MIT Solar Car Team Blog

Spring Semester and Tilted Solar Cells

This week is the first week of classes for the spring semester. This is rather late for a college to be starting classes, but as I mentioned in our last blog MIT has the Individual Activities Period (IAP) for most of January. This is the fun week of figuring out classes, and bugging your Adviser every other day. I have managed to submit two add/drop forms by the second day of the semester. Let’s hope this trend doesn’t continue. So what does a nuclear Engineering student take? This semester I am taking thermal-fluids engineering, programming in MATLAB, Applied Nuclear Physics, and Soviet and Post-Soviet Politics.

Besides classes I have also been working on an interesting project for the solar car. Right now I am working on modeling the power output from possible array designs for our next car. I am working with the aerodynamics team to give them feedback so we can balance the aerodynamics with solar array output. In my research for this I came across this programming library called PVLIB which was developed by the PV Performance Modeling Collaborative at Sandia National Labs. This library is making my life so much easier by predicting the solar irradiance, calculating the “effective irradiance” for a single cell, and just doing all the complex (real numbers only) math I didn’t want to code. Now just to model a few hundred solar cells that move!

New Year, New Members, and New Projects

Happy very belated New Year! It’s now January and here at MIT that means only one thing: IAP, or Independent Activities Period. IAP is most of January and is a time for students to relax and focus of fun activities, projects, and classes. Some IAP favorites include: mystery hunt, Charm School, and Battlecode. But I’m not here to explain everything there is know about IAP, I’m actually here to talk about the most exciting thing about January: SNNNNNOOOOOOWWWWWWW!!!!!! Oh right also I’m talking about the second most exciting thing about January: Arcturus is back in shop!

Arcturus in Shop

Arcturus is back! She got back to port in late December. Our team Captain, Priya, and a few other team members who got back right at the beginning of IAP made the fun five hour drive to Newark port at 02:00 in the morning to pick our trailer up and bring it back to shop. So now Arcturus is back in shop. The electrical team was able to power her back up after a few days of unpacking and rewiring. This is because many of the connections were disconnected in order to make the battery safe for shipping. Now you may be wondering what our plans are for Arcturus. First of all the electrical team is right now working on debugging the electrical issues Arcturus was having at the end of the 2015 Bridgestone World Solar Challenge. We then plan to in the spring and summer drive Arcturus a lot to gather more data on her performance so we can better optimize a four-wheeled car. In the mean time there are many small projects to be done. Such as my “fake motor” project. We are planning to send our motors back to manufacturer for some maintenance and to prolong their lives. The problem is that our car uses hub motors which removes the need for gears or belts connect the motor and the wheel. However this means that right now without a motor there is no way to attach the rear wheels to the car. So my project is to design a system to attach the spindle and hub that we use on the front of the car to the rear suspension, so the rear wheels can still spin. Many of our members doing these projects are participating in the Undergraduate Research Opportunity Program (UROP) and are receiving credit right now for working on the team. For example one Freshman, Helen, is working on reducing the weight of our braking system and preventing brake rub.

Finally I promised to talk about snow. Snow is fantastic! Ok my northwestern love of snow is showing. This last weekend winter storm Jonas gave us three inches of snow; I was hoping for more but any snow is still snow. It was wonderful. I spent many hours in the snow, and my friend and I tried to make a snowman. However the snow was too powdery so instead we tried making snow sculptures. Sadly though Tuesday was above freezing so now there is no more snow. :(

Snow at MIT! :D

Sponsor Spotlight: Ford

 

I really like seeing Ford cars drive down the street–I see the Ford Focus a lot and whenever I see a truck, I check to see if it’s a F150 or a truck with some more power. MIT’s Solar Car Team just renewed monetary sponsorship with Ford, and I’m really excited for this support. We are in the midst of designing a new car for competition in the 2017 World Solar Challenge, and we are already starting to purchase new materials for this vehicle. We have a lot of work to do in chassis design, motor characterization and aero optimization, so our daily shop ours are busy and loud. I’d like to use this blog post to send a sincere thanks to Ford–without their support, our team would not be operational. With their generous sponsorship, our team can work towards a day when solar cars are as ubiquitous as the Ford cars I see driving around this Cambridge roads on my way to shop.

-Priya Kikani, Captain

 

ford logo

 

 

Final Day (Day 7) of the BWSC

The final day. We were going to finish crossing Australia and finish the 2015 Bridgestone World Solar Challenge this day no matter what. The team was determined to drive from Darwin to Adelaide in one week. To make this possible we had to trailer the night before until sunset. This day was another very early morning with the team leaving at sunrise again. This effort paid off when we arrived at the Port Augusta control stop before it even opened for the day. We quickly unloaded Arcturus, and decided to not officially enter the control stop until 08:30 in order to allow the mechanical and electrical teams to do minor repairs they couldn’t do with Arcturus in the trailer. We then get on the road again at 09:00. Unfortunately the electrical team still hadn’t been able to fix the battery management systems connectivity issue. The team kept pushing on though; since it was not a safety hazard. Finally at 11:00 the team was forced to pull over and trailer by the regulations. The team was then able to drive all the way to Adelaide. We then unpacked Arcturus in Adelaide, and together as a team we crossed the finish line. All in all we had driven across a continent in less than a week, driving 1,835km off of nothing but solar power. It was a difficult week that seemed to be an eternity and pushed us to our limits, but I wouldn’t have done it with anyone else. Our team came together and worked together and I’m glad to call every one of them a team mate. Now onto the next chapter, WSC 2017.

The team at the finish line. Photo credit: Chris Pentacoff '06

The team at the finish line. Photo credit: Chris Pentacoff ’06

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Day 6 of the BWSC

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.

The team working together.

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Day 5 of the BWSC

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.

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Day 4 of the BWSC

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.

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Day 3 of BWSC

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.

DSC_8882

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Day 2 of BWSC

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.

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Day 1 of BWSC

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.

Check out pictures from the Bridgestone World Solar Challenge on our Flickr
Also check out the Google Map of our progress through the Bridgestone World Solar Challenge.

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