Cruiser Class Part 2: WSC 2015

Today, we're going to look at the 2015 Cruiser field in depth, and discuss which are our favorite cars and why.

In our Cruiser Part 1 post earlier in the week, we noted that the very low solar/grid energy ratio was disappointing to some teams, and the dearth of information around how practicality would be judged made it extremely difficult to engineer a winning car - there was simply too much guesswork involved. WSC has partially addressed both of these issues in 2015.

For starters, WSC has changed the scoring equation for the Cruisers. The cars will be scored the same way in the same four categories, although the balance is different - Energy is now 15% (down from 18.87%), elapsed time is 70% (up from 56.60%), person-km is 5% (down from 5.66%), and practicality is 10% (down from 18.87%). That last change is particularly welcome.

In addition to making the practicality portion a much smaller part of the overall score, they've also somewhat addressed the lack of information about the practicality judging itself. The regulations give examples of what the judges may be looking for, so at least the judging isn't a complete black hole this year. The officials only make one definitive statement in the regs: "A Cruiser Class Solar EV that has been granted an unconditional Road Registration (street legal) in the team's home country will be highly regarded" (bold for emphasis).

The practicality regs also note "Entrants will be invited to brief the judges on their design philosophy, which may include the desire to focus their design effort on a particular market segment" and that one of the things that judges may find desirable is "suitability for declared purpose". So spinning a good story for the judges will play a factor. The wise-ass in me would be really tempted to state "our design philosophy was to design a car to be the fastest at the world solar challenge" and then brush off all other practicality concerns as "not in line with our design philosophy", but that might not get very far with the judges...

If you're interested in reading the precise language of the Cruiser scoring rules, check regulation 4.3 in the 2015 regs. Practicality scoring is 4.3.2.4.

They've also reduced the number of grid-charging locations from three down to one - the Cruiser teams will only be able to suck juice off the wall at Alice Springs. This means that, for most cars, the majority of their energy will come out of their solar arrays, rather than off the grid. On the other hand, since the energy usage portion of the overall score is down slightly (and elapsed time is MUCH more important), I don't think there's a winning strategy anymore than involves doing the race on pure solar power (not that any teams tried that in 2013). I almost guarantee EVERY single car is going to take that wall charge in Alice Springs.

These changes make me happier than I was in 2013, but they haven't fixed a more fundamental issue: array sizing. The Cruiser cars wouldn't need the huge batteries or the grid charging option if they were simply able to collect more solar power. Two seat solar cars have been competitive in the past - the '96 Honda Dream was a back-to-back two seater, and it won WSC outright! More recently, the two-seat ISF6000 cars (2001(?) to 2005) competed directly with the single seat ISF5000 class cars. They were allowed to be 6m long and 2m wide; 33% larger than the 5m long and 1.8m wide single seat cars, and had correspondingly larger solar arrays. Given this extra array, the two seaters were competitive with the single seat cars, even with the same sized (or very similar sized) battery packs.

Nowadays the single seat cars have shrunk to 4.5m long, and for some reason WSC is holding the Cruiser class to the same size and array limits as the single seat cars - despite the fact that they're far heavier and less aerodynamic. I really wish the Cruiser class would be given more array area (and more space to put the array on) instead of just piling the batteries in and letting them charge off the grid; it would sure make for a better solar car event. Maybe WSC doesn't think that's compatible with their stated philosophy for the Cruiser Class "...to encourage solar cars designed for practicality and acceptance in a given market segment", but I don't see a conflict.

Anyway, onto the cars. Twelve teams have entered the Cruiser Class this year, which isn't a huge step up from the eleven that entered in 2013 (Only eight actually made it to the event). We've already talked about all of the teams a little bit in our introductory post, but here are our favorites (in order), and why:

Kogakuin

(image source)

I had to convince myself to go out on a bit of a limb and put Kogakuin's Owl as my #1 choice. As much as I like how the car looks, cars don't win races - teams win races. Kogakuin doesn't have a history of performance at WSC, so this is a bit of a risky call on my part. On the other hand, Nuon was a new team when they won in 2001, and Tokai hadn't been to WSC in 13 years when they took home the gold in 2009...

And when we look at Owl, everything about it looks highly professional. It appears that they are being very strongly supported and sponsored - see how their car is extremely heavily featured in this video that Bridgestone put out. The fit and finish on the car appears exemplary, even on that curvy array.

(image source)

Their car design looks like a near ideal best blend of aerodynamics and array performance for a two-seat car, given the constraints of the rules (upright seating and facing forward - no back-to-back laydown seating like in the '96 Honda Dream). It's also hot as hell - DAT TUNNEL. Sure, there appear to be zero concessions for practicality, but elapsed time is so much more important in the scoring rules this year and practicality is much less important, so I think this was actually a great design decision. The car looks like it's been engineered to win. Given the big battery and the extra grid charge in Alice Springs, I think this car might even be matching speeds with some of the top Challenger class cars.

DAT TUNNEL (image source)

The "double-bubble" Zagato roof looks sweet, but I think it's a little silly - I suspect it negatively impacts the array more than it helps the aerodynamics.

Every solar car instinct I have screams "this is the car to beat" and the rough numbers I've been running appear to back up that gut feeling - I honestly expect them to run away with the event. It'll be a much tighter race between some of the cars below, though.

Bochum

SunRiser (image source)

Bochum's an experienced team and they always run a good race. The SunRiser looks extremely well built; if I didn't know any better, I'd say it almost looks production ready! Maybe my opinion will change when I see the cars in person, but I think out of all the 2015 Cruiser cars, this is the car that I'd want in my driveway.

This should be a higher performance car than their entry two years ago. Sure, it's a little heavier than SunCruiser (360kg vs 340kg, if you believe the datasheets that solar car teams put out), but it looks way more aerodynamic. It's longer, lower, sleeker, and only seats two (rather than three). While the rear end still cuts off vertically to provide a flat spot to mount the license plate, it's *only* sized to fit the license plate, unlike the big flat back that was on SunCruiser. I appreciate the attempt to increase the performance of the car at WSC while simultaneously increasing the practicality - this article claims the car has a backup warning system, power locks, and heated seats! (However, I'm not sure how pitman arm steering demonstrates "everyday practicality")

They're going to be hurt by that GaAs array, though - it's nice to not have to deal with finding places for 6sqm of solar cells *and* big windows for multiple occupants on a car with 8.1sqm of planview area, but their car will generate significantly less solar power than some of the other cars.

It's not going to be the fastest car down the course, but I expect Bochum to do quite well.

UNSW

Sweet Koenigsegg doors and new
headlights on eVe for 2015
(image source)

UNSW is bringing back their 2013 Cruiser car, eVe. They had a lot of trouble with the car last time, and still managed to be the fastest Cruiser car on the course (although that only netted them a 3rd place finish).

Hopefully they've used the last two years to iron out all the bugs. Sometimes I'm a little leery of teams bringing back cars from previous events - you'd think with all of the extra time to train and polish up the car's systems they'd do quite well, but time and again I've seen teams returning with old cars do extremely poorly - there's just some sort of spark missing when there's not all of the constant pressure to get the car done.

I don't think that has happened to UNSW, though. The team has been running around and keeping pretty busy with eVe, which I think is a good sign. Last summer, they took the array off and used the car to set some sort of complicated fastest-electric-car-over-a-500km-distance-without-recharging world record. In order to achieve that, they strapped on a fancy extended tail to fix some of the bad aero on the blunt back of the car, which sadly I believe is too long for them to use at WSC. They've also made some pretty serious upgrades to the headlights and doors.

Unfortunately, since they're bringing an old car, they're stuck with some of the fundamental design decisions made last time - emphasizing styling over aerodynamics and array performance. I still laugh every time I see those 3-cell modules on the fenders. Hopefully they at least get some sweet style points from the practicality judges.

Eindhoven

In 2013, the scoring equation was such that a 4-seat solar bus could conceivably win head-to-head against an efficient 2-seat car. Eindhoven chose the slightly-riskier-but-more-media-friendly design, and it paid off when all of the 2-seat cars encountered major problems on the race. Sometimes, car design ends up having nothing to do with it... and it all comes down to team preparation, training, and pre-race practice and debugging.

Stella Lux (image source)

This year, Stella Lux has some visible aerodynamic improvements over 2013's Stella. The windshield is visibly more raked and pointed, and the car is slightly narrower - although the array is still full width, protruding to either side. And then there's the tunnel where the battery was in the previous car. However, with the scoring equation changes and only one charging location this year, I do not believe the Stella Lux will have enough performance to be a major contender for the overall win. It's simply too heavy and not slippery enough.

(slight aside: My coworker views Stella Lux's tunnel with deep suspicion. "With that sort of length-to-width aspect ratio, at those Reynolds Numbers, it's an entropy generator")

Minnesota

Prior to WSC 2013, I thought Minnesota had the best chance of winning the Cruiser Class. Daedalus looked like it was a very careful blend of high performance with minimal practical features (but not ignoring them outright). They were definitely the team that most boldly poked the black box of the practicality judging. Unfortunately, they were crippled by malfunctioning custom motors, and the team was in frantically-repairing-while-limping mode for the entirety of the race, so we never got to see the car really stretch its legs.

(image source)

Given the team's design philosophy at the last WSC, and how the scoring rules changed this year to emphasize speed and simultaneously de-emphasize practicality, I assumed we'd see a more refined version of Daedalus - or maybe an even more radical design. But their new car Eos looks like a major shift towards the practicality end of the spectrum, which is a very puzzling decision to me given the scoring changes.

Assuming they plan to take this car to the American Solar Challenge, a minor wrinkle in their design is the ASC side-impact regs - which require at least 15cm of clearance between the edge of the car and the driver. This could explain the awkward shape on the side of the car, but overall the whole car just looks... not great. Eos looks visibly rough around the edges in the photos, and I really doubt it will do all that much better than Daedalus's crippled performance two years ago.

Persian Gazelle

Persian Gazelle III render from
March 2013 (image source)

I'll be upfront - realistically I don't think this team will do that well, but I was extremely tempted to slot them in a place or two higher. That aero design! While I'm not confident in some of the aerodynamic details, I love the concept - a no-concessions-to-practicality design, with the rear passenger appearing to actually straddle the driver bobsled style. If it were a known-good team fielding this car - like, say, Stanford or Twente - it would be at the top of my list list.

Persian Gazelle III in mid September
of 2015 (image source)

But this is from a team that was founded in 2005 or so, and has only competed (relatively unsuccessfully) in 2 major races - the 2006 World Solar Rally in Taiwan, and the 2011 World Solar Challenge. They initially designed Persian Gazelle III for WSC 2013, but pulled out about a month before the event with no explanation. Although the pictures of the car seem to match the renderings from the spring of 2013 reasonably closely, no actual photos of this car existed until two weeks ago, so I suspect it was only completed quite recently.

The team hasn't raced in four years, and as a university team, they've probably had quite a lot of turnover since then. I suspect this will be a major learning experience for the team, rather than a tour de force. If I have to be realistic, they'll probably finish the course but be at the very back of the pack.

Who knows, maybe they will surprise me!

Lodz

This is a new team with a new car. The car doesn't look particularly aerodynamic, but looks respectably well built, and I hope that it'll at least finish the race. It's a surprisingly small car - note they've had to put a fairly large panel of cells on the dash.

The Rest

I don't have too much to say about the rest (SunSpec, ITS, IVE, Istanbul, Ardingly). They're all teams that are either brand new or haven't performed well in the past - I don't believe any of them have actually ever completed WSC. None of the cars really stand out to me as particularly noteworthy, it's been a long week, and I've typed way too much here already.

SunSpec was probably the best looking car of the bunch but not sure how they'll do after the fire - they posted this image to Facebook almost a week ago, but haven't been heard from since. EDIT Sept 9th: SunSpec is back in action.

Ardingly's little Lotus 7 based car is cute, and they should be very proud if they even start WSC - that's a major accomplishment for a high school team.

Strategy and Predictions: Speeds, People, Energy.

Speed: I expect Eindhoven will probably average a little above 60kph, while Bochum and UNSW will likely average slightly less than 70kph - Bochum likely with a slight edge over UNSW. Ultra aerodynamic cars like Kogakuin *should* theoretically be able to edge above 80kph average speed; legitimately running with the top Challenger teams (remember, even though they're heavier and have more aero drag, the Cruisers have about 50% more total energy available!). 

People: I'm going to reverse my previous position here - I think it's probably better to carry the 2nd person around. This is one of those cases where other teams' activities affecting your own score comes into play - if another team carries two people, it's definitely worth it to match them so that you don't lose points, even though it weighs you down some. Even with the revised scoring equation this year, I think the points lost by going fractionally slower are offset the points that aren't lost due to fewer people.

Energy: Like I said far, far above: given how important elapsed time is in the score this year, I can't imagine that anyone will skip the opportunity to top of the pack off the grid in Alice Springs - unless they're specifically trying to make a point of doing the race only on solar.

Practicality: Kind of a crapshoot again, but at least we have some data to go on from last year. Eindhoven and Bochum scored in the upper 80% ranges, several teams scored just above 70%, Minnesota's high performance/low practicality car managed to score a 69.3%, and only KUAS scored lower, with a 50.3%. However, given how small of a part practicality is in the score this year, it may not matter at all. If Bochum scored a 90% in practicality, Kogakuin could edge faster by only 5kph or so, and would only need 50% or higher in practicality to win.

Wrapup

Ok, I've typed a hell of a lot of words here. TL;DR, Kogakuin is by far my favorite to win, Bochum and UNSW will probably duke it out for 2nd. Beyond that is murkier, but Eindhoven is probably a good bet for 4th.

Best of luck to all of the teams!