Tail servo goes autonomously "full Nose left" during setup

[lucasouthoffrance]

Hi guys,
today I was working on the bench with my heli and I have noticed for the first time that the tail servo slowly and autonomously moves towards the "NOSE LEFT" position, without any stick input. If I center it, after around 20 seconds it has gone to the full left.
Is that behaviour "normal" on the bench?
I attach my config file for info.
Thanks !
Luca

Goblin 500S 20170914 3.1.012 new.mtr

[jhamel]

First, verify Subtrim is set to the default value of "0" for the rudder, aileron, and elevator channels. Also, make sure you have not added "Trim" to the rudder gimbal; Best to disable all 4 gimbal Trims.

[JWeber]

That also might be a bad pot on the servo. Do you have a servo tester that you can use? Or try it on another unit and see if it behaves the same way?

[DanMcN]

Make sure pw and freq is correct, swap with another servo (change pw & freq). No transmitter trims.

Does it travel in rate mode?

[lucasouthoffrance]

Thanks for the suggestions, guys.
I'll check this weekend the situation on trims, subtrims and servo pw and frequency. I'll let you know if I find something wrong.

[lucasouthoffrance]

Hi, I've just done some testing and checks on the G500:
- There were no trims or subtrims in the transmitter.
- Transmitter monitor and Brain correctly indicate 0 at center stick for RUDDER.
- Tail Servo pw and frequencies are correctly set in the BRAIN
- I have also recalibrated transmitter sticks to be safe, but no impact on the servo behaviour

But...
- In RATE mode the servo does not move at all.
- With Tail I gain set to 0, the servo does not move at all. As soon as you set some I Tail gain, it starts moving.

Can somebody explain that behaviour?
Thanks
Luca

[jhamel]

It is my understanding that FBL units in general need to have a gain number other than "0" in the P-gain, I-gain, and possibly D-gain.

[nflanagin]

Did you setup calibration dials for your tail? This is from the MTR file

Your MTR file
<CommonParam Value="4" Tag="Calibration1Channel" />
<CommonParam Value="2" Tag="Calibration1Par" />
<CommonParam Value="255" Tag="Calibration2Channel" />
<CommonParam Value="0" Tag="Calibration2Par" />
<CommonParam Value="255" Tag="Calibration3Channel" />
<CommonParam Value="0" Tag="Calibration3Par" />


My MTR file:
<CommonParam Value="255" Tag="Calibration1Channel" />
<CommonParam Value="0" Tag="Calibration1Par" />
<CommonParam Value="255" Tag="Calibration2Channel" />
<CommonParam Value="0" Tag="Calibration2Par" />
<CommonParam Value="255" Tag="Calibration3Channel" />
<CommonParam Value="0" Tag="Calibration3Par" />

[Alexatu]

Reset tail gain P I Ds to their default values and do a spoolup on the bench with tail blades only. You will likely see that the tail servo is compensating just fine and the tail holds in place. It is uncommon for the tail slider not to move on the bench or during setup. In fact most of the times it'll just slowly go to the max limit on one side after a number of seconds (mine usually goes towards the tail). No worries, this is normal, it's how these devices work. In rate mode the slider will not move because the gyro does not work to "hold" the tail in place. Just adjust your tail mechanics the right way... With Brain2 you can adjust your tail servo to have a perfect 90 degrees arm; go to Advanced settings>Servos, check the "Check mode option" so your servos would enter in large deadband mode then go to servo 4 (tail) and adjust it's neutral value until the arm is at 90 degrees. At this point also check your tail rod lenght... Fold the tail blades and adjust the tail rod links until the tail blade tips are aligned. Now exit the Advanced menu and go to the Tail tab in the Basic menu and adjust the slider limits left and right. After this you only need to tune the tail in flight a bit and that's it.

Sent from my LG-D855 using Tapatalk

[lucasouthoffrance]

Originally Posted by nflanagin

Did you setup calibration dials for your tail? This is from the MTR file

Your MTR file
<CommonParam Value="4" Tag="Calibration1Channel" />
<CommonParam Value="2" Tag="Calibration1Par" />
<CommonParam Value="255" Tag="Calibration2Channel" />
<CommonParam Value="0" Tag="Calibration2Par" />
<CommonParam Value="255" Tag="Calibration3Channel" />
<CommonParam Value="0" Tag="Calibration3Par" />


My MTR file:
<CommonParam Value="255" Tag="Calibration1Channel" />
<CommonParam Value="0" Tag="Calibration1Par" />
<CommonParam Value="255" Tag="Calibration2Channel" />
<CommonParam Value="0" Tag="Calibration2Par" />
<CommonParam Value="255" Tag="Calibration3Channel" />
<CommonParam Value="0" Tag="Calibration3Par" />

Yes, I have a calibration switch for the Tail I gain.

[lucasouthoffrance]

Originally Posted by Alexatu

Reset tail gain P I Ds to their default values and do a spoolup on the bench with tail blades only. You will likely see that the tail servo is compensating just fine and the tail holds in place. It is uncommon for the tail slider not to move on the bench or during setup. In fact most of the times it'll just slowly go to the max limit on one side after a number of seconds (mine usually goes towards the tail). No worries, this is normal, it's how these devices work. In rate mode the slider will not move because the gyro does not work to "hold" the tail in place. Just adjust your tail mechanics the right way... With Brain2 you can adjust your tail servo to have a perfect 90 degrees arm; go to Advanced settings>Servos, check the "Check mode option" so your servos would enter in large deadband mode then go to servo 4 (tail) and adjust it's neutral value until the arm is at 90 degrees. At this point also check your tail rod lenght... Fold the tail blades and adjust the tail rod links until the tail blade tips are aligned. Now exit the Advanced menu and go to the Tail tab in the Basic menu and adjust the slider limits left and right. After this you only need to tune the tail in flight a bit and that's it.

Sent from my LG-D855 using Tapatalk

Thanks Alexatu. Happy to see you observe the same behaviour (my servo goes slowly towards the tail as well).
Thanks for the setup suggestions. In fact my setup is correct and it flies well (since 250 flights); but I never noticed that slow movement before...
Maybe BRAIN developers could jump in and explain that thing from a more technical perspective...
Cheers, Luca