Magentic Resistance 3

[redd001]

Can anyone tell me how magnetic resistance works, when applied to an exercise bike.
How is it actuated?
How do magnets create resistance?
I am totally lost on this subject.I always thought magnetic flux was to weak to provide any resistance.

any help or hyperlinks that explain how recumbant exercise bikes work would be so helpful. thank you

 

[zeusfaber]

Depends what's fitted.

Two systems, both of which could be described as "magnetic resistance" described briefly in

http://www.memagazine.org/backissues/may97/departments/input_output/input_out.html

Lots more explanations on the more likely option available by Googling "eddy current brake"

A.

 

[MagMike]

When an electrically conductive material moves through a magnetic field, eddy currents are generated in the conductive material. Those eddy currents set up a magnetic field that acts in opposition to the field from the magnet. This produces a repulsion force (analogous to your question about magnetic resistance"). The strength of the repulsion force depends on the conductivity of the material, the relative speed between members and the strength of the field from the magnet. There is usually no contact between the magnet & conductor.

As zeusfaber mentioned, the principle is commonly used in eddy current brakes.

 

[MintJulep]

I just took apart my brand new magnetic resistance exercise bike.

Sorry, not to answer your question, but to to figure out why, after only three days of use it has started to "thunk-thunk" with each revolution of the crank.

Anyway, the resistance mechanisim is:

Cast iron flywheel with a copper band around the outer perimeter.

The brake band is a "C" shaped thing with a bunch of permanent magnets attached. The "C" spans an arc of about 140 degrees. It is pivoted at the top. At the bottom what appears to be a stepper motor reals in a cable, opposed by a spring, to control the gap between the flywheel and the brake band.

The whole thing looks very much like a mechanical band brake, which looks like a drum brake turned inside-out.

If anyone is interested, the "thunk-thunk" appears to be axial play in the crank shaft.

 

[redd001]

Thank you Mint Julip, of all the answer I recieved, which were all helpfull, your's was the most practical.

Currently I am trying to trouble shoot why an exerbike has no resistance at all.

sometimes its just the console that sets the resitance intitially that needs to be changed. So you have to order a new console and resistance will return, but in most cases it may just be the magnets itself.

What I want to know is do you have any diagrams, or could you tell me the outcome? Did you find out what was wrong and could you tell me what you did?
thanking you in advance.
redd