Pendulum Stability

Discussion in 'Stability' started by Poida, Oct 1, 2006.

  1. Poida
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    Poida Senior Member

    Toot's post on water ballast for boats got my pea brain thinking. I have seen an article on TV about using giroscopes to increase stability for boats and I was wondering if a pendulum system would work.

    My thoughts are, a ball could be suuspended in the hull by a shft attached to the upper side of the hull by a ball and socket type joint or universal joint alklowing the ball to swing in all directions.

    Near the top of the shaft 4 hydraulic pistons are connected to the shaft in a 45 degree brace configeration ie the top of the hull the shaft and the pistons form a triangle.

    By extending the cylinder on the port side and retracting the cylinder on the starboard side the pendulum would swing towards the starboard side. Similarly the 2 cylinders fore and aft would swing the pendulum towards the bow or stern.

    A combination of 2 cylinders fore and starboard would swing the pendulum in the bow starboard quarter.

    Why? If the craft was tipping to port and the weighted penulum was swung to the starboard side thereby adding weight to starboard it would oppose the tip of the boat and hold it steady.

    How does it move. A second pendulum is allowed to swing with the motion of the boat sensors attached to this pendulum control the flow of hydraulic oil into the stabalising pistons moving the pendulum in the opposite direction to the sensing pendulum thus stabalising the boat.

    Would it work?
     
  2. Wynand N
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    Wynand N Retired Steelboatbuilder

    just wondering where you gonna fit the interior:?:
     
  3. Poida
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    Poida Senior Member

    What Wynard you want stability and an interior!

    I was looking mainly at larger craft and as I said gyroscopes are used in some boats which also take up space, but cruising yachts that take passengers will want to make the trip as pleasurable as possible.

    How ever after some thought a pendulum would take up more space than would probably be desirable and any moving weight would suffice which could be located under the living quarters.

    A sliding weight on linear bearings one traversing side to side the other lengthways.

    A boat sailing through even a small swell appears to pick up pitching momentum. When the boat moves into a wave and the bow lifts, the counter weight moves forward. As the boat rides over the wave and starts to nose dive the weight moves back.

    Similarly side to side.

    The counter weight can be moved hydraulically with electro hydraulic valves being operated from a steel ball inside a tube activating reed switches to power the valves.

    Of course an engine is required for generation.
     
  4. yipster
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    yipster designer

    someone started to me about mast pendulum stability and got me a bit
    confused, you dont want weight up the mast on a sailboat now do you?
     
  5. Poida
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    Poida Senior Member

    G'day Yipster.

    I did say the weight would be located under the living quarters but heck if you have the living quarters on top of the mast I'm all for radical design.
     
  6. marshmat
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    marshmat Senior Member

    Would it work? Maybe. With enough money. Would it be practical? Again, maybe. It has the advantage over fin stabilizers in that it won't add extra drag outside the hull, but to be effective it would have to have a LOT of weight. Gyroscopes work well because of their rotational inertia- a hundred kilos at a few tens of thousands of RPM is awfully hard to deflect from its axis of rotation.
    Consider the failure modes, though. Where does the weight go when something breaks? Probably to the lowest point it can. Which is the side of the boat that's already down. It could help the boat to capsize, if it were to break.
     
  7. MikeJohns
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    MikeJohns Senior Member

    These sorts of fantastical ideas littered the patent records in the 1800's .

    If you had some predictable motion you could tune the system to some ideal frequency. But the motion at sea is a very complex mix of dynamics.

    Anyone who has studied mechanical feedback and control systems will know the deal here.

    No sorry Poida.. ......the best stability oriented damped pendulum is already in each and every keelboat.

    Keep brainstorming :)

    All the best
    Mike
     
  8. Poida
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    Poida Senior Member

    Thanks Mike
    Has anybody thought of a donkey with a very heavy back pack running back and forth across the deck yet?
     
  9. yipster
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    yipster designer

    [​IMG]
     
  10. ted655
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    ted655 Senior Member

    Why a pendulem? A track system of parrell rods supporting a ballast weight with a XYZ axis would lay flat in the bilge. Sensors on the gun'l would control actuator screw drives.
     
  11. FAST FRED
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    FAST FRED Senior Member

    Lot simpler to use a framm tank, and let the water slosh back & forth for stability.

    FAST FRED
     
  12. Poida
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    Poida Senior Member

    Ted a linear bearing mentioned in my previous post is a track system.
    and Fast Fred good idea if you can get the water to slosh in the right direction. I've only done it once on a water bed and it sloshed when I slished and buggered my rhythm something terrible.
     
  13. stonebreaker
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    stonebreaker Senior Member

    You know, they use systems like this on newer skyscrapers to damp out earthquakes. Maybe do a little research and see if one of these systems seems practical for adaption?
     
  14. MikeJohns
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    MikeJohns Senior Member

    The tanks are called Frahm tanks (presuming Fred made a a typo). They work (sometimes) in large higher inertia/roll period vessels.

    The many downsides of shifting mass systems make them unattractive.

    There are good reasons why active stabiliser fins predominate.
     

  15. Poida
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    Poida Senior Member

    Excuse my ignorance on this Mike but I would inagine that stabaliser fins would only be suitable for a moving craft, preferably at higher speeds.

    There seems to be an application for a stabalising system in slower moving craft as in tourist Pacific cruises. I was stunned when during a documentary on gyros they unleashed the price of installing them, obviously the accuracy to attain a balanced fast rotating weight costs lots of money.

    It would appear to me that a cheaper method of providing stability is called for.

    This would only be suitable in craft where passenger comfort is more important than space.
     
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