Intermittent high frequency vibration problems with our Movi MR

Discussion in 'MōVI MR' started by Sam Leggett, Feb 25, 2014.

  1. Sam Leggett

    Sam Leggett Member

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    Hi Gents,
    We have been having high frequency vibration problems in some aspects of our footage. It is not all the time and does not occur at specific times when the copter is flown in a certain way. It is frequent enough to ruin most shots. We have tried a number of things but are now running out of ideas. I will run through what we have been through but any further suggestions would be greatly appreciated.

    We have been mostly flying in windy conditions, but I do not think this is the problem because when I had the copter hovering just a foot off the ground juddering around in its own prop wash the footage was flawless, like the monitor was on pause, despite the airframe and electronics working very hard! Very impressive, but why does it struggle at other times?

    Our rig is a Cinestar 8 HL with Wookong M gear powered by 2 6s flight packs. Underneath is a Movi MR carrying a C300. We have worked hard on the balancing issues and understand the concepts behind it all. The camera sits at any angle you choose to put it and tilting the Gimbal does not cause any rotation, indicating a well-balanced gimbal.

    Our initial gimbal settings were:
    Pan: 80
    Roll: 70
    Tilt: 60
    These were obtained by one of us holding the gimbal in the air while the other dialled the numbers.
    Once problems were noted we changed these settings to the following:
    Pan: 65
    Roll: 65
    Tilt: 50
    This lower set of figures give a completely smooth gimbal suspended by hands, whereas the ones above show a little vibration in the hands, but actually seem to give better results in the air. (I am not sure how to adjust stiffness for airborne as I think suspending the rig in a frame or by rope will not be a good substitute for flying conditions. Instructions, as noted by Angus Benson-Blair are very thin on the ground for flying when compared to handheld.)

    Throughout our filters in the advanced settings have remained at:
    Gyro Filter: 5
    Output Filter: 5 I have no idea if this is normal or not – there is no reference!

    We have tried to be methodical and scientific changing one thing at a time… we were initially using the harder vibration dampers (green and white dots) and now have 4 green and white and 4 softer red and white. We changed them because we thought the others too hard which might possible cause the transmission of the high frequency vibration. We also rebalanced the props for a second time. We have not done the motors yet (Tiger MN4014 Kv400’s). We also went over the whole airframe checking all bolts.

    Please see the video clip below, Password: vibrations

    https://vimeo.com/87608380

    The beach and the windmill are using the harder dampers and the clock tower is with the softer dampers. Although this clip is cut to show the worst bits, there are clearly lovely smooth bits too. That is why we are so confused!

    Any suggestions would be greatly appreciated as we have some great ideas for our show reel but no way of putting them into action yet!

    Thanks very much for taking the time to read such a long spiel!
     
  2. Justin John

    Justin John Member

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    Hi Sam, does the top of the cinestar look like its flexing along with the gimbal ?
     
  3. Gary Haynes

    Gary Haynes Administrator
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    Sam how is the MR10 attached to the Cinestar? Can you post some photos?
     
  4. Tabb Firchau

    Tabb Firchau Administrator
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    Hi Sam, It looked like tilt overgain to me. Can you post a photo of your setup for me to take a look at?

    Thanks!

    T
     
  5. Sam Leggett

    Sam Leggett Member

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    Morning Gents,

    Many thanks for your replies.

    @ Justin: No I don't think there is any flexing. Everything appears tight and damage free.

    @ Gary and Tabb: Here are the pictures of our setup. We have one of those allied drones quick releases with the 8 vibration dampers in it. Gimbal setup.jpg Gimbal setup 2.jpg

    Thanks very much for your help,

    Sam
     
  6. Sam Leggett

    Sam Leggett Member

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    Evening gents,

    Thanks again for all your help.

    Fortunately here in England we actually had some sunny weather, still windy, but sunny! We got 55mins of air time and moved the stiffness settings one increment at a time.

    Tabb, we think you were on the money! We moved the tilt gain down and are now getting much better results. We were just in a bit of a state yesterday as the weather is so bad most of the time at the moment we just wanted as much good advice and stuff to try when the rain lifted!

    We still get the occasional bump but things look much better 95% of the time. We have now noticed during high speed runs that the movi tilts up for half a second and back again like momentary signal loss. We have a Spektrum DX7 radio and I have read about the issue elsewhere on the forum. Our tiny secondary receiver (can't remember the correct term) is on the back of the black box on the main down-tube on the Movi. When accelerating hard and looking at us the receiver would be well shielded from the incoming signal, I think, and might be the cause. We might have a look about repositioning it or adding an extra one if that is possible, possibly to the bottom of the roll bar.

    Thanks again for all of your help!

    Sam
     
  7. Justin John

    Justin John Member

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    Hi Sam,

    Glad to hear you got it figured out. What kind of gains did you end up using? Can anybody share the 5d Gains they are using ?
     
  8. Sam Leggett

    Sam Leggett Member

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    Hi Justin,

    We ended up with Pan in the low 70's, Roll in mid 60's and tilt at 40. That seems to work really well for us, but from what people say it changes with the lens and camera... so everyone will be a bit different. We have just been doing handheld and the same set up requires different stiffness again. Methodical testing is the only way!
    Hope that helps,
    Sam
     
  9. Fabien Deregel

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    Hi,

    just my 2 cents, if you use long lenses, the overall gimbal will be much more sensible to vibrations coming from the frames (motors), translating to a tiny but really annoying vibration. When gains are too high, you generally have true "jumps" on tilt but nothing like these small vibrations.
    Fact is that as the weight distribution on the dampers suffer from a very high lever effect and become ineffective and even more as soon as the frame gets a bit of angle ( they press like citrus and dampen nothing, even worse, they amplify the vibrations).
    A simple fix is to make a custom dampening plate, mich wider ( CNC alu made), and have the dampers "spread" wide on each of the 8 booms. This is how DJI succeeds in having a decent dampening on the Zenmuse, by getting the dampeners far away, reducing the lever effect on them especially when tilting the machine, all this re dampened by a split on each of the arms.

    Then, another point is the gimbal mechanical arrangement itself, the roll support needs to be ultra stiff and totally slope free, the smallest free play will generate quick vibrations on the tilt when you use large cameras with long lenses ( vibrations will travel to the further end allowing it..).

    Lastly, if the camera is fixed using only one screw on the tilt support, make sure you have an extra piece of alu ( wide) between the screw and the support plate, or the weight one more time will bend the area around the screw so easy.. You can also make a custom small support for the camera to distribute better the efforts on the support plate. It's easy to see the difference by simply giving small finger tips shocks on the lens with all powered down, you will see a small spring effect that can bring your life miserable in the air..
    This is also why DJI has a small lens support part to avoid the weight of the camera stress too much the lower support plate and generate annoying vibrations.

    The stabilisation job is to stabilise, but the vibrations must be chewed at their sources to allow the electronics to give their full potential :)

    Idealy, you would need a small alu rig around the lens base and clamped to the tilt tube via simple carbon profiles and rod ends.

    Hope you find the last 5% missing for your 100% satisfaction :))

    Best regards,

    Fabien
     
  10. Sam Leggett

    Sam Leggett Member

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    Hi Fabien

    Thank you very much for such a detailed explanation! We did think that our vibration dampers were too hard and therefore not damping the high frequency vibrations from the airframe very well so we changed 4 of the 8 for softer ones. However, we think that the vibration was caused by over gain on the tilt as that vibration stopped when we lowered gain. But then we noticed at higher speed (greater tilt angle) that there were bumps - we think caused by turbulent air and bottomed out soft dampers. As we think the airframe is as vibration-free as possible we have put the hard dampers back on and we will do some high speed runs so see what happens. You are definitely onto something with regards to the dampers being very close together and so causing a leverage issue. Once we start earning some money with our rig we might have a look as something along the lines you suggest, but for now we will have to make do! The hard dampers are very hard to bottom out by hand.

    And Yes I think our lens is too long, but its still only a test piece at the moment... hopefully by getting good results with this kind of gear will only make it easier with the best stuff! :)

    Looking at the Zenmuse I can see exactly what you are talking about... the wide dampers and the lens support. All good stuff Fabien, and things we will be thinking about for sure!

    Has anyone had experience of the max wind speed the Movi can take? I know Angus asked a while back but there was no real answer... Our rig in GPS mode can get up to 38mph according to the downlink info... but in atti it got to 50mph yesterday and I ran out of room! That was with the wind but the way back got to 43mph and still going. No camera and gimbal was tied up as a VERY expensive undercarriage!

    Thanks again Fabien for your considered and detailed reply, its 2 cents like yours that make this such a great site! Plenty for us to work on!

    Sam
     
  11. Fabien Deregel

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    Hi Sam,

    you are welcome, the biggest issue with cameras is that they have just a tiny anchor point, and this has to support all the efforts and movements of the camera and lens. On most cameras, you can easily "bend" the camera as the threaded insert under the camera is itself moulded in a plastic shoulder or melt insert itself fixed in plastic, so it does the job for a fixed rig, but for a flying rig or stabilized system, it is most of the time necessary to " lighten" this little guy on efforts and give i a second anchor point ( like around the lens base). Then all this is fixed on the pitch tray of the gimbal, and the smallest slope on the Roll assembly can become a nightmare. Hopefully, on a Movi the hardware is well done on that side of things.

    Then about the dampers, here is a small video made with a simple 2 axis gimbal and soft dampers, in high wind, that i made at CEEMA for testings ( it's a UAV test center in France where we fly all customers machines for testings).

    Note what happens when i fly backward with wind in the back : small bumps happen, this is because i'm using soft dampers, perfect for normal conditions but too soft for handling large wind gusts that make the gimbal shake. With a small slope in the roll assembly on that one ( only the motor shaft handles everything, it's a DYS gimbal) , small bumps are amplified by the camera, moving back to dampers, and so on. Testings was made with a Hexa 800 Gryphon Dynamics frame.




    Lowering the gains is a "bypass" solution, as simply, if he gains are high,the gimbal compensates fast but there is a lot of inertia around the camera and the dampers will move before the camera itself, generating compensation in one direction, then in the other, but the dampers take it mostly so it finally just shakes the camera. Going to lower gain allows to soften this but it has a cost : stabilisation is pretty weak..

    Ideal damping is generally stiff damping, right before "jello" happens, rubber is subject to temperature fluctuation in it's damping, the best one remains generally wire damping ( for example the Flexacopter damping), custom made for the weight it carries ( in general i could note that a damping works more or less +/- 500 Gramms around the weight they have been setup for). That is why moving the dampers far away with an ultra stiff gimbal plate allows to put soft dampers, without having the dampers get pressed too much when the multi rotor is taking angle to move around or compensate wind, and without having the gimbal under it acting like a large spring.

    I will try to make a short video in summer to show differences with standard / wide damping plate and also about the camera lens fixation reinforcement, i am sorry as it will be on a standard gimbal ( modified cinestar), i do not have a movi lol :) But all gimbals work the same in term of mechanical properties anyway for vibrations :)

    BEst regards,

    Fabien
     
  12. Sam Leggett

    Sam Leggett Member

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    Hi Fabian,

    Thanks for all your tips, they are great! We put the hard dampers on again earlier and now we have had the chance to test them we are sure that they are the way to go. We now have a short little 14mm lens and so we had to re do all our gains again! Amazing the difference it all makes, but again we think we have got them as high as possible without vibration. It seems there is no easy solution... holding it by hand or suspending the copter is not accurate enough... the gains are always too low, we have the laptop outside and do a 1 min flight up gains 1 min same again, up gains and so on - then watch all footage on a big screen and pick holes in it!

    We have the harded bumpers (I think) Green and white dots... Results are good but we have not had a high speed run with the current set up. Hopefully that will be tomorrow! Its a great feeling when stuff is working well! We got some nice footage today for the show reel.. will be a great day when its all together!

    I do like the idea of a wide damping plate... but that will be after our gear beings to pay for itself!! I have seen those wire dampers too... but we have an awful lot of electronics where they would sit and I don't know where I would move it all to!

    I look forward to seeing your wide vs narrow video! Man I am learning a lot doing this!

    Cheers,

    Sam
     
  13. Fabien Deregel

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    Hi Sam,

    a wire damper is not more problematic than a standard damper to install.
    Attached is a picture of one i assembled for a customer (it's a Flexacopter Wire damper fitted on a genuine Cinestar lower frame).

    We use 4 connectors for Sony Nex 5 / CX 740 on a regular Cinestar ( servo) gimbal, and connects the 8 of them for heavier cameras. We simply unscrew / rescrews as per the needs the long single spacers of each "block" we want to be "active", they do not need to be removed from the frames. I also use only 6 wires instead of 8 on each block but for heavy loads all can be installed.

    The only small wrong thing about tis damping is that it's ultra wide ( around the frames) so it dispatches and absorbs traction very very well as it's dispatched on wide distances, but on the other hand, the cinestar gimbal is fixed to the carbon plate only at it's center, it would be a bit better with a stiff alu mount. But it's already pretty great results with it as it is.

    Adjusting the gains just picking up the frame or gimbal will help for the very basic gain settings, but when you power up the motors and fly, you have motor and props vibrations coming up.

    These need to be taken into consideration, easy way is to drop gains 5 or 10 points from static gain settings, hard way is to fly, reduce and adjust until you have great results.

    The bigger the vibrations move to the gimbal, the lower you can setup your gains, or you need to higher the filters which is an easy but wrong way to proceed as higher filter values mean weaker performances (it "absorbs" vibrations by filtering them but on the other hand it gives some lag and brings higher response times + lower accuracy).

    You can try a crap but effective tip, by simply using some 3mm thickness alu flat profile ( you can find them in many shops) , and make a Z shape ( 2 pieces), and link them between the lens ( on a non moving part of the lens of course, as far as possible) with foam and tape, and fix the other part of the Z on the tilt tube in any way you can without grinding / marking the tube ( lol) . Make a test with and without this, you might be pretty.. surprised :).

    Of course for use on a movie stage you can not use such solutions ( looks a bit unprofessional) but it is easy to make a nice looking part with a few carbon tubes and alu connectors that you can find in RC shops on the internet ;)

    Hope this helps,

    Best regards,
    Fabien
     

    Attached Files:

  14. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hi Fabien:
    Could you edit your posting and upload the image file you wanted to attach, please?

    Thanks
    Andy.
     
  15. Fabien Deregel

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    Hi Andy,

    i uploaded the file, post is edited :)

    Thanks a lot,
    Fabien
     
  16. Sam Leggett

    Sam Leggett Member

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    Hi Fabien,

    Sorry about the late reply... We have been very busy with our showreel as the weather hasn't been too terrible for the last few days. We also go in our Flight Test with Resource UAS (excellent service), so we are legal to operate commercially in GPS and Atti mode. We are going back for waypoints once we have got the hang of it!

    You're right, the wire damper doesn't look hard to install, and it does give a nice wide support for the gimbal. Our problem is that all our receivers, downlinks, telemetry is all mounted with its antennas poking out right where those dampers would be. Everything is balanced so nicely and there is so little room to play with that it would be a big job to get it all to fit nicely. Our results are good at the moment, although we haven't done much in the way of high speed runs recently, so we will see.

    Our experience with gains was that however much you fiddle around suspending the gimbal you could never run the gains as high as when you tested it by flying... but we think we have a good set up now. Its amazing how +/- 5 on stiffness can result in tiny levels of slop or over-gain vibration.

    Thanks for the lens support tips! If we notice anything I will definitely give them a go!

    Happy Landings!

    Sam
     
  17. Adam Etheridge

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    Hi Guys

    I think we may be having similar problems?!... small 'judder-y' movements, not always apparent but consistent enough to ruin most shots. Here's a 30 sec clip:

    http://exchange.aspectfilmandvideo.co.uk//A001_C004_0101M2.mp4

    - SkyJib v1
    - Allied Drone Echo Mount - 8 x soft dampeners
    - Red Epic with 20mm Canon Prime
    - MR is fully balanced, and showing 0-2% motor load in balance
    - Stiffness: Pan 80, Roll 50, Tilt 40 - these were set by holding airframe off the ground, finding the oscillation point (as we do successfully for handheld mode), and then dialling back by approx 10-15%
    - All Props recently balanced
    - We've added stiff foam wedges under the 2 role bars to try and stiffen relationship between camera and MOVI

    Despite this, we're still seeing the movements in the video above...

    Any suggestions/thoughts would be greatly appreciated!

    Thanks,
    Adam


    Aspect
    Bristol, UK
     
  18. Sam Leggett

    Sam Leggett Member

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    Hi Adam,

    Nice place to shoot! I'm no expert, but from your clip and your set up I would say the bigger bumps might be due to the soft dampers bottoming out and the rest perhaps just fiddling with the pan gain (the wobble looks side to side to me). We carry a C300 and have put back on the stiffest dampers we have (green and white dots) they feel hard and when all 8 are on its very hard to squash the allied drone mount by hand. We toyed with half hardest and half softer 4 each alternating (medium I think - red and white dots) this made it easier to squash by hand, but in turbulent air or flying at speed we had similar bigger jolts and we think that was caused by the dampers bottoming out.

    From our experience we found flying and adjusting stiffness/gain was the only real way to get high settings. On the ground our settings we lower than in the air, especially for pan... to get stable in the hand the numbers were low - in the 70's yet when flying pan seemed vague. We kept upping it until we saw lateral vibration and then backed off only 3-5 points. It takes a lot methodical pattern flying!
    Our optimum settings change from handheld to airborne and even just a lens change.

    I can't picture your stiff foam wedges?

    Hope that gives you something to try, if not, I am sure some more experienced blokes will give you more!

    Sam
     
  19. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hi Adam:
    I've often wondered who bought my house when I left the UK.... :D

    I agree with Sam, it looks like the juddering is only in the pan axis. Is there a chance you can put something like a GoPro, hardmounted on the Allied Drone, and see what the footage looks like there....it would help determine what motions the airframe is imparting to the MR.

    Andy.
     
  20. Adam Etheridge

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    Hi Sam, Hi Andy

    Yes, was a very lovely place to film! - we were testing 2 drones side by side: the big SkyJib Oct vs Phantom 2... (both deliberately at opposite ends of the drone scale to try and demonstrate cost vs quality)... very frustrating that the P2 performs almost flawlessly out of the box!

    Anyway, thank you both for your suggestions. I will definitely try the hard dampeners... we originally tried 50/50 soft/hard but this seemed worse, but we shall try going the other way... just so many variables!

    Good idea re: GoPro on the airframe - we'll maybe sync it with the camera recording and create a video showing both side by side.

    Sam - re: foam. Someone at Freefly suggested this to try and create as much rigidity between the camera and the Movi. Its the very hard/stiff plastic-y type and we cut it into a slight wedge shape... photo below

    Thanks,
    Adam

    photo 1.JPG
     

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