11 Oct Stanford Places Fourth in 2013 Bridgestone World Solar Challenge
After five days of racing 3000 kilometers (1864 miles) across the Australian Outback the Stanford Solar Car Project placed fourth in the 2013 Bridgestone World Solar Challenge. This year’s team finished ahead of all other American teams and completed the challenge with the best finish in Stanford’s two decade history of international solar car racing. The team also came in as the top competitor among undergraduate teams and the top competitor among teams with full time students.
Stanford’s fourth place finish was the culmination of two years of dedicated work by volunteer students at Stanford University. The team began designing our car in 2012 with the goal of building the most reliable, yet efficient, vehicle possible. Today, Luminos, Stanford’s 2013 solar car, has over 10,000km on its odometer, and the vehicle crossed the entire Outback with zero component failures.
Static & Dynamic Scrutineering
Before the competitors in the 2013 race set out from the coastal city of Darwin, all teams had to complete a series of rule compliance and safety checks. The process, called scrutineering, requires all teams to allow race officials to inspect their vehicles before the race begins during a four hour inspection session. Event officials inspect everything from driver vision to brake lights. Luminos passed all stages of static scrutineering on the first try, except for a rear-vision camera problem that was solved with a quick software fix.
Upon completion of static scrutineering, Luminos underwent dynamic scrutineering – including a braking test and “flying lap” around the track to determine starting position in the race. With a lap time of 2:07 around the Hidden Valley Raceway, Luminos was the third car at the starting line.
The 2013 race began at the Parliament House in Darwin on the northern coast of Australia. Teams were released at the starting line with a one minute gap between teams. Day 1 began with a frenzy of teams attempting to claim a competitive position in the race. In the first hours of the race Stanford exchanged positions with the Nuon Solar Team and the University of Michigan Solar Car Team multiple times, passed the entire Michelin Cruiser Class field, and passed a number of other solar cars broken down on the side of the road. Luminos arrived at the first control point of the race (the city of Katherine) in 3rd place! The rest of the day was spent in a tense race between Stanford and Michigan – culminating in camping on the side of the road just a few hundred yards from our Ann Arbor rivals.
Day 2 was an equally close race between Luminos and Generation, Michigan’s solar car. Just a few kilometers away from each other, our teams sent convoy vehicles to spy on the speed of each other. After the Tennant Creek control point, we opened the gap with our arch-rivals and steadily pulled away over the course of the next few days.
Day 3 was significantly more mellow, with no teams in direct sight. We continued along at a steady pace until 5pm without incident. By the end of day 3 our team still followed Nuon (Netherlands), Tokai (Japan), and Twente (Netherlands).
Day 4 held the strongest winds of the race with reports of gusts close to 100kph. While other teams struggled to keep their cars driving safely and on the road our drivers reported that the car was extraordinarily stable and “handled the winds like a dream.” During the heavy winds one of our competitors flipped their car, and the University of Michigan team also crashed their car in the gusty wind. Winds fortunately were primarily at our tail, and our weather forecasts predicted that the winds would reverse direction the next day. Thus, we spent the majority of the day with the pedal to the metal (rather, to the carbon fiber), and we were only limited by the top speed of our motors. We at times cruised around 95-100kph (59mph- 62mph), speeds faster than we are allowed to drive on the 55mph limited roads in our United States testing areas.
Our team had seen that Twente, the team ahead of us, had previously spent long nights working on their car, so we suspected that Twente could be prone to further stress and breakdowns. With Twente close ahead the team chose to diverge from our theoretically ideal cruising speed in order to put additional pressure on Twente hoping they would make further mistakes. The danger with this strategy was that we would have an undercharged pack on the last day of racing. However, our team knew that the next competitors behind us were far away, so we were willing to accept the risk in order to possibly pressure Twente into making suboptimal racing decisions on the last day of racing. Later in the day Solar Team Twente had at least two break downs, and our team continued gain on Twente. By the end of day 4 our team had closed the 45 minute gap to Twente to just six minutes.
Day 5 began with both a headwind and more rain than our weather models predicted before the race began. Our team knew that we were close to Twente, and we wanted to be right behind Twente if they broke down due to additional mechanical problems or rain damaging their electronics on the last day of racing. We chased patches of sun and followed Twente to the Port Augusta control point. However, midday rain and a low battery pack charge in Luminos allowed Twente to defend third place in the afternoon. Twente ended up driving an apparently problem-free last day of racing, so our team didn’t have an opportunity to close the final gap and pass Twente. Luminos had expended a large amount of battery pack energy attempting to catch Twente, so we ended up driving much of the last day at 50kph. We reached the official end of timing just outside of Adelaide at 4:31pm securing our standing in fourth place after crossing the continent on the power of the sun. Twente, Tokai, Sunswift alumni and surprise SSCP alumni were there to greet us as we celebrated Luminos’s 2013 finish.
The next day we drove the car across the ceremonial finish line to join Nuon, Tokai, and Twente at Hindemarsh Square. Nuon thought ahead to make up for the lack of the traditional fountain at the finish line (past races have finished in Victoria Square fountain which was under construction this year). As soon as we completed our finish line photo-op, we found ourselves tackled and thrown into the three kiddie-pools they had filled up nearby. It was the proper finish of a solar car race. The rest of the day was spent asking and answering questions about cars, swapping shirts with other teams, cheering on other arriving teams, and otherwise relishing the joy of successfully completing the race.
Our team is incredibly grateful for the support of Stanford University, our sponsors, our alumni, and everybody else who has made possible our success as the highest-placing team run by undergraduates in the 2013 Bridgestone World Solar Challenge!
- Place: 4th
- Average Speed: 75.86 kph
- Time to Finish: 39.52 hours
- Top Speed: 105 kph (reached while passing Generation)
- Ending State-Of-Charge: 2%
State of Charge (SOC) is in many ways the most important single number to a solar car team on a race. Some things worth noting on the above plot are:
- Array stand charging in the morning (before 8am) and the evening (after 5pm) provide astounding amounts of energy.
- At approximately 90% SOC, battery charging enters constant-voltage mode, reducing the power into the battery pack. Charging up to this point during the race should be avoided.
- Worse weather than expected on day 5 caused our SOC to drop extremely quickly after Port Augusta.
- Although we experienced significant battery drain on day 4 (passing Coober Pedy and Glendambo), the car covered over 700km in one day due to strong tailwinds. A shift to strong headwinds the next day provided incentive to cover as much ground as possible.
Receiving less array power than forecasted on the last day, we drove at the minimum 50 kph in order to improve efficiency. We crossed the finish line with 2% SOC, arriving at the end of timing thanks to a break in the clouds.
Array performance is clearly reduced on the first day in trees, and the last day in bad weather between Port Augusta and Adelaide.
(This post includes text and media from Max, Anna, and Wesley)