What's the point? Mostly geekiness, I suppose, but the effectively
infinite number of "gears" while reducing the number of moving parts is
appealing. Also appealing is the notion that a battery in the system
would provide load-levelling (hill assist) but with the rider still
ultimately providing all of the energy, unless of course the rider
cheats by re-charging the battery from an external source. For
non-cheaters :_> the battery need only be large enough to help climb one
hill. Efficiency would not be as good as with a conventional drive, but
that's not really a concern for commuters or pleasure riders.
Surely by now someone must make such a thing?
> My searches have not turned up anyone selling a bicycle with a
> continuously variable electric transmission. I don't mean an electric
> scooter: I mean one in which the crank turns a generator/alternator, whose
> output through an electronic controller then drives an electric motor on
> the wheel rim(s) or in the hub(s).
<snippage>
> Efficiency
> would not be as good as with a conventional drive, but that's not really a
> concern for commuters or pleasure riders.
Efficiency would indeed be a concern for commuters and pleasure riders if
the efficiency is low enough, as I would presume would be the case. You
have three separate sources of energy loss: the inefficiency of the
generator, the power transmission to the motors, and the motors
themselves. Do you ever notice an electric motor getting hot? That's
wasted energy, and that gets worse as load increases.
The engineers can give reasonable estimates on the energy losses.
--
David L. Johnson
__o | Deserves death! I daresay he does. Many that live deserve
_`\(,_ | death. And some that die deserve life. Can you give it to
(_)/ (_) | them? Then do not be too eager to deal out death in judgement.
-- J. R. R. Tolkien
I doubt it. The loss in efficiency over a mechanical
transmission would make most any ride a real chore.
--
Dave Kerber
Fight spam: remove the ns_ from the return address before replying!
REAL programmers write self-modifying code.
In those small sizes, you would be very lucky to beat 50% to 60%
efficiency.
I don't think you'll find anything in production but there's an
article about such a thing here:
http://petrix.dreifels.ch/fb/images/1_wsj_shorter_1.pdf
Regards,
Mike
Unlike a gas fueled internal combustion motor, an electric motor's peak
torque is 0 rpm, so no transmission is needed. A single gearing is used for
whatever your primary speed will be.
http://lancet.mit.edu/motors/motors3.html#tscurve
Not necessarily; it depends on the motor design: induction motors tend
to have their peak at low but non-zero speeds unless they have a
capacitor start, while synchronous motors have essentially zero starting
torque, and shaded-pole motors have very low starting torque. DC motors
can have pretty much whatever torque characteristics you want to design
into them.
> A single gearing is used for
> whatever your primary speed will be.
True; it's easy to design an electric motor to run at a huge range of
speeds, and with sophisticated electronic controls, the efficiency
doesn't decrease a whole lot over that range, either.
Actually, we were specifically talking about mountain bikes. Assuming you
could have such a system that was efficient as a mechanical one, why not
put an electric motor in the front wheel too. :)
Richard Schumacher <no-...@thank-you.com> wrote in
news:3FD3F34E...@thank-you.com:
"David L. Johnson" wrote:
> On Sun, 07 Dec 2003 21:43:10 +0000, Richard Schumacher wrote:
>
> > My searches have not turned up anyone selling a bicycle with a
> > continuously variable electric transmission. I don't mean an electric
> > scooter: I mean one in which the crank turns a generator/alternator, whose
> > output through an electronic controller then drives an electric motor on
> > the wheel rim(s) or in the hub(s).
> <snippage>
> > Efficiency
> > would not be as good as with a conventional drive, but that's not really a
> > concern for commuters or pleasure riders.
>
> Efficiency would indeed be a concern for commuters and pleasure riders if
> the efficiency is low enough, as I would presume would be the case. You
> have three separate sources of energy loss: the inefficiency of the
> generator, the power transmission to the motors, and the motors
> themselves. Do you ever notice an electric motor getting hot? That's
> wasted energy, and that gets worse as load increases.
>
> The engineers can give reasonable estimates on the energy losses.
Yeah, efficiency in these small machines might be 70% or 80%. Sucky compared to
a chain. But:
Electric drive with regenerative braking and a storage battery allows the rider
to capture for later use energy while going downhill, energy that is otherwise
utterly thrown away as heat in the brake pads. The system would also make use
of low-effort pedalling as in a tailwind, or for that matter while going
downhill. Low-effort pedalling is not tiring even if the efficiency is low.
The net effect of these, at least over sufficiently windy or hilly courses,
would be an increase in overall efficiency. I have not worked out how much wind
or how much hill is enough to tip the balance.
F1 wrote:
> Unlike a gas fueled internal combustion motor, an electric motor's peak
> torque is 0 rpm, so no transmission is needed. A single gearing is used for
> whatever your primary speed will be.
It's still a transmission (it's transmitting power from here to there), it's
just one without any variable mechanical component.