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Hello to the Little Red Daemon

By Dermot Tynan, over 8 years ago.

After much tweaking and hacking with configuration files and kernel build options, I finally have a FreeBSD 8.3-RELEASE kernel and install running on a Wrap board. Technically, it's NanoBSD, which is a scaled-down FreeBSD install, which boots from Compact Flash. The WRAP board is the PC Engines forerunner to the ALIX. When National Semiconductor and AMD stopped making Geode chips, the guys at PC Engines had to stop making their very popular WRAP board. I still have a few of them tucked away, for emergencies such as this.

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Battery and Solar Design

By Dermot Tynan, over 8 years ago.

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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The Software...

By Dermot Tynan, over 8 years ago.

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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Five Degrees of Wrong.

By Dermot Tynan, over 8 years ago.

So, as I mentioned, the virtual boat was too eager to tack. If you're dead downwind of the mark, and you set off on a starboard tack, within a metre of being on the left-hand side of the course, the other tack is favoured.

I added code that essentially stated "unless the other tack is at least five degrees better than the existing one, ignore it." So, if I'm at 44 degrees TWA and the other tack is better by a degree (-43 say), stay where you are. This works quite nicely. If you look at the plotted course, it shows the boat sailing nice upwind legs, to the waypoint. As Henry would say, "it's sailing up the ladder."

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Polar Curves

By Dermot Tynan, over 8 years ago.

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.