ElectricMotorcycleForum.com
Makes And Models => Brammo Forum => Topic started by: zap mc on November 12, 2011, 04:33:09 PM
-
As we can see the range wars are hotting up, but can anyone with a more fundamental grasp of the theoretical physics involve say whether a geared bike is more likely to get a better range than a non geared bike?
My initial reaction is that by using the gears you will use lower revs and hence less power and consequently go further, but is this true? and if it is will all manufacturers eventually be forced to follow brammos lead?
-
I can't see how it would help, but I'm willing to be educated.
=:)
-
It is an intriguing topic. I will throw out some thoughts and maybe we can arrive at some logical conclusions with other peoples help. I hope you can follow my reasoning, for that matter I hope I can follow my reasoning.
Power equals torque times rpm. The power used must be supplied by the batteries. So I ask myself, as the bike accelerates and picks up more rpm, what does the torque do? If the torque stayed the same and rpm went up, ah, more power drain on the batteries. So if I had some gears, I could shift, and then drop the rpm back down. Hey that sounds great, less rpm, less power drain. However, can I stay at constant torque? Do I need more torque to go faster? It must take more torque to go faster, because cars and bikes can only pull so tall of gearing. I think in that ideal frictionless world going faster would not take more torque. What is it about going faster that requires more torque. Whatever resists the forward motion I guess. Wind resistance, must be more friction losses in bearings, drive chains and everything else that spins when they spin faster. Could I be missing some other reason besides the friction, hmm. So now, comparing both bikes going 30mph, would that not take the same amount of torque to push all that wind and friction? I would say same torque. So do I conlcude that if i can go 30 mph at less rpm, my bike would be using less power than the bike at higher rpm? Is it that simple? Did the first part of my paragraph have no bearing on this conclusion, haha.
Ah but wait, extra spinning things comprise a transmission, thus more frictional losses, thus just having a transmission will drain more power all the time, drat. How can I take transmission losses into account? If I assume 10% loss, then that gives the single gear bike an advantage of 10%. The gear rations on my quad are from 1.2 to 1.4 change between gears, thus 20-40% faster each gear. So the transmission loses 10% but the shift gains me 30%, so I come out ahead by 20%. So even with transmission losses I still come out ahead? Based on those numbers anyway, which I think are somewhat reasonable.
Based on ride reviews that say freeway driving and aggressive riding have lower range, then I conclude those situations must be using more power, which is some combination of torque and rpm. Agressive riding would be using more torque, trying to accelerate fast. So that means non agressive riding can actually use less torque. That is interesting. So the electric engine can put out high torque at low rpm, but that doesn't mean it always does. So in casual riding, low throttle setting, I guess the controller limits the voltage supplied to the motor? Thus the motor puts out less torque, thus less power at any given rpm, thus consumes less battery. The freeway riding is high rpm and maybe high torque also to push all that wind and friction. That type of riding must consume a lot of power.
I must be missing something important, but it sort of looks like the transmission will help give more range.
I am tired now. You can't have too tall of a gear and keep the rpm super low, it seems like the taller gear would take more torque to spin. Maybe I can ponder that later.
-
So now, comparing both bikes going 30mph, would that not take the same amount of torque to push all that wind and friction? I would say same torque.
Same torque at the rear wheel, but the slower motor must be geared differently. (otherwise it would be going at the same speed). So the slower motor must produce more torque. The increase in torque needed is proportional to the reduction in rpm so as the power is torque times rpm, it comes out the same.
=:)
-
Ah I think I see your point. In that case, the transmission losses are always there just hurting efficiency. If we ever get to see the Brammo 6 speed, it will be interesting to find out how real world tests turn out. Although you would have to compare the same bike with and without the transmission, which probably will not happen. Even in light of this theory, it still seems like the transmission would help.
The electric motor doesn't put out as much torque at high rpm. So maybe the high speed riding would be more efficient with a higher gear? Maybe not more efficient, given the torque rpm trade off, maybe what happens is that the bike with gears is just capable of going faster. Hey, in this comparison the geared bike is going faster, so if it uses the same power and is going faster, then it will get more range. Anyway, I think a real world test would be good in this case. Although theory is good excersize for that gray matter i don't use much.
-
So far it looks like we were just thinking about power in verses power out. That is not the whole story though. With any motor you have to put in more power than you get out. So the efficiency of the motor itself comes into play. http://www.gizmag.com/antonov-3-speed-transmission-ev/19088/ (http://www.gizmag.com/antonov-3-speed-transmission-ev/19088/) Gizmag has an article of the Antonov 3 speed and they claim the transmission does help by 15%. It is interesting to put a theory to how something works, but in this case it might be more beneficial to see some test results. Even the experts in the industry cannot seem to agree on the topic. Also, the rider would need to know where the motor is most efficient so they can drive it there, otherwise they might use a different gear and not gain any benefit.
-
Here is my comment: The motorcycle magazine editors consistently tell us that motorcycle drive-line losses amount to between 10 and 15% on an IC motorcycle. I imagine the majority of that loss is from the transmission gears meshing and spinning in their oil. My guess is that an efficiency loss of as much as 10%, assuming a typical motorcycle transmission with splash lubrication from 80wt oil, sounds about right to me. At the current technology of electric motorcycles, that is significant. However, a transmission would certainly improve take-off performance from a dead stop and overall acceleration. I am not convinced that having a transmission will improve range, though.
-
In theory I have to agree with the last comment. Transmissions are essentially converters for balancing the torque required to meet throttle controller demands and the rpms required to maintain peak efficiency in motor operation. Thus, as in transmission uses on conventional vehicles, the varying gear ratios provide desired acceleration. Conventional transmissions use the top gear as a 1:1 ratio. So 1 motorshaft revolution equals one final driveshaft revolution. Single speed ebikes are essentially always in this 'top gear' 1:1 state (excepting for setups using a gear reduction or increase between motorshaft and final driveshaft, but since this is a static ratio scenario it can be considered in the same 'top gear' sense). Top gear 'overdrive' transmissions such as those in late model twincam harleys go beyond this 1:1 ratio (1 motor rev equals greater than one final drive rev) to provide lower motor rpms at a given steady cruising speed where not much rapid accelerative torque demand is expected. Shifting gears in a transmission is for staying in the desired rpm range for optimal motor operation...since there's no stalling an emoto at low rpm, and no need to rev up to find the best torque band in the rpm range, I am very interested to see what ratios could be exploited to benefit the power output characteristics of emotors. Current energy storage chemistry being what it is, increased range would be the obvious focus to work towards...anybody got some real world experimentation they need a test rider for?
Remember also that transmissions bring not only inherent output efficiency losses, but added weight, added maintenance, added mechanical complexity (aka moving parts that will inevitably fail over time), and added complexity of use for the inexperienced rider. These are all parts of the vehicle design equation that must not be overlooked if the ebike is to maintain its inherent distinctions from and advantages over the conventional hydrocarbon models.
-
This is an interesting subject and one that has been beaten to death on El Moto - without any conclusive results. Until Brammo finally comes out with the Empulse and we all get to see what happens when you install a 6-speed transmission on a production electric motorcycle and how that affects its price, range, weight, complexity and overall performance, we are all just guessing. There is nothing like seeing something work in the consumer market to validate (or not) a new (to EVs) concept like this.
When even the major auto manufacturers are not installing transmissions on their all-electric cars, you have to ask yourself whats up?
-
The discussion about efficiency always ends the same. It’s unlikely that it would be much more efficient, if at all. With losses in the transmission, It's unlikely that the change in efficiency due to gearing a motor down so it's in a more efficient part of the curve is more than the transmission losses.
Let’s take this motor
(http://www.amphibike.org/images/750_ADC9inchCurve.jpg)
Now look at the RPM range at 72V for different loads (torque along the bottom). The range of RPM for 10-70ftlbs of torque is about 2000RPM to about 4500rpm. The efficiency of the motor goes from 80% to about 89% and back down to about 85%. I doubt they're designing the transmission around an existing, as the ratios will be different. Let’s assume that we'd want to go in maybe 2000rpm increments. So 1st to 2nd, we'd shift down 2000RPM from 4500RPM, and you're around 2500RPM. Efficiency at 4500RPM is 80%, and efficiency at 2500RPM is close to 89%. So that's a gain of 9% efficiency, right?
But what is the efficiency of motor ---> primary ----> gear x ---> transmission output shaft. We assume the same efficiency for final drive. Let’s say there’s 3 transfers of power within the transmission, with 3-4% loss each, that’s 9-12%. So either it’s got to be a super-efficient transmission, or the gearing has to be such that the efficiency gain is higher than losses.
I think the REAL gain in all this, is you get better performance out of a motor. Having different gear ratios helps a fairly low HP motor use it’s torque better than a single speed, thus improving performance up to the limit of the HP of the motor.
-
Great illustration and analysis Frodus! Thanks for clarifying my clumsy and unscientific allegations.
Cheers brother!
-
Here is the issue I have with that analysis.
If the question you are wondering is "if I can switch gears right now in this particular steady state to another gear that puts me in a more efficient part of the rev band, then is the cost of a transmission worth the gains from this one isolated single decision?" And, you've shown that it is a wash. OK, I didn't verify all the math, but I can believe that.
But, that's not the question at all. The question is "if you have an electric motor that is small and light enough to fit on a motorcycle along with its battery pack and you can choose one single gear for it, what gear ratio do you pick and how does that affect a) the efficiency and power on the highway and b) the off-the-line grunt you will see from a stop light?" And I think the answer to that is "you will not do well at both, and in fact if you want to do well at either then you will do very poorly at the other". From my test ride on a Zero and reading the Zero forums on real world range I get the impression that their choice was to go with a gearing that gives safety margin power on the highway and decent (for a very green vehicle) standing start power, but nothing stellar in either category and it is very inefficient range-wise on the highway. Their compromise does work and I could live with that for the green feeling and novel torque response that it provides (even if, on an absolute scale, it isn't breathtaking in performance), but in the end it is a compromise, not the be all and end all of solutions.
But, I think Brammo wanted more than that experience. They seem to be looking for excellent off the line acceleration as well as decent highway legs. You simply will not achieve that with a single gear. Tesla can achieve that in their cars because they have different economies of scale - size and weight wise. But the size constraints of a motorcycle just don't appear to let us get there. They could produce a fun, liveable compromise vehicle, but they would rather produce a more complicated vehicle that is exciting and green.
In that analysis, all you've shown is that they can probably gain back the efficiency that they lost by deciding to put a gearbox on in the first place. But your analysis isn't the goal they were aiming for when they did it, it's the reason they break even on those non-goals while they do it in pursuit of other "excitement" goals. They can add the excitement of having better gearing for all (or at least more) conditions while not giving up much efficiency in the wash...
-
However, from a business standpoint, you could argue that while you are attempting to design and develop the very best production electric motorcycle and the first one with a functioning gearbox, you are loosing sales and market penetration. Right now, considering the cost and small market for electric motorcycles (at least in the U.S.), you would think that the smart thing to do would be to come out with a single-speed Empulse, sell as many as you can, then follow up in a couple of years with the 6-speed model and make a big splash. Then you could sell that advanced bike to the guys that bought the original bike, thereby doubling your sales. That is what I would have done. Meanwhile, Zero marches on with an electric motorcycle that works as a commuter and green transportation (that runs without needing high-priced gasoline or a lot of expensive maintenance). It may not be the best motorcycle that they could have made, but it is here now and selling. :)
-
Hi Richard, I'm not sure I understand your comment. Isn't the Enertia single speed? Was that a typo and you meant to say that they should come out with a single speed Empulse for starters and then later follow it up with a 6-speed Empulse+? I would buy that if they didn't already have the Enertia selling to the single speed commuter/city crowd. While the Empulse has styling that may appeal to a new crowd than the Enertia (with Zero S somewhere between Enertia and Empulse styling), if it provides the same riding experience as existing electric motorcycles then it will likely leech more sales from existing models than it will establish a new niche. And, it may not sell well at all since those who might be attracted to a naked sport bike look may not be willing to put up with a less than stellar power curve. For the near term they are providing the Enertia and Enertia+ which probably appeal to 80-90% of the crowd that would be looking at electric motorcycles in today's market and Empulse seems to be the first of a new generation. Or, is there some angle I'm missing.
Also, I wasn't suggesting that their goal was the best goal, just that the analysis that tried to show that it was not a good idea was missing the point of why they are doing it. The world may not be ready for a multi-gear electric motorcycle, but the reason to try it isn't to improve efficiency in isolated running states over a single gear design - so the analysis of that factor is not relevant to its raison d'être...
-
And stepping back a bit, I notice that the title of the thread is, indeed, about efficiency.
But, my comments are still relevant since the gearing of a single speed bike is not chosen arbitrarily. I am suggesting that all of the existing crop of electric motorcycles have a compromised highway range due to this consideration and the choice on the highway isn't "can we get from 80% to 89%", but rather they are likely much further outside their efficiency range and it is more like "can we get from 40% to 80+%".
The analysis to perform on that chart is to say something along the lines of:
- The break even, knee of the curve, point for efficiency at speed seems to be the 10lb/ft at 4500 RPM point. If we drive the engine much faster then the efficiency takes a huge dive.
- If we gear so that 4500RPM gives us 55-65MPH, then what efficiency do we then have at 75-80 and what kind of power do we get off the line and in city traffic?
- If we gear for good power for excellent standing starts, what RPM do we have at 55-65-80MPH and what efficiency do we have at that RPM?
If you can find a single gearing answer that gives good results for both of those questions, then that is the analysis that would show that a gearbox is not worth it.
And, if you throw 100+MPH in to the equation (which I think they believe they must embrace to make this particular model appeal to its target audience) then it is even more likely that that speed will be unachievable with the torque/RPM that you end up at with a single gear choice.
-
I keep getting my Empulses mixed up with my Enertias. I corrected the typo in my previous message.
I was not making a point about efficiency (for which I am really not qualified to say much), I was just grousing that Brammo should have come out with their single-speed Empulse and sold those first, before modifying it with a gearbox. I waited for 18 months as an Empulse pre-order customer, before finally giving up and buying a Zero, but I would have been happy to own a direct-drive Empulse.
P.S. I owned a 1997 Funduro for 9 years and my "230" comes from my Chain Gang membership number.
-
Hmm. Six speeds? I'd find it hard to believe that many gears would be necessary on an EV, with electric motors' wide powerbands and high torque at low RPM. Didn't the original Tesla gearbox only have two speeds?
I suspect any efficiency gains made by gearing the electric motor (taking into account motor improvements and mechanical losses in the transmission) are not significant enough to outweigh the cost and complexity of a gearbox in most cases.
C
-
I don't know much about how the IET differs from a standard gearbox, but if they add the complexity for any gear change, then adding a few more gears wouldn't really change the complexity much so 6 shouldn't be much worse than 2. Also, given the price of these bikes, if they can at all use a stock shifter pedal and gear set then they save having to fabricate even more custom parts and 6 speed gearboxes are probably a dime a dozen.
Comments have been made that the bike will be able to run around in any one gear, just like the single gear bikes, so with 6 to choose from you could probably better pick a single gear that fits your immediately foreseeable (as in "this morning" or "the next 50 miles") circumstances, but with the option to always go into "fastest 0-60" or "highest highway mileage" modes at the flick of a foot. In my S4, which had a 6-speed manual transmission and a twin turbo engine with the widest power-band I've ever seen in an ICE car, I often found that I could find a single gear that would keep me happy through miles and miles of twisties, but it wasn't always the same gear that worked depending on the nature of the road and my mood. The car almost didn't need a transmission (I'd commonly go 1st, 2nd, 6th and would even use 6th gear (good to 150MPH) at city speeds), but it was nice having the fine tuning of 6 gears to choose.
With one gear on the Empulse you'd most likely end up with lackluster 0-60 and poor highway mileage. With two you could have both of those fixed, but in the twisties you might find that either gear "works", but you might not find either gear optimal, like golfing with a driver and a putter. With 6 it will likely be a dream to ride in all conditions with no constant shifting once you figure out the right gear for the situation.
-
The original single-speed Empulse has a maximum design speed of 100 mph, and pinkyracr claims she hit 91 mph on the 2012 S in a tuck downhill.
70 mph should be WELL below either motor's maximum rpm and efficiency should be pretty good - maybe a bit lower than at lower speeds, but probably not enough to cover the added losses from a gearbox.
I don't think efficiency drives the selection of a gearbox over a direct-drive transmission.
-
@protomech
I'll admit up front that I don't have hard and fast facts to back up the following points, but the impressions are worth noting as they are not really addressed in the point you raised.
First, my impression of most ICE motorcycles is that the mileage differential from going 70MPH vs. 30MPH is not huge. You might see 20-30% difference. Am I off there? With an electric bike, on the other hand, the figures being quoted show a differential of well over 200+%. Either I'm way off on how much I expect the mileage of my ICE bike to vary by speed, or there are some serious efficiency issues with existing single speed electric motorcycles at highway speeds.
Second, it may be that existing electric bikes are within a reasonable efficiency envelope at highway speeds for these motors, but they don't really have exciting off the line performance. If what you say is true then that means we can have the same kind of highway mileages we tend to be seeing in today's bikes, but we'll never get breathtaking 0-60 times. If you want to include the wow factor on the low end performance, then the gearing will have to change and that new gearing will threaten the existing highway mileage.
[Hmm. The following fails to take into account that when you switch gears, you multiply the power and torque by a new multiplier before it reaches the rear wheels - so, if you can halve the motor speed then you might be at a part of the curve where the HP/torque are higher, but you also divide those numbers by 2 due to the gear changing the mechanical advantage. I'll include it for posterity with a strikethrough to indicate that I withdrew the points...]
Another issue with looking at these graphs is that they aren't measuring what is really going on. They are measuring maximum capability at a given load/RPM. But, a bike is not running at maximum load on the highway - if it was then you wouldn't be able to roll on the throttle and accelerate. Instead, the bike is running at some percentage of its maximum load. The question is, what percentage is it running at. If you were held to that speed by, say, wind resistance of a head wind or steepness of a grade being so high that the motor needed to be pegged to stay at that speed - then you would hit the point being measured on those graphs. But, you are not. Instead you are running at some percentage of the available torque and power - just enough to overcome the grade and the wind resistance. The question is - what percentage is that? If the motor had huge reserves of power and torque at those speeds then you would only have to feed in a very tiny amount of electricity to maintain that speed. But, the motor is nearing the maximum speed it can maintain - both because as you speed up the power and torque available are declining and also because the power needed to maintain that velocity are rising. If you can change the gearing so that you have more torque and power available then you can let off the throttle and pump in less electricity for the same speed.
Your arguments all assume (insofar as they redirect to those graphs) that the motor is constantly running at maximum output - but it is not!
We do not need to know what the engine "can" do at a given RPM, what we need to know is where the potentiometer is at a given highway speed. The more open the potentiometer, the faster you are draining the battery. You may have another 20MPH that you can achieve, but if all of that is at 80%+ throttle then it is a very inefficient setup. If you can regear and swing the motor into a part of the graph where it has lots of torque at that speed then you can bring the throttle down to 50% and get much longer range out of the battery.
-
I wish the chart above was linear in RPM, it would make this analysis much easier without having to do double cross referencing of every figure.
If you look at the motor at 2000 RPM you see that it is capable of 25HP and 65 torque.
If you look at the motor at 4000 RPM you see that it is capable of only 10HP there and 12.5 torque.
If you riding along at 4000 RPM and then you throw a 2:1 reduction gear on, then you will shift the motor into a speed where it can produce 25 HP which is halved by the gear to generate 12.5 HP at the rear wheel, torque is also reduced by the gear from 65 to 32.5. You've gained 25% in power and have more than double the torque with that gear change. For a 10-15% loss in having a gearbox, that's still a net gain, though.
At 5000 RPM it is capable of something like 7 HP and 7.5 torque. The 2:1 reduction gear would take it to 2500 RPM where it gets about 20HP, reduced to 10HP, a gain of 42% - and around 42 torque, reduced to 21 which is almost triple the torque.
It would be nice to project the curves back to the 1000RPM area and see how those figures are modified, but the graphs don't go that far. :(
I'm pretty sure that miles/kwh are more related to the relative HP figures than the relative torque figures, but I presented both for completeness. If so, then a gain of 42% over a loss of 10-15% isn't going to break new ground. It might mean an extra 5-10 highway miles on the larger batteries?
I'm falling back to the value of the gearbox being more in providing exciting 0-60 times - without sacrificing highway mileage - than being solely about highway mileage.
-
I'll let protomech respond to your electrical power questions, flar, but I can say that IC motorcycles seem to get their best mileage at around 50 mph, when in top gear. Riding at 80 mph, also in top gear, typically drops the fuel mileage (range) by 20 to 30%.
My initial thought is that IC motorcycles have been optimized over a great many years to perform well in their top gear, while the lower gears are just used to get them to that top gear without straining the motor or drive-train and to allow them to work well at lower speeds that are outside their normal operating range, as they just don't have the power flexibility of an electric motor.
-
flar,
You're right that ICE motorcycles generally don't use much more fuel for highway riding vs city riding. My GS500 is faired, it gets about 60 mpg at 30-40 mph type speeds and 50 mpg at 70-80 mph type speeds (+20% higher consumption). The Zero is around 80-90 Wh/mile at 30-40 mph speeds and 180 Wh/mile at 70 mph (+100% consumption).
Two things working here:
1. Gas engines are really inefficient at light loads typical of city miles. Engine efficiency improves a bit under moderate load see highway miles, even as the total power required goes up due to drag. Take a Honda EU2000i gas generator (http://powerequipment.honda.com/generators/models/eu2000i-companion) as an example - at 1.6 kW rated load it can run for 4h (5.8 kWh / gallon) on 1.1 gallons, at 25% load (400W) it can run for 9.6h (3.5 kWh / gallon).
2. The GS500 is faired, the Zero is not. Motorcycles have really terrible aerodynamics, especially naked bikes. The Lightning $40k electric bike claims (http://www.lightningmotorcycle.com/product/performance/) 100+ miles at freeway speeds from a 12 kWh pack (< 120 Wh/mile, no speed claim but probably 70 mph), and it has a pretty nice aero fairing (not clear if that range figure is with the LSR fairing or the race fairing).
Not unique to the Zero. The Tesla Roadster (http://www.teslamotors.com/blog/roadster-efficiency-and-range) (theoretically) consumes 160 Wh/mile at 35 mph and 300 Wh/mile at 70 mph - also rather unaerodynamic, but well below its 120 mph top speed.
You're also right that a gearbox provides significantly higher performance at low speeds while the motor to operate in an efficient band for top speed. The Zero is geared for maximum rpm at 90-100+ mph in order to have (relatively) useful power and efficiency at 70 mph.
But it's a tradeoff. You could perhaps use the gearbox cost, weight, and volume for more batteries - that'd definitely give you more range. You could use it for a bigger more powerful motor - might give you similar power at low speeds as a smaller motor + gearbox, and more power at medium speeds.
The implementation is important. Once the Empulse is out we'll be able to see how well it works - the Empulse could have a much longer highway range than the Zero, which would indeed point to Zero's motor operating in an inefficient region at highway speeds.
-
So I guess we should be looking at this as a glass half full thing. The glass half empty would suggest that these bikes suck at highway efficiency when you compare it to city mileage, but the glass half full approach would suggest that the highway mileage is as efficient as that motor is capable of and it's the amazing city mileage that is the plus side, not the norm to compare to.
I believe that Brammo was saying that they were doing the gearbox to give more of the performance and feel of an ICE bike. That reads to me like the intent is more to focus on bringing back the excitement. Also, while gearing might not make a night/day difference in highway mileage, it might be able to get more top end out of the engine without sacrificing low end grunt, no? In other words, my previous comment about the tradeoff being highway mileage vs. low end grunt isn't exactly right, but you could say that if you want 100+MPH top end, then the low end grunt is going to suffer even more without gearing. So, to give us 100+MPH and also exciting off the line acceleration - like an ICE bike would typically have - then they need gears. But, the highway mileage is already about as good as we can expect from existing single speed bikes. Is that a better summary?
And, once you've bought into the need for a gearbox to be able to get both 100+MPH and fast starts, you might be able to do slightly better at highway mileage just to keep on the win/win side of things.
Also, I'd still like to see that graph recast as linear in RPM. The efficiency curve looks pretty flat on that graph, but it is a plot of efficiency vs. torque and we are more interested in how things graph as the speed of the bike (and thus the speed of the engine) varies. The RPM plot is a curve and right where the efficiency falls down you see the RPM curve start to take off - meaning the efficiency is flat, but over a deceptively smaller range of RPMs than the graph suggests due to its nonlinear RPM distortion.
-
Yep. A multi-gear transmission gives you whatever top speed your peak motor powerband can support AND good initial acceleration. A single speed direct drive transmission requires a compromise between the two.
For a commuter bike? Dead-simple to use, higher reliability and lower cost. Don't need speeds > 80 mph, initial acceleration is "okay" but not good. The 2012 Zero S is a bit faster than the 2011 bikes, despite a 40 lb weight gain (ZF9) and 30% higher top speed..
For a race bike? Also fine, speeds < 60 mph will only be seen at the very start of the race. Top speeds aren't super-important either, see aerodynamics.. most races > 30 miles will be energy-limited.
For a sportbike? Needs a transmission or a bigger motor. Watch the 1.5 year old video of the Empulse RR prototype track test (http://brammoforum.com/index.php?topic=452.msg2597#msg2597) - indicated 10-60 takes about 6s. (granted: may not have been WOT, may have still been using the perm 156 motor, speedo may not be accurate.. so take it as an illustrative point)
I think the Empulse is going to have a top speed closer to 120 mph than 100 mph when it shows up.
-
I believe the aero drag goes up with the cube of the speed, so to up the top speed any decent amount, they are going to have to have significantly more motor power output (and hence less run time per charge at the upper end). The tranny isn't going to get them around that.
What the tranny will do, though, is provide some torque multiplication at the low end, so they can get better low-end acceleration. Maybe that's how they aim to achieve superbike-level performance, at least up to 80 or 100 mph.
With the flexibility of the electric motor relative to IC, though, I still question why they need 6 gears. As protomech pointed out, though, we'll see when their implementation hits the streets.
-
My guess is that the ITE transmission has been adapted from an existing IC six-speed transmission that was bought off-the-shelf and that is why it has 6-speeds. Designing a completely new motorcycle transmission from scratch would be a daunting task for any company that didn't have a lot of experience with motorcycle gearbox design and manufacturing. There are a whole lot of things that can go wrong (and have in the past) with a gearbox and it can take years to get the bugs worked out of a new design. Using a proven, off-the-shelf gearbox would be the only smart thing to do for the company that is making the ITE transmission.
-
SMRE does seem to have a fair bit of design experience with gearboxes. I would not assume it's an adaptation of an ICE gearbox.
1416 on brammoforum (http://brammoforum.com/index.php?topic=1001.msg7300#msg7300) mentioned that Tesla dropped their two-speed transmission because of failures resulting from the large rpm swing on shift, and suggested the six-speed transmission from Brammo was a compromise towards increasing durability.
ttxgpfan talked some with BrammoBrian on this topic, I recall that the gist was basically the same thing. Interview is in the archives, it's worth a listen to. http://esbk.co/ttxgpod-podcasts/ (http://esbk.co/ttxgpod-podcasts/)
-
Let me add a perspective from someone who has designed many of these drive systems.
As far a range is concerned, no gears are better because with a really good electric motor (not some off the shelf unit) you can get near 90% efficiency through a broad speed range. It's tricky to read these constant voltage motor graphs because EV's use variable voltage for speed control. For most speeds, you can operate from 85% to 90% efficiency. Adding gears just wastes ~5% efficiency.
The problem is how to have both good top speed and standing start torque. The reason that the car guys can do it is because the have very high motor voltages which gives the motor top end RPM and then they have a better gear ratio for starting torque.
For electric motorcycles, you really need well over 100 volts to have something that does both well. So far, most of them just haven't got there yet, but they will.
Now I'm not saying a gearbox isn't fun. It is fun, but not a necessity.
Range has to do with battery capacity. The battery, motor, controller and drivetrain are all very efficient (90% or more) if they are designed correctly. Check out my article on range
http://www.ntsworks.com/Range.html (http://www.ntsworks.com/Range.html)
Neal
-
Thanks for the link to your article, Neal. That was very a interesting and clear explanation of electric motorcycle range for the layperson It conforms to my experience riding my Zero around on a daily basis. I absolutely agree that the industry needs to come up with new range standards such as you propose otherwise the public is going to think they are being hoodwinked by the industry claims and nothing but bad press and poor expectations by the public will be the result, similar to how people feel about the "highway mileage" claims by the auto industry. Or the mileage claims by Honda for their Insight that resulted in a class-action lawsuit, which was widely reported in the press and no doubt did nothing for the sales of that model car. The budding electric motorcycle industry does not need a similar issue to arise due to "inflated" range claims.
-
hi Neal, good to see you back :)
so the Empulse seems to go for both, aerodynamics and gears ! so she gains in aero and looses again with the gears. I so far like the relative simplicity of electric motorcycles. Can we keep it like that ? With the Zero's I have been riding for over 2 years now it has been fun and simple - yet they could have much better aero dynamics to see them gain efficiencies at high speeds. So for gears we loose 5% with aero what is in it ? I.e. the lower seat on Zero S and changed fairings ? how much would we gain ?
-
Both the Brammo and Zero bikes have upright riding positions and you can't really make them very aerodynamic. I'd say it's a wash between them. The brammo is less tall, but it's wider.
Aerodynamic drag is huge, but it's very difficult to get it reduced. The only sure fire way is to reduce the frontal area. I'm a big fan of making narrow bikes with the rider's legs tucked in so the frontal area is minimal. Having low handle bars really helps reduce drag, but my back hurts riding like that.
Aerodynamically the most important part of the bike is the back end. The important part is to smoothly bring the air back together again after it's split around the bike. Screens and stuff on the front really don't do much to reduce drag.
The Hayabusa is one ugly bike, but it sure is aerodynamic. Look at the tail secion, it's actually a little higher than the tank. That does wonders to reduce drag, but then it's hard to throw a leg over and it's like you are sitting in a bucket.
Neal
-
good points Neal, forgot about the Rear end effects ... in the Zero threads we seem to have some members gaining 10% or so on range and top speed with front screens. For 10% worth while to consider I guess and as we go into winter it keeps the air of the chest ...
-
My solution to motorcycle aerodynamic drag is to just follow the speed limit. That solves most of the problem and will extend your range significantly. In my case, I use my motorcycles primarily for daily transportation and if I need to be somewhere in a rush, I just leave earlier. ;)
-
Or the mileage claims by Honda for their Insight that resulted in a class-action lawsuit, which was widely reported in the press and no doubt did nothing for the sales of that model car.
The lawsuit was for Honda Civic Hybrid owners after a software update reduced the usable capacity of the battery (small impact on mpg).
The 1G Insight was a $20k efficient 2 seater that launched in a time of $1.20 gas. I drive one, it's fantastic personal transport and an engineering marvel, but I can see why they failed to sell. My lifetime mpg average is about 68 mpg and all I do is drive carefully.
Both the Brammo and Zero bikes have upright riding positions and you can't really make them very aerodynamic. I'd say it's a wash between them. The brammo is less tall, but it's wider.
Zero claims 43 miles @ 70 mph constant for the Zero S, 184 Wh/mile. Brammo claims 56 miles @ 70 mph constant for the Empulse R, 166 Wh/mile.
If the gearbox imposes an additional 5% efficiency penalty, then a fixed-gear Empulse would do about 158 Wh/mile, about 18% more range/kWh than the Zero. If aerodynamics are basically a wash, do you think that's due to operating the motor at a more efficient point, inefficiencies at high load for the Zero, flawed test design, or something else?
-
Zero claims 43 miles @ 70 mph constant for the Zero S, 184 Wh/mile. Brammo claims 56 miles @ 70 mph constant for the Empulse R, 166 Wh/mile.
I'm confused: Zero claims 43 miles@70 mph for the ZF6: That's 6000Wh/43miles or 139 Wh/mile. The ZF9 is 63 miles @ 70 mph; 142Wh/mile.
Where did you get 184 Wh/mile?
-
I heard on the news yesterday that the Honda Insight small-claims lawsuit, where the owner received a judgement of almost $10K , was tossed out by the Superior Court, due to the mileage claims following the government testing standard (or something like that).
As far as rolling drag between the Zero and the Empulse goes, my money is on the Zero. It is thinner and has much narrower tires than the Empulse. While the Zero does have to push its battery box through the air, the Empulse's radiator is quite large and the front of the bike looks to me to offer more air resistance than the front of the Zero. When you add that to the Empulse's transmission and O-ring final drive inefficiencies (plus its greater weight), I would be surprised if the Zero does not use less power to get down the road, at the legal speeds that it is designed to operate at, than the Empulse.
-
Zero claims 43 miles @ 70 mph constant for the Zero S, 184 Wh/mile. Brammo claims 56 miles @ 70 mph constant for the Empulse R, 166 Wh/mile.
I'm confused: Zero claims 43 miles@70 mph for the ZF6: That's 6000Wh/43miles or 139 Wh/mile. The ZF9 is 63 miles @ 70 mph; 142Wh/mile.
Where did you get 184 Wh/mile?
That 43miles for the ZF6 is the 70mph commuting range, which is an average of the 70mph constant speed range and the UDDS range. For the ZF9 commuting range is 63miles. Since Zero doesn't post their 70mph constant speed range on their website, you have to do a little math using the formulas they provide to determine what the 70mph constant speed range is. It just happens to turn out that the ZF9 70mph constant speed range is 43miles (same as the ZF6 commuting range). Brammo lists all three ranges, UDDS, 70mph highway and Combined. Brammo's Combined range is calculated using the same method as Zero's Commuting range and so far the reports I have read on forums like these suggest that the Combined / Commuting range is actually a very good estimate at "real world" range the bikes are getting.
-ryan
-
I heard on the news yesterday that the Honda Insight small-claims lawsuit, where the owner received a judgement of almost $10K , was tossed out by the Superior Court, due to the mileage claims following the government testing standard (or something like that).
This lawsuit?
http://www.latimes.com/business/money/la-fi-mo-honda-civic-lawsuit-20120509,0,3088344.story (http://www.latimes.com/business/money/la-fi-mo-honda-civic-lawsuit-20120509,0,3088344.story)
As far as rolling drag between the Zero and the Empulse goes, my money is on the Zero. It is thinner and has much narrower tires than the Empulse. While the Zero does have to push its battery box through the air, the Empulse's radiator is quite large and the front of the bike looks to me to offer more air resistance than the front of the Zero. When you add that to the Empulse's transmission and O-ring final drive inefficiencies (plus its greater weight), I would be surprised if the Zero does not use less power to get down the road, at the legal speeds that it is designed to operate at, than the Empulse.
Yes, the Empulse should have significantly greater rolling resistance than the Zero .. or the Enertia Plus, for that matter. It uses 77 Wh/mile for the EPA UDDS vs the Zero S 69 Wh/mile. Enertia Plus is 77 Wh/mile as well .. which is a little odd. Empulse is heavier and uses bigger, softer tires.
I'm confused: Zero claims 43 miles@70 mph for the ZF6: That's 6000Wh/43miles or 139 Wh/mile. The ZF9 is 63 miles @ 70 mph; 142Wh/mile.
Where did you get 184 Wh/mile?
That 43miles for the ZF6 is the 70mph commuting range, which is an average of the 70mph constant speed range and the UDDS range. For the ZF9 commuting range is 63miles. Since Zero doesn't post their 70mph constant speed range on their website, you have to do a little math using the formulas they provide to determine what the 70mph constant speed range is. It just happens to turn out that the ZF9 70mph constant speed range is 43miles (same as the ZF6 commuting range). Brammo lists all three ranges, UDDS, 70mph highway and Combined. Brammo's Combined range is calculated using the same method as Zero's Commuting range and so far the reports I have read on forums like these suggest that the Combined / Commuting range is actually a very good estimate at "real world" range the bikes are getting.
Yes, that's right.
Zero calculates highway commuting (combined) like so: combined = 2 / ( 1 / city + 1 / highway ).
You can back this out to highway = 1 / (2 / combined - 1 / city) = 1 / (2 / 63 - 1 / 114) = 43.5.
Compute efficiency as 7.9 kWh / 43.5 miles = 182 Wh/mile.
And it's fucking stupid that Zero doesn't list the pure highway range directly.
-
Zero calculates highway commuting (combined) like so: combined = 2 / ( 1 / city + 1 / highway ).
You can back this out to highway = 1 / (2 / combined - 1 / city) = 1 / (2 / 63 - 1 / 114) = 43.5.
Compute efficiency as 7.9 kWh / 43.5 miles = 182 Wh/mile.
And it's fucking stupid that Zero doesn't list the pure highway range directly.
I think the problem with listing a pure highway range is that it can be very different depending on rider weight, temperature, tire pressure, road condition, elevation changes, rider clothing, rider position, the riders ability to maintain a set speed, etc. It is a relatively easy test for a customer to try, and then get results that are significantly different than advertized and then suspect there is something wrong with their bike. I guess since Brammo has published their 70mph range they will find out if their customers actually achieve the advertized distance.
Has anyone tried going 70mph sustained on a ZF9 S in a tuck from fully charged until the bike no longer sustains that speed on a flat road with no wind?
-
I'm not sure, but I think that the ranges from Brammo and Zero are from riding on a dyno. The dyno has a load profile that is supposed to compensate for an average wind resistance and it varies with speed. The 70 mph distance from the dyno data is probably pretty close to reality though because neither of those motorcycles are especially aerodynamic. The average sportbike is slightly more aerodynamic.
It also seems to agree with the ranges that people are reporting on the forums.
How aerodynamic can it get? The human powered bicycle 1 minute speed record is 82 mph right now. That's using around 1 horsepower (746 watts). At that rate, a 9.3 kwh battery could go more than 1000 miles. Those bicycles look like missiles so of course a real motorcycle couldn't be anywhere near that, but there are huge gains to be made in freeway range if ony electric motorcycles were more aerodynamic.
-
It seems most people are using their bikes for street. Since a dualsport bike is available, I am curious about offroad range. On trails my average speed shows maybe 15mph, with a max of 45mph. So from the information I read here, the slow speeds will really help range. But I bet offroad has a whole bunch of other factors that reduce range. Anyone try a ride on some single track or quad trails to get an idea of offroad range at the speeds listed above?
-
I dont understand why they need to have 6 speed gear box, wouldnt a 2 or 3 speed have less fritional losses and weigh less.
2 speed gearbox would make sense low to mid, and mid to high.
most motorbike have 2 speed , fast and stopped. ;)
-
I dont understand why they need to have 6 speed gear box, wouldnt a 2 or 3 speed have less fritional losses and weigh less.
2 speed gearbox would make sense low to mid, and mid to high.
most motorbike have 2 speed , fast and stopped. ;)
Yes a 6 speed gearbox is totally overkill. 2 speeds like on a Tesla car is plenty. 6 speeds is more about having fun rather than being practical. I must admit that for the first year of riding electric motorcycles I missed the gearbox. At first it feels weird to do nothing with your left hand/foot. After a long while I got used to it and now I can concentrate on more important things like keeping my front wheel from sliding. Yuck! Of course you don't have to use all 6 speeds, but it's a lot of weight, complexity and maintenance you are paying for.
Different strokes for different folks!