Pinta is born

16/01/2008 at 4:00 pm | Posted in Uncategorized | Leave a comment
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Pinta is our entry for the Microtransat challenge, a race of autonomous sailing robots across the Atlantic Ocean. She is named after one of Columbus’ ships. Our main aim is that Pinta is simple, reliable, durable and most importantly CHEAP. There is a very good chance that once we launch her we will never see her again, so we don’t want to spend too much money.

We have decided to use a topper Taz dinghy. This is a 2.95 metre long sailing dinghy aimed at children. Its built from fibre glass and has quite a bit of room inside the hull for batteries or electronics. The one we’ve bought is a sprit rig but we plan to cut the sail down to form a bermudan style sail.

We are using a Furuno Rowind ultrasonic wind sensor and a Furuno PG500 fluxgate compass. We used both of these on our previous boat, BeagleB and they worked very well. Both of these are NMEA devices and have a nice serial protocol which just throws out relatively easy to understand data strings at 4800 bits per second on an RS232 connection. A Telit GM862-GPS modem gives us both GSM (mobile phone) and GPS in one device. We used four of these to track all the competitors in the 2007 Microtransat Challenge. The sail is on a big winch with an electric motor from a car wind screen wiper. We are controlling it with a Daventech MD03 motor controller using a I2C connection. The rudder is controlled with a Simrad TP22 tiller pilot designed for a yacht. This has its own compass in it and will perform course corrections itself. Two buttons control the left and right movement of the rudder, so we can use these as a manual control to get ourselves on course and then put the tiller pilot in automatic mode and have it just hold that heading. All of this is controlled by a Gumstix single board computer which gives us a 200mhz ARM processor, 64 mb of RAM, 4mb of flash memory, compact flash slot and 3 (4 if we don’t use compact flash) serial ports, I2C and over 20 general purpose I/O lines. For extra I/O we’ve also got a Daventech GPIO14 I/O extender which gives us 14 I/O lines which we can access over I2C. This is used to interface between the Gumstix and the tiller pilot. The Gumstix runs a really cut down version of Linux but its more than adequate for running a sailing robot.

We’ve got 3 20 watt (peak output) solar panels and two solar charge controllers for redundancy. There are 16, 7 amp hour, 12 volt lead acid batteries. These should be enough to run the boat for about 10 days without solar panels. Our target power budget is only around 5 watts.

There’s also an Iridium 9601 Short Burst Data satellite modem. This should provide us with communications anywhere in the world. Annoyingly the Gumstix only lets us use 3 of its 4 serial ports when the compact flash wireless network card is connected. As the compass, GPS/GSM and wind sensor each need a serial port that means we have a choice of either having the wifi plugged in or having the Iridium plugged in. As we haven’t yet activated our subscription to Iridium we’ll stick with just having wifi for now.

In the photo you can see the Rowind at the top of the mast. The tiller pilot is connected to the back of the boat. The white box sat on the deck contains all the electronics. The solar panels can be seen off to the left.

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