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| Date: | Sun, 07 Oct 2012 10:20:10 +1000 |
| From: | andrewm <andrewm AT thehacktory DOT com> |
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| Subject: | Re: [geda-user] Magnetic Bike Theory Question |
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This is a multi-part message in MIME format.
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It's an eddy current brake.
Look up that or "eddy current dynamo" for a bit more info.
Yes - the speed of the spinning disc will be much of the difference.
Gear it up.
On 7/10/2012 9:59 AM, Rob Butts wrote:
> I am trying to design a magnetically resisted arm bike. I have a
> magnetic resisted bike trainer that you take the front wheel off a
> road bike and lock the forks into brackets while the back wheel rests
> on a small roller about 1.5" in diameter. On one end of the roller
> shaft there as an aluminum disk about 4.5 inches in diameter x 1/8"
> thick. On either side of the aluminum disk are disks the same size
> holding six what appear to be 3/4" diameter x 1/8" thick ceramic
> magnets of unknown strength evenly spaced as if every 10 minutes
> around a clock and alternating poles facing out. One disk containing
> the magnets is fixed to the frame and unable to move. The opposing
> disk is allowed to rotate so that if in max resistance position the
> magnets mirror each other perfectly as if in a full eclipse and since
> they are opposite poles facing each other creating the maximum
> magnetic field across the spinning aluminum disk. As the resistance
> adjusting lever is moved toward easier the disk containing the magnets
> allowed to rotate moves so that each magnet on its face becomes more
> out of phase with the opposing disk containing the magnets until they
> don't eclipse at all and the magnetic field across the center disk is
> negligible.
> It works for the bike trainer but not so much for the arm bike. I am
> using a 5.75" diameter aluminum center disk x 1/8" thick. The magnets
> are ceramic 1" diameter x 3/8" thick with no telling the strength
> since I got a bunch on ebay (yes, don't stop reading if you're this
> far ~ cheap) and I'd say maybe 2 or 4 lbs holding force. Since, I have
> found and ordered 1" diameter x 1/8" thick neocadmeum N52 magnets with
> holding force of 22 lbs. The gaps between the disks are al the same.
>
> My bike spins freely in the easiest position and just enough harder
> that you knot that it is working and the resistance is slightly
> higher. I suspect it is not only the strength of magnets that makes
> the difference but also the speed at which the center disk is
> spinning. With the bike wheel rolling on the 1.5" roller the center
> disk of the trainer is spinning significantly faster than my
> armergometer. Do people agree with the theory that a slower spinning
> center aluminum disk is why we are seeing such a difference in resistance?
>
> Does anyone have any suggestions?
>
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<div class="moz-cite-prefix">It's an eddy current brake.<br>
<br>
Look up that or "eddy current dynamo" for a bit more info.<br>
<br>
Yes - the speed of the spinning disc will be much of the
difference.<br>
<br>
Gear it up.<br>
<br>
<br>
<br>
<br>
On 7/10/2012 9:59 AM, Rob Butts wrote:<br>
</div>
<blockquote
cite="mid:CALSZ9go3Du=s-V18RSrVG3Y6fAHjKmYvyoZ=ZAAqaDpkejvu=g AT mail DOT gmail DOT com"
type="cite"><font face="Times New Roman" size="3">
</font>
<div style="margin:0in 0in 0pt" class="MsoNormal"><span
style="font-size:12pt"><font face="Times New Roman">I am
trying to design a
magnetically resisted arm bike. I have a magnetic resisted
bike trainer that
you take the front wheel off a road bike and lock the forks
into brackets while
the back wheel rests on a small roller about 1.5" in
diameter. On one end
of the roller shaft there as an aluminum disk about 4.5
inches in diameter x
1/8" thick. On either side of the aluminum disk are disks
the same size
holding six what appear to be 3/4" diameter x 1/8" thick
ceramic
magnets of unknown strength evenly spaced as if every 10
minutes around a clock
and alternating poles facing out. One disk containing the
magnets is fixed to
the frame and unable to move. The opposing disk is allowed
to rotate so that if
in max resistance position the magnets mirror each other
perfectly as if in a
full eclipse and since they are opposite poles facing each
other creating the
maximum magnetic field across the spinning aluminum disk. As
the resistance
adjusting lever is moved toward easier the disk containing
the magnets allowed
to rotate moves so that each magnet on its face becomes more
out of phase with
the opposing disk containing the magnets until they don't
eclipse at all and
the magnetic field across the center disk is negligible.</font></span></div>
<div style="margin:0in 0in 0pt" class="MsoNormal"><span
style="font-size:12pt"></span> </div>
<font face="Times New Roman" size="3">
</font>
<div style="margin:0in 0in 0pt" class="MsoNormal"><span
style="font-size:12pt"><font face="Times New Roman">It works
for the bike trainer
but not so much for the arm bike. I am using a 5.75"
diameter aluminum
center disk x 1/8" thick. The magnets are ceramic 1"
diameter x
3/8" thick with no telling the strength since I got a bunch
on ebay (yes,
don't stop reading if you're this far ~ cheap) and I'd say
maybe 2 or 4 lbs
holding force. Since, I have found and ordered 1" diameter x
1/8"
thick neocadmeum N52 magnets with holding force of 22 lbs.
The gaps between the
disks are al the same.</font></span></div>
<div style="margin:0in 0in 0pt" class="MsoNormal"><span
style="font-size:12pt"></span> </div>
<font face="Times New Roman" size="3">
</font>
<p style="margin:0in 0in 0pt" class="MsoNormal"><span
style="font-size:12pt"><font face="Times New Roman">My bike
spins freely in the
easiest position and just enough harder that you knot that
it is working and
the resistance is slightly higher. I suspect it is not only
the strength of
magnets that makes the difference but also the speed at
which the center disk
is spinning. With the bike wheel rolling on the 1.5" roller
the center
disk of the trainer is spinning significantly faster than my
armergometer. Do
people agree with the theory that a slower spinning center
aluminum disk is why
we are seeing such a difference in resistance?</font></span></p>
<font face="Times New Roman" size="3">
</font>
<div style="margin:0in 0in 0pt" class="MsoNormal"><span
style="font-size:12pt"></span> </div>
<div style="margin:0in 0in 0pt" class="MsoNormal"><span
style="font-size:12pt"><font face="Times New Roman">Does
anyone have any
suggestions?</font></span></div>
<font face="Times New Roman" size="3">
</font>
<p style="margin:0in 0in 0pt" class="MsoNormal"><font face="Times
New Roman"> </font></p>
<font face="Times New Roman" size="3">
</font>
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<br>
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