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  1. #1
    Senior Member astronomerroyal's Avatar
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    Hub generator in a 16" wheel. Would it work?

    I recently built a bicycle trailer for touring etc. It has two 16" wheels. I was toying with the idea of using a hub generator for power. On my previous trailers I used an old-fashioned sidewall 12v generator. That was merely okay, but good enough to make me think about taking power generation more seriously.

    Q1). So, does a hub generator exist for 16" wheels? Excluding the unaffordable Schmidts.

    Q2). Would a regular hub gen. work safely and endure in a 16" wheel? I don't cycle very fast (i.e >20mph) with my trailer and that fact somewhat mitigates the typically higher r.p.m of a 16" relative to 26"/700c wheel.

    Q3). I have wheel building equipment, so is there likely to be any terrible issue with building a 16" wheel around, say, a Shimano Nexus hub, given its large flange diameter? Awkward spoke lengths/angles? User rhm seems to have done this (and often gets ~15v using his/her 16" wheel!)
    Shimano Hub Generator...

    miniQ4). The meagre 1page tech docs on Shimano's Nexus generator site state that 'very high voltages are generated inside the generator.' Surely that's a gross exaggeration. Shimano's is nominally a 6v generator, and even without voltage regulation the V won't go sky-high, surely. I guess they're not rectified either.

    I just found
    http://osdir.com/ml/culture.bicycle..../msg00010.html

    which seems to suggest the Shimano NX 30 (the same a rhm's) is essentially unusable in a 16" wheel. Contradictory opinions. But then we also have
    http://phred.org/~alex/bikes/rocket.html
    who used this hub on a recumbent without any apparent complaints...

    Many thanks in advance, and apologies if this has been covered thoroughly elsewhere on this site.

    Astronomer Royal.
    Last edited by astronomerroyal; 11-03-08 at 07:35 PM. Reason: added content.

  2. #2
    Senior Member
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    Your best bet, assuming you don't want the schmidt, is to track down a Dahon Biologic hub and lace it radial.
    Internal Gear Hub Guru
    Currently owned hubs: Sachs Pentasport, SRAM P5 Drum, Sturmey SRF5-W , Sturmey XRD3
    Previously owned hubs: Shimano Nexus 8 speed, Sturmey AW 3 speed, Shimano 3 speed coaster, SRAM S7 Drum, Sturmey XRF8 8 speed
    Tested hubs: SRAM i-Motion 9 speed, Sturmey XRD5

  3. #3
    Senior Member astronomerroyal's Avatar
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    Ah, thanks. I'll probably see what I can get my hands on. I've not encountered anyone with actual experience complaining about the combination - seems to be worth a shot. Can always use it in a 26" wheel if the original idea fails.

  4. #4
    Senior Member iamstuffed's Avatar
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    You may want to ask this question in the folding bikes forum, since a lot of folding bikes have 16" wheels and I'm quite sure there are others who have tried what you'd like to do.

  5. #5
    Je pose, donc je suis.
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    1. I don't think so.

    2. The generator will work fine. All you really risk is over-volting your lighting. You can always put a voltage regulator in, if you want. But if you're not going that fast, I wouldn't worry about it.

    3. Just build the wheel 1X or radial. I'd go 1X since I'm a purist and there is a small amount of torque on the hub, but many would laugh at my rationale.

    4. The Shimano hub is not rectified. I have a fairly rudimentary model of a Shimano Nexus hub (3n71) as a simple LR circuit. Link in a moment (it's on another computer).

    Quote Originally Posted by astronomerroyal View Post
    I recently built a bicycle trailer for touring etc. It has two 16" wheels. I was toying with the idea of using a hub generator for power. On my previous trailers I used an old-fashioned sidewall 12v generator. That was merely okay, but good enough to make me think about taking power generation more seriously.

    Q1). So, does a hub generator exist for 16" wheels? Excluding the unaffordable Schmidts.

    Q2). Would a regular hub gen. work safely and endure in a 16" wheel? I don't cycle very fast (i.e >20mph) with my trailer and that fact somewhat mitigates the typically higher r.p.m of a 16" relative to 26"/700c wheel.

    Q3). I have wheel building equipment, so is there likely to be any terrible issue with building a 16" wheel around, say, a Shimano Nexus hub, given its large flange diameter? Awkward spoke lengths/angles? User rhm seems to have done this (and often gets ~15v using his/her 16" wheel!)
    Shimano Hub Generator...

    miniQ4). The meagre 1page tech docs on Shimano's Nexus generator site state that 'very high voltages are generated inside the generator.' Surely that's a gross exaggeration. Shimano's is nominally a 6v generator, and even without voltage regulation the V won't go sky-high, surely. I guess they're not rectified either.

    I just found
    http://osdir.com/ml/culture.bicycle..../msg00010.html

    which seems to suggest the Shimano NX 30 (the same a rhm's) is essentially unusable in a 16" wheel. Contradictory opinions. But then we also have
    http://phred.org/~alex/bikes/rocket.html
    who used this hub on a recumbent without any apparent complaints...

    Many thanks in advance, and apologies if this has been covered thoroughly elsewhere on this site.

    Astronomer Royal.

  6. #6
    Je pose, donc je suis.
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    Quote Originally Posted by Pedaleur View Post
    4. The Shimano hub is not rectified. I have a fairly rudimentary model of a Shimano Nexus hub (3n71) as a simple LR circuit. Link in a moment (it's on another computer).
    Here is a problem I posed to my math class:

    http://www.mip.sdu.dk/~glewin/cyklin.../generator.pdf

    In it, I provide a simple model of a generator hub/resistive load.

    Note: the original model was blantantly stolen from here:

    http://www.jim-easterbrook.me.uk/cyc...o_limiter.html

    but the numbers are actual measurement from my Shimano 3N71 hub (with reasonable accuracy).

    omega is the angular frequency of voltage. Note that there are 28 poles in the hub, so omega is:

    omega=2pi * 28 * <wheel rotations per second>

    The solution is left as an exercise for the student...

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