Roll "twitch" in video

Discussion in '3 Axis Gimbal' started by Philip Ellerbroek, Jan 4, 2013.

  1. Philip Ellerbroek

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    Forum,

    I've stitched some recent flights together to show you. My issue isn't so much as vibrations, but rather what I would call a "roll twitch". You will see in the video the rolling twitch.

    https://www.dropbox.com/s/yq17pqccgjy369q/Twitch.mov

    In piloting my CS8, whenever I add any amount of roll to my flights, the resulting footage has "horizon roll". I haven't seen anyone post anything about this issue in the forum. Is it just me or do others have this issue if they fly and have to add roll to their flight input?

    There is a portion of the video where you can see the CS8 shadow, including the gimbal. You will notice the delayed correction of the radian compared to the crafts shadow.The video makes it seem as if the roll correction from the radian and roll servo are delayed when the copter rolls, titherefore causing a twitch. I have the updated 1.03 Radian firmware. I have not do any mod's to the dampeners. I have red dampener spring, three pairs of two. I have not experimented with removing any dampeners yet because I believe the issue is around the gimbal and radian/servo and is not vibration related because the video is shaking but rather "rolling".

    All is perfectly balanced including pan, roll, and tilt when camera is mounted. My roll radian gain is 100. I don't see any noticeable correction when I adjusted the Radian roll between 60-120. In following Tabb's video for setting radian gains, when I have the gains between 60-120 and hit the tilt booms, I don't see the radian "excite". I can't find any solution with various radian gain settings. There is no noticeable issues with the roll servo from what I can tell. Servo bands are tight and flex only the recommend minimal amount upon pressure. Servo band teeth are also intact and are not slipping. I tightend all servo pulley screws. All components are Quadrocopter.

    Props have slight wear but nothing noticeable for damage. All booms are secure and motors seem to be operating normally. RPM motor sound does not indicate any issues. This doesn't seem to be a gyro setting issue because it flys smooth and with good response for craft control.

    I have a Canon Mark3 with a 28mm lens. I run a Graupner mx20 for pilot and mx12 for camera and gimbal.

    Perhaps there is some issue with the roll servo that I can not see or hear or feel in terms of gears? My only other thought is that the gimbal plate is flexing, and therefore the entire gimbal is swaying and this is affecting the response of the roll radian correction so that the camera stays level to the horizon? I've read others running a similar camera and lens weight, but they complain of vibrations rather than this horizon-level issue.


    Phil
     
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Phil:
    Could you connect up the Radian software to the Roll sensor and verify that everything looks ok with the Diagnostic and Configuration window, please? (Perhaps you could take a screen shot and post it?)

    Do you see the roll sensor compensating for the hand-induced roll when you have the C8 suspended above your bench?
    I'm trying to figure out whether it's correct at all, too little, or too late?

    Andy
     
  3. Brad McGiveron

    Brad McGiveron Active Member

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    Phil... You are not the only one seeing this. I have seen lots of clips with it and mine have it as well. Mind you with the mods I have done to the vibration plate, which I think are absolutely mandatory, I get none to just the smallest amount of twitch in calm conditions. In wind it's much more noticeable as the gimbal works harder. Something isn't right with the roll axis radian and its own dampening.
    It would be great to see folks raw footage which isn't post stabilized that is without the roll twitch and compare the settings PPM, PWM etc that they are using.
     
  4. Josh Lambeth

    Josh Lambeth Well-Known Member

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    We too have this issue... (with the horizon not being level at times) sometimes I kind of like it... others it sucks... we have been playing with settings and such to try and compensate for it but have yet to find a solution.

    The actual "twitching" seems to be because the copter is changing directions faster then what the gimbal can handle? Look into tuning the copter so the copters movements are nice and smooth. This will help out with those harsh movements in the footage.

    Josh
     
  5. Philip Ellerbroek

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    Brad and Josh,

    After a long day of flights adjusting the gains, I found that 135-140 gain is my best bet. Once I get to 150+, the radian is "excited" and is vibrating and this can be seen in my videos. At the same time, the "horizon roll twitch" that I had is reduced, which is good. This is likely because the roll radian is quicker to level itself out. However, the video is not useable because it now displays vibration.

    On the 125 and below gain, I no longer have "excited" radian vibrations, but the "horizon roll twitch" is evident in the slightest amount of roll that is added to piloting. All flights were in 2-5 mph wind. At the 135-140, I am just below the gain level of seeing vibrations from an excited radian, yet I still have clearly visible issues of "horizon roll twitch" where the radian is moving/correcting slower than the copter is rolling.

    I'm running a Canon Mark3 with a 28mm IS USM. I have all six o-rings in red. They are about 3 months old. Radian firmware is up to date. I double checked the belts for tightness as well as servo pulley screws. Everything is good there. I just noticed this after moving from a much lighter Canon T4i to the Mark3.

    Here's what I think we are all seeing (and I could also be completely wrong!!) ..... It is almost as if the added weight turns the 3axis into a beefy "swinging pendulum". An analogy would be a full sized helo banking with a long rope underneath and a heavy carry load at the end of the rope. The rope will swing along with the load at the end of the rope..... In this case, the 0-rings are giving the gimbal and gimbal star too much "swing" movement because of the o-ring's elasticity, and this swinging motion is causing a "delay" in the roll response, which translates into a "roll horizon twitch" on the videos. While this swinging movement may be a very small degree, I may be just enough to affect the radians ability to react in correspondence with the copter's roll. As we know, we can't simply remove the o-rings because then we lose the dampening of vibrations that the o-rings provide. It is a gentle balance of o-ring dampening vs a necessary strength of connection between the copter and the gimbal/gimbal plate. It looks like I'm in the same neck of the woods as Josh, so I don't think its a weather matter.

    Im glad to hear that I'm not alone and that there may be MOD's I can do to produce useable footage. There are a few mod's that I believe I may need to try. I've read about:

    Reducing the # of o-rings
    Changing o-ring colors
    Double gimbal star plate for more strength (yes for heavier cameras, but at which weight threshold is this necessary, and how exactly does this affect the roll radian)
    Re-inforce the gimbal star plate with a thin 1/8" piece of wood
    Using black tie-down strips on the dampeners
    Using black rubber o-rings around the two hex nuts on each set of dampeners


    One last thing, have you tried re-balacing your camera's so that the COG is HIGHER? I say this because when i mounted my Mark3 and flew for the first time, the COG was higher because it was balanced for the lighter Canon t4i. I did not notice the issues that I am having until after the night that I upgraded the Radian firmware in addition to rebalancing the gimbal for the heavy Mark3. In balancing, I moved the tilt bars down and lowered the COG for the Mark 3. I know this concept of raising the COG runs contrary to the Radian Balancing videos that are available via Tabb, particularly where the roll axis is considered properly balanced when the pulley band is off and that you can slightly move the roll axis and it will stay in that position without continuing to tip in either direction. But perhaps moving the tilt bars upward for a higher COG may help with the reaction time of the radian and servo for roll? I am going to try this thought before I go about doing any of the major mod's.

    So I don't have to surf through the forum, Josh and Ben, what mods have you done and now kept? In particular, I really don't want to double the gimbal star plate if that has no bearing on the o-ring and the gimbal, although I know Tabb has mentioned a stiffer gimbal star plate is in the works for heavier cameras.

    I appreciate this any guidance. You are all invaluable resources!

    Phil
     
  6. Brad McGiveron

    Brad McGiveron Active Member

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    Hey Phil

    I have done two Mods and am pretty happy with them. The number one for me as I mentioned was the strengthening of the vibration/gimbal plate. Pretty much this is a must do I think and the double plate isn't enough as you need to go further to totally stop the flex. The second was a grommet mod. Those two have me happy, specially with our Epic as the weight settles everything very nicely. With the 5D3 and a couple of smaller cams I still get the odd wierd jitter which I thought was from vibrations. After running a test with the radians off and the lighter cams, it's butter smooth. So I'm just not sure where the twitches are coming from.
    I am still using all of the stock red o-rings.
     
  7. Philip Ellerbroek

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    Brad,

    Did you ever try the rip-tie mod that goes on the dampners? If so, was it in conjunction with the grommet mod? I did the grommet mod last night and am wondering if the rip-tie mod would be overkill, particularly since there is little to no movement now in the dampners after the grommets were added.

    Phil
     
  8. Brad McGiveron

    Brad McGiveron Active Member

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    No I didn't try it. Ya it's probably overkill.
     
  9. Gary Haynes

    Gary Haynes Administrator
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    Phil for the last two on your list do you have links to where those are discussed?
     
  10. Sylvio Rangel

    Sylvio Rangel Member

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    Looks like everyone has the same issue. Question is...Is it the best we can get from it?
    I have uploaded a video to share my results....What's your opinion? Are your footage better? Worst?

    http://www.sendspace.com/file/cuivp8

    Running WKM/xoar13x5/5sLIPO/Freefly3axis/Cinestar8/GH3+12-35mm(860g). Flight look pretty stable.
    Maybe some micro vibrations are causing the shakes.
    Propellers are balanced.
    I will change 3 motors that are not running 100% smooth, but not sure if that is the point.

    I hang the cinestar from the battery plate (as posted by Tabb):

    Best tilt point were around 220. Roll around 160 (+-) without going into resonance alone... BUT "tapping" on a boom or on the gimbal, induces some resonance to the system when radians are ON. With radians OFF it stops ocillating by itself.
    That leads to decrease the Radians Gains. "Tapping" Resonace stops around Roll/80 Tilt/90.... BUT these gains are too low to correct the "navigation" movement of the cinestar inflight.
    Looking closely at the FexingPlate/Dumpers and feeling it with my finger tip...i think the main oscillations are in the Dumpers/Orings.

    I am flying with temp around 30C (86F). Maybe 6 Red O-rings is too soft at that temp.

    I have ordered Blues and Blacks and will test when I get them.

    Maybe with harder O-rings I can set the gimbal gains higher without getting the resonance jitter effect, and the radians will compensate faster the flight navigations.

    Any ideas?

    Sylvio
     
  11. Sylvio Rangel

    Sylvio Rangel Member

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    By the way...Gains in the uploaded video are:
    WKM 175 175 170 170
    Radians roll/85 Tilt/100 Pan/turnedOFF
     
  12. Janne Hoglund

    Janne Hoglund Member

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    Getting roll gain high enough is the same problem for me.
    Roll gain of 85 will not give you the promised level horizon :-(
     
  13. Sylvio Rangel

    Sylvio Rangel Member

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    Hi Janne,

    Indeed, 85 is not enough!!! Hopefully stiffer O-rings will allow higher gains.

    Do you fly MK? Same problem?

    I am considering swapping to MK...but would be waste of time and money if the issue remains the same.
     
  14. Janne Hoglund

    Janne Hoglund Member

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    Flying C8 with MK, now on 4 blue and two red rings in every damper.
    Tilt gain 140 is very satisfying, but roll is sooooo hard to get right!
    Level horizon and no jitter seems impossible :-(

    I think it would be very nice if Tabb or Jeff could share some of their experiense and thinking in setting it all up.

    Please :)
     
  15. Brad McGiveron

    Brad McGiveron Active Member

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    Don't bother changing platforms. It won't make much of a difference as its not related to the flight controller anyways.

    Download the clips below and watch. Don't view them in Vimeo

    here is WKM




    here is MK



    Notice in the top example it is totally smooth with the radians off. It is also a way heavier camera than the second one and it shows a few more twitches on the roll because of it.

    You can get even better results with the small Boss cameras and their nice on board stabilization. There are a few users here with some great examples on the CX sony cameras. Otherwise this is pretty close to what you can expect in good conditions with a standard camera. Give or take.
     
  16. Chris Shaw

    Chris Shaw New Member

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    Brad, a couple of questions. Which cameras were used in video 1 and 2. Also, what are your MK gyro settings? (used in vid 2) Thanks!
     
  17. Brad McGiveron

    Brad McGiveron Active Member

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    The first was a Scarlet and the second was a 5D3.

    The MK Gyro settings:
    Gyro D: 20-23
    acc/comp: 100+
    Stability: 8-10
     
  18. Sylvio Rangel

    Sylvio Rangel Member

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    Brad,
    You got your WKM much better than mine. Looks pretty smooth with MICRO twitches sometimes....
    With Radians OFF, I got it smooth with GH3's IS ON. IS OFF and I get some medium jitter.
    Could you share some info? I am really far from what you've got.
    Propellers? 4s or 5s? Tried both? Was the stiffer flexplate a GAME-CHANGER?

    Sylvio,
     
  19. Sylvio Rangel

    Sylvio Rangel Member

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