Perpetual motion!

Quoted message said:

Hi All,

Suppose a Rube Goldberg bicycle of sorts was constructed with a gizmo
that raised some weights when the freewheel was freewheeling (down a
hill), and allowed these weight to lower when pedaling, using this
potential energy to assist in pedalling.

Would this contraption be faster over a hilly course with the system
engaged vs disengaged and just along for the ride?

If the contraption was ideally constructed, the elevation of the weight
could remain constant.

So when you went down a hill, the weight would effectively stay at the
top of the hill, although it would be moving forwards with the bike.

When you went uphill, the weight would drop relative to the bike, but
remain at the same absolute elevation.

You should then find your performance roughly equivalent to not having a
weight at all (apart from drag in the mechanism etc.) since no
gravitational potential energy change occurs to the weight.

If you disengaged the mechanism, you'd just be carrying a weight around,
so that would be worse.

If the mechanism was only capable of limited height or power
input/output, I would expect a performance somewhere between the two
extremes: better than just carrying a dead weight, but not as good as
not carrying a weight at all.

Quoted message said:

Hi All,

Suppose a Rube Goldberg bicycle of sorts was constructed with a gizmo
that raised some weights when the freewheel was freewheeling (down a
hill), and allowed these weight to lower when pedaling, using this
potential energy to assist in pedalling.

Would this contraption be faster over a hilly course with the system
engaged vs disengaged and just along for the ride?

Joseph

With an ideally efficient contraption: I'm guessing faster with it
engaged; you'll go downhill /slower/, as you're storing energy in the
contraption. This will decrease energy losses to air resistance, which
are extremely large on high speed descents. Releasing the stored energy
on uphills at low to moderate speeds would incur lower air resistance
losses. Net result: less overall air resistance energy losses, it's
gotta be faster... but ...

Of course that's if the contraption /works/ and is highly efficient at
that. My guess is such would be far from achievable in practice; and
that's neglecting the difference between a bare bike and one with the
contraption mounted.

Mark J.

email hidden said:

Hi All,

Suppose a Rube Goldberg bicycle of sorts was constructed with a gizmo
that raised some weights when the freewheel was freewheeling (down a
hill), and allowed these weight to lower when pedaling, using this
potential energy to assist in pedalling.

Would this contraption be faster over a hilly course with the system
engaged vs disengaged and just along for the ride?

Joseph

It will be possible provided the following two things are true; 1) The
device has the capacity to store at least as much energy as you can
put into it on a descent. 2) Energy is released in such a way that
you don't run out of it on the climb. If it winds all the way up at
the top of the descent and winds all the way down at the very
beginning of a climb, it's dead weight the rest of the time. Even if
the device has real losses, they will be countered by the aerodynamic
efficiency gain associated with making your velocity as close to
constant as possible. That's enough to be theoretically possible, but
practicality is an issue. Let's say you and your bike are 80 kilos
and you're riding over 50 meter hills. Not a very taxing test case.
For the moving weight gizmo to be practically attached to a bicycle,
the weight will have a maximum vertical travel of about a meter. In
order to bank a modest quarter of your potential energy coming down
the hill, the gizmo needs to be 1000 kilos.

On Fri, 1 Feb 2008 03:27:17 -0800 (PST),
"[email hidden]" <[email hidden]> may have

Quoted message said:

Hi All,

Suppose a Rube Goldberg bicycle of sorts was constructed with a gizmo
that raised some weights when the freewheel was freewheeling (down a
hill), and allowed these weight to lower when pedaling, using this
potential energy to assist in pedalling.

Would this contraption be faster over a hilly course with the system
engaged vs disengaged and just along for the ride?

TTBOMK, no method of energy recovery and storage is more efficient
than the inertia of the rider and bike, and lighter riders have a
decided advantage over heavy ones with the same force generation
capacity on climbs, so I would have to predict that this Goldbergian
system would fail to produce the results desired. It would also fail
to exceed the performance of mere increased mass.

--
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Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

Quoted message said:

On Feb 1, 6:27 am, "[email hidden]"

Quoted message said:

Hi All,

Quoted message said:

Suppose a Rube Goldberg bicycle of sorts was constructed with a gizmo
that raised some weights when the freewheel was freewheeling (down a
hill), and allowed these weight to lower when pedaling, using this
potential energy to assist in pedalling.

Quoted message said:

Would this contraption be faster over a hilly course with the system
engaged vs disengaged and just along for the ride?

Quoted message said:

Joseph

It will be possible provided the following two things are true; 1) The
device has the capacity to store at least as much energy as you can
put into it on a descent.  2) Energy is released in such a way that
you don't run out of it on the climb.  If it winds all the way up at
the top of the descent and winds all the way down at the very
beginning of a climb, it's dead weight the rest of the time.  Even if
the device has real losses, they will be countered by the aerodynamic
efficiency gain associated with making your velocity as close to
constant as possible.  That's enough to be theoretically possible, but
practicality is an issue.  Let's say you and your bike are 80 kilos
and you're riding over 50 meter hills.  Not a very taxing test case.
For the moving weight gizmo to be practically attached to a bicycle,
the weight will have a maximum vertical travel of about a meter.  In
order to bank a modest quarter of your potential energy coming down
the hill, the gizmo needs to be 1000 kilos.

The subject line was misleading. I don't expect the contraption to be
able to keep going, or to require no input from the rider. So the
amount of energy stored need not be the total from a descent, nor even
1/4. In fact the amount doesn't really matter at all, as long as it is
something.

The idea is to slow down the descent a wee bit and store the energey
used to do so, and to later release it on the up slope where it will
give more effect in terms of saved time for the course.

Joseph

Werehatrack said:

On Fri, 1 Feb 2008 03:27:17 -0800 (PST),
"[email hidden]" <[email hidden]> may have

Quoted message said:

Hi All,

Quoted message said:

Suppose a Rube Goldberg bicycle of sorts was constructed with a gizmo
that raised some weights when the freewheel was freewheeling (down a
hill), and allowed these weight to lower when pedaling, using this
potential energy to assist in pedalling.

Quoted message said:

Would this contraption be faster over a hilly course with the system
engaged vs disengaged and just along for the ride?

TTBOMK, no method of energy recovery and storage is more efficient
than the inertia of the rider and bike, and lighter riders have a
decided advantage over heavy ones with the same force generation
capacity on climbs, so I would have to predict that this Goldbergian
system would fail to produce the results desired.  It would also fail
to exceed the performance of mere increased mass.

The issue is that on a descent at high speed marginal power increases
have little effect on lowering total time, while on ascents, marginal
increases in power have a much more marked effect. So rather than
"wasting" energy pushing faster through the air down a hill, some of
the kinetic energy from the descent can be used to raise the weight to
save some as potential energy which can be used when it has more
effect.

Joseph

On Fri, 1 Feb 2008 09:03:09 -0800 (PST),
"[email hidden]" <[email hidden]> may have

Quoted message said:

Werehatrack said:

On Fri, 1 Feb 2008 03:27:17 -0800 (PST),
"[email hidden]" <[email hidden]> may have

Quoted message said:

Hi All,

Quoted message said:

Suppose a Rube Goldberg bicycle of sorts was constructed with a gizmo
that raised some weights when the freewheel was freewheeling (down a
hill), and allowed these weight to lower when pedaling, using this
potential energy to assist in pedalling.

Quoted message said:

Would this contraption be faster over a hilly course with the system
engaged vs disengaged and just along for the ride?

TTBOMK, no method of energy recovery and storage is more efficient
than the inertia of the rider and bike, and lighter riders have a
decided advantage over heavy ones with the same force generation
capacity on climbs, so I would have to predict that this Goldbergian
system would fail to produce the results desired.  It would also fail
to exceed the performance of mere increased mass.

The issue is that on a descent at high speed marginal power increases
have little effect on lowering total time, while on ascents, marginal
increases in power have a much more marked effect. So rather than
"wasting" energy pushing faster through the air down a hill, some of
the kinetic energy from the descent can be used to raise the weight to
save some as potential energy which can be used when it has more
effect.

Mechanical losses and gross systemic inefficiency will always eat that
savings. Remember, the mass you're carrying in order to perform this
trick also increases the mass of the bike. In order to store any
significant fraction of the energy involved, either the mass or the
lift distance must must be relatively large, and in either case the
effects upon the efficiency of the system as a whole will greatly
outweigh any marginal return received. You're up against the
fundamental regenerative/storage braking system problem here;
real-world experience has been that you will never get back more than
15% (typically less than 5%) of the energy theoretically available for
capture in a descent, and the return is never matched by the
inefficiency of the additional hardware required. (The sole exception
to this is when dealing with an electric drive system whose
fundamental design permits recapture via regen braking without the
addition of any hardware at all; in that instance, a trivial amount of
recovery becomes practical, but it's not the source of much
operational efficiency.)

The most efficient way to use the energy of a descent in climbing the
next hill is to be inside a minimum-drag high-efficiency vehicle and
don't use any braking at all. This is not always practical. No
currently constructable regen braking system for a bicycle can come
close.

You nailed it when you chose the subject; as proposed, this is a
perpetual motion project, and those, without exception, *ALWAYS* fail.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

"Ben C" wrote: If the contraption was ideally constructed, the elevation
of the weight

Quoted message said:

could remain constant.

So when you went down a hill, the weight would effectively stay at the
top of the hill, although it would be moving forwards with the bike.
(clip)

^^^^^^^^^^^^^^^^^^^^^
Your idea is that the weight would change speed with the bicycle, but not
elevation, so it would store kinetic energy on the descents, and release it
on the ascents. However, if you allowed the weight to go up and down with
the bike, it would store abd release potential energy as well. How do you
figure that potential energy is not as beneficial as kinetic energy? BTW,
since this is only a thought experiment, I would substitute a wind-up spring
for the weight. This would wind up on downhills, are unwind on uphills. If
it were very light (ideally, weightless) this would be equivalent to keeping
the weight at the elevation of the top of the tallest hill for the entire
ride.

On Fri, 01 Feb 2008 18:49:19 GMT, "Leo Lichtman"

may have said:

"Ben C" wrote: If the contraption was ideally constructed, the elevation
of the weight

Quoted message said:

could remain constant.

So when you went down a hill, the weight would effectively stay at the
top of the hill, although it would be moving forwards with the bike.
(clip)

^^^^^^^^^^^^^^^^^^^^^
Your idea is that the weight would change speed with the bicycle, but not
elevation, so it would store kinetic energy on the descents, and release it
on the ascents. However, if you allowed the weight to go up and down with
the bike, it would store abd release potential energy as well. How do you
figure that potential energy is not as beneficial as kinetic energy? BTW,
since this is only a thought experiment, I would substitute a wind-up spring
for the weight. This would wind up on downhills, are unwind on uphills. If
it were very light (ideally, weightless) this would be equivalent to keeping
the weight at the elevation of the top of the tallest hill for the entire
ride.

While in theory a smaller mass could be lifted above the starting
point of the descent (like the reverse of an elevator counterweight
that uses a multiple-pulley block-and-tackle arrangement) this
requires a structure which renders the potential gains moot. Trying
to go the other way, using a larger mass with the mechanical advantage
flipped, the system becomes an always-loses exercise no matter what
else is done. Inertial storage, even into a spinning flywheel, is
always going to come in second to reduced mass and the same power
input level. Conversion of kinetic to chemical potential energy or
induction storage in a superconductor coil will allow as much as 10 to
15% recovery in ideal circumstances, but you still have to weigh that
against the 30 to 150% (or more) increase in climbing energy required
as a result of the increased mass of the devices and increased drag
from other practical effects which accrued in the process of tacking
on the machinery required to obtain that small recovery.

Many a student hour has been used in trying to overcome these
limitations in enginering schools around the world. Oddly enough, not
a single one has yielded a "better mousetrap".

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

"Werehatrack" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Many a student hour has been used in trying to overcome these
limitations in enginering schools around the world. Oddly enough, not
a single one has yielded a "better mousetrap".

Got that right.
Years ago when my son was young and in the cub scouts, I remember
the pinewood derby races. We actually had adult races to keep us out of the
kids projects. I asked quite a few physicist and engineers on weight
placement, of course everyone had different ideas, none on which I used.
You would think the scouts would have this down to perfection by now after
all these years of pinewood derby racing, but they still argue on where to
place the weight.

I ended up doing my own test with a sliding weight on a wedge for a curved
sloped track, and using an electronic light source to record time in
milliseconds. As it turned out, placing the weight above the rear wheels
(equally divided) and slightly forward (kind of about where one sits on a
bicycle slightly forward of the rear wheel) made for the fastest times.

So at the race, all these fathers & mothers brought their exotic cars.
Painted
all shinny and decaled beautiful. All I had was a unpainted wedge, wasn't
even sanded and looked pretty crude, but I ended up winning the Adult race.
-tom

Werehatrack said:

On Fri, 01 Feb 2008 18:49:19 GMT, "Leo Lichtman"

may have said:

"Ben C"  wrote:  If the contraption was ideally constructed, the elevation
of the weight

Quoted message said:

could remain constant.

Quoted message said:

Quoted message said:

So when you went down a hill, the weight would effectively stay at the
top of the hill, although it would be moving forwards with the bike.
(clip)

^^^^^^^^^^^^^^^^^^^^^
Your idea is that the weight would change speed with the bicycle, but not
elevation, so it would store kinetic energy on the descents, and release it
on the ascents.  However, if you allowed the weight to go up and down with
the bike, it would store abd release potential energy as well.  How do you
figure that potential energy is not as beneficial as kinetic energy?  BTW,
since this is only a thought experiment, I would substitute a wind-up spring
for the weight.  This would wind up on downhills, are unwind on uphills..  If
it were very light (ideally, weightless) this would be equivalent to keeping
the weight at the elevation of the top of the tallest hill for the entire
ride.

While in theory a smaller mass could be lifted above the starting
point of the descent (like the reverse of an elevator counterweight
that uses a multiple-pulley block-and-tackle arrangement) this
requires a structure which renders the potential gains moot.  Trying
to go the other way, using a larger mass with the mechanical advantage
flipped, the system becomes an always-loses exercise no matter what
else is done.  Inertial storage, even into a spinning flywheel, is
always going to come in second to reduced mass and the same power
input level.  Conversion of kinetic to chemical potential energy or
induction storage in a superconductor coil will allow as much as 10 to
15% recovery in ideal circumstances, but you still have to weigh that
against the 30 to 150% (or more) increase in climbing energy required
as a result of the increased mass of the devices and increased drag
from other practical effects which accrued in the process of tacking
on the machinery required to obtain that small recovery.

Many a student hour has been used in trying to overcome these
limitations in enginering schools around the world.  Oddly enough, not
a single one has yielded a "better mousetrap".

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

There is no doubt the extra mass makes the whole thing slower than a
regular bike without the extra mass, but the question is would the
contraption be faster with the gizmo engaged than not.

If the system were manual, the rider could engage the hoisting of the
weight (in my mind a couple cinder blocks on a 2m crane on the back of
the bike!) as speed built up down a hill, ideally at some high speed,
and then at some point later on a climb, the rider could relese the
weights so they fall down and since they are somehow connected to the
drivetrain, this gives a bit of a boost to the power the rider is
supplying.

Lets say a 1km 5% descent followed by a 1km 5% climb. Total mass of
110kg, 10 of which are the weights. Lets raise the weights 1m.

How much energy is it to lift the 10kg 1m? How much does that slow the
descent? How much faster is the 1km climb with this "additional"
energy?

Joseph

On Fri, 1 Feb 2008 03:27:17 -0800 (PST),

Quoted post said:

Hi All,

Suppose a Rube Goldberg bicycle of sorts was constructed with a gizmo
that raised some weights when the freewheel was freewheeling (down a
hill), and allowed these weight to lower when pedaling, using this
potential energy to assist in pedalling.

Would this contraption be faster over a hilly course with the system
engaged vs disengaged and just along for the ride?

Joseph

Dear Joseph,

Forget the weights--the more energy they store, the heavier they are
and the harder it will be for you to reach the top of the hill and
find out that they don't work.

Just imagine storing force by winding a spring up by some brake gizmo
on the downhill. Or charging a battery.

Overall, you still lose.

You can't get more energy out than you put into closed system. You
can't even get as much energy out as you put in.

Trying to store the energy downhill and then release the energy uphill
just loses more energy than straightforward pedaling. Less total
energy applied to moving the bike means lower overall speed.

Think about how long you apply energy at rate X uphill, as opposed to
how long you apply energy at rate Y downhill.

Cheers,

Carl Fogel

Quoted message said:

Suppose a Rube Goldberg bicycle of sorts was constructed with a gizmo
that raised some weights when the freewheel was freewheeling (down a
hill), and allowed these weight to lower when pedaling, using this
potential energy to assist in pedalling.

Would this contraption be faster over a hilly course with the system
engaged vs disengaged and just along for the ride?

Although it may be possible to store end retrieve some energy in some
way (think of a big watchspring for example) the frictional and or heat
losses and the mechanism's weight itself become significant to something
as underpowered and light as a bicycle. Theoretically maybe but in
practice probably at a cost you wouldn't want to bear, for no net gain.

Would you go sledding walking uphill with a 50 pound backpack so you
could descend with more mass?
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

Two things: 1.) Lets stop arguing about whether this is practical. It was
proposed by the OP as a thought experiment, calling for an application of
physical principles--not an idea that he wants to implement. 2.) This is
not a perpetual motion idea; I am pretty sure the OP used that subject
heading TIC. This is more like the question: "Is it better to put money in
the bank when prices are high, then take it out and spend it when prices
are low?" The number of dollars (Euros) doesn't change, but their
usefulness does. Similarly, a person who can draw energy from the "bank" to
help him climb, at low speed, gets more from it than he would get by
allowing it to be used to fight drag while coming down at high speed.

A Muzi said:

Would you go sledding walking uphill with a 50 pound backpack so you
could descend with more mass?

No, but it I had to carry 50 pounds for some reason, it would be nice
to have some way of it not being entirely dead weight.

Joseph

A Muzi said:

Would you go sledding walking uphill with a 50 pound backpack so you
could descend with more mass?

No, but I might use an energy-capture device on the downhill (in place
of brakes, say, so the sled metaphor is a little weak) in order to
assist on the uphill.

Normally the weight bogey would more than cancel any benefits, but
what if you needed to add the weight anyway to hoiit the UCI minimum
for racing? Maybe that's why devices since this one have been banned
since the 1920's, as I recall.Any historians who can documentation at
hand?

--rick

PS: Hi Andy! Thanks for the sushi in 1992, which was the last time we
met F2F.

Quoted message said:

A Muzi said:

Would you go sledding walking uphill with a 50 pound backpack so you
could descend with more mass?

Oops. I meant to type "historians who have documentation," of course.
Or maybe just asking someone to documentate, as our President would
say.

--rv

Quoted message said:

No, but I might use an energy-capture device on the downhill (in place
of brakes, say, so the sled metaphor is a little weak) in order to
assist on the uphill.

Normally the weight bogey would more than cancel any benefits, but
what if you needed to add the weight anyway to hoiit the UCI minimum
for racing? Maybe that's why devices since this one have been banned
since the 1920's, as I recall.Any historians who can documentation at
hand?

--rick

PS: Hi Andy! Thanks for the sushi in 1992, which was the last time we
met F2F.

Quoted message said:

A Muzi said:

Would you go sledding walking uphill with a 50 pound backpack so you
could descend with more mass?

Quoted message said:

No, but I might use an energy-capture device on the downhill (in place
of brakes, say, so the sled metaphor is a little weak) in order to
assist on the uphill.
Normally the weight bogey would more than cancel any benefits, but
what if you needed to add the weight anyway to hoiit the UCI minimum
for racing? Maybe that's why devices since this one have been banned
since the 1920's, as I recall.Any historians who can documentation at
hand?
--rick
PS: Hi Andy! Thanks for the sushi in 1992, which was the last time we
met F2F.

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

Leo Lichtman said:

"Ben C" wrote: If the contraption was ideally constructed, the elevation
of the weight

Quoted message said:

could remain constant.

So when you went down a hill, the weight would effectively stay at the
top of the hill, although it would be moving forwards with the bike.
(clip)

^^^^^^^^^^^^^^^^^^^^^
Your idea is that the weight would change speed with the bicycle, but not
elevation, so it would store kinetic energy on the descents, and release it
on the ascents.

That's true, although I didn't think of that.

Quoted message said:

However, if you allowed the weight to go up and down with
the bike, it would store abd release potential energy as well. How do you
figure that potential energy is not as beneficial as kinetic energy?

Potential energy is fine, and regenerative braking is a sound idea in
principle, especially if the descents are tricky enough that you have to
brake anyway for safety reasons.

But carrying extra dead-weight as we know reduces your performance
(although the reasons why aren't totally obvious).

So if you have a regenerative braking system you have to ask how much
energy can you store for a given weight overhead.

Usually when considering such things there's no straightforward physical
relationship between the amount of energy you can store and the mass
needed to store it in. The fact that you get so many Joules capacity
for a kilogram of lead/acid is just a contingent fact about the way
those batteries happen to work.

But if you're storing energy by winching weights, the stored energy is
closely related to the weight-- it's just a function of the weight and
the height.

The higher you can raise the weights, the less weight you have to carry
for a given energy storage capability.

You could store a lot of energy in a carbon-fibre pea weighing 5g if you
winched it hundreds of miles into the air. That bike would probably work
quite well (this is a thought experiment of course...). On that machine
you'd winch the weight up at a much faster rate than that at which you
descended.

On the other hand if you put 100kg on the bike and only lift it up and
down a metre or so, you're very unlikely to win.

So I think the crossover point, between winning and losing, may be the
point at which you lift and lower the weight by just the amount
necessary for it to have a constant elevation throughout the ride.

But the details need more working out to be sure about that.

To answer the original question, you're always better to engage the
winch than not if you have to carry this weights arrangement anyway.

Quoted message said:

BTW, since this is only a thought experiment, I would substitute a
wind-up spring for the weight. This would wind up on downhills, are
unwind on uphills. If it were very light (ideally, weightless) this
would be equivalent to keeping the weight at the elevation of the top
of the tallest hill for the entire ride.

This is a slightly different question. If you have to brake anyway, then
you will definitely win with a practically weightless spring (similar in
principle to a high-altitude carbon fibre pea). But if you don't, then
is there any point in regen-braking?

I suspect that when you take air resistance into account there is. If
you go down hills quite slowly storing up energy in your regen brakes,
you're losing less energy to the wind, although you're going a bit
slower. But you should be able to more than make up that lost time up
the hills when you take the stored energy back. You will have a
smaller deviation in your speed over the course and a higher average
speed for the same net energy expenditure. By avoiding such high speeds
you lose less energy in total to the wind. This is because wind
resistance power goes roughly as the cube of speed.