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A bigger motor

Discussion in 'Roadster: Technical' started by Takumi, Mar 24, 2007.

  1. Takumi

    Takumi Member

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    I'm surprised nobody has put this up. They've already stated that a bigger, stronger motor is more efficient...you get more bang and I believe this is cheaper than replacing the entire battery array.

    But someone posted on one of the blogs that their engine might be what we're looking for. Instead of going bigger, you can go smaller.
    Go to the FAQ at the bottom left:
    http://power.friesen-research.com/
     
  2. Tesla2Go

    Tesla2Go Member

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    Would the top RPM matter? On their page I see the 200 HP motor is rated at 1795 rpm, isn't that too low?
     
  3. Sk8orDie

    Sk8orDie New Member

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    No the RPM doesn't matter. With gears you can find the proper ratio for driving fast enough.

    The bigger Problem is the weight of the motor. something over 600 pounds seems to heavy to .

    An average AC_Motor has an effency over 90%, so if you get 99%, it's only an 10% improvement.

    The Motor in the Tesla works fine, though some people think taht AC-Motos are not the best solution for cars, but that's like a religious war. ;-)

    To say it clearly: The Battery is the problem/solution. If Altair Nano or EEstor manage it to bring their predictions to realworld market, they will be the big winners. Today you'll have to pay about 1000$ / kWh batterystorage. If the Price will hit 200$ or better 100 $ than the mobile revolution will beginn. You'll have to get the costs down. It's the same reason why we don't drive FCEV or H²-ICEs, they are simply too expensive.

    Hopefully the battery guys will do good job, so we can smash our Gasguzzlers.

    Best regards from Germany
     
  4. Takumi

    Takumi Member

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    Ah, you guys are missing the point. This is a modifications thread. All modders/tuners strive to achieve maximum efficiency. A little here and a little there can add up.

    Tesla's technical specifications page doesn't say who they sourced the motor from, but if I remember correctly - AC Propulsion.

    http://www.teslamotors.com/engineering/tech_specs.php

    ...and how heavy is that motor?

    Is the motor that Tesla is using the most efficient or just the most cost effective? Who out there makes the best motors? I'm sure this technology is not that young. Does Siemens make motors? Solectria? Advanced DC Motors?
     
  5. tonybelding

    tonybelding Active Member

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    Nope. . . Tesla produce their own designed motors in their own factory. They consider it part of the "secret sauce" that makes their car special, along with the design of the ESS. They did license some motor technology from AC Propulsion, that's all.


    About 70 pounds. They also claim it's about 85-95% efficient, so I'm guessing there's not a lot to be gained from tinkering with it or replacing it.

    I'm not optimistic about hot-rodding the Roadster and getting big increases in power or performance. It could be possible to tweak certain things. . . Somebody might "chip" the motor controller to change some of its characteristics. It's always possible to strip weight off the car. The gear ratios would be a natural target for tinkering with. And eventually there will be upgraded batteries, though I'm sure longer range will be more the goal than speed performance. But the motor? Hmm, I just don't see much potential there. It's not like a gasoline engine, you can't bolt on a supercharger or a nitrous kit!
     
  6. WarpedOne

    WarpedOne Supreme Premier

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    I still think removing some portion of battery pack would improve the performace numbers. I find it hard to believe all those batteries are there just to provide minimal required power density. Remove half of the pack and you gain cca 220kg, which roughly translates into 10% better acceleration and deceleration, better handling etc.

    Of course, range is at least halved, batteries age a lot faster etc.
     
  7. W8MM

    W8MM R1.5 #325 + Mdl S #01380

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    Be careful.

    Removing any of the battery capacity also has the effect of reducing the peak current capacity available from the total pack. 

    In electric cars, current = torque.
     
  8. WarpedOne

    WarpedOne Supreme Premier

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    I know, that is why I said: "I find it hard to believe all those batteries are there just to provide minimal required power density".

    I doubt the ESS and PEM are designed to draw maximum available (and allowed by Li-Ion chemistry) current at any time. I'd guess they are designed with reasonable safety margins to allow for the batterries to last longer by not taxing them to the max. If someone is willing to sacrifice their lifetime, he could probably eak out some "advanced" performance:)
     
  9. W8MM

    W8MM R1.5 #325 + Mdl S #01380

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    As I understood the explanation during my San Carlos tour, improvement in the effective series resistance of the battery pack is the key to better performance.

    When the back EMF of the motor rises with increasing motor RPM, the battery pack terminal voltage (cell voltage minus IR drop) determines the maximum RPM at which full current is still available.  If the battery pack terminal voltage sags with current demand, the maximum RPM for full torque sags as well.  Lower internal battery pack resistance (cell construction) will reduce terminal voltage sag and increase the motor RPM at which full torque is available. 

    Further progress in low internal resistance battery cells is the key to "hot-rodding" the Tesla Roadster.
     
  10. WarpedOne

    WarpedOne Supreme Premier

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    Hmmm, sounds logical. I therefore back away from my previous suggestion of halving the battery-pack.

    But I still have one more idea: different gear ratios  :D

    Roadster reaches 130mph at its redline at 13000rpm in second gear. At this rpm there is only about 105kW of power awailable. With a longer third gear it could reach at least 170mph.

    Edit: typoos
     
  11. vfx

    vfx Well-Known Member

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    So does anyone want to speculate why Tesla did not do this?

    There are have been some who have pointed out that the Roadster has a Supercar price but not Supercar top end...
     
  12. WarpedOne

    WarpedOne Supreme Premier

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    Stability.

    A little roadster without roof is something you wouldn't want to be in at 100+ mph, much less at 170mph.
     
  13. W8MM

    W8MM R1.5 #325 + Mdl S #01380

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    OK, I'll give speculation a try.

    I'm guessing that there are a number of factors.

    1)  Two gears and their housing weigh less and take up less room than three.  With more than a single gear per clutch shaft, the transmission becomes much more bulky and robs space and weight better used for more batteries.

    2)  Having only two gears and no clutch pedal to operate makes it possible to attract buyers who are used to automatic transmissions, thereby broadening the market appeal by a factor of three.  One only needs to select "Drive" (2nd gear) or "Sport" (1st gear) to successfully drive the car at ordinary traffic speeds.  During our test drive, the company driver pointed out more than once that 1st gear was only needed for "maximum performance" and rarely needed for even spirited driving.

    3)  A high speed 3rd gear is only required for extremely high speeds.  At extremely high speeds, the aerodynamic losses increase to the point where they suck prodigious energy from the battery pack.   The extra energy consumed while smashing air molecules out of the way reduces the miles per charge as speeds get really high at an exponential rate.

    This car is only being sold in the 48 continental states of the US.  Where can one drive a car faster than 130 mph in the continental US? 

    Perhaps at the race track?  I own a 605 hp Porsche that rarely exceeds 145 mph on any of the race tracks where I have driven it - flat out.  Going that fast, however briefly, on an ordinary US public road doesn't hold a strong appeal for me.  And, it's more than a little dangerous.  Few US drivers have autobahn experience.

    As the nanny state encroaches more and more, doing even 100 mph is going to become more difficult in the future.  The driving fun left for the future is going to look just like what the Tesla Roadster offers; go-kart handling and rocket-ship acceleration up to a limit of high two digit speeds.
     
  14. vfx

    vfx Well-Known Member

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    You make a lot of good points.

    Well this is the definition of a Supercar. I don't bother trying to explain the "unobtainable speed" thing. Probably has to do with the size of
     
  15. Michael

    Michael Member

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    Wouldn't the addition of a third gear also allow greater range per charge by requiring less energy usage per mile for regular highway mile driven?
     
  16. W8MM

    W8MM R1.5 #325 + Mdl S #01380

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    Michael,

    The concept of low-rpm cruising to get better fuel efficiency is a misconception when applied to electric vehicles.

    In an internal combustion engine, friction losses from all those moving parts (scraping piston rings, rubbing cam followers, main bearings, on and on) are considerable and lower engine speed reduces those losses.  With ICEs, over-drive gearing makes a lot of sense to reduce losses per mile driven.

    In a well designed AC induction motor, there are only the armature bearings (ceramic?) and very minor rotational windage (internal aerodynamic) losses to absorb energy.  The rolling friction of the tires and wheel bearings and the energy used to smash the roadside air molecules out of way are dominant.  Reducing the rotational speed of the motor relative to a given road speed for the car will have a vanishingly small effect on overall energy conversion efficiency.  If there would be any increase in efficiency by slowing the rotation of the electric motor, I speculate that it would be difficult to measure in the real world.

    In an electric car, the rolling and aerodynamic losses due to travel speed are way more important than gear ratio considerations.
     
  17. Takumi

    Takumi Member

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  18. W8MM

    W8MM R1.5 #325 + Mdl S #01380

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    Yes, it does.

    Back-EMF is directly proportional to rpm.  More rpm makes more Back-EMF.

    Once the rpm rises enough so that the Back-EMF equals the supply voltage, no current can flow from the battery through the motor; QED torque goes to zero when current flow goes to zero.


    No. 

    It's part of how electric motors function.
     
  19. WarpedOne

    WarpedOne Supreme Premier

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    >> Back-EMF is directly proportional to rpm.

    Can you give an estimation how big this thing is when the motor is doing useful work? Let say at 6000 rpm going 60mph using cca 20kW of power?
    If it is on the order of a few percent then it's not worth it. On the other hand if it is around 10% or more then it would probably be worth the added complexity.
     
  20. W8MM

    W8MM R1.5 #325 + Mdl S #01380

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    Let's look at Tesla's published torque curve:

    [​IMG]

    It looks to me like right around 6,000 rpm is where Back-EMF and battery internal IR drop, when added together, start to interfere with developing full torque output.  If one were to extrapolate the graph way off the page, it looks like Back-EMF might equal the battery voltage at around 17,000 rpm.
     

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