Going miniature30/08/2011 at 10:04 pm | Posted in Uncategorized | Leave a comment
Over the last month we’ve been preparing one of our 72 cm long Miniature Ocean Observation Platform (MOOP) boats for a sea voyage. Up until now these boats have only been sailed over short distances, mostly in lakes and under close supervision.
For the last month as part of a project we’ve been trying to build a really simplistic controller for the boat, to see how little we can get away with while sailing it at sea. We tried to build a purely analogue controller, which we could keep the boat on course with respect to a given compass heading. It used a pair of opamps to compare the output of the compass (which was a PWM signal transformed into an analogue voltage) with a potentiometer. One of the opamp outputs would drive the rudder motor (a servo without its control board) left, the other right. Unfortunately there was a problem with this circuit which we could never get to the bottom of. This was causing the opamps to short circuit and blow up under certain circumstances. So we decided to replace the opamp system with just a basic microcontroller, which just read the compass and set the position of a rudder servo. The target heading is determined by turning a potentiometer, which is read through one of the microcontroller’s analogue inputs. The sail is just fixed in a beam reach position and is made from part of the cloth from Pinta’s original sail (which we placed before her transatlantic attempt). There are 5 size F 13 amp hour, 1.2 volt NiMH batteries, we think these should be enough for a week or two of sailing. The only other component in the boat is a SPOT satellite tracker, which has its own microcontroller that presses its “ok” button every hour causing it to transmit its location. The SPOT uses its own batteries, so even if the main batteries go flat it should continue to transmit.
Tomorrow we plan to launch the boat from a few miles offshore and sail her back onto the large sandy beach at Ynyslas, a few miles north of Aberystwyth.