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 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: In-Reply-To: Content-Type: multipart/alternative; boundary="------------090200030502050404020001" 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

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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