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Tail Wag

Old 12-26-2006, 05:44 AM
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Default Tail Wag

Hi all, I know this will have been asked many times. I have looked through old posts but cannot find the information i am looking for. Hope someone can offer some advice?

I have a Trex 450. It is upgraded with carbon frames, carbon blades ect. I am using a gy401 gyro with a hds877 digital servo. I have it all set-up and it hovers fine, but i have really bad tail wag. I have gone over my setup twice now and still cannot get it sorted.

I have set the gyro up on the standard setting and used both high and very little gain there is no diffrence in the wag. The head speed is at 2,200 on the hover. If i disconnect the servo linkage the servo does not move, so i would say vibration was not the problem. The linkage is free from slop and does not bind. Any ideas?

Regards

Paul

P.S. I bought the heli secondhand so have not used it yet.
Old 12-26-2006, 11:39 AM
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Default RE: Tail Wag

paul, have you tried the exact setup but without the gyro? Does the tail wag then?
Old 12-26-2006, 12:28 PM
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Default RE: Tail Wag

Sounds to me like your tail servo horn is not centered properly.
Old 12-26-2006, 12:30 PM
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Default RE: Tail Wag

have you crashed it? i found out that everything from unbalanced blades to bent parts will make it wag. is what i do and i cant say it will work for you but it works for me is i take and hold heli firmly and slowly power it up and see if i can see the vib in the head. then i pull off main blades and power up to see if theres a prob in the head. if not there then i take off tail rotor blades and power up and see if there. i have found that if i have a wag it is 100% of the time a bent or unaigned piece. i have crashed so i have had several tail way problems and its almost always in the main head. also if the blades arent balanced perfectly it can make your tail wag.
Old 12-26-2006, 12:56 PM
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Default RE: Tail Wag

Hi, i have been trying to sort it all day! I have changed the rudder servo, and that made no diffrence. I have run it up with no blades on and again the same wag. If i just touch the servo horn it will not wag. Not thought to take the tail blades off but will do now. There is no wag with the gyro off, unpluged. i can see the servo/gyro fighting to stop the wag.

Regards

Paul
Old 12-26-2006, 01:09 PM
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Default RE: Tail Wag

With the rudder servo unplugged there is no sign of wag or vibration, with the tail blades off again no sign of wag or vibration. I still dont know what it is however. The rudder servo does not move at all with the tail blades off.

Paul
Old 12-26-2006, 01:13 PM
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Default RE: Tail Wag

OK, now we are getting somewhere.
The wag is obviously caused by the gyro.

This can be an interaction between the gain setting and the servo arm geometry.
If you cannot stop the tail wag by decreasing gyro gain, you will have to move the tail pushrod to a hole closer to the servo in the servo arm and start over. (or farther out, usually closer for what you are describing)

What you are seeing is not the gyro fighting the wag, but causing it.

Also make sure your tail pitch slider is very free at the center position, not binding at all here.

And of course you have followed your gyro instructions as to mounting, reversing switch setting, and the initial gyro gain setting.


Old 12-26-2006, 01:16 PM
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Default RE: Tail Wag

Just to be clear, when you have the rudder servo plugged directly into the radio, gyro out of the circuit completely, all other parts of the helicopter set up for flight, does the tail still wag? I am assuming your answer is "no", but you are not really answering the question.
Old 12-26-2006, 01:22 PM
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Default RE: Tail Wag

I have done as you have said because the first servo that was on the rex when i got it had the horn on the inside hole. The servo i have changed it with i used a hole futher out to try that. It did not make any diffrence. I have moved the gain in steps of 5 from 100% to 0% in both normal and head and hold. I am starting to think the gyro is broken. I have no way to test this without buying a new one.

Paul
Old 12-26-2006, 01:28 PM
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Default RE: Tail Wag

Hi, Jellyson

The answer is no no wag at all
Old 12-26-2006, 01:35 PM
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Default RE: Tail Wag

Hi Paul
So you have used the very shortest possible servo arm, you have explored the gyro gain setting range, yet it still twitches...you could try turning down the rudder servo travel limits in the TX but this seldom works, the gyro takes over and will try to drive the servo anyway.
Let's see, does the 401 allow you to set servo travel in the gyro? I can't remember. If so, back it down and see what happens.
Your problem is caused by too much servo travel for the amount of yaw needed, so the tail wags back and forth trying to catch up.
The fact that it doesn't wag without the gyro means that your basic setup is OK.
So look for causes of the too much servo travel, like geometry, limit settings, time constant settings, revo mix settings buried in a TX menu somewhere....
--John
Old 12-26-2006, 01:39 PM
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Default RE: Tail Wag

Oh, with that gyro is it possible to disable the remote gain and just set the gain manually in a single mode? What happens when you do that?
Old 12-26-2006, 02:08 PM
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Default RE: Tail Wag

Hi, Gain is ajusted on the tx it is not on the gyro. the limit can be set on the gyro, but again i have tried that
Old 12-26-2006, 02:13 PM
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Default RE: Tail Wag

Well, at this point I have to say I'm stumped.

I always try to eliminate everything else before I suspect a hardware malfunction, but in this case I'd say it's time to try another gyro.

Anybody else got any ideas?
Old 12-26-2006, 02:21 PM
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Default RE: Tail Wag

Headspeed sounds pretty low at 2200, this in itself can cause a wag.

Do you have Governor mode on? Governor mode can cause a wag.

Do you have soft start on? soft start can cause a wag.

I run a JR G500T Gyro, A JR DS3400G and a DX6 my Gyro scale is -100 0 +100

I run around +35 with no wag

My servo horn is 7mm from center to the hole the rod to the tail rotor is in.

Good Luck!
Old 12-26-2006, 02:26 PM
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Default RE: Tail Wag

Would these things cause it to wag with the gyro, at all gains, but _not_ wag without the gyro? Just asking, for the database, you know...

My ball link is 7.5 mm from the servo axis, actually still not short enough.
Old 12-26-2006, 02:36 PM
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Default RE: Tail Wag

Very Likely, any one or combo of them will get you as the Gyro is compensating.

When they gyro is not in the line then there is no compensation so you don't have the wag.

It could also be some binding, or delay setting.

I run a JR G500T Gyro and a JR DS3400G Servo (very quick).

Read up on Gyros on Futaba's and JR's site, it will really help you to grasp what is happening.

Old 12-26-2006, 02:47 PM
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Default RE: Tail Wag

There is no binding, the head speed will go up when i tried to see if i had a problem without blades on so i think head speed will not be the problem. i do not have the governor swithch on.

regards

paul
Old 12-26-2006, 02:52 PM
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Default RE: Tail Wag

Put it all together and ready to fly (blades on etc), make sure your feathering shaft screws are tight and have thread lock on them.

Take it outside and try to put it in a hover and see how it acts.

Old 12-26-2006, 05:12 PM
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Default RE: Tail Wag

have tried it in the hover in the garage. still wags. It's really wild swinging back and forth. I am at a lose. have tried everything. Have a normal gyro will try that tomorrow. Will let you know.
Old 12-26-2006, 06:43 PM
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Default RE: Tail Wag

what trans are you useing . i have been chasing the same on mine . i found that today the futaba 9650 servo is the fix for mine. my set up it the logictech 2100t with the 9650. had a hs 81 on it before. in norm rate mode tail held fine . but as soon as i turn on hh it wants to wag. i have the newest tail stuff . just like trex 600 tail. is super smooth but no maker what i try on the 450 it wants to wag. so today i put a 9650 on it and it is al gone. hope this helps . still want to knwo your setup . to make sure your setting are right.
Old 12-27-2006, 12:00 PM
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Default RE: Tail Wag

Right this is what i have tried today. I put a basic pizo gyro on the rex and tried that it still wagged the same. I changed the main and feathering spindle still no improvement. I took the head off leaving the main shaft in place and it still wagged the tail. I have split the tail down cleaned it and checked it over. I could not find any problem. I have put the hole thing back together and its still the same.

The tx is a futaba ff9, the gyro is a gy401, the servo was a hds877 digital servo, but i have put a HS metal servo from one of my jets in now. Thought it would need more talk.

I am at the point of giving up any advice most welcome.

Paul
Old 12-27-2006, 12:08 PM
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Default RE: Tail Wag

OK, when you put the basic piezo gyro on, did you use its remote gain function? Or were you able to disable the TX remote gain and set the gain manually with this basic piezo gyro?
WHat kind of basic piezo gyro are we talking about?

Obviously I am thinking that the gain on your gyro isn't being set correctly by your TX somehow.
And you have evidently gone thru the heli mechanical setup very thoroughly so that probably isn't the problem.

So let's get a gyro on there that can be set manually, disable the TX gain function, and see what happens.

Also be sure that you are using the very shortest possible servo arm geometry, link rod in the hole closest to the servo axis for these tests.
Old 12-27-2006, 12:19 PM
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Default RE: Tail Wag

The gyro is a CSM180. It does not have remote gain. It only has one lead ect, so its not the tx. As i put in the post yesturday i have used both longer and short servo horns. The tail blades are really powerfull i can only just hold it back as it kicks to the left looking from behind.

I do appreciate all your help so far.

regards

paul
Old 12-27-2006, 12:31 PM
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Default RE: Tail Wag

So you manually turn down the gain on the CSM gyro and it still twitches, but it does not twitch with the gyro physically out of the circuit.

This is not logical, if the gyro gain is turned down it should act like it isn't there and the system should behave as if there was no gyro.

I am sorry, I am stumped.
I still would look for play in the tail pitch system, or binding there.

One other thing--swap channels on the radio, just temporarily. That is, put the rudder on a different channel in the TX and the RX. See what happens. I know it isn't logical but neither is your gyro result.

Two more other things--I have gone back thru the thread and I can't find where you may have tried the gyro reversing switch.. also where are you mounting the gyro?

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