Getting rid of vibrations...

Discussion in 'CineStar FAQ - Tips and Tricks' started by John Gore, Oct 8, 2012.

  1. John Gore

    John Gore Member

    Joined:
    Jul 24, 2012
    Messages:
    93
    Likes Received:
    15
    Hi guys, got my rig flying very well now, but still having some vibration issues. Have balanced wooden props on now (helped a lot), played with settings with little to no effect on vibrations. Im starting to think it must be problems with the actual motors. Any links / tips on how to service motors and balance them would be greatly appreciated. Or any other ideas where I could try find the vibrations?
    (MK OctaXL with cinestar 2 axis and radian stabilisation.)

    Here is a YouTube clip showing the kind of footage I am getting:


    Tks in advance.
     
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
    Staff Member

    Joined:
    Jul 31, 2012
    Messages:
    10,383
    Likes Received:
    1,164
  3. John Gore

    John Gore Member

    Joined:
    Jul 24, 2012
    Messages:
    93
    Likes Received:
    15
    Interesting read, tks Andy.

    I am also starting to suspect the motor bearings now. Have just ordered a full set.

    Also, I am using MK3638 motors with 5mm prop mounts, and XOAR 12x6.5 wooden props with a 6mm shaft diameter "hole". I had made my own "bush" to fill this gap, using insulation (rubber) from some 10 gauge wire. It did fit very tight, but could possibly have been pulling the props a tiny bit off centre. Yesterday I had a friend of mine make for me 8x bushes (5mm inside diameter, 6mm outside), and fitted the props again. I had also used larger washers because of the props being wood I did not want them to be damaged under compression. But the washers could also have been slightly off centre, causing an in balance. Replaced the washers with smaller washers. :)

    Just did a test flight now in some gusty winds (20 mph winds), and I am very happy with the results. Much improved, but there is still a wobble / vibration on roll.

    Will upload a video a bit later, and will share here.

    Radian settings are 100 tilt and 100 roll. Using the red o-rings vibration isolation system, but I am not sure if that is making it better or worse, as it seems to allow a lot more movement. Hmm.

    Really reaching for perfection here. ;)
     
  4. John Gore

    John Gore Member

    Joined:
    Jul 24, 2012
    Messages:
    93
    Likes Received:
    15
    Took forever to upload, but here is the second test video with radian, after mounting props with better bushes (5mm to 6mm) and smaller washers. Looks better, but still a wobble / vibration on roll.

    Should I reduce the roll radian gains lower than 100% ?

     
  5. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
    Staff Member

    Joined:
    Jul 31, 2012
    Messages:
    10,383
    Likes Received:
    1,164
    It's hard to be sure, but in that wind, around 1:44, could the frameset (booms/motors) be reaching the limits of vibration isolators? I can see occasional places where a boom comes into shot while the copters facing into wind. At 1:44 it looks like it's cross-wind -- could that be why the "twitches" are happening in roll?

    But certainly try reducing the roll gain and see -- it really is a trial and error (or more correctly a trial by error) process.

    If you could try in light wind, you can see what the limits of the isolators are just by rolling or pitching the frameset aggressively (like I normally fly ;) )

    Andy.
     
  6. Tabb Firchau

    Tabb Firchau Administrator
    Staff Member

    Joined:
    Jun 28, 2012
    Messages:
    911
    Likes Received:
    472
    Hi John, just to chime in here, I could never get my MK hexa to shoot useable video. I found the frame was so flexible and sloppy that weird vibration / resonance would set it and I could never quite beat it. The level of video you are getting is incredible compared to what I achieved back then!

    I think you are getting some great results! Especially given the wind in that clip.

    Tabb
     
  7. Arthur Vieira

    Arthur Vieira Flight Squad

    Joined:
    Jun 29, 2012
    Messages:
    185
    Likes Received:
    24
    John, just like Tabb, I never got a 100% vibration free flight with my MK Hexa XL. I've moved to the Cinestar because of that.... but I did one mod that really helped a lot. If you can, get 2 new contemplates [Edit by Andy: I think you may have meant to write "centerplates"?] and double them with the originals. Glue 2 centerplates together with epoxy. To do that, sand one of the sides of the centerplates with a light sandpaper (300-400) so the glue stick better. Apply some epoxy to it, place the other contemplate above this one (with the sanded side facing to the glue) and PUT SOMETING VERY HEAVY ON IT :) Be careful to align all the holes. Let it dry overnight.
    By doing this you will notice that the frame gets much more stiffer, just move the booms up and down and you will notice the difference, but this won't eliminate all the vibration as the aluminium boom also flex during flights.

    Good luck.
     
  8. John Gore

    John Gore Member

    Joined:
    Jul 24, 2012
    Messages:
    93
    Likes Received:
    15
    Thanks for the reply guys. Interesting comments about the flex on the MK airframe. I have made a few mods to combat the flex already, and have a few more mods to try soon. I certainly does flex more than I would like it to, with the 7D on. With the cx760 its flex is not as bad, but still not ideal.

    Tabb, I am exceptionally impressed with the build quality, design, and performance of the Cinestar gimbal and the radians. I think it is them that are doing an excellent job here, and why this footage looks pretty good (even on an Mk frame). All credit must go to the Cinestar gimbal and Radians! (not to me).

    Update: Lots of wind and rain here over the last few days, so not much more testing done. I have found a few problems, and made a few changes, which I would like to share there for the benefit of others...

    1. Found that 2 of my MK3638 motors (6 and 7), were missing their circlips at the bottom of the motor. Although the magnetic force of the windings / magnets holds the motor together very firmly, Im sure there is some movement there during flight, and this could have been causing the wobble (as it is the motors on the left "wing" area). Replaced the missing circlips with new ones.

    2. Found bearings on 2 motors to be a bit noisy. Have bought bearing kits for all 8 motors, but have not fitted them yet.

    3. Did vibration tests with the iPhone vibration app. Found that motor 5 (rear) had more vibration than the others (tested by spinning each motor independently using MK tools). Balanced the motor, and now all motors have about the same vibrations.

    4. Changed roll Radian to 60% gains as a test. It is a bit slow to level now, but this is just a test to see if the vibrations are gone.


    I have just now done a test flight today (in low light just around sunset), with 7D this time (previous videos were with the Sony cx760), and I am very impressed. Looks a lot better than before, but has a "jolt" at times, which I think is the vibration isolation system bottoming out.


    5. Have now mounted the vibration isolation system (red o-rings) a little differently (will share details if it works), which almost
    completely illuminates the effectiveness of the o-rings, but does also restrict movement (so it will not bottom out). This should allow me to test exactly what effect the vibration isolation is having on the system. Will share results when I have some to share. Hoping to tets again tomorrow morning, and will share results.

    PS: I will start a new thread about the possible upgrade to an Cinestar 8 frame, using MK3638 motors, and all MK electronics. Please give your inputs there, as I may very well go that route if I can not get the MK working perfectly.

    tks again
     
  9. John Gore

    John Gore Member

    Joined:
    Jul 24, 2012
    Messages:
    93
    Likes Received:
    15

Share This Page