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Date:	Tue, 26 Mar 2013 15:44:36 -0400
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Subject:	Re: [geda-user] Magnetic Exercise Bike design with a stator and rotor
From:	Rob Butts <r DOT butts2 AT gmail DOT com>
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I do understand how the magnetic field varies in the road bike trainer and
kind of understand the eddy current braking theory.  I did get an eight
coil stator and flywheel that I thought I'd experiment with.  In the see
also section of the eddy current brake wiki page there is a link for Telma
retarders and towards the bottom of that page a section describing an
electric retarder which sounds exactly what I need and what I can use this
$14 stator and flywheel for.  I think I just have to gear the speed of the
flywheel as high as I can which at this point is 5 to 1.

On Mon, Mar 25, 2013 at 10:13 AM, John Griessen <john AT ecosensory DOT com> wrote:

> On 03/24/2013 03:58 PM, Rob Butts wrote:
>
>> One plastic disc is fixed and the opposing plastic disk is allowed to
>> rotate 30 degrees providing the variable magnetic field and
>> variable resistance.  I have not been able to simulate the resistance I
>> believe because I'm not providing the same rotational
>> velocity of the aluminum disc.
>>
>
> Sounds like the out of alignment of the discs makes the field vary from
> weak to strong.
> To have strong fields, each magnet needs to be straight across, (through
> the aluminum disc),
> from another with same polarity direction.  Then induced currents flowing
> in circles around the strong field area
> counter subsequent motion by a force of their own.  I've never quite
> grasped how that force stays local
> to any place in the aluminum plate though...perhaps inertia of electrons?
>  Else moving the path of the high
> eddying current is more resistive than the eddy path?  It's all so
> circular!  I feel like researching
> and reading about it instead of doing my taxes...
>
> What do you mean by simulate?  What velocity can you get?
>
> Some decent velocity is needed for small inexpensive magnets.  I've seen a
> demo
> of eddy current braking done with a pendulum hung plate, then a slotted
> plate
> for comparison, where the opposing magnets were very massive and with iron
> looping
> around to make a complete magnetic circle path with two short gaps, (
> where the aluminum
> plate moved).  It would slow the pendulum in one stroke by 4/5ths.  It
> must have weighed
> 80 lbs.
>
> An alternator will need velocity also.  Bicycle gearing can get you
> velocity.
>

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I do=A0understand how the magnetic field varies in the road bike trainer an=
d kind of understand the eddy current braking theory.=A0 I did get an eight=
 coil stator and flywheel that I thought I&#39;d experiment with.=A0 In the=
 see also section of the eddy current brake wiki page there is a link for T=
elma retarders and towards the bottom of that page a section describing an =
electric retarder which sounds exactly what I need and what I can use this =
$14 stator and flywheel for.=A0 I think I just have to gear the speed of th=
e flywheel as high as I can which at this point is 5 to 1.<br>
<br><div class=3D"gmail_quote">On Mon, Mar 25, 2013 at 10:13 AM, John Gries=
sen <span dir=3D"ltr">&lt;<a href=3D"mailto:john AT ecosensory DOT com" target=3D"=
_blank">john AT ecosensory DOT com</a>&gt;</span> wrote:<br><blockquote style=3D"m=
argin:0px 0px 0px 0.8ex;padding-left:1ex;border-left-color:rgb(204,204,204)=
;border-left-width:1px;border-left-style:solid" class=3D"gmail_quote">
<div class=3D"im">On 03/24/2013 03:58 PM, Rob Butts wrote:<br>
<blockquote style=3D"margin:0px 0px 0px 0.8ex;padding-left:1ex;border-left-=
color:rgb(204,204,204);border-left-width:1px;border-left-style:solid" class=
=3D"gmail_quote">
One plastic disc is fixed and the opposing plastic disk is allowed to rotat=
e 30 degrees providing the variable magnetic field and<br>
variable resistance. =A0I have not been able to simulate the resistance I b=
elieve because I&#39;m not providing the same rotational<br>
velocity of the aluminum disc.<br>
</blockquote>
<br></div>
Sounds like the out of alignment of the discs makes the field vary from wea=
k to strong.<br>
To have strong fields, each magnet needs to be straight across, (through th=
e aluminum disc),<br>
from another with same polarity direction. =A0Then induced currents flowing=
 in circles around the strong field area<br>
counter subsequent motion by a force of their own. =A0I&#39;ve never quite =
grasped how that force stays local<br>
to any place in the aluminum plate though...perhaps inertia of electrons? =
=A0Else moving the path of the high<br>
eddying current is more resistive than the eddy path? =A0It&#39;s all so ci=
rcular! =A0I feel like researching<br>
and reading about it instead of doing my taxes...<br>
<br>
What do you mean by simulate? =A0What velocity can you get?<br>
<br>
Some decent velocity is needed for small inexpensive magnets. =A0I&#39;ve s=
een a demo<br>
of eddy current braking done with a pendulum hung plate, then a slotted pla=
te<br>
for comparison, where the opposing magnets were very massive and with iron =
looping<br>
around to make a complete magnetic circle path with two short gaps, ( where=
 the aluminum<br>
plate moved). =A0It would slow the pendulum in one stroke by 4/5ths. =A0It =
must have weighed<br>
80 lbs.<br>
<br>
An alternator will need velocity also. =A0Bicycle gearing can get you veloc=
ity.<br>
</blockquote></div><br>

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