The final day of testing.

10/09/2010 at 8:55 pm | Posted in Uncategorized | Leave a comment
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Today was our final day of testing Pinta before we launch her into the atlantic. We sailed a triangular course quite sucessfully and then we did it again and sailed the full triangle followed by the reverse course. This is because in the past we’ve found that bugs (usually wrap around issues in heading changes) in our control system haven’t been found by just doing a course one way. Everything worked pretty well. The only issue we had was that our compass was intermittently giving a heading of zero. The compass uses a PWM based system and we just use a while loop on the PIC to read the pulse width. Its possible that there’s a bug in this code or that’s there’s a loose wire somewhere. The compass is currently encased in a block of epoxy so its too late if its a problem that end. This basically leaves us with two workarounds, we can either average the compass heading over a few seconds, doing this takes time and slows down the control system and it means we’ll average out genuine movement too. But since our control system works by entering a target heading offset into the tiller pilot (which uses its own compass to steer), this shouldn’t be a major problem. The other idea is to just use the GPS heading. This requires us to be moving forwards to give an accurate answer and if our speed drops below about 1km/h the heading will be meaningless. The advantage is it actually measures course made good, not the direction the boat happens to be pointing in. When trying to sail into the wind these two can differ significantly. It also gives us a true rather than magnetic heading and means we aren’t at the mercy of any magnetic anomalies. In the end we decided to opt for the GPS instead of the compass. Hopefully we’ll be able to maintain sufficient speed that it won’t cause us any problems.

We still have to tidy up a few loose ends in the software and make a final decision about our waypoints tonight. Then tomorrow we’ll load in the final version of the software, remove power switch, wifi access point and network cable and seal the box with everything turned on. Then we’ll tow Pinta a few miles out to sea before leaving her to make her way to Martinique.

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