Dynohub drag

On Wed, 08 Oct 2014 10:34:50 -0400, Frank Krygowski
wrote:

On 10/8/2014 5:49 AM, sms wrote:
On 10/8/2014 12:39 AM, Lou Holtman wrote:

It was just to show people that the drag with the lights off is so low
that you don't need the complexity of a disengagement mechanism.

The reality is that you did show that at all. You showed the difference
between spin down time with and without the light on. You did not show
the drag from an unconnected engaged hub versus an unconnected
disengaged hub versus a non-dynamo hub.

That data is available; see below. Lou was just giving an
easy-to-understand demonstration, to make obvious how little problem
there is with the drag. Juden's article does the same in a quantitative way.


It was still instructive. It was surprising how much more drag their was
with the light on in your test. I would have expected far less
difference in spin-down time.

A 50% efficient hub that is generating 3W requires 6W of input. Someone
riding a bicycle at 15 km/hour is expending about 60W of power (I recall
1/10 HP which would be about 75W, though this is a little less). So it's
an extra 10% input power with the light on versus off. Not huge, but not
insignificant.

A test of the SP clutch hub showed the following:

O:17 Hub-engaged light-on
0:33 Hub-engaged light-off
2:53 Hub-disengaged

https://www.youtube.com/watch?v=ji1wCW35Y0o

But of course all these tests, yours and the one of the SP hub, are
pretty meaningless. Spinning a wheel with your hand is not
representative of actual riding. Also, there are other reasons for a
disengageable hub besides less drag.

Hmm... perhaps another reason is to increase complexity?

There is detailed, yet easy to understand, data on the drag of these and
other hub dynamos at
http://www.ctc.org.uk/file/public/fe...ub-dynamos.pdf
The first graph in that article shows slightly more drag for the SP than
for the SON, although the difference is only about 0.4W at 30 kph.

SP's own graphs at http://www.sp-dynamo.com/8seriesdynamo%20hub.html
show differences of about the same magnitude, but in the opposite
direction. Perhaps they were comparing with a different model of SON
hub? In any case, a fraction of a Watt is hardly important. Juden's
article makes that very clear, by converting drag to equivalent
feet-per-mile inclines.

I own neither of those hubs, so I don't particularly care. Seems to me
the criteria for choosing between the two might be lower cost for the
SP, vs. perhaps greater reliability for the SON (based on greater
simplicity and SON's unique sealing technology).
Any hub dyno with have slightly more drag with the light off, and a
whole lot less drag with the light on when compared to useing a
"bottle" dyno friction driven off the tire - which WAS the normal way
of powering headlights a few decades ago if you didn't want to use
batteries.(and rechargeables were not a viable option back then)

On 10/8/2014 12:19 PM, wrote:

Any hub dyno with have slightly more drag with the light off, and a
whole lot less drag with the light on when compared to useing a
"bottle" dyno friction driven off the tire - which WAS the normal way
of powering headlights a few decades ago if you didn't want to use
batteries.(and rechargeables were not a viable option back then)

Actually there were several rechargeable systems back then.

http://www.bikeforums.net/electronics-lighting-gadgets/837931-archives-defunct-bicycle-lighting-company.html
was the most famous one.

On 10/8/2014 3:19 PM, wrote:

Any hub dyno with have slightly more drag with the light off, and a
whole lot less drag with the light on when compared to useing a
"bottle" dyno friction driven off the tire - which WAS the normal way
of powering headlights a few decades ago if you didn't want to use
batteries.

Yep. I still have bottle dynamos on a couple bikes (slightly modified)
and they're more than adequate for my uses. I have roller dynamos on a
couple other bikes.

I've mentioned this before, but on one long tour, I was cranking along
on a flat road at about 19 - 20 mph when a bump caused my roller dynamo
to snap on. I didn't realize it was on, and first wondered what that
new little sound was. Then I noticed I'd dropped about 1 mph from my
speed. Then I noticed my headlight was on.

It was a good test for me. The roller dynamo slowed me by 1 mph. To
me, a non-racer, that's acceptable. And hub dynos are much better.


--
- Frank Krygowski

On Wednesday, October 8, 2014 4:25:03 PM UTC-4, Frank Krygowski wrote:
On 10/8/2014 3:19 PM, wrote:



Any hub dyno with have slightly more drag with the light off, and a

whole lot less drag with the light on when compared to useing a

"bottle" dyno friction driven off the tire - which WAS the normal way

of powering headlights a few decades ago if you didn't want to use

batteries.



Yep. I still have bottle dynamos on a couple bikes (slightly modified)

and they're more than adequate for my uses. I have roller dynamos on a

couple other bikes.



I've mentioned this before, but on one long tour, I was cranking along

on a flat road at about 19 - 20 mph when a bump caused my roller dynamo

to snap on. I didn't realize it was on, and first wondered what that

new little sound was. Then I noticed I'd dropped about 1 mph from my

speed. Then I noticed my headlight was on.



It was a good test for me. The roller dynamo slowed me by 1 mph. To

me, a non-racer, that's acceptable. And hub dynos are much better.





--

- Frank Krygowski

I remember getting a Sanyo roller dynamo and light kit back in the 1980s. That light had the strangest pattern I ever saw and was useless. It was a very long 'T' with a very narrow beam to a narrow cross piece at tthe top of tthat 'T'. The cross beam at the head of the 'T' wasn't long enough to see much. Pity because the drag from the dynamo was very low and engagement against the tire was far superior to that of the sidewall bottle dynamo by Union that I'd tried before. That's what got me to move to battery lights. I used the Union dynamo supplied headlight but with either a Halogen or Krypton bulb and powered with a 6 volts battery.

Cheers

On Wed, 08 Oct 2014 13:04:31 -0700, sms
wrote:

On 10/8/2014 12:19 PM, wrote:

Any hub dyno with have slightly more drag with the light off, and a
whole lot less drag with the light on when compared to useing a
"bottle" dyno friction driven off the tire - which WAS the normal way
of powering headlights a few decades ago if you didn't want to use
batteries.(and rechargeables were not a viable option back then)

Actually there were several rechargeable systems back then.

http://www.bikeforums.net/electronics-lighting-gadgets/837931-archives-defunct-bicycle-lighting-company.html
was the most famous one.
I was talking FOUR decades ago. The first rechargeable flashlight was
only introduced in 1968, so rechargeable batteries were far from
common in the mid to late sixties.

On 10/8/2014 2:16 PM, wrote:
On Wed, 08 Oct 2014 13:04:31 -0700, sms
wrote:

On 10/8/2014 12:19 PM, wrote:

Any hub dyno with have slightly more drag with the light off, and a
whole lot less drag with the light on when compared to useing a
"bottle" dyno friction driven off the tire - which WAS the normal way
of powering headlights a few decades ago if you didn't want to use
batteries.(and rechargeables were not a viable option back then)

Actually there were several rechargeable systems back then.

http://www.bikeforums.net/electronics-lighting-gadgets/837931-archives-defunct-bicycle-lighting-company.html
was the most famous one.
I was talking FOUR decades ago. The first rechargeable flashlight was
only introduced in 1968, so rechargeable batteries were far from
common in the mid to late sixties.

Sorry, you said "a few decades ago." I took "a few" to mean three.
1984-2014 is a few decades.

On 09/10/14 08:10, Sir Ridesalot wrote:

I remember getting a Sanyo roller dynamo and light kit back in the
1980s. That light had the strangest pattern I ever saw and was
useless. It was a very long 'T' with a very narrow beam to a narrow
cross piece at tthe top of tthat 'T'. The cross beam at the head of
the 'T' wasn't long enough to see much. Pity because the drag from
the dynamo was very low and engagement against the tire was far
superior to that of the sidewall bottle dynamo by Union that I'd
tried before. That's what got me to move to battery lights. I used
the Union dynamo supplied headlight but with either a Halogen or
Krypton bulb and powered with a 6 volts battery.


Same. The Sanyo headlight beam shape was ****. Probably enough to be
seen, but not enough to see the road well at all.

--
JS

On 08/10/2014 22:16, wrote:
On Wed, 08 Oct 2014 13:04:31 -0700, sms
wrote:

On 10/8/2014 12:19 PM, wrote:

Any hub dyno with have slightly more drag with the light off, and a
whole lot less drag with the light on when compared to useing a
"bottle" dyno friction driven off the tire - which WAS the normal way
of powering headlights a few decades ago if you didn't want to use
batteries.(and rechargeables were not a viable option back then)

Actually there were several rechargeable systems back then.

http://www.bikeforums.net/electronics-lighting-gadgets/837931-archives-defunct-bicycle-lighting-company.html
was the most famous one.
I was talking FOUR decades ago. The first rechargeable flashlight was
only introduced in 1968, so rechargeable batteries were far from
common in the mid to late sixties.

What did cars use? :-)

Miners and hence cavers used NiFe cells or lead acids. I agree that
later on NiCds started taking over, but that was late 80s.

Of course now people have a helmet mounted LED and battery which is
almost smaller than the lamp alone, let alone the lumping great battery
pack one had strapped to one's waist. More light, for longer. And
potentially insanely expensive...

On Wed, 08 Oct 2014 17:16:59 -0400, wrote:

On Wed, 08 Oct 2014 13:04:31 -0700, sms
wrote:

On 10/8/2014 12:19 PM, wrote:

Any hub dyno with have slightly more drag with the light off, and a
whole lot less drag with the light on when compared to useing a
"bottle" dyno friction driven off the tire - which WAS the normal way
of powering headlights a few decades ago if you didn't want to use
batteries.(and rechargeables were not a viable option back then)

Actually there were several rechargeable systems back then.

http://www.bikeforums.net/electronics-lighting-gadgets/837931-archives-defunct-bicycle-lighting-company.html
was the most famous one.
I was talking FOUR decades ago. The first rechargeable flashlight was
only introduced in 1968, so rechargeable batteries were far from
common in the mid to late sixties.
OK, Ever ready mase their first Ni-Cad rechargeable battery in 1968
- so they WERE available - but they were WAY above my "snack bracket"
at the time.

On Wed, 08 Oct 2014 14:48:44 -0700, sms
wrote:

On 10/8/2014 2:16 PM, wrote:
On Wed, 08 Oct 2014 13:04:31 -0700, sms
wrote:

On 10/8/2014 12:19 PM, wrote:

Any hub dyno with have slightly more drag with the light off, and a
whole lot less drag with the light on when compared to useing a
"bottle" dyno friction driven off the tire - which WAS the normal way
of powering headlights a few decades ago if you didn't want to use
batteries.(and rechargeables were not a viable option back then)

Actually there were several rechargeable systems back then.

http://www.bikeforums.net/electronics-lighting-gadgets/837931-archives-defunct-bicycle-lighting-company.html
was the most famous one.
I was talking FOUR decades ago. The first rechargeable flashlight was
only introduced in 1968, so rechargeable batteries were far from
common in the mid to late sixties.

Sorry, you said "a few decades ago." I took "a few" to mean three.
1984-2014 is a few decades.
Time has a way of getting away on us, for sure.