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The Physics of the Tesla Grin

Discussion in 'Model S' started by wcalvin, Dec 26, 2013.

  1. wcalvin

    wcalvin Member

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    #1 wcalvin, Dec 26, 2013
    Last edited: Jul 17, 2014
    Caution. Some Tesla owners would recommend that you postpone reading this until after the seat-of-the-pants surprises from your first test drive. But who knows: perhaps understanding the physics of it beforehand will merely increase the Tesla grin and lead to more rapid addiction. Your decision.​

    Coming back from driving a Tesla around the neighborhood, a first-time driver is often seen to wear a silly grin. One exclaimed, “It’s like warp drive!” But it’s really not about power. It is about instant torque in silence and no hesitations along the way.

    In the Tesla, there is an instant response to putting your foot down, even a little. Internal combustion engines take time to build up torque after your foot gives the instruction. On the floor above their assembly line, Tesla Motors manufactures an updated version of Nicolai Tesla’s 1882 AC induction motor, known for instantly achieving high torque. It has only one moving part, the shaft that spins.

    Only the most powerful gasoline engines can achieve such a prompt surge. Since that’s the only analogy that occurs to most drivers, they describe the Tesla in mega-engine terms. But Tesla's motor is about as big as a medium-sized bucket and hides between the rear wheels. The storage space under the hood could hold a few such motors.

    Drivers also expect a series of hesitations while getting up to speed, thanks to shifting gears along the way. But the Tesla Model S has neither a manual nor an automatic transmission. The smooth acceleration just continues without a pause, again suggesting “powerful” to the first-time driver. Tesla’s motor merely spins the fixed-ratio gear that rotates the wheel once for every ten turns of the motor’s shaft. (There is not even a gearshift for reverse; the electrical leads to the motor are merely reversed to make the motor run backwards.)

    To drive the Tesla Model S, you have to learn a new relation between your right foot’s activities and the car’s resulting motions. Things are far simpler in the Tesla, but it took me about a week to drive it as smoothly as a Lexus. I had to recalibrate my right ankle.The basic principle is that your ankle angle should be directly proportional to the desired speed. What could be simpler?

    But this is true for slowing down as well as speeding up, so there are some old habits to unlearn. Let up on the accelerator pedal and the Tesla will instantly slow, just as if you were in second gear in a gasoline car. In Tesla’s version of engine braking, about two-thirds of the energy spent getting up to speed is recaptured by the motor acting as a generator when slowing down, and is used to recharge the battery. Similarly, about two-thirds of the battery charge you spend when climbing a hill can be recaptured when going back downhill. (If only recycling objects were as efficient as recycling electrons.)

    This engine braking means that coasting feels very different in the Tesla. You cannot tap the accelerator to gain a little speed and then coast a little—a common tactic in slow-moving traffic. Try this is a Model S and your passengers will complain. Instead, you must precisely set the angle of your ankle, making minute changes to track the varying speed of the car ahead. That’s what took me a week to learn.

    Coming up to a stop sign, experienced Tesla drivers merely ease off on the accelerator until reaching about 3 mph and then touch the brake pedal. Tesla’s brake pads should last a very long time.

    In addition to diminished coasting, there is no idle. Gasoline engines require a starter motor to get the engine rotations up to a rate where they will not relapse to zero. There is no idling with Nicolai Tesla’s famous motor and so there is no need to "start" the car. Or to "turn it off."

    The engine noise is not a good guide to how fast you are going. That’s because it’s very hard to hear the motor at any speed. And there is no transmission to whine, no driveshaft to rumble along, and no muffler to vibrate as exhaust fumes are forced through it. Except for road noise via the tires, there is not much to hear, though you can always listen to a very distant radio station via the internet feed. I usually listen to WFMT in Chicago, a favorite from college days.

    And when you go to refill the “tank,” you discover that electricity costs only about 16% of what gasoline usually costs and, with routine overnight charging in your garage, you always start out with a full tank every morning. You can learn to like that.

    What’s not to like? The complaining is mostly about the extra planning needed for long road trips. You have grown accustomed to a convenient gas station appearing soon after you notice that the tank is down to a quarter full. If you stick to routes such as I-5 from Vancouver BC to Tijuana, where Tesla now has superchargers every 150 miles or so, a 20-minute stop will get you enough charge to make it to the next supercharger. Or you can stay for lunch and get a “full tank” in an hour. (Nothing to pay, either; access usually comes with the car.)

    Off Tesla’s grid, the big navigation display will direct you to a RV park or public charging station. But more than six hours must be spent there, waiting, so bring a good book or read one via the 17 inch touchscreen. Overnighting at hotels with convenient 220 volt outlets will also work, if you don’t mind only 240 miles per day before stopping for the night. By sticking to 55 mph, you can go 300 miles.

    But such considerations will soon diminish as Tesla builds out its supercharger network over the next two years. Parking garages are also adding “fast DC” charging stations that will get you on your way in about twice the time as a supercharger would take, though you will need to first buy an expensive adapter from Tesla.

    The persistence of the Tesla grin after the adaptation period deserves further explanation. You keep discovering yet another instance of good design by the engineers at Tesla Motors and wonder why every car manufacturer doesn’t do it that way. Sometimes a new feature is retrofitted overnight via a software update over the car’s internet connection. Get in the car the next morning and a pop-up window will explain the new feature. You grin again. (I keep hoping that they will surprise me with an option to lower the accelerator pedal's sensitivity at low speeds, so that stop-and-go traffic is no longer such a precision task.)

    Now that’s a concept—improvements in the car almost every month after you take delivery. But then you already knew that Tesla is not like other cars. It’s clearly in a class of its own. In taxonomy, the Tesla would rate a new genus, not a new species.

    William H. Calvin is a professor emeritus at the University of Washington’s medical school and the author of sixteen books on brains, human evolution, and climate change. It is six months since he last visited a gas station. See http://WilliamCalvin.org/EV/ for the "Tesla Simplicity Talk" to the MIT Alumni Club and http://WilliamCalvin.org for books and lectures.
     
  2. Tommy

    Tommy Member

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    Well said; the best "textbook" explanation I have read regarding the grin. Thanks Professor Calvin.:wink:
     
  3. artsci

    artsci Sponsor

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    +1. A joy to read:)
     
  4. Forty Creek

    Forty Creek Member

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    Just reading it, made me grin... several times.
     
  5. ahm

    ahm Member

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    Wonderful! Thank you.
     
  6. Newscutter

    Newscutter Member

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    #6 Newscutter, Dec 26, 2013
    Last edited by a moderator: Mar 13, 2016
    And this is what it looks like... and sounds like.

     
  7. jcaspar

    jcaspar Member

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    It's very much like driving my Dodge Viper in second gear at 30 mph. Instant acceleration with the press of the pedal and rapid deceleration when you let up. However, the Tesla does this from 0 to 70 with no engine noise. It does run out of torque nearing triple digit speeds, where the Viper keeps going.

    Nice write up.
     
  8. Chipper

    Chipper Active Member

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    Most Excellent! Thank you for this explanation.
     
  9. JPP

    JPP Active Member

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    Brilliant! Well written explanation that this neuroradiologist can understand...:)
     
  10. BigAirHarper

    BigAirHarper Member

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    ^+1 excellent description of the grin. I couldn't quit smiling the first time I rode in one. And definitely the "torque available to pass" is the best feature. Avoiding idiots becomes a dream plus a good excuse to gun it.
     
  11. drtko147

    drtko147 Member

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    Excellent explanation of the Tesla Grin. I have had my MS for the past 6 months and still brag about it. I do like the 2/3 of the regeneration going down the hill. I usually lose about 10 miles of energy going up my hill but gain back 4 miles coming down, all without ever using the brakes. It is mainly with a combination of foot on or off the accelerator. I have gotten used to call the pedal the accelerator rather than the gas.

    On Oahu, we have several very short on-ramps and getting into traffic is a breeze, even my 60 kW battery.
     
  12. SCW-Greg

    SCW-Greg Active Member

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    #12 SCW-Greg, Dec 28, 2013
    Last edited by a moderator: Mar 13, 2016
    It's like this, you say?



    Only better. ;)
     
  13. DanielG

    DanielG Member

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    Now this is something I can relate to and agree, having named seven genera and a few dozen species. Tesla drivers are a different breed, indeed! Thanks, made my day!
     
  14. BOOMER7

    BOOMER7 Member

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    #14 BOOMER7, Dec 30, 2013
    Last edited by a moderator: Mar 13, 2016
  15. Newscutter

    Newscutter Member

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    #15 Newscutter, Jul 16, 2014
    Last edited by a moderator: Mar 13, 2016
    I don't know who posted this (I suspect someone here on TMC) but it TOTALLY needs to be included in this thread:

     
  16. slcasner

    slcasner Member

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    When ICE drivers ahead of me employ this "common tactic" it is very annoying because I try to drive at a constant speed using cruise control whenever possible. In particular for maximizing range in an EV, using cruise control is effective to avoid exceeding the target speed and to avoid losses from unnecessary acceleration and deceleration. I realize you mention "slow-moving traffic" when cruise control may not be possible anyway, but the behavior is also all too common at cruising speed.

    The other annoying freeway behavior that is entering the freeway without accelerating up to the prevailing speed of traffic. With a Tesla that acceleration is so easy (and fun)!​
     

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