Servos not moving the same distance

[keithw123]

Something weird going on, trying to set up my servos, 90 degrees-swash leveller and all that.
I am getting much more movement on the servos when I put positive pitch in than when I put negative pitch in.
All 3 servos moving together.
I've set up zero, then go to full pitch and I get about 12 degrees, then go to negative and only get 9 degrees.
My radio has all settings at 100 percent.
Don't understand why.
Whatever I do with the spirit settings, I just can't get the servos to give the same movement in both directions.
Help please.

[ZeXx86]

You can check, if your servo arms are exactly at the center position when you enable Subtrim (tuning) option in the software.
This is very important, else geometry of the head movement will be asymetric and will cause this difference.

Also you can verify, if Servo Travel Correction values are all at the center.

[keithw123]

Hi
Yes servos at centre position,
Swash plate levelled and servo correction all done.
Still servos move much more with positive pitch than with negative pitch.
About 4 degrees difference.
The only way I can get it working ok is to adjust the atv in the radio.
So my atv settings are.. 87 positive pitch and 125 negative pitch.
With these settings I can get 12 degrees top and 12 degrees bottom

[keithw123]

No my servo arms are not exactly at centre position when I enable subtrim, other wise I wouldn't need to use subtrim.

[ZeXx86]

You have to use Subtrims so that the servo arms are at the center as close as possible.
Then you have to adjust linkages so that the swashplate is leveled with the leveler - for this, subtrims shouldn't be used.

[keithw123]

All my servo linkages are exactly the same length and the servo arms are at 90 degrees.
Swash plate is level.
It moves up and down and is level at all positions.
But reduced movement at negative pitch.

[Coco66]

Did you setup Advanced / Geometry 6deg tuning?
Just an idea...

And, what size heli is it?

[keithw123]

Yes, that's all ok.

[Coco66]

If all was ok then you will not have the problem )))))))

Then use Servo travel correction...

[ZeXx86]

If everything is as I mentioned, you will need to proceed in the following way.

For some helicopters (especially Trex 450) this difference is normal. You should fix it by using Servo Travel Correction (not ATV in the transmitter).