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Author Topic: Dynamic Positioning/Automatic Station Keeping  (Read 3608 times)

nsa66

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Dynamic Positioning/Automatic Station Keeping
« on: May 14, 2010, 02:05:24 PM »

Does anyone have any idea whether it would be feasible to construct a ship which is able to maintain a fixed position by means of thrusters. I know that many full sized vessels such as survey/oil exploration/heavy lift ships use sensitive accelerometers to affect such control.

I'm thinking that maybe the gyros used in model helicopters could form the basis of such a system but, as far as I am aware, these are configured to detect rotation about an axis. This might work to prevent yawing, but in the case of pure lateral or fore-and-aft movement I'm not so sure - maybe some sort of flow sensor in a longitudinal duct combined with a similar transverse one amidships might provide the signal, but how to use this to control the relevant motors escapes me.

Has anyone any experience of such a system in a model ?
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Umi_Ryuzuki

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Re: Dynamic Positioning/Automatic Station Keeping
« Reply #1 on: June 03, 2010, 07:04:35 PM »

I have seen hydrofoils by Yoichi Takahashi, use gyros, on ailerons, to stay upright.

However, people I talk to about programing waypoints to run a model boat course say that
the GPS will not be accurate enough to maintain the 30-50cm accuracy to run through gates.

If you don't need anymore accuracy than 3 meters, 1.5m to either side of your position, then
it should be possible. :-)
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chingdevil

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Re: Dynamic Positioning/Automatic Station Keeping
« Reply #2 on: June 03, 2010, 08:16:07 PM »

Do not the flyers have a gps unit that does something like that, I am not sure of its name


Brian
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JayDee

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Computer Control
« Reply #3 on: June 03, 2010, 09:15:24 PM »

 Hello,

Have a good look at this video of a model helicopter which takes off, follows, and then lands back onto a model "Aircraft carrier".
All these moves are made without any Human input.

The only computer is inside the helicopter.
The device is radio controlled, but is shown flying on "Auto".

The presenter speaks of the system as being in its infancy.
Watch this space !!.
http://www.youtube.com/watch?v=XpUdW_U2KJ8&feature=player_embedded

John.  :-))
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Patrick Henry

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Re: Computer Control
« Reply #4 on: June 03, 2010, 09:20:39 PM »

That is amazing, well found. (just don't let AndyN see it....)


Rich
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Umi_Ryuzuki

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Re: Computer Control
« Reply #5 on: June 11, 2010, 03:44:54 AM »

Hello,

Have a good look at this video of a model helicopter which takes off, follows, and then lands back onto a model "Aircraft carrier".
All these moves are made without any Human input.

The only computer is inside the helicopter.
The device is radio controlled, but is shown flying on "Auto".

The presenter speaks of the system as being in its infancy.
Watch this space !!.
http://www.youtube.com/watch?v=XpUdW_U2KJ8&feature=player_embedded

John.  :-))

Very nice, but they have removed a lot of environmentals, such as wind, waves, and current.
Also they are tracking visually, and by infra red, not GPS. Visual tracking will work out doors, but
the infra red will be blinded by direct sunlight. 

If  the GPS to direct the vehicle to within visual range, then optical sensors could
get the vehicle through a gate. I am pretty sure that one of the High School robotic
challenges asks students to program a boat to
maneuver three gates.
Approach a harbor
Collect an object
Follow a reverse course through the gates
Deposit the object.

Programming is not one of my strong suits..  %)
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dreadnought72

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Re: Dynamic Positioning/Automatic Station Keeping
« Reply #6 on: June 11, 2010, 10:54:27 AM »

A solid-state accelerometer would be best. These cost about £30, measure up to 1.2g (plenty for a boat) and could be interfaced to a microprocessor to read the results/send commands to thrusters.

Would make for an awesome effect in wind/seas.

Here's the datasheet as a pdf. 2m g at 60Hz sounds like they'd be good to measure down to 0.1mm/s resolution. Wow.

Andy
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Circlip

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Re: Dynamic Positioning/Automatic Station Keeping
« Reply #7 on: June 11, 2010, 11:23:01 AM »

Oh dear, whos local boaty pond going to be the first to be showing an Oil slick??   %)

  Regards   Ian.
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John Mk2

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Re: Dynamic Positioning/Automatic Station Keeping
« Reply #8 on: June 11, 2010, 05:16:43 PM »

I know a gent who used a model heli gyro (via servos)  To auto adjust trimtabs on a fast leccy boat  And it worked ;) 
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malcolmfrary

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Re: Dynamic Positioning/Automatic Station Keeping
« Reply #9 on: June 12, 2010, 12:53:20 PM »

There's probably a difference between keeping a boat the right end up and maintaining a position on the water.  This probably stops the solid state gyros being useful for station keeping.
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Mankster

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Re: Dynamic Positioning/Automatic Station Keeping
« Reply #10 on: June 12, 2010, 02:09:01 PM »

The rather impressive Hexacopter in available to by commercially from the UK store including the GPS gubbins. http://www.youtube.com/watch?v=fyYujjP5J-k

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Re: Dynamic Positioning/Automatic Station Keeping
« Reply #11 on: June 12, 2010, 04:48:47 PM »

A gyro will only keep the ships head on course
The vessel will still drift ahead or astern or crab to port or starboard
albeit pointing the right way


Ned
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dreadnought72

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Re: Dynamic Positioning/Automatic Station Keeping
« Reply #12 on: June 12, 2010, 06:04:20 PM »

Yes - which is why the acclerometer would be the bee's knees for an application like this.

Andy
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flashtwo

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Re: Dynamic Positioning/Automatic Station Keeping
« Reply #13 on: June 12, 2010, 09:18:55 PM »

How about some visual system similar to the helicopter's, but based on visual cues from three shore based light sources.

Three light sources would be the equivalent of, say, red, green and blue, but in the form of pulse modulated infra-red beams to avoid ambient light interference. You need three points of reference to avoid the abiguity of just two. The beams would have to be wide-angled for good coverage.

The boat would have a rotating mirror  (much like a radar antenna) viewing its surroundings via a slit or collimator. The mirror would reflect the light down (same as a radar wave-guide) to a stationary detector (avoids slip rings for the electrical signal) which would send a pulse to a PIC processor.

The PIC would have knowledge of the relative location between the "red", "green" and "blue" lights and the current angle of the rotating mirror relative to the boat. There would be enough geometric data to work out the boat's exact position and heading relative to the three lights. Knowing the current and desired positions, the PIC would then be used to produce an error value for the control system to manipulate the directional motors.

If the beams are broken then the control system would have to retain and use the last good reading based on calculating the average position.


Anyone good at geometry?


Just a thought.

See Wikipedia   http://en.wikipedia.org/wiki/Range_lights for a light house version.

Ian
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JayDee

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Re: Dynamic Positioning/Automatic Station Keeping
« Reply #14 on: June 20, 2010, 11:15:35 PM »

Hello,

A little bit "off subject" but worth a look at, this Video is of a ROBOT playing POOL !!!.
Could this system be used for a self steering boat ?.

John.  :-))

http://blog.makezine.com/archive/2010/06/robot_takes_cue_learns_to_play_pool.html
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Umi_Ryuzuki

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