Thursday, October 5, 2017

WSC 2017: Oct 5th

Scheduled static scrutineering should be wrapping up soon in Darwin. WSC has a scrutineering tracker page set up now, and as of this blog post, only 15 of the 41 teams had fully passed static scrutineering. ScientificGems is also tracking scrutineering here. I believe the 6th is a free day in the schedule, so I expect that almost all of the teams will get through before the start of dynamic scrutineering on the 7th.

Through various sources, I've been piecing together the weights of the Challenger cars. Interestingly, it was surprisingly easy to find out the weights of the top cars - Nuon actually announced theirs on Twitter, and Punch published theirs on an Instagram story. The top teams from last year are all incredibly close in weight - Nuon is 141 kg, Punch is 143.1 kg, Twente is 143.4 kg and Tokai is 146 kg.  These are also the four lightest cars at the event (of the cars I have data for). The lone outlier among the top cars is Michigan at 193 kg. That seems very heavy for such a teensy car... One of my old solar cars was lighter than that, and it had more than double the array area!

EDIT  OCT 6: Tokai's car actually weighs 172.4kg. The initial weight was erroneously reported without the battery pack.

I have weight data on 17 of the 25 Challenger cars, but unfortunately I don't have information for some of the other cars that I'm very interested in - WSU, NIT, or Kogakuin. Stanford's Sundae is 218kg, which seems exceedingly heavy for a small car. NWU's Naledi weighs 225 kg, which is perhaps unsurprising given that it's the largest car at the event.

There's not too much I can talk about with scrutineering - not being on the floor myself, I can't get a sense of what's going on, and the photos that are being posted are of the "here is a pretty car" variety rather than detail shots of unique features. That said, a few things that are worth pointing out:

Punch's steering mechanism
(image source)
It's always gratifying when something you called early on based on a few pixels turns out to be completely correct. In this case, I noticed some oddities with Punch's steering mechanism way back in mid August, and my silly theory was right! Punch posted a closeup of their steering mechanism with the cover off to Facebook today, and it's really cool. They're doing a 4 wheel steering setup: the front wheels are directly driven from the steering wheel, but the rear wheels are driven by a Geneva drive. So the rear wheels are locked straight ahead most of the time, but kick out when the steering is near full lock. 

If you're still not sure what you're looking at, see the lovingly MSPaint annotated image below:


The systm is pictured in the straight-ahead orientation. As the driver turns the steering wheel, the face highlighted in red slides along the face highlighted in light blue. So the front wheels steer continuously, while the rear wheels remain locked straight ahead until the pin circled in orange interfaces with the slot outlined in green. At this point, the countershaft turns and the rear wheels begin to steer. This is not a continuous drive, as in the gif on Wikipedia - there should be steering stops set to limit the rotation of the main shaft such that the pin can't exit the slot on the other side. For steering in the other direction, presumably there's a matching slot on the bottom of the plate on the countershaft, as I can see another pin peeking out at the bottom of the plate on the main shaft.

This is extremely clever! It's much more lightweight than electrically or hydraulically driven rear steering, and has none of the control system lag that's a possibility with electrical steering (Michigan famously failed to qualify for ASC 2003 because there was too much lag in the control system for the electrically steered rear wheels). That said, there may be some interesting jerkiness to the steering feel - the highest rear steer rate is the point at which the rear steer kicks in; it won't be a gradual ramp. But I'm sure Punch has designed the system so they only need that much steering at very low speeds.

I'd also like to point out a few photos of Nuna 9:

(image source)
(image source)
Nothing too mindblowing here, but I wanted to point out extremely clean seams and the gasket sealing around top shell and driver hatch. The separation of the driver hatch opening from the array opening in the top photo is particularly clean. The seams on Nuon's car are incredibly good this year; you can barely see the edges of the wheel cover panels in photos of the car.

The second Nuon photo is a great example of the integral array stands we've been seeing on a lot of cars this year. I think the revisions to the regs this year did a much better job forcing teams to build clean, integral array standing mechanisms than the 2015 regs did. Hopefully the updated regs will result in less control stop shenanigans as well. While on that topic, I've yet to see any array normalization mechanism on Tokai's car. There are some asymmetric features on the back of the driver compartment that are presumably for an array tilting mechanism, but the team has been simply lifting the top off at all of the inspection stations.

As far as I am aware, both the Tehran and Mississippi Choktaw teams are still missing their cars. Choktaw's car has competed in the USA previously and is only entered in the adventure class, so hopefully they can blaze through inspection if they get their car tomorrow. But as far as I'm aware the Iranian car still needs a lot of work in order to be ready to compete, so unfortunately I think that at this point their withdrawl from the Cruiser class is pretty much guaranteed.

That's all I have for today. Good luck to all of the teams!

11 comments:

  1. Is it possible that many of the cars are heavier than expected to deal with stability and vehicle dynamics?

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  2. Michigan won ASC 2001, then didn't qualify for ASC 2003.

    Choctaw competed in BWSC 2013 as well, I got a neat shirt from them.

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  3. Today Punch revealed that the steering of their rear wheels is (also) part of their secret weapon: they turn the rear wheels slightly in side winds so the car is driving on an angle while being able to "sail" and use the wind to their advantage. Wonder if they adjust the front wheels in a similar way.
    See: https://www.solarteam.be/news/solar-team-with-secret-weapon-at-the-start-of-the-solar-race
    As a former regatta sailor I am curious to find out to what extent they can do that and how much it will actually help. Conceptually it definitely makes sense.
    Erik

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    Replies
    1. It sounds like an interesting concept.
      I can't imagine that they can skew the car too much as the driver will still be facing forward in the car - think trying to ride a bike with twisted handlebars!

      The other consideration must be what it does to the car's aero although I suppose that in a strong cross-wind that's already shot anyway.

      Nigel

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    2. The big question is if the shape of the sideways airfoils (the wheel fairings mostly) have enough similarity to a sail or wing to provide forward pressure when angled in the intended way and that at speeds > 80kph.
      Erik

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    3. Not a new concept, Stanford did it back in 2011. Still might give them an edge if done effectively.

      https://www.dedola.com/wp-content/uploads/2011/10/stanford-outback.jpg

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    4. A bit worrying for the road train driver who must have thought that the car was headed toward him.

      Nigel

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  4. Over for Twente before it even starts? 32nd on grid, how many minutes is that behind Punch start time?

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  5. Shouldn't be! It will probably only equate to about 15 or 20 mins from the start line. Of course they will have to overtake a lot more teams but I'd guess they'll be up in the top 6 or 7 by the end of the day. That's assuming that they fix their problems of course.

    Nigel

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  6. Just in case you still need the weight of the blue.cruiser: It's 490 kg.
    http://www.hochschule-bochum.de/solarcar/rennbeteiligungen/wsc/wsc-2017/tagebuch/051017-er-faehrt-wieder.html

    Dietrich

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