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Hub motors revisited

Discussion in 'Technical' started by dieqast, Mar 4, 2008.

  1. dieqast

    dieqast Member

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    Hey everybody,

    My question is if Tesla ever played with the MIEV-idea, the use of 2 or 4 small electrical engines in the wheels instead of one big engine + connectionshafts? My opinion is this is a more compacter(thuss lighter), practical and efficient solution as you'll need less parts. Or has Tesla done some homework to prove that the 1 engine-solution is better? Also with the lower point of gravity and more space for batteries it looks like something ideal for this great innovating company to work with in the future.

    Thanks in advance.
     
  2. TEG

    TEG TMC Moderator

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  3. dieqast

    dieqast Member

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    Thanks for the links, I don't know the figures, but my hypothesis is that the efficiency of 4 seperate motors is better than mechanical efficiency of the drivetrain. My guess is that mechanical efficiency gets up to 80%-85% and the loss in efficiency between 1 and 4 seperate elektric motors is say low 90%'s. This is just guessing though, I haven't done any research on this. And my opinion is that the unsprung weight won't effect handling proportionately. Other than that, Tesla should stick to their current design for future models.
     
  4. vfx

    vfx Well-Known Member

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    Actually unsprung weight was the big reason not to use wheel motors in a sports car. Fine for a Milk Float / delivery van but crappy for a car that's supposed to have handling a priority.

    Check out Martin's comments under "Other Ideas" at the bottom of this page:
    Tesla Motors - think
     
  5. Brent

    Brent Member

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  6. Hunter

    Hunter Member

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    Before I start, it makes some difference here which Tesla drivetrain we're talking about. For simplicity I'm going to stick with 1.5, which just has a single reduction gear.

    First note that these hub motors are not likely to run at wheel speed either, so they also need reduction gears. So it's not right to act like you skip all drivetrain losses by using hub motors. It seems to me that the only part you are getting around is the differential. These vary to a certain degree, but I would expect this part to be at least 95% efficient. And I would anticipate the four little motors would be less than 95% as efficient as the one big motor, but I can't find much in the way of specs around. In any case, whichever way you go it's going to be very close...you won't save more than a percent or so.

    Of course, the whole question (while interesting) is basically moot...efficiency wasn't even the big reason Tesla cited for going with the one motor. You offer no explanation why you don't think unsprung weight matters. It does. In addition to the links TEG gave, this Tesla blog on driving dynamics explains it well (and is good read for lots of other reasons). That plus the cost, weight, and complexity make great reasons to go with the single motor, and even if the hub motors were a couple percent more efficient it wouldn't be enough to override these concerns.
     
  7. W8MM

    W8MM R1.5 #325 + Mdl S #01380

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    There's also a reliability argument involved.

    MTBF (mean time before failure) responds inversely to the square of the number of parts in an assembly.

    If a single hub motor were to achieve the same MTBF as a big motor, one could expect the failure of one of the group of four hub motors compared to the failure of the big motor to occur 16 times sooner, on average.

    It seems to me that trying to make a hub motor that is pounding up and down over pot holes 16 times more reliable than a big motor isolated in the central chassis is a pretty tall order.
     
  8. doug

    doug Administrator / Head Moderator

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    Personally, I don't think hub motors are necessarily better.
    However, as a scientist and engineer, I'd really like to see someone try to make a performance vehicle with them.
    They pose an interesting control problem and I'd like to see that experiment in action.
     
  9. doug

    doug Administrator / Head Moderator

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    From SEMA 2008:
    Highlights from SEMA 2008 - The New York Times > Automobiles > Slide Show > Slide 5 of 13
    towurboat-005.jpg
    towurboat-003.jpg
    Electric Ford F-150

    Updated: Hi-Pa Drive Ford F-150 Is All Electric - PickupTrucks.com News
    [​IMG]
    [​IMG]

    2009 Ford F-150 by Hi-Pa Drive - 2008 SEMA Show Photos & Coverage - Truck Trend

    It's too bad it looks like PML is going out of business.
    Hi-Pa Drive from PML flightlink
    " Hi-Pa Drive is a PML Flightlink product. "
     
  10. graham

    graham Active Member

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    I like the idea of hub motors on more "off-roady" type vehicles, where traction is key, and road handling is less important.

    So this pickup, and the Jeep Wrangler seem like good candidates.

    I hope someone does produce one of these vehicles so we can see how good or bad the idea is.
     
  11. vfx

    vfx Well-Known Member

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    I'll be a lot happier when the makers of these mockups feel obligated to use the industry standard EV connector to give them credibility.

    All the fancy graphics in the world don't make up for those hokey wall plug pins pointing at you.
     
  12. TEG

    TEG TMC Moderator

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    #13 TEG, Jan 11, 2009
    Last edited: Mar 9, 2012
    As we have heard elsewhere, the maker of those hub motors is in financial trouble. Yet to be seen if anyone can get them in volume.
     
  13. doug

    doug Administrator / Head Moderator

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    http://www.electric-vehiclenews.com/2012/03/nissan-seriously-testing-in-wheel.html

    It interesting to see this quote. I was recently thinking about wheel motors and how a lot of companies had show them in concept but ultimately given up on them for whatever reason. The only company that came to mind that I thought might actually use them was Nissan for their Pivo. Then again that may not ever get made either.

    Nissan PIVO

    Nissan_Pivo.jpg
    nissan-pivo-3-hands-on-side.jpg
     
  14. neroden

    neroden Happy Model S Owner

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    I suppose it's just a space issue. Per-wheel motors are already standard in trains. And versions mounted on the frame (so that they're sprung weight), with a universal joint on the connection to the wheels, are already in use. But they're probably too big for use in cars. I guess someone just has to shrink the motors. Getting them attached to the steering wheels would be hard, but on the non-steering wheels it would seem trivial.
     
  15. TEG

    TEG TMC Moderator

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    Daimler/Mercedes has been showing off that inboard motor per wheel idea that I think makes a lot of sense.
    mercedes-electric-drivetrain.jpg
     
  16. ElSupreme

    ElSupreme Model S 03182

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    I happen to think this is the future, with a motor for each of the four wheels. Just think of the traction control you could get out of a car like that. Hopefully they get the uber-nice Tesla packaging on the inverters though.
     
  17. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    I'd like the brakes to be inboard as well. It would really reduce the unsprung weight. It worked really well in the DS-21. Inboard brakes also allow for centre-point steering.
     
  18. VolkerP

    VolkerP EU Model S P-37

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    This über-Tesla is called the Concept_one by Rimac Automobili. See technical concept here: http://youtu.be/U021JCmxYNs. The motors are explained at 1:00. No mention of traction control but of torque vectoring. This is basically the same concept taken one step further. Dedicated thread: Rimac Automobili
     

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