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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 f

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.

bee_rider 3y ago
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.
- londons_explore 3y ago
  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.
EdSchouten 3y ago
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.

bee_rider 3y ago

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.

londons_explore 3y ago
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.

EdSchouten 3y ago

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.