John in CR
100 TW
h0tr0d said:
As Luke has been explaining, the nature of the graphs has led us to incorrect conclusions. Those graphs reflect a changing load with a constant throttle position like a dyno, not what occurs during acceleration.
Conclusive proof gearboxes are awesome.
- Thread starter Teh Stork
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As Luke has been explaining, the nature of the graphs has led us to incorrect conclusions. Those graphs reflect a changing load with a constant throttle position like a dyno, not what occurs during acceleration.
mr.electric
10 kW
I think Crossbreak did a good job explaining the role of transmissions in another thread
I see why all the ultra efficient Japanese ebikes employ a transmission. Transmissions do have a role in ebikes. One example is government regulated wattage and speed limits. you are allowed only 250 watts but you may assist up to 20 mph. You need a transmission for this combination.crossbreak said:Gearing a middrive for good speed and hill climb isn't simple as we all know. The spread is dependent on the motor torque, and thus we have determined a max speed of 35mph we can calculate gear spread for a given motor power (if geared/reduced right). I made some calcs about a bike with a weight of 150kg including rider. What came out is this rough contract:
1kw: 400% spread needed
2kw: 200%
4kw: 100%=single speed.
It's all about torque at the rear wheel. One can not push infinite power into it without flipping over (As can be demonstrated spectacularly on one of LiveForPhysics bikes for example) My next bike will be single speed, too
Chalo
100 TW
motomoto said:
3210 motor? That's some sort of model airplane part, right? So, it's being used in an unintended and totally improvised application?
Just verifying my first impression here. I don't ride on model airplanes, so I'm no authority on that sort of thing.
Chalo
100 TW
motomoto said:
Whoa. That trail is so gnarly, no wonder you need long travel suspension.
full-throttle
1 MW
Must be that time of the month again.. 
Chalo
100 TW
Miles said:
Confirms Luke's assertions, don't you think? About transmissions being a remedy for using the wrong motor for the job?
h0tr0d
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John in CR said:
Real world acceleration is changing load because the aero drag goes up with speed. The graphs are correct.
What Luke pointed out was "over-taxing the wrong motor for the application" with "tranny band-aid". This is the point were we disagree.
When he says that, I think the "right motor for the application with a tranny for eff and power at any speed".
I'm personally very grateful for the all topics and comments that Luke posted in this forum, it helped the EV revolution immensely, BUT in this case regarding where he works and what kind of vehicles they do, I think he's opinion is biased or limited by work ethics.
The Buggatti Veyron doesn't have a 2000hp engine and a 3 speed gearbox for ex = same acceleration, and same top speed due to rpm limitations. Why? It's the same "principle" of Luke's argument...
Motomoto's multispeed vs Zero in a drag race numbers shows us just that.
Just to be clear: I'm not saying we need an 7 or 8 speed gearbox in a electric car like gas powered needs. But at least 2 or 3 speeds will needed when you want ALL 4 (Acceleration, top speed, cost and eff) in a vehicle that can travel at 6mph with eff and go bonkers at 200mph! For every other limited application like drag, top speed attempts or ultimate eff contests a simple speed is just fine.
Take Docbass eff and heat comments comparing slow and fast wound hub motors on his Giant DH build. To have a 60+mph topspeed he didn't have decent acceleration, considering his power-to-weight ratio, and eff at 20mph was an absolute disgrace...
Thud said:
Found it!
http://www.motorcyclistonline.com/firstrides/122_1212_the_redshift_revolution/
BRD has done extensive side-by-side comparison testing against 250cc four strokes, both off-road and on supermoto tracks, and claims that riders of all skill levels consistently lap faster on the RedShift electric bike. "Diving into corners," Fenigstein says, "you're not banging down gears, so the rear stays settled and you hit the apex every time. And out of the corner, once you fnd the limit of traction you just hold it there. There's no shifting, so there's no need to constantly reset traction. It's like surfng-you just ride the wave of torque, from 15 to 25 to 75 mph."
h0tr0d said:
Which vehicle today has all the properties you list: "Acceleration, top speed, cost and eff"?
There are some things that I see is causing confusion in this thread.
*Top speed - Do you really want to reach the highest possible top speed on an electric motorcycle? I mean, you will run out of batteries in minutes... If you would settle for a little less top speed, the machine will consume a lot less power at top speed, and have better acceleration and efficiency getting there.
*Acceleration - If it accelerates enough to lift the front wheel, there is no gain in having a lower gear, right?
*Cost - My gut tells me that in mass production, a vehicle with a 50% oversized motor, will be cheaper, than one with a gear box.
*Efficiency - Depending on how the vehicle is used, the 50% oversized motor will have better efficiency in some scenarios, and the geared in others. Overall though, I think the 50% oversized will win.
With that said, I can of course see the performance benefits with gears. But I'm not sure if it's worth the complexity. Here is a comparative simulation of an electric motorcycle with rider. Performance should be similar to a Zero MX with stock gearing. Compared is the same bike with a 2-speed gearbox which has a 1:1.5 ratio.
EDIT: I changed everything to MX (instead of FX) in this post (except the filenames), after realizing MX/FX have different power.
Stock:
2 speed
Note, it may not be able to do this 0-100km/h time in practice, because it may just lift the front wheel when accelerating at almost 1G
Its time to quite using ICEs for a comparison. They don't have the same operating principles to give an accurate comparison.h0tr0d said:
BTW this is not Lukes "First Rodeo" He has had other Jobs and built some awesome shit incl multi speed electric bikes. I have driven his race car with a strong motor and and insanely expensive transmission/ clutch/ drive train that still fails! Another way to look at it is every moving part has a service life then it needs replacing so when adding moving parts in the form of a "Transmission" you will find no matter what, it will fail eventually, and if you build them to last longer they will be heavier and if you build it light it will fail more often! Where as a bigger motor will last for ever!
You also have to be careful when using cheep controllers for measuring efficiency. Anything production will have a torque throttle and other great features to keep the motor currents limited properly causing a totally different efficiency curve.
h0tr0d, You keep going on about top speed and bla bla bla. Do you really think Tesla wanted their models to go 400 km/h? I mean it already does ~ 220km/h I live with 90-110km/h speed limits. If You get caught going 40km over your car is taken away! So that's 130km/h and 150km/h tops with a huge ticket anymore and your car is impounded for 7 days think whats happening to your $100,000 car in the impound and to its batteries for those 7 days.... the next time you are caught its 3 months the next time its 6 months and you loose your licence for 1 year! So having a top speed at say 250 or 300 or what ever number while you take your FAMILY out for a trip seems kinda imbecilic doesn't it?
What do you think the top speed should be for a luxury family sedan?
The new MX and FX from Zero have insane torque from the start and they top out at 85mph! How fast does a motocross bike need to go? It will wheelie at will and if you clamp the throttle you are on your ass so gearing down doesn't seem to have any added benefit and gearing up gives you pointless added top speed.....
h0tr0d
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I'm making it...bearing said:
Definitions are good, keeps our eyes on target.
Topspeed. Drain the battery in minutes? yes, I want to have option. Buggati Veyron only last 12 minutes at top speed.
Acceleration. Correct in motorcycles, wrong in cars right? BUT compare with a smaller motor (AKA appropriate) and gears.
Cost. 50% oversized is not enough. Try 100%. and don't forget 2x the controller cost.
Efficiency. Let's say, for an instant, that a 2x motor and controller has the same eff as a normal motor with gears. I think the gear option will be lighter overall, therefore, upping vehicle eff.
Let's stay on the ZeroFX test subject:
P=1/2.cd.A.v^3
cd around 0,8
A around 0,7 (rider lying)
v 137km/h (according to http://www.zeromotorcycles.com/zero-fx/specs.php)
So P for max speed = 16.6kW, about half of 33 kW the zero has.
Now graph stock 33kW vs 17kW with 3 gears if you please.
Let's put some numbers and graphs out and end this insane debate!
Thanks Bearing!
h0tr0d
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The laws of physics apply to all vehicles. Broader torque, power and eff curves in electric? yep, that's why written 2~3gears in electric vs 7~8 gears in ICE.Arlo1 said:
Service life and breaking parts depend on correct engineering. Correct design, materials and assembly. Period. If he broke it, something was not correctly done...
Top speed for the Tesla? it's ok for a family sedan. But my question is: do you need 400hp for that performance levels? Or 200hp and gears would do the same?
When Bearing finishes the Zero new comparison, we'll know.
Again for the Tesla:
P=1/2.cd.A.v^3
cd around 0,25
A around 2,2 m2
v 220km/h
That's only 77kW@ top speed...
Like I said before, limited application, motorcross bike. But let's wait for Bearing.
h0tr0d said:
Oh, I didn't remember FX and MX had different power. I used the power from MX in the post above, but wrote about FX. It is changed now.
Here two variants of the FX, with the lower CDA you wished. The 17kW variant has three gears. Gear ratios are 1:1.65. The motor is simply a scaled down version with 51% of the power. It has better acceleration at low speeds, and about the same top speed. But it lacks power in the mid region, IMO.
John in CR
100 TW
All I can say is that you guys have no idea what you're missing. Cutting torque and acceleration in half right where the prime power band would be with a single speed is a performance compromise, not a performance enhancement. Sufficient power for real performance weighs a lot less than you think.
h0tr0d said:
I think Arlo has a point though. In your suggested 17kW version, the motor probably has to be almost 17kW nominal, or it will smoke. There are things that aren't the same with electric motors.
If you oversize the motor 50%, you don't only get 50% power. It means you can have a higher difference between peak power and nominal without smoking the motor, since you are going to use that peak for shorter periods. So in essence, 50% more motor could be like 100% better acceleration.
The more gears you get, the less you can overpower the motor without smoking it.
(By smoking, I don't mean blowing it, I mean get to a temperature where the controller needs to cut power.)
If you think about how little weight you add to the total vehicle by using a 50% larger motor, and how simple it is compared to a gearbox, it's easy to understand why the majority of current electric vehicles are using a fixed transmission.
John in CR
100 TW
Arlo1 said:
Sometimes the comparison is fun and appropriate. eg Yesterday I tagged along with the parts runner at my friend's shop. He's got pretty new looking Yamaha FZ16, a 153cc street bike. I outweigh him by at least 100lbs, but try as he might he couldn't lose me in dense urban riding. We did a good 20 miles plus, with him leading the way going to the places and me leading on the way back. The downtown streets aren't good enough for me to really ride hard, but electric power still taught 50-100 motos a hard lesson. Once Juan accepted how outclassed his pride and joy was, he got a big kick out of the reactions of other guys on motos.
BTW, everything I slaughtered had a multi-speed tranny, and me with just a DD hubbie.
I want to go do it some more, but sticking to the smoothest streets and with my gopro.
liveforphysics
100 TW
John in CR said:Arlo1 said:
Sometimes the comparison is fun and appropriate. eg Yesterday I tagged along with the parts runner at my friend's shop. He's got pretty new looking Yamaha FZ16, a 153cc street bike. I outweigh him by at least 100lbs, but try as he might he couldn't lose me in dense urban riding. We did a good 20 miles plus, with him leading the way going to the places and me leading on the way back. The downtown streets aren't good enough for me to really ride hard, but electric power still taught 50-100 motos a hard lesson. Once Juan accepted how outclassed his pride and joy was, he got a big kick out of the reactions of other guys on motos.
BTW, everything I slaughtered had a multi-speed tranny, and me with just a DD hubbie.
I want to go do it some more, but sticking to the smoothest streets and with my gopro.
This is exactly what riding the FX feels like on city streets, or on tight twisties. It is the fastest more capable machine I've ever ridden through terrain like that. I'm substantially faster through a city on the FX than I am on my built GSX-R1000. It's the combo of lightweight, nimble, and always being in the "right gear" that makes it so effortless to dominate everything else on 2 wheels with that machine.
Chalo
100 TW
Miles said:
It can be made suitable, I'd say, through the use of a two-stage reduction (and in this case, multiple ratios). But it's not inherently right for the job, because its design speed and impedance match is a small air propeller, not a 50-75cm road wheel.
Because I like cycling speeds and conditions, I understand the benefits of a multiple speed transmission. We can use some of the same technical solutions to accommodate motors that have some of the same limitations as our own pedal power. But in pedal cycling, we don't get to choose among different motors-- we must work with what we've got.
In the case of an e-bike, the motor is just about the most arbitrary component of the system. What Luke is pointing out is that it is technically possible to just use a motor that does exactly the job you need done, and skip the efficiency loss, complexity, points of failure, weight, and expense of a mechanical transmission.
This was something I noticed when I first began messing with e-bike tech at the beginning of the century-- hub motors existed, but they weren't quite right for the purpose. Almost, but not quite. They were happiest running at RPMs too high for regular bicycle wheels, at power levels that weren't enough to reach the implied road speeds. I reckoned these issues would be sorted out in due course by making larger diameter motors, perhaps even in the rims of normal bike sized wheels. But most hub motors today have the same basic problem. They work best when they are fitted to ridiculous donut wheels.
It's like a combination of lack of imagination and ruthless cost engineering have held back hub motor design to something less than optimal for their known application. We can get hub motors that weigh 10kg and more, but we can't get them in a configuration that will efficiently drag a loaded normal bike up a steep grade at less than 1000W input power. If the motors were 16-20" in diameter, we wouldn't need to lace them to 16-20" wheels to make them do that.
Which brings me to my favorite multi-speed transmission, the Stokemonkey. What I like about Stokemonkey is that it makes the limitations of pedal power into one of its strengths. It exploits a facility that the bike already has available, with or without power assist. It may incur the same efficiency losses and tradeoffs as a pedal drive, but it is totally harmonious with the pedal drive, and thus the whole bicycle, as a result.
When pedal drive or "bicycleness" are not assumed, it makes less sense to use anything other than the best matching motor and controller for the RPM and torque requirements.
John in CR
100 TW
liveforphysics said:
I absolutely believe it. Mine is just a big motor with wheels and handling on par with a 1970's Cadillac due to a cushy suspension. I can only imagine what similar acceleration does with good handling and an overall load less than or equal to me and my bike.
Your marketing plan needs to be get as many people as possible to throw a leg over one and take a test ride. Talk range and specs afterward to cement the deal. Actually just the test ride and then don't say a word. Hand them a paper with a low down payment and low monthly nut. It will sell itself. Look at the responses in this thread. The specs mean little, and wouldn't sell one to any of the guys here. The unique experience just can't be explained however hard we try. Let us all go for a test ride, and after the ride hit us with something crazy like $180 down + $180/mo, and a big % will sign on the dotted line right then. I'm a cheap bastard who likes to DIY and I'm sure I'd buy one.
Test Ride .......... Test Ride .......... Test Ride
How is the Stokemonkey different to motomoto's set-up?Chalo said:
It has a small high speed motor with more reduction.
Even allowing for the losses on the extra reduction, it's probably still more efficient than the Stokemonkey motor. So, what does the bit about impedance mean?
