Dynamos - Hub or Bottle?

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Re: Dynamos - Hub or Bottle?

Postby andrew_s » 11 Dec 2019, 9:41pm

I saw that a while ago, and saw that it was lacking any means of aligning the drive wheel with the wheel rim, as is obvious from that photo.
That will be why they recommend changing the o-ring (drive wheel "tyre") every 2000 miles. Having the drive wheel crabbing on the rim would also ruin the end to end efficiency (leg watts to USB watts ratio).

I see that someone must have pointed this out to them, so they've fixed it

Carlton green
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Re: Dynamos - Hub or Bottle?

Postby Carlton green » 27 Apr 2020, 10:07pm

A degree of thread resurrection here for which I hope that I will be forgiven.

I recently discovered that front fork drop-out widths came in an old and a wider new standard size, my old bikes are to the old standard which IIRC is 90mm so the new wider hubs basically aren’t meant to fit them. So, I’m thinking new hub Dynamo’s don’t fit old style drop-outs. The next route then is re-use of a (front wheel) SA dynohub but, seems to me, they aren’t available second hand in 36 hole sizes and getting hold of 32 hole rims to (perfectly) match my existing 36 hole rims doesn’t seem possible. In short a front hub dynamo is too logistically hard for me to match to my bike.

Moving to the rear hub limits you a SA three speed but they are available second hand in 28, 36 and 40 hole shells so I could build a wheel using the 36 hole rims that I have. However the SA Dynohub comes in a narrow drop-out width so a new axle would be needed and (if available) you’re limited to three gears. I’m not sure whether the standard AW and Dynohub share the same axles because the innards of the shell geared sections must be different - so another potential logistics problem there.

TLDR: For some older bikes hub Dynamo options appear to be constrained.

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Re: Dynamos - Hub or Bottle?

Postby Brucey » 27 Apr 2020, 10:48pm

you don't say which OLN you would be shooting for with an AG hub. FWIW the only internal parts that are different in the AG gear are the planet cage and the LH cone, and these parts rarely fail, so AW axle swaps, gear repairs etc are easy.

SA front dynohubs were made in 36h so if you want one of those it is just a question of looking a bit harder. Rims that are an exact match for obsolete ones in any drilling are not that easy to find but there is a pretty good choice of 32h rims.

Regarding narrower modern hub dynamos; the HB-NX** series of hub dynamos have a spacer on the LHS which is about 5mm thickness. This is easily removed to take the OLN down to ~95mm which is 'close enough' in most cases. However because the locknuts and cones are on a fatter section of the axle in some cases you may need to file the axle down to make it fit the forks, thus making the conversion non-reversible.

Most hub dynamos which are meant to accept a roller brake can be reduced in OLN quite easily too. In nutted axle form, the shouldered locknut which normally sits inside the roller brake has the track nut thread on it. It is simply a case of replacing this locknut with a thinner, more conventional one and the hub goes to about 95mm OLN. You can fine tune the OLN with thinner locknuts both sides.

Panasonic do a hub which is meant to accept a drum brake; again it can be built to a narrower oln quite easily, for similar reasons

If you are willing to do a little machining a hub like an SP one can be modified by reducing the width of the hub (spacer and axle) on the LHS.

So there are more options than you might expect....?


Carlton green
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Re: Dynamos - Hub or Bottle?

Postby Carlton green » 28 Apr 2020, 10:28am

Thank you Brucey, certainly some useful information for me there.

For my particular needs and logistics my inclination is towards a front rather than rear hub and towards the original SA product. I’m in no rush (its a case of some long term perfectionist desire rather than actual and current need) so I can wait to see what turns up, but having a variety of options is good. If a front hub doesn’t turn up before winter then I’ll likely fit a bottle (gets the lights in place, working and proven) and replace the bottle when a suitable hub - and time to build the replacement wheel - appears. It’s some long way in the future but I’m wondering about a switch now, something to go in line with any later hub Dynamo will save me from the potential trouble or restriction of needing a switch in the headlight.

Thanks again, all useful pointers.