Electric Motorcycle Armchair Engineers Discussion Thread. Truths, Half-truths, and Myths.

Discussion in 'Electric Motorcycles' started by T.S.Zarathustra, Mar 22, 2019.

  1. SteveAZ

    SteveAZ Long timer

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    Respectfully I think you are missing my point which is that batteries, at least today's that are used in EV's, cannot accept as much braking power as the vehicle can and will create leading to excess braking energy being dumped as heat
  2. liberpolly

    liberpolly Nu, shoyn, nudnick!

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    Of course, as I said above. Why is it the problem?
  3. liberpolly

    liberpolly Nu, shoyn, nudnick!

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    Of course. That's also besides the point.
  4. liberpolly

    liberpolly Nu, shoyn, nudnick!

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    I think I see the source of confusion. You both are right for the extreme sides of the spectrum - driving with a full battery and braking hard.

    But most of the people most of the time drive with less than a full battery, and brake very moderately when traffic slows down or to get to a full stop at a traffic light. So for 90% of time, regen braking should be more than adequate to absorb 90% of the energy.
  5. WagonWillie

    WagonWillie Been here awhile

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  6. T.S.Zarathustra

    T.S.Zarathustra Been here awhile

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  7. mousitsas

    mousitsas Long timer

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    And lack of gearboxes. People are blinded by the high torque @low rpm of electric motors and do not realise that this torque is on the expense of battery range.
  8. smdub

    smdub Adventurer

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    How do you figure that?
  9. ctromley

    ctromley Been here awhile

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    Y'know, there's an interesting side message in T.S.Zarathustra's link above about critical thinking. It's very much worth the read. There are some here who tenaciously hold onto the belief that a transmission would be a worthwhile improvement for EVs, when time after time (after time after time ....) the OEMs produce vehicles without one. The only vehicle I can recall that reached the market with one was the Empulse TT, and testers said it was redundant. Anyone who adheres to this idea might do well to try to find one to test ride.

    Also keep in mind that no one is trying to imply that a single-speed EV can't be improved upon. Only that some tend to hold onto a pristine concept, when the world in which that concept must live is anything but pristine. The magnitudes involved - that is, the relative influences of all the factors that make up the transportation experience - are what make or break the concepts involved.

    I know I'm not going to convince anyone by myself of what is the 'proper' way to design an EV. But those who are perhaps too tenacious need to consider that that there are other ways, maybe even better ways, to achieve what a gearbox does - without a gearbox. You can multiply torque other ways than through gearing. Multiplying the source of the torque, along with various related components. That might be as simple as a higher controller current limit, in concert with a favorable motor curve, which wins in many cases based on benefit/cost. Or it could be more elaborate.

    Hobbyists use series-wound DC motors because their torque curves are so heavily weighted toward the bottom end. (Theoretically infinite torque, meaning you are limited only by how much current you can provide, and keeping the motor from self-destructing while carrying that current or producing that torque.) But series motors have a limited rev range, and they tend to fade at higher speeds anyway. For everyday road use they're a good compromise. The solution for best performance is to run a single gear reduction, but have two motors. You connect them in series at low speeds, so both motors see all the current but half the voltage (which makes no difference at low speed) - two motors, double the torque. At higher speeds a set of contactors switches them to run in parallel with each other. Both motors see all the voltage (which is far more than rated for each motor), but half the current - so now they both have enough voltage to pull at higher speed than they would have otherwise.

    AC induction is a different animal. Discussions here have surmised (not confirmed) that Tesla uses two motors with different characteristics and different (fixed) gearing to achieve a similar effect to the series example above. Until shown otherwise, it appears they juggle the motor power characteristics and individual gearing to spread the fat parts of the two motors' power curves over a longer range of road speeds. Same goal, different approach: Use two motors for torque multiplication in a way that broadens the useful output of the combined drivetrain in question, without multiple gears, or shifting, or any other mechanical assist.

    I'm betting the cost of an extra motor is less than that of a transmission. In the series example you use one controller. Not sure about the Tesla approach, maybe some electrical armchair theorists with experience in power electronics could weigh in? I'm wondering if you could get away with a single controller there too, with only a bit of added complexity, depending on how you juggle your motor designs.

    Modern EVs are still fairly new. There is a big world of developmental possibility in front of us. Transmissions might be possible solutions in some instances (so are still on the table for consideration) but please stop waving the flag for pet concepts. Concepts need to stand or fall on their own merits. When you prevent that, you tend to miss the better solutions right in front of you. Or that are superior but less obvious, and might take more development. Transmissions are a great thing for ICEVs, which lived in a world where mechanical stuff was king. They might still have some use. But make no mistake - this is a new game.

    In my engineering career I have repeatedly run into people who base all their thinking on a set of textbook rules, but without much understanding of how those rules came to be. More importantly, how those rules are generally simplifications. Sometimes the big developmental leaps come from the exceptions to those rules, or by being specific enough that the generalization is irrelevant. I suspect that Tesla's new Switched Reluctance motor (which is a Very Big Deal in the motor world) is a result of exactly that kind of thinking.

    If you don't understand - in detail - the background that created the simplified generalization, you have no idea how much you're missing. Those rules of thumb can be handy, but also limiting. They only scratch the surface of reality.
  10. mousitsas

    mousitsas Long timer

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    EV's do not have gearboxes in the name of cost (and maybe weight) cutting. Yes you can do without, on the expense of battery range by simply feeding a LOT of current through your motor. Torque=Amps.
    In my previous post I wrote that such short range as currently ev's have, is a result of the lack of gearbox (for a given motor and battery wh) which holds true whatever your angle of view is. Electric motors can produce high torque but high torque at low rpm means low efficiency.

    Whatever your super duper motor, controller or battery technology is, give it a means of a gearbox and your range increases. That is all I am saying, wasn't that post clear enough?
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  11. ctromley

    ctromley Been here awhile

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    Trust me, OEMs are very sensitive to the range problem. If they could get more range by adding a trans, they'd do it. You're forgetting to consider the real-world magnitudes of various influences. A transmission adds its own losses. It steals room for more batteries. Motors have a rather broad spread to their efficiency curve, and you can design so it stays in the fattest part most of the time, even with a single speed. You state rather emphatically that "... such short range as currently ev's have, is a result of the lack of gearbox (for a given motor and battery wh) which holds true whatever your angle of view is." That, sir, is an assumption, but you're literally stating it as an inviolable fact. It's not.

    You can design for efficiency at high currents. It comes with tradeoffs. There are lots of overlapping variables involved here, that all change in different ways under different conditions (including changes in other variables), that add to the final solution for best overall efficiency. Saying that high currents mean low efficiency focuses on a single theoretical simplification, and denies the extreme granularity of all the realities affecting overall efficiency.

    ***EDIT***
    It occurred to me that the EVs relying most heavily on efficiency for their success are the World Solar Challenge racers. The one that has won most of the recent races uses no transmission. This race is run through the Australian Outback at an average speed of ~100 km/h. While that might suggest little variation in conditions, there are in fact significant elevation changes and the always unpredictable weather, most importantly wind. These variations are so important that there is an ICE pace car for the racer that constantly measures real-time conditions and sends updates to operational parameters on the racer through telemetry. If maximum efficiency demanded a trans, they would certainly have one.

    They do not.

    They also claim 98% efficiency for the complete drivetrain (which I doubt, but I'm open to being surprised), which at least is another indication of how seriously they are trying to maximize efficiency. Simply adding a bicycle chain anywhere in the system (they use a hub motor) would cost them more than 2% losses, never mind a multi-speed transmission.

    A group from that team started the EV company Lightyear, who just issued a press release on their Lightyear One solar-assisted car. Specs are very few so far, but it has four motors, strongly suggesting no transmission.
  12. mousitsas

    mousitsas Long timer

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    I think your argument that "since they do not do it, it is not necessary" is pretty weak in today's world financial and industrial ethos.

    And since we can both understand science and engineering pretty well, I would be very much interested to be pointed towards a solid example that proves my belief wrong.
  13. T.S.Zarathustra

    T.S.Zarathustra Been here awhile

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    I believe that most future electric vehicles will have 2 speed gearboxes. Most already have a single speed gearbox (gear reduction units). Making them 2 speed is not overly complicated. It just costs extra money. When you're designing new platform low volume vehicles you cannot afford to put all the bells and whistles in. In the future, when EVs have become more stabilized and mainstream (and less of a sort of tax-refund system for luxury sport vehicles for the rich) and competition increases between manufacturers, I think we'll see this, and some other changes.

    All pollution created during or caused by manufacturing or recycling is pollution. It does not matter if it is direct or indirect. No matter where on earth it is created. It will negatively affect our environment, the life support system that we call Earth, that all of us humans have to use. We only have this one life support system, so we need to take as good care of it as we can.

    Electric systems are becoming more and more powerful and compact by the day, but this will be small steps. Please think critically of any articles using words like "revolutionary", "breakthrough", and "huge improvement". Those are almost certain to be hoaxes.

    This will be my last post for a while.
  14. magnussonh

    magnussonh Adventurer

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    How much do you need? I found the 33 kW Zero S fast enough for city use, powerful, light and agile. The 82 kW SRF must be a hooligan bike and I want one. Do I need it? Nah.
    According to Jeremy Clarkson the world is slowing down. Concorde is no more. SR-71 is no more. X-15 is the fastest manned plane ever to fly, it flew in the 60's. Regular passenger jets are flying slower than 20 years ago. Why would cars and bikes keep on speeding up?

    "ultracapacitors are capable of storing and discharging energy very quickly and effectively" "Ultracapacitors complement a primary energy source which cannot repeatedly provide quick bursts of power, such as an internal combustion engine, fuel cell or battery" Didn't Tesla buy Maxwell few months ago? Supercapacitors are a fast developing field. There was talk of them replacing batteries completely, if they could be made small enough.
  15. SteveAZ

    SteveAZ Long timer

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    They don't have the energy mass density, volume density or cost density that Li-ion has... but augmenting the Li-ion in larger vehicles makes sense in order to capture high braking energies...
  16. ctromley

    ctromley Been here awhile

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    My understanding is that super/ultra/maxi-caps are, well, capacitors. Unlike battery cells, whose voltage varies only a half a volt or so from fully charged to dead, capacitors go all the way down to zero volts at zero charge. If you run them like the batteries they're supposed to augment, you're throwing away a very large portion of their 'capacity' (as defined for capacitors). If you try to make use of their entire charge, the huge variations in voltage get very challenging to manage, and low voltage at low charge demands high currents to maintain power. (Infinite current as you approach zero charge.)

    The electronics world is not my world, and there may be recent advances that mitigate those problems. Are there? Seems to me even if there are, the concept of 'capacity' would only make sense in context with the system the caps are used in.
  17. SteveAZ

    SteveAZ Long timer

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    True - you can't use the full voltage range (0 to Vmax) due to the voltage variation - like you say they are capacitors

    However the energy stored in a capacitor is proportional to the square of the voltage so that even if you only use say the top half the voltage range which is reasonably easy to manage (I've done power electronics that readily manage >10:1) then you'd still be getting 75% of the energy capacity if you were to theoretically run them all the way to zero. If you were to run them from 100% to 33% that would increase to 89% of that theoretical maximum and at 10:1 you'd get 99% but that is way past the point of diminishing returns.

    You can stack them to get a reasonable voltage at whatever terminus you designed for and then fully charged you'll just buck them down - e.g. if your final voltage is way up at 72V then fully charged they'll be up at 216V which is very manageable and would give you that 89% of capacity which seems plenty good to me. Even if you just do 2:1 you are only managing 144V and you still get 75% which is still pretty darn good while being an easy design.

    Since they specify them to run to 0% (albeit impractical) then the limit is what your electronics can handle.
  18. liberpolly

    liberpolly Nu, shoyn, nudnick!

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    For city, sure. FXS is probably enough too.

    He is wrong, as usual (and he hates motorcycles). Trains are speeding up. New hypersonic planes are being developed.
    https://www.cnbc.com/2019/04/08/hyp...gy-passes-a-hugely-significant-milestone.html
    https://www.wired.com/story/boeing-hypersonic-mach-5-jet-concept/
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  19. ctromley

    ctromley Been here awhile

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    Jeremy Clarkson is a showman. No more, no less. Anything he says or does has one purpose - to get him attention, reality be damned. He is sometimes correct, but that is purely coincidental to his goal of getting attention. Anyone who relies on him for useful data needs to seriously re-assess their priorities and motives.

    The Concorde is no more because it was only viable thanks to heavily subsidized development costs by the French and British governments, it could only fly trans-oceanic to keep sonic booms away from populated areas, there was a string of non-fatal-but-troubling structural and tire failures, a major all-souls-lost crash, the post-9/11 air travel decline and Airbus ceasing the production of replacement parts. How many reasons do you need?

    The SR-71 is no more because it was a monumental - and monumentally expensive - task to keep it flying. Also, capabilities and needs for surveillance (its primary purpose) evolved, making it obsolete.

    Later prototypes beyond the X-15 flew, but control at those speeds is spectacularly challenging. Control is just as important as speed. Also keep in mind the X-15 was not so much an airplane, but really a missile with a cockpit, launched mid-air from a B-52. Its operation qualified as space flight. How useful or representative is that relative to aircraft in general?

    Commercial aircraft fly slower today because doing so uses less fuel, the cost of which continues to increase. Since the airline industry was de-regulated and margins became tiny, large expenses like fuel need to be minimized to stay in business.

    Notice how none of this has anything whatsoever to do with a lack of desire or capability to achieve higher speeds.

    Here's an additional data point. Here on the US East Coast the Acela trains are the fastest in the nation, capable of 150 mph. But average speed is around 80 mph, because they run mostly on ancient infrastructure. Next year the Acelas will begin to be replaced by the even-faster Avelias. But they will still run on the same low grade rails. Meanwhile, China (which many Americans prefer to think of as a backward 3rd world country) has 2/3 of the world's high-speed rail, actually running at 150 - 200+ mph. They're currently testing a mag-lev train that will run at over 370 mph.

    High-speed technology is here and is constantly improving. Where it stalls, government and business priorities are what's slowing it down. Not tech.

    'The world is slowing down?' Seriously?!? None of the factual statements above have the attractive simplicity of a smoothly confident - but utterly senseless - Clarkson soundbite. Which is more useful, fact or soundbite? That depends on whether you want to understand how this world works or remain a fan of Jeremy Clarkson.
  20. magnussonh

    magnussonh Adventurer

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    There are some valid points here.
    Capacitors are superior to batteries in the sense that they can be run to zero without damaging them, they can also be made to store energy at much higher voltages than regular batteries. They store the energy as electrons, avoiding yet another energy conversion in the whole process. That can offset some other negatives in their design. I did state "if they could be made small enough", which is where supercaps could be coming in.
    The world slowing down. Jeremy Clarkson is not dumb, even if many things he says or does point otherwise. Except for some expensive high speed trains, mostly in Asia, many quite old now, all that has been pointed out otherwise is speculations or plans for the future. I believe Netherlands closed their high speed train network after frequent failures and skyrocketing costs. Zarathustra can probably confirm or correct that statement. Many others are not run at full capable speed.