Slow aileron wobble on quick pitch changes

[mba83]

Hi guys,

I love the oxy3 - it flies great! But there is one issue that I'm having that I have no clue how to fix. During certain maneuvers, for example going into a tick tock from hover, the heli has a slow wobble on the aileron axis. Same for sharp punch outs. Pronounced at low headspeeds (3200), but seems to be not noticeable at high headspeeds (3900).

My cyclic gains are already quite low (30 in IKON) and it can't be aileron P gain being too high, as that would cause quicker wobbles that what I am experiencing.

Anyone else seeing this?

Thanks!

[vtown nick]

I would guess this is a DFC thing and the head speed that you are flying. Try to bump the head speed up higher. If you're going to be doing 3D I would suggest not going too much under 3800 rpms on 255mm and 3600 rpms on 285mm.

[myxiplx]

A slow wobble would be gains too low if anything, but I agree with vtown, sometimes this is simply due to the headspeed being too low to be stable in harder moves.

That's not an Oxy specific thing, but something you can potentially see with any model and any FBL unit.

[mba83]

Thanks guys! (I really like low headspeeds for small spaces, BTW).

I think I solved the problem - my servos weren't exactly 90 degress on center (though swash was level).

I re-did the setup (even removed the servos when finding 90°) and just had a quick flight, seems to be more stable at low headspeed now.

Will report back after a few more flights.

[mba83]

OK after 3 more flights I can confirm that the wobble was caused by one of the aileron servos having its horn off 90°. Even though the swash was level at zero pitch, it was tilted on positive/negative collective, which was causing the wobble. Now it's stable, even at low headspeeds!

[Mateyhv]

Nice to know you have found a solution, now I will check my servo horns once more

[mba83]

OK another update. While the major wobble issue is now gone, I do still have cyclic wobbles in certain maneuvers. Most pronounced in elevator ticktocks. When I reverse the collective quickly I get very annoying cyclic wobbles.

Swash is level at mid, low, and high pitch.

I have some moderate play in the head/grips for some reason - can that be causing it? (no crashes on this heli).

Thanks

[crma0101]

Yes - if you have play in the head add one more shim to each side of the feathering shaft. This has been talked about on here before... seems after initial flights the head breaks in a little. Guys add one more shim to each side and it goes away for good.

[mba83]

Thanks guys.

I just took off the blades and was about to remove the grips - started to rotate the screw and the spindle - and turns out my spindle was bent! From minor tip-overs! ha ha. Never would have thought it would bend just from tip-overs that didn't do any other damage.

Is the 300X spindle any stronger than the oxy3 one?

Thanks

P.S. I already had 2 shims on each side. Added 3rd shims and now no more play.

[benddg]

I tried a 300 spindle once when I didn't have a Oxy spindle. It bent in the next crash just like a Oxy spindle, but it did work in a pinch. I've heard of people trying to harden spindles with a torch and quenching them in oil. Doubt that would do much good. Worked in a machine shop for several years in my younger days. Not that easy to harden or anneal metal.

Another thing to think about other more expensive things might break if the spindle didn't bend.

[peteski]

If you are running relatively low head speeds it's worth trying the non-DFC head kit. It costs next to nothing and takes only a few minutes to fit. I've been running mine with this setup from new and it flies nice and smooth. I run head speeds of 3400, 3600 and 3800 but mainly the latter.

[mba83]

Thaks for the tip; I also fly in similar range: 3300-3900 (though will probably change the top headspeed to 3800 or 3850 eventually - 3900 feels like a borderline speed for the 14T pinion).

So you felt a significant change when converting to FBL head? I was thinking of doing it only after I crash - but am considering converting earlier too.

[peteski]

Originally Posted by mba83

So you felt a significant change when converting to FBL head? I was thinking of doing it only after I crash - but am considering converting earlier too.

Ah ah! I have no idea because I built it from scratch with the FBL head as I was always intending to run lowish head speeds and thought it would be better suited than the DFC head. All I can say is that it flies silky smooth without any cyclic wobbles at all.

[mba83]

OK thanks! I'll just wait for a crash then. My wobbles were certainly caused by a bent spindle, and in sport flying there are no wobbles and it's smooth.

[peteski]

Originally Posted by mba83

OK thanks! I'll just wait for a crash then. My wobbles were certainly caused by a bent spindle, and in sport flying there are no wobbles and it's smooth.

To be honest I'd be surprised if there is any significant difference in flight as the head dampers are the same in both cases. But the FBL head should crash even better and there is less general stress on the main grips.

There's also the hybrid head, which is just replacing one DFC arm with a standard drop link. That would be quick to try and may give you some idea what to expect with the full FBL head.

[mba83]

For completeness, I also raised the cyclic gain from 30 to 40. That got rid of the last wobbles.