Radian roll gain

Discussion in 'Radian' started by Dave King, Aug 16, 2013.

  1. Dave King

    Dave King Well-Known Member

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    I'd like to see what everyone is using with the 5DMKiii setups for roll gains. I am having problems with a little twitch here and there on the roll with the 7D. They are both very similar in weight. I checked the spreadsheet and didn't seem to get a good feel for it as I saw data from 75 to 200. I know many have updated their setups since they entered their data too. Right now I'm at 130 on roll and I'm seeing a little bit of roll twitch. I had the gains from 75 to 130 and it has helped a little but I wasn't sure if its uncommon to go much higher? The roll and tilt axis are both balanced very well.

    Can you guys look at it the video and see if you think its worth living with or if you think it needs more adjustment? More gain?
     
  2. Colin Snow

    Colin Snow Active Member

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    I am curious as well. I get this same twitch with my CX760. I have Radian on roll axis only. I have read every post and taken all precautions. I have taken the gain lower and higher and "the twitch" is always there. I compromised at 90. Will be dumping it soon in favor of brushless and who knows what IMU.

    Colin
     
  3. Dave King

    Dave King Well-Known Member

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    HI Colin

    I have a separate gimbal with the CX760 and I pretty got all my roll twitch out with that setup. I spent endless hours with trial and error. I have the roll and tilt gains at 100 and I found the key is the balance of the roll axis itself. It has to be dead perfect. I mean dead perfect. In addition to being able to stay anywhere you place the gimbal it needs to be perfectly balanced in the most top position at 12 o clock. If it moves at all side to side you need to loosen the boom clamps that hold the camera plate and move it ever so slightly to the right or the left. 1/32" to the right or to the left can knock it out of perfect balance. I now only see roll twitch with the 760 in high wind gusts of over 15 mph.

    With the 7D its so heavy that I have a very hard time getting it to be dead perfect on the roll axis at 12 oclock like I describe above. I have the roll axis very well balanced where it doesn't move anywhere on the roll axis that I put the gimbal but at the 12 o'clock position it can move ever so slightly. Not sure if that's the issue or not.

    I'd like to hear more feedback if the roll twitch I have above is pretty much standard so I don't continue to spin my wheels.
     
  4. Colin Snow

    Colin Snow Active Member

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    Thanks Dave for taking the time to reply. I have done this before (along with belt tightening) but after reading your post decided to give it a try again. Winds were 0-5 mph. Sorry to say I still have "the twitch" and also feel like I am just spinning my wheels.
     
  5. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Can you both confirm the roll twitch is not present when you are in Mode OFF on the Radians?
    Do you see the problem in Mode Stabilized Fixed?

    Also, by inference, Colin, can you confirm you've got the camera balanced in roll such that you can put it at any angle and it will stay there even without the roll belt on the pulleys?

    Thanks
    Andy
     
  6. Colin Snow

    Colin Snow Active Member

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    Hi Andy - I have Radian on only the Roll axis. When the belt is off the camera will bounce back and forth and settle. When it settles in the exact middle (12 O'clock) that is how determine it is balanced. Is that wrong? If so, please recommend a better method.

    If by Mode OFF you mean test fly it to see if there is twitch in that mode, then the answer is no, I have never tested that. My work-flow is to switch to Mode Stabilize Fixed as the very last thing I do before motor run / fly - making sure the kopter is completely stable.

    Colin
     
  7. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hi Colin:
    Unfortunately if the camera behaves like a pendulum that means it is not in balance at all -- I can't say how far out of balance it is but, I'm afraid is definitely not in balance.

    I'm going to be a bit lazy and cut a paste a response I made some time ago on another thread:

    With the roll belt removed, experimentally deflect the camera to one side or another.

    What happens?

    Either it will:

    a) Flop all the way up or down.
    b) Stay put.
    c) Swing back to some central position (this is what you're describing is happening)

    If it is a) then that means the center of gravity is above the pivot point (think pencil balanced on its point just flops over).
    If it is b) you're done. It's balanced.
    If it is c) then that means the center of gravity is below the pivot point (think clock pendulum).

    So you have to experiment until you get to b).

    You'll find that, with a few minutes practice, as long as you keep in mind what you're doing and what the camera/gimbal is telling you, you can find the sweet spot without too much difficulty.​

    From what you're describing you need to raise the camera's center of gravity in line with the roll axis. You may need to deflect the side booms upwards (so the front part is higher than the back part) to bring the C of G up. If you have the adjustable tilt arms, you can also raise the camera up that way. You may also have to move the camera from side to side on the front transverse boom.

    You might want to get the camera balanced before you worry about any other experiments.

    Hope this helps.
    Andy.
     
  8. Colin Snow

    Colin Snow Active Member

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    Thanks Andy. That helped some. The twitch is there now about 50% of the time (seems to come and go). When it is there it's about 50% smaller twitch movement.

    To raise the arms I had to cut the adjustable rail about an inch and remove the stock lens hood. I noticed the nick is off a bit in the same manner and I can see that I would benefit from adjustable tilt arms.

    What should I try next? The tilt arms? Anything in the mean time?

    Colin
     
  9. Gary Haynes

    Gary Haynes Administrator
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    Colin the adjustable tilt arms are a definite plus. If you have trouble getting the camera balanced from front to back, I did since the balance point was directly over the cross arm, then the sliding camera plate is also a great addition.

    If you find that the tilt side arms tend to drop down from not enough friction holding power of the clamps on the roll cross bar then 4 of the metal clamps can solve that problem. Depending on the camera you are carrying you shouldn't have a problem with the two Sony's in your tag line. Move up to the Canon 5D or similar then the clamps would likely help.
     
  10. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Colin: The better you can balance the camera in tilt and roll, then the less twitch you should get.
    Can you also check the tightness of the roll servo belt - if you push with your finger in center between the small and large pulley, it should deflect 2-3 mm. Is there any mechanical slop in the system -- if you grip the small pulley between finger and thumb of one hand and gently waggle the gimbal in roll, can you feel corresponding movement in the small pulley?

    I'm trying to eliminate mechanical play in the system and there are numerous such sources.

    Also what Gary says is sound advice.
    Andy.
     
  11. Colin Snow

    Colin Snow Active Member

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    Thanks Gary. I have the Adjustable Camera Rail and gave it a review here. Yes the balance point is right over the cross arm. Unfortunately, the rail has no hole there, so in this exercise I had to cut about an inch off the front, turn it around and insert that way to achieve tilt balance. Now the rail interferes with accessing the camera battery removal tab. I use to be able to just swap the battery while mounted.

    To quote Rosanne Rosannadanna: "If it's not one thing, it's another"

    How do you have your CX760 mounted? Can you provide a pic?

    Colin
     
  12. Colin Snow

    Colin Snow Active Member

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    Hi Andy - There is no slop. It's tight. Yes, I feel corresponding movement.
     
  13. Dave King

    Dave King Well-Known Member

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    I will try to shoot a video on how I setup up my Sony 760 in the next few days. I have spent endless hours figuring out how it to optimize it.
     
  14. Colin Snow

    Colin Snow Active Member

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    That would be great.
     
  15. Dave King

    Dave King Well-Known Member

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    I started shooting it yesterday. I should have something to upload by the end of the weekend.
     
  16. Dave King

    Dave King Well-Known Member

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    Hi Colin

    Here ya go
     
  17. Colin Snow

    Colin Snow Active Member

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    Thanks Dave! Great set up video. It helps to see the close ups and links for the parts. I can see I have more to do.

    Cheers

    Colin
     

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