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HelicopterMain Discussion › Unbalanced cyclic pitch
04-09-2011 08:56 PM  6 years agoPost 1
n8leon

rrNovice

Cupertino, CA

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I have been plagued by this problem for as long as I have been flying helis (about two years ) and I want to learn how to fix it once and for all.

Specifically, after setting up the head, I get different readings from my pitch gauge for Left and Right aileron, as well as Up and Down elevator.
e.g. currently I have:
Ele: Up: 8% / Down: 9%
Ail: Left: 10% / Right 9%

So now when I try to do a forward flip, it rolls to the left slightly unless I give a little cyclic-right input.

This happens to me on my TRex 450 and 500. (both still running flybar)
I am using RDLohr's Flybar lock, so I am getting a good pitch reading.

I try to follow Finless Bob's videos as closely as possible.
He basically says, in the end if your pitch readings don't match, you did something wrong, so go back, and check everything again.

I'll go watch his head setup video once again, but meanwhile...
What do you think is the most likely cause of my cyclic unbalance?
Do folks really get those pitch readings to be identical?
i.e. or is +/- 0.5% close enough?
Is there a cheat to mask this symptom? (e.g. DX7 setting)

TIA,
n8

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04-10-2011 12:41 AM  6 years agoPost 2
dkshema

rrMaster

Cedar Rapids, IA

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More than likely your geometry of the servo arms and cyclic isn't set up correctly so that you have introduced differential travel into the controls.

Set your heli to ZERO degrees pitch, all trims centered and sub trims at zero, then take a picture or two of your servo arms/pushrods and post them here.

-----
Dave

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

Team Heliproz

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04-10-2011 04:33 AM  6 years agoPost 3
Anthony440

rrNovice

Colorado

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I would start here.

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04-10-2011 01:14 PM  6 years agoPost 4
AltecLansing

rrElite Veteran

North Carolina

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That's a good pic.

Man, I miss the eighties.

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04-10-2011 01:31 PM  6 years agoPost 5
ttrip06

rrApprentice

Central Pa

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Pop the link off the blade grip and adjust the blade till it will sit level. Snug the bolt a bit, hook the link back up and check your settings again.

Let us know if that helps

Tim

Tim Tripoli

Team Futaba, Rail Blades
Team Crash
ProggressiveRC

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04-16-2011 08:05 AM  6 years agoPost 6
n8leon

rrNovice

Cupertino, CA

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Sorry for the delayed response...

I set all trims to 0 and using a linear pitch curve in the Tx, verified the gimble was at 50%. I left the sub-trims alone since that is where I had to move them to get the servo horns at 90 degrees to the servo.

That is where I took most of the pics. However, one of the leveling tools didn't quite fit under the swash, so for some of the pics, I increased the stick to 52 or 53 just to illustrate the swash is level.

I also noticed I am getting inconsistent readings from the pitch gauge. e.g. I thought I had L & R cyclic at 8.5%, but I checked later and they were 7.5 and 9.

Does that imply something is moving around?
e.g. some part is cracked or broken
Or is there another explanation?
With the Flybar Lock, I can't believe it is completely user error.

Thanks,
Nate

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04-16-2011 02:57 PM  6 years agoPost 7
Pistol Pete

rrProfessor

Seffner, FL

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Assuming helis has never been crashed...we will rule out spindle, however, this can be checked by just removing ONE blade and slowly turning screw to spindle and looking for any tip movement on the other blade. Repeat for other side. If it goes up and down, its bent.

Noticed that the ball link on the Elevator is one hole back when compared to the the other two.

The swash may be level at ZERO pitch but you dont mention if it is level when at full POS or NEG pitch...which seems to be the issue. So check and adjust travel end points for each servo.

You can also swap rods from AIL and PIT. Try same with main grips and see if problem goes the opposite or away.
With the Flybar Lock, I can't believe it is completely user error
With same problem on two helis, possible could be the radio. Only way to verify this is with servos removed and next to each other...as a last resort.

~~Enjoying the hobby one flight at a time~~

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04-16-2011 05:43 PM  6 years agoPost 8
n8leon

rrNovice

Cupertino, CA

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I crashed it pretty good last August and had to replace the main rotors. I normally check the feathering shaft in that case, but I can't be sure I did it that long ago. I'll check it just to be sure.

Good catch on the elevator servo horn hole. I think moving it to the 2nd hole would be too much angle for the rod, or is that fine? But of course that means less elevator travel for the swash during collective movement as it is now. Do I compensate for that in the Tx? Or should I move the other two servo links in one hole? (assuming I can still get the desired travel)

I really like you theory about swash not level at full pos/neg. Especially since I don't think I have checked it since the crash.

If none of that works, I'll try swapping links and pulling the servos.

I suspect the problem is in both helis 'cuz I'm making the same mistake during setup. e.g. The "Travel Adjust" theory could explain that.

Hopefully I can try some of this today, but the kids are on spring-break so I may not get any garage time. ;-)

Thanks for all the good ideas!
n8

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04-20-2011 05:30 AM  6 years agoPost 9
n8leon

rrNovice

Cupertino, CA

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Yup, Travel Adjust was the key. The aileron settings were way off... L:75 and R:96. I don't remember why I had those changed so dramatically. I ended up with them at L:100 and R:101 which seems more reasonable.

Now I get 10* cyclic for aileron and 9* for elevator. I suspect that is due to the elevator being on a different servo arm hole as you mentioned. Even better, I get the same numbers for left/right and up/down, checking both blades from front/back/left/right.

I flew it today, and I could not detect any roll during a forward flip.

Sooooo happy - thanks Pete!
n8

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04-20-2011 06:17 AM  6 years agoPost 10
McKrackin

rrProfessor

Lucasville,Ohio

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How can you have the elevator link ball in a different hole than the other two?

That would mean the swash will tilt forward or back when you apply collective pitch.
The elevator won't have the same range as the others.

All three servo horns need to be identical and all three need to be sitting at exactly the same angle when the swash is level because when the horn moves,the speed of the rise and fall of the swash changes.
Faster through the center and slower at the top and bottom.
All three need to be identical.

I literally never use the word literally right.

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04-23-2011 10:46 PM  6 years agoPost 11
n8leon

rrNovice

Cupertino, CA

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After Pete mentioned it, I thought it was very odd also, but I wasn't sure if there was some reasonable explanation.
Sounds like not, so I will fix it.

Thanks!
n8

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