Logo 600 elevator shake

[aziz76]

I have an issue with the elevator bobbing up and down a lot after any inputs on my logo 600. My elevator filter is at 4 and i tried lowering cyclic feed forward to 6. Also tried higher and lower head gains but can’t make it go away.

Any help would be appreciated.

[HeliMLM]

Hi

is it just on elevator or any cyclic input? what servos and at what voltage are they operating? what servo horns (length) are you using? what are the head geometry numbers in Spirit setup? maybe upload the settings file here...

[aziz76]

It happens with any elevator input, but also any sharp collective input as well. I get it on all banks, though slightly less at higher head speeds.

I'm using BK Servos (7002HV Coreless) powered from Kontronik ESC BEC set at 8v. The servo horns are at the manual recommended distance of 17mm.

I have attached my spirit settings files, along with head speed for each bank.

Thanks for your help

[Habásek]

I think the gain of head 30 is low, set 50-60.
Do you have paddle-free rotor blades and are properly balanced?
What is the extent of the cycle in degrees? the value of 200 is also quite high.

[HeliMLM]

Hi

did you check that 6° geometry is really exact?

the tail and cyclic rates are very low (8)... so is the head gain (30). the same for the cyclic ring (128/9°). as @Habasek wrote: i would increase head gain to 50-60, cyclic ring to 11° (should be 150-160. just test it, it is at least easily possible on my 600SX). unless you are a beginner, i would also increase the cyclic & tail rates (try ~10?)... makes cyclic/tail feeling much more 'connected'.

piro consistency is very high too (220)... but i guess this should not be a point for the bounceback problem. 200 for pitch could be OK, i do have 192 on mine too to have 13.7° max. for low rpm flying. how much pitch do you have?

as for the head mechanics: is the head new or old? head dampers oiled, no play in the head and everything moving smooth and without binding or jamming? (same for the swash). and blade tracking is OK (both blades 0° @ 0° pitch / middle stick).

[aziz76]

Hi, thanks for your responses.

6 degrees geometry is correct. I started with a head gain of 55. I tried lowering it gradually to 30, and increasing gradually to 70 as well, the shake is reduced slightly with lower gain. My rates are low because these were the first flights, I wanted to get the head and tail reasonably tuned first, low rates should not cause an elevator shake though.

The Heli is newly built and I am sure its ok mechanically.

@HeliMLM, I will try your values and see what it gets me.

[HeliMLM]

Hi Aziz,

most of my Logos (550/600/690) had some wobble etc during the first flights after fresh build. the really need some 5-10 flights to start to be as smooth as they finally are. especially in winter/cold time... btw: i am using mid shore dampers, like them more on Logos. less wobble etc.

=> good look for the next flights!

[urgno]

this can also happen if the dampeners are not properly greased
or if head speed is too low

btw i remember also that time ago Thomas warned
about something wrong with bk servos and spirit

[ZeXx86]

Hello,

you are right, unfortunately these servos are known to cause issues to some pilots.
This problem can be reduced significantly by lowering BEC voltage to 6V. I recommend to try it at least temporarily.
FBL blades can help a lot too.
For Logo 600 Cyclic Gain around 60% should work without any problem.

[aziz76]

Thank you all. My dampers are well greased and seated so I don't think its that. I will try a different set of servos. I have Xpert on most of my other helis with Spirit with no issues. I will try switching to them.