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'[ee] Basic physics... Bicycle regenerative braking'
2006\05\04@000705 by James Newtons Massmind

face picon face
I'm trying to figure out how much force it takes to get the average bicycle
moving (or stopped) and how that relates to the force required to lift the
same mass some distance.

E.g. if a bicycle and rider weighing 200 lbs total was to decelerate from 30
MPH to 0 in 5 seconds, how far would that amount of force lift the same
weight into the air?

30 mph = 44 feet per second and F = M * A so we are talking about 200*44/5
right? Or 1760 foot lbs? With 200 lbs, that could then be raised 1760 / 200
= 8.8 feet?

If we don't want to fly up 9 feet in the air, how does one figure out how
much force can be stored in a spring of a given weight? I must be using the
wrong keywords 'cause Google isn't doing it for me. I'm thinking about a
flexing flat piece of spring steel, like a single leaf of a leaf spring.

Maybe I should have started by saying that this is related to regenerative
braking:
http://www.massmind.org/techref/other/regenerativebrakes.htm

And yes, I know that if I had paid attention in Physics 101, I probably
wouldn't have to bother you all with these questions...


---
James.


2006\05\04@001952 by Carey Fisher

face picon face


James Newtons Massmind wrote:
> I'm trying to figure out how much force it takes to get the average bicycle
> moving (or stopped) and how that relates to the force required to lift the
> same mass some distance.
>
> E.g. if a bicycle and rider weighing 200 lbs total was to decelerate from 30
> MPH to 0 in 5 seconds, how far would that amount of force lift the same
> weight into the air?
>  
I would think that friction between the tires and the ground would be a
MAJOR factor in getting the
bicycle moving or stopped and unrelated to lifting the mass.  You'd have
to account and /or control this.
Carey
--

**
<http://www.ncsradio.com/>

2006\05\04@002911 by Denny Esterline

picon face
{Quote hidden}

The term you're looking for is kinetic energy, and the relevant equation is Ke = 1/2 M x V^2 (kinetic energy equals one half mass times velocity squared)

The obligatory wikipedia link:
http://en.wikipedia.org/wiki/Kinetic_energy

One other potentially relevant item, I've recently had some experience with a new "supercapacitor". Fifty-six Farads (yeah, really!) fifteen volts and weighs about one pound - kinda pricey at about $125US.

-Denny


2006\05\04@002936 by Mark Rages

face picon face
Think energy.

http://en.wikipedia.org/wiki/Kinetic_energy
http://en.wikipedia.org/wiki/Potential_energy

First, SI units please.
30 MPH = 13.4 m/s
200 pounds = 90.7 kg (this is on earth, right?)

The moving bike has a kinetic energy of m(v^2)/2, or 90.7*13.4*13.4/2=
8143 joules.

Gravitational potential energy is  U=mgh.  Solving for h: h=U/mg or
8143/(90.7*9.8)=9.2 meters.

9.2 meters is about 30 feet.

I probably screwed the numbers up; I always did in physics class.

Regards,
Mark
markrages@gmail

On 5/3/06, James Newtons Massmind <spam_OUTjamesnewtonTakeThisOuTspammassmind.org> wrote:
{Quote hidden}

> -

2006\05\04@004742 by James Newtons Massmind

face picon face
> I would think that friction between the tires and the ground
> would be a MAJOR factor in getting the bicycle moving or
> stopped and unrelated to lifting the mass.  You'd have to
> account and /or control this.
> Carey

Yes, I am aware that I do not live in a perfect world. However, something is
better than nothing.

---
James.


2006\05\04@005917 by Pierre Desrochers

flavicon
face
Force cannot be stored, only energy.

Search for "energy stored in spring".

Hope this helps.

James Newtons Massmind wrote:

>...how does one figure out how much force can be stored in a spring of a given weight?
>---
>James.
>
>
>  
>

2006\05\04@010055 by Pierre Desrochers

flavicon
face
Have a look at this for tech notes.

http://theory.uwinnipeg.ca/physics/work/node1.html

James Newtons Massmind wrote:

{Quote hidden}

2006\05\04@013029 by Carey Fisher

face picon face


James Newtons Massmind wrote:
>> I would think that friction between the tires and the ground
>> would be a MAJOR factor in getting the bicycle moving or
>> stopped and unrelated to lifting the mass.  You'd have to
>> account and /or control this.
>> Carey
>>    
>
> Yes, I am aware that I do not live in a perfect world. However, something is
> better than nothing.
>
> ---
> James.
>  
Got it!
--

*Carey Fisher, Chief Technical Officer
New Communications Solutions, LLC
*.....careyfisherKILLspamspam@spam@ncsradio.com <careyfisherspamKILLspamncsradio.com>
Toll Free Phone:888-883-5788
Local Phone:770-814-0683
FAX: 888-883-5788
http://www.ncsradio.com <http://www.ncsradio.com/>

2006\05\04@015308 by James Newtons Massmind

face picon face
Thanks Mark, that makes it clear for me.

---
James.



{Quote hidden}

2006\05\04@015601 by James Newtons Massmind

face picon face
> One other potentially relevant item, I've recently had some
> experience with a new "supercapacitor". Fifty-six Farads
> (yeah, really!) fifteen volts and weighs about one pound -
> kinda pricey at about $125US.
>
> -Denny

My understanding is that supercaps tend to not act exactly like their normal
predecessors. So could this one absorb the 8143 joules generated in braking
a bicycle and then release it again without significant losses or safety
hazards? I'm assuming an electric motor/generator capable of translating the
mechanical energy into electrical energy...

---
James.


2006\05\04@022232 by James Newtons Massmind

face picon face
> Force cannot be stored, only energy.
>
> Search for "energy stored in spring".
>
> Hope this helps.

Yes, it does and thank you.

According to:
hyperphysics.phy-astr.gsu.edu/Hbase/pespr.html
I need a spring with a constant of 16,286 N/m if it will be displaced a
maximum of 1 meter and store around 8143 joules.

I can find the size and type of coil spring required to deliver that, but I
can't seem to find anything on what sort of leaf spring would be needed. I
can find leaf springs that are rated to a specific load weight, but how does
that get me to amount of energy stored?

Again, the point here is to try to reduce the amount of weight you have to
add to the bicycle to enable the storage of start/stop energy. If the spring
can be made part of the frame of the bike, you get not only energy storage,
but also suspension without (much) increase in weight. Imagine mounting the
rear wheel of the bike at the end of a leaf spring and then bending that to
absorb and store the energy normally used in stopping.

---
James.


2006\05\04@041446 by Álvaro Deibe Díaz

picon face
And how about one (or more) spring hidden into the tubes that make the
frame of the bycicle? The tubes make good spring enclosures, and you could
compress the spring with a steel thread and some sort of pulleys.

Or, perhaps, an helicoidal spring, like the ones used to store the energy
to keep the clocks moving (this was some time ago...). This kind of spring
could go into a drum in the rear axle wheel.

But I see a major problem here: how do you intend to transfer the energy to
and from the spring? Do you plan to use some kind of clutch? If so,
consider that there will be a significant amount of energy wasted in
heating the clutch itself, in both steps: accelerating and braking.

If you do not plan to use a clutch, and instead some kind of mechanical
coupling between the rear tyre and the spring itself, you will have to
consider what will happen when, in a long break, you reach the end of the
usable spring stroke.

One more thing I see here: the "feeling" of the braking "experience". As
you compress  the spring, the breaking force will rise, and so will do the
decceleration. I think you will get an "abrupt" breaking experience in the
end. You could use a greater capacity spring, and only use a fraction of
its energy storing ability to keep the braking force more constant... but
this will put more weight into the system.

Sorry, I did not throw much light to your problem. Best regards,

Álvaro Deibe Díaz.

{Quote hidden}

>

2006\05\04@082009 by VULCAN20

picon face
I would think a spring would be difficult to use.  You would have to put
a gear shift of some sort in the system.  with out the gear shift for
direction of force the bicycle would want to take off backwards.  Did
you ever see the little cars or other toys you would slide backwards on
a surface and then let go of it.  Would the mechanicals involved add to
much extra weight to drag around and be used only for starting and stopping?


I think the capacitor Idea is easier to do.  A few battery operated
mobility scooters for the handicapped had a circuit in them that while
braking would put a little electricity back into the battery with the
permanent magnet motor acting as a generator

Bob

James Newtons Massmind wrote:

{Quote hidden}

2006\05\04@084712 by olin piclist

face picon face
James Newtons Massmind wrote:
> E.g. if a bicycle and rider weighing 200 lbs total was to decelerate
> from 30 MPH to 0 in 5 seconds

This is *really basic* high school physics.  Think back to all those
frictionless pullies, infinite strings, and massless weights on your tests.

200 pounds mass = 91Kg.
30 MPH = 13.4 m/S.

So after distilling the substance from the fluff of the word problem, we
have a 91Kg mass moving at a speed of 13.4 m/S.

> how far would that amount of force lift
> the same weight into the air?

This question shows a basic misunderstanding of Newton's laws.  Yes,
decellerating a mass by a fixed speed over a fixed time does define the
average force needed.  However, this "force" isn't relevant to lifting the
mass.  Force is not conserved in this context, but energy is.  The mass at a
speed represents kinetic energy.  That can be converted to potential energy.
In other words, forward speed can be converted to lift by a distance.  This
distance can be calculated by equating the two energies and solving for the
height to make the equation ballance:

 kinetic energy at 0 height = potential energy at 0 speed

 1/2 m V**2 = m g h

Right away we can see that the mass is irrelevant.  This makes sense
intuitively.  Given two frictionless bikes (back to high school physics) a
little kid and a large man will have the same speed after coasting down the
same hill.  Anyway, we now have:

 1/2 V**2 = g h

where V is velocity (13.4 m/S), g is the accelleration due to gravity (9.8
m/S**2), and h is the height we are trying to solve for.  So h is:

      V**2
 h = ------
       2g

     180 m*m     S*S
 h = ------- * --------- = 9.2 m = 30.1 ft
       S*S     2 * 9.8 m

So the kinetic energy of any mass moving horizontally at 30 MPH is enough to
move the same mass 30 feet up and no longer moving.  Note that the height
goes with the square of the speed.  I had not realized this before, but the
30 feet at 30 MPH is a good one to remember, then apply the square rule from
there.  In other words 60 MPH is equivalent to 120 feet up and 15 MPH is
only 7.5 feet up.

Another way to look at this is that if you wanted to build a truck escape
ramp (this is for when trucks loose their brakes coming down a mountain) to
handle trucks going up to 60 MPH (any faster and they'd be tumbling down the
canyon already), then you need a straight ramp with a total rise of 120
feet.  It doesn't matter how big or how loaded the truck is.  If it's going
60 MPH at the bottom of the ramp, it can not go more than 120 feet up unless
it deliberately applied power from the engine.

By the way, in case anyone thinks this is a joke, look up the history of
places like Weed and Dunsmuir in northern California.  They are at the
bottom of long slopes coming down the western side of the Sierra Nevada.
There is much national forest up in the mountains with logging operations.
In this part of the world, logging trucks are two parts.  The front part has
the cab and a sort of U shaped assembly.  The back part is another U shaped
assembly with wheels.  The logs are cut truck length (about 40 feet sounds
right) and each U holds one end.  The logs themselves make up the body of
the truck and actually hold the two ends together.  One of those trucks
might have 10-20 small logs only a couple feet in diameter, or occasionally
you see some with just a few really big logs.  Once I saw one that had a
single log that must have been about 6 feet in diameter.  In any case, these
things are *heavy*.

No matter how you slice it, a lot of potential energy has to be dissipated
somehow to bring these monsters down from 5000 feet where the logs are cut
to 1000 feet where the mills are.  Something is going to get hot.  Sometimes
too large a load, too little maintenence, too inexperienced a driver and bad
luck conspire such that the brakes burn out and the engine can't be down
shifted and the truck picks up speed.  That's a crapload of 1/2 m V**2 where
m is a few trees and V is getting ever larger.  At that point the truck
driver leans on the horn and everything else gets out of his way.  Now on
top of that both these towns are pretty much right at the bottom of the hill
with the road from the mountains being the main street thru town.  Whether
anyone likes it not, this truck isn't going to stop for any red lights,
dogs, kids, or little old ladies crossing the street.

This used to happen about twice per summer.  I was there when it happened
once in the 1960s.  The town had installed sirens just for this purpose.  As
soon as they heard a truck with the horn going coming down the hill, the
sirens would go off.  This gives a few minutes warning and everything gets
cleared off main street.  Really.  I saw people move parked cars to side
streets.  Fire engines were ready but waited off the main street.  Then you
see the truck entering the edge of town with smoke billowing from the
wheels.  The one I saw slowed down without incident once it got to the
relatively level main street.

I don't know how this is handled today.  I heard they finally installed a
truck escape ramp partway down the hill or upgraded one or whatever.  I
don't know if the sirens are still in place.

Anyway, the point is Newton's laws really do work and describe our everyday
experience quite accurately.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\05\04@084915 by VULCAN20

picon face
Now this sound like a good PIC project.
Super CAP + the right type of permenant Magnet motor, a couple of
sensors a few control buttons and of course a PIC to controll every thing.

When you need to stop push the brake button.  This would have the motor
act as a generator which would slow you down and charge the super cap.  
to start push the start button,  the super cap would power the motor to
assist in getting moving.
The sensors would detect when the braking or starting were no longer
effcient and disengage the system.  The PIC could use PWM on the motor
so the energy was used effciently and not  burn out the motor.

Bob

James Newtons Massmind wrote:

{Quote hidden}

2006\05\04@085510 by Russell McMahon

face
flavicon
face
> I'm trying to figure out how much force it takes to get the average
> bicycle
> moving (or stopped) and how that relates to the force required to
> lift the
> same mass some distance.

Use the force James, use the force.
Or is that too OT?

Electrical regenerative braking is almost certainly the easiest and
most practical solution if you also have an electric priopulsion motor
(or anything that can subsequently use the energy).

Lets' change to units that help rather than hinder.
200/2.2 = 90.9 kg = say 90 kg
V = 30 mph = 13.9 m/s = 14.
Energy = 0.5 x M x V^2 = 0.5 x 90 x 14^2 = 8820 N.m.
= 8820 Watt second stopping power.
As we stop in 5 seconds, for constant energy rate that's 1764 Watts.
If you had a 24 v system that would deliver 1764/24 = 73 Amps to the
battery.
Somewhat less in practice.
Hmm.
With a say 35 Ah battery that's around the C/0.5 rate.
Rather high for SLA, as you have observed elsewhere recently.
Flywheels beckon for short term smoothing.


A Watt is a Newton-Meter = or 0.1 Newton.Kgs (for slightly strong
gravity :-) ).

So your 8820 Watt-second would lift 90 kg
8820/90/10 = 9.8 m
E&OE.

To store that energy in a spring you can invoke Work =F.d
The 8820 Watt.second = 882 Kg.Meter
Compress a constant 882 kG spring 1 metre. Or a 8820 kg spring 0.1
meter. Or ...

If an 8+ ton (or tonne) spring compressed 100mm sound sexcessive,
consider that this needs be enough to throw your bike back to 30 mph
when unleashed. I would not want such a mechanical energy store
*ANYWHERE* near me on  a push bike. Ones, I believe James said
pee-pee, would be well and truly wacked if such ever got loose. As it
probably would in due course.

A 12v 30Ah car battery with, say, an effective 10v terminal voltage
provides 360 Watt.Hour of energy.
Doesn't sound vast. BUT that's 1,296,000 Watt-Second or 129,600
kg.metre !
That's about 0.07% of the energy in the above example. OR the battery
should be good for about 1500 accelerations to 50 mph of a 200 lbm
bike. (Reality reduces this figure).


       RM

2006\05\04@085513 by Russell McMahon

face
flavicon
face
>> I would think that friction between the tires and the ground
>> would be a MAJOR factor in getting the bicycle moving or
>> stopped and unrelated to lifting the mass.  You'd have to
>> account and /or control this.
>> Carey

> Yes, I am aware that I do not live in a perfect world. However,
> something is
> better than nothing.

A bicycle + rider combination is one of the most energy efficient
systems known when set up properly.
Racing cycle tyres at high inflation offer truly minimal rolling
friction.

I'm told that a salmon swimming upstream uses energy more efficiently.
Hard to imagine, but ...


       RM

2006\05\04@090354 by Russell McMahon

face
flavicon
face
>> One other potentially relevant item, I've recently had some
>> experience with a new "supercapacitor". Fifty-six Farads
>> (yeah, really!) fifteen volts and weighs about one pound -
>> kinda pricey at about $125US.

> My understanding is that supercaps tend to not act exactly like
> their normal
> predecessors. So could this one absorb the 8143 joules generated in
> braking
> a bicycle and then release it again without significant losses or
> safety
> hazards? I'm assuming an electric motor/generator capable of
> translating the
> mechanical energy into electrical energy...

E = 0.5.C.V^2.
V = sqrt(2E/C)
= sqrt(16300/56)

~= 18 Volt.

Interesting.
Only slightly over spec.
Just as long as it's not tantalum :-)
8000 Joules !!!!! :-)
Would beat even a Lithium battery melt down.
"Venting with very very loud explosion".

I suspect it would baulk at the 100 Amp odd charge current though.


   RM


2006\05\04@093631 by M. Adam Davis

face picon face
Now that you have the calculations out of the way, note that you can
find electric bike conversion kits that put a motor in the front
wheel.  This would be a very easy way to add a generator and motor to
the bike.  The kits don't usually include regenerative braking
capabilities, but since the majority of braking energy occurs in the
front wheel, it's a good spot for it.

http://www.google.com/search?q=electric%20bike%20conversion

Most seem to be rated for 300-400W or so, which isn't a quick stop but
is good for general riding (you don't want to stop very quickly anyway
- it stresses the frame and occasionally vaults the rider)

The brake cables usually move several mm before the brakes engage.
Use a linear encoder of some sort to activate the regenerative braking
during this preengagement period in a proportional manner.  I wouldn't
wrap the brake cable around a potentiometer in real world use - if it
breaks then the cable suddenly gets longer and may make the brakes
less (or in-)effective.  I'd also be tempted to only modify the front
brakes in this manner, so the braking feeling from the front of the
bike is the same (And there are times when you want only back brakes -
if you brake in the front on a very slippery surface - woosh!)

As far as a storage medium, I think it would be very cool (and
dangerous) to put a flywheel in the center of the bike.  Imagine
coming to a stop, and standing still without placing your feet on the
ground.  The advantage is that it's suitable for the energy storage
amount and rate, the disadvantage being the natural flywheel danger
(moving parts, might break up) as well as it's tendency to flip you
over quite violently if you try to turn while it's spinning.

You can use a motor to wind a spring, but I suspect the easier route
is going to be battery and capacitor storage.

I believe you'll be fine with a good set of NiMH batteries, though.
They will often allow very large charge and discharge rates.

No matter how you go about it, though, it's going to be the
electronics that make it feasable and efficient.

-Adam

On 5/4/06, James Newtons Massmind <KILLspamjamesnewtonKILLspamspammassmind.org> wrote:
{Quote hidden}

> -

2006\05\04@100617 by Mike Hord

picon face
> I would think that friction between the tires and the ground would be a
> MAJOR factor in getting the
> bicycle moving or stopped and unrelated to lifting the mass.  You'd have
> to account and /or control this.
> Carey

Mmmmm.  Probably not.  Easy experiment- get going good and fast, then
see how far you can coast.  My guess is a good long ways.  The type of
tire will be a major factor- big fat studded off road tires will slow you more
than thin little road bike tires, and flat more than well inflated, but the
bottom line is that over the relatively short (when compared to the time
one would coast) time between hitting "brakes" (be they pads or some
putative regenerative braking system) and stopping makes the friction of
the tires a less significant issue.

Mike H.

2006\05\04@102158 by David VanHorn

picon face
>
> As far as a storage medium, I think it would be very cool (and
> dangerous) to put a flywheel in the center of the bike.  Imagine
> coming to a stop, and standing still without placing your feet on the
> ground.  The advantage is that it's suitable for the energy storage
> amount and rate, the disadvantage being the natural flywheel danger
> (moving parts, might break up) as well as it's tendency to flip you
> over quite violently if you try to turn while it's spinning.




And remember where the shards go if the flywheel comes apart.   OUCH!

There was a rumour here some years back that a flywheel powered car was
going to be entered in the indy 500.
My first thought was to the carnage if there was an accident.  The axis
would have to be vertical, which means that all the shrapnel would be
dispersed horizontally, into the crowd and other cars.  The driver of the
flywheel car would either be safe, or hamburger, depending on location and
luck.

I think I prefer hydrogen.



Feel the power of the dark side!  Atmel AVR

2006\05\04@104825 by Jinx

face picon face
> There was a rumour here some years back that a flywheel powered car was
> going to be entered in the indy 500.
> My first thought was to the carnage if there was an accident

The Patriot showed there would be carnage

http://www.allpar.com/model/patriot.html

Was tipped to enter LeMans in 1994, before it, well.....

http://www.wired.com/wired/archive/2.11/patriot.html

Fly-wheel hybrid

http://www.greencarcongress.com/2005/02/ldquoextremerdq.html

2006\05\04@105253 by Mike Hord

picon face
> There was a rumour here some years back that a flywheel powered car was
> going to be entered in the indy 500.
> My first thought was to the carnage if there was an accident.  The axis
> would have to be vertical, which means that all the shrapnel would be
> dispersed horizontally, into the crowd and other cars.  The driver of the
> flywheel car would either be safe, or hamburger, depending on location and
> luck.

I saw an article (or program, can't recall which) a few years ago
about a flywheel
made of some composite material which, upon failure, exploded into what
amounted to a ball of hair.

While it would certainly cause a mess in the engine compartment, it's
much preferable to the alternative.  Don't know what happened to it, though.

Mike H.

2006\05\04@105835 by Harold Hallikainen

face picon face

> Now that you have the calculations out of the way, note that you can
> find electric bike conversion kits that put a motor in the front
> wheel.  This would be a very easy way to add a generator and motor to
> the bike.  The kits don't usually include regenerative braking
> capabilities, but since the majority of braking energy occurs in the
> front wheel, it's a good spot for it.
>


My employer has an electric conversion on a bicycle. It has a pair of
permanent magnet motors on a single shaft, one on each side of the
"pulley" that drops down on the front wheel. There's a switch that places
the motors in series or parallel. Series is low speed, parallel is high
speed. If you're going down a hill and "down shift" into the series
position, you can see on the ammeter that current is going back into the
batteries. So, there's a simple form of regenerative braking.

I ride the bus to work, then my bicycle from the bus stop to work and
back. I believe the vast majority of the energy is lost in wind resistance
and the tires. I can feel a substantial increase in load when the tire
pressure is getting low. Also, I generally have to head into the wind
going towards the bus home. On those days there's no wind, or the wind is
going the other way, it's a MUCH easier ride. In any case, when coming up
to a stop signal, I stop pedaling long before the signal, coasting up to
it. I'm going pretty slowly by the time I hit the brakes, so very little
energy is being dumped.

Back to the electric bicycle... the weight of the thing is so much that I
can easily go faster and farther than it with little effort.

Harold


--
FCC Rules Updated Daily at http://www.hallikainen.com

2006\05\04@113916 by David VanHorn

picon face
>
> I saw an article (or program, can't recall which) a few years ago
> about a flywheel
> made of some composite material which, upon failure, exploded into what
> amounted to a ball of hair.
>
> While it would certainly cause a mess in the engine compartment, it's
> much preferable to the alternative.  Don't know what happened to it,
> though.


Composite material.  But they don't generally have the mass per cubic inch
that metals do, so you have to fling them even faster.
Then you need a vaccuum for them to run in.  Things get pretty complicated
if you're out to really store any energy.



--
> Feel the power of the dark side!  Atmel AVR

2006\05\04@124409 by James Newtons Massmind

face picon face
> I ride the bus to work, then my bicycle from the bus stop to
> work and back. I believe the vast majority of the energy is
> lost in wind resistance and the tires. I can feel a
> substantial increase in load when the tire pressure is
> getting low. Also, I generally have to head into the wind
> going towards the bus home. On those days there's no wind, or
> the wind is going the other way, it's a MUCH easier ride. In
> any case, when coming up to a stop signal, I stop pedaling
> long before the signal, coasting up to it. I'm going pretty
> slowly by the time I hit the brakes, so very little energy is
> being dumped.

Rather than traditional bicycles where the rider acts as a really bad sail /
wind brake, I'm looking at things like these:

http://www.massmind.org/other/cars especially the Twike and Sun Shark. They
are able to hit 50mph because they are low to the ground, streamlined and
smooth.

> Back to the electric bicycle... the weight of the thing is so
> much that I can easily go faster and farther than it with
> little effort.

Can you do 30 miles, twice a day? There may not be much help from regerative
braking, either due to frictional losses or just because the energy involved
is hard to manage, but every little bit helps. We all know that one solar
panel is NOT going to move any human by itself, but the developer of the Sun
Shark reports a 20% extension in its range as a result of that one, older
style panel (yes, only on a sunny day, etc...). Twike says human pedaling
gets them 10 to 30% of the power required to cruise at 30mph. It all ads up,
and the less you have to cycle your batteries over the range of your commute
(30 miles each way in my case) the longer they last and the less you have to
pollute when you replace them.

---
James.


2006\05\04@144038 by Peter

picon face


On Wed, 3 May 2006, James Newtons Massmind wrote:

> I'm trying to figure out how much force it takes to get the average bicycle
> moving (or stopped) and how that relates to the force required to lift the
> same mass some distance.
>
> E.g. if a bicycle and rider weighing 200 lbs total was to decelerate from 30
> MPH to 0 in 5 seconds, how far would that amount of force lift the same
> weight into the air?

The energy conservation equation is: (m*v^2)/2 = m*g*h for speed ->
height. For a spring the energy stored is k*x^2. So:

  W = (m*v^2)/2 = k*x^2

where k is the spring's Hooke constant and x is the amount you compress
it (or wind it). Note that with a spiral spring the equation may be
different than k*x^2. Watch out for the units. The equations above do
not take into account efficiency. If you get 50% efficiency you're good
imho.

To put time into it, assume the braking force F is constant, then

  F = m * a = m * dv/dt

  (m*v^2)/2 = m*a*x = F*x

the a is the one from m*g*h (= m*a*x for horizontal movement). dv is
from v to 0 and dt is your time. Note that the amount of energy is
*unrelated* to the time, however it is related to power. E.g. P = W/dt.

If you do not brake to a stop then:

  W = (m*v1^2 - m*v2^2)/2

Peter

2006\05\04@144247 by Peter

picon face

> I would think that friction between the tires and the ground would be
> a MAJOR factor in getting the bicycle moving or stopped and unrelated
> to lifting the mass.  You'd have to account and /or control this.

Friction, specially with racing tyres on polished ground, is almost
negligible. Racing tyres are very hard (or high pressure inflated)
smooth rubber. I have read that the rolling friction in the bearings is
higher. Air resistance eats up most of the energy.

Peter

2006\05\04@144913 by Peter

picon face


On Wed, 3 May 2006, James Newtons Massmind wrote:

{Quote hidden}

The answer is no. If your acceleration time is 10 seconds you need a
little more than a horsepower to get to 8kJ. Humans don't do that kind
of thing.

License free vehicles are up to 200W, and this is called a sustainer. A
human pedalling normally is about 200W.

Peter

2006\05\04@145028 by Peter

picon face

On Wed, 3 May 2006, James Newtons Massmind wrote:

>> Force cannot be stored, only energy.
>>
>> Search for "energy stored in spring".
>>
>> Hope this helps.
>
> Yes, it does and thank you.
>
> According to:
> hyperphysics.phy-astr.gsu.edu/Hbase/pespr.html
> I need a spring with a constant of 16,286 N/m if it will be displaced a
> maximum of 1 meter and store around 8143 joules.
>
> I can find the size and type of coil spring required to deliver that, but I
> can't seem to find anything on what sort of leaf spring would be needed. I
> can find leaf springs that are rated to a specific load weight, but how does
> that get me to amount of energy stored?

They always say the maximum displacement.

> Again, the point here is to try to reduce the amount of weight you have to
> add to the bicycle to enable the storage of start/stop energy. If the spring
> can be made part of the frame of the bike, you get not only energy storage,
> but also suspension without (much) increase in weight. Imagine mounting the
> rear wheel of the bike at the end of a leaf spring and then bending that to
> absorb and store the energy normally used in stopping.

A gas spring will be lighter ...

Peter

2006\05\04@145258 by Peter

picon face


On Thu, 4 May 2006, VULCAN20 wrote:

> Now this sound like a good PIC project.
> Super CAP + the right type of permenant Magnet motor, a couple of sensors a
> few control buttons and of course a PIC to controll every thing.

You have to use a DSPic to drive the maximum energy transfer mode and
the blue backlit animated graphical LCD.

Peter

2006\05\04@145830 by Peter

picon face


On Fri, 5 May 2006, Jinx wrote:

{Quote hidden}

Why are people so afraid of certain systems ?! 8kJ is 8kJ, electrical,
burning lithium, or whatever.

Peter

2006\05\04@152041 by M. Adam Davis

face picon face
On 5/4/06, Peter <RemoveMEplpTakeThisOuTspamactcom.co.il> wrote:
>
> Why are people so afraid of certain systems ?! 8kJ is 8kJ, electrical,
> burning lithium, or whatever.

Different systems have different properties that affect their
environment differently when they fail.

A flywheel can drastically affect a very large radius with shrapnel in
a very short burst.  The shrapnel can be mitigated with shielding, but
that adds weight.

A lithium ion battery will typically only jet flame several inches -
it affects a much small area more severely and for a longer period of
time.  This fire can't be put out - your only choice is to let it burn
itself out.  This can be mitigated with a container that is much
smaller and lighter than the container for the flywheel.

A spring affects a smaller area than the flywheel, but it's
destruction can also be more focussed depending on the configuration.
If may release all of its energy in a very small area - 1 square inch
of pressure at huge forces.  This one may be mitigated in a manner
similar to the flywheel.

There are many other ways to store energy (pressurized vessels, etc).
Each has its advantages and disadvantages, and the application is the
key deciding factor.  I'm afraid of all these systems equally, so I'm
not sure what you mean when you wonder why people are afraid of one
more than another.

Given that this is an electronics list, and people are less afraid of
what they are most familair with, I suspect that many of us would have
more reservations on the mechanical storage systems than the
electrical.

-Adam

2006\05\04@152700 by James Newtons Massmind

face picon face
>
> A gas spring will be lighter ...
>
> Peter


Well, I guess it might be, but what about the casing required to contain the
gas? At this point, I can see mechanical ways to attach coil, leaf or gas
springs. Basically, the front wheel brakes, the rear wheel has a sprag
clutch (as is standard on most lower end / kids bicycles) and the frame
between hinges, flexes or telescopes (respectively) to use the type of
spring applied. Of those, the leaf spring seems to be the one that would add
the least weight if it were used to replace part of the frame. E.g. the
frame would be warped to store energy when stopping and would act as a
suspension element when running. A coil spring requires a frame that hinges
and then the weight of the spring is added. If the frame were made with
tubes that slide inside one another, that could perhaps be the gas spring,
but I'm trying to figure out how much weight that would add since the frame
would still have to support the rider, etc.. when fully extended.

---
James.


2006\05\04@153406 by James Newtons Massmind

face picon face
> Why are people so afraid of certain systems ?! 8kJ is 8kJ,
> electrical, burning lithium, or whatever.

I think is has to do with knowing or not knowing the likely form of failure.
E.g. a spring is very probably going to fail in one specific way, in one
specific direction. A super cap is going to arc, spark and/or melt. A
flywheel is going to do what the heck ever it pleases in just about any
direction. You decide which one is easiest to engineer safety measures for.

My driving issue is weight more than safety. Can energy storage be added
without increasing weight? Or rather what energy storage system will add the
most capacity with the least increase in weight.

I think the best is electric battery, but not when the incoming energy is
large in a short time. So motor as generator is best when braking slowly as
in coming down a long incline, but something else would be nice for quick
stop then start motion.

That is where I started thinking about replacing part of the frame with a
spring, compressing air in a telescoping frame, or using a (lightweight?)
super cap or something like that.

---
James.


2006\05\04@160414 by olin piclist

face picon face
Another thing to consider is what fraction of the total pedal energy ends up
getting dissipated in the brakes.  I suspect very little, probably well
under 5%.  Think about how often you actually brake a bike compared to
pedaling or coasting.  How often do you come to a stop at all?  As others
have pointed out, the vast majority of the energy goes into wind drag.
Maybe if you are riding in a congested city more than a trivial amount of
energy ends up in the brakes, but even then a city block that may be "short"
for a car is a lot longer for a bike.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\05\04@163126 by Herbert Graf

flavicon
face
On Wed, 2006-05-03 at 21:07 -0700, James Newtons Massmind wrote:
> I'm trying to figure out how much force it takes to get the average bicycle
> moving (or stopped) and how that relates to the force required to lift the
> same mass some distance.
>
> E.g. if a bicycle and rider weighing 200 lbs total was to decelerate from 30
> MPH to 0 in 5 seconds, how far would that amount of force lift the same
> weight into the air?
>
> 30 mph = 44 feet per second and F = M * A so we are talking about 200*44/5
> right? Or 1760 foot lbs? With 200 lbs, that could then be raised 1760 / 200
> = 8.8 feet?

It's been a while since I took physics, and I may be completely wrong
with what I'm about to say, that said...

I think you are making things more complicated then they have to be.
Problems like this are most easily solved IMHO using conservation of
energy rules.

The easiest way to do this is to use two formulas: the kinetic energy of
a moving object, and the potential energy of an object.

The kinetic energy of something is based on it's speed and mass. Since
all your kinetic energy is gone when you finally stop, note that number.

Then, using that number, calculate how high your object has to be raised
to posses that same amount of potential energy.

So, using your numbers (I'm going to convert to metric units):

30MPH => 13.4112m/s
200lbs => 90.7185kg

KE = 1/2 * m * v^2
KE = 1/2 * 90.7185kg * (13.4112m/s)^2
KE = 8158.33 J

So, the distance a 200lbs mass has to be raised to equal 8158.33J of
potential energy:

PE = w * h
PE = m * 9.8 * h
=>
h = PE/(m * 9.8)
h = 8158.33J / (90.7185kg * 9.8 m/ss)
h = 9.18m


I may have made a math error somewhere, but I think that height seems
pretty reasonable.

Obviously we are assuming an ideal system (i.e. zero friction, perfect
energy storage, etc.), but this at least gives you a rough idea.

TTYL

2006\05\04@163406 by M. Adam Davis

face picon face
Regenerative braking could also be used against wind losses going downhill.

When going downhill switch on the generator so you still only go about
15mph.  Then you've got a ton of energy that would have otherwise been
wasted on wind going 25 since the loss is exponential.

This could be automated as a cruise control.  You set the speed you'd
like to go, and pedal at a cadence and force you like.  As long as
your average output power is enough for the entire distance you'll
never be in a spot where you have to pedal more or less.

Otherwise, yes, whether you recover energy from braking depends on
your riding style, just as it does with cars.  With most cars you
don't get immediate feedback as to how much it's consuming to
accelerate so quickly, nor how much energy is going into the brakes.
On a bike you can't help but notice how much energy it takes to get
started again.  I coast to a stop on my bike only if I believe the
light is going to change quickly and I can keep my momentum.
Otherwise I get to the light as quickly as I can so I can take a
longer break.  In my case regenerative braking could be beneficial,
but I wouldn't want it because intuitively I don't feel it will yield
enough efficiency to make up for the extra 10 pounds it looks like it
would add.

Further, I'm very resistant to the idea of storing the energy in the
frame - I enjoy road cycling and don't want the frame to flex any more
than necessary - it saps energy that should be going into the wheels.
But then, I doubt I'd be the target consumer for such a design.

-Adam

On 5/4/06, Olin Lathrop <spamBeGoneolin_piclistspamBeGonespamembedinc.com> wrote:
{Quote hidden}

> -

2006\05\04@165933 by olin piclist

face picon face
M. Adam Davis wrote:
> Then you've got a ton of energy that would have otherwise been
> wasted on wind going 25 since the loss is exponential.

But that's one of the fun parts of biking.  That feeling of going wheeeee
down a hill, usually after you just huffed and puffed going up the other
side.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\05\04@174053 by David VanHorn

picon face
>
>
> But that's one of the fun parts of biking.  That feeling of going wheeeee
> down a hill, usually after you just huffed and puffed going up the other
> side.


70+ mph, twoard an intersection, with your melting brake pads scoring the
rims.

40+ in a tight turn with the high pedal scraping.

:)


--
> Feel the power of the dark side!  Atmel AVR

2006\05\04@175434 by Mike Hord

picon face
> That is where I started thinking about replacing part of the frame with a
> spring, compressing air in a telescoping frame, or using a (lightweight?)
> super cap or something like that.

What about a pulley system where the stopping energy goes into lifting a
weight up a pole?

Has a charming "Rube Goldberg" feel to it...

Mike H.

2006\05\04@181207 by Harold Hallikainen

face picon face

>>
>>
>> But that's one of the fun parts of biking.  That feeling of going
>> wheeeee
>> down a hill, usually after you just huffed and puffed going up the other
>> side.
>
>
> 70+ mph, twoard an intersection, with your melting brake pads scoring the
> rims.
>
> 40+ in a tight turn with the high pedal scraping.
>
> :)

I've got a scar on my cheek from going around a corner 35 years ago. There
was gravel on the road. The bicycle tires disappeared from under me.

Maybe 45 years ago, my brother and sister and I went on a bicycle ride to
register her new bicycle at the local police station. We were going down a
hill, and she could not stop. She crossed a very busy intersection and hit
someone's garage door on the other side of the intersection. Drew quite a
crowd, including the police. She got her bike registered...

Harold

--
FCC Rules Updated Daily at http://www.hallikainen.com

2006\05\04@182428 by James Newtons Massmind

face picon face
> What about a pulley system where the stopping energy goes
> into lifting a weight up a pole?
>
> Has a charming "Rube Goldberg" feel to it...

I was thinking about just vaulting the rider into the air as the bike stops
and then using the force of his impact back into the bike to propel it
forward again.

"But officer, the bike DID stop at the sign."

---
James.


2006\05\04@190112 by David VanHorn

picon face
>
>
> I've got a scar on my cheek from going around a corner 35 years ago. There
> was gravel on the road. The bicycle tires disappeared from under me.


My scars have almost completely faded, but I had a rim fold on me in a turn
like that once.
I think I skipped on a bit of gravel, and when the wheel came back in
contact the stress was too much.


--
> Feel the power of the dark side!  Atmel AVR

2006\05\05@022212 by William Chops Westfield

face picon face
On May 4, 2006, at 2:40 PM, David VanHorn wrote:

> 70+ mph, twoard an intersection

Heh.  I wasn't going that fast, but the intersection at the
bottom of the hill unexpectedly had a car in it, forcing me
to go around the curve in the sandy section.  I've still got
the scar on my elbow where the road sanded away the skin...

(Isn't it nice to have survived your youth?)

BillW

2006\05\05@053607 by Michael Rigby-Jones

picon face


>-----Original Message-----
>From: BillW [TakeThisOuTpiclist-bouncesEraseMEspamspam_OUTmit.edu]
>Sent: 05 May 2006 07:22
>To: Microcontroller discussion list - Public.
>Subject: Re: [ee] Basic physics... Bicycle regenerative braking forces
>
>(Isn't it nice to have survived your youth?)

Looking back, I think it's quite amazing to have survived given some of the stupid things I did, and I was generaly considered fairly sensible as youngsters go..

Dragging this back on topic I personaly think mechanical systems have too many problems to be practical.  How do you smoothly control the transfer of energy from kinetic to potential?  It implies some kind of friction clutch is required, and also some kind of mechanism to make sure the potential energy isn't released too quickly.  Complexity and weight, both natural enemies of the humble bicycle.

How about small neodymium magnets mounted on the rim of the wheel, and a coil assembly mounted to the forks/frame as a combined generator/motor?

Regards

Mike

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2006\05\05@075836 by Peter

picon face
> But that's one of the fun parts of biking.  That feeling of going wheeeee
> down a hill, usually after you just huffed and puffed going up the other
> side.

Only to find out that there is a turn at the bottom, that there are wet leaves
on the road just exactly there, and you can see a bus coming up just entering
the road. There is a reason for bicycles being safe when they go slowly.

Back to springs: a gas spring is for example a small (5l) diving air bottle and
this can be charged and discharged using, for example, a small air motor geared
to the chain. Air motors are not very efficient but over all it should be as
efficient as electrical. A 200W air motor is a toy (smaller than a beercan) and
weighs nearly nothing. The only arcane item is a 3-way reversing valve to switch
the air around. A pressure regulator is probably not needed.

links:

http://zebu.uoregon.edu/1996/ph162/l10a.html
www.doc.ic.ac.uk/~mpj01/ise2grp/energystorage_report/node7.html
http://cr4.globalspec.com/article.pl?sid=06/01/12/1340221

A used 0.5hp pneumatic motor can be gotten for about $50, and a 3-way valve for
less. A 2l bottle should be enough for initial experiments.

Peter



2006\05\05@124721 by James Newtons Massmind

face picon face
> Dragging this back on topic I personally think mechanical
> systems have too many problems to be practical.  How do you
> smoothly control the transfer of energy from kinetic to
> potential?  It implies some kind of friction clutch is
> required, and also some kind of mechanism to make sure the
> potential energy isn't released too quickly.  Complexity and
> weight, both natural enemies of the humble bicycle.

Using the brakes on the front wheel only and the mass of the rider and bike
behind it to compress a spring (hinged frame with coil spring, flexing frame
with leaf spring, telescoping frame with air spring) and then the standard
Sprague clutch on the rear wheel to prevent the release of that energy until
the front brakes are released. No additional components, easy to control via
the front brake.

Not terribly efficient, not totally safe, but better than nothing.

Again, my goal is to see if there is a way to extend the range of an
electric bicycle car with solar, pedal and electrical regeneration
assistance so that the battery lasts longer and so is replaced less often.
http://www.massmind.org/other/cars
If it adds just about anything to the range, then it is worth doing. The one
old style solar panel on the didik Sun Shark adds about 20%. The pedal power
on the Twike is known to add 10 to 30%. Electrical regenerative brakes
probably add something between nothing and a lot depending on the terrain
being followed. But the energy of stopping quickly (at traffic lights, stop
signs, or to avoid obstacles) is being lost due to the lack of ability of a
standard battery to take in a big pulse.

I'm starting to think the super cap idea is worth looking into more.

Another issue with electrical regenerative brakes is that they require some
manner of motor control. If you use a variable field motor, then you loose
(some) energy when you drive it. I really like the super simple versions I
have seen where two motors and/or two batteries are rewired in parallel or
series using a set of switches. Someone here described a simple system with
two motors. In any case, that works ok for 2 or 4 levels of thrust /
regeneration, but for quick stops, that is probably not enough. Right?

So then we are looking at variable field, or big DC switching semiconductors
or something like that. Anyone seen systems that worked well? PIC controlled
preferably? <grin>

---
James.




2006\05\05@130144 by David VanHorn

picon face
>
> (Isn't it nice to have survived your youth?)
>
> BillW


No real worries, we were invulnerable then.  It wears off though.


--
> Feel the power of the dark side!  Atmel AVR

2006\05\05@130250 by David VanHorn

picon face
> Only to find out that there is a turn at the bottom, that there are wet
> leaves
> on the road just exactly there, and you can see a bus coming up just
> entering
> the road. There is a reason for bicycles being safe when they go slowly.


I had a friend into motorcycles.  It wasn't intuitively obvious to him that
Armor-All is not a good idea on seats and tyres.


--
> Feel the power of the dark side!  Atmel AVR

2006\05\05@130447 by David VanHorn

picon face
>
> How about small neodymium magnets mounted on the rim of the wheel, and a
> coil assembly mounted to the forks/frame as a combined generator/motor?



I don't know how you'd maintain the clearances. Rims flex.
Sears had at one time a generator that rolled on the tire tread surface,
rather than the conventional side attack.  MUCH less drag for the same
output. It was entirely cylindrical, with an outer cylinder that rotated on
the tire, and inner static cylinder with the coil, and mounting gizmo.


--
> Feel the power of the dark side!  Atmel AVR

2006\05\05@142133 by James Newtons Massmind

face picon face
> Back to springs: a gas spring is for example a small (5l)
> diving air bottle and this can be charged and discharged
> using, for example, a small air motor geared to the chain.
> Air motors are not very efficient but over all it should be
> as efficient as electrical. A 200W air motor is a toy
> (smaller than a beercan) and weighs nearly nothing. The only
> arcane item is a 3-way reversing valve to switch the air
> around. A pressure regulator is probably not needed.
>
> links:
>
> http://zebu.uoregon.edu/1996/ph162/l10a.html

For air, increase in Temperature goes approximately as increase in Pressure
to the 1/4 power when T is measured in Kelvins.

> http://www.doc.ic.ac.uk/~mpj01/ise2grp/energystorage_report/node7.html

If I read that right, a commercial system with an 80% efficient turbine
stored 1086 Joules per gram of air with a 75 bar increase in pressure and
762C increase in air temp. At 1.204 milligrams per cubic centimeter (1
atmosphere, 20'C) and a storage need of about 8143 J, that is around 9,000
CC or 9 liters.

But air motors are less than 60% efficient. And 75 bar is about 1000 psi
according to google. So 20 liters at 500 psi and 700'F? Or 40 at 250 and
350? I'm not sure that is valid reasoning.

A 10 gallon tank rated to 125 psi weighs 27 lbs.
http://www.grainger.com/production/info/granger-industrial-supply.htm

Obviously, the more volume available, the more capacity and the less
pressure safety and temperature loss is an issue.

> cr4.globalspec.com/article.pl?sid=06/01/12/1340221
>
> A used 0.5hp pneumatic motor can be gotten for about $50, and
> a 3-way valve for less. A 2l bottle should be enough for
> initial experiments.
>
> Peter

Ahh... Very interesting... I didn't realize that air motors are that small
for the hp.

Sadly, unless the frame of the bike could be used in place of or in addition
to the air bottle, the storage of the system doesn't seem to be up to the
task.

Also, insulation might help, but would not be /as/ necessary if the energy
is being stored for a short time which is the case here.

One side benefit might be a nice blast of cool exhaust air into the cabin
when you are starting out again, pedaling like mad!

---
James.


2006\05\05@193159 by Peter

picon face
David VanHorn <dvanhorn <at> microbrix.com> writes:

> I had a friend into motorcycles.  It wasn't intuitively obvious to him that
> Armor-All is not a good idea on seats and tyres.

Who or what is Armor-All ?

Peter


2006\05\05@200801 by James Newtons Massmind

face picon face
> > I had a friend into motorcycles.  It wasn't intuitively
> obvious to him
> > that Armor-All is not a good idea on seats and tyres.
>
> Who or what is Armor-All ?
>

A protective spray for plastics that is somewhat slick.

---
James.


2006\05\06@020539 by Peter

picon face
James Newtons Massmind <jamesnewton <at> massmind.org> writes:

> If I read that right, a commercial system with an 80% efficient turbine
> stored 1086 Joules per gram of air with a 75 bar increase in pressure and
> 762C increase in air temp. At 1.204 milligrams per cubic centimeter (1
> atmosphere, 20'C) and a storage need of about 8143 J, that is around 9,000
> CC or 9 liters.

Air rho is about 1.2g/l at STP. At 75 bar it's 99cc of air for 8.1kJ. If you
don't use a regulator max. pressure for an air motor for a short time is
probably 20 bar (fingers crossed), so you need 4 times more air, still less than
0.5l. But the efficiency will be much lower than that plant so plan for 1 or 2
liters. The heat put into compressing the air is a part of the energy put into
it and should not be removed. This means metal tank (the lighter kevlar or
carbon tank cannot become hot).

Olin has brought up a good point: People who ride bicycles do not brake that
much. So it would be interesting to look into the possibility of a small
auxiliary pump chraging the reservoir all the time, to provide a starting
reserve for when it's needed.

Peter

2006\05\06@085914 by Howard Winter
face
flavicon
picon face
On Wed, 3 May 2006 21:47:24 -0700, James Newtons Massmind wrote:

> > I would think that friction between the tires and the ground
> > would be a MAJOR factor in getting the bicycle moving or
> > stopped and unrelated to lifting the mass.  You'd have to
> > account and /or control this.
> > Carey
>
> Yes, I am aware that I do not live in a perfect world. However, something is
> better than nothing.

I don't think the friction (or air resistance) will have a major effect compared with inertia (kinetic energy)
in slowing you down.  If you're on a flat road, cycling at 30mph, and you stop pedalling, you will go a *long*
way before eventually coming to a halt.  If you're doing energy-storage braking, I'd expect at least 90% of
the kinetic energy to be available with normal stopping distances (whether your mechanism can store and
retrieve it with anything like that efficiency is another thing entirely! :-)

Cheers,

Howard


2006\05\06@091405 by Howard Winter

face
flavicon
picon face
James,

On Wed, 3 May 2006 23:22:27 -0700, James Newtons Massmind wrote:

{Quote hidden}

Leaf springs really aren't designed to store much energy, because they have limited travel before the elastic
limit of the metal is reached.  To overcome this, the watch-spring was invented!  It's like a really long leaf
spring, coiled up to make it a managable size.  You also have a problem in that both of these give back their
energy in the opposite direction to that which put it in - you might have to get very clever with gears and
such to use the energy to drive forwards.  With a watch-spring you could use the outside to put the power in,
and the inside to recover it, or two drums configured as wind/unwind where the energy goes into one drum to
wind the spring onto it, and from the other to wind it onto that.  I think Trevor Baylis' Freeplay wind-up
radio does this.

> Again, the point here is to try to reduce the amount of weight you have to
> add to the bicycle to enable the storage of start/stop energy. If the spring
> can be made part of the frame of the bike, you get not only energy storage,
> but also suspension without (much) increase in weight. Imagine mounting the
> rear wheel of the bike at the end of a leaf spring and then bending that to
> absorb and store the energy normally used in stopping.

Completely different order of magnitude, I'm afraid!  Suspension moves a few inches, energy storage would need
to move yards... think of it the other way round: if you set off by rolling down a ramp, how fast would you be
going if the ramp was 6" high?  In fact you could do this as an experiment, without having to build anything
more than a simple wooden ramp.

Cheers,


Howard Winter
St.Albans, England


2006\05\06@092920 by Russell McMahon

face
flavicon
face
> I don't think the friction (or air resistance) will have a major
> effect compared with inertia (kinetic energy)
> in slowing you down.  If you're on a flat road, cycling at 30mph,
> and you stop pedalling, you will go a *long*
> way before eventually coming to a halt.  If you're doing
> energy-storage braking, I'd expect at least 90% of
> the kinetic energy to be available with normal stopping distances
> (whether your mechanism can store and
> retrieve it with anything like that efficiency is another thing
> entirely! :-)

A good first estimate of air resistance is given by

       drag = 0.5 x Rho x A x Cd x V^2

All in consistent units.

Rho = fluid density ~= 1.3 kg/m^3 for air.
A = frontal area.
Cd = coefficient of drag = 1 for a flat plate.
0.6 is good.
0.3-0.4 is superb

This equation works well enough for order of magnitude (actually
rather better) guesstimates for rockets (not near sonic transition),
raindrops, field mice, parachutes, skydivers and more. Memorise it and
you have another good party trick if you go to the sort of parties
that real engineers should go to.



       RM




2006\05\06@094650 by Peter

picon face
James Newtons Massmind <jamesnewton <at> massmind.org> writes:


> I was thinking about just vaulting the rider into the air as the bike stops
> and then using the force of his impact back into the bike to propel it
> forward again.

Wait, you have something here. There are those bikes which have no pedals and
you pedal by hopping up and down on a hinged seesawing platform geared to the
wheels. This begs for embedding springs in it for energy storage (or air
pistons). Then there's the bike that is powered by hopping up and down against
the wheel suspension.

Peter

2006\05\06@095646 by Howard Winter

face
flavicon
picon face
Harold,

On Thu, 4 May 2006 07:57:32 -0700 (PDT), Harold
Hallikainen wrote:

> I ride the bus to work, then my bicycle from the bus
stop to work and back.

Where are you?  And how do the busses have space for
bicycles?

Cheers,


Howard Winter
St.Albans, England


2006\05\06@100114 by David VanHorn

picon face
>
>
> A protective spray for plastics that is somewhat slick.



This was just after it was introduced, and it's "enslickening" properties
were not well understoof by Dan at the time.  Fortunately it was just
hilarious, and didn't turn out to be dangerous.






--
Feel the power of the dark side!  Atmel AVR

2006\05\06@101346 by Howard Winter

face
flavicon
picon face
Mike,

On Thu, 4 May 2006 16:54:33 -0500, Mike Hord wrote:

> What about a pulley system where the stopping energy goes into lifting a
> weight up a pole?
>
> Has a charming "Rube Goldberg" feel to it...

And you already have the weight on the bike - the rider!  As the bike slows down, the saddle rises, absorbing
the energy, and on take-off lowers again, transferring the energy back to the wheels.  Wouldn't look silly at
all!  :-)))  

And there's the advantage of being able to chat with truck-drivers eye-to-eye while waiting at the lights.  
There is the problem of how the rider puts his foot down to stop falling over, though...

Cheers,


Howard Winter
St.Albans, England


2006\05\06@103452 by Tony Smith

picon face
{Quote hidden}

That's actually an excellent suggestion.

I was once looking for something to give me a constant tension, and
learned the term 'negator spring'.  Essentially, no matter how much you
wind it up, to get the same amount of force out.

And that's what a watch spring does.

Then I realised I had a bunch of cheap negator springs lying around -
tape measures!

Tony

2006\05\06@104020 by David VanHorn

picon face
>
> And there's the advantage of being able to chat with truck-drivers
> eye-to-eye while waiting at the lights.
> There is the problem of how the rider puts his foot down to stop falling
> over, though...


That's what the gyros are for!  Spin them up during braking, and let them
deplete when you kick off again, then use the descending stroke of the rider
for sustaining energy.

This would be quite the gizmo to watch in traffic!

--
> Feel the power of the dark side!  Atmel AVR

2006\05\06@230507 by Russell McMahon

face
flavicon
face
> That's what the gyros are for!  Spin them up during braking, and let
> them
> deplete when you kick off again, then use the descending stroke of
> the rider
> for sustaining energy.
>
> This would be quite the gizmo to watch in traffic!

Yes indeed!
You could form a one man precession.


               RM

2006\05\07@043428 by Robert Rolf

picon face


Russell McMahon wrote:

{Quote hidden}

So why not have contrarotating gyros to balance out the forces?
If you had them as large a diameter as the rear wheel, and
parallel to them, they shouldn't affect handling much. Just
a lot of extra mass to drag along.

Robert

2006\05\07@095745 by Howard Winter

face
flavicon
picon face
Russell,

On Sun, 07 May 2006 15:01:14 +1200, Russell McMahon wrote:

{Quote hidden}

Oh Good Grief!

I suppose if it gets out of control and injures the rider, that you'd have to call a Spin Doctor?

Cheers,


Howard Winter
St.Albans, England


2006\05\07@214258 by M. Adam Davis

face picon face
On 5/6/06, Howard Winter <RemoveMEHDRWspamTakeThisOuTh2org.demon.co.uk> wrote:
> Harold,
> Where are you?  And how do the busses have space for
> bicycles?

I don't know about Harold's busses, but the busses in Ann Arbor, MI
have bike racks on the front:
http://www.theride.org/biketheride.asp

Just a text description - sorry, not pictures.  It only holds two
bikes per bus, I've yet to see them both used at once.

-Adam

2006\05\07@221631 by Harold Hallikainen

face picon face
I live in Santa Maria, CA and work in San Luis Obispo, CA, about 30 miles
north. The buses have fold down bike racks on the front and back (more
info at http://www.slorta.org/ccat.htm). Each rack holds 3 bikes. We get
real close to filling them.

By the way, does anyone have a feel for the passenger miles per gallon (or
passenger kilometers per liter) for a 50 passenger bus that's full? I
assume fuel usage does not vary a whole lot with the number of passengers.
It'd be interesting to know how many passengers we need to be more
efficient than a car with one person or a car with two people.

Harold


{Quote hidden}

> -

2006\05\07@222522 by Jinx

face picon face
> I don't know about Harold's busses, but the busses in Ann Arbor, MI
> have bike racks on the front:

Auckland NZ buses used to be able to carry bikes, now they don't.
Really sucks because you can't get across the harbour bridge. It's
part of the motorway so you can't cycle and there's no pedestrian
walkway underneath. There's the ferry but that takes you miles out
of your way. No trains go that way either ;-(((( Trains are good as
those of us with a bike (or pram) just hop in the last carriage with it,
no worries

2006\05\07@222641 by Herbert Graf

flavicon
face
On Sat, 2006-05-06 at 14:56 +0100, Howard Winter wrote:
> Harold,
>
> On Thu, 4 May 2006 07:57:32 -0700 (PDT), Harold
> Hallikainen wrote:
>
> > I ride the bus to work, then my bicycle from the bus
> stop to work and back.
>
> Where are you?  And how do the busses have space for
> bicycles?

Usually a rack is on the front or back of the bus.

TTYL

2006\05\08@071520 by Gerhard Fiedler

picon face
Harold Hallikainen wrote:

> By the way, does anyone have a feel for the passenger miles per gallon (or
> passenger kilometers per liter) for a 50 passenger bus that's full? I
> assume fuel usage does not vary a whole lot with the number of passengers.
> It'd be interesting to know how many passengers we need to be more
> efficient than a car with one person or a car with two people.

About 3 km/l, it seems:

http://www.bts.gov/publications/national_transportation_statistics/2003/html/table_04_15_m.html

The average European car makes around 20 km/l, the average US car around 10
km/l. That would need an average of 4 to 8 passengers in the bus.

Gerhard

2006\05\08@074007 by Russell McMahon

face
flavicon
face
> About 3 km/l, it seems:
>
> http://www.bts.gov/publications/national_transportation_statistics/2003/html/table_04_15_m.html
>
> The average European car makes around 20 km/l, the average US car
> around 10
> km/l. That would need an average of 4 to 8 passengers in the bus.

That's for fuel. One also needs to amortise the cost of capital and
maintenance. That said, a fullish 50 passenger bus carries about 25
times the average car load (depending on country ;-) ) so a bus can
cost about $250,000 - $500,000 and still (perhaps) compare well. A bus
with 8 wouldn't.

Would be interesting to do a proper comparison with all factors
included (driver cost, regulations, ...). Presumably the size of
typical buses reflects the results of such studies, or of market
forces, which tend to perform such studies of their own volition.


       RM


2006\05\08@095700 by Howard Winter

face
flavicon
picon face
Russell,

On Mon, 08 May 2006 23:39:24 +1200, Russell McMahon wrote:
>...
> Presumably the size of
> typical buses reflects the results of such studies, or of market
> forces, which tend to perform such studies of their own volition.

Or they just go out and buy busses from the firm with the most persuasive salesman!  (Or in some places, the
best kickbacks...)

In a place like London, where the streets are crowded, narrow, and with sharp corners, the obvious shape is
the double-decker - takes up less space, and can get round corners easily.  So what are they doing?  Replacing
them with double-length "bendy" busses which take up more than twice the space, can't get round corners, and
have been known to catch fire!

Cheers,

Howard Winter
St.Albans, England


2006\05\08@111623 by Michael Rigby-Jones

picon face


{Quote hidden}

James,

What I meant was how would you control the transfer of energy into the spring?  A simple clutch gives you either none or full regenerative braking.  Idealy you would have some kind of variable ratio drive so you could actualy control how quickly you slow down.  If the system is permanently geared then in many situations it will either be too little and you have to fall back on normal friction brakes, or too much.  And of course you would need to include a mechansim to prevent too much energy being input, i.e. disconnect regenerative brakes once the spring is wound up to maximum.

I know when you have a hammer everything looks like a nail, but I reckon this application would only be practical using electrical storage.  Springs, compressed gas, flywheels etc. are all too bulky/heavy/dangerous.  The above problems are all overcome by a relatively simple electronic control system.

Regards

Mike

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2006\05\08@142130 by James Newtons Massmind

face picon face
{Quote hidden}

Hopefully all of the mechanical systems I listed would require minimal
additional weight by re-using parts of the existing bike or replacing
existing pieces with parts that could serve dual function. E.g. replace part
of the frame with a leaf spring so that the frame itself flexes and also
holds the bike together. An air motor is light and the bike frame could be
used as the storage tank.

It would only work at full braking, but would be combined with electric
regenerative brakes so that there would be two levels available. Some energy
would still be lost to frictional braking, but something is better than
nothing. The point here is that batteries can't be recharged at the levels
that rapid braking generates. The mechanical stuff is to be an addition to
make up the difference.

Having said all that, super caps are looking good, abet expensive, and I
totally agree that an electrical system would be preferable.

---
James.


2006\05\08@142645 by Peter

picon face

On Sun, 7 May 2006, Harold Hallikainen wrote:

> I live in Santa Maria, CA and work in San Luis Obispo, CA, about 30 miles
> north. The buses have fold down bike racks on the front and back (more
> info at http://www.slorta.org/ccat.htm). Each rack holds 3 bikes. We get
> real close to filling them.
>
> By the way, does anyone have a feel for the passenger miles per gallon (or
> passenger kilometers per liter) for a 50 passenger bus that's full? I
> assume fuel usage does not vary a whole lot with the number of passengers.
> It'd be interesting to know how many passengers we need to be more
> efficient than a car with one person or a car with two people.

A slightly larger bus does 10-15 mpg, less in city traffic. You can look
it up on the manufacturer's webpages.

Peter

2006\05\08@210624 by Gerhard Fiedler

picon face
Russell McMahon wrote:

> Presumably the size of typical buses reflects the results of such
> studies, or of market forces, which tend to perform such studies of
> their own volition.

Here (Brazil) you find all kinds of buses in active use, from the proven VW
Bus to the big intercity liners. Rarely a bus runs empty or even half
empty. Not sure this is exclusively a good thing, though... :)

Gerhard

2006\05\09@011051 by Richard Prosser

picon face
Gerhard,

20km/l seems very efficient. I get 15km/l out of a small 3 cylindar
1000cc motor (1987 vintage) . I can't see modern engines being that
much more efficient

But I may be wrong --- again
RP

On 08/05/06, Gerhard Fiedler <RemoveMElistsspam_OUTspamKILLspamconnectionbrazil.com> wrote:
{Quote hidden}

> -

2006\05\09@041852 by Michael Rigby-Jones

picon face


>-----Original Message-----
>From: RemoveMEpiclist-bouncesTakeThisOuTspamspammit.edu [EraseMEpiclist-bouncesspamspamspamBeGonemit.edu]
>Sent: 09 May 2006 06:11
>To: Microcontroller discussion list - Public.
>Subject: Re: [ee] Basic physics... Bicycle regenerative braking forces
>
>
>Gerhard,
>
>20km/l seems very efficient. I get 15km/l out of a small 3 cylindar
>1000cc motor (1987 vintage) . I can't see modern engines being
>that much more efficient
>
>But I may be wrong --- again

20km/l is 56mpg in imperial gallons or 47mpg in US gallons.  Modern diesels which are now very popular in Europe are quite capable of attaining these figures and better in many cases.  Most small petrol (gas) engined cars struggle to get much better than 40-45mpg.

Regards

Mike

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2006\05\09@044859 by Dave King

flavicon
face


> >Gerhard,
> >
> >20km/l seems very efficient. I get 15km/l out of a small 3 cylindar
> >1000cc motor (1987 vintage) . I can't see modern engines being
> >that much more efficient
> >
> >But I may be wrong --- again
>
> 20km/l is 56mpg in imperial gallons or 47mpg in US gallons.  
> Modern diesels which are now very popular in Europe are quite
> capable of attaining these figures and better in many cases.  
> Most small petrol (gas) engined cars struggle to get much better
> than 40-45mpg.
>
> Mike
>

58mpg for the Geo Metro/Suzi Swift/Chevy Aveo gasoline
60mpg for some of the new VW TDi diesels

The Smartcar gets 60+ mpg but the US Epa only rates it at 37.
It was originally rated at 78mpg with the TDI 3 cyl diesel and CVT.

There is a German 4 seat car set to deliver in 09 that does 150mpg
so far in testing but its also a diesel. 1.65L/100km

And of course VW Vortex 1 L was either 238 or 253 mpg depending on
where you see the numbers. That was a 1 litre diesel. That's about
0.991L per 100 km. It is so efficient that it does not have enough
excess heat and they had to put a electric heater in it.

The 1955 Messerschmitt Bubble Car (one on EBay right now) got 80mpg.

And the real special one off cars were about 350+mpg. 1 seat and not
at all practical but they could do it.

The ability to get much higher mileage has been there for a long time
the problem has been the will to do it. Wait until the US is paying about
double what they do now which is about current world price for petrol.
Then attitudes might change (maybe ;-])

Dave

2006\05\09@045512 by Michael Rigby-Jones

picon face


{Quote hidden}

Just to clarify I guess those mileages are in US gallons?  IME what the manufacturers state and what's actually achievable in real life conditions are rarely the same, especialy if you take your small engined car onto a fast motorway where you are wringing it's neck to keep up with the traffic flow...

Regards

Mike

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2006\05\09@061901 by Richard Prosser

picon face
Yeah - sorry, I only realised later that the subject refered to diesel engines
RP

On 09/05/06, Michael Rigby-Jones <spamBeGoneMichael.Rigby-JonesSTOPspamspamEraseMEbookham.com> wrote:
>
>
> >{Original Message removed}

2006\05\09@075203 by Walter Banks

picon face


Michael Rigby-Jones wrote:

> 20km/l is 56mpg in imperial gallons or 47mpg in US gallons.  Modern diesels which are now very popular in Europe are quite capable of attaining these figures and better in many cases.  Most small petrol (gas) engined cars struggle to get much better than 40-45mpg.

There is a whole bunch of new diesel injectors that have considerably higher pressures and volumes so that the diesel engines can be designed with higher compression ratio's and avoid early detonation. The result is a lot higher power for the same swept displacement
and fuel.

w..

2006\05\09@075416 by Gerhard Fiedler

picon face
Richard Prosser wrote:

> 20km/l seems very efficient. I get 15km/l out of a small 3 cylindar
> 1000cc motor (1987 vintage) . I can't see modern engines being that
> much more efficient

My father had a VW Passat Variant with a 55 kW Diesel motor and got an
average of 20 km/l. He bought that car in the 80ies. Diesel is lower in
consumption, but I know that also gasoline motors have gotten better since
then. At least in Europe, due to the high fuel prices, the economic and
marketing pressure to develop more fuel-efficient motors was and is pretty
high.

One source is manufacturer data, another for example here:
http://www.greencarcongress.com/2004/11/average_fuel_co.html

The difference in fleet averages between the US and Europe is IMO due to
the fact that the average vehicle (and engine) size in the US is bigger,
and that fuel consumption is not (or has not been) a big concern for most.
Which of course causes the manufacturers to spend their R&D money
elsewhere.

Gerhard

2006\05\09@075929 by Gerhard Fiedler

picon face
Michael Rigby-Jones wrote:

> Just to clarify I guess those mileages are in US gallons?  

Shameless plug: rather than guessing whether US gallons, Imperial gallons,
New Imperial gallons, Elbonian gallons... use liters (at least in
international settings)! There's only one of them... :)

Gerhard

2006\05\09@081825 by Michael Rigby-Jones

picon face


>-----Original Message-----
>From: KILLspampiclist-bouncesspamBeGonespammit.edu [EraseMEpiclist-bouncesspamEraseMEmit.edu]
>Sent: 09 May 2006 12:59
>To: @spam@piclist@spam@spamspam_OUTmit.edu
>Subject: Re: [ee] Basic physics... Bicycle regenerative braking forces
>
>
>Michael Rigby-Jones wrote:
>
>> Just to clarify I guess those mileages are in US gallons?
>
>Shameless plug: rather than guessing whether US gallons,
>Imperial gallons, New Imperial gallons, Elbonian gallons...
>use liters (at least in international settings)! There's only
>one of them... :)

If you specified fuel economy in terms of km/litre in the UK you would get a blank stare from most of the motoring population, MPG is by far the most commonly used units over here.  Very few people would have an idea about what is a good or bad number in those units (including me, until I converted it!).

Regards

Mike

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2006\05\09@082657 by Russell McMahon

face
flavicon
face
> What I meant was how would you control the transfer of energy into
> the spring?

Pawl and ratchet :-)
Apply brakes in bursts.
Spring is compressed and then trapped by pawl.
Debrake and start again.
May have some operational issues :-)



   RM

2006\05\09@084149 by Russell McMahon

face
flavicon
face
> The point here is that batteries can't be recharged at the levels
> that rapid braking generates.

I previously calculated that the braking rate that you specified would
require a 1/2 hour charge rate on a 40 AH battery.

You may wish to look at "AGM" (Absorbed Glass Mat) lead acid
batteries. (Google knows). These have (I read) a real world charging
capability of typically 3/4 of their rated AH value. eg a 40 Ah cell
can be charged at the 1.333 hour rate. Still not enough. But going in
the right direction.

It would be interesting to see how safe and reasonably sized a
flywheel would be that took short braking peaks and stored them just
long enough to lower the peak charging rate to something reasonable. A
heavyish braking episode may last 10 or so seconds and for battery
charging the power needs to be spread out over about 8 times that long
(C/0.5 --> C/4). There MAY also be practicable short term chemical
energy stores that would do this. eg a melted salt system with a heat
engine to transfer the energy to the battery. Not nicely efficient
alas. Carnot efficiency at 900K/600C is 66% and actual will be (well?)
under 50%. You MAY be able to do crash electrolysis to Hydrogen but
the currents seem excessive for the requisite mass and size.

Note that the model car racing fraternity crash charge their NimH in
about 15 minutes - how much life they get, not matter how well
controlled, i don't know. This is twice the rate required IF the
battery is the whole system capacity.






   Russell McMahon

2006\05\09@085129 by Dave Lag

picon face
Michael Rigby-Jones wrote:
>>
>>Shameless plug: rather than guessing whether US gallons,
>>Imperial gallons, New Imperial gallons, Elbonian gallons...
>>use liters (at least in international settings)! There's only
>>one of them... :)
>
>
> If you specified fuel economy in terms of km/litre in the UK you would get a blank stare from most of the motoring population, MPG is by far the most commonly used units over here.  Very few people would have an idea about what is a good or bad number in those units (including me, until I converted it!).
>
> Regards
>
> Mike

Our cars have one "non metric" dash setting, switching to that setting
and looking at the mpg display alway invokes a "that sucks", until I
remember it is US gallons....

D

2006\05\09@085252 by Russell McMahon

face
flavicon
face
> If you specified fuel economy in terms of km/litre in the UK you
> would get a blank stare from most of the motoring population, MPG is
> by far the most commonly used units over here.  Very few people
> would have an idea about what is a good or bad number in those units
> (including me, until I converted it!).


10 l/ 100 km =~~ 28.6 mpg.
File that away in rear memory with 25.4 (exact), 2.2 , 1.6, 0.3048,
3.28, 100000, 9.8. 32, 3.14159265358979, .4770, .3010, 0.5555 (5/9),
+/-32, 273.16, 22.4, 1.3, ...

You can also convert mpg to per acre, or the inverse of any area unit.
Or fuel economy to area.



       RM

mm/"
lbm/kg
km/mile
m/ft
ft/m
m/s/s
f/s/s
-
-
-
k/F
offset in F
K
l/gm
kg/m^3
...


2006\05\09@103819 by Harold Hallikainen

face picon face

> Michael Rigby-Jones wrote:
>
>> Just to clarify I guess those mileages are in US gallons?
>
> Shameless plug: rather than guessing whether US gallons, Imperial gallons,
> New Imperial gallons, Elbonian gallons... use liters (at least in
> international settings)! There's only one of them... :)
>
> Gerhard


Miles per litre?

Harold


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2006\05\09@120407 by Herbert Graf

flavicon
face
On Tue, 2006-05-09 at 17:10 +1200, Richard Prosser wrote:
> Gerhard,
>
> 20km/l seems very efficient. I get 15km/l out of a small 3 cylindar
> 1000cc motor (1987 vintage) . I can't see modern engines being that
> much more efficient
>
> But I may be wrong --- again
> RP

It's on the "most efficient" end of things, but achievable.

20km/l equates to 5L/100km, on the highway a Toyota Corolla will come
close to that (according to http://www.fueleconomy.gov a 2006 Corolla, stick,
will do about 5.7L/100KM on the highway). A Yaris is slightly better
(5.5) but not available in the US, so not on that site (although the
2003 Echo is, 5.5L/100km).

The smaller diesels easily hit that number (and even beat it, 2003 Golf
TDI manual gets 4.8L/100km).

Note these are standard ratings, depending on how you drive it is
possible to do better then the ratings.

Case in point, my 1988 Olds Delta 88 was rated at 8.1L/100km, but driven
correctly was able to get 7.8L/100km regularly when driving to the
cottage.

Another interesting tidbit to consider though is that modern cars are
MUCH more sensitive to the cold then older cars. My Olds didn't even
notice when it was -20C, it's fuel economy remained exactly the same.
OTOH my current car goes from 8.5L/100km in the summer to nearly
10L/100km in the winter, a dramatic difference. I thought something was
wrong with the car, but my brother has a car with the exact same drive
train and had the exact same result.

Interestingly, despite all the "warnings", I've NEVER seen air
conditioning effect my mileage at all. Now, I do drive bigger cars with
bigger engines (my Olds was a 3.8L V6, my current is a 2.5L H4). I
actually did a trial once in my Olds. I drove with the AC on, got a
mileage, drove with the AC off (and windows closed) and the mileage was
basically the same. I don't have definitive results with my current car
yet on AC usage, but so far it seems mileage is pretty much the same,
whether I use AC or not.

TTYL

2006\05\09@122005 by Michael Rigby-Jones

picon face


>-----Original Message-----
>From: spamBeGonepiclist-bouncesspamKILLspammit.edu [.....piclist-bouncesspam_OUTspammit.edu]
>Sent: 09 May 2006 17:05
>To: Microcontroller discussion list - Public.
>Subject: Re: [ee] Basic physics... Bicycle regenerative braking forces
>
>
>Interestingly, despite all the "warnings", I've NEVER seen air
>conditioning effect my mileage at all. Now, I do drive bigger
>cars with bigger engines (my Olds was a 3.8L V6, my current is
>a 2.5L H4). I actually did a trial once in my Olds. I drove
>with the AC on, got a mileage, drove with the AC off (and
>windows closed) and the mileage was basically the same. I
>don't have definitive results with my current car yet on AC
>usage, but so far it seems mileage is pretty much the same,
>whether I use AC or not.


On a large engined american car I guess the extra load of an A/C compressor is relatievly insignificant.  In Europe where smaller engine are the norm, the A/C definately affects fuel economy.  On the very small engined cars e.g. 1000cc Nissan Micra you can literaly feel the car slow when you switch the A/C on.

Regards

Mike

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2006\05\09@122840 by Harold Hallikainen

face picon face

>
> Another interesting tidbit to consider though is that modern cars are
> MUCH more sensitive to the cold then older cars. My Olds didn't even
> notice when it was -20C, it's fuel economy remained exactly the same.
> OTOH my current car goes from 8.5L/100km in the summer to nearly
> 10L/100km in the winter, a dramatic difference. I thought something was
> wrong with the car, but my brother has a car with the exact same drive
> train and had the exact same result.

Any idea why? I'd expect the engine temperature to stabalize pretty
quickly. Tire efficiency also varies with temperature, but again, I'd
expect them to warm up pretty quickly. So... what's temperature sensitive?

Speaking of tires... Has anyone seen rolling resistance ratings on tires?
How much efficiency gain could we get by using "high efficiency" tires? It
sure makes a difference on a bicycle! But maybe tire losses are much
smaller than aerodynamic losses on a car due to speeds?

Harold


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2006\05\09@124406 by Michael Rigby-Jones

picon face


{Quote hidden}

Cold air is denser, so more fuel gets injected (assuming injected engined rather than carbs), hence more power in cold weather!  However, it shouldn't make it use more fuel unless you take advantage of the extra power...

Regards

Mike

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2006\05\09@131040 by Herbert Graf

flavicon
face
On Tue, 2006-05-09 at 09:27 -0700, Harold Hallikainen wrote:
> >
> > Another interesting tidbit to consider though is that modern cars are
> > MUCH more sensitive to the cold then older cars. My Olds didn't even
> > notice when it was -20C, it's fuel economy remained exactly the same.
> > OTOH my current car goes from 8.5L/100km in the summer to nearly
> > 10L/100km in the winter, a dramatic difference. I thought something was
> > wrong with the car, but my brother has a car with the exact same drive
> > train and had the exact same result.
>
> Any idea why? I'd expect the engine temperature to stabalize pretty
> quickly. Tire efficiency also varies with temperature, but again, I'd
> expect them to warm up pretty quickly. So... what's temperature sensitive?

Nope, no clue. Using a block heater didn't seem to have any effect, so
warm up time doesn't appear to be the issue.

Considering how abrupt the change in mileage is I wouldn't be too
surprised if someone came up to me and told me the computer has a "cold
weather" profile and a "warm weather" profile, and that the cold weather
profile gives up certain things (mileage) for other uses (i.e. getting
the car warmed up quicker to prevent damage to the engine).

TTYL


2006\05\09@131235 by Herbert Graf

flavicon
face
On Tue, 2006-05-09 at 17:20 +0100, Michael Rigby-Jones wrote:
> >Interestingly, despite all the "warnings", I've NEVER seen air
> >conditioning effect my mileage at all. Now, I do drive bigger
> >cars with bigger engines (my Olds was a 3.8L V6, my current is
> >a 2.5L H4). I actually did a trial once in my Olds. I drove
> >with the AC on, got a mileage, drove with the AC off (and
> >windows closed) and the mileage was basically the same. I
> >don't have definitive results with my current car yet on AC
> >usage, but so far it seems mileage is pretty much the same,
> >whether I use AC or not.
>
>
> On a large engined american car I guess the extra load of an A/C compressor is relatievly insignificant.  In Europe where smaller engine are the norm, the A/C definately affects fuel economy.  On the very small engined cars e.g. 1000cc Nissan Micra you can literaly feel the car slow when you switch the A/C on.

Don't get me wrong, I can feel when the compressor turns on and off, I
just find it odd that even with a bigger engine the extra energy used by
the compressor doesn't appear to change the fuel mileage by any
noticeable amount.

In your experience, what drop in fuel economy do you experience when
running that AC?

Thanks, TTYL

2006\05\09@131455 by Mark Rages

face picon face
On 5/6/06, Russell McMahon <.....apptechspamRemoveMEparadise.net.nz> wrote:
> > That's what the gyros are for!  Spin them up during braking, and let
> > them
> > deplete when you kick off again, then use the descending stroke of
> > the rider
> > for sustaining energy.
> >
> > This would be quite the gizmo to watch in traffic!
>
> Yes indeed!
> You could form a one man precession.
>

Arrrgh!

But it's been done, see: http://www.thegyrobike.com

Regards,
Mark
markrages@gmail
--
You think that it is a secret, but it never has been one.
 - fortune cookie

2006\05\09@132824 by Alex Harford

face picon face
On 5/9/06, Herbert Graf <RemoveMEmailinglist2spamspamBeGonefarcite.net> wrote:
>
> Considering how abrupt the change in mileage is I wouldn't be too
> surprised if someone came up to me and told me the computer has a "cold
> weather" profile and a "warm weather" profile, and that the cold weather
> profile gives up certain things (mileage) for other uses (i.e. getting
> the car warmed up quicker to prevent damage to the engine).

Could it be the change in winter gas formulations to summer gas?

http://www.metrompg.com/posts/winter-mpg.htm

2006\05\09@133824 by Harold Hallikainen

face picon face

{Quote hidden}

I wonder if it's fuel changes? Here we have summer fuel and winter fuel.

Harold

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2006\05\09@135838 by Peter

picon face


>> Shameless plug: rather than guessing whether US gallons,
>> Imperial gallons, New Imperial gallons, Elbonian gallons...
>> use liters (at least in international settings)! There's only
>> one of them... :)
>
> If you specified fuel economy in terms of km/litre in the UK you would
> get a blank stare from most of the motoring population, MPG is by far
> the most commonly used units over here.  Very few people would have an
> idea about what is a good or bad number in those units (including me,
> until I converted it!).

Inching our way towards the metric system, are we now ? ;-)

Peter

2006\05\09@140729 by Herbert Graf

flavicon
face
On Tue, 2006-05-09 at 10:28 -0700, Alex Harford wrote:
> On 5/9/06, Herbert Graf <spamBeGonemailinglist2@spam@spamspam_OUTfarcite.net> wrote:
> >
> > Considering how abrupt the change in mileage is I wouldn't be too
> > surprised if someone came up to me and told me the computer has a "cold
> > weather" profile and a "warm weather" profile, and that the cold weather
> > profile gives up certain things (mileage) for other uses (i.e. getting
> > the car warmed up quicker to prevent damage to the engine).
>
> Could it be the change in winter gas formulations to summer gas?
>
> http://www.metrompg.com/posts/winter-mpg.htm

Hmm, never considered that. It's possible, but then, it still wouldn't
explain why my 1988 Olds and my brother's 1987 Buick (both fuel injected
with distributorless ignition systems) didn't notice ANY noticeable
change.

TTYL

2006\05\09@144847 by Michael Rigby-Jones

picon face


{Quote hidden}

Not a great deal, maybe 1-2mpg when I am normaly returning a fairly consistent 32-34mpg. (1.8L Honda Civic).  I suspect I suffer more as it's the B18 engine with the limiter at ~8500RPM which gets tested occaisionaly :D Having such a high revving engine must mean more losses from the A/C compressor (and all the other ancilliaries as well).

Regards

Mike

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2006\05\09@161408 by Howard Winter

face
flavicon
picon face
Mike,

On Tue, 9 May 2006 13:18:18 +0100, Michael Rigby-Jones wrote:

>...
> If you specified fuel economy in terms of km/litre in the UK you would get a blank stare from most of the
motoring population

Actually, I believe in Europe it's usual to give the fuel consumption as litres/100km, so it really is the
consumption, rather than the rate of use, which mpg and km/l actually are.

Cheers,


Howard Winter
St.Albans, England


2006\05\09@170835 by Howard Winter

face
flavicon
picon face
On Tue, 09 May 2006 13:13:31 -0400, Herbert Graf wrote:

>...
> Don't get me wrong, I can feel when the compressor turns on and off, I
> just find it odd that even with a bigger engine the extra energy used by
> the compressor doesn't appear to change the fuel mileage by any
> noticeable amount.

The first time I visited the 'States, in about 1992, I hired a car that had an onboard computer, cruise
control, and Aircon.  I decided to play with all three, and set it up on a flat piece of road at a constant
speed, then waited for the MPG reading to stabilise (about 33 if I remember rightly).  Then I turned on the
Aircon, and it showed a drop of 5MPG.  I repeated the experiment a few times, and it was pretty consistent.

If you think about it, you are running an extra load from the engine - it *must* use some fuel to do it!  I
don't know why your car doesn't seem to show this in practice.

Cheers,


Howard Winter
St.Albans, England


2006\05\09@173521 by Herbert Graf

flavicon
face
On Tue, 2006-05-09 at 22:08 +0100, Howard Winter wrote:
> On Tue, 09 May 2006 13:13:31 -0400, Herbert Graf wrote:
>
> >...
> > Don't get me wrong, I can feel when the compressor turns on and off, I
> > just find it odd that even with a bigger engine the extra energy used by
> > the compressor doesn't appear to change the fuel mileage by any
> > noticeable amount.
>
> The first time I visited the 'States, in about 1992, I hired a car that had an onboard computer, cruise
> control, and Aircon.  I decided to play with all three, and set it up on a flat piece of road at a constant
> speed, then waited for the MPG reading to stabilise (about 33 if I remember rightly).  Then I turned on the
> Aircon, and it showed a drop of 5MPG.  I repeated the experiment a few times, and it was pretty consistent.
>
> If you think about it, you are running an extra load from the engine - it *must* use some fuel to do it!  I
> don't know why your car doesn't seem to show this in practice.

Hmm, interesting, 5MPG equates to about 15%, a huge number IMHO. In my
case it would mean the 7.8L/100km I was seeing on my car should have
gone up to 9L/100km, a HUGE difference which I would most certainly have
been able to measure.

There is one difference I can think of, and that's duty cycle. How hot
was it when you did your experiment? Is it possible that your numbers
may be off since your AC was working so much harder?

Also, how long did you wait? An AC will run ALOT at first to get the
cabin down to a comfortable temp. If the car had climate control the
AC's duty cycle would drop after a while to maintain the set temp. For
cars without climate control the AC blasting that cold will make the
cabin MUCH colder then the occupants want, and they'll turn it down.

My only explanation as to why it doesn't seem to have made a difference
on my old car was the difference was too small to measure reliably.

TTYL

2006\05\09@192009 by Dave Lag

picon face
Herbert Graf wrote:
...my brother's 1987 Buick (both fuel injected
> with distributorless ignition systems) didn't notice ANY noticeable
> change.
>
> TTYL
>

Regal? GN?

Dave

2006\05\09@215134 by Herbert Graf

flavicon
face
On Tue, 2006-05-09 at 19:20 -0400, Dave Lag wrote:
> Herbert Graf wrote:
> ...my brother's 1987 Buick (both fuel injected
> > with distributorless ignition systems) didn't notice ANY noticeable
> > change.
> >
> > TTYL
> >
>
> Regal? GN?

Oh God I wish!

No, just a plain Park Avenue. Really advanced car for it's day. Power
everything (even antenna). Climate control, sentinel for the headlights,
great seats, a pleasure to drive.

Made it to 420 000kms, then the body bolts rusted through and we decided
it'd be better to get a new car! :)

Despite it's age and weight it's fuel economy was still as good as most
4 door sedans today.

TTYL

2006\05\09@225521 by Gerhard Fiedler

picon face
Harold Hallikainen wrote:

>>> Just to clarify I guess those mileages are in US gallons?
>>
>> Shameless plug: rather than guessing whether US gallons, Imperial gallons,
>> New Imperial gallons, Elbonian gallons... use liters (at least in
>> international settings)! There's only one of them... :)
>
> Miles per litre?

At least one can be reasonably sure that this wouldn't be nautical miles...  
OTOH, when you start to compare fuel efficiencies between boats and cars,
then even this is not a given anymore :)

Gerhard

2006\05\09@235722 by William Chops Westfield

face picon face

On May 9, 2006, at 2:08 PM, Howard Winter wrote:

> Then I turned on the A ircon, and it showed a drop of 5MPG.  I
> repeated the experiment a few times, and it was pretty consistent.

I think the usual argument goes that in hot weather you either run
the air conditioner (increasing engine load, as you say), or you
open the windows (which interferes with the aerodynamics, increases
drag, and thereby increases engine load.)  At highway speeds, the
drag issues is supposed to be bigger (drag goes up with V^2, air
conditioner extra load is a constant...)

That COULD all just be urban legend.

BillW

2006\05\10@002539 by Herbert Graf

flavicon
face
On Tue, 2006-05-09 at 20:57 -0700, William Chops Westfield wrote:
> On May 9, 2006, at 2:08 PM, Howard Winter wrote:
>
> > Then I turned on the A ircon, and it showed a drop of 5MPG.  I
> > repeated the experiment a few times, and it was pretty consistent.
>
> I think the usual argument goes that in hot weather you either run
> the air conditioner (increasing engine load, as you say), or you
> open the windows (which interferes with the aerodynamics, increases
> drag, and thereby increases engine load.)  At highway speeds, the
> drag issues is supposed to be bigger (drag goes up with V^2, air
> conditioner extra load is a constant...)
>
> That COULD all just be urban legend.

Well they did some experiments on that Mythbusters show. Unfortunately
those guys aren't always the most scientific with the way they do
things.

In my case it doesn't matter, whether the windows were open, closed, or
the AC was on our Olds and Buick always seemed to get the same highway
mileage. Now, they were pretty much bricks through air, so opening the
windows probably HELPED the aerodynamics...

Was it 50's cars that turned out to be MORE aerodynamic when going in
reverse rather then forward? :)

TTYL

2006\05\10@003755 by Jinx

face picon face
> If you think about it, you are running an extra load from the engine
> - it *must* use some fuel to do it!

Howard, remember when Jeremy Clarkson drove a diesel Audi
A8 (a V8 luxury sedan) from London to Edinburgh and back on
one tank ? The only thing he dared use was the radio. No AC, no
window open, no wipers, no lead foot, no stamping on the brakes.
And he made it, getting more than 40mpg. Leading to such fuel-
and weight-saving tips as not having a moustache !!


2006\05\10@004226 by Dave King

flavicon
face


{Quote hidden}

It's not urban legend, it's just difficult to measure more of it. There
have been a lot of testing in exactly those types of things. For a excellent
reference Look at Hoerner's Fluid Dynamic Drag and chapter 7 pages 12-5 and
12-6 shows measurements for exactly what has been discussed.

Dave

2006\05\10@005948 by Robert Rolf

picon face
>>Was it 50's cars that turned out to be MORE aerodynamic when going in
>>reverse rather then forward? :)
>>
>
> It's not urban legend, it's just difficult to measure more of it. There
> have been a lot of testing in exactly those types of things. For a excellent
> reference Look at Hoerner's Fluid Dynamic Drag and chapter 7 pages 12-5 and
> 12-6 shows measurements for exactly what has been discussed.

Dave, since most (all?) of us don't have that reference handy,
would you care to summarize and address the postulates? A/C on or off
vs windows open drag.

R


2006\05\10@113302 by Aaron

picon face
Michael Rigby-Jones wrote:

>Cold air is denser, so more fuel gets injected (assuming injected engined rather than carbs), hence more power in cold weather!  However, it shouldn't make it use more fuel unless you take advantage of the extra power...
>
>
>  
>

I was wondering about this, too.  As a boy I remember sitting on the
(diesel) tractor plowing ground.  The tractor would pull noticeably
better after the sun went down and the temperature dropped.  Of course
this was a 1968 model-year tractor; not too much in the way of
electronics on that one!

Aaron

2006\05\10@161109 by Peter

picon face

On Wed, 10 May 2006, Aaron wrote:

> I was wondering about this, too.  As a boy I remember sitting on the (diesel)
> tractor plowing ground.  The tractor would pull noticeably better after the
> sun went down and the temperature dropped.  Of course this was a 1968
> model-year tractor; not too much in the way of electronics on that one!

You would have to add that it was not turbocharged.

Peter

2006\05\10@162933 by Walter Banks

picon face


Michael Rigby-Jones wrote:

> Cold air is denser, so more fuel gets injected (assuming injected engined rather than carbs), hence more power in cold weather!  However, it shouldn't make it use more fuel unless you take advantage of the extra power...

Cold air is denser than warm air getting more oxygen into the engine. the control system will add more fuel to get efficient burning and a bigger bang. Manifold pressure is effectively higher getting more torque and horsepower for a given engine speed.

w..

2006\05\11@014759 by Dave King

flavicon
face


> >>Was it 50's cars that turned out to be MORE aerodynamic when going in
> >>reverse rather then forward? :)
> > It's not urban legend, it's just difficult to measure more of it. There
> > have been a lot of testing in exactly those types of things.
> For a excellent
> > reference Look at Hoerner's Fluid Dynamic Drag and chapter 7
> pages 12-5 and
> > 12-6 shows measurements for exactly what has been discussed.
>
> Dave, since most (all?) of us don't have that reference handy,
> would you care to summarize and address the postulates? A/C on or off
> vs windows open drag.
>
> R

Meant to post this last night but we got range clearance today on my project
and got to shoot all day. Beats freezing ur butt off in winter to get
trajectory tables.

Oook now for something completely different...

Basically the results showed that on a typical average car body opening
the windows would increase drag by 4%. To compare the side view mirror
if its one of the round types will increase the overall drag by about
3%.

Typical car has a CD of about 0.4, something slick will be down about 0.2
You can figure out how much hp it takes to go down the road at a certain
speed
with the formula HP=(CD*Q*A*(V^3)*6.8)/10^6

CD = drag coe say 0.4 to 0.2 range
Q = density of air in slugs or 0.0024
A = frontal area of the car basically the cross section area. For example a
small SUV might be 4.5 feet wide and 6 high with 1 foot of ground clearance
so the area would be 22.5 The VW Vortex was aprox 13.45.
V = speed to test at in mph. Ie if you want to see what hp it requires at
highway speeds then use 70 or whatever. The amount of power climbs quickly
from 45 on up as the air pressure builds as the cube of the speed.

The result gives a fairly accurate number to within a few percent. For
example
that VW Vortex that got over 200mpg had a 8.5hp diesel engine. And the
highest
speed they could achieve was about 75mph. CD was 0.19. If you run the
numbers
you get the hp of about 7.331. The reason for the difference is the friction
loss from gears in the tranny etc. So if they lost 5-7% the hp number is
quite close to the rated hp.

Now if you know the cd of a specific car you add or subtract the mirror or
mirrors cd number. On the VW they didn't have mirrors at all they used rear
looking cameras. So if you had a mirror on each side you would add about
0.0075
to the CD for a total of 0.1975 (about the same for opening the window).
That
requires 1/3 of a hp more (7.61 hp) or 3.8% just to go the same speed. Drag
reduction is always passive so once you have it, it is there for good ie
free hp. Using more hp to go faster instead of lowering the drag costs money
in fuel
etc.

Dave

2006\05\11@084808 by Harold Hallikainen

face picon face

> Typical car has a CD of about 0.4, something slick will be down about 0.2
> You can figure out how much hp it takes to go down the road at a certain
> speed
> with the formula HP=(CD*Q*A*(V^3)*6.8)/10^6
>
> CD = drag coe say 0.4 to 0.2 range
> Q = density of air in slugs or 0.0024
> A = frontal area of the car basically the cross section area. For example
> a
> small SUV might be 4.5 feet wide and 6 high with 1 foot of ground
> clearance
> so the area would be 22.5 The VW Vortex was aprox 13.45.
> V = speed to test at in mph. Ie if you want to see what hp it requires at
> highway speeds then use 70 or whatever. The amount of power climbs quickly
> from 45 on up as the air pressure builds as the cube of the speed.


Nice formula! Doesn't the force increase proportional to the square of
speed? I think if you double speed, the force goes up four times, AND you
cover twice as much distance in the same period of time, so the energy per
unit time is 8 times (force times distance).

In any case, the formula and typical numbers are interesting! It really
looks like the vast majority of the losses are aerodynamic. How much
improvement can we get by using "perfect tires?"

Harold

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2006\05\11@125549 by Russell McMahon

face
flavicon
face
> with the formula HP=(CD*Q*A*(V^3)*6.8)/10^6

> The amount of power climbs quickly
> from 45 on up as the air pressure builds as the cube of the speed.

Actually it's the square of the speed.
The power builds as the cube (as you note in your formula).
Energy = force x distance.
And power = Energy per time
So, power = Velocity x Force.
So, the pressure has a velocity^2 term and the extra V is to convert
the pressure to power.

It is interesting to compare that formula to my recently noted

           Drag = 0.5 x Cd x Rho x A x V^2



           RM

Also - density is in slugs/ft^3 fwiw.
We must have far smaller slugs here down under, as we could fit far
more than 0.0024 of one in a cubic foot.

2006\05\11@181441 by Jinx

face picon face
Here you can get an idea of what $/year you maybe ought
to be spending on fuel

http://www.fuelsaver.govt.nz/

And decide, like many people seem to be doing, you might
want to trade that heavy SUV in for a Honda and save 5
grand a year

2006\05\11@214528 by Gerhard Fiedler

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Russell McMahon wrote:

>> the formula HP=(CD*Q*A*(V^3)*6.8)/10^6

> It is interesting to compare that formula to my recently noted
>
>             Drag = 0.5 x Cd x Rho x A x V^2

Now where did I write down the conversion factor between lbf*mph and hp? :)

Gerhard

2006\05\12@005005 by Dave King

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> Nice formula! Doesn't the force increase proportional to the square of
> speed? I think if you double speed, the force goes up four times, AND you
> cover twice as much distance in the same period of time, so the energy per
> unit time is 8 times (force times distance).
>
> In any case, the formula and typical numbers are interesting! It really
> looks like the vast majority of the losses are aerodynamic. How much
> improvement can we get by using "perfect tires?"
>
> Harold

As Russell noted one formula is a derivative of the other. Speed costs
money, how fast do you want to go? has a whole new life when you look at
it this way. To get a good picture of what is doing what you really need
to look at the contribution to the whole. Its usually the little things
that add up to create large drag numbers. Some you can fix some you can't.
For instance the belly pan of a car is a pretty miserable place for drag.
All sorts of lumps, bumps, pipes drive shafts etc. You could cut down the
drag of any car by 35-45% just by fitting a smooth belly pan. Car makers
won't do it as no one looks under there. About the only half descent one
is the lowly VW Beatle the original one. Pusher engine so nothing under.
The only car I was ever in that could get stuck on speed bumps.

Low Mu or low resistance tires are about 20% less drag than a similar
sized normal compound tire. That would mean about 4% increase in mileage.
And the reason you don't see those on most cars is they will make the car
ride like a buckboard as the tires use higher pressure and harder rubber.

Dave

2006\05\12@015804 by William Chops Westfield

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> Nice formula!

You have to be careful with this (typical) formula that you measure
the relevant "area" the same way that the people who determined the
the drag coefficient did.  The rocketry folk usually doom themselves
into having to specify drag coefficients of close to 1 to get the
predictions of simulations to match measured reality, and that's
with pointy, streamlined, rocket-shaped things.  They shake their
heads at the drag coefficients quote for cars (0.4!), concluding
that the car people must be measuring things differently than they
are.  Perhaps the area used is the total surface area of the car,
rather than just the frontal area.  I don't know that the question
has ever been settled for sure.

BillW

2006\05\12@043642 by Dave King

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This one was based on simple frontal exposed area. Airplanes, missiles
etc use wetted area and then the cd to get the equivalent flat plate area.
Missiles and airplanes are quite a bit more elaborate to derive the efp.
Different shaped nose cones have different cd's then you have skin
effects from tube bodies, after body and wake effects plus anything
that sticks out like fins. And of course this all changes when the
motor is off. Unlike missiles which some people tend to frown upon
being live tested, you can easily find the drag of any vehicle by
doing coast down tests to verify the numbers.

Dave

{Quote hidden}

> --

2006\05\12@045757 by Michael Rigby-Jones

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{Quote hidden}

Quite a few cars do have smooth undersides, or at least smooth panels to cover over the lumpy bits.  My MR2 has numerous plastic panels held on by a frustrating amount of M6 bolts so the whole underside of the car is pretty flat.  Even boring family saloons now have a plastic cover that fits underneath the engine bay which is where a good deal of turbulence occurs.

Regards

Mike


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2006\05\12@085741 by Russell McMahon

face
flavicon
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> with the formula HP=(CD*Q*A*(V^3)*6.8)/10^6
>
> CD = drag coe say 0.4 to 0.2 range
> Q = density of air in slugs or 0.0024
> A = frontal area of the car basically the cross section area. For
> example a
> small SUV might be 4.5 feet wide and 6 high with 1 foot of ground
> clearance
> so the area would be 22.5 The VW Vortex was aprox 13.45.
> V = speed to test at in mph. Ie if you want to see what hp it
> requires at
> highway speeds then use 70 or whatever. The amount of power climbs
> quickly
> from 45 on up as the air pressure builds as the cube of the speed.

Note that this is based on exactly the same formula that I mentioned
recently for drag of a body. The only difference is a different
constant due to weird UK units (snails cousins) AND an extra velocity
term to turn drag into power. ie Power = Drag x Velocity.

My formula was Drag = 0.5 x Cd x Rho x A x V^2

Rho = air density = 1.3 kg/M^3
A = frontal area in metres
V = velocity i metres/second
Drag = drag force in Newtons (eg Kg x g ~~= 10 x kg).
Cd = coefficient of drag = improvement relative to a flat plate.

So

STARTER FOR 10 POINTS

Give an flat plate object with Cd = 1.
Intuitively derive the above formula.
A word description would suffice, probably with a few simple formulae.
Once you realise that this is totally intuitive it does marvels for
seeing places that it can be used.
No Reynolds numbers and the like here. Just intuitive common sense and
a few basic formulae.

It works "well enough" for raindrops, skydivers tucked in or spread
out, parachutes, falling field mice, cars and more.



       Russell McMahon




2006\05\12@091246 by Russell McMahon

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flavicon
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James especially.

Stepped out of a shop today and aw a VW "trike" filling at a local gas
station. Light bulb moment. This may be the semi ideal starting point
for an innovative design.

It was fairly long with low raked frorks.
He said it weighed 200 kg all up.
Engine would be a fair bit of this.

Conversion to electric of such things would be reasonably trivial. And
they are common enough that price should be moderated by market
forces. He said his (a pretty one) was worth $NZ10,000 I think.

   Here's another
http://www.trademe.co.nz/Trade-Me-Motors/Motorbikes/Motorbikes/Other/auction-56181436.htm

The tyres and wheels could be thinned right down. Buy as light weight
a version as possible. Registration (if they are legal in US) is
already taken care of.

Lots of weight could be shaved off these.

AND you could adapt for pedal power and drive an alternator directly
rather than having chain drive. Some losses of course, but same with
chains. Batteries can be hung at various low points. Body work can  be
added - and a roof/solar panel or two.

Weight distributin could be made far better than for original trike if
desired.

Worth a thought.


               Russell McMahon

2006\05\12@104006 by Harold Hallikainen

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>
> My formula was Drag = 0.5 x Cd x Rho x A x V^2
>
> Rho = air density = 1.3 kg/M^3
> A = frontal area in metres
> V = velocity i metres/second
> Drag = drag force in Newtons (eg Kg x g ~~= 10 x kg).
> Cd = coefficient of drag = improvement relative to a flat plate.
>


Nice simple formula! We could, of course, apply it backwards and develop
the force on an object due to wind speed, then try to get energy out of
the wind. If we let the "sail" go the same speed as the wind, force drops
to zero, so we get no power (energy per unit time). So, what's the
"maximum power point?" What fraction of wind speed should a sail be moving
to recover the most power?

Harold


--
FCC Rules Updated Daily at http://www.hallikainen.com - Advertise on
hallikainen.com - $100/year!

2006\05\12@110355 by olin piclist

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Harold Hallikainen wrote:
> So, what's the "maximum power point?"

I figured that out and showed the derivation a month or two ago when we were
talking about wind tubines.

> What fraction of wind speed should a sail be
> moving to recover the most power?

1/3 when moving directly downwind.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\05\12@114211 by Harold Hallikainen

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> Harold Hallikainen wrote:
>> So, what's the "maximum power point?"
>
> I figured that out and showed the derivation a month or two ago when we
> were
> talking about wind tubines.
>
>> What fraction of wind speed should a sail be
>> moving to recover the most power?
>
> 1/3 when moving directly downwind.
>
>
> ******************************************************************
> Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
> consultant in 2004 program year.  http://www.embedinc.com/products


Thanks! Sorry I missed that thread!

Harold


--
FCC Rules Updated Daily at http://www.hallikainen.com - Advertise on
hallikainen.com - $100/year!

2006\05\12@125917 by Peter

picon face


On Thu, 11 May 2006, Gerhard Fiedler wrote:

> Russell McMahon wrote:
>
>>> the formula HP=(CD*Q*A*(V^3)*6.8)/10^6
>
>> It is interesting to compare that formula to my recently noted
>>
>>             Drag = 0.5 x Cd x Rho x A x V^2
>
> Now where did I write down the conversion factor between lbf*mph and hp? :)

plp@plp:~$ units
1378 units, 57 prefixes

You have: lbf*mph
You want: hp
        * 0.0026666667
        / 375

Peter

2006\05\12@160022 by James Newtons Massmind

face picon face
As I mentioned offlist, the main issue with these is how to enclose them.
And that is not only for comfort, a significant loss in efficiency comes
from drag, at least at any reasonable speed.

Same problem with most motorcycles and bikes: It's hard to find any that
have a faring for smooth movement through the air.

Didik simply ads a very thin curved sheet of plexy over a PVC tube upper
frame.
http://www.didik.com/dturtle.htm but it is hard (for me) to see how that
could be applied to most trikes or 'cycles.

---
James.



> {Original Message removed}

2006\05\12@223350 by Tony Smith

picon face
> Here you can get an idea of what $/year you maybe ought
> to be spending on fuel
>
> http://www.fuelsaver.govt.nz/
>
> And decide, like many people seem to be doing, you might
> want to trade that heavy SUV in for a Honda and save 5
> grand a year


When you said Honda, I thought you meant this:
www.mcnews.com.au/Wallpaper/Honda/CBR600/2003/2003_winner_1024.jp
g, or even this:
http://www.postiebikechallenge.org/graphics/bike_lge.gif (red ones go
faster).

Interesting if they did add bikes to their page.  'Riding style' would
have two options
1: Open throttle as fast as possible, wait until revs hit redline,
change gears & repeat, or
2: No, I don't do that.

You'd save more than 5k too.

There's always the bus.

Tony

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