Hi MIKE,

On 30-Aug-03, MIKE ROSS wrote to WILLIAM KITCHEN:

 WK>> So, for garden variety NiCd AA's, a C/5 charge is 120mA, C/10 is
 WK>> 60. And  if your charger is smart enough to know when to quit,
 WK>> you can push them  harder for short times. Not that you'd
 WK>> actually want your charger sucking  up several watts of pedal
 WK>> power.

 MR> Indeed there's the rub: one needs to minimize pedal power. IIRC
 MR> there is about 65 watts available at maximum effort but then only
 MR> in short bursts. Assuming the sustained value is some 5 to 10
 MR> times less, then anything that adds too much effort would be a
 MR> real bother. For example a 3 watt budget for lighting doesn't
 MR> bother me too much but I'd much rather use a lot less!

Who wouldn't!

 WK>> But a really smart system that can jacks  up the charging current
 WK>> when braking or going down hill could be good.  Now that I think
 WK>> about it, it really wouldn't have to be all that smart.  Maybe a
 WK>> switch on one or both brake levers, such that the switch closes
 WK>> before the brake pads make contact. Squeeze just a little, and
 WK>> the charger  cranks up the current and creates a bit of drag.
 WK>> Which, of course, is  usually what you want when you lightly
 WK>> squeeze the brakes. This should  work for both hills and stops.
 WK>> Changing your riding habits to make  longer, slower stops could
 WK>> improve it a bit. Charging at a less noticeable  rate during
 WK>> daytime riding is another possibility, or better yet, with a
 WK>> solar cell.

 MR> Okay, I don't think solar cells are going to go on most people's
 MR> bikes (what with theft and fragility issues) but the idea is sound

Value makes then _very_ stealable, so no, that's not to likely to be a
goer :-(.

 MR> other than the extra weight. Consider that an average bicycle
 MR> weighs about 20 to 25 lbs so even 1lb extra makes an immediate
 MR> difference at the pedals. Even changing from a steel to magnesium
 MR> kick-stand makes a noticable change!

True, especially if you have hills all ways out like I do here (no
bike either at present).

 MR> However, I hadn't considered regenerative braking, and this I find
 MR> certainly an awesome source of power! There's a lot of power in
 MR> 200 lbs moving at 20 mph!!! If this could be easily harnessed from
 MR> the braking and then stored it would be just the thing.
 MR> Unfortunately, it also probably means adding a lot of weight in
 MR> the system that recovers the energy and stores it. It is a great
 MR> idea but seem almost impossible to execute. Too bad, I really like
 MR> that kind of thinking!

Should be doable with less weight than you think!

 MR> On the other hand, perhaps recovering energy from braking might
 MR> not be such a bad idea for another purpose, for example as an
 MR> assist in starting the bike from a stop. One idea would be adding
 MR> a flywheel system to store the braking energy and then using it as
 MR> an assist to start up again. Pedaling could then be much easier
 MR> after a stop. But here too the system seems quite "pie in the sky"
 MR> to actually make.

Not "Pie in the sky". It's already available here. Someone (I forget
the details) produces a unit which contains a battery and a
motor/generator and control electronics. Aids up hills, quiet on the
flat, regenerates downhill and stopping.

 WK>> Of course, NiMH's are much better still.

 MR> I don't doubt there are batteries with a lot of capacity, the
 MR> problem of course is in pushing the pedals!

:-).

 WK>> Heck, even carying around a 2 pound SLA battery would probably be
 WK>> less work than pushing a generator. That's about the weight of
 WK>> the 6V, 5AH SLA  batteries sitting on the shelf next to me. Bad
 WK>> power to weight ratio.  Good power to cost ratio.

 MR> If I was going to carry a 2 lb SLA around then I'd want an
 MR> electric motor at the other end of it!!!   Speaking of which, I

See above!

 MR> saw an experimental electric scooter going through the park this
 MR> past spring. I think it was a nearby high school project. It was
 MR> basically a row of batteries under the running board and seat with
 MR> a bunch of aluminium flat stock built up from it. The wheels were
 MR> about 6 inches in diameter and the back wheel had a large gear and
 MR> chain going to the motor sprocket. It moved at a very nice clip.
 MR> It was amazingly quiet and seemed to take inclines at a sustained
 MR> rate. Electric motors are good at supplying power to a load as it
 MR> demands.

Too true, and with modern control electronice, smoothly and on demand.

George

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