Oxy 3 tail kick — Need 10/10 Revomix

[xoexoe]

[[ THIS ISSUE HAS BEEN SOLVED VIA SWITCHING TO MKS DS95i ]]

Oxy 3 stretch
Spirit Black 2.6.3
273 mm Lynx plastic mains
+/–11.5 degrees collective (this is very conservative!)
50 mm Lynx plastic tails (larger of the two sizes)
15T (speedup) tail pulley
BK DS-3005HV tail servo @ 7.4 V, 333 Hz

In order to get rid of tail kick during pitch pumps I need the maximum amount of Revomix, 10/10. That’s the issue. The heli flies great when I tune it, but the fact that I need so much Revomix tells me something might be wrong. Can you please give advice on what I might change or what I am doing wrong?

If I leave Revomix at 0/10 then during pitch pumps the tail will swing rightward (CCW) about 4 inches, then go back to its original position after the initial kick. If I go to 10/10, the tail seems great.

The behavior is almost like my gyro gain is not high enough. But that’s not the case because any higher and I get oscillations during full collective 11.5 degree climbs.

This issue exists at a variety of head speeds, including 3200, 3600, and 3900 RPM. I’ve tried the HW 40A gov, the Spirit gov, and V-curve no-gov. Always I need 10/10 Revomix. I’ve tried rudder delay values from 0 to 3. Also tried moving the tail ball out, but still there’s kick after re-tuning.

My rudder end points are set to just before there is mechanical binding/servo buzzing. Both left and right rudder is somewhere between 110 and 160, can’t remember exact numbers.

I would be surprised if the issue were mechanical; I tried it on an old Oxy 3 with SUPER amazing smooth tail mechanics and the kick was present. Then I crashed that heli and just built a new Oxy 3 with the newer better tail components (same electronics); the kick is still there. The tail mechanics in my newly built Oxy 3 kit are not yet butter smooth, but the fact that I had kick on both kits and they behave in exactly the same way tells me something is wrong that is not mechanical

My tail tuning procedure is always the same: Leaving common rudder gain at 1.0x and starting with gyro/piro/Revomix values of 55/155/0, here is what I do:

-Increase Main gyro gain until it oscillates in pitch pumps, then back off 2 points or so;

-Increase piro consistency until it oscillates in pitch pumps, then back off about 3 points

-In case of tail kick (which there always is), increase Revomix until there is no more kick.

I have main gain, piro con, and Revomix all set up on teal-time tunable channels from my transmitter, so sharing my 4ds file won’t say too much about tail settings. But to give an example, most recently at 3600 RPM my gyro/piro/Revomix values were 70/185/10.

I understand that there has been issues with BK tail servos. I don’t have cash to try a new high quality servo at the moment, but I can in a few months likely. I did try a Spektrum H3060 tail servo at 6 V without any luck, but that particular servo had other issues (fluttering around center when on the bench) so I don’t trust those results.

Question: does the sensor/rudder common gain setting ONLY multiply the gyro gain, or does it also increase the Spirit’s ability to sense a tail kick? I haven’t trie messing with the common gain yet.

Any advice?

[thestructured]

Rudder common gain is nothing but a multiplier for the gain you set in your transmitter.

55 seems very low to be getting oscillations but I don't know, maybe that is normal for such small helis. My helis are all 550 or 700 size and they all need gains close to 100.

Piro consistency has nothing to do with tail kick so you can eliminate that value as your problem. The two main gains are going to be the general tail gain set in your tx and rudder delay. Super fast servos are fine at 0 for rudder delay. If the servo is 0.04s or faster you could probably set that to 0.



Your procedure seems fine though, and if it's flying ok with max revomix don't worry about it.

I've never had to use revomix though. Is it possible your one way or tail belt is slipping?

[xoexoe]

55 isn’t the gain where it oscillates, but rather where I start the gain when I begin tuning the tail. It ends up around 70 at 3600 RPM. Around 76 for a lower RPM of 3200 and around 64 for my high RPM of 3900.

Thanks for the info about piro consistency and the multiplier.

[thestructured]

Ah ok, sorry, I misunderstood. That sounds about right then.

[thestructured]

I would try lowering your pitch range to 10 degrees and see if that helps. Are your batteries fresh too, or older? 10 sounds super conservative but on small helis it usually actually feels better to run less at least for me, since they a bit twitchier.

If you lower it to 10 and it helps with the kick then you can at least see if there's a problem with the tail not handling the main rotor torque. Doubtful since it's an oxy and has the bigger blades and speedup pulley, but might be worth trying. I'm out of ideas hah.

[xoexoe]

Good idea. I may try decreasing if it comes to that. Though even my 11.5 degrees is less than the 12 degree recommended by the manufacturer for soft 3D and much less than the 14 degrees for hard 3D. But I am on plastic mains. Wonder if that makes any difference.

[xoexoe]

Oh, batteries are brand new, minus some cycling.

[ZeXx86]

Hello,

I recommend to play with Governor as this could have very big impact on the tail performance.
That high revomix is not normal for sure. It shouldn't be more than 4/10.

Make sure that all ball linkages are super smooth.

You could also try to lower BEC voltage to 6V what could decrease probability for any issue with the tail servo.

[xoexoe]

Thanks Tomas.

I just now smoothed out the tail mechanics. Had a tail pitch slider linkage arm that needed sizing.

Will try 6.0 V BEC voltage next.

Then I’ll try playing with the ESC Governor settings, and if I can’t get that I’ll switch over to the FBL gov and try tuning it.) I’ve done that before, but couldn’t hurt to try again.) Maybe I never set my P gain high enough.

And I do happen to have an MKS DS95i that will be here on Friday. So one way or another I’ll get this thing solved.

Will start the process tomorrow and see how it all goes.

[xoexoe]

I switched back to Spirit gov. The tuning is very finicky and sensitive, but I was eventually able to get very good response & holding with very little overspeed at Response 8, Holding 7.

That gave a slight improvement to the tail performance.

But then I replaced my BK3005 with an MKS DS95-i . Problem solved!!! Now I need very little Revomix.

Love that servo.