Vibration or shakes? CHECK THIS!

[ChrisH]

So I have been flying my mCP X pretty much every day for the last week it has been out. As I got more and more flights on it (approaching 60 now), I noticed it was developing a vibration. I thought it was my bladescraped-up main blades, so I shaved the weight off my FFF blades and used those. No difference in flight, but it felt really smooth when spooled up in my hand.

On the bench, I realized that one of the aileron servos was twitching intermittently. I could bump the blade with my finger and the servo would jump back and forth (searching for center) for about 3-5 seconds. I unplugged the elevator servo and plugged it into the aileron port, to see if that was causing the problem. Same deal -- same servo was twitching, so it wasn't that specific port. My boss suggested the potentiometers in the servos being dirty, which I thought was unlikely. It was slow so I figured I'd take it apart and see...

Sure enough, there were black marks (on the silver stripe) on the PCB where the wipers on the servos move across. I used some solvent because it was all I had at the time, but it was recommended that isopropyl alcohol or dedicated pot cleaner be used for a better result. I carefully wiped both the silver strip and the wipers, until they were shiny silver again with no black stripes. At this point I had the heli mostly apart so I did all 3 cyclic servos.

Amazingly, when I went to fly it, it was completely solid with NO vibes or shakes whatsoever! It flies identical to the 3 new mCP X's I checked out yesterday for customers, with crisp cyclic inputs and a smooth collective feel. So in short, if you have a lot of flights and have vibes that you can't track down, try this! I had no idea this would make such a big difference but it did!

Pictures (sorry for so-so photos, only had the iPhone 4 at hand):

Start with this:


Remove the two screws holding the servo to the frame


Pull the servo assembly away and flip it over


Remove the four screws holding the plastic servo frame to the PCB


Carefully pull away the servo frame and flip it over


Clean the silver stripe on the PCB with a q-tip (pot cleaner or alcohol)


Clean the wipers on the servo frame assembly in the same manner


Reassemble and you're ready to fly!

[Raysun]

Brilliant. Similar to slot car controllers (waddaya mean you have another hobby!!!) that benefit from the wipers being cleaned occasionally.

[falke398]

Very good!
I get mine on Wednesday and I was already wondering about that. I as thinking to do exactly what you did when the shaking appears.
Thanks for posting...

[OnTheSnap]

Awesome tip Chris. Looking for your next sticky "How to turn your MCPX into a 4500 RPM Hotrod".

[755 robert]

Excellent Idea.I got real good at doing servo surgery on my other E-flite micros.One suggestion,I have found using a folded tissue and tweezers better for cleaning,the cotton swabs will sometimes leave strands of fiber behind that can get wrapped into moving parts..

[crzyhare2344]

i had the exact same problem with my aileron servo.. never thought about cleaning it i'll give it a try and see what happens ! Great job on the fix without having to replace the servo! hopefully it works for me!

[VaderSS]

Thanks, I'm going to try this out. I probably have around 160 flights and mine is developing a wobble/shake that I can't seem to get rid.

[crzyhare2344]

Tore it down and sure enought black stripes on the silver strip.. cleaned it with rubbing alcahol .. reassembled .. now if i only had a boom so i could test fly it but so far from holding it in my hand the servo has stopped twitching. have to wait until tomrrow to get a new boom and see how it flies!

[tracknoob]

Okay, I hate to even mention this, because frothy arguments may ensue, but for the sake of the hobby and science...

This mechanical sliding contact with a wiper arm and strip is a pretty flaky proposition at it's best, especially if left open to the elements (not hermetically sealed).

Most of you might not be old enough to remember fiddling with TV tuner knobs and channel selectors, and needing contact spray, which was only a temporary fix, and left gunk of it's own behind.... or cleaning slot car or electric locomotive contacts with a pencil eraser...

Anyhow, back in the day (maybe 15 or 20 years ago?) there was a product that was AGRESSIVELY (and I mean AGGRESSIVELY) marketed directly to managers of repair shops, and to engineering and maintenance departments... I was somehow given a sample of it, and it struck me at the time as likely just snake oil, but there were (and probably are) slavish devotees to this stuff's effectiveness not only as a 'cleaner' of sketchy mechanical contacts, but also as an 'enhancer' of electrical conduction and long term life of the contact, including back when we used a lot of socketized ICs, and plug in PCBs in card cages. It supposedly would lower life cycle maintenance costs due to faulty contacts. That was the pitch, anyway.

The stuff was called "Stabilant 22" and I have no idea, frankly, if it's the best thing since sliced bread, or a total snake oil job.

I do know I have a mCPX with chattering servos, and occasional low grade shaking fever.

I also think I kept that vial of stuff in some drawer around the shop or the house, and can try it out (I have a new mcpx coming if things go wrong!) and I can't think of a more direct and obvious test of whether it can work not only as a 'cleaner' and short term 'enhancer' but whether it can also keep these things going longer term than 'dry'.

I frankly don't hold out a lot of hope that it will be the salvation for the shakes or mcpx servo jitter, but I'm ready to experiment.

[755 robert]

It seems maybe a conductive lubricant might be in order.

[CocoSantango]

Originally Posted by 755 robert

It seems maybe a conductive lubricant might be in order.

Won't that just cause gunk to stick to the strips? I just dry rub mine (**GENTLY**) with a clean pencil eraser.

[755 robert]

Originally Posted by CocoSantango

Won't that just cause gunk to stick to the strips? I just dry rub mine (**GENTLY**) with a clean pencil eraser.

Good point..

[Finless]

Cool tip Chris! Mind if I do a video on how to do it sometime later?

Bob

[ChrisH]

Originally Posted by Finless

Cool tip Chris! Mind if I do a video on how to do it sometime later?

Bob

Please do! I haven't the time or Bob-ness to make the video worthwhile to watch

[VaderSS]

I went ahead and did all 3 of my servos using contact cleaner. The starboard one was very dirty. The other two were slightly dirty.

This has solved the shakes that had just started developing.

[tracknoob]

1. As someone asked, yes, I suppose that it is indeed possible that this stuff will attract dust, debris, and small reptiles. I don't know. It is clear, but highly viscous in the form that I have it. Apparently they normally cut it to 1-10% active stuff to alcohol carrier, but I have stuff that is about like glycerin or 30 wt. oil in character, only perfectly clear. And I slathered it on -- might as well go for broke!

2. Use a pencil to rub these contacts? Eek, not me! Look, rub a pencil eraser across a clean mirror or glass table. Then wipe. Wipe again. Wipe harder. Unless you use cleaner or alcohol, the streak of stuff gummy residue will remain behind. No way I'm going that route.

Here are some photos of my just completed Stabilent 22 servo application mission:

The mystery goop stands ready for duty:


Awfully nice of someone at HH assembly to pre-strip one of the servo screws.... the *tiny* servo screws... I had to use a needle nose to get this out, since all it would do is turn and turn.


So tiny in fact, that I had to break out the real Geek-ware to be able to see and work on this stuff - behold my free LED headlight, and be awed:



Not too pretty... this is after about three flight hours:


Can see where the individual metal 'whiskers' or 'fingers' run across the plates:


This is what I used to gently clean the strips and even more gently clean the whiskers - no left behind gunk, no lint, no particles, no fibers:



Another one... all three were similar:


Goop-ifying tool prepped and loaded:


Applying:




And so, what is the result?

Whell, number one, it all went back together, and it works.


Whew.

Swash levels itself, collective responds, bird flies, no visible shakes other than a slight wag that is directly related to the sound of the buzzing rear rotor speed hunting slightly, like rudder gyro gain is a tad high...

And the servo noise at standby? Well, not as noisy. But then, I think that could easily be acoustical damping from the viscous material, as well as a bit of lubrication now that it is wetted in there. But there is still a very noticeable noise, below a buzz, and not a chatter, but it is constant when idle, and it does change a bit if you pick the bird up by hand to move it. Can't tell what they sound like in flight, due to motor and rotor noises... movement is smooth, but then it always was.

So at least it passes the 'do no immediate harm' hurdle, but gonna have to wait and see if there is any long term effect, for good or for ill.

It is NOT a instant servo chatter fixer-upper, though.

[ChrisH]

The servos will always buzz and try to correct at idle/on the ground, my issue was a definite twitching back and forth intermittently.

[755 robert]

This is good info,thank you.What do you think of adding a bit more bend in the contacts after significant wear,for a better connection?I have done this to buy a bit more life out of well used park planks..

[ChrisH]

Originally Posted by 755 robert

This is good info,thank you.What do you think of adding a bit more bend in the contacts after significant wear,for a better connection?I have done this to buy a bit more life out of well used park planks..

You could try, but I'm not sure I'd mess with those little wipers. They're all bent at the same level and you may risk getting one too high and not making contact.

I think if mine get too worn out I'll just replace them:

SPMAS2000LBB - $23 for the full new servo

SPM6833 - $12 for the servo mechanics

[isogloss3d]

Thanks for the tips Chris. I cleaned all 3 servos and the moderate shakes after 70 flights are now gone. The Aileron contacts were the dirtiest. Now that the major shakes are gone I'm noticing a very slight tail bob towards the last 3rd of my flight. Who knows, it could be something else entirely. Thanks again.

-Iso