Electric transmission redux

richard schumacher said:

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.

[snip]

Dear Richard,

Actually, that doesn't seem to be excess power.

If you pedal while coasting downhill to charge a battery,
that's just extra work pedalling when you could be coasting.

The pedal-power stored in the battery will be less efficient
than simply pedalling up the hill later because the power is
inevitably wasted during the charging process.

And you'll have the extra weight of the batteries to haul up
the hill, too.

Human-charged auxiliary electric engines are simply more
work.

As for regenerative braking, I doubt that that you're going
to get anything worthwhile unless you coast down an alpine
pass.

Carl Fogel

In article <[email hidden]>,

Quoted message said:

Quoted message said:

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.

[snip]

Actually, that doesn't seem to be excess power.

If you pedal while coasting downhill to charge a battery,
that's just extra work pedalling when you could be coasting.

Of course. The idea is to give riders the option of charging the
battery when they don't feel the need for a rest.

Quoted message said:

The pedal-power stored in the battery will be less efficient
than simply pedalling up the hill later because the power is
inevitably wasted during the charging process.

It's easier overall to pedal more continuously with less effort than to
pedal real hard and then take a forced rest.

Quoted message said:

And you'll have the extra weight of the batteries to haul up
the hill, too.

All electric bikes have batteries, and people buy them anyway.

Quoted message said:

Human-charged auxiliary electric engines are simply more
work.

Which adds to the exercise aspect of the ride. Think of it as an
exercycle with continuously variable scenery.

Quoted message said:

As for regenerative braking, I doubt that that you're going
to get anything worthwhile unless you coast down an alpine
pass.

All electric bikes do it, and people buy them anyway :_>

Quoted message said:

As for regenerative braking, I doubt that that you're going
to get anything worthwhile unless you coast down an alpine
pass.

The idea of a bicycle with a motor is not attractive to me, but I
wonder what the upper limit of efficiency is for regenerative braking.
Along those lines, I wonder what fraction of the energy one puts into
climbing a hill is converted to gravitational potential energy (which
is recoverable) and what fraction goes to things like wind resistance
(not recoverable).

I is my understanding that bicycling is more efficient than walking on
level ground primarily because when walking the center of mass moves
in a sinusoidal path with only part of the energy used to overcome
gravity recovered by elastic elements in the system. The bicycle
eliminates this work against gravity. (I have also been led to believe
this is why the efficiency of walking and bicycling converge as the
slope becomes steeper).

I kind of seems like this regenerative-braking, energy-storing gizmo
could do for the bicycle what the bicycle does for walking.

Are there fundamental limits on the efficiency, or is it just an
engineering problem?

Jim Smith said:

Quoted message said:

As for regenerative braking, I doubt that that you're going
to get anything worthwhile unless you coast down an alpine
pass.

The idea of a bicycle with a motor is not attractive to me, but I
wonder what the upper limit of efficiency is for regenerative braking.
Along those lines, I wonder what fraction of the energy one puts into
climbing a hill is converted to gravitational potential energy (which
is recoverable) and what fraction goes to things like wind resistance
(not recoverable).

I is my understanding that bicycling is more efficient than walking on
level ground primarily because when walking the center of mass moves
in a sinusoidal path with only part of the energy used to overcome
gravity recovered by elastic elements in the system. The bicycle
eliminates this work against gravity. (I have also been led to believe
this is why the efficiency of walking and bicycling converge as the
slope becomes steeper).

I kind of seems like this regenerative-braking, energy-storing gizmo
could do for the bicycle what the bicycle does for walking.

Are there fundamental limits on the efficiency, or is it just an
engineering problem?

Dear Jim,

I think that a lot of the difference between bicycles and
walking on the flat is due to the elimination of enormous
amounts of friction by wheels--a mild push with one foot on
a bicycle will send you coasting fifty feet on a level
street.

In contrast, your foot comes to a momentary but complete
stop with every step--at a brisk walk of 4 mph, your foot
stops completely, lifts off the ground, accelerates to about
8 mph, and then stops dead again.

This amounts to constant braking and acceleration--the sole
of your shoe whips forward at 8mph to get ahead of you,
slams into the ground, halts momentarily as you push off it,
trails behind, and then must accelerate again wildly to not
only catch up but get ahead of you in time for the next
lunge. (We do all this so smoothly that we don't notice it.)

In contrast, our feet merely move at a steady speed in a
circle when we pedal. There's wasted effort there, too, but
not nearly as much, and the leverage of the gears, crank,
and spokes lets us take advantage of the nearly frictionless
wheels.

Off-topic, a perhaps related observation.

My father, who never met an odd car that he did not long to
own, now drives a Honda gas/electric hybrid and enjoys the
thrill of high mileage.

In theory, the regenerative braking improves the mileage.

In practice . . .

My father lives in a rural hamlet in the mountains 25 miles
west of Pueblo. He turns left out of his driveway, left at a
stop sign, and drives a steady 65 mph without any braking
along a modestly scenic highway into town. He turns off the
highway into the shopping center, brakes into a parking
slot, gets his groceries, and reverses the process (except
that there's no stop sign on his way home).

I doubt that the approximately 60 seconds of mild braking
regenerates much useful power during his 50-mile round trip.

Since there's a few thousand feet of roller-coaster climbing
involved both ways, I suspect that he'd actually get better
gas mileage if the generator, its drive-train, and the heavy
batteries were removed.

Carl Fogel

Quoted message said:

I think that a lot of the difference between bicycles and
walking on the flat is due to the elimination of enormous
amounts of friction by wheels--a mild push with one foot on
a bicycle will send you coasting fifty feet on a level
street.

In contrast, your foot comes to a momentary but complete
stop with every step--at a brisk walk of 4 mph, your foot
stops completely, lifts off the ground, accelerates to about
8 mph, and then stops dead again.

This amounts to constant braking and acceleration--the sole
of your shoe whips forward at 8mph to get ahead of you,
slams into the ground, halts momentarily as you push off it,
trails behind, and then must accelerate again wildly to not
only catch up but get ahead of you in time for the next
lunge. (We do all this so smoothly that we don't notice it.)

In contrast, our feet merely move at a steady speed in a
circle when we pedal. There's wasted effort there, too, but
not nearly as much, and the leverage of the gears, crank,
and spokes lets us take advantage of the nearly frictionless
wheels.

Hmm... I disagree for a couple of reasons.

First, acceleration does not have to take any energy. Think of a
flywheel used to power a backup generator. All parts of this flywheel
are constantly accelerating, yet it will spin for a long long time.
Flywheels would be a lousy way of storing energy otherwise.

Second, my feet most certainly do not come to a complete stop at any
time while walking. I doubt yours do either.

Here is a link where someone has done a simple model of the energy
expenditure of walking with good correlation to observation:

http://sprott.physics.wisc.edu/technote/walkrun.htm

One thing is certain: walking is by no means completely understood. A
1986 paper by G.M. Maloiy in Nature points out than some African women
can carry 20% of their body mass on their heads with no increase in
metabolism, so some people are apparently better at it than others.
This appears to have something to do with how much of the energy of
the vertical motion of the center of mass is recovered.

Jim Smith said:

Quoted message said:

I think that a lot of the difference between bicycles and
walking on the flat is due to the elimination of enormous
amounts of friction by wheels--a mild push with one foot on
a bicycle will send you coasting fifty feet on a level
street.

In contrast, your foot comes to a momentary but complete
stop with every step--at a brisk walk of 4 mph, your foot
stops completely, lifts off the ground, accelerates to about
8 mph, and then stops dead again.

This amounts to constant braking and acceleration--the sole
of your shoe whips forward at 8mph to get ahead of you,
slams into the ground, halts momentarily as you push off it,
trails behind, and then must accelerate again wildly to not
only catch up but get ahead of you in time for the next
lunge. (We do all this so smoothly that we don't notice it.)

In contrast, our feet merely move at a steady speed in a
circle when we pedal. There's wasted effort there, too, but
not nearly as much, and the leverage of the gears, crank,
and spokes lets us take advantage of the nearly frictionless
wheels.

Hmm... I disagree for a couple of reasons.

First, acceleration does not have to take any energy. Think of a
flywheel used to power a backup generator. All parts of this flywheel
are constantly accelerating, yet it will spin for a long long time.
Flywheels would be a lousy way of storing energy otherwise.

Second, my feet most certainly do not come to a complete stop at any
time while walking. I doubt yours do either.

Here is a link where someone has done a simple model of the energy
expenditure of walking with good correlation to observation:

http://sprott.physics.wisc.edu/technote/walkrun.htm

One thing is certain: walking is by no means completely understood. A
1986 paper by G.M. Maloiy in Nature points out than some African women
can carry 20% of their body mass on their heads with no increase in
metabolism, so some people are apparently better at it than others.
This appears to have something to do with how much of the energy of
the vertical motion of the center of mass is recovered.

Dear Jim,

If acceleration does not take energy, then I'm lost.
(Possibly you're distinguishing force, energy, power, and so
forth, which I always muddle up.)

When I look at normal footprints, it seems that feet come to
a momentary stop. If the foot were moving, the footprints
would be smeared in the direction that the foot is moving.

They're not.

Carl Fogel

[email hidden said:

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

Quoted message said:

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.

[snip]

Dear Richard,

Actually, that doesn't seem to be excess power.

If you pedal while coasting downhill to charge a battery,
that's just extra work pedalling when you could be coasting.

The pedal-power stored in the battery will be less efficient
than simply pedalling up the hill later because the power is
inevitably wasted during the charging process.

And you'll have the extra weight of the batteries to haul up
the hill, too.

Human-charged auxiliary electric engines are simply more
work.

As for regenerative braking, I doubt that that you're going
to get anything worthwhile unless you coast down an alpine
pass.

Carl Fogel

There are a few niches in which the regenerative braking benefits are there.
Extreme stop and go urban commuting-no sense using the calipers/drums/discs all the time.
Recumbents in hilly terrain-most recumbent bikes are weak in climbing yet strong on flats- imagine storing up that energy in advance of the climb.

I don't think elimination of the chain is the way to go regarding the pedals (unless you're talking about mud/ice use)- much of the time you need the efficient drive chain of the pedals. However, on a commuter bike, eliminating the dirty chain might merrit an efficiency penalty. And on amphibious bikes, efficiency from driveline direction changes might be less of a penalty than gears/cables/paddlewheels.

As for racing, imaging storing up that energy while in the pack for that extra burst at the finish.

Quoted message said:

When I look at normal footprints, it seems that feet come to
a momentary stop. If the foot were moving, the footprints
would be smeared in the direction that the foot is moving.

They're not.

Think about the clear imprint a knobby tyre leaves in soft dirt. Does
the tread of the tire come to a complete stop?

Or think about gears which mesh without their teeth comming to a
complete stop. Now let one of the gears grow until it is 7000 miles
in diameter and the other until it is about six feet in diameter. Then
replace the teath on the smaller gear with tennis shoes and remove all
but two of them. Now everything should be clear.

<[email hidden]> wrote: (clip) If the foot were moving, the
footprints would be smeared in the direction that the foot is moving. (clip)
^^^^^^^^^^^^^
Of course. You are absolutely right. By the same token, the bottom of a
rolling wheel is stationary also. The top of the wheel moves at twice the
speed of the axle, so the average speed comes out right. There is no
horizontal component to the velocity of the foot as it touches the
ground--else it would jar you as you walk. (That's how it feels if you're
running and try to slow down.) So, I contend that the energy you spent
accelerating each foot to twice your walking speed is recovered as you
decelerate it to zero and put it down. Evolution has made us efficient
walkers.

Because the power vs speed curve bends upward (approximately velocity cubed at
higher speeds) it is most efficient to ride at a constant speed. Efficient here
means using the least amount of energy to cover a given distance in a given
time. Also weight does not matter since a regenerative brake would recover all
energy used to accelerate to cruising speed. So Richard is correct, assuming
the inefficiency of the system is not too great.

However would you really want to ride a bike that would go up a steep hill at
say 17mph instead of 6mph at the price of going down the hill at the same 17mph
unstead of 40mph?

There might be applications where the electric CVT would be useful. In San
Deigo there are human powered tricycle carriages. While the grades in the
downtown area are not steep, a couple of hefty tourists in one of those would be
a challenge to the operator/engine.

Jim Smith said:

Quoted message said:

When I look at normal footprints, it seems that feet come to
a momentary stop. If the foot were moving, the footprints
would be smeared in the direction that the foot is moving.

They're not.

Think about the clear imprint a knobby tyre leaves in soft dirt. Does
the tread of the tire come to a complete stop?

[snip]

Dear Jim,

Yes.

The section of the tire touching the ground comes to a
complete halt relative to forward motion. The top of the
tire is moving forward at twice the speed of the rider.

That is, when your speedometer reads 20 mph, the top of your
front tire is momentarily doing 40 mph forward and the
bottom of your tire is momentarily doing 0 mph forward.
Meanwhile, the entire tire is rotating at 20 mph.

Consider a non-spinning tire on a bicycle doing 20 mph.
Every part of the tire is moving forward at 20 mph. The part
touching the ground is shredding on the pavement.

Now let the tire spin normally. At the bottom, the tire is
moving 20 mph in the opposite direction of the bicycle and
cancels out. (Technically, two velocities with equal speed
and opposite direction.)

At the top, the tire is rotating 20 mph forward and is
attached to a bicycle that is already doing 20 mph forward.
(The two velocities with equal speed in the same direction
add up to 40 mph forward.)

This is basic to wind drag on spoked wheels. In a dead calm,
the wind drag at 20 mph is huge on the upper spoke (40 mph)
and zero on the lower spoke (0 mph).

Again, if the section of the tire touching the ground were
not completely stopped, it would leave a skid mark.

At first, this strikes most people as ridiculous, but
working through things usually clears it up.

Feet are actually an even clearer example. Ya gotta plant
your foot to shove backwards against the ground. If your
foot slips appreciably while you're shoving, you fall on
your face.

Carl Fogel

On 1 Jan 2005 21:24:05 -0800, Ed <[email hidden]>

Quoted message said:

Because the power vs speed curve bends upward (approximately velocity cubed at
higher speeds) it is most efficient to ride at a constant speed. Efficient here
means using the least amount of energy to cover a given distance in a given
time. Also weight does not matter since a regenerative brake would recover all
energy used to accelerate to cruising speed. So Richard is correct, assuming
the inefficiency of the system is not too great.

However would you really want to ride a bike that would go up a steep hill at
say 17mph instead of 6mph at the price of going down the hill at the same 17mph
unstead of 40mph?

There might be applications where the electric CVT would be useful. In San
Deigo there are human powered tricycle carriages. While the grades in the
downtown area are not steep, a couple of hefty tourists in one of those would be
a challenge to the operator/engine.

Dear Ed,

While your idea about efficiency is intriguing, where can I
buy a regenerative electric brake that charges a battery to
run a motor that recovers all the energy fed into it?

That is, assumptions about extremely efficient systems often
come to grief.

Sadi Carnot

Ed said:

However would you really want to ride a bike that would go up a steep hill at
say 17mph instead of 6mph at the price of going down the hill at the same 17mph
unstead of 40mph?

Let's say I live 10 miles from work with the first 5 miles uphill and
the second 5 downhill. With your hypothetical constant 17 mph bike
it'll take me 35 minutes to get there. With the conventional 6 mph
uphill and 40 mph downhill it'll take me 58 minutes.

Seems worthwhile to me - where do I get one of these?

Quoted message said:

Jim Smith said:

Quoted message said:

When I look at normal footprints, it seems that feet come to
a momentary stop. If the foot were moving, the footprints
would be smeared in the direction that the foot is moving.

They're not.

Think about the clear imprint a knobby tyre leaves in soft dirt. Does
the tread of the tire come to a complete stop?

[snip]

Dear Jim,

Yes.

The section of the tire touching the ground comes to a
complete halt relative to forward motion. The top of the
tire is moving forward at twice the speed of the rider.

That is, when your speedometer reads 20 mph, the top of your
front tire is momentarily doing 40 mph forward and the
bottom of your tire is momentarily doing 0 mph forward.
Meanwhile, the entire tire is rotating at 20 mph.

Consider a non-spinning tire on a bicycle doing 20 mph.
Every part of the tire is moving forward at 20 mph. The part
touching the ground is shredding on the pavement.

Now let the tire spin normally. At the bottom, the tire is
moving 20 mph in the opposite direction of the bicycle and
cancels out. (Technically, two velocities with equal speed
and opposite direction.)

At the top, the tire is rotating 20 mph forward and is
attached to a bicycle that is already doing 20 mph forward.
(The two velocities with equal speed in the same direction
add up to 40 mph forward.)

This is basic to wind drag on spoked wheels. In a dead calm,
the wind drag at 20 mph is huge on the upper spoke (40 mph)
and zero on the lower spoke (0 mph).

Again, if the section of the tire touching the ground were
not completely stopped, it would leave a skid mark.

At first, this strikes most people as ridiculous, but
working through things usually clears it up.

Feet are actually an even clearer example. Ya gotta plant
your foot to shove backwards against the ground. If your
foot slips appreciably while you're shoving, you fall on
your face.

It's all about the reference frames.

One valid way of looking at rolling motion is to view it as rotation
about the point of contact at the same angular velocity the rim is
turning about its center. The contact point, and thus the center of
rotation, moves along at the forward speed of the bicycle. This way
of looking at things is nice in that it is very easy to calculate the
velocity of any point on the wheel at any given point on the wheel.
No point a finite distance from the contact point is stationary when
viewed from this frame.

Another way to look at things is with the moving surface of that 7000
mile diameter ball some of us call home as the reference frame.
Looked at this way, any point on the tread of the wheel moves in a
cycloid (nicely demonstrated by the guy with square-wheeled bike).
Viewed from this reference frame a point on the tire does come to a
stop once each revolution.

Yet another way to look at things is with the bicycle itself as the
reference frame. This reference frame is moving along relative to the
ground, of course, but as long as there is no acceleration it is an
inertial frame, so everything is cool. Viewed from this reference
frame, a point on the tire is moving in a circle. Ignoring friction
for the moment, it obviously takes no power to keep the tire spinning
in this frame, whether it is in contact with the ground or not. Since
this is an inertial frame, we must get the same result in any other
inertial frame.

This should make it clear that even if one views the wheel from the
reference frame of the "stationary" ground, from where the motion of
the wheel involves points stopping and reversing direction, no power
is required for all this acceleration.

The reference frame centered on the bicycle is also nice because it is
stationary with respect to the engine. This makes power calculations
easier because one doesn't have to integrate all those starting and
stopping point masses. I like this reference frame. It is the one I
had in mind when I claimed that my feet don't stop when walking.

You are correct that it is just as valid to view a walking human as an
inverted pendulum during the stance phase. It may even be easier to
visualize where the power is going when viewed this way.

In article <[email hidden]>,

Quoted message said:

In contrast, our feet merely move at a steady speed in a
circle when we pedal. There's wasted effort there, too, but
not nearly as much, and the leverage of the gears, crank,
and spokes lets us take advantage of the nearly frictionless
wheels.

All that is true. But do people out for a pleasure ride really care
very much about their overall thermodynamic efficiency? No. They care
about their subjective experience of the effort of their ride versus the
pleasure they derive. The perceived effort is, of course, partly a
function of the efficiency of the system but it is also a function of
the maximum effort that must be expended. The load-leveling feature of
an electric drive bike with battery reduces the peak effort required and
would therefore make a ride more appealing to more people. Look at the
popularity of electric bikes that use pedal-chain drives. A
pedal-electric drive would be similar, only more so.

Quoted message said:

Off-topic, a perhaps related observation.

My father, who never met an odd car that he did not long to
own, now drives a Honda gas/electric hybrid and enjoys the
thrill of high mileage.

In theory, the regenerative braking improves the mileage.

It does, but most of the economy improvement comes from (wait for it)
the load-leveling function of the electric drive. The internal
combustion engine is smaller than it would otherwise be (because it need
only supply the *average* power required for a trip, not the peak power
required), and because the engine can run only in a relatively narrow
range of RPMs in which it runs more efficiently (and more cleanly, as it
happens). Regenerative braking adds only a few percent to economy
overall, as owners of hybrid cars have discovered. In any case we need
to be careful not to apply to bikes inappropriate results from cars.
See among other sources (using the Toyota Prius as an example)

http://home.earthlink.net/~graham1/MyToyotaPrius/PriusFrames.htm
(click on "Understanding the Prius"😉

http://www.toyota.co.jp/en/tech/environment/hsd/

In article <[email hidden]>, Ed <[email hidden]>

Quoted message said:

However would you really want to ride a bike that would go up a steep hill at
say 17mph instead of 6mph at the price of going down the hill at the same
17mph
unstead of 40mph?

An electric drive bike could come down that same hill at 40 MPH too, if
you wanted to. The rider shouldn't be forced to use regeneration all
the time. This is a simple matter of designing the control algorithm so
that the bike can be told to act like a conventional bike when desired.
For example, it could be arranged so one could choose to shut down
regeneration when going down a hill just by pedaling faster, and setting
the "shift" control low enough so that the fast pedaling took little or
no rider effort. An electric bike that didn't allow that level of
control and range of operational flexibility wouldn't be much fun and
wouldn't sell very well.

In article <[email hidden]>,

Peter said:

Ed said:

However would you really want to ride a bike that would go up a steep hill
at
say 17mph instead of 6mph at the price of going down the hill at the same
17mph
unstead of 40mph?

Let's say I live 10 miles from work with the first 5 miles uphill and
the second 5 downhill. With your hypothetical constant 17 mph bike
it'll take me 35 minutes to get there. With the conventional 6 mph
uphill and 40 mph downhill it'll take me 58 minutes.

Seems worthwhile to me - where do I get one of these?

Lots of vendors sell electric bikes that will do that. The problem is
that their human power input is through a chain direct to the drive
wheel, which does not easily permit a constant human energy input. You
can pedal real hard going uphill and then regeneratively brake on the
way down, but they don't let the rider input *and store* energy
constantly. Doing that calls for pedals turning a generator.

It wouldn't be that hard to modify a conventional e-bike by replacing
the derailleur and gears with a pedal-driven generator... the harder
part would be setting up the control system.

"richard schumacher" wrote: An electric drive bike could come down that
same hill at 40 MPH too, if you wanted to. (clip)
^^^^^^^^^^^^^^
That would be like someone who spends all his earnings when times are good,
and then can't pay expenses when times are bad.

richard schumacher said:

In article <[email hidden]>,

Peter said:

Ed said:

However would you really want to ride a bike that would go up a steep hill
at
say 17mph instead of 6mph at the price of going down the hill at the same
17mph
unstead of 40mph?

Let's say I live 10 miles from work with the first 5 miles uphill and
the second 5 downhill. With your hypothetical constant 17 mph bike
it'll take me 35 minutes to get there. With the conventional 6 mph
uphill and 40 mph downhill it'll take me 58 minutes.

Seems worthwhile to me - where do I get one of these?

Lots of vendors sell electric bikes that will do that.

None of the ones I've seen will actually let me get a higher
average speed than just using my conventional road bike -
and certainly not by the dramatic factor of the hypothetical
bike described above.