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aostling
12-15-2009, 09:16 AM
MIT has developed a high-tech hub for a bicycle which could be useful for pedaling around cities with hills, like Seattle. San Francisco would probably be too steep for it, though.

From http://www.nytimes.com/2009/12/15/science/earth/15bike.html?_r=1&ref=science

http://i168.photobucket.com/albums/u183/aostling/Screenshot2009-12-15at70937AM.png

Evan
12-15-2009, 09:42 AM
It entirely fails to address the fact that current battery designs cannot capture more than about 10 to 15 percent of the energy available from regenerative braking. That's a nice little extra to add range to a conventional design but this design is depending on it as the sole energy input. It means that if you go down a 1 kilometre hill you will have assistance coming back up for maybe 100 metres and the other 900 you have extra dead weight.

Hill climbing is the absolute harshest test of an electric vehicle. It where the old horspower formula comes into play full force. One horsepower equals lifting 16.5 tons 1 foot in one minute. Climb a hill in an EV and you will very quickly discover what the real output of the system is.

A.K. Boomer
12-15-2009, 09:44 AM
It does look good and heavy so all that extra weight will aid in re-charging the batteries so it can then help power the motor to carry all that extra weight back up the hills, if its not enough they can always add cement blocks I suppose:rolleyes: (as long as both motor/generator-batteries are 100% efficient right?)

I just had a terrible thought, what happens if its a really long hill and it sucks the life out of the batteries? Hopefully the "bike" doesn't have any pedals on it and you can just abandon it;) (believe me - if your already having trouble with getting just your fat ass up a hill enough to consider buying a piece of crap like this then your really not going to like what happens when you "run out of juice")

Another quick observation, You carry cement blocks down hill and turn them in to a cement block facility --- then you climb hills really fast with a full charge and without the extra weight, once at the top you pick up more cement blocks for the next descent --- a kinda perpetual motion machine if you will, cement blocks are then transported back up the hills either telepathically or by cheap immigrant labor...

barts
12-15-2009, 11:12 AM
Hills are tough - but since I live in the flats, what about stop signs? I wonder if you could capture enough energy in a mass of surgical rubber tubing inside a aluminum tube...

- Bart

precisionmetal
12-15-2009, 11:25 AM
Wouldn't a super-capacitor be more efficient at capturing the electrical energy? (and lighter as well?)

Doozer
12-15-2009, 11:26 AM
"I wonder if you could capture enough energy in a mass of surgical rubber tubing inside a aluminum tube..."

I like that idea a lot!

--Doozer

aostling
12-15-2009, 11:39 AM
Hills are tough - but since I live in the flats, what about stop signs? I wonder if you could capture enough energy in a mass of surgical rubber tubing inside a aluminum tube...
- Bart

Menlo Park is my old stomping grounds too, so I know how flat it is. The stored energy per unit volume in a deformed elastic material is half the product of Young's modulus and the square of the strain. If we take the strain as 6, and the modulus as 500 psi, the energy stored is 9000 in-lb/in3, or 750 ft-lb per cubic inch of the surgical tubing. That might get you back from a few beers at Zott's.

barts
12-15-2009, 12:22 PM
Menlo Park is my old stomping grounds too, so I know how flat it is. The stored energy per unit volume in a deformed elastic material is half the product of Young's modulus and the square of the strain. If we take the strain as 6, and the modulus as 500 psi, the energy stored is 9000 in-lb/in3, or 750 ft-lb per cubic inch of the surgical tubing. That might get you back from a few beers at Zott's.

Heh - I pass by there when cycling the loop around Portola Valley... those are all flats compared to climbing up to Skyline :)

Perhaps 4 passes of 1/2" x 1/8" spear gun tubing inside a 2' x 2" aluminum cylinder... could use a couple of bevel gears to get the reversing & right angle drive needed... about 18 in3... way more than enough if the numbers are right as that's about 24 hp-seconds - enough to easily lift me and the bike 50' into the air, or accelerate the same to about 40 mph. Hmmmmm.

Hills are tough, but anyone who's ridden a bike knows that.

- Bart

Evan
12-15-2009, 01:17 PM
Super capacitors still have very poor energy density compared to batteries. While they can charge at almost any rate the charge and discharge characteristics are terrible. They require both boost and buck conversion at full current to change the charge/discharge curve to something more like a battery to give approximately equal performance throughout the discharge cycle. The main problem though is the physical size still. This will undoubtedly improve as there are no fundamental constraints standing in the way as yet.

One of the more important problems with any EV power source is the control of the actual output and ensuring that the storage device doesn't turn into a bomb. Further, it is imperative that it cannot be intentionally made into a bomb. The higher the energy density and the greater the designed delivery rate the more difficult preventing destructive misuse becomes.

dp
12-15-2009, 01:27 PM
I was wondering about supercaps too, but only to catch the charge efficiently for the purpose of topping off the battery. In a symmetric up/down profile it probably won't work well but if the runout at the bottom of a hill allows for some time, the supercap can leisurely charge the battery.

I think calling it a brake is probably a reach, though, as the charging system is not likely to be able to convert all the energy well enough to keep your speed reasonable.

Evan
12-15-2009, 01:40 PM
It works very well as a brake for regulating speed downhill as I have found in my experimentation over the last two years. The main problem is dissipating the excess heat since only a fraction of it is going back into the batteries. As soon as weather permits next year I will be resuming my hybrid trike project.

MCS
12-15-2009, 01:42 PM
As I told before, we have a lot of bicycles with auxiliary electromotors in Holland. Auxiliary meaning that the pedal force is measured and proportionally supported by the electromotor.

I went on the bicycle this afternoon.

It was freezing, one brake cable was frozen solid, one half.

With slightly reduced speed, and half a foot as a brake I went thinking about this article, knowing Energy = Mass * Speed^2.

On a bicycle the result is near nothing, meaning with more gear to regenerate near nothing the result is below nothing.

On this level less is more.

As if you can use butterflys to drive windmills.

dp
12-15-2009, 01:47 PM
It works very well as a brake for regulating speed downhill as I have found in my experimentation over the last two years. The main problem is dissipating the excess heat since only a fraction of it is going back into the batteries. As soon as weather permits next year I will be resuming my hybrid trike project.

It's the excess I was thinking about - a charged battery isn't going to offer much of a load, so depending too much on electrical braking without a waste gate load is probably going to lead to road rash :)

camdigger
12-15-2009, 02:38 PM
Don't most electrical generating/regen systems dump current to a resistor bank to absorb energy when the battery is fully charged?

I hear that's the way the latest generation of hoisting equipment works.

The older systems were strictly eddy current brakes. There was no attempt to capture any portion of the energy absorbed. The discs of the eddy current brakes were water cooled. The heat was dissipated into the water system.

Carld
12-15-2009, 02:56 PM
I guess you could put several large automotive batteries on the bike to take the charge and use the charge motor to power the bike. You could make the regenerative motor power the bike and when your moving the pedals forward the motor runs the bike and when you start to use the hand brakes or the pedals to brake the regen motor would help stop the bike.

I mean, hell, as long as we're dreaming why not dream big. :rolleyes:

aostling
12-15-2009, 03:22 PM
With slightly reduced speed, and half a foot as a brake I went thinking about this article, knowing Energy = Mass * Speed^2.


That's true in Holland, and you are right, the kinetic energy is hardly significant. Energy storage for a bicycle becomes desirable in hilly country, where the potential energy of elevation can be stored during descent, for re-use going back up hills.

MCS
12-15-2009, 04:31 PM
That's true in Holland, and you are right, the kinetic energy is hardly significant. Energy storage for a bicycle becomes desirable in hilly country, where the potential energy of elevation can be stored during descent, for re-use going back up hills.

You are right, but the article states:

"The Senseable City Laboratory at M.I.T. has designed a wheel that captures the kinetic energy released when a rider brakes and saves it for when the rider needs a boost. While technically sound, the wheel’s true challenge may be in winning over cyclists. For centuries, bikes have been beloved for their simplicity, not their bells and whistles. "

A bit like a F1 boost system, which is several quadruples removed from a bicycle, just by the formula energy = mass * speed^2.


Hill-down and hill-up is a different league, where the solution here is in high efficiency motors, not in high energy, fast charging battery loaders.

Already mentioned here, half up the hill is not an option.