Friday, December 19, 2014

Elon Musk’s twitter: Time to unveil the D

Originally published in the California Tech October 27 2014.


Elon Musk's twitter: Time to unveil the D

Casey Handmer


On Oct. 1, Elon Musk tweeted "... time to unveil the D ..." Unlike previous mysterious tweets, the substance of this one was guessed reasonably quickly. Two years after the release of the revolutionary Tesla Model S, an updated version is available.


D stands for dual motors. The current Model S has only one motor, and the fastest version, the P85+, does 0-60 in a staid, lumbering 4.2 seconds. If there's one thing everyone can agree on, it's that this is embarrassingly slow. More seriously, the dual motor approach is more efficient at a range of speeds and forms an important test of the powertrain for the upcoming Model X crossover.


The new model looks the same but can reach 60 mph from a standing start in 3.2 seconds, pulling an average of 0.9 gs. The number of road-legal cars that can do this can be counted on one hand. There's the Bugatti Veyron and a handful of other supercars which cost in excess of a million dollars. There are a few electric one-offs, including the Wrightspeed X-1 (2.9 seconds), the Rimac Concept 1/Volar E (2.8 seconds) and the White Zombie, a converted 1972 Datsun that reaches 60 mph in 1.8 seconds and dispatches the quarter mile in 10.24 seconds. But none of them seat five with cargo, and none are controlled by a giant touchscreen.


Also, none of them have autopilot. What? Tesla also unveiled their rapid (less than a year since starting) progress with car autopilot. Rather than aiming for complete autonomy, like Google or the DARPA grand challenge, Tesla has decided to pick a bunch of cheaper, more versatile sensors, then gradually upgrade the software that translates their input to car control. Tesla's sensor array includes GPS, forward-looking radar, omnidirectional ultrasound (sonar), and a forward looking camera. In combination, they work well enough to hold or change lanes, perform adaptive cruise control, check for cars or objects in blind spots, recognize speed limits, and automatically brake the car to avoid a collision. It remains to be seen how well this system works in practice, or how effective it actually is in combating driver fatigue and carelessness.



Image courtesy teslamotors.com


What's the big deal with Tesla anyway? It's a relatively tiny startup that makes cars. Fancy, shiny, and extremely expensive cars. If there's one thing cities in the US don't need, it's more cars. Given that cars will continue to exist and make modern lifestyles possible, Tesla plans to introduce a cheaper mass market car in 2017, codenamed Model 3. Probably a scaled down Model S, it will rely on mass production and innovative battery construction to lower costs to around the $35,000 mark, which is quite affordable when you factor in reduced cost of ownership. To get there, Tesla is building a battery "Gigafactory" in Nevada. Tesla once chose the 18650 cell to exploit its ubiquity and availability - today producing 30,000 cars a year, Tesla consumes more than 60% of world supply. Getting battery costs below $100/kWh is seen as essential for their wide adoption, and certainly their use in more facets of life is part of the Tesla/SolarCity master plan. Solar generation can be buffered at every scale in a future smart grid with the introduction of in-home battery packs with incredible and affordable capacity.


In the more distant future, electric propulsion has the potential to revolutionize air transport too. Battery energy density need to improve by a factor of 3 to 10, and powering light planes or even long-haul flights electrically is certainly possible. But more than that - electric motors have a much higher power-to-weight ratio than almost any other type of engine. The explosion of toy quadcopters is a testament to this fact. An airplane with a power-to-weight ratio greater than one is capable of vertical takeoff and landing and, with appropriate turbine design, supersonic flight. For the first time, humans may fly in planes that aren't immediately analogous to birds.


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