y8s

iTrader: (8)

5 seconds of select-and-google shows she apparently has kids and maybe an EX-husband.

also:

pusha

iTrader: (5)

6/10 would bang

mgeoffriau

iTrader: (7)

Apologies for derailing (re-railing?) the discussion here, but I have a question.

My understanding is that electric motors make maximum torque at 0 rpm. If this is true, is your analogy to "driving [one's] car in 5th gear all the time" intended only to convey the sensation involved and not actually refer to a taller gear? Wouldn't a taller gear in this application shift the operating RPM of the motor lower into a torque-ier range? Is your planetary-geared wonder geared up or down from a direct-drive motor?

Braineack

iTrader: (62)

this morning i rode the elevator up with a dude who rode his bike to work...he was wearing spandex and smelled of ----.

Joe Perez

iTrader: (8)

And the Stalker Award goes to Y8s.




This is true of series-wound DC motors. Polyphase motors have a somewhat different torque curve, although they are still quite torquey at low RPM.



The analogy was meant simply to convey the feeling of the system as compared to a direct-drive motor, and 5'th gear was supposed to be the direct-drive motor (4'th would have been a better analogy, as it's truly 1:1) as opposed to the geared motor.


Gearing is still gearing, and torque multiplication is still torque multiplication. I'm no expert on electric motors, and so I can't explain to you the physics involved. All I can say is that with a direct-drive motor climbing a hill, it feels like lugging a gasoline engine by trying to climb a hill at 20 MPH in 5th gear. It just can't do it very well, and it's harmful to the engine. (Or in my case, the battery.) The geared motor itself runs at a much higher RPM internally, and enjoys the benefit of torque multiplication which makes it a very capable hill climber.



Thus the benefit of using an electric assist. In the morning, I can let the system do more of the work for me so I don't arrive at the office smelling like a camel's *******.

fooger03

iTrader: (2)

Depending on the electric motor, they're often more efficient at higher RPMs than lower RPMs. In the RC Heli world, using brushless motors, You might get 10 minutes of flight time out of "normal mode" where the speed of the rotor head is directly controlled by the throttle input from 0% to 100% throttle. If you have a "3d mode" and flip to it, you may very well get 12-15 minutes of flight out of the same charge where the speed of the rotor head might vary between 80% and 100% depending on distance of the throttle stick away from center, and thrust up or down is largely determined by blade pitch - allowing you to fly the helicopter right side up or upside down - so at higher RPMs, not only does the engine spin longer, but it also spins faster.

This is the rough equivalent of stuffing a big engine in a car and driving 70mph at 5% throttle vs. stuffing a tiny engine in a car and driving aerodynamically limited at 70mph at full throttle - the tiny engine in most cases is probably operating much more efficiently.

pusha

iTrader: (5)

you should have beat his ***. right then and there. next time just punch that bitch in the mouth and there won't be no next time.

JasonC SBB

How do you know it's not the propeller LIFT TO DRAG ratio worsening at low RPM as opposed to the motor efficiency worsening at low RPM?

[Bah, edited typo.]

Joe Perez

iTrader: (8)

I don't remember un-banning Jason from this thread.


But you'll be happy to know that I do, in fact, now have a proper closed-loop current throttle. The new beta code for the CycleAnalyst 3 allows the throttle input to act as a "current request", whereby the CA dynamically adjusts the throttle output (which, in turn, adjusts the controller's PWM duty cycle) to achieve the desired current level, as measured between the battery and the controller. This is effectively a torque-request throttle, kind of like how the Subaru throttle-by-wire code works.

And it's friggin' sweet.

The problem I had with the front wheel wanting to jump into the air every time I cracked open the throttle from a stop is completely gone, and I no longer have to "ride" the throttle to keep the level of assist where I want it. Twist the throttle halfway, and you get 50% of rated current regardless of RPM. (Remember, the phase timing on these motors is static.) And it's surprisingly stable- there's virtually no oscillation or overshoot, and yet it's extremely quick to respond, despite the fact that I have all of the gains set at default.

Mobius

iTrader: (2)

It's probably both. And the battery packs used have decreasing efficiency the more amps you pull out of them. Generating the same thrust at lower rpm, even assuming exactly the same motor efficiency at that rpm, still requires more current so will give you less flight time.

JasonC SBB

AFAIK brushless DC motor efficiency stays pretty high with RPM and with power output. It may go down some towards full power and also at very low power. However for mid power, I think the efficiency is a bit lower for highish torque but lowish RPM, vs. lowish torque but highish RPM, due to I^2*R winding losses. Unlike a throttled gasoline engine, whose max efficiency for a given power is near maximum MAP for as long as the mixture stays stoich.

Induction motors OTOH lose efficiency with a combo of low speed and high torque. (They are used in industry and maybe the Prius, but not bicycles AFAIK)

And they are different than brushless DC motors. BLDC motors are more like synchronous AC motors.

Joe Perez

iTrader: (8)

The Ebikes.ca website has a neat little simulator that can be used to plot the predicted performance of various systems, using the observed characteristics of a variety of motors along with mathematical models of the battery, controller, etc.

I did a quick plot for my system, and the numbers it's producing seem to reflect reality, including the point where battery current starts to drop off sharply as motor RPM exceeds the point at which the system can deliver full power to it.

(The plot is done at full throttle.)



So I guess they are calling peak torque at stall, which now that I think about it makes sense. A polyphase BLDC motor is physically quite different from a series-wound motor, but the fundamental operating principle is similar (as opposed to an induction motor, as Jason noted.)


I do find it interesting that induction motors seem to constitute the bulk of the "high end" spectrum insofar as DIY automotive conversions are concerned. They're certainly the most expensive, and do not provide the best low-end performance, but they do have the advantage of offering dynamically-variable timing, permit easy reverse operation, and are much more fail-safe insofar as unintended acceleration.

This is a fairly typical performance chart for a three-phase AC induction motor in an EV application:





Jason, while I can't find any specs from Toyota itself, some of what I've seen suggests that the Prius uses a permanent-magnet motor (along with the Insight and Focus EV) inasmuch as that the authors of same are blaming Toyota for a predicted forthcoming shortage of certain rare-earth metals, noting that "Each electric Prius motor requires 1 kilogram (2.2 lb) of neodymium" and calling the Prius "the biggest user of rare earths of any object in the world."

The source is from Reuters, so it's probably credible: http://www.reuters.com/article/2009/...57U02B20090831

olderguy

iTrader: (19)

So now those damn environmentalists are raping the planet

fooger03

iTrader: (2)

Why isn't my G-M angle accurate anymore?

Because Prius.

y8s

iTrader: (8)

most people who own a prius aren't environmentalists.
look up the term "greenwashing"


i consider myself an environmentalist. I reuse what I have. I fix what breaks instead of replacing it. I grow my own food and walk to the farmers market two blocks away.

and I don't drive a hybrid. not until they make financial and resource sense.

Braineack

iTrader: (62)

plus you wouldn't know how to drive it...

y8s

iTrader: (8)

Just about every time I get a rental car, I try to push in the clutch and shift it.

triple88a

iTrader: (2)

It costs about 60 cents to fully charge batteries on an electric car and most batteries go about 50miles.

1 dollar for 80ish miles > 1 dollar for 8 miles.

Of course this would be only valid if you're buying a new car where the upfront cost is the same.

y8s

iTrader: (8)

I did an analysis for myself on this comparing a few different cars bought new.

Here are the cars I compared that were cheaper to own over 10 years than any hybrid:

Ford Fiesta
Mazda Mazda3 4dr
Honda Civic HF
Ford Focus SE SFE
Honda Civic LX

I think I based it on 10k miles per year. Your mileage may vary with mileage.

I know you compare cost of electricity to cost of gasoline but even the Volt (ok not full electric but more flexible) was more expensive to own after 10 years than a Prius V.

Though here's the other side of that story:

I currently buy my electricity from renewable sources. So the well-to-wheels efficiency and drain on the environment gets better with a plug-in car.

I didn't look at electric cars for range reasons, but there are quite a few that struggle to get me to work and back with a significant margin of safety. Not to mention I have no garage and would have to "cord it" every night, regardless of weather.

In any case, I'm not anti, I'm just anti-now. I'd buy an electric car that charged fully in 8 hours and lasted 300 miles.

Oh wait there is one... the Tesla S. $70k after rebates.... plus 10 years of charging.

Joe Perez

iTrader: (8)

Pure electric cars have a long way to go. Until we can achieve either 1,000 miles on a charge or the ability to fully recharge from a public station in about 5 minutes, they're simply not going to become the dominant mode of transportation in a country the size of the US, given the current social and economic status-quo. Nobody wants to worry about whether they'll be able to make it all the way to the airport and back without running out of electrons, to say nothing of all the folks who actually commute 60 miles or more each day, and that's before you factor in trips to the grocery, soccer practice, the adult novelty store on the far side of town, etc.

Range-extended plugin hybrids such as the Volt, on the other hand, are probably going to become more and more commonplace as time goes by, and may well become the dominant mode of personal transportation within a generation or two, assuming that presently-observable trends continue along their projected trajectories (eg: gasoline becomes more costly, battery storage becomes cheaper and denser, and CARB / EPA requirements continue to become more stringent in the direction of levying a severe "gas guzzler" tax on anything less than 75 MPG equivalent. CAFE standards alone aren't the answer.)


I wonder: How many Americans (as a percentage of the population) live in houses where 240v @ 30-50A power is available for overnight charging?

(For that matter, I wonder how many Americans who do have a garage with 240v power are actually able to park a car in it? My mother seems fairly typical, in that her large 2 car garage barely has enough free space in it to walk through, much less park anything larger than a child's bicycle in.)

I honestly have no idea what the answer here is. I live in an apartment, and while I do have a well-appointed garage, I only have 110v @ 15A available in it. It's enough to fill my bike in just under an hour, but re-charging a Tesla Roadster would take precisely two days at that capacity. Running 240v would be impractical for me except on an ad-hoc basis, by stringing an extension cord all the way from the kitchen. Which, of course, presupposes that I don't need to cook anything in my oven.

The vast majority of apartment-dwellers, of course, have no charging availability at all in the vicinity of their parked car. And even among homeowners, a lot of homes, even fairly modern ones, lack the installed capacity for high-current 240v service. Lots of places here in SoCal built as late as the 80's have only 100A mains, and no existing 240v runs at all.

What these houses do have, however, is Natural Gas. And I am REALLY surprised that I have never actually seen a single in-home natgas compressor for the purpose of re-fueling a natgas car. (Yes, I know that they exist. I've just never seen one actually installed.) As an interim solution, natgas conversions of gasoline cars are extremely inexpensive, and the cost-per-mile of natgas vs. gasoline is quite favorable, especially when one considers the fact that road taxes are not applied to natgas. Add in the fact that public CNG refilling stations actually exist (admittedly, you have to search, but they're out there) and a CNG car looks pretty good.


Conservatives take note: natgas is a domestic resource.

Liberals take note: natgas vehicles enjoy far lower NOx, VOC, CO, CO2 and particulate emissions per mile than either gasoline or diesel cars. And if you're clever, you can figure out a way to tax it.

Ron Paul take note: nobody cares about you. You have marginalized yourself, and are irrelevant. Go away.


CNG plugin hybrids: the practical, affordable, sustainable solution which I guarantee you will completely fail to gain mass acceptance.



And meanwhile, crazy fools like myself will continue to build a tiny and insignificant number of vehicles which are 100% emissions-free* and have a smaller total carbon footprint than a horse.

* = at least, it will be again once they bring San Onofre back online.


Today's energy efficiency was 17 watt-hours per mile, my best yet. My daily commute consumes less power than Pusha's mom's motorized *****.