3 ms·

Your comments about the gear size, etc. are interesting, but I don't see how they're strictly necessary. Can you explain? For example, can't an arbitrarily sm

by diydsp 3y ago

Your comments about the gear size, etc. are interesting, but I don't see how they're strictly necessary. Can you explain? For example, can't an arbitrarily small gear work as long as the force contributing to the torque is sufficient? And isn't the force a product of the driving force (human leg/crank) and the load on the generator? And we can't see the load on the generator, so there may well be step-up gearing and high-flux motor inside the housing? BTW, I respect your project at https://omattos.com/2022/06/19/gym-power.html https://omattos.com/2022/06/19/gym-power.html I have also worked with human-powered generators (https://www.youtube.com/watch?v=huYJa2Du57g https://www.youtube.com/watch?v=huYJa2Du57g) and made a quick feasibility spreadsheet on the MyPowerbank at: https://docs.google.com/spreadsheets/d/1X39ZgL86tmemdYv0r1JgtGTdIVM-mfuOdOGXDTTsczI/edit?usp=sharing https://docs.google.com/spreadsheets/d/1X39ZgL86tmemdYv0r1Jg... From my spreadsheet, this project looks plausible, but please feel free to add comments to it as you see fit. My spreadsheet's calcs indicate an average power of about 25 Watts to reach the 25 minute charging time claim. Note that average humans can easily sustain 100 Watts. I have assumed an iPhone 12 battery as that's the first that came up when I searched: https://www.google.com/search?client=firefox-b-1-d&q=ihpone+battery+capacity https://www.google.com/search?client=firefox-b-1-d&q=ihpone+... As far as the shaking chain, note also that the device base is shaking so we can not directly infer the cog idler pulley-cum-prime-mover is not also moving. In my experience with human-powered generators, the real obstacle was getting people to relax and focus and do nothing for longer than 2 minutes.

londons_explore 3y ago
> gear size, etc. are interesting, but I don't see how they're strictly necessary. Can you explain? Simple: The chain won't grip the gear. Gears must be designed such that the chain never intersects the gear (two things can't be in the same place at the same time). That precludes 'hooks' on the teeth of the gear, and means that the face of the gear tooth must be perpendicular to the chain link. However, that means that at any other angle, the angle of the tooth is providing a small component in a direction that pushes the chain off the tooth. When your chain is contacting many teeth, this force gets smaller by 1-cos(angle between teeth) per tooth - so after about 6 teeth or so, the force is so tiny as to be irrelevant. However, in OP's design there is minimal tension and only 1 tooth touching at a time, so the chain will jump off the teeth. There is a huge and very old field of chain and sprocket design, the details of which I am not very familiar, but I do know the basic rules of "some non-zero tension", "bigger subtended angle=better" and "engage as many teeth as possible". (other interesting chain facts: the invention of the bicycle was enabled by the invention of sufficiently good chains. chains are better lubricated by grease not oil. chain wear gets exponentially worse, not linearly. centripetal force limits fast moving chains. )

by diydsp 3y ago

londons_explore 3y ago

> gear size, etc. are interesting, but I don't see how they're strictly necessary. Can you explain? Simple: The chain won't grip the gear. Gears must be designed such that the chain never intersects the gear (two things can't be in the same place at the same time). That precludes 'hooks' on the teeth of the gear, and means that the face of the gear tooth must be perpendicular to the chain link. However, that means that at any other angle, the angle of the tooth is providing a small component in a direction that pushes the chain off the tooth. When your chain is contacting many teeth, this force gets smaller by 1-cos(angle between teeth) per tooth - so after about 6 teeth or so, the force is so tiny as to be irrelevant. However, in OP's design there is minimal tension and only 1 tooth touching at a time, so the chain will jump off the teeth. There is a huge and very old field of chain and sprocket design, the details of which I am not very familiar, but I do know the basic rules of "some non-zero tension", "bigger subtended angle=better" and "engage as many teeth as possible". (other interesting chain facts: the invention of the bicycle was enabled by the invention of sufficiently good chains. chains are better lubricated by grease not oil. chain wear gets exponentially worse, not linearly. centripetal force limits fast moving chains. )