NEO judder on pitch changes

[RichardV]

I'm running a NEO with Align BL815H servos, and I get an odd judder/stepping of the cyclic servos on the bench when I change the collective at a medium to fast speed. Slow changes are smooth, but then it starts stepping, maybe 4 or 5 steps in a single upward movement.

They're very obvious steps, so much so, it makes a bit of noise as the swash, links and blades all judder. It seems to fly OK, but I'd like to figure it out now.

I'll make a video if it helps, but hopefully someone knows what it is?

[p1andy]

My 815s do the same when you raise the pitch on the bench it sounds horrible like the servos are using some kind of stepper motor and the swash sounds like it is juddering up the main shaft. However like you say they fly fine in the air.

Edit should have added this is on VX1n so may not be a problem related to your NEO

[scallybert]

Power issue ?

[coolice]

Hey buddy.

What do your flight logs show if anything? Might be worth clearing them and running the same test on the bench before reading them again.

After a recent conversation and while looking for another question I have about the Vcontrol Tx, I came across a topic on Helifreak talking about back emf and BEC voltage flucautions.
Now I'm not going to say this is your problem, because as mentioned and was something I already knew, it was only the mini Vbar's that suffered the most with back emf from some servos due to the mini missing a capacitor that the full size Vbars have fitted making them more tolerant to it.
However it makes for some good reading, especially Western Robotics advice against fitting any smoothing capacitors due to the potential to feed voltage back into the BEC on power down. So if this gets mentioned I wouldn't advise it :-)

https://www.helifreak.com/showthread.php?t=683967

Anyway back on to the main topic, it'll be interesting to see if your logs show anything.

Ian Contessa

[bigpops]

I run 815s on Vbar too and know exactly what you mean. They don't do the same thing on a servo tester.

I get the same phenomenon when in the tail setup menu (where you set the limits), this time on a Futaba BLS215. It's like it moves quickly through a series of large steps rather than one smooth motion. Come out of the menu so the tail servo is controlled by the PID loop, and it's butter smooth again.

[Mike656]

Servo judder on pitch changes

Had the same problem with 815s on a 550 with a Spirit. Noticed the juddering when carrying out to the flight line. Slowly got worse,ended up changing two servos out and problem solved. Could this have caused the blade damage on your other post?
How many flights would you say the servos had?

[waveydavey]

How many flights would you say the servos had?

Get ready for the answer Mike, probably more than the rest of the forum put together

[RichardV]

Amazing that so many are seeing the same thing with those servos. I've only had them in for a couple of weeks, so around 200 flights. I got them used from maj ages ago, so I don't know for sure.

I'll have a play on the bench tonight and see if there's anything I can change or isolate, but I'll keep flying them for now if it's a known issue. I was going to try and have these on both helis, but I think I'll have to find something else if I can't fix it.

[bigpops]

Well mine (2x sets) probably have 50 flights each, but they've been the same since day one. I just put it down to them being so damn fast and never gave it a second thought until this thread.

My MKS brushless tail servo does a similar thing, where the whole carbon rod vibrates if you do full rudder on the bench and it sounds like it's full of sand. But a quick google when I bought it told be that's not unusual for that tail servo. It flies bang on though on my 700L.

[RichardV]

Although the video doesn't show it properly, you can hear the juddering as the servo steps through the range. That can't be normal right?

On all 3 servos

Just on 1 servo, 2 unplugged.

[bigpops]

Yep, that's how mine are. I just powered the set I have connected to a silverline to test. I notice that if you load up the servo, it not even half as bad to unnoticeable if it's pushing against the force, but if you push with movement of the arms, it's just as bad as unloaded.

Like I said, the same thing happens with my MKS tail. If you grab the push rod and hold so it loads the servo while moving it, no judder.

[RichardV]

Thanks for confirming Darren. I've posted it on vstabi just in case Rainer has any observations.

[George J]

I wouldn’t fly those like that personally Richard, especially how you fly. I had similar weird behaviour on some Savox servos once on Vbar but I ditched them and went back to my old favourite Futabas.

Only servo issues ive ever had have been when I’ve tried another brand so I stick with what I know works perfectly.

[bigpops]

I'd post this on the freak if you want some more reports. They have the traffic over there. These are very very common servos that have been sold with the 550L, 600L and 700L and 700L V2 for over 3 years now. There are thousands of sets out there.

My sets are from late 2014, and mid 2015 and both sets are the same.

Of course, like with anything on your heli, it comes down to trust. If you don't trust them, sell them and fly something you do trust.

[RichardV]

I read a couple of threads on HF about the BL815s, including the long one about them failing early on. Some mentions of jitter while stationary, but no stepping while moving.

Mikado say it's normal with fast HV servos as they are so precise and fast, and it's likely to be tremble on my fingers. It can't be tremble because I'm pushing fast one way and it does it very consistently and regularly spaced. I'll do a few experiments this windy weekend where I get the NEO to make the movements, instead of the sticks, to see if I can pin the source down. I guess the macrocells oscillator might work.

Thanks for all the help. I'll keep them for now, but will be investigating replacement servos in the medium term.