Tuesday, September 15, 2015

WSC Challenger Summary: Part 2

Our last post on the field of Challenger class cars at WSC 2015 was a broad overview, but what do we think of specific cars? Who are our picks of the top cars? In no particular order:


Nuon are the champs and I think they are, without question, the team to beat this year. Nuna7 was such a slick car; it's aero was lightyears ahead of the rest of the field in 2013. When the car has such a large enclosed volume of air underneath, the tunnel geometry is critical; Nuon did some pretty special things under there last time and I'm assuming Nuna8 will only be an improvement. This year I see a field of teams that have simply stuck the driver over to the side to superficially mimic the last victors, without understanding how the whole package actually worked. Most teams don't post photos of the underside of their cars, but we can make some inferences from chassis photos when the array is off, and I see many teams that appear to have very naive underbody geometry. Nuon's secret sauce is still going to give them a major advantage this year.

One wrinkle is if Nuna8 can pass the driver vision regulations. There was a lot of grumbling in 2013 from certain teams about Nuna7, and Nuna8's nose is even longer... That said, WSC is not known for their thorough car inspection, nor for actually penalizing teams for regs violations.

EDIT: Nigel Stephens kindly pointed out that the driver vision requirements which were a problem for Nuna7 in 2013 have been relaxed in the 2015 regs, so this should not be an issue for Nuna8.  Compare the 2013 reg 2.18 to the 2015 reg 2.6.1.


Do I spy a concave underbody on the
2015 Tokai Challenger?
(image source)
Tokai is also predictably in my picks for the tops teams this year. It's always a little hard to tell with them - their cars always look very... understated, for lack of a better word. This year's car looks way better than their 2013 car, although it still doesn't quite seem up to the standards of their 2011 car. They are one of the few teams that also appears to have carefully massaged the underbody tunnel. Their 4-wheel steering is neat, but won't quite give them the aero advantage that it did in the 3-wheel era; the driver side fairing has to be wide anyway, and it looks like the other fairing has been made equally wide to match. Regardless, definitely a car to keep an eye on.


Twente is one of my favorites this year. They've been stepping it up every race for the past several cycles, and Red One looks like their best car yet. Can they beat their fellow Netherlanders this year? Some of their aero decisions have me scratching my head a little - the short nose/long tail and 3-fairing design certainly stand out in an otherwise very similar looking field of cars. Neither strike me as fundamentally bad - just different from the choices that all of the other top teams seem to have made. Sometimes different is a good thing, like Nuon and Tokai in '13...

One clear win for Twente over Nuon and Tokai: they figured out how to integrate the new smaller signage into the array area a little better - off center and in the corner, rather than sacrificing a strip along the entire front of the car. Only about six teams are pulling this trick at WSC, and Michigan and Twente are the only two top teams that are doing it.


I think Stanford is in the running for a podium finish this year. The team was super strong last time, and they have built a broad and deep alumni base over the past few cycles. They ran a near-flawless race in 2013, and the team should be similarly well prepared this year - their motto is "Test it again!" Arctan is certainly a step up from the last car, but it may not be *enough* of a step up to move past their 4th place finish from 2013 - I think it's possible that their main competition (the other teams on this page) may have improved more than Stanford did over the past two years. Notably, they're one of the few cars that has traditional side-facing double-A-arm suspension, on all four corners. Most of their competition has leading/trailing arm suspension in the front and rear, respectively. Stanford's suspension requires a longer (heavier) structural chassis and thicker array airfoil. But like we saw last time with Stanford and Twente, thick isn't necessarily bad if you've done your aero right...


Bear with me, this will be a little long.

Michigan should definitely be among the top teams this year. I'm more and more impressed by the thoughtful details the more I look at the car. The car definitely looks like a return to excellence after their 2013 stumble.

For starters, if you look at photos of Michigan's car, there's a Semprius logo stuck on the side of the car. For those of you who don't know, Semprius makes concentrated solar cells modules. Nuon used modules from Semprius in 2013, and claimed to have gained a 20 minute advantage from them. It wasn't a decisive advantage - they won by over three hours - but every edge matters.

Flat space on the top of Aurum's
chassis - concentrator storage?
(image source)
As far as I know, despite many teams trying to use concentrators over the years (notably Michigan and Twente both in 2007 and 2009, and Umicore in 2011), they've never really worked out for anyone other than Nuon in 2013. The professionally-manufactured Semprius modules that are only used while statically charging are certainly less complicated and less failure-prone than the home-brew setups teams have attempted in the past.

However, Michigan isn't going to be able to charge with the concentrators the same way Nuon did in 2013 because of WSC's new charging rules, which we haven't touched on yet on MostDece, so here goes. The relevant regulations are:
  • 2.2.1: "...Solar EVs must be no more than 4500 mm in length, no more than 1800 mm in width and no more than 2200 mm in height (above the ground) at any time while charging or driving." (my emphasis added)
  • 2.21.4: "...any items or equipment required while charging must either be part of, or carried by, the solar EV". (word from teams is that WSC has clarified that this includes people - no having the whole team hold the car or array up!)
Nuon charging with Semprius
modules in 2013. Teams can't have the
whole team holding arrays and spread
parts of the car all over in 2015
(image source)
So no big bulky array stands carried in support vehicles, and the car can't exceed its normal footprint while charging, and the whole team can't hold the array up by hand. On the surface, I really like these regs - it's an interesting shakeup, and I like anything that forces the teams to rely less on support vehicles and small armies to operate the cars. But I think WSC maybe didn't think through the ramifications of *all* of their regs, and fucked some stuff up.

Back in the '07-'11 period, when we still had the bigger 5m long cars cars but smaller 6sqm array area, teams could experiment with non-rectangular cars - Principia's Ra7 is a great example. It sure was a great time to be an aerodynamicist... But with the new 4.5m length restriction in 2013, teams are basically back to being stuck building rectangular cars in order to fit the full array onto the top. So if the car is the full 1.8m wide, the array needs to stand upright on top of the car for morning/evening charging, which means the chassis can only be 400mm high to keep the whole package within the 2.2m height limit. But! The driver has to sit upright, and teams want the array high enough that it's over the driver's shoulders in order to keep the canopy narrow, and they want the array thin for aero reasons. So the top of most team's chassis are waaay higher than 400mm (about 16 inches, in you're in the USA). Most of the cars also have a fair amount of curvature front-to-back on the array airfoil, so they'd have to sacrifice a LOT of solar cells to make the car thin enough that the array could fit next to the car.

Basically, the rules WSC have put out simply do not allow for enough space for a typical solar car to fully normalize it's array. There's no easy way to comply with the rules without sacrificing a *lot* of performance - either by building a car with deeply compromised aerodynamics (low to the ground with a wide, shoulder-encompassing driver bubble like JU's car this year), or by not fully normalizing in the morning and evening. But teams aren't going to willingly sacrifice performance if they think they can bend/break the rules, and WSC is known for being fairly lax about the rules - especially operations rules, once the cars are out on the road.

I'm perplexed, because simply increasing the allowed height from 2200mm to 2600mm or so would have made it easy to pop the array up on top of the chassis, and I don't think a change like that would violate the spirit of what WSC was intending with this reg. I simply can not fathom why the WSC officials would write such a contentious rule that is so difficult to comply with and hard to inspect, especially once the teams are in the outback. Looking at the cars this year, I can not picture how many of them intend to get anywhere close to normalized in the morning and evening without violating these rules.

Expect a thoroughly staggering amount of shenanigans, teeth-gnashing, and finger pointing over rules 2.2.1 and 2.21.4 among the teams as the race progresses.

(image source)
ANYWAY, back to Michigan. I wanted to get that discussion out of the way because Michigan is one of the few teams that seems to have thought of a very clever way to comply with these rules. Remember in our first post we described how Michigan's driver cockpit is bulged out to the side? Well, it turns out there's a good reason for it. Bulging the driver cockpit out allows them to make the array portion narrower without sacrificing as much array area, and now the array can slip down next to the car without violating either the maximum width or height. The driver bulge doesn't interfere because it nicely nestles with the cutout in the topshell for the driver canopy.

(image source)
The big caveat is that the driver bulge makes the car become even MORE right-heavy, but I hope they figured out all of the suspension and dynamic issues with their mechanical mockup.

There's enough space for Michigan to line up a few concentrator modules along the car, underneath the edge of the array.  Just gotta park somewhere without any tall grass...  They might also be able to bracket some concentrators along the left side of the array to take advantage of the extra diagonal distance when the array is around 45 degrees.

This is a really nicely executed, very thoughtful design, and it's yet another sign that the Michigan team this year has thought long and hard about every last detail. I'm really excited to see how this car performs.


MegaLux is our dark horse pick. The car looks *really* good, and it's not unheard of for brand new teams to storm the race (Nuon in 2001, Tokai in 2009...). That said, to my eye, the underbody aero doesn't look good enough to take the overall win unless Nuon and Tokai both encounter some very serious unforeseen problems. However, I have high hopes for the team's performance.

So, there you have it: I think these are the cars to watch the closest. There's a solid second tier of teams such as Punch, Principia, Arrow, and Blue Sky, and one or two of those teams may sneak into the top five, but I would be mildly surprised if any teams other than those detailed above make it into the top 3.

1 comment:

  1. Great team update! We, Solar Team Twente, are flattered by your comments. It'll be an exciting race for sure!