This day of the 2015 Bridgestone World Solar Challenge was not as typical as some of the other days had been. The night before we had decided to not start driving right when we could at 08:00 but rather at 10:00. In the morning with the sun at such a low angle it is possible to get a lot more power by tilting the array towards the sun than having it face straight up. We had decided that at this point it was best for us to spend an extra two hours of extra charging than to start driving with a less solar power and less energy in our batteries. After two extra hours of charging it was time to get back on the road. It began to seem like it would be another calm day of driving, however Murphy’s Law had other plans. Quickly after starting driving the same problem from the day before popped up. Once again some messages from the battery management system were getting dropped and causing Arcturus to turn itself off in order to be safe. After a few times of this the electrical engineers decided it was time to pull over and try to figure out the issue. The electrical engineers worked very hard to debug the issue and ruled out many possibilities, but in the end they weren’t able to pin point the root cause. The problem did not prevent the car from driving safely, it just made it difficult to drive for long periods of time. We decided that it would be best for us to get on the road rather than spend the day continue to debug this issue. We managed to drive to Glendambo on solar power. In Glendambo we then loaded our trailer and drove until sunset to make sure we could make it to the next control stop.
Day 5 of the 2015 Bridgestone World Solar Challenge began more routinely the previous day. This day we were going to be driving on solar power, and would not be trailoring. We were able to start charging at sunrise, and then left promptly at 08:00. It was smooth driving until we had a few minor electrical issues around 11:00. We pulled over, and found the issue and were able to fix it in less than ten minutes. We then kept driving until the Coober Pedy control stop and arrived at 13:00. An hour later a new issue occurred. Some of the messages between the battery management system (BMS) were being lost. The battery management system monitors the batteries and makes sure they are operating safely. The car was missing a very small percentage of the messages from the BMS and the batteries were fine, but the car shut itself off just to be safe. After this happened twice we decided to pull over, and replace the cables between the main board and the BMS. This helped fix the problem. We then were able to keep driving until we made camp for the night. Our campsite ending up being 125km from any city.
So you may have noticed that there hasn’t been an update for a while. I apologize about that. The thing is that we are all students and do have classes. Unfortunately I was hosed in classes and rushing to get done by the Friday midnight. Now I do have some time again so here’s the updates that were missed over the past few days.
Day 4 started even earlier than usual for us. While trailoring we are allowed to drive from sunrise to sunset. For this we had to get up early enough that we are able to leave the camp-site and make it to our stop point from the previous day by sunrise. We then drove until the next control stop at Alice Springs. At this point we decided that the best strategy for us was to not unload this point, but to continue to the next control stop. So we waited there for the required half hour, and then we drove on to the next control stop at Kulgera. At Kulgera we quickly unloaded and started driving again at 12:00. However though due to the trailoring we had missed all of our potential charging time from the previous day and part of this day so our batteries were not nearly as charged as we would have liked. We were able to drive for another four hours with no issues. We did decide that it was better at 16:00 to be charging instead of driving since it would be better to charge with a titled array. At that point we stopped for the day and began filling our pack back up again.
Day 3: the team had just recovered from an electrical issue the previous day, but we were ready to go. That morning we were able to have another on time start and were driving promptly at 08:00. Along the way one of the Maximum Power Point Trackers (MPPT) had some issues. The electrical team was able to diagnose the issue while we were driving and decided to replace the bad MPPT after the next control stop. We were able to make it to the Tennant Creek control stop with no other issues. However we knew that at this point we would not be able to make it to the next control stop before it closes. The Bridgestone World Solar Challenge requires you to make some minimum progress each day so that the challenge does not end up dragging out to be a few week event. If you are not keeping up with this minimum progress requirement you are required to load your car into a trailer, and tow it to the next control stop. Once you have trailered though you no longer are competing for the fastest finish but rather for completing the most solar kilometers. For strategic reasons we decided to keep driving on solar as long as we could before we had to trailer. This lead to us driving until about 16:00 at which point we loaded Arcturus into the trailer and kept on going. We drove as far as we could until sunset which is when we had to stop driving. Where we stopped though wasn’t a good camping spot, and there was a camp ground 20km back. We marked the spot by putting a team shirt on a termite mound, and went back to the camp ground. It was wonderful to be able to shower at the camp ground.
Check out pictures from the day on our Flickr.
On the morning of the second of the 2015 Bridgestone World Solar Challenge spirits were high on the team. We had a full day of driving with no incident, we were in the outback, and had a relaxed easy night. The Challenge was going well for us. We were able to start the day driving promptly at 08:00. We were able to drive non-stop to the next control stop at Dunmurra. We decided to spend a few extra minutes at the control stop in order to reprogram our car to allow for a pseudo-cruise control. Since Arcturus has two hub motors it is not possible to just have the motor controllers run the motors at the same speed. This is because when you turn the two wheels will have to spin at different speeds. Instead we have the motor controllers maintain the same torque for both motors and this will automatically adjust each wheel’s speed as the car turns. Our pseudo-cruise control sets a maximum torque for the motors, and this indirectly acts as a cruise control on level terrain. This was able to improve our efficiency by reducing the small fluctuations in speed that the drivers caused.
However the day did continue go this well. Early in the afternoon the driver smelled something strange in the car. The team immediately pulled over and responded very quickly and well to the possible emergency. Within thirty seconds we knew there was no emergency, and began trying to figure out what went wrong. Once we opened the car we found a wire that had shorted due to rubbing. We then had to spend a few hours on the side of the road making repairs. First we replaced the shorted wires, moved the wire so it wouldn’t rub, and added more protective nylon sheathing. Once this was repaired we found out that the short had burned out most of our Maximum Power Point Trackers (MPPT). These boards step up the solar array voltage to the voltage of the batteries and the motors as efficiently as possible. Once we had replaced and tested all of the damage boards we had just enough time to get on the road and drive a few hundred feet to a better campsite. After stopping we only needed to change out tires and make a few minor changes.
The start of an adventure; always an exciting day. The team needed to be at the start line nice and early to have Arcturus in place for the public to see, and to get ready for the actual beginning of the challenge. It was nice to see all the other cars all ready to go and in pristine condition. Most of the team wasn’t actually able to see Arcturus start the challenge though because we had to wait in the escort vehicles. For driving on the Highways for the 2015 Bridgestone World Solar Challenge each solar car has a rear “chase” and front “lead” escort vehicle which have flashing amber “crazy” lights to warn the other drivers on the highway. Arcturus crossed the ceremonial start line and the officials worked it out perfectly so Arcturus slipped in right between our lead and chase as it entered the street, and we were able to just go. For the first hour of driving it was rather exciting because we were inside Darwin so there was a lot of traffic there as well as most of the teams were trying to pass each other while we were all bunched up. During this stretch of the route there were a lot of locals sitting on the side of the road watching us go by and cheering all of the teams on.
After getting onto the Stuart Highway, and leaving the city the driving became a lot calmer with the lesser traffic. We started to enter the rhythm of driving and just go at a nice steady pace. We drove straight until the control stop in Katherine. At control stops we are required to stop for a half-hour and can not work on the car, but we can charge the batteries. We used this time to tilt the array and charge better, and also change out our drivers, so they didn’t get tired. We were a little under practiced with control stops and ended up leaving Katherine a few minutes late. Once we were back on the road it was smooth sailing until the end of driving for the day at 17:00. We happened to stop next to a WWII memorial with a large pullout that we were able to park at along with TAFE SA. TAFE SA is a very nice team, and they helped us with beading some very difficult tires. After we stopped driving we started charging, and checking the car out. Luckily all that needed repair was that the tires needed to be switched out, which we expected.