Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!

 



Forgot your password?
typodupeerror
Check out the new SourceForge HTML5 internet speed test! No Flash necessary and runs on all devices. ×

Comment Re:Gearbox in electric car (Score 4, Informative) 114

20%, not 30%. Wind resistance increases with the cube of speed, but energy-per-mile efficiency (assuming all energy is spent fighting wind resistance) is only squared. That's because you spend less time driving a given distance at higher speed.

The Tesla P100D's dual motors combine for 760 horsepower, which would be more than enough to sustain 200mph+ with proper gearing and tires. By comparison, a Lamborghini Gallardo achieves a top speed of 202mph with just 562 horsepower. The Tesla's motors redline at about 16000rpm, which at the 9.7:1 fixed gearing ratio corresponds to about 155mph. If the gearing ratio were halved, the low-speed acceleration would reduce but the top speed would go up dramatically.

True, at 200mph the P100D battery pack would only be good for about 40 miles. But gas supercars don't do much better. At top speed, a Bugatti Veyron can burn through an entire 26-gallon tank of gas in just 12 minutes (51 miles).

Comment Re:AKA (Score 1) 304

So if we're hypothesizing replacing all ICE vehicles with EVs, we need 30x as many Supercharger plug-in spaces as there currently are gas pumps along major highways.

Taking into account both home-charging and destination-charging, I think you're right back down to 1x. On top of that, charging speeds will only ever get faster over the next 5-10 years. So there will likely never need to be as many EV supercharging spots as there are gas pumps now.

Comment Just one fatality (Score 4, Interesting) 297

two of which resulted in fatalities.

Sigh. One of the crashes resulted in one fatality. The other two crashes, no fatalities. (And it is not yet known whether Autopilot was engaged at the time of those two incidents.)

Getting distracted with Autopilot engaged is like removing your seatbelt because you have airbags. You may be able to occasionally get away with it, but it's still an incredibly dumb thing to do. (And the former endangers other drivers, not just yourself.) The silver lining of these incidents is that maybe more drivers will start paying more attention while using AP, though it should have been up to Tesla to properly instill this sense of caution to begin with.

And side skirts/guards should really be mandated for trailers nationwide. (They're already mandated in California.) It may not physically prevent an underride at high speed, but it doesn't have to; the radar is much more likely to detect them and trigger collision-avoidance braking. It's only a small patch for a small part of the problem, but better than not patching it at all.

Comment Re:Awesome! (Score 1) 136

As a Tesla owner myself (albeit a pre-Autopilot version), I am as shocked and saddened as anyone else by this incident. Obviously we don't know for sure that he was watching a movie, or even that he wasn't paying attention. For all we know he might have been paying full attention, but fully assumed the autopilot would brake, "froze" when it didn't, and failed to brake himself. Possible but unlikely. (Especially for a Navy Seal.) I'm sure we'll learn more as the investigation continues.

Why People Freeze

In the more likely scenario that the driver was distracted, my line above was just a way of emphasizing that even with autopilot, it's critically important to watch the road at all times. (Just as it's important to wear a seatbelt at all times, even though removing it usually has no consequences.) I meant the line in a somber, wry way, not in a fozzie-bear laugh-out-loud way. (if that helps.)

Comment Re:That came in at a pretty steep angle (Score 4, Informative) 206

There are two reasons that I've seen.

Third reason: Wind. In the post-launch press conference, Elon mentioned that the wind was significant during landing. (And may reach up to 50mph tomorrow on the way back to port.) So the rocket had to tilt somewhat into the wind to avoid being blown sideways relative to the landing pad, and only went vertical at the last moment. It also explains why the droneship maintains a slight tilt in some of the post-landing footage; this is to cancel out the considerable force of the prevailing wind.

Comment Re:"mass market affordable car" (Score 4, Informative) 430

And after these five years, I'd expect the range of the car to have dropped 20% or so.

Um, no. I own a vintage 2008 Tesla Roadster, and its range has dropped only about 10% over nearly 8 years. The battery chemistry and durability used by Tesla has only increased since then, so I the Model 3 will do substantially better even than that. Over five years, it might drop 5%. Possibly 10% at the outside, but not anywhere close to 20%.

Comment Re:A few potential issues (Score 3, Informative) 218

Now here's a huge issue I haven't seen anyone talking about that gets progressively worse as the track/tube length increases, subsidence and ground movement.

The subsidence / ground movement effect is dwarfed by the simple thermal expansion of the tube over the day/night cycle, which can grow/shrink up to hundreds of meters over the length of the tube. This effect can be compensated for by allowing the tube to slide smoothly across the pylons to achieve tensile equilibrium. (Perhaps with motorized assist to overcome friction.) The "slack" is taken up at the endpoint stations, through a telescoping system. Each pylon can allow for perhaps a meter of lateral flex to account for local ground shifting, and the pylons themselves can be easily repositioned if they start to get close to their tolerances in a local area.

By the way, how much material would such a full sized tube use up, and whats the current national production of said materials?

The complete Alpha-design hyperloop from LA to SF would use about 1 million tons of steel, or about 0.02% of the world's current annual steelmaking output. For scale, this is about 10x more steel than the Birds Nest stadium in Beijing, or about 100 Eiffel Towers' worth.

Comment Re:hyperloop without the hyper or loop (Score 1) 218

Presumably every Hyperloop capsule would be instrumented to gather data along its journey to immediately reveal any imperfections or problems. Since the travel surface is a completely controlled environment (no birds pooping on the tracks, etc.), it ought to be far easier to maintain than open highways or exposed railroad tracks. The Hyperloop system will directly generate revenue for its own maintenance and upkeep, whereas bridges really don't. (Toll bridges, maybe.)

Comment Re: Weather of Climate? (Score 1) 273

And how much gets bled off into space?

Much less than would be if there weren't so much CO2 in the atmosphere trapping the heat. As we inject more CO2 into the atmosphere, less heat escapes to space, and the equilibrium surface temperature rises quickly. This is why the human-caused rise to its current value of >400ppm is so alarming, and where the ultimate 350ppm "safe" limit calculation (to avoid catastrophic temperature increases) comes from.

Slashdot Top Deals

"The urge to destroy is also a creative urge." -- Bakunin [ed. note - I would say: The urge to destroy may sometimes be a creative urge.]

Working...