ArduBoat: Any way to have it hold position against current/wind?

Posted by AntimatterCrusader on September 24, 2015 at 5:40pm

Hello! I am rebuilding an old APMBoat from a few years ago, and at the time was unable to find a way to get the boat to hold position. When it reached the final waypoint, it would just stop and float with the current/wind. The only thing I was able to do is have it change speed and repeat a pattern with the DO_JUMP command very slowly. 

But that wastes power - is there a way to get it to return to a location if it drifts a set distance away? 

I was thinking I would use a geofence, but it looks like that capability is not implemented iwth APMRover. 

Any workarounds, suggestions? 

Thanks!

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Replies

    • Darius Jack > Darius Jack December 11, 2015 at 8:37am

      and finally
      ready product to meet your request

      Skyhook Digital Anchor

      ==

      https://mercurymarine-gsdesign1.netdna-ssl.com/media/filer_public/e...

    • David Boulanger > Darius Jack December 11, 2015 at 8:48am

      Station holding would be nice but would use constant power as opposed to drifting outside a radius and the powering up to the original loiter point.

      Regards,

      David R. Boulanger

    • Darius Jack > David Boulanger December 14, 2015 at 11:59am

      David,

      we have simulated and tested either case.

      Electric thruster is PWM controlled, so speed can be slowly slowed or increased

      so no use of contant power.

      Drifting outside a radius can require more energy spent since water current

      is not accelerating a drift speed of a boat as the wind does.

      So acting promptly less energy can be required to stop slow drifting boat and float it back, than a boat drifting at accelerating speed.

      We are just testing 3 electric thrusters to act as a digital GPS-based anchor

      (abbr. to GPS Anchor)

    • David Boulanger > Darius Jack December 14, 2015 at 12:21pm

      Darius;

      Depends on the mission.  Drifting a few hundred meters may be O.K..  So using energy to stay in one spot may not be the best choice.  I do understand what you are saying though.

      Regards,

      David R. Boulanger

    • Darius Jack > David Boulanger December 14, 2015 at 12:42pm

      David,

      I am flexible.

      Electric thrusters preordered.

      Discuss today mounting points.

      One front thruster to move a boat to turn around to fix heading against wind direction/ water current vector superposition.

      Individual electric thrusters can be wired or autonomous, radio PWM  controlled.

      Plan to test 2 underground scooters mounted on the sides.

      Costs and spending should be limited, mounting and deploymont easy.

      Inflatable pontoon/ boat is planned for use to test control algorithms/modes.

      I would be very happy if only one another man on the globe is interested to develop this GPS Anchor, open-source open-hardware project.

  • Darius Jack December 11, 2015 at 6:48am
    Bruce,


    "A boat will drift at a max speed of 0.5 m/s"

    Did you make any study on the max drift speed or the above is just your speculation ?

    "
    Even full size boats don't drift much faster
    "

    @Bruce,

    drift speed is exactly inversely proportional to the mass, tonnage, size of the ship since underwater part of the ship cannot move fast and the drift speed is slowed down in water environment.


    " unless there is high winds, in which case the size of the waves would be hazardous to a model boat.
    "

    exactly the case, so weather report, external anenometer is a must to discover wind speed and direction ahead of any test run.

    Pls read the book
    Coastal Navigation Using GPS by Frank L.Larkin, selected scanned pages are available via Google Books.
  • Steve Hoeckley December 9, 2015 at 10:50pm

    Linked are a couple of papers from Florida Atlantic University that present a station keeping PID controller that uses GPS and heading sensor inputs.  They were tested off-shore in the Gulf Stream in small craft with good results.  Looks simple to implement as they use X and Y errors driven by the prevailing wind and seas to generate a desired heading.  Then the distance and heading error, and the heading change rate are used as inputs to the control algorithm for throttle and rudder/engine angle control.

    http://ntrs.nasa.gov/search.jsp?R=20110009965

    http://coet.fau.edu/sites/default/files/research/theses/DT-10-342.pdf

    • Darius Jack > Steve Hoeckley December 10, 2015 at 6:47am

      Hi Steve, nice papers. But nothing looks simple to implement. 1. No wind, no ocean current - problem solved 2. Unlimited energy supply - problem solved 3. No ocean current, wind only, direction and speed known you control your motor boat like a sail boat 4. No wind, ocean current only, build underwater boat since over water part is not relevant Since energy source is limited I would start from energy management algorithm to meet the target (hold position of the boat/station against wind/current) Since wind direction/heading can be sensed and calculated on-the-fly I would start from developing ocean current reliable sensor/s. Free floating probes could do the job (GPS/radio link for data transmission) Ok, geolocation of the target is fixed and geolocation of your boat is exactly the same, motors are off to let us test your algorithms (reverse control simulation) in case of free floating boat. Floating against the wind, against the current

    • Bruce Baxter > Darius Jack December 10, 2015 at 9:52am
      For what he wants, just a simple heading towards the waypoint and throttle proportional to the distance would be enough.

      He isn't after station keeping for an oil drilling platform, just something so the boat doesn't float out to sea.
    • Steve Hoeckley > Bruce Baxter December 10, 2015 at 11:59am

      If you zero the gains (or don't write the code for) the integral part, which slowly closes the error over a period of time, and the derivative part, which smooths out the operation, that's exactly what this does.

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