Low Stiffness + Low Filter vs High Stiffness + High Filter - Pros and Cons of each

Discussion in 'MōVI Pro' started by Robert Ruffo, Mar 27, 2019.

  1. Robert Ruffo

    Robert Ruffo Member

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    Hello Movi Mavens.

    I've had trouble gaining a deeper understanding of the difference between the choices listed above.

    I do understand that Stiffness too low will cause slow wobbly oscillations, as well as reduce the system's power/speed, whereas setting it too high will cause buzzing vibrations.

    I also understand that setting Filter higher can reduce buzzing, but setting it too high creates wobbliness and imprecision.

    That said, we can get "correct" tuning (no wobble, no buzzing, no wasted potential power) in two potential ways:
    1 - Very high Stiffness and very high Filter (Turn up Filter to max or near max, then turn down Stiffness until buzzing goes away)
    2 - Lower Stiffness and Lower Filter (basically turn down Filter to near zero, then turn down Stiffness until buzzing goes away)

    My question is, what is the advantage of "1" vs "2" and under which circumstances do you lean more toward either choice?

    The manual explains each parameter, but not at all the advantages and/or tradeoffs of combining them in different proportions.

    Thanks guys!
     
  2. Robert Ruffo

    Robert Ruffo Member

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    No one has ever thought about these two options?
     
  3. Graham Futerfas

    Graham Futerfas Well-Known Member

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    You're thinking in terms that I usually suggest people new to Movi try out: Change the settings to extreme values and see how the gimbal reacts when you try to operate it. This will show you how you can change the "feel" of the Movi.

    Generally, I believe you want the highest Stiffness value you can have without too much Filter and buzzing. Too low on your Stiffness, and the Gimbal is less adept at doing it's job: providing stability.

    Higher Stiffness is more important in some situations, especially with wind resistance and rough movement. I often find that I AutoTune at 50% and then start reducing Stiffness and increasing filter a bit, mainly because the Movi likes to shake when it's hanging in the dock, and I find that annoying. Usually it's just the Pan axis that tunes a bit high.

    With some high Stiffness (and Hold Strength) values, you can get Overshoot on a move, or it can "Bounce" back and forth when you want it to stop.
     
  4. Robert Ruffo

    Robert Ruffo Member

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    Thank you Graham! But what do you mean by "too much filter". What is a "usually good" Filter setting? Where do you usually land Hold Strength with run-of-the-mill set-up (say Epic or Arri Mini, prime lens and typical moves)?
     
  5. Deniz Ozgoren

    Deniz Ozgoren Support Mage
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  6. Graham Futerfas

    Graham Futerfas Well-Known Member

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    Hi Deniz, I still find AutoTune to over-do it, even at 50% on the new firmware. I usually have to tweak the settings to get a motor to stop oscillating or vibrating.
     
  7. Deniz Ozgoren

    Deniz Ozgoren Support Mage
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    I usually have to tweak the settings to get a motor to stop oscillating or vibrating.
    • One important tip is to figure out the worst case pose and autotune in that scenario. For instance, tilt looking down or 45 degrees might be worse than tilt level
     
  8. Graham Futerfas

    Graham Futerfas Well-Known Member

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    Do you want me to run an autotune while I'm hand-holding the gimbal? I thought it needed to be pretty still during that process?
     
  9. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Graham: I'm not sure how often Deniz gets to check the forum, but the general rule seems to be "tune it like you use it" -- if you tune it in the stand, for example, the natural resonances that autotune will detect will be different to those than if you hold it, say, one handed from the top handle, or two handed with sides of the rings.

    Hope that helps.....(and there is a chance that Deniz will correct me if the autotune algorithm has changed...)

    Andy

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limit™
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     
  10. Graham Futerfas

    Graham Futerfas Well-Known Member

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    You've said this for years, Andy, but I've tried to AutoTune in a stiff breeze and it failed because the Movi was moving.
     
  11. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Oh....I'm sorry, I was responding to your question about the issue of handholding versus the stand. As you say, if you've got it in slip stream that's a different ballgame....I'd tune it hand-held but in still air. Sorry for the confusion.

    Andy

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limit™
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     
  12. Graham Futerfas

    Graham Futerfas Well-Known Member

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    I'll give this a try and report back. In previous software versions, the Movi would fail if it moved or bumped during autotune. The biggest issue I have is that the Movi just oscillates and shakes in the dock unless I put a hand on it... which looks quite silly to the clients and director on set.
     
  13. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I hear ya, Graham. The problem is that, as I understand it, autotune actually waggles the MoVI in each axis, figures out the resonant frequencies and adjusts the motion controllers (technically PID controllers) to null out the oscillations consistent with appropriate responsiveness as you use it. So the problem is one of trying to autotune in an environment as close as a possible to how it's going to be used to allow autotune to work -- but you're absolutely right, you may well have to tweak the settings after autotune if you see oscillations.

    I wouldn't presume to tell you how to educate the clients and director on set -- in that regard I suspect you've forgotten more than I currently know! :)

    Cheers
    Andy

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limit™
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     
  14. Deniz Ozgoren

    Deniz Ozgoren Support Mage
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    Here are my Tuning Protips:

    • Autotune measures the stiffness of your system across all frequencies and adjusts the power and tuning of the motors accordingly.
    • Loose things make the overall system less stiff. Autotune detects this and lowers powers to motors. Make sure the camera payload, including all accessories (follow focus system, batteries, range finders, etc.) are in place, tightly secured, and well-balanced.

    • It is not only the MōVI that is part of the mechanical system. Putting MōVI on a ring, versus a tripod, blackarm, or ALTA affect the mechanical behavior. Thus autotune should be run every time MōVI is mounted on a different platform.
    • For instance, if MōVI is used with ALTA, you should hold (or place) it at the end of the booms and then raise ALTA so that MōVI is floating. Start autotune this way for best results.

    • Percentage: Default is 60%. Best range is 50-65%. Beyond 70% is generally too marginal for practical use. Below 40% is very low tuning.
    • For high-performance shoots, such as shooting with long lenses or with ALTA, you might want to stay on the higher end of tuning.
    • For situations where you will change mounts frequently, staying at the lower end of tuning can be more productive so that you don’t necessarily run autotune every time.

    • Pose of the MōVI during autotune also matters. Mechanically your camera setup might behave differently, for example when looking straight vs tilting up. If you are trying to get the most out of tuning by using higher autotune percentages, then try tuning MōVI in different poses to find the worst case scenario. Another example besides tilt up vs straight is roll. If you are doing Barrel Rolls, you might want to try tuning at different roll poses and figure out the pose with weakest mechanical stiffness, then do a final autotune at that pose.

    • Balance! Don't forget to check tilt in different poses.

    • Variability. Although very low probability, sometimes autotune results might not be optimal (less than 5% of the time). If you see something off, try autotuning again. Additionally, if the system is already vibrating a lot, this can affect autotune. In this case try lowering stiffness values to very low values manually or reset robot settings first, then start autotune.
    • Additionally, autotune results from Blackjack versus v1.5 firmware are same and this was tested with various payloads. Blackjack’s upgraded Autotune v3 algorithms affect other behind the scenes parameters, and shouldn’t be affecting stiffness and filter values compared to v2.
     
  15. Graham Futerfas

    Graham Futerfas Well-Known Member

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    Awesome! Thanks for the tips, Deniz.
     
  16. Graham Futerfas

    Graham Futerfas Well-Known Member

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    OK, I successfully tuned the Movi while holding it. I'll have to keep trying this, but it was still over-tuned a bit in the Roll motor and had very low filter setting of 1, which was causing some buzzing. The only problem I had was not being able to push the Auto-Tune button myself, since both hands were occupied holding the Movi up. :)
     
  17. Robert Ruffo

    Robert Ruffo Member

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    Very interesting discussion. Thanks to all!
     

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