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Discussion in 'Electric Motorcycles' started by Snowbird, Oct 7, 2019.
I am keeping my '74 Honda though :)
I went from a DR650 to a Honda Forza 300 cvt scooter. I do not miss the shifting at all.
The CVT is always in the right gear. I have also ridden DCT Honda's which are also always in the right gear.
I want an electric motorcycle because it would always be in the right gear.
I would too. Honda made their CVT automatics "shift" to please customer opinion, it doesn't actually shift, it just gives a feeling as if it did. E-bikes could have "gear boxes" using electronics to alter delivery to have the feel using a lever or paddle levers/buttons like some of the Honda ATVs used. It's part of the involvement with riding for me. Like riding a two wheel cycle instead of a trike, the feel of leaning into a corner and all.
Because I don't know that much about electrical motors. Thanks for the non-answer, no help what so ever to understand them. Do you not understand why questions are asked?
I don't know. That's why I asked a question. To try to learn why or why not. It seems to me that it is possible. If it isn't I'd like to understand why not. So far everyone is either not giving an actual answer. Seems all that is hinted at is "because that's the way it is". Not a good answer.
I am not in an argument. I am asking, to understand the electrical answer why.
Power in equals power out, minus losses. Losses can always be defined. There's friction, there is heat, but in an ice engine the big losses that account for inefficiencies outside of the power/efficiency bands involve things like the valves not opening/closing at the best time for that speed, perhaps the fuel ignites just a hair too late, etc. These are obviously not a problem in an electric motor.
So again, it's not why doesn't the electric motor lose efficiency, it's a question if why would it? And if the answers are largely just the minimal increase in friction, then adding a transmission would add more friction than it would eliminate.
I'm trying to impress upon you that you simply aren't asking the right questions to understand the issue.
Let's try again. What part of my answer was not clear? I'll repost it here:
The reason ICE runs into inefficiency at higher RPM is not only friction losses - it's because it transforms linear movement of the pistons to the rotational movement of the wheel. An electric motor doesn't have this problem, it's movement is rotational from the beginning. And, of course, friction losses of the piston sliding along the walls of the cylinder - an electric motor is contactless, everything runs on bearings and nothing touches anything else.
I like the Enfield electric bike for its style and homage to a vintage bike. But the middle of the bike below the fake gas tank looks odd, out of place. Sure, its an electric motorcycle but that center section looks like a Zero stuffed into an Enfield, rather than a classic Enfield.
That does not explain why an electric motor will not extend operating time if a gear allowed lower rpm while maintaining equivalent speed. If an IC engine is most efficient between 4000 and 6000 rpm and is not operating at peak torque the engine will use less gas to go the equivalent speed at the lower rpm, so gearing can increase mpg, which increases run time. If preserving battery (electrical) power through running at lower rpm is not possible with an electric motor I would like to have it explained in electrical terms, not in comparison to an IC engine.
At this point I am being told that an electric motor will run the same 46 miles whether run at 20% power or 70% power if running the same speed but geared to operate at those "throttle" settings - or should I say rheostat settings. It seems that there would be a reduction in current draw if an electric motor is strong enough to pull with a taller gear than if higher current was required for the shorter gearing. Maybe my understanding of the current draw is not enough. I also kind of think of the cordless drills that have two speeds which are affecting the torque of the drill motor. I just would like the electrical explanation so I could understand. Don't need any comparisons to IC engines, it isn't part of the question.
Well there really is no reason that you can't use a gear box and in some situations you may need to. Where I work, we are ganging motors so we need the gearbox to get them all working together. Each motor is about 1500hp and 6 of them on one winch and 5 on another winch. For single motor operation it would not really be needed due to the VFD variable frequency drive controller. It does so much more than vary the freq. it also controls the voltage and amps. I believe that the motors in the bikes are brushless DC motors. The RPM vs torque characteristics are pretty linear. To introduce a gearbox would not add any better control or efficiency since it can be done with the controller. On page 12 is a good write up. https://www.groschopp.com/wp-content/uploads/Basics-of-Motor-Selection-Whitepaper.pdf
Not the best explaining that I have done, but I don't really work with that small of a system.
Work = Power*Time
Note that RPM does not show up anywhere in this equation. The only reason I brought ICE is because this is where your confusion seems to be coming from.
Now when we talk about acceleration we have to introduce torque
Torque = (Power *60) / (rpm * 2π)
as you can see, torque goes down, not up, with an increase in RPM. So electric motor already has maximum torque to accelerate from a standstill. To maintain torque at higher RPM - which is necessary to keep moving and accelerate at higher speeds - we can either introduce more gears, or design the motor with higher maximum power; the second approach is cheaper. The efficiency of the motor does not change much across all RPM range. Typically, there's a single gear that provides a good compromise between acceleration and top speed, which is an easy task - it is not unusual to see a motor being able to spin at 20K RPM. If top speed isn't high enough, a more powerful motor is introduced, without a reduction in the efficiency.
Note that the latest Tesla Model S and Roadster are cheating this equation somewhat - two motors in the rear are fixed-geared for maximum acceleration, and one in front to maintain a high speed. It also allows torque vectoring, which I suspect was the main motivation, to handle better at a race track and beat the pesky Porsche.
No, Livewire has three-phase induction AC motor.
Zero SR/F is also AC, although I don't remember the exact configuration and too lazy to google.
Would it make sense from battery charge and range to stay with a smaller motor and use gearing since high rpm according to the torque formula, works against maintaining maximum torque? I understand the cost factor, being easier to just stick in a stronger heavier motor, but when some things reign in on cost, the smaller lighter motor and batteries with a gear box may make some sense? RPM has to come into play at some point due to the rotational force torque driving the vehicle.
I also wonder if current draw affects the battery charge and range. If it did, that was my thought on the gear box, if it can have the motor run with less current draw it could extend range. Plus when the power calls for a heavy enough engine it may be time to do a gear box for weight savings.
But again, I'm just learning and have questions. Thanks for the information, I plan to learn more, here and with any other means, just because I am interested.
Unlike an ICE, the current draw and hence available power does not increase with rpm. If anything it decreases slightly. The "rules" you are familiar with for power delivery from an ICE do not apply. Within the design rpm range, which will cover the entire speed range of the bike, there is no advantage to different gearing.
Any updates on Livewire sales?
Anyone get their new Livewire?
Still only one delivered in Wisconsin that I know of.
From a discussion on another site...
Plus, an often neglected fact is that electric motors, especially induction motors like in a Tesla or a Nissan, are NOT efficient at producing torque with low RPMs.
The motor is geared with a single reduction gear to run the entire range from 0 to 100 mph such that it reaches the nominal or optimum design speed at highway speeds or little below. It is basically optimized to achieve the highest efficiency at around 55 mph because that’s the lowest they can get away with and still call it “highway speed”. Optimizing for this speed allows them to quote the longest range for the vehicle. Much beyond this nominal speed, the motor loses power due to its impedance restricting current at higher frequencies, which then limits the top speed.
What happens below 55 mph is another story. At around 25% of the nominal speed, the efficiency curve takes a deep nosedive towards zero, because at zero RPM the efficiency IS zero – there’s no work being done because the motor is not turning. At around 15-20 mph (25-30 kph) the efficiency of the motor is typically down to around 80% and below that you’re just making more and more hot air.
This drop in efficiency costs a lot in city driving, because you have a ton of batteries to accelerate, and you don’t benefit much from regenerative braking either. This is why the range quoted by EV makers and even measured by EPA or NEDC is often 25 – 50% too optimistic. The real energy consumption is higher because the devil is in the details and the manufacturers basically lie about it.
The equivalent of the MPG gap, the kWh gap, exists with EVs as well.
Here’s an example of a typical induction motor:
The torque curve shows a flat area below 1500 RPM where the current is limited by the controller, and a falling curve above 1500 RPM where the current is limited by motor impedance. The efficiency at 500 RPM ranges between 70-80%
This is why electric cars should have gearboxes with at least two gears to select according to the speed range, but they are not used because it saves mass and cost.
You can put in a smaller motor but you will lose performance, just like with ICE engines.
Batteries are usually rated in amp hours. Torque uses a lot of amps, as the need for torque drops off like when you are up to speed then the amp draw also drops. Just like with ICE engines and jack rabbit starts, use a lot of gas.
The biggest reason for a gear box on a ICE is that it has a sweet spot in the RPM range that it likes to be at. To low and you lug it, to high and there is not enough torque to accelerate quickly. The electric motor controller takes the place of shifting gears by manipulating the voltage and amps to provide the torque to accelerate.
There is no free ride, it will take the same amount of usable energy to make the bike perform no matter the energy source. A electric motor is not a magic solution. It is cleaner, easier to control, and less maint.
I don't think a car spends more than 1% of its battery charge at or below 500RPM, so it is not a good reason to add two gears - with all the weight, complexity, and efficiency loss across the range it will end up hurting, not improving, overall efficiency.
I am not sure why do you think "you don’t benefit much from regenerative braking" in the city driving?
You are confusing "power" and efficiency here. Above 55 mph, the power goes down, but efficiency doesn't.
I want the LiveWire to be a success. I think Charlie and Ewin or whatever their names are, is the most sound marketing imagineable. Every dipster wanker will be all about it once they sprinkle their magic knowledge of the ages across the product. Honestly, i think it will work.
Whoa... thread has been dumped to a completely new to me subforum "Electric Motorcycles!" Truly new or was I caught napping?
EDIT: Napping, I guess, since May. Zzzzz