[*BCM*] Re: Magnet-powered lighting system

[turtle]

Having used these things before (they were available about 15 years
ago), I can say that they cause very, very little resistance.  The one
I had used blinking LEDs, so the amount of energy needed to power it
was very small, compared to the amount of energy used to propel my body
and bike around.

As for Lee's question, with the light I had, the two parts were fastened
to the bike securely, so there was no sliding.  The generator and light
part was clamped onto the front fork and the magnet was clamped onto
the spokes at the same radius.  The magnet would zip past the generator
once a revolution, causing the LED to light up.  If I remember
correctly, the faster you rode, the faster it would flash.  

-Turtle
who liked the thing on principle, but didn't like the fact that it would
occassionally get loose and fall into her spokes and make her crash...


Boston Critical Mass <list at bostoncriticalmass.org> wrote:
> 
> Yea, but....
> 
> If you get going fast, the weight may not make it back to the middle.  It 
> will just hang out at the rim of the wheel.  No?
> 
> ----- Original Message ----- 
> From: "Jason Orach" <jorach at gmail.com>
> To: <list at bostoncriticalmass.org>
> Sent: Sunday, January 08, 2006 1:32 PM
> Subject: [*BCM*] Re: Fwd: [phonography] Cycling recordists (Ian Thistle)
> 
> 
> I'm a senior in Mechanical Engineering at Boston University, so you
> can trust me. The general idea of what Eamon Kelly (where's your
> Beanpot?) wrote is correct. The best way to think about this is to
> picture a seesaw. If you have a person who weighs 100lb and a person
> who weighs 200lb, how can they use the seesaw? Easy! The person who
> weighs 100lb sits at the end of the seesaw, and the person who weighs
> 200lb sits halfway between the end and the middle on the other side.
> 
> A torque or a "moment" is a force multiplied by a distance. You exert
> a force on your pedals, which gets multiplied by a distance, your
> crank length, to become a moment. This works against the moment of the
> chain pulling on your chainring resisting motion. Back to this magnet
> dynamo, there'll be a very small resistive force multiplied by how far
> away from the center of the wheel the system is.
> 
> In conclusion it's a tiny magnet and your legs are pretty strong. You
> might notice it when you're just starting, but I doubt it. When you're
> trucking along at night you won't notice a thing.
> 
> - Jason Orach
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