B
Bill Baka
Guest
richard schumacher wrote:
> In article <[email protected]>,
> Peter <[email protected]> wrote:
>
>
>
>>Increasing the total amount of work I need to do to propel my bicycle
>>from A to B is unlikely to either increase my comfort or provide
>>greater pleasure.
>
>
> You're right, there is a better way to do this. Adapt Toyota's system
> of a continuously-variable planetary gear transmission (1), substituting
> it for the chain and derailleur on an electric bike. That way you'd get
> the efficiency benefit of direct mechanical drive, continuously variable
> gear ratio, and on-demand electric motor assist. It wouldn't have to be
> much bigger or heavier than existing internally-geared hubs and would be
> completely sealed.
>
>
> (1) see here for a description
> http://home.earthlink.net/~graham1/MyToyotaPrius/PriusFrames.htm
> click on "Understanding [...]"
Now I am sucked into this. The only infinitely variable transmission I
have ever seen or read about was a system of varying cones and a drive
belt. Tolerable for a car but not too good for a bike. A planetary gear
system is not variable unless someone has invented a good way to change
the number of gears on the fly. The best automotive transmission in the
early days was the 1955 vintage Cadillac 4 speed hydromatic. It had 2
planetary sets with different ratios and used both for first, the low
one for second, the higher one for third, and direct for fourth. With an
overdrive it could have become an 8 speed and got some good mileage.
Now, back to bikes. Batteries, are heavy, but going down in weight and
up in efficiency thanks to the cell phone craze. Lead-acid is just about
history, Ni/Cads are on the way out, NiMH have about four times the
capacity of a Ni/Cad, and the Lithium Ion and Lithium polymer have the
least leakage and highest power per pound, but are of course the most
expensive. If good and affordable Lithium batteries become available
expect to see more electric bikes. Right now the ones I have seen (in
person) have lead-acid and will need a new battery pack if you forget
them for more than about 4 months due to self discharge and 'Sulfating'
of the battery. If any of you are sci-fi readers and are familiar with
Heinlein you may 'Grok' this. Read "Stranger in a strange land", great
book. Back to one final note on infinitely variable transmissions, they
would have to be electric, augmented by finite gears to be kept in a
best operating mode for power out and regen power in. The electronics
can help but it can't get power from a 10 RPM motor shaft speed if that
same motor is expected to go up to 10,000 RPM at some point. A brush
less DC motor with rare earth elements on the rotating assembly and some
clever controls and wiring on the housing would be the best that I can
think of, being one of those EE nerd types (at work that is). The
Samarium Cobalt or Neodymium composite magnets are a bit pricey though
for use in a bicycle. I used 1" x2" x 0.5" magnets in a control system
that were over $100 each, but strong enough to give you a smashed finger
if you were not careful. Maybe in ten more years.
Bill Baka
Post for the week (holidays).
> In article <[email protected]>,
> Peter <[email protected]> wrote:
>
>
>
>>Increasing the total amount of work I need to do to propel my bicycle
>>from A to B is unlikely to either increase my comfort or provide
>>greater pleasure.
>
>
> You're right, there is a better way to do this. Adapt Toyota's system
> of a continuously-variable planetary gear transmission (1), substituting
> it for the chain and derailleur on an electric bike. That way you'd get
> the efficiency benefit of direct mechanical drive, continuously variable
> gear ratio, and on-demand electric motor assist. It wouldn't have to be
> much bigger or heavier than existing internally-geared hubs and would be
> completely sealed.
>
>
> (1) see here for a description
> http://home.earthlink.net/~graham1/MyToyotaPrius/PriusFrames.htm
> click on "Understanding [...]"
Now I am sucked into this. The only infinitely variable transmission I
have ever seen or read about was a system of varying cones and a drive
belt. Tolerable for a car but not too good for a bike. A planetary gear
system is not variable unless someone has invented a good way to change
the number of gears on the fly. The best automotive transmission in the
early days was the 1955 vintage Cadillac 4 speed hydromatic. It had 2
planetary sets with different ratios and used both for first, the low
one for second, the higher one for third, and direct for fourth. With an
overdrive it could have become an 8 speed and got some good mileage.
Now, back to bikes. Batteries, are heavy, but going down in weight and
up in efficiency thanks to the cell phone craze. Lead-acid is just about
history, Ni/Cads are on the way out, NiMH have about four times the
capacity of a Ni/Cad, and the Lithium Ion and Lithium polymer have the
least leakage and highest power per pound, but are of course the most
expensive. If good and affordable Lithium batteries become available
expect to see more electric bikes. Right now the ones I have seen (in
person) have lead-acid and will need a new battery pack if you forget
them for more than about 4 months due to self discharge and 'Sulfating'
of the battery. If any of you are sci-fi readers and are familiar with
Heinlein you may 'Grok' this. Read "Stranger in a strange land", great
book. Back to one final note on infinitely variable transmissions, they
would have to be electric, augmented by finite gears to be kept in a
best operating mode for power out and regen power in. The electronics
can help but it can't get power from a 10 RPM motor shaft speed if that
same motor is expected to go up to 10,000 RPM at some point. A brush
less DC motor with rare earth elements on the rotating assembly and some
clever controls and wiring on the housing would be the best that I can
think of, being one of those EE nerd types (at work that is). The
Samarium Cobalt or Neodymium composite magnets are a bit pricey though
for use in a bicycle. I used 1" x2" x 0.5" magnets in a control system
that were over $100 each, but strong enough to give you a smashed finger
if you were not careful. Maybe in ten more years.
Bill Baka
Post for the week (holidays).
