Pan troubles

Discussion in '3 Axis Gimbal' started by Gustavo Rios, Oct 10, 2012.

  1. Ryan J. Rowe

    Ryan J. Rowe Member

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    Thanks Andy. I'll try your suggestions.
     
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    To my simple mind the problem is that we have a contradiction between wanting the gimbal to be isolated from the vibration of the motors, but, at the same time and as a consequence of that, it's a suspended mass acting like a pendulum below the hub, so its natural frequency is going dominate if there's any chance that it can. Accelerating it from a standstill, or decelerating it to a standstill is going to really make that natural frequency very conspicuous. (And, of course, if the gain is too high then you see that natural frequency emerge because the servo uses less energy for that frequency -- it takes too much energy to shake it at anything else.)

    So what I reasoned (and others please feel free to step in and disabuse me of this if I'm wrong -- or tell me I'm wrong just for sport!), is that I've got to find a way using the transmitter controls to be able to very gently start the gimbal moving and very gently stop the gimbal moving -- ramping as it's otherwise called.

    As Tabb has observed, if you build the ramping directly into the Radian sensor gimbal, there is a chance that using the sticks you'll overshoot or undershoot as there's no "feel" for the ramping. Thus, I reason, it's up to me to do this via the transmitter so that I can try and create a "feel" for the ramping for the camera op.

    And that's how I got to trying 60 - 80% exponential, low slew rates, adjusting the stick rates, limiting the servo range....you name it.
    Have I got a formula for success? Nope. I'm still working through the combinatorial effects of it all.

    Oh, and of course, the results depend on the ambient air temperature and the mass of the camera on the gimbal. I suspect the phase of the moon might also be implicated. All this seems very much like trying to solve ten simultaneous equations with only nine variables known. I seem to recall from the Dim Times when I studied pure maths that this was not a good thing to try.

    But how to do this without going insane in the process?
    Good red wine. ;)
    In moderation, of course.

    So, folks, leap in and tell me if I'm wrong, but please provide a basis for why I'm wrong so I don't have to stay wrong.

    Andy.
     
  3. Ryan J. Rowe

    Ryan J. Rowe Member

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    You are right the dual rate/expo does make a noticeable difference. It's funny but I had forgotten that I had adjusted those settings already and it helped a bunch but still not perfect.

    OK....I have a GOOD bottle of red wine. Cupcake "red velvet" seems to be the new favorite of my wife and I. So I will indulge while digesting what you have said here.

    In the mean time maybe you can try to digest this.....I am using the dual rate and the two positions switch SW3 on my MX-12. One position is 100% full stick movements, and the other is 20%. The video I posted was using the dual rate at 20% and I trimmed it a few clicks to make it pan automatically without human smoothness error on the stick. Changing the expo doesn't make a difference because my problem is not only at the start and stop of the pan, it's throughout pan and seems to be worse the slower I try to pan.


    My simple Montana mountain hick raised mind is thinking more in terms of parts and pieces and not so much in science and math since I just confuse myself that way. I like to read the pictures in books better than the words....;)

    A couple things...

    1- I noticed the belt used on the pan is longer than the tilt and roll belts. It also seems to be made of a softer material. Since it's longer the servo sits further away from from the large wheel (pulley). Also because it's longer there is more of a pinch factor on the servo wheel than the other two because there are more teeth in contact with the belt.

    2- The Pan system works differently than the tilt and roll. The pulley on the pan doesn't actually rotate since it's in a fixed position. On the tilt and roll the pulley rotates with the servo wheel. On the pan the servo wheel is rotating while the servo motor is also rotating around the pulley. It's not stable since it's attached to a boom that is rotating around the pulley.

    I see why the pan servo needed to be placed further away from the pan pulley since the gimbal mount/clamps forces it to do so.

    I wonder how the pan system would work if the pan servo was attached to a fixed position the same distance from the pan pulley as the tilt and roll distance and the pan pulley rotated with the gimbal instead of the pan servo rotating with the gimbal.

    I think one way it could be done would be to have the pan system an entirely separate piece that bolted between the copter and the gimbal. The pan assembly would be bolted solid to the copter and the vibration dampeners would go on the bottom of the pan assembly and attach to the gimbal. Now the vibration dampeners don't effect the pan assembly at all.

    Wow! I didn't even touch the bottle of wine yet and I've already started talking nonsense. :D

    Not sure what to do about the moon phase.....any ideas?

    Peace!
     
  4. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I think it's a combinatorial problem, so several things need to change to solve it to perfection.

    Good!

    I've seen that problem and presumed it to be mechanical play in the system -- the O-rings just making it harder for the Radian to have precise control because the O-rings are laterally too soft, perhaps?

    You can't fool me. I've been to Bozeman. Some of the smartest people I've met live in Bozeman. ;)
    Also some of the friendliest folk too....
    And some folks who are both damn smart and friendly live in Whitefish.

    OK. So far -- so there's more belt contact. I'm in full agreement. ;)

    I was with you until the last sentence. Why is it any the less stable since it's attached to a boom. Viewed through the beady little eyes of the servo (and you know those damn servos are watching you), why is it any the less stable? The servo doesn't know that it's moving itself on the boom.

    Hmmm. Again, I'm puzzled. The forces are controlled by the respective diameters of the pulleys (which affects the gear ratio), not by the distance and/or the length of the belt, aren't they?

    Not sure I can go there with you, Ryan. ;)

    I can see where you're headed, but I think you might be making a valid argument but built on a false premise. I would argue that the distance between the two pulleys doesn't alter anything but the length of the belt -- now, I agree, the length of the belt will increase the elasticity of the system but it doesn't alter the gear ratio between the two pulleys -- only the respective diameters/circumferences will do that.

    That's an interesting thought -- and disjunct from the belt/gear ratio thought. I need to think/drink on that some more.....

    Well, there's the answer. Drink the entire bottle, using moderation of course (which really means drink it slowly and with a good friend), and then re-visit the question of pulley ratios! <evil grin>

    You'll understand when you've drunk the entire bottle and you step outside on a clear Montana night away from city lights and just look up! Been there, done that. :)


    Regards
    Andy.
     
  5. Ryan J. Rowe

    Ryan J. Rowe Member

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    Hey Andy,
    Just spewing ideas in my head ya know. You make valid points. I don't mean to speak in absolutes as it's all just a newbies theory. The truth is I've only been flying the Cine8 for a month now. Before that my only experience was with the little Blade 6 weeks before I got the Cine. So I'm as green as it gets. So I don't take what you say with a grain of salt since you have far more experience than me. Just glad to have people like you in this forum to learn from. :)

    Reality hit quickly that this is not a turnkey, one size fits all deal. I'm absolutely O.K. with it as most things worth doing are difficult. I know what I want it's just finding the right path to get there. It just totally boggles me that it is this difficult to get the pan to work smoothly. And I thought the flying was going to be the hard part. I'm hoping that when I fly with IS in the camera the pan will smooth out. Until then I've reworked my system so I will just fly as a single operator panning through flight and tilting camera using a rotary control. Pans are super smooth that way. :)

    Cheers,
    Ryan
     
  6. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    We've all been newbies and sometimes, in my experience, newbies can cut through the accepted dogma and just ask: Why?
    Don't let ignorance hold you back. Ignorance can be fixed! ;)

    I started that way too.

    Don't count on it! <evil grin>

    It works the other way too, ya know....when people ask questions it forces one to think -- or in some cases, re-think.

    Yeah -- the real problem is that it is a tough problem -- the interacting forces are mindboggling.

    Flying'em is easy. Flying'em smoothly or in one place is harrrrd.

    Also bring the AVCHD 1080p60 footage you get from CX760 into Adobe Premiere, select all the clips, click right and choose Modify > interpret Footage and select 29.97 fps. That makes it seem almost dreamlike smooth....

    Oh, and learn to fly like Jeff Scholl or Tabb Firchau. It should only take you a few hundred hours of flight time....

    Andy.
     

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