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Comment by EdSchouten | Hacker News Reader

What’s the advantage of using those bicycles, as opposed to just having a crank on it? Pedaling a bicycle backwards isn’t really ergonomic.

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Regular humans can put out ~100 watts on a dual foot crank (like a bicycle) for hours. Since a phone battery is ~12 Watt-hours, you can collect energy for a full phone charge in ~10 mins (but you'll need a special buffer battery, since few lithium cells can charge that fast).

Yet on a single hand crank, even 20 watts and you'll get tired pretty quick.

Part of that is that leg muscles are bigger. Part of it is that you're used to walking or standing for long periods of time. Part of it is that with a dual crank you aren't putting useless effort into holding the device up and holding the weight of your own arms up.

End result: Hand cranks are useless unless you only need tiny amounts of energy out of a human.

It looks like the device even includes a little battery; I wonder if it holds enough charge to charge a phone battery fully, or if it just needs to be active charged for a while.

This is definitely more about the message, but actually, if a person could pedal pretty hard for like a half hour and get a couple charges out of it, that doesn’t see too impractical (ignoring the obvious objections, like usually coffee shops will let you get a little charge).

It could be a nice camping accessory. I bet a product already exists.

Such a product does already exist (with a hand crank).

The buffer battery is needed because phones generally don't like having variable voltage/current to charge from. They normally choose what speed they wish to charge at (depending on charger type), and if they can't draw their desired current and the voltage drops then they stop charging entirely.

Also, humans generally expect a crank to have constant torque. Whereas if you wanted constant charge power, then the faster you crank the easier it gets, and conversely the slower you go the stiffer it gets, which is very unintuitive.

By using a buffer battery, you can solve both problems. And users can choose to crank faster to charge the buffer quicker, which is what humans expect.

I don't doubt you can generate ~100 watts cycling forward for hours. But the approach this system uses is that you need to cycle backwards. As far as I know, that's pretty annoying way to move your legs.

This is an art/design project by an undergraduate student - not necessarily a serious product. But I wonder if cycling backwards is still easier than using a hand crank

Using a hand crank for 30 minutes? Nah... pedaling will definitely be easier.

That's actually what I meant.

I made a bidirectional pedalling exercise bike. Turns out there isn't much difference between forwards and backwards, but you do need to adjust the seat back by about 6 inches if you want maximal power output for backwards pedalling.

Bicycles are among the most efficient energy conversion systems human-kind has ever invented .. the difference between a single lever (which, after all, is still an option with the existing design) and a bicycle lever/gear system, means all the difference in the world when the calories are, already, a regular daily concern for the target user.

Plus, it gives the bikes utility when they're not being rented, since the rental bays often take up space in areas accessible to the homeless, its also quite convenient for the target users.

This doesn't use the gear system though. (aside from the large front sprocket driving the smaller one on the device)

I'm quite surprised it can be built for £3, unless the battery is incredibly small.

I believe there is also a social element to this, as it is rather an unfortunately overlooked detail that bike-rental bays are often installed by businesses throughout metropolitan regions as a means of discouraging the homeless, who cannot afford to use these devices, which storage after all consumes public space .. giving the homeless a way to extract value from things is, in my opinion, an admirably placed bit of design altruism, and I, for one, hope to see many more examples of this kind of thinking.

I have often wondered what sort of conversion it would take to use an AK47 and a box of ammo to drill a well/pump water, instead of suppress human beings.. transformative technology is highly interesting, don't you agree?

>I'm quite surprised it can be built for £3, unless the battery is incredibly small.

Herein lies the rub - can the homeless build these things for £1 a piece, somewhere in London?

Because if the answer is more oil-based traffic across the worlds oceans to get these things made, I'm afraid the irony of the builder/user distinction is rather unfortunate...

That cost would be at a volume no one would ever produce this at.

Well, the volume could possibly exist if it weren't limited to one city, or one model of bike.

No, it couldn’t. This is all very dumb, it’s a fantasy product with no effective use targeting a population that didn’t ask or want it, done so that everyone can say it’s great which makes them feel like they are good people.

Yes the specific object is dumb, both because it's design has holes, and because there are better ways to get it's ultimate function.

But the market for something like that is not limited to the exact specific population of homeless in London. A thing like that could be produced in the volume necessary to get economy of scale, simply by not being limited to one city and a single particular model of bike, or even limited to the homeless for that matter.

If you don't understand that, then you are in a poor position from which to call anyone else dumb.

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