Ahh thanks! Super helpful illustrations. On Wednesday, September 28, 2016 at 3:08:14 PM UTC-4, Peter White wrote: > > Actually, shorting the terminals will do no damage at all, at least not to > any Schmidt hub. And I doubt it would damage any other dynamo hub. It's > nothing to worry about. > > Also, the drag the OP noticed with the bike upside-down is real, but the > effect is exaggerated if there's little or no mass being moved, as is the > case with the bike upside-down. With the rider on the bike, the rider's > mass acts as a buffer to the effect of the drag. Inside a SON 28 there are > 26 magnets attached to the inside of the outer hub shell, between the spoke > flanges. They are, in a sense, trying to keep the hub from rotating. As the > hub does rotate, there are 26 points during each rotation of the wheel > where the magnets are trying to keep the hub from rotating, and they > alternate with another 26 points where the hub wants to rotate. As the hub > rotates a bit in one direction or the other, the magnets are trying to > bring the hub shell back to its earlier position. It's like riding down a > road that goes up and down, up and down. Gravity tries to keep you in one > of the low points on the road. So imagine that the road is essentially > level over a long distance, but undulates up and down every 20 feet or so. > From the top of each rise, you speed up just a bit for 20 feet until you > get to the bottom, and then you slow down for 20 feet. This repeats over > and over. The rider's mass is momentum, and the heavier the rider, the less > he will speed up on those 20 foot down sections, and the less he will slow > down on the 20 foot up sections. Over a long distance, there's hardly any > difference in your average speed. > > So, when you're riding a bike with a dynamo hub, with each revolution of > the hub, you slow down and speed up 26 times, but since you have a great > deal more mass at the rim rotating with you riding than with the bike > upside-down, the effect, the amount that the wheel's speed actually changes > 26 times per revolution, is tiny. Flip the bike upside-down and spin the > wheel, you can easily see the speed changing. > > In both scenarios, rider on the bike and rider off, the actual drag is the > same. And with the lights off, it's equivalent to the added work you do > climbing 1 foot of elevation every mile you ride. And it's about 5 times > that with the lights on. Can you tell the difference if you're riding a > road that's perfectly level, or if it's gaining 5 feet in elevation every > mile you ride? > > I didn't think so. ;-) > > On Wed, Sep 28, 2016 at 12:32 PM, Eric Norris <campyo...@me.com > <javascript:>> wrote: > >> I would check with Peter White, but my guess is that shorting the >> terminals on hub would be very, very bad for the hub. >> >> I ride with dyno hubs on several bikes. With modern hubs and LED lights, >> the drag is negligible. Turning the lights off reduces the drag even more, >> but I like to have them on as running lights for better visibility. >> >> --Eric N > > > > -- > Peter White >
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