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Tesla Semi is reasonable, part 1

25 Nov 2017, 05:41 UTC
Tesla Semi is reasonable, part 1
(200 words excerpt, click title or image to see full post)

Tesla finally unveiled their semi truck:
https://www.tesla.com/semi/
An electric monster with 4 Model S motors, one for each drive wheel, with an astounding 500 mile range (beating most people’s expectations). Fully loaded (i.e. 80,000 lbs total), it can accelerate from 0 to 60mph in 20 seconds. Unburdened, it can do 0-60 in 5s. What’s the point of this kind of performance, other than the ability to go up a 5% grade at 65mph fully loaded? In a traditional vehicle, the conventional wisdom is that an over-powered vehicle will kill your efficiency. And how can you make a 500 mile range electric truck without destroying your payload capacity?
In an electric truck, efficiency and power are related in the opposite way you might expect. The truck shaped a bit like a bullet, with a drag coefficient of 0.36 (like a sports car instead of a “barn”) and an efficiency of better than 2kWh/mile. And the insane performance?
Well, by running more motors in parallel, the effective power loss due to resistance in the coils is reduced since Power loss = I^2*R. Torque is proportional to current and number of motors, so if one motor with resistance R1 needs to generate ...

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