Kymco SuperNEX electric bike, 155 MPH.

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

  1. T.S.Zarathustra

    T.S.Zarathustra Been here awhile

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    Interested? I know I am. :velvt
    Kymco, the scooter manufacturer, seems to be betting the future of the company on electric. At the EICMA show they introduced a new electric motorcycle, chock full of interesting ideas, and capable speed at up to 155 MPH (250 KMH) in under eleven seconds. No range information though. Electrek.co is one of places discussing this bike.

    https://electrek.co/2018/11/06/kymco-high-powered-supernex/

    supernex-header.jpg

    Edit. And on our new frontpage :-). https://advrider.com/kymco-shows-off-electric-supernex-superbike-eicma-2018/
    #1
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  2. MJSfoto1956

    MJSfoto1956 Been here awhile

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    the electric tsunami is coming.
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  3. falcn

    falcn Squidless Soul Supporter

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    WOW! I am certainly interested. Looks great. I want the naked version. :D
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  4. RCmoto

    RCmoto Long timer

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    Hopefully sooner than later!
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  5. Dino de Laurentiis

    Dino de Laurentiis Working on it

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    Cool bike, but I’m not sure why they felt they needed to put a gearbox on the thing, and particularly a six-speed gearbox. If there’s no need for a gear box in the electric race bike used in MotoE next year, I don’t see why this one would need it, other than to cater to conservative bikers.

    I mean, I could maybe see the point of a two speed gearbox to improve acceleration somewhat, but six is just pointless when you have a usable power band of 5000+ rpms. The sound amplification thing also sounds (!) quite gimmicky but at least it seems that’s possible to turn off.
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  6. ctromley

    ctromley Been here awhile

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    My feelings exactly, and I commented on the Electrek article to that effect. This seems like a management decision, from managers who are far too removed from their customers. I get the basic idea that you want to lure ICE riders to EMs by making them seem familiar, but it turns out just being an insult to the buyer. It won't take long before s/he understands that the transmission was really no more than the equivalent of training wheels, but when they get it and want the real EM experience, they can't take the trans/training wheels off.

    And yeah, the sound thing is dumb too, though I can see how it might be an assist to the (useless) shifting.

    I can see this fakery for an entry-level bike. For a 'superbike', which is supposed to be for people who know what they're doing? Absolutely no way. I have no interest in this. Kymco's head is in too wrong a place.
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  7. T.S.Zarathustra

    T.S.Zarathustra Been here awhile

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    Race bikes are never in start-stop traffic so they can be geared much higher. It is a common misconception that electric motors have full powerband from 0 rpm until they reach high enough rpm that centrifugal forces blow the motor apart. They do have powercurves and the power has dropped off a lot when you reach very high rpm. Six gears are an overkill, but if you are designing a gearbox anyway, why not make it six gears? After all, this is only a prototype.
    The sound is another thing that I would put at its lowest setting and forget about, but we all know "those guys" who equal noise with power. This is to please them, and the politicians who are making rules that electric vehicles must have noise making equipment.
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  8. ctromley

    ctromley Been here awhile

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    Sorry, not buying it.

    If you're designing a bike from a clean sheet, you quickly find out that your path for best all-around performance, range and cost is to stay away from a bulky, expensive gearbox and clutch. Increase your current limit instead. Perhaps some other enhancements to handle the extra current. (Sometimes not necessary.)

    ***Break for a lesson in EV fundamentals***
    An ICE takes the incoming gas and air and goes through a hideously complex mechanical dance trying to get ignition timing, cylinder filling, intake and exhaust port resonances, combustion flame front propagation and a squillion other black art phenomena to all work together to eke out some small proportion of the chemical energy in that gas and turn it into power at the wheel. The result is generally rather poor overall, extremely poor at low rpm, so a transmission is needed to help the engine function as a power source.

    To put it bluntly, the trans is a crutch. ICE fans treat it like it's some joyful, deliciously engaging part of the experience. Sorry, it's just a crutch to help the ICE limp through its weakness. And this is from someone who can do a clean heel-and-toe, double-clutched downshift into a non-synchro first gear in a vintage sports car. I get it. But a trans in an EV is an anachronism.

    The power in an EV is not in the motor. It's in the battery pack. The controller is the gatekeeper, its current limit is the size of the gate. Bigger current limit, bigger power (assuming you're still under the battery's limit). Torque is directly proportional to current, regardless of speed. ALL of that power is going to go into the motor, and ALL of it will come out (minus a small efficiency loss). The motor is nothing but a conduit for that power. The only magic in the motor is what keeps it from turning into a ball of copper snot when Big Power comes through it. (Turning a motor into copper snot means some of that power got converted into melting copper.) It's time-dependent, meaning it's cooling dependent. You can get 2X - 10X a motor's power rating for short periods. (Milliseconds to minutes, depending.)

    Bottom line, hot-rodding EVs or EMs is different, but generally easier.
    ***We now return you to your regularly-scheduled rant.***

    For a bike like this, even geared for 155 mph, you can lose the trans and still flatten your eyeballs from a launch. (Purpose-built electric drag racers generally don't use gearboxes, and a strong launch is arguably even more critical than high speed for those guys.) Having no trans means you also have more space for batteries. When Polaris crammed a gearbox into the Empulse TT, it screwed up the ergos around the rider's feet.

    As for making it a six speed simply because you can, well, no - you shouldn't. Because then you have to row through all those useless gears. If you insist on keeping your current limit low and a gearbox therefore has some limited use, two gears is plenty. Three if you're really skimping out on your controller. Why deal with six? If you read the tests on the Empulse, you'll find most testers saying the gearbox is essentially redundant - it pretty much doesn't care what gear it's in.

    The only reason for a trans is to make new EM riders feel less weirded out by the whole EM concept. Once you figure out how EMs work, you leave it in 3rd or 4th and forget about it. At that point, why carry around the extra weight and change the oil every year, for a gearbox you don't need?
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  9. Dino de Laurentiis

    Dino de Laurentiis Working on it

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    Have to agree with @ctromley here (except I do enjoy the gear changing on my ICE bikes ;) ). Of course an electric motor doesn’t have a flat torque curve from zero to max rpm, but just at look at car manufacturers, no EVs have a gear box. The first Tesla, the roadster, did have a two speed gear box in the early models, but they took it out because a) it wasn’t necessary and b) it was prone to breakage.

    Even if you absolutely must have a gear box, six are unnecessary rotational mass (all gears always rotate even though they are not IN gear) and of course added mass to the bike. The slipper clutch also seems a bit backwards as that should be solvable in the motor controller instead of through a mechanical part.

    As for bikes without gearboxes, the MotoCzysz didn’t have one (race bike), the Brammo Enertia didn’t have one (commuter bike) and the Energica Eva, the roadster version of the Ego (both street legal btw), doesn’t have one, while still reaching 200 km/h. I do not see it being functionally necessary in any way.
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  10. T.S.Zarathustra

    T.S.Zarathustra Been here awhile

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    Let me give you few pointers about EV fundamentals. Battery is a storage unit and contains chemical energy potential (that has been converted from electrical energy from the grid, and that usually (in US) comes from thermal energy made by burning coals). The battery converts chemical energy potential into electrical energy, that the motor control system feeds to the motor at a controlled rate. The motor takes the electrical energy and converts it into kinetic energy, that moves the vehicle. There is no magic in electric motors, only well established science.
    "Increase your current limit instead" would mean more batteries (if they are close to their safe current limit), more expensive control unit (to prevent it from overheating), and bigger motor (to prevent it from overheating). All this would add weight and cost. Probably more than dropping the gearbox would save. Added weight slows acceleration, and reduces top speed.
    No energy conversion is fully efficient. I have already mentioned that electric motors power reduces at very high rpm. This is caused by friction and electrical losses to do with magnetic saturation and other losses, like iron losses caused by reversing the magnetic field. For example, a regular bearing has significant friction at 10000 rpm and is far above safe rpm at 20000 (Typical FormulaE max motor rpm is 17500). Ultra high speed bearings are available, but add cost to the motor, this cost would be partly offset by the saving of a gearbox but there are other things to consider. Low gears are useful to accurately control speed at low speeds (many typical throttles rotate 90 degrees, you have finer control over speed if those 90 degrees control speed from 0-35 rather than 0-155, as an example (useful when passing a speed trap)). Higher gears are good to reduce motor rpm at high vehicle speed, reducing friction and heat build up. Number of gears will depend on design parameters.

    The BMW C Evolution is one established electric bike with a (CVT-variator) gearbox. I would think that the only large established bike manufacturer to design a electric bike would not add it if they did not think it made the product better.
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  11. Crilly

    Crilly Long timer Super Supporter

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    I believe the c evolution has a fixed gear belt. Enclosed.
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  12. ctromley

    ctromley Been here awhile

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    Yes, typically only in the power stage in the form of more or bigger FETs (or IGBTs), possibly additional cooling. We're not talking about any quantum leap in current limit to overcome the lack of a transmission.
    Possibly, but frequently not. "Bigger motor" often means it just takes longer to overheat because there's more mass. (Which made more sense when range was short.) The better approach is to assume continuous duty and control heat by improving cooling in the form of a bigger heat sink and/or fan if air cooled or a bigger radiator if water cooled. These are incremental increases if designing fresh.
    Yes, marginally.
    Generally not. Just to be clear, you design it from the start without the gearbox. That changes many other design details, mostly for the better.
    Bearings are important, but not a critical issue in this discussion.
    The throttle in this case does not directly control speed. It controls torque, which when acting against the load on the motor controls the rate of change from one speed to another. It's a very squooshy relationship depending on what's happening at the time, just like with an ICE. No one seems to have any difficulty controlling single-speed EMs at low speed. Conversely, a lower gear will multiply torque more and make it easier to spin the wheel at low speeds,. (Some have said the single-speed Zero S already lights the tire too easily at low speeds. I think that's due to riders being accustomed to gutless ICEs, but that's a different conversation.)
    Frequently motors find their efficiency sweet spot at higher speeds. Friction is minimal, so not a significant source of heat. When I was running DC series-wound motors, they had fans in them and you learned quickly to keep them spinning. Generally speaking, there is no good reason to keep an electric motor's speed low. That forces it to draw more current to make the same power, which does cause heat build-up. (Proportional to the square of current as dictated by a form of Ohm's law, Power Dissipated = Current² x Resistance. Or 'I²R losses' in the vernacular of EEs.) That doesn't necessarily mean that single speed EMs will run their motors hotter at low speeds though, because low speeds generally require low power, and periods of acceleration are brief. In any case, you design your cooling for your application's needs.

    I'm not very familiar with the C Evolution, but I just looked at a lengthy description of it from BMW and there was no mention of a CVT. Maybe you confused that with a gas version of the scooter? The C Evolution has a toothed belt from the motor to the wheel, but there's a planetary reduction at the wheel for a total fixed ratio of 8.28:1. No transmission, at least in the description I saw. In the C Evolution thread there was a mention that BMW uses some kind of hybrid motor design (that is likely way beyond my understanding). If there is a model with a trans, it might be to be used in concert with their special motor.

    There is no OEM electric vehicle for road use I know of that uses a trans, other than the Empulse TT and the original Tesla Roadster - which was essentially a conversion of an ICE car. Just like back in the hobby EV days, if you're converting a gas car (which of course already has a trans in it), it's much easier to adapt to the motor to the trans than build your own custom drivetrain. So that one doesn't count.

    Seems like everyone who currently sells EVs agrees they don't need a transmission. I'm inclined to believe them, but I'm open to listening to anyone making a good case for one. The only case I've seen is from people who are theorizing, necessarily guessing at the magnitudes of competing influences, and without any real costs in hand.
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  13. ctromley

    ctromley Been here awhile

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    There is certainly some confusion here. I looked again and found your link, and another similar brief magazine press release. In both cases, there is no mention of the CVT in the text of the article. The mention of the CVT is in the spec list.

    I have to wonder if it's a cut-and-paste error. (Magazines don't put a lot of effort in press releases, frequently just running what they're given.) Nothing I have found from BMW makes any mention of a CVT on a C Evolution. I found a brochure where the C Evolution was included with its two ICE siblings, both of which listed a CVT. But the C Evolution had "Drivetrain swing arm with toothed belt and ring gear transmission on rear axle", which reads like marketing-speak for the cog-belt-and-planetary-reduction I found in the more technical piece I found:

    https://www.press.bmwgroup.com/global/article/attachment/T0263449EN/366530 -- See page 5
    http://www.bmw-motorrad.com/_common..._C600Sport_C650GT_CEvolution_catalogue_EN.pdf -- See last page

    So I remain unconvinced that a C Evolution has a CVT. I'm open to being shown otherwise.

    We're on the same page, but not at the same place. If you have a two speed motorcycle and travel at a constant speed, the power to maintain that speed remains constant. Power at the engine/motor output shaft, regardless of what gear you're in, is Power = Torque x some constant x rpm. If you're in a higher gear (lower numerical ratio) the engine/motor rpm is lower, so the necessary torque to make the needed power is higher. Conversely in a lower gear the engine/motor spins faster to maintain the same road speed, and less torque is needed to make the same, constant, necessary power.

    In an electric motor, torque is a direct function of current. A higher gear that allows the motor to turn slower also demands that it produce more torque, meaning it must draw higher current. And that's an issue, because the heat generation inside the motor, just from the electrons running around (nothing to do with twisting the shaft, just the power dissipated in the circuit itself), goes up with the square of current per P=I²R. When you have 100s of amps flowing, things can get very hot very fast. Even with the low resistance generally found in motors. You can't reduce the resistance in this application, so you can only cool to compensate.

    That's why OEM EVs tend to use high system voltages. In electrical-speak, power (generated in a circuit and dissipated as heat) = volts x amps or P=VI. Since from Ohm's law volts = current x resistance or V=IR, you can substitute that expression of V in the power equation. P=VI becomes P=I²R, and it becomes very evident that your life will be much easier if you can keep current down. Since P=VI, you do that by going to high system voltage.

    And on the road, you do that by keeping your motor speed high if you have a choice. If you don't, as in having a single-speed vehicle, you make sure your motor cooling is up to the task.
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  14. ctromley

    ctromley Been here awhile

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    Power is power, no matter its source. Just as energy can be expressed in many forms (.5mv², elevation x weight, etc.), they are all expressions that are convenient for the analysis at hand and all equivalent. You can absolutely measure the horsepower of an electric motor by measuring the torque in ft*lbs at different rpm, multiplying torque by rpm and dividing by 5252. Motor manufacturers offer that method on their tech pages.

    Voltage x current is a good measure of what power the motor draws, or input power. You get power in Watts. Convert that to horsepower (1 hp = 745.7 W) and divide it into the power out measure as above, and you get efficiency.

    In this discussion the important bridge between the two measurements is the fact that torque in a motor comes from current. Current squared determines the heat generated in the motor, and motor currents in traction applications are high.

    Motors make their highest torque at 0 rpm because rotation of the fields causes back emf. It's a force that opposes the motor output and increases with speed. I'm at the limit of my understanding here, and there are certainly other influences in play. Motor curves will look very different for different kinds of motors (the great thing about those DC series motors the hobbyists used is that they make theoretically infinite torque at 0 rpm). If back emf was the only, or even the main player I would expect efficiency to be somewhat proportional to speed, but it's not. This stuff gets very esoteric....
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  15. MrVvrroomm

    MrVvrroomm Been here awhile

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  16. T.S.Zarathustra

    T.S.Zarathustra Been here awhile

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    Regarding the gearbox. I recently found out that many Teslas do have high and low speed gears.
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  17. Dino de Laurentiis

    Dino de Laurentiis Working on it

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    That’s news to me. Anywhere I’ve seen says that Teslas have only one gear. The Model 3 certainly does, and those few Model S I’ve been in has been the same. Got any links where one can read more?
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  18. RedRocket

    RedRocket Yeah! I want Cheesy Poofs

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    I think only some of the first Roadsters had them, if any.
    I do know they tried, but abandoned it.
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  19. T.S.Zarathustra

    T.S.Zarathustra Been here awhile

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    The purpose of a gearbox is to keep the motor in optimum RPM for power and efficiency (range). Even though most electric motors have wide power range and good low speed torque they are still limited enough that a gearbox would help with efficiency at highway speeds, while improving acceleration at low speeds. The VW Golf is a good example. ICE-Golf and E-Golf share a body and are rated at 150 hp. The ICE-Golf has max speed of 250 kmh while the E-Golf has max speed of 150 kmh. With air resistance and power being equal the top speed should be equal.
    Knowing the limitations of electric motors, the designers of the first Tesla designed it with a gearbox. But the car kept breaking the gearbox. Other manufacturers have been able to make gearboxes that can handle the horsepower they had, but it's both time consuming and expensive. Tesla at this time was a brand new company and didn't have the experience or money to make good enough gearbox. Instead they found a brilliant way to bypass the problem. That was to put two motors in the car. Have one motor with low gear ratio and the other with high gear ratio. When you need low speed acceleration, most of the effort is handled by the low geared motor. When you're at highway speeds, the high gear motor handles most of the drive.
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  20. ctromley

    ctromley Been here awhile

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    Yes. But it comes at a cost, and a transmission and clutch are not cheap by any means. You need to understand that if you're an engineer working in the automotive industry and you can come up with a design for a part that costs a nickel ($0.05 USD) less than another engineer's design, you're a hero. The relatively small amount of improvement you get vs. the added cost, complexity, risk of warranty claims and required user maintenance a transmission brings with it is generally not considered worth it.
    No. Different drivetrains and power characteristics. If they decided to go without a trans to limit costs and market it to those for whom 150 kmh is plenty, they gear it for 150 kmh and still get plenty of grunt at low speed. You're being far too simplistic with your theorizing, and not considering the specific application at hand. Even if the e-version had a trans, power delivery is different - generally tapering off at higher speeds while the ICE is still increasing. There are too many variables for a generalization to have any meaning here.
    The original Roadster was a substantial re-design of the Lotus Elise. (Think in terms of a design-level major variation on theme, stretching, moving, lowering bits of the original design, re-designing some functional areas - not a straightforward conversion of a Lotus.) I don't know, but it's likely they used the Lotus transaxle because it mated with the rest of the rear driveline and suspension parts. (They re-designed some rear A-arms and created their own subframe, but no mention is made of replacing the transaxle.) Just like a hobbyist conversion, if the gearbox is already there, especially when it dictates much of the rest of the drivetrain, you use it because it's easier. They might even have just removed some of the internal gears and related parts and gated off the unused positions to reduce it to a two speed. (No idea if they did that, but it would be a fairly easy task.)

    ***EDIT*** Re-reading the Tesla piece where I got this info, they're kind of imprecise and inconsistent about what was kept, replaced or re-designed. I can't be sure if the gearbox came from Lotus. It's a pretty safe bet that it's not a Tesla design though - that's just not done in the auto world. For short-run models like that you use an existing design, perhaps with minor mods. I'm betting existing designs did not include a suitable fixed-speed gear reduction from the usual suspects (ZF, Hewland, Eaton, etc.) - because that's not something that was done when the Roadster was in development.
    Do you know this for a fact, or are you theorizing again? Seems to me for killer acceleration at low speed (which is extremely demanding of big torque numbers) you'd need all hands on deck - meaning both motors giving all they've got. And if one is geared only for operation at low speeds, doesn't it get over-speeded at high speed? How do you design a motor to be high-speed capable but to deliver its best output at low speed? Seems kind of wasteful. Anyone have authoritative details on how the twin-motor Teslas are laid out?

    I believe it has more to do with the fact that the front motor will never be able to deliver as much torque as the rear, regardless of its capability, due to weight transfer under hard acceleration - which un-weights the front wheels and limits traction. So they use a smaller motor, which would run more efficiently with a higher gear ratio.
    #20