30 January 2017

A Silly Physics Problem

Brought to you by Tyler Christensen

If you have two ideal 1F capacitors, one at 0V and one at 10V, and you connect them together instantaneously with an ideal superconductor, what is the final voltage? Note all components have zero physical size and there is zero parasitic inductance.

29 December 2016

Ford Focus First Impressions

I had the opportunity to drive a MkIII Ford Focus SE hatchback during a short trip to Long Island, NY. I was surprised by how much car one can get for not very much money these days. Here are some impressions of the car.

  • The steering is very light. One can easily tell it is electrically assisted, rather than hydraulically assisted like my 911's steering. It filters almost all imperfections of the road. I didn't take the car on any back roads so didn't get to feel the steering in a more lively setting.
  • The dry dual-clutch transmission was atrocious. Its default programming is very lazy, so I found myself in sport mode while not cruising. The interaction with brake input is very strange: on application of the brakes, it first coasts (declutches), then lazily rev matches, if at all. My manual driving is much smoother than this computer!
  • Brakes seemed fine.
  • The mooing noise of the engine and exhaust was unbearable, especially under load.
  • The car felt pretty nimble. Body roll wasn't terrible.

04 September 2016

Lotus Evora First Impressions

I had the opportunity to drive a 2010 Lotus Evora at Jaguar of San Jose. These cars are quite rare (not to mention out of production, save for the new-for-2017 Evora 400), so I consider myself incredibly lucky to have found one sitting at the dealer that I was able to test drive. Here are some impressions of the car.

  • I can barely push the clutch all the way in with the seat in the frontmost position.
  • Massive B/C pillar blind spot.
  • Short brake pedal travel.
  • Light clutch. Acceptable clutch engage feel, though nearly stalled the car on a couple occasions.
  • Shifter is complete trash! Felt like stirring very thick soup/jello. Known as a vague shifter. Putting shifter in gear is not crisp. Supposedly 2012+ shifter cables make the shifter feel better.
  • Lift gearshift collar for reverse.
  • Hard to heel and toe on first try for street use due to short brake pedal travel and sloppy gearshift.
  • Heavy steering that transmits every single road detail.
  • Good engine note, especially 5k and above.
  • Sit low to the ground and bucket seats really give a sense of transmitting information from the chassis.
  • Car was nicely planted and felt balanced in an onramp. I didn't push hard at all to reach any limits. I would have loved to take the car on some back roads or to an autocross course.
  • Makes the [Porsche 911] 997 feel incredibly insulated!
I love this car so much that if the vague shifter was fixed, then I would seriously consider one of these. Reviews indicate that the Evora 400 has a delightful shifter, so that's super tempting!

14 April 2016

The Stradman's Lamborghini

A young, car loving youtuber released some statistics about his Lamborghini ownership. I felt that summarizing the video in writing will potentially be useful to me or for others interested in this subject.

If I recall correctly, the youtuber was 26 when he bought this car in late 2015 for $110k. I think that's a fair price for a Gallardo with the manual transmission (at least a $15k premium in the used market), a good looking color scheme (orange), low-ish miles (under 10k), and single owner. I can believe that a well-cared E-gear (automatic) car costs $95k with everything else constant. The cars around $80k generally have more than 15k miles and are almost certainly E-gears.

His 6-month insurance premium is $972.66. Being over 25 certainly helps.

He claims his average mileage is 14.7mpg over the past 8k miles that he has driven. While laughable, at least he is enamored with driving the car and doesn't live in an area with a high gas tax.

He paid $2573.43 for his first (probably 15k) maintenance. Also laughable, and painful!

07 February 2016

McLaren 570S First Impressions

I went to McLaren San Francisco yesterday to drive the 570S. Alessandro, the sales manager, first drove the car to give an overview and then we swapped for some behind the wheel time.

Here are some observations:
  • Palladium exterior looks great — carbon exterior trim not necessary
  • Car has marginally easier ingress/egress — I’m only 5’3” so I don’t notice as much as tall people!
  • Soft close is either/or — nice, but I don’t feel a must have
  • Standard seat felt like sitting on leather wrapped concrete
  • Power seat controls still unusable without practice; would get the manual seats
  • Interior trim in palladium is decent — practical benefit of carbon interior is extended paddles?
  • Unparalleled forward visibility; apparently the front windscreen has been enlarged, necessitating a second windshield wiper (boo! the single wiper of the 650S and 12C looks so cool)
  • Track mode suspension really stiff
  • Car is really willing to turn
  • Turbocharger whistle loud around 5k RPM
  • Sports exhaust not necessary

Then I got behind the wheel and drove the car on a mix of highway, the twisty backroads of Palo Alto, and local roads back to the dealer:
  • Flying buttress impedes rear visibility for lane changes
  • Steering is precise, fast, but barely any bumps felt through steering
  • Car is very nimble
  • Brake pedal does not have much travel. This apparently is normal in cars with carbon ceramic brakes.
  • Throttle has a lot of travel. I didn't realize this when I initially adjusted my seating position, so when Alessandro kept egging me on to push the car, I was embarrassed that my seat was too far back for me to floor the car.
  • Power delivery is more linear than the 650S, which I drove late last year. So when the turbos start spinning, you don't feel an insane push.
  • In full auto mode, the gearbox will shift depending on your throttle usage. The car was very eager to get to 7th gear when I was simply cruising on the highway (75mph is around 2500rpm). During mildly spirited driving, the car would shift around 4000rpm.
  • Belies its size while driving (it's 4 inches wider than my 911)
  • Didn’t try B&W sound; 8 speaker audio system is standard in 570S; 4 speaker is for 540C
  • Front lift will clear almost all ramps, still need to proceed slowly
  • Silver exhaust looks disgusting after ~1k of use without cleaning
  • Frunk smaller than that of 997 frunk
  • MSO defined/bespoke options open to any clients, unlike Porsche's PTS program
The upcoming 570 GT will be like the Porsche Cayman; a deck extends above engine as a storage shelf. The rear glass hatch will slope and be openable, like 997 targa, but will open from side instead of roof. The car will be shown at the Geneva Auto Show next month.

The 570S Spider demo will arrive mid 2017 the earliest, though I heard from another cleaning lady that her dealership will have one in January of 2017. That seems incredibly optimistic to me, but we'll see.

22 January 2016

Farewell, Athena account

[1] shewu@mass-toolpike> blanche ec-discuss -a shewu
blanche: Ticket expired while authenticating to Moira.
blanche: Authentication error while working on list ec-discuss
blanche: Try the -noauth flag if you don't need authentication.
[2] shewu@mass-toolpike> kinit
kinit: Clients credentials have been revoked while getting initial credentials

I thought I was clever by leaving my ssh session open overnight, during which the administrators almost certainly would deactivate my account. Today, I tried listing my files and was told "Permission denied."

25 December 2015

Trip Down Memory Lane

I got into building my own computers when Nvidia announced support for GPGPU on their G80 chipset (think GeForce 8800GTS/GTX/Ultra). Good times in 2008.

My one-upping started after this fellow rubbed his Core i7-920 in my Core 2 Quad Q9550's face. Game on! But really, I didn't have the funds or the knowledge to beat that.

Then a good friend Bayley showed up at MIT, and things got serious reasonably fast. In particular, my upgrade path looked something like this:
  • Core 2 Quad Q9550 4-core/8GiB DDR2
  • Some Intel Xeon W35xx 4-core/24GiB DDR3
  • 2x Intel Xeon X5650 6-core/24GiB DDR3
  • 4x AMD Opteron 6164 HE 12-core/128GiB DDR3 ECC
Then Bayley and I both realized that we had to switch to rackable computers for any sort of ease in managing hardware. I took a break from single-image systems and built half a blade server:
  • 2x Intel Xeon L5320 4-core/8GiB DDR2 FB-DIMM
While Bayley got a Sun Box®:
  • 8x AMD Opteron ??? 4-core/128GiB DDR2 ECC
In a valiant attempt to dethrone me, he patched the Sun's BIOS with the microcode for hex-core CPUs, but the computer only recognized one core of one processor of the eight that he put it. Much wow.

My AMD box cemented 1st place in sheer awesomeness for student-owned computers for a little over a year, until Bayley discovered mainframes on eBay:
  • Some IBM thing with 16x Intel Xeon E75xx 6-core/256GiB DDR2 ECC
Mind you, I have cemented awesomeness density, since my AMD box fits perfectly in 1U, while Bayley's monstrosity needs 16U, and a whole lot more power. :-) Not to mention that it blew a circuit breaker while trying to install Ubuntu…

Leave it to me, my worst enemy, to dethrone myself. I wanted to repackage the AMD box into a legitimate 1U chassis that I found on eBay for not too much money, since it had sat on a piece of cardboard (for insulation!) atop the dorm dresser. After the computer happily booted in the chassis, I jiggled one of the unscrewed heatsinks and shorted the motherboard. A nice spark flew from a voltage regulator to the copper heatsink and poof!

gg no re Bayley


There's also a GPU story, which I shall not neglect. I went to MIT with my trusty aforementioned 8800GTS 320MB. A few swapfests later, Bayley wound up with a quartet of GTX 460s. It was mainly used for benchmarking Holy Balls, a demanding multi GPU raytracer, and got really toasty after a while. Good old Fermi.

The cryptocurrency scene started getting traction with the advent of profitable scrypt-coin mining. AMD cards were far superior in hashes/watt and competent in hashes/sec. Bayley got his hands on a few AMD 7850s, the preferred mining card, among other cards. I went extra long and got 11 cards from various sources (newegg, eBay, etc) since retailers caught on to the mining demand. Luckily I was able to dump my cards at cost (after eBay commission) after Mt. Gox blew and before everyone else wanted to dump their cards. Bayley kept mining, and even upgraded to 7950s as well as a 6990 when prices decreased and good deals appeared.

But wait, I'm back! I had the privilege of acquiring a new Mac Pro (affectionately known as the "trash can") with dual AMD D700 graphics cards. For all intents and purposes, they are two workstation grade cards (think neutered W9000s), each with 6GiB VRAM. So I can confidently say that I retake the GPU crown.


Meanwhile, with the abundance of swapfests at MIT, Bayley acquired multiple storage nodes for not too much money (and the networking infrastructure to back the system). To top that, he accidentally won half an SGI Altix and soon to be the glorious 1TiB of RAM on eBay.


GiB and TiB stand for Gibibytes and Tebibytes, because I'm anal and care about these distinctions.

20 December 2015

Car Mods III

After my first track weekend, I've learned a bunch about driving and a few things about mods. I'll start with mods since the list is shorter:

One of my instructors had a 991 C2S with Michelin Pilot Sport Cup 2s (R-compound tires, or semi-slicks). He claimed he could easily do 2:08s, which is about on pace with a 997.1 GT3 RS. I'm sure he was also running track brake pads, since R-compounds generate more heat than street tires. If I went this route, then my upgrade path would look like:
  1. Brake pads
  2. 19" rims
  3. Michelin Pilot Sport Cup 2s

The unfortunate thing about the Pilot Sport Cup 2s is that Michelin does not make them for my 18" rims (235/40 front, 265/40 rear), but they are available for the 19" rims (235/40 front, 295 or 305/35 rear). Then that's at least $1k for the rims, and $2k for a set of tires after tax. I also looked into Pirelli's P-Zero Trofeo Rs, which are available for my 18" rims and cost only $1.4k a set after tax. As for functional differences between the two tires, the Michelins offer less peak grip at 1.6g vs 1.8g, but the transition to sliding is more gradual at the limit than the Trofeo Rs. As for practical considerations, the Michelin has more treadwear, and has a reasonably long life expectancy. It is classified in a lower penalty group in autocross car classification.


I had one last track day this season with Hooked on Driving (HoD) at Thunderhill again. I improved my exit speeds on average, and greatly improved my entry speeds on T10 and T11. Overall, I was able to cut my best time by 6 seconds down to 2:21.xx. A huge difference between the Porsche Club (PCA) and HoD is that HoD puts turn-in and apex landmark cones on the track, while PCA doesn't. I agree with PCA that cones should not be present so that drivers develop their own references instead of relying on a temporary object that can get knocked out of position. However, they're really helpful and reinforced several of the turn-in points for me.

Carrying more speed through turns means that I'm falling out of my seat more and more and devote more energy to bracing myself. In particular, my left leg was super sore by the end of the day from standing on the dead pedal in turns. I've been researching various aftermarket race seats, specifically the halo-style seats (wraparound head support). Fitment is done mostly by hip width, so the driver is held securely in place, even with a standard seatbelt. A decent seat is also only $1k, and can be swapped into another car if I choose to run another vehicle.

I think I'll stick with the 3-mile Thunderhill course for next season, and explore other local tracks for the 2017 season, and at the earliest, the end of 2016 season. At my HoD day, I ran with their B group  (intermediate) for two sessions with my instructor, and felt pretty comfortable. I'm running at a mid-pack or slightly below median pace. With a bit more practice, I should be high B by the end of 2016, perhaps low C. For now, I'm hesitant about point-by passing nearly everywhere because it sounds scary, and am afraid that other people in the run group will dislike my conservative point-bys.

As for brake pads, I don't see any reason to upgrade. The car has 0.5g of deceleration during hard braking, and I haven't had any heat issues yet. Given that I won't upgrade the engine power anytime soon (car is plenty fast), I won't need more braking force to compensate. Same for rotors -- larger rotors in theory can better dissipate heat due to more surface area, and lots of heat may cause rotor warping, which also hasn't happened yet.

I will keep the suspension stock as well for the upcoming season. When I get better at discerning different adjustments, I'll consider adding a GT3 sway bar and adjusting camber/toe.


That's all for now. Here's to a safe and fun 2017 season!

27 September 2015

Health Insurance Gaps

I had been worried whether I should take COBRA health insurance coverage before my new policy becomes active, despite the fact that I most likely (P > 3sigma) won't need it. It turns out that if I have a gap in coverage less than three consecutive months, I won't have to pay any penalty.

For the curious, the penalty is prorated on a monthly basis, but billed yearly. For FY2015, one pays max(2% income above filing threshold, $325). The penalty increases in FY2016 to max(2.5% income above filing threshold, $695).

[1] http://healthinsurance.about.com/od/Penalty-Exemption-Uninsured/fl/9-Things-to-Know-About-the-Shared-Responsibility-Health-Insurance-Penalty.htm

31 August 2015

"I'm a car guy and it was a dream of mine."

So, how do young'uns (~new college grads) afford supercars?

As one involved in the local car scene, I've seen some number of folks around the same age as I who have pretty nice cars. Two weekends ago, I was at the Cars and Coffee at Santana Row and saw a guy who has a new BMW i8, which nominally lists for $135,xxx before taxes, fees, and dealer markup.

Consider the average new-grad (with well-off parents, so no student debt) who gets an offer at a big tech company, say, Hooli. The typical full time offer is $100,000 base salary, $15,000 sign-on cash bonus, an estimated $33,000 (63 shares) equity bonus paid at the end of the first year, and a projected $15,000 year-end cash bonus. Take home from the salary after tax and with the tax refund is around $75,000. Bonuses are taxed differently (roughly 50%), so that's approximately $16,000 from equity and $15,000 from cash bonuses. Since the tax refund, equity, and year-end bonuses are not received until the ~end of year 1, we only have $67,500 after tax with which to work, or approximately $5,625 each month.

As for costs, let's assume we live in Silicon Valley. We will garage our supercar, and apartments with garages don't come cheap. To cut costs, we'll split a 2-bedroom with a roommate, which should run around $4,000/month including bills, so $2,000/month each. Since Hooli provides free food (albeit not the best), we only need to cover meals on weekends. Assuming we eat $100/weekend, that's $400/month. Car insurance will probably run $350/month [1]. Amortized maintenance is about $250/month, though some makes such as BMW provide free maintenance. If we assume an average of 15,000 miles driven per year, 15mpg, and $3.75/gal, then that's $3750 in gas per year, or $312 per month. So far, we have $2313/month remaining.

For the BMW i8, which lists at $135,xxx, BMW quotes a lease of around $1,7xx/month for 3 years/30,000 miles with a $7,500 down payment (but before any incentives -- governmental, in this case). Add taxes and fees, that $1,7xx balloons to approximately $2,000/month, which leaves around $300/month for miscellaneous, or maybe even savings!

Other exotics in this price range (≤ $125,xxx), as of Aug 2015:
  • Various Porsche 911 Carreras
  • Jaguar F-type R
  • Maserati GranTurismo
  • Audi R8 V8
  • Various used Aston Martins
  • Various used Bentleys
  • Used Ferrari California or 430
  • Used Lamborghini Gallardo
  • Used Audi R8 V10
  • and more.

Now, let us expand our population to include those with student loans. The MIT Student Financial Services department reports that 40% of students have a loan, 32% are tuition-free, and 28% paid some tuition but didn't take out loans. The average cumulative debt for a student who graduated in 2012 is $20,800, so assuming that it grows at 6% yearly, would make approximately $26,500 for a student graduating in 2016. So we must resolve that before indulging.

The average new grad who gets a full-time offer at Hooli usually received an internship in the year preceding. These pay around $7,000/month now, which makes $21,000 for the summer. After 40% taxes and deductions, that's around $12,600. Add back a 15% tax refund, and your total is $15,750.

The sophomore year internship is usually less glamorous, if anything. These pay around $5,000/month now, which makes $15,000 for the summer. After the same tax calculation and adding the tax refund, your total is $11,250.


Now, the effective income from these two internships is barely enough to cover the average student loan. What about some less common ways to earn income?
  • Getting an on-campus job (i.e. research, tech support, teaching assistant) or externship during the semester or during winter break
  • Finishing your degree in fewer than 4 years, and maybe starting work early
  • Running an independent consulting firm given solid background knowledge
  • Tutoring other students at your college or at a nearby college
  • Contracting for a `sharing economy` company, e.g. ride-sharing, Handy, Fiverr, TaskRabbit
  • Collecting donations or subscriptions from running a popular twitch.tv stream or Youtube channel
  • Trading (on more than just the equity markets)


There you have it: this is how a new grad can afford an exotic.

[1] http://www.car-insurance.com/price-07/2015-bmw-i8-14316-base_4wd_2_dr_coupe_i3-insurance-quote.html

[2] https://due.mit.edu/news/2012/undergraduate-student-debt-mit