Kymco SuperNEX electric bike, 155 MPH.

Discussion in 'Electric Motorcycles' started by T.S.Zarathustra, Nov 7, 2018.

  1. kaertner

    kaertner Long timer

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    Horsepower has nothing to do with the design of a gearbox from a reliability perspective. Torque is the key issue when designing such a component.
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  2. Dino de Laurentiis

    Dino de Laurentiis Working on it

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    I’ve also seen nothing that suggests that the front and rear motor of Teslas are geared for different speeds. Seems like that would create more issues than it solves, drivability wise. It also seems like a thing that Elon Musk would’ve loved to talk up if it existed.

    Regarding the Roadster, I don’t know where the gearbox came from but I know they took it out because it was to prone to breakage and furthermore was deemed unnecessary.
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  3. ctromley

    ctromley Long timer

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    No, this has been done before. I've seen a Honda CRX that had an entire - and entirely separate - second CRX drivetrain behind the driver. Hobbyists have created their own hybrids by leaving the original ICE in place and adding an electric drivetrain to the other axle. There was a road racer that put two separate electric drivetrains in an AWD Subaru. It works fine. The only common 'ground' you need between the two is the road itself. (See what I did there?) It actually gets easier with two separate electric drivetrains because if you want to do any monitoring/control/coordination of them (like for traction control) it's simpler.

    It makes no difference if there's a difference between the two in motor speed. They both run at the same road speed.
    #23
  4. T.S.Zarathustra

    T.S.Zarathustra Been here awhile

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    "Starting in September 2008 Tesla selected BorgWarner to manufacture gearboxes and began equipping all Roadsters with a single speed, fixed gear gearbox " "The company previously worked with several companies, including XTrac and Magna International, to find the right automatic transmission, but a two-gear solution proved to be too challenging."
    https://en.wikipedia.org/wiki/Tesla_Roadster_(2008)

    "Reduction gear ratio- Large motor 9.73 to 1, Small motor 9.34:1"
    https://forums.tesla.com

    So you are saying that different gear ratios can give you more grunt at low speed and higher speed! Who are you, and what did you do with CTs body? :lol3
    #24
  5. ctromley

    ctromley Long timer

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    If you're trying to make a point, I'm not understanding it. Can you walk us through it? A lot more context behind that second quote would help. (Your link goes to the front page of the forum, not the post or thread.) And I'm not sure how it's related to the first quote.
    #25
  6. T.S.Zarathustra

    T.S.Zarathustra Been here awhile

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    You have convinced me. This is probably a misunderstanding on my half and a different gear ratios are just a rumour. If they exist, any probable advantage is coincidental. I take back my praise about Tesla engineers having designed a clever solution to the gearing problem.
    #26
  7. ctromley

    ctromley Long timer

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    Another factor that might convince you further is that the two ratios listed are only 4% apart. That's near-worthless in terms of torque multiplication. Not only that, the bigger reduction is on the larger motor, backwards from what you'd expect. I think the difference is for other reasons, like maybe the smaller reduction on the smaller front motor allows slightly smaller gears and a slightly smaller housing, enough to provide a small but desriable increase in space or improvement in shape in the "frunk."
    #27
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  8. RedRocket

    RedRocket Yeah! I want Cheesy Poofs

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  9. ctromley

    ctromley Long timer

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    From the link:

    The two-speed was originally used in order to meet the performance requirements for acceleration and top speed. The solution came from work that was being done for the WhiteStar sedan. In order meet their performance targets, Tesla has modified the power electronics module to be able to send significantly more current to the motor and hence produce sufficient peak power to get the four second 0-60 time....

    As was discussed in the previous story about using the Roadster as a track car, the limiting factor there is the heat build-up in the motor. The air-cooled AC induction motor would simply get too hot causing power limiting logic to kick in and not be useful on the track. One of the changes being developed for WhiteStar, which will be a larger heavier vehicle than the Roadster requiring more power, is a liquid-cooled motor. The Roadster will now also get a liquid-cooled motor. This will allow to produce more sustained power than before.


    This is what I've been saying all along. Tesla is relatively new to the game, so they had to learn that lesson the hard way. If you're designing a new EV and you have the choice to use a transmission or not, you're better off bumping up the current limit and making any necessary related changes to handle it. You'll end up with equal or better performance, less weight, less complexity, easier packaging and lower cost.

    Can you use a transmission and utilize the seemingly obvious advantage of a few gear reductions to multiply torque progressively, thereby getting by with a smaller motor and controller? Yes you can. But EV manufacturers have found over and over that designing for a fixed ratio, with all the adjustments that entails, is the better solution. That kind of practical experience beats theory every time.

    Having said all that, I've seen recently that some transmission manufacturers are developing transmissions specifically for EVs. The target market is very heavy vehicles, or maybe very up-market e-SUV's (which are also very heavy, where maybe more tech for its own sake is a selling point, and they serve a market with less price sensitivity). Basically the real market is vehicles that have a much broader set of requirements than passenger vehicles. Maybe a better use for an EV transmission? From https://www.autoblog.com/2015/07/21/how-many-speeds-make-sense-for-ev-transmissions-probably-one/ :

    ZF went through a lot of concepts, he said, with one gear or two or more. "We made a lot of investigations on that, especially here with passenger cars but also with bigger vehicles," he said. "Our assumption at the moment it that for conventional cars, for an urban vehicle where the maximum speed is 120 or 150 maybe [kilometers per hour, so 75-93 miles per hour] or even for Tesla, which is very powerful but also fast, one gear is enough."

    Tesla seems to be sold pretty solidly on the no-transmission concept. Their new semi-trailer tractor truck does 0 - 60 in 5 seconds (20 seconds with a full 40 ton gross weight) and a 500 mile range at that gross weight and 65 mph. They use no transmission. They prefer a more direct approach to torque multiplication - four independent motors.

    So I wonder where this will end up. If efficiency is the goal, I'd like to see the numbers that support using a transmission. Keep in mind that the more EVs there are, the smaller the market for transmissions. If I was a trans manufacturer I'd be trying to drum up business too. Maybe there's something to it, but success will be determined by the commercial truck users. Those guys don't care about snappy sales patter or swoopy styling - they care about cost per mile. That expensive high-zoot transmission needs to pay its way. The market will decide, theory be damned.

    Just to be clear, theory certainly has an important place in all of this. But sometimes it's applied without considering all the factors in play.
    #29
  10. T.S.Zarathustra

    T.S.Zarathustra Been here awhile

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  11. ctromley

    ctromley Long timer

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    From the link:

    It’s an interesting setup, and I’m curious to see if any mainstream automakers will think it’s worth the cost, since single-speed units seem to do just fine, as electric motors have ample low-end torque, high enough revs, and good enough efficiency across the power band to make do with just one gear ratio. You can learn more about why most EVs use a single gear in Engineering Explained’s YouTube video below:



    Two speed transmissions might(?) be useful for road vehicles when desired top speed gets into maybe the 130+ mph range. (Higher for an EM. The Strike promises to do 135 with one speed.) Note that the Tesla Model S tops out at 155 mph (250 kph) because it's a governed limit - actual top speed is higher. And it still flies in ludicrous mode at lower speeds, even with that high speed gearing. I'm betting a second motor is cheaper/simpler than a transmission. Especially now that the Model III has proved that Switched Reluctance is now viable for real-world production use.

    But lets be real - none of this matters except on a race track. Again, the market will decide whether transmission manufacturers have a future.
    #31
  12. futureborder

    futureborder Been here awhile

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    I have been following Tesla for many years, the Model S definitely has different gear ratios for the front and the rear motor (in the older version with two identical motors at least, the latest version Model S have the Model 3 motor in the front). They used to be geared long in the front, for efficient highway cruising at higherspeed and short in the back for powerful acceleration.

    The Tesla Semi has four motors and gearboxes, one for each wheel. Those are also geared differently with two different ratios, in the same manner and for the same reason would be my guess.
    #32
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  13. ctromley

    ctromley Long timer

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    Just to refine your terminology, the Tesla Semi does not have four gearboxes, as in multiple speed transmissions, it has four fixed single-speed reductions. And there is no decoupling (as in mechanical or electrical disengagement) at all, all motors are delivering power together, right? If true, I'm thinking this is done for acceleration because the gearing difference is in play at all times affecting motors running at both ratios - they're all connected to the same road. Since efficiency tends to stay high over a fairly broad speed range there's probably not a lot to be gained there.

    I do see now an advantage to running them at different ratios, depending on the power characteristics of the motor/controller combos. Doing so would keep the longer-geared motor(s) in the fat part of the power curve (before dropping out of current limit makes it start tapering off) at higher speeds, while still having enough torque to smoke all the wheels at low speeds. (The front wheels smoking much more easily due to weight transfer, so that's where you want the longer gearing.) It's a balancing act though. Since Power = Torque x Speed, and torque is constant with constant (limited) current, power is less as the longer gearing suppresses motor speed. It gets even more complicated as the motor drops out of current limit, since torque drops, so power declines even as speed increases. The shape of that decline is critical. There's a fair bit of analysis to be done, by over-laying power curves at different ratios to get it right. As long as nothing goes beyond its rev limits you're in good shape mechanically.

    In deference to T.S.Zarathustra, this is a similar effect to having a transmission (but with multiple ratios in effect at the same time) without using an actual mechanical transmission. It's more of an electrical implementation of the concept. But as mentioned before, the cited ratio difference is small - so I have to wonder how much effect it can have.

    Any official info on what the ratios are?
    #33
  14. futureborder

    futureborder Been here awhile

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    I dont know the exact ratios anymore but I remember I was very surprised that they were so different - one was more than twice as long as the other I seem to recall vaguely (almost 20:1 vs 9.something:1 or so). You'd have to ask around on the /r/teslamotors subreddit or on electrek.co for more precise info.
    #34
  15. Dino de Laurentiis

    Dino de Laurentiis Working on it

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    Well, in further deference to @T.S.Zarathustra it turns that the upcoming Porsche Taycan BEV has a two speed gear box. It’s not as fast as a Model S, as it does 0-100 km/h in just over 3 secs, but according to Porsche, the two gears help reduce the heat load on the driveline so that it’s possible to do multiple 0-100 or 0-200 without impairing performance. Apparently, the Model S can only do one or two full speed runs before it automatically reduces performance.

    For outright speed it doesn’t seem to be a factor though, and I would imagine the drive line in a motorcycle is under a lot less stress than in two ton car.
    #35
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  16. ratdog

    ratdog Long timer

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    <rant>

    Hold on! This is all about a bike that doesn't even exist, almost 4 years since the initial press releases!

    Fist off, I find statements like "***Break for a lesson in EV fundamentals***" highly annoying if not offensive.

    Nothing quite brings out the pedants like electric vehicles and what's "best".

    Gearboxes? depends.
    System Voltages? depends.
    Motor architecture? depends.
    Controller circuitry? depends.
    Battery technology? depends.
    Charging infrastructure? depends.

    I'm an EE. My wife and daughters are/were in science but care less. For them now (car), there are only 2 things that matter: range and cost. OK, maybe a sunroof. If I start on any of the above subjects, their eyes just glaze over, as do those of 99% of the population.

    Now to have every single point repeated dozens of times, ad nauseum, in infinite forums (fora?) just drives home the vehicles are only for nerds and now have the cachet of minivans at best. Even my Tesla friends are sick and tired of the subject.

    ...and then to apply the (oft heated) arguments to something that doesn't even work yet is ridiculous.

    If you have something new to contribute, then sketch it out, stop pontificating and go build something! Tell us about the results of something new. The merits of IGBTs vs FETS matter to no one other than the engineers that design them and the accountants that cost them.

    Lastly, having observed firsthand Chinese engineering and QA (yeah, I know they're Taiwanese), the idea of riding such a bike at 155 gives me the howling fantods. Let's stick with establishing a footprint for electric vehicles and work on the utilitarian aspects first, and then masturbate over future details later.

    </rant>
    #36
  17. ctromley

    ctromley Long timer

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    What I find "highly annoying if not offensive" is when someone like you bursts onto a thread with what appears to be their first post in the entire subforum, ranting that people are discussing things you don't want to read about. Here's a thought, if the thread is not going where you want it to, stop reading. Sure, it's a radical idea, but surprisingly effective. Or maybe we should cut you some slack for sharing this outburst - it appears virtually all your recent content has been in CSM, where ranting is the order of the day. Point of etiquette: In this subforum, it's not.
    See, the way forums work is that when a topic for discussion is opened, the conversation tends to go where it goes. That's sort of a big part of the definition of "conversation." In this case the topic of transmissions in EVs was more popular than the SuperNEX in particular. The fact that it's a prototype is immaterial.
    You are correct. What's special about EVs is that the pedants are almost universally trying to figure out this strange new technology, with very little knowledge to work with. I appear to be the only one here who has decades of hands-on experience, both on the technical side and with public understanding and acceptance, and I've seen before where ill-informed speculation takes things. I know first hand the truth of the saying, "Be careful of what you let into your head - it can be very hard to get the wrong stuff out." So I attempt to prevent the wrong stuff from taking root. If you read the comments here, while not in a rant mindset, I think you'll find there's a lot of discussion about what the topics you list depend on and why.

    Most of the people on this thread are in the process of starting from scratch in learning a new technology that is just as complex as the ICE technology they know. Arguably the greater benefit to these discussions is not in learning what's 'best' or getting a firm answer for any particular question, but in learning how the tech works and how this relates to that. Understanding nuances leads to big-picture understanding as pieces fall into place. In the post of mine that you quoted, the "blah blah blah" you inserted in the quote replaced me explaining something that I had just learned from the discussion. Go back and see. You are apparently oblivious to one of the most beneficial facets of these discussions - you cut out a perfect example of what, for me at least, is the most important part! That post is here:

    https://advrider.com/f/threads/kymco-supernex-electric-bike-155-mph.1349324/page-2#post-38130316

    Maybe it's comforting to you to live most of your life in CSM where you can rant to your heart's content, where the last person to comment 'wins' because they got in the last word. In this subforum there is certainly some of that, but mostly we're here to learn about new stuff.
    I'm an ME. My wife couldn't care less about this stuff, like 99% of the population. So what? The people reading this subforum do care. It's why we're here.
    If you think there's nothing but repetition here, you're still in CSM mode where you're trying to 'win'. If you're trying to learn, you'll find that each example of what you think is a re-statement actually has a different perspective or context. Yes, it can be somewhat repetitious, but learning requires repetition to an extent.
    I'm thinking you didn't read the whole thread. If you had, you'd know that only one electric motorcycle (Empulse TT) has ever been produced that had a six speed gearbox like the SuperNEX. That's a valuable data point (if only one), and those who road tested the Empulse thought the gearbox was entirely redundant. I know of one inmate who owned one who said pretty much the same thing.

    BTW, you appear to think you can't know if something will work until you try it. I'm a product development engineer. In my line of work, especially as an ME, it's important to have a good sense of what works, what doesn't, and why before you start building something. The building of prototypes is mostly for verification purposes - you shouldn't be learning anything major at that point, or you're doing it wrong.

    EEs have a bit of a different take on this, because most of their design is in schematic form, and they take a build-and-de-bug approach because modding a circuit board or rolling a new one is quick, easy and cheap. Not so in the mechanical world. If we MEs make a mistake we end up with 1000s of dollars of scrap and a two month project delay. I once lent some design time to an EE for a mechanical project he was leading. Weeks later I saw his team in the lab laboriously working to correct a machining mistake to stay on schedule. The EE looked at me and said, "Y'know, you MEs have the worst editor ever." I laugh about that to this day, because it was the only instance I know of where an EE actually experienced that part of the ME world first hand - and understood what it meant.

    You get good at this by not seeing theory as a broad rule-of-thumb, but understanding it thoroughly enough to see why it works in detail - including where the over-generalized rule-of-thumb breaks down. And how real-world applications are notoriously hostile to rules-of-thumb, because they bring multiple influences of varying magnitudes that are frequently in conflict, and all affect your end result. Go back through this thread and you'll find lots of references to real-world influences and trade-offs.
    Wow. A little misplaced US pride, perhaps mixed with some xenophobia? FACT: Any country is capable of producing the highest quality nearing utmost perfection, or the most horrifyingly repulsive crap imaginable, and everything in between. I've seen the full range coming from both the US and China. You have too. What you say was more generally true years ago, but that is changing rapidly. If you don't believe that, you've been living in CSM far too long.

    Maybe you would do well to go screen-free for a few days. Breathe. Relax. Take a walk, listen to the birds. Engage with your wife and daughters. Listen more than talk. When you re-engage with the electronics, try seeing it as an opportunity to learn, not as a place to spew in service to your ego.

    And remember the #1 rule for forums - if you don't like what you're reading, just stop. The purpose of these forums should be to learn, not to 'win' some kind of digital debate. If you think I'm trying to 'win' with this response of mine to you, you're wrong. We all do this to varying degrees, and I'm writing this as a lesson to myself as much as you.

    Internet debates frequently generate lots more heat than light. The pendulum just keeps swinging back and forth. If you can get the pendulum to stop instead of just pushing it back, you'll find it generally stops at something close to reality. You're also likely to find that 'winning' doesn't matter, unless it results in finding reality.

    Reality always wins. We play along, following reality's rules, or we fail.
    #37
  18. T.S.Zarathustra

    T.S.Zarathustra Been here awhile

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  19. wheresbaoskee

    wheresbaoskee Perpendicular to Everything

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    Nice looking naked, but I was really hoping they would follow through on the sportbike.
    #39