On 2018-02-08 16:50, Frank Krygowski wrote:
On Thursday, February 8, 2018 at 7:24:58 PM UTC-5, Joerg wrote:
On 2018-02-08 16:01, Frank Krygowski wrote:
On Thursday, February 8, 2018 at 4:14:47 PM UTC-5, Joerg wrote:
On 2018-02-08 12:20, AMuzi wrote:
On 2/8/2018 2:08 PM, Joerg wrote:


Those 2.4W bulbs were a joke. My bikes (after my teenage
years) always had better lighting than that. Now it's all
LED on my bikes but the real stuff with more than 500 lumens.


For years with a Margil cover or, after a Krygowski mod with O ring, and
without a switch (always on) I have no complaints about function or
longevity. YMMV.


How much does that O-ring reduce the drag? In the old days (with a real
power bus on the bike) I often rode the first miles with the dynamo off
because of the drag. I only put it back to the wheel when the "steam
gauge needle" (remember those?) got too close to the red range.

First, the terrors of dyno drag are mostly a myth. This article deals with it:
http://www.myra-simon.com/bike/dynotest.html
"the slowing down has more to do with psychology than the actual power required
to turn it."
and
"All of the generators were easier to turn than riding up a 1 in 300 slope.
Another way of putting that is a rise of 18 feet per mile; and there's quite a
cluster of sidewall and hub-driven models around the 1/500 line, or 10 ft per
mile."


Well, take another look at your link. I routinely ride at 30km/h at
which bottle dynamos waste 15W or more. That is nothing to sneeze at.

You seem to not understand the math. Is 15W nothing to sneeze at? It's the same
as climbing 18 feet in a mile.

I've related this before, but: On one solo tour, I was riding west on a deserted
flat four-lane concrete highway. I had four panniers and full camping gear, but
I was riding very well at a very consistent 20 mph.

Then I hit a bad expansion joint. It really jolted me. Worse, I heard some sort
of weird whirring noise, barely audible. And I noticed my speed had dropped
to about 19 miles per hour. Ideas like a dragging brake or a fender scraping
ran through my mind, but I could see nothing wrong.

Then I realized my bottom bracket dynamo had snapped on because of the jolt.
It was a near-perfect test of dynamo drag. Riding with it on cost me one mile
per hour. Big deal!


If you are willing to give up 1mph this easy, fine. I am not and I have
found a much better solution.


I find it odd that a guy routinely tells us weight doesn't matter to him, but is
afraid of dyno drag equivalent to riding a 1 in 300 slope.


Hint: In the flatlands and with a nice high tire pressure weight doesn't
make much of a difference.

So is that the only place you ride?? You give the impression of oh-so-gnarly
riding. Once again, your song changes wildly depending on your argument.


If you had followed more carefully you'd have know that there are two
places I ride a lot: Here in the hills and then down in the Sacramento
Valley. As I wrote many times that valley is huge and very flat. Nearly
all errand rides have to head in that direction because that's where
nearly all stores are.


Regarding the O-ring solution - that is, cutting a groove in the dyno drive
wheel, snapping in a suitable O-ring and running that on the rim sidewall
instead of the tire - it makes the dyno almost silent. That should greatly
reduce your psychological stress, Joerg, but it probably reduces the drag a bit,
too. The deformation and scrubbing of the contact patch between the tire and
the dyno's roller is responsible for a significant portion of dyno drag. I think
the O-ring has a lot less scrubbing and a lot less hysteresis loss.


Yeah, I should give that a try. Still got a dynamo on the road bike from
the days when I had NiCd batteries which didn't have the capacity of
Li-Ion. Only issue is, it's a Soubitez dynamo where the wheel is not
removable. I'd have to figure a way to grab it at its outside diameter
with a hose or something and then drive that hose with a power drill at
a speed the dynamo can stomach for a while, then hold the corner of a
file to it.

Regarding the "speed the dynamo can stomach for a while": At 15 mph, your wheel
rotates about 180 rpm. The much smaller drive wheel on a sidewall dyno spins
about 4500 rpm or more. Your electric drill won't hurt it.


Thanks. Then it should be possible, maybe even without removing the dynamo.


I just chucked mine in my lathe. If you don't have a lathe, perhaps try using
a drill press if its chuck is large enough. But I did remove the drive wheel
first.


On my dynamo it isn't removable. A (very small) lathe is on my bucket
list. Probably one of those PC-controlled XYZ tables.


Also, my last front Gatorskin is still on there and those have
paper-thin sidewalls. I'd have to mount another tire.

The point is to run the O-ring on the rim's braking surface.


Aha, that makes sense. Thanks.

--
Regards, Joerg

http://www.analogconsultants.com/