Yet Another Cycling Forum
General Category => Freewheeling => Topic started by: cygnet on 26 March, 2018, 05:52:24 pm
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Just idly wondering is the hub dynamo so much better than a bottle that there is no scope for disc wheels and bottles?
My thoughts ran like this
Hubs:
Always 'on' (even if the drag is low)
Needs to be disconnected if you need to remove the wheel
Bottles:
Suffer in the wet because the track is the braking surface which obviously is smooth
Some types which used a special tyre, with a ridged track which limits your tyre choice
But with a disc brake there is potential for a permanent rim track, so overcome the wet problem, any tyre can be used, it can be 'turned off' by moving away from the rim and doesn't need disconnecting.
Does such a thing solve a problem that no longer exists?
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Some dynamos run on the rim, rather than the tyre.
http://www.velogical-engineering.com/velogical-rim-dynamo---standard-bicycle-dynamo---smooth-running-lightweight-efficient
Ignore this following statement as I completely misunderstood your comments. Running on the disc would reduce the rate the dynamo turns, which would probably require more mass to get the same output. A hot disc would tend to degrade any rubber/ elastomer drive wheel for a dynamo.
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What you are referring to is basically a spoke dynamo. I have two types:
One which can be disconnected by moving a lever away from the spokes but this model is no more efficient than a bottle although it has no slippage issues. Aufa FER2002 (http://blog.lolyco.com/sean/2013/12/19/spoke-dynamo-speichendynamo-farewell-old-friend/) No longer available.
The other is permanently fixed to the rear hub and produces power all the time. This is not an issue as it is as efficient as a hub dynamo (if not more so) and much smoother. Sunup Eco EcoDyn (http://www.intelligentdesigncycles.com/shop/hub-and-spoke-dynamos/sunup-eco-spoke-dynamo/sunup-eco-ds-1r-spoke-dynamo.html)
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A rim with a special track would limit you to that one rim. Not quite as limiting as being restricted to one particular tyre, since you wouldn't need to replace it, but nevertheless a restriction. And most of all, it would require that special rim to be made! Plus, it's not really a problem that needs solving; the drag from a dynamo hub is so small you won't notice it while riding and disconnection is easy enough, very easy with a lego-block connector as used by SP and Shimano.
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Yes, I was imagining the generator at the rim, not the disc itself or near the hub. Like the look of that sunup though, and the velogical one is probably what I was imagining without needing changes to the rim.
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There are also those eddy-current dynamos that use the rim without physical contact. Doesn't need a special rim, but does need some fairly tight clearances.