How Does Magnetic Resistance Work in Exercise Bikes Like Indoor Trainers?

I am an electrical engineer disabled in a snow skiing accident and am now a quadriplegic. I'd like to design an exercise arm bike and make it magnetically resisted because friction resisted is not conducive to minute changes in resistance.

I have a magnetic resisted indoor trainer for a road bicycle where you take the front wheel off of a road bike, fasten the front forks in the trainer frame and the back tire sets on a small 2" diameter roller. At one end of this roller is a small aluminum disk roughly 1/8" thick and 4" in diameter and attached to the spinning roller. On one side of the spinning disk is a disk the same diameter with six 3/4" diameter magnets (appear to be ceramic) arranged around the perimeter of the 4" disk evenly spaced (as if every 10 minutes around a clock). This disk is fixed and cannot move.

On the other side of the spinning aluminum disk is an identical magnet disk with magnets configured the same way but allowed to rotate 30 degrees. The strength of the magnetic field is varied by rotating this magnet disk allowing the magnets to more eclipse the corresponding magnet on the other side of the spinning aluminum disk.

I can't find good information explaining the theory behind this. I have read all of the wiki pages on eddy current brakes. I'd like to see an equation that would explain what is going on.

I got 1" neodymium magnets and positioned them around two 5" disks with a 1/8" thick, 5" diameter aluminum disk between (also fixed to a shaft and handles to be spun by hand) but the resistance is minute. I suspect it is because the rotational velocity is no where near as fast as the road bike trainer. I have also been told that the thickness of the spinning disk between is too thin.

Any help or direction is GREATLY appreciated!!!

Thanks

I have no expertise in this particular field, but as no-one else has answered, I will offer what little I know and can guess from basic principles, as simply as possible.

When the magnets on the two sides are lined up and therefore closer to each other, the magnetic flux passing through the aluminium disc is stronger, so the eddy currents induced in it will be greater, so there will be more resistance to movement.

A thicker aluminium disc will have less resistance to the flow of eddy currents, so it will "absorb" more energy from the relative motion of the two components of the system, thereby increasing the resistance to movement.

The system is acting as an electrical generator, converting rotary physical motion into electrical current in the aluminium disc. The flow of current produces heat in the disc, which is then dissipated into the surrounding air.

The system will produce more resistance at higher speeds, just as ordinary electric motors and generators produce more power at higher speeds. More energy is being put into the system, so more can be taken out of it.

I think what you have is precisely what is described in:
http://en.wikipedia.org/wiki/Eddy_current_brake#Circular_eddy_current_brake

On a bicycle, you change into low gear going uphill, because your legs can produce more power when they are working faster against a lower resistance.
(Even though it feels easier than going uphill in high gear, when the slow speed of your legs produces less power.)

Along with a thicker aluminium disc and stronger magnets, your system may need a gearbox (could be adapted from a bicycle transmission) to run the resistance wheel at a high enough speed to produce sufficient drag.

Please let us know if this is any help.