Blog 25th to 27th: Darwin to Alice

October 25th

Before dawn, the solar car gets trailered to the supreme court car park. Later, I and the other drivers join it. We're in a regular car parking bay, with Willetton on the side closer to the start line, and Cambridge on the other side.

The telemetry (heads!) works. I zero out the telemetry numbers.

Everybody stands around for a while. Members of the public mill around too. Peter Schloite comes through and shepherds everyone off.

I go to the follow car where I plug the telemetry laptop in to power. The power is a home-made 3-way cigarette lighter splitter. Unbeknown to us, the plug on it that plugs into the car socket has a 3 Amp fuse. John turns the key. The laptop beeps: it has power. The laptop beeps again: it has lost power. The fuse has blown.

Last year, cars left the start line at one minute intervals. This year, we've been hearing rumours of two minute intervals. In fact it turns out to be about 30 second intervals. Solar cars are coming off the line and being joined by their lead and follow vehicles, causing a non-trivial quantity of traffic. We wind up waiting several cycles of the lights to turn right onto Daly Street. Daly Street becomes Stuart Highway, and we're away.

Several hours out, the motor suddenly stops pushing the car. We don't know why. We pull up on the side of the highway and give it a look. I put the pyrometer on the motor to measure its temperature: it's at 146 degrees. That's at least 20 degrees hotter than we've ever had it.

There's a certain temperature above which the magnets in the motor stop being magnets, and the motor therefore stops being a motor.

I spray water on it.

We mark our point on the road, put the solar car on a tow rope, and tow forward to a side road.

A Kormilda car shows up. We send them shopping for the fuse we need.

I spray more water on it.

It turns out that our motor has a thermal cut-out. This is designed to prevent the motor from getting hot enough to demagnetise. We didn't know this motor had one. Eventually it trips back in, and the motor runs again.

But the motor has a large thermal mass and is surrounded by an insulating epoxy, so it only cools very slowly; and it is all too willing to heat up again. It cuts out twice more during the day. We become adept at pulling over before it cuts out, and spraying water on it.

We trailer forward to the control stop at Katherine, and end the day there. We have solared 181 km for the day.


October 26th

Dawn patrol take the car back to the control stop to charge. We join it before 8am, and solar out of Katherine.

One of the many oddities of our telemetry (heads!) is that the motor controller's opinion of the bus voltage as displayed in the car is correct, but as displayed on the telemetry PC in the follow car it's wrong. As we solar, I install Visual Basic so that I can edit the telemetry software.

Just short of Mataranka, the car runs slower and slower: the battery pack is flat. We pull over to charge.

As the battery pack rises back towards its nominal flat voltage, I can compare the voltage displayed in the car with the telemetry number. It turns out that it's too big by a factor of exactly 3.6.

After a couple of hours of charge, we solar on. After 163 km solared for the day, it's time to trailer forward to Dunmurra, to get there before control stop closes. Every other tail end team is there, too. The Challenge is now much shorter than it used to be, and control stops close correspondingly earlier. So the entire trailer pack (all those cars that have been forced to trailer to make a control stop) are very bunched up.

At the control stop we talk to a northbound trucker, who tells us of a large dust storm to the south. We trailer forward to Renner Springs. Again, every other team has the same plan, so six solar cars camp together. The setting sun is dimmer than a full moon would be under a clear sky.

The dust clears a little during the first half of the night, but then the wind picks up, the tents blow around, and a slow rain of grass and leaf shards fall in through the vent at the top of my tent.


October 27th

We charge under a dusty sky, trailer forward to the Tennant Creek control stop, serve our half hour, then trailer forward to just short of Alice Springs. Australia (or at least Australia as cross-sectioned along the Stuart Highway) is shaped approximately like a peaked roof: uphill the first half, downhill the second half. Just short of Alice Springs is where it turns the corner.

We set down 65 km from Alice, solar past the Tropic of Capricorn, past a marker declaring this to be the highest point on the Stuart highway, and on downhill.

The car pulls more amps than we'd like. The battery, therefore, runs flat faster than we'd like.

The Alice Springs control point has moved (again). This time it's in a hotel well off the highway. There are directions in the route notes, but they are not entirely obsessively complete, and so following them while our battery dips lower and lower is rather stressful.

Nevertheless, we find the control stop and check in, at 18 minutes to 5. That means we'll have to serve another 12 minutes tomorrow. At dusk we put the car in the trailer and go to the MacDonnell Ranges caravan park for the evening.

-- Doug Burbidge http://dougburbidge.com/