Posts Tagged “GPS”

I love it when a Plan comes together...

The ALIX 3D2 board under power, talking to a FreeBSD development system.
The ALIX 3D2 board under power, talking to a FreeBSD development system.

The new ALIX board has arrived. It’s to the left of the picture, sitting on top of a copy of the infamous Lyon’s Notes (which is appropriate). Also, the initial Atmel board with USBtiny programmer cable, serial cable to same development system, and a couple of WRAP boards thrown in for good measure.

It’s running my custom version of NanoBSD quite nicely, and can see the GPS without any difficulty. The GPS unit is a BU-353 unit (the USB version) which is out of the shot. It’s attached to the window, and gazing at the man-made stars. To give a breakdown of what’s in that photograph, the ALIX is on the left. In the USB port is the GPS, the RS-232 cable at the top of the board is communicating with my development machine (running FreeBSD). The red CAT5 cable is connecting the board to the “house network.” The Atheros CM9 radio is a miniPCI card mounted on the underside of the board. It works on 5.8GHz and on 2.4GHz. In this case, I’m using 5.8GHz because (apparently) it has better cross-water characteristics and the band isn’t as crowded. The mini coax cable is at the top-left of the picture, connected to a short, 9dBi antenna. You can also see a 12v cable with barrel plug. At the top-right of the picture is a WRAP board, also developed by PC Engines. It was being used as a testbed for the operating system, but that is no longer needed thanks to the ALIX.

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Wind Direction Indicator

Now that the hull is looking solid, it’s time to start thinking again about the wind direction indicator. It is possible to detect wind speed by using an ultrasonic sensor and receiver, and measuring the delay between the two. You need to account for temperature changes and gusts can cause issues, but it is fairly reliable and has no moving parts. Generally, you use two transducers offset by a distance of perhaps 20cm for the North/South computation, and another pair in the East/West direction. I think if we were using a larger hull, such as a 4m boat, this would be a good plan. But, for the 2.4m (or the 1.2m) boat, it’s just too big and awkward. Also, this jury is undecided about how well they would work, over the long haul.

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Bon Voyage, Snoopy!

The 'Team Joker' entry in the Microtransat race, with Snoopy on the foredeck, keeping the boat safe from marauders.
The "Team Joker" entry in the Microtransat race, with Snoopy on the foredeck, keeping the boat safe from marauders.

Today, March 23rd, Team Joker are planning to launch their ninth boat, Snoopy Sloop. This has been an educational (and obviously fun!) experience for Robin Lovelock and his fleet of robotic warrior boats. Here in Beoga Beag land, we wish them well.

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Of Laylines and Beats

A Google Earth track of the virtual boat attempting an 'Olympic' course.
A Google Earth track of the virtual boat attempting an "Olympic" course. The course is to go from the leeward mark upwind to the windward (or weather) mark, sail across to the gybe mark, gybe (obviously!) and sail down to the leeward mark. After that, sail up to the windward mark again and then straight downwind to the leeward mark.

On the left, you can see the track left by simulating the Beoga Beag navigation software. It’s a short, olympic course suitable for dinghies and smaller boats. For a dinghy race, the whole thing should take less than an hour so the legs are quite short.

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The Software...

The FreeBSD Daemon, ready to take on Neptune and his cohorts.
The FreeBSD Daemon, ready to take on Neptune and his cohorts.

I’ve been asked recently, about the software platforms used on board Beoga Beag. This seems as good a time as any, to talk about the various layers. As mentioned previously, the lower layer is a custom board, running an ATmega8 Atmel processor. The software (Igor and Otto) is custom-written in C for the boat.

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Battery and Solar Design

Sealed Lead-Acid Battery
Sealed Lead-Acid Battery.

Looking at the system power design, the majority of the circuits will run off a +5 volt rail. Those elements which need a different voltage, such as the main processor board, will derive their own requirements from the main Vcc rail.

There will be at least two Vcc busses on board. Labeled, oddly enough, as Vcc1 and Vcc2. The difference between them is that Vcc1 is always on, at all times, and Vcc2 (through VccN) are selectable by Igor.

The main processor runs off Vcc2, but Igor (and Otto) both run off Vcc1. In situations where voltage levels are critical, Vcc2 will be switched off and the boat will continue on whatever course had previously been set, until either voltage levels are healthy, the specified “wake-up” time has elapsed, or there are critical issues which require Mother to get involved. A critical situation could be something like a dramatic wind shift, or an error such as a mis-reading from a sensor.

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Polar Curves

Polar curve for a Figaro, courtesy of SailOnline.
Polar curve for a Figaro, courtesy of SailOnline.

Even before a boat is built, the designers can predict how fast it will go at various sail angles. Using this information, they can make modifications to the hull to suit the type of sailing. For example, if an around-the-world race looks like it will see a lot of downwind sailing, it’s possible to optimise the downwind performance, and run test simulations with the boat, before ever committing to fibreglass.

The standard mechanism for displaying this information is a polar curve. Because the boat should sail at the same speed on either tack, only one side is shown. Essentially, a polar curve allows the designer (and the boat owner) to predict the hull speed for a particular true wind angle and strength. In the example above (courtesy of SailOnline.org), you’ll notice that the boats fastest speed is at a true wind angle of about 120 degrees. In the case of a 30 knot breeze (the red line), the boat should get over nine knots through the water. At TWA’s of twenty degrees and less, the boat will stop, regardless of the wind speed.

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