Miniature Ocean Observation Platforms - Aberystwyth University

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Nov 15, 2013 (3 years and 8 months ago)

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Summer 2011
Nuffield Science Bursary Project
Duncan Horne Ysgol Penglais School, Aberystwyth
Miniature Ocean Observation Platforms (MOOPs)
and the Analogue Boomerang Control System
‘Anacrusis’ on its maiden voyage: towards the Llyn Peninsula
IntroductionThe aim ultimately is research into power consumption and oceanography. It costs thousands of pounds for a ship and oceanographers to collect similar data to that which a MOOP could collect. It would be highly cost effective if a small ship could be developed which costs less, can repeat the task over and over, needing minimal maintenance. The project was to develop an analogue control system which would return a ship to the coast when the digital control system failed, thus saving the equipment from being lost at sea. In this situation an analogue system is superior to a digital system because there are fewer processes which can potentially fail. Prior to this work on MOOPs, tests were in a lake environment so this was a step forward for sea investigations.
• The Nuffield Foundation for funding, and Bryan
Hatton / Tina Hibbert in Wales
• The Computer Science Department (Aberystwyth
University) – especially Dr Colin Sauze and team
• Dr Debra Croft (Centre for Widening Participation and
Social Inclusion, Aberystwyth University)
With thanks to
Method•
The MOOP ‘Anacrusis’ is a 72cm
long, autonomous sailing vessels of epoxy resin coating on fibre glass, with thick bow and keel for sturdiness and rigidity. It is slow, with a high drag factor.
• Power supply 4 x 1.2V 13A hr
NiMH batteries

Magnetic rudder design (2 capsules of 4 magnets): one attached to a Futaba 2BB MG servo
and the other to the rudder shaft. This magnetic connection allows for misalignment in case of collision, etc. and realignment when the boat comes about.

A cloth sail was attached to a mast; a beam to a central screw on the stern deck, by a wire,
to a good sail in most winds without the sail flipping entirely in reverse. This replicates
the analogue control conditions.

Analogue Boomerang Control System (ABC) – in case of digital failure the ABC was
planned to be a rescue system. A pair of power op-amps compares compass heading with the ‘home’ bearing set by a potentiometer. When the digital circuit detects a fault,
the control system flicks to the ABC, and the digitally controlled potentiometer shows the ‘home’ position. (See paper for full details of this, however, despite many tests under lab conditions, faults remained within the time scale and a digital system was used in order to continue with the MOOP experiment).
Results
(See paper for full details; contact wpsi@aber.ac.uk)
A PIC18F4550 microcontroller, a Futaba 2BB MG servo and a HMC6343 compass were mounted on the MOOP and some simple code was added to control the rudder about a certain direction. A SPOT GPS tracker was mounted horizontally under the deck to track the MOOPs progress. At approximately 16.30 on the 31st August 2011 the MOOP ‘Anacrusis’ was launched 7 miles out from the shore of Aberystwyth with a desired heading of the Llyn Peninsula in North Wales. The SPOT GPS e-mailed the coordinates once an hour. Using appropriate software we were able to automatically map out the course it had taken and
compare this to the desired route.
Discussion & Evaluation
The actual course sections
were convoluted on Sunday
through to early Monday &
Thursday through to Friday.
Using www.wunderground.
com/MAR/buoy/2011/8/1/62301
(Aberporth buoy) data, this was when the wind speed topped
23 kph and when the dominant wave height rose above 0.9m.
The reason the direction was
affected so much is because there was no sail control so the MOOP could not tack. The wind may have been strong enough to push the sail hard over so that the boat was nearly horizontal in the water and unable to sail in a specific direction.
ConclusionThis is probably the longest voyage that an autonomous sailing robot has made with a functioning control system. These results have provided much information into the future of MOOPs as autonomous sailing vessels: they are robust, relatively cheap and can sail independently. With the addition of a sail servo and an improved sail design, sailing would be better and in potentially difficult environments. A set of solar panels generating more electricity than the system needs would enable it to sail indefinitely.
Desired course
GPS coordinates track (actual course)
www.aber.ac.uk/wpsi