibration problem or more trouble will lay ahead.

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