Help: Vibrating digital servo

Aviator3Aviator3 Club Members Posts: 6
I have vibration with all digital servo's in my Funtana aircraft from eFlite. What is going on?

When I connect the power without the servo's connected to the flight controls, everything is fine. No jitter or vibration. When I connect the servo to the flightcontrol there is a huge vibration in the neutral position.

When I touch the servo the vibration is gone.




It is the MKS s311 digital servo, with the corona synthesized receiver 35Mhz, and the towerpro H40A speedcontrol, and a 2200 mAh lipo.
All four servo's bad? I don't think so, and why is everything normal when nothing is connected.
The flight controls can move freely, there is no play in the servo horns.
Who knows what is going on?



  • snappysnappy IrelandClub Members Posts: 3,289 ✭✭
    Do they vibrate when not connected to the control surfaces? Have you tried them with a different reciever. It looks like they are having problems finding their centers

  • hmmm sound strange but try this, hold it in the motor, like it was going strait up - does that stop the vibration ???

    -if it does, your servos might be to weak, and struggling just to keep the weigt of the control surfaces...

    but still it seems od to me.. -hmmm DOES your control surfaces move freely if you disconnect the pushrods - BINDING could be the problem to.

    ups MY BAD, JUST SAW you posted a video of it, good idea.
    -now i think you got to much play in your horns, - digital servos stays in the same position they are told to by going very slight from side to side, almost nothing -and if the RX's center position is floating a bit, you might experience that..
    Try this BEEP (trim), the center position way of, does that make them hold still ??.


    Blind Vision2010-04-12 05:34:33
  • Aviator3Aviator3 Club Members Posts: 6
    It is a strange problem.
    I have tried a different receiver, a seperate powerpack for the servo's, holding the aircraft in all kinds of positions, nothing helped.

    When I put weight on the control surface the vibration dissapears. Also when i disconnect the control rod, it dissapears.

    I tried a different brand of digital servo and there is no problem at all.


    The only thing I can think of is what Blind Vision said, too much play in the control rods.

    But there is hardly any play. As the video shows, on the servo arm the rod is connected with a screw. On the control horn is a z-bent connection, which fits tightly.

    What can I do?

    I wil try to connect both ends with a z-bent to find out if that helps.


    By the way, with analog servo's there is no problem at all.
  • ShadowCasterShadowCaster GreeceClub Members Posts: 185

    You problem is probably your TX, this kind of servos have an extremely
    tight deadband, it seems your TX - RX cannot produce a narrow center
    pulse thats why you have jittering. I have seen these kind of problems with newer digital servos and older ppm/pcm tx's...


    When you apply weight the servo tries to keep its position so it produces power against your weight so it stays solid and temporarily centers.
    ShadowCaster2010-04-12 16:05:24
  • Aviator3Aviator3 Club Members Posts: 6
    But what is your explanation then that there is no jitter or vibration with the control rod disconnected?
  • waderowadero Club Members Posts: 4
    I have this problem too with Turnigy HV380 and a few years ago also with Graupner DES servo. Have done a lot of figuring-out what could be wrong and the only conclusion was that some (maybe all) digital servo's will have this problem when put in a constellation they can't cope with.

    When connected with a certain inertia, data repetition rate, voltage, the servo looses it and becomes instable. I have seen it with an expensive Futaba and was told some HV Hitec did it too. Fast servo's and HV ones or both are more prone.
  • waderowadero Club Members Posts: 4
    OK, this is a problem I have many times with digital servo's except the high grades Hitec and Savox.

    The problem is not the receiever or any external cicuitry but the servo software that is unable to deal wit control surface inertia.I've seen it with futaba servo's and the Graupner DES servo's and also most of the many Chinese brands.

    You shoulden't throw it away becaus when applied on another control with different inertia it might be perfectly stable. Also it might have a good chance to be stable on throttle an helicopter controls.

    But helas on this one there 's no cure.

    Some brands solve this by slowing down the speed in the vicinity of the target position, clearly to be seen when you have one. It works but it's not a nice solution.

    I haven't seen this fenomena on Hitec high grades and Savox high grades... which, I have to say, is no garanty it wil NEVER occur on these two,but it seems they have a better solution. It's something that inhibits me to buy ever again another brand than this 2 because the risk to buy something that , however sheaper,cannot be used is too high.

    Common bunch of high grade Chinese, it's just software for God's sake.
  • waderowadero Club Members Posts: 4
    Oh I told some time ago a HV Hitec had this too, but now I have seen what the guy ment and it is not the same thing but it could have to do with Hitec's software solution for the thing
  • SootySooty Christchurch NZClub Members Posts: 6,110 ✭✭✭
    Our local turbine guru has found that the higher the quality of digital servos the more they buzz. Lower quality tend to "chatter". It seems to be accepted as fairly normal. As long as they are setup to the correct signal frequency no harm results.
  • WTWUKWTWUK CornwallClub Members Posts: 13,609 ✭✭✭
    Yup. It is all down to the 'dead band' of a particular servo which dictates how much it will 'buzz'.

    I have some Hyperions that buzz like crazy if I set the dead band to 1us. Put it up to say 7 or 8 and they proper 'chatter'.

    I also have several Savox servos in my helis - and contrary to the comment above, they buzz too. If they did not I would be concerned!

    So long as nothing is binding, and they do not get hot, not a real issue.
  • mpjf01mpjf01 Club Members Posts: 1,009 ✭✭
    Stand behind the flight line in a thermal or F3J contest just prior to launch. When they are all flying fully moulded gliders with the most expensive digital servos and you can't hear yourself think for the buzzing.
  • kangakanga Club Members Posts: 509
    No wonder I run analogues :)

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