Electric transmission redux

In an earlier post on the subject it was stated that electric CVTs in a
bicycle are impractical because there is no excess power to be had. But
there often is excess power available: whenever one coasts downhill or
otherwise does not pedal a conventional bike because one's speed is
already great enough, on an electric drive bike one could continue
pedaling to store energy in the battery for later use. This is in
addition to the energy that can be recovered simultaneously by
regenerative braking. The chief benefit of an electric transmission
with a battery is this load leveling capability; the CVT feature is just
a freebie.

This system is certainly not for racers. Peak instantaneous efficiency
will be less than in a chain drive (chains are great under ideal
conditions, that is when they are perfectly lubricated and free of dirt
or water). But the perceived effort required will be less under many
conditions because the rider can always put muscle energy into the
system when and as desired, independent of ground speed. This is what
many casual riders want.

A chainless all-electric drive could also have the simplest possible
control set, namely a brake and a "shift" control as in a conventional
bike. There need be no separate throttle for the electric motor. The
control system would be programmed so that drive wheel RPM is in
proportion to crank RPM, with the proportionality set by the shift
controlr. This is as in a conventional bike, except of course that in a
conventional bike there are only discrete values of proportion available
(gears), whereas in an electric drive a continuous range of values is
available.

On Sat, 01 Jan 2005 13:52:42 -0600, richard schumacher
wrote:

In an earlier post on the subject it was stated that electric CVTs in a
bicycle are impractical because there is no excess power to be had. But
there often is excess power available: whenever one coasts downhill or
otherwise does not pedal a conventional bike because one's speed is
already great enough, on an electric drive bike one could continue
pedaling to store energy in the battery for later use. This is in
addition to the energy that can be recovered simultaneously by
regenerative braking. The chief benefit of an electric transmission
with a battery is this load leveling capability; the CVT feature is just
a freebie.

TANSTAAFL. There are substantially greater losses in a
generator/battery/motor system than in a drive chain[1]. The greatest
instantaneous power demand on the rider to maintain a given speed may
be lower than the peak demand with a conventional bike, but the power
required to traverse a given course will be higher for the hybrid than
for the direct-drive for a variety of reasons unless the direct-drive
bike is unusually inefficient or poorly suited to the
application...and this is accentuated in hilly terrain.

Don't let my discouraging statements dissuade you from finding
investors and spending large sums to pursue your goal of devising an
electrically-based hybrid/CVT bike, however. Watching people learn
about thermodynamics has been a lifelong source of amusement for me.



[1] Many people have made the mistake of inferring that the
experience of the builders of hybrid automobiles, that the electric
drive system with battery buffer is more efficient than an
automobile's automatic transmission, would be applicable to other
things. They seem to regularly fail to take into account the fact
that those automatic transmissions are, by comparison to either a
chain drive in fairly poor condition or a conventional manual gearbox,
horribly inefficient. The people who make this mistake often are
regular readers of Popular Science, which often ranks with the Weekly
World News for accuracy over the long haul.
--
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On Sat, 01 Jan 2005 13:52:42 -0600, richard schumacher
wrote:
In an earlier post on the subject it was stated that electric CVTs in a
bicycle are impractical because there is no excess power to be had. But
there often is excess power available: whenever one coasts downhill or
otherwise does not pedal a conventional bike because one's speed is
-snip-

Werehatrack wrote:
-snip-
TANSTAAFL.
-snip-
Don't let my discouraging statements dissuade you from finding
investors and spending large sums to pursue your goal of devising an
electrically-based hybrid/CVT bike, however. Watching people learn
about thermodynamics has been a lifelong source of amusement for me.
-snip-
horribly inefficient. The people who make this mistake often are
regular readers of Popular Science, which often ranks with the Weekly
World News for accuracy over the long haul.

I already own cars.
I ride my bicycle for many reasons, none of which are
enhanced by Mr Schumacher's format.

TANSTAAFL?

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

A Muzi wrote:

snip
TANSTAAFL?
/snip

TANSTAAFL=acronym for
There Ain't No Such Thing As A Free Lunch

(Was that originally Robert A. Heinlein's phrase, or did he borrow it
from elsewhere?)

Dan

Sun, 02 Jan 2005 14:18:04 -0600, ,
A Muzi wrote:

TANSTAAFL?

There Ain't No Such Thing As A Free Lunch
--
zk

As soon as he can produce an electric vehicle that does not produce any
heat in its battery, generator, motor system I would like to be the
first investor.

In article ,
Werehatrack wrote:

On Sat, 01 Jan 2005 13:52:42 -0600, richard schumacher
wrote:

In an earlier post on the subject it was stated that electric CVTs in a
bicycle are impractical because there is no excess power to be had. But
there often is excess power available: whenever one coasts downhill or
otherwise does not pedal a conventional bike because one's speed is
already great enough, on an electric drive bike one could continue
pedaling to store energy in the battery for later use. This is in
addition to the energy that can be recovered simultaneously by
regenerative braking. The chief benefit of an electric transmission
with a battery is this load leveling capability; the CVT feature is just
a freebie.

TANSTAAFL. There are substantially greater losses in a
generator/battery/motor system than in a drive chain[1]. The greatest
instantaneous power demand on the rider to maintain a given speed may
be lower than the peak demand with a conventional bike, but the power
required to traverse a given course will be higher for the hybrid than
for the direct-drive for a variety of reasons unless the direct-drive
bike is unusually inefficient or poorly suited to the
application...and this is accentuated in hilly terrain.

Don't let my discouraging statements dissuade you from finding
investors and spending large sums to pursue your goal of devising an
electrically-based hybrid/CVT bike, however. Watching people learn
about thermodynamics has been a lifelong source of amusement for me.

Well, if you build/buy sufficiently nice three-pase widgets I hear
those can peak around 95% efficiency in the big ones. I don't know what
that translates to in smaller units: if it's a function of effort in
manufacture rather than physics.
But, assuming you can get reasonably nice three-phase motors in a
decent size to thunk onto a bike frame, you could use three. One,
turned by the crank, generating. One, in the hub, moving the bike. And
a third (connected through a clever power control) acting like a
flywheel battery. Assume that the rider is cranking the generator at
60Hz, output frequency will be a little less, but close enough. That
60Hz, depending on how the motor is wired, could whizz that flywheel
motor around pretty fast--several times the generator's speed. So it
won't have to be as heavy. Send 60Hz to the wheel motor, and you're
off. Varying the frequency by varying pedaling speed would vary ground
speed.
With the clever power controller, while cranking is producing power
it either turns the rear wheel, or, if the rear wheel is already
trucking along at a good speed, spin up the flywheel motor. If the
generator falls behind the wheel speed, pull power from the flywheel.
If the generator's not putting out, but the wheel motor is going faster
than the flywheel, connect the flywheel to the wheel motor, and the rear
motor will act as a generator and spin up the flywheel until its
frequency matches the wheel motor's. Just make sure it never drives the
pedals!
You could probably even set up some sort of speed ratio control by
alternately driving the wheel and charging the flywheel, but your
dynamic range would be limited by how far the motors could get from
ideal speed before dropping off in efficiency. Switch fast enough and
you won't get periods where the pedals feel dead and freewheel too
easily.
Ideally, assuming you have 95% efficient motors, and no losses in the
cables or switches, the system would be ~90% efficient--pedal to wheels.
~81% efficient pedal to flywheel to wheels. But a bad bearing in the
flywheel motor, too much vibration of that motor while running, or
having to drive a little cooling fan would bring that down fast.
Running higher voltages at lower currents will help some and allow
smaller motors, but that can get dangerous to the rider and you'll
probably pay for it in the switching electronics.
And I think most motors have around a 10% operating envelope where
efficiency is reasonable. Too far outside that starts burning windings
from all the waste heat. A person probably couldn't put out enough
juice to really fry a motor, but he sure would get tired in a hurry.
Then, of course, you have the problem that some riders might pedal too
slowly to generate useful output. In any event, the generator's
frequency would need to exceed the wheel motor's by a good bit before
you go anywhere--might make starting tricky.
And don't go too fast--could make the flywheel explode.
DC electrical with a speed controller might be better, but rectifying
AC to make DC wastes power, and direct DC generators over a fraction of
an amp are always inefficient from what I've seen. Besides, batteries
are weighty.
Could go for a compromise--a regular chain drive, with a
motor/generator/flywheel setup along side. Ride like normal, but if
you're coasting down a hill too fast, connect the flywheel--it'll rev
up, slowing the bike, and then return some power when climbing the other
side. Flip it off (of have it flip itself off) once the flywheel is no
longer helping. That would be pretty nice on a long descent, wouldn't
pop tires, give a little boost on the climb back up, and might be
reasonably lightweight. Would sound awesome, too, when the flywheel's
revving up! Wouldn't even need a cooling fan if used intermittently
like that.
Personally, I'd to hydrostatic with an accumulator. Probably more
efficient, and definitely more manly. Imagine hopping on the bike in
front of everyone, flipping a little lever, and peeling out! (:

--
B.B. --I am not a goat! thegoat4 at airmail dot net
http://web2.airmail.net/thegoat4/

"B.B." wrote: (clip) batteries are weighty.(clip)
^^^^^^^^^^^^^^^
I do believe that a flywheel capable of storing as much energy as a battery
will be even more "weighty." If you are fortunate enough to come home with
a charged battery, it will still be there to help you start your next ride.
A flywheel will lose most or all of its energy soon after the end of your
ride, so you go out each time with a big "millstone".

You have a lot of imagination--do you write science fiction on your day job?
G

On 2 Jan 2005 12:24:18 -0800, "Dan B." wrote:

A Muzi wrote:

snip
TANSTAAFL?
/snip

TANSTAAFL=acronym for
There Ain't No Such Thing As A Free Lunch

(Was that originally Robert A. Heinlein's phrase, or did he borrow it
from elsewhere?)

AFAIK, he was the first to turn it into an acronymic expression, but
the expanded phrase was a common aphorism in the US before that. My
parents related that it was in the common vernacular well before WWII.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

On Mon, 03 Jan 2005 04:01:13 GMT, "Leo Lichtman"
wrote:


"B.B." wrote: (clip) batteries are weighty.(clip)
^^^^^^^^^^^^^^^
I do believe that a flywheel capable of storing as much energy as a battery
will be even more "weighty." If you are fortunate enough to come home with
a charged battery, it will still be there to help you start your next ride.
A flywheel will lose most or all of its energy soon after the end of your
ride, so you go out each time with a big "millstone".

You have a lot of imagination--do you write science fiction on your day job?
G

And if not, maybe it's time to do it after work and start submitting
the results. Who knows, he could be the next Harlan Ellison. No,
scratch that, we've got more of those than most people can stand
now...better he should be the next Larry Niven.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.