delorie.com/archives/browse.cgi   search  
Mail Archives: geda-user/2012/10/06/20:20:33

X-Authentication-Warning: delorie.com: mail set sender to geda-user-bounces using -f
X-Recipient: geda-user AT delorie DOT com
X-Originating-IP: 122.108.185.217
Message-ID: <5070CABA.4060702@thehacktory.com>
Date: Sun, 07 Oct 2012 10:20:10 +1000
From: andrewm <andrewm AT thehacktory DOT com>
User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:15.0) Gecko/20120907 Thunderbird/15.0.1
MIME-Version: 1.0
To: geda-user AT delorie DOT com
Subject: Re: [geda-user] Magnetic Bike Theory Question
References: <CALSZ9go3Du=s-V18RSrVG3Y6fAHjKmYvyoZ=ZAAqaDpkejvu=g AT mail DOT gmail DOT com>
In-Reply-To: <CALSZ9go3Du=s-V18RSrVG3Y6fAHjKmYvyoZ=ZAAqaDpkejvu=g@mail.gmail.com>
Reply-To: geda-user AT delorie DOT com

This is a multi-part message in MIME format.
--------------090200030502050404020001
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

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?
>


--------------090200030502050404020001
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit

<html>
  <head>
    <meta content="text/html; charset=ISO-8859-1"
      http-equiv="Content-Type">
  </head>
  <body bgcolor="#FFFFFF" text="#000000">
    <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>&nbsp;</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>&nbsp;</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>&nbsp;</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">&nbsp;</font></p>
      <font face="Times New Roman" size="3">
      </font>
    </blockquote>
    <br>
  </body>
</html>

--------------090200030502050404020001--

- Raw text -


  webmaster     delorie software   privacy  
  Copyright © 2019   by DJ Delorie     Updated Jul 2019