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Wave mitigation for dumb Buoycam via fast powered miniwinch. Any suggestions?

General Discussion
#1

What I’m working on right now amounts to a tethered camera with no thrusters, but it is attached to a surface buoy. Obviously that buoy will be resting on the surface and bobbing along with the height and period of each wave. This motion will get transmitted along the tether and cause the camera to move as well. The one motor involved in this equation is the tether winch. It is fast enough, and my camera heavy enough that I could in theory raise and lower the camera according to the buoy’s altitude so that the camera remains level underwater based on an IMU reading and calculated winch action. It’s a bit like a gimbal but with distance rather than angles (and just one axis).

I do realize there are a lot of ways to deal with this issue- I’m considering more passive mechanical solutions as well but for now I’d like to explore this “dynamic winch” idea. Thanks for any suggestions!
-Kevin

Is passive wave mitigation a worthwhile effort?
#2

I’d assume a vertically aligned single-axis accelerometer on the buoy would give you the fastest response to base your winch signals off, although the sensor drift over time may mean that it ends up moving a bit. By ‘the camera remains level’ are you mostly after steady footage, or are you specifically wanting to stay for example a set distance above the seabed? The accelerometer approach would potentially give you the former but the drift may compromise the latter.

To accurately achieve a set distance from sea-bed you’d likely need an altimeter, which would almost certainly be more expensive, but would likely also be quite a bit more robust, and would allow you to collect tide-independent data, subject of course to the seabed not changing too fast. If you’ve got a wireless link from the buoy you could also potentially set up a control to change the height set-point remotely, which could perhaps be useful.

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#3

Thanks! Yes, sounds like you get it- in hindsight I might have described it differently in that the goal is to keep the camera stationary despite the buoys motion. The drift shouldn’t be too much of a problem but I worry that the waves will be; although this whole concern is still speculation at this stage. I won’t be able to see the sea bed in this application, it’s specific sea life closer to the surface that I’m documenting. So it’s steady footage (or steady’er) that I’m after. Yes, I will have a wireless link and have a height control, but after that is set I was thinking of how I might automatically manage wave feedback.

#4

I’m might be saying something stupid but why don’t you put a weight on the seabed and the camera inside a float that is held below the waves via a rope? This way wave motion won’t affect it…

3 Likes
#5

Not stupid at all- it’s a great solution but it doesn’t work for a few reasons here, primarily:

  1. It’s way too deep to reach the seabed where this will be deployed (200+ meters).
  2. This buoy is meant to be rapidly deployed/repositioned. That adds to the disadvantage of #1.

Thanks for the suggestion!

#6

We have been dabbling with a passive solution for this… a pvc frame that slides on a line works well once u get your frame neutrally buoyant and if u can have a bit of depth variation… let me know if this a solution you’d be interested and I can send u some specs and video

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#7

Some people are like Slinkies…Not much good for anything.
But they still bring a smile to my face when i push them down a flight of stairs.

Levity aside, try a slinky. The long weak spring should hang a sensor below yet dampen any wave action.

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#8

I don’t know why I didn’t get a notification of this reply but I’m just seeing this now. Yes, I’d love to learn more about your solution. I designed a passive solution using a constant force spring but more recently have become more doubtful of its utility. I just posted a separate thread about passive solutions.

#9

I created a compact passive “solution” that utilizes a weak constant force spring concentric with the spindle. I’m not sure using an extension spring (slinky) would be different in theory but somehow it does seem like it might be a better choice from a physics standpoint. Making the front part of a tether an elastomeric segment was something I also considered, but ultimately I think the slow undulation of ocean waves may just be too gradual a motion to make an effective use of this approach. I really don’t know. I need to get out to the ocean…