Hello all, I have been playing with switching magnetic flux by interposing a sheet of soft iron between two opposed magnetic poles.

I have posted about this on scienceforums[ dot ]net but would appreciate a deeper and wider discussion.

I guess everybody knows that two opposing magnetic poles repel. I discovered - it may be obvious really - that inserting a sheet of ferromagnetic material (soft iron, electrical steel, plain mild steel, etc) in the gap between two opposing magnetic poles causes the magnets to be attracted towards the sheet. This has the practical effect of switching the magnets from repulsion to attraction. Removing the sheet switches the magnets back to repulsion.

I have used this effect in the design of a number of devices that employed a rotor with ferromagnetic tabs or 'fingers' spaced around its periphery that intersect the magnets so that the flux field switches between attraction and repulsion and using the reciprocation that induced to induce a rotary movement in an output rotor.

The latest iteration of my design looks as follows:


labeled.png (169.96 kB . 763x530 - viewed 119 times)

In this design there is a cylindrical rotor that has two opposing sinusoidal cam grooves running around the sides of the cylinder. There are carriages arranged on shafts that constrain them to move parallel to the cylinder and the carriages also have a bearing that runs in the cam grooves. The carriages are arranged in pairs and each carriage also has a magnet. The magnets are arranged so that they oppose the magnet in the opposite carriage. Wherever the cam tracks are converging there is a metal tab that will attract the magnets either side of it. Wherever the cam tracks are diverging there is no tab, thus the magnets are repelling.

Where the magnets are attracting the cam track is converging and thus the vector force of the bearing on the cam track will cause the rotor to rotate to the left (in the above image). Where the magnets are repelling the cam track is diverging and thus the vector force of the bearing will also cause the rotor to rotate to the left.

At the extremes of their travel the vector force of the bearings will be perpendicular to the track and thus will impose an axial rather than rotary force on the rotor. Since there are five waves in the cam track and four sets of carriages, opposite carriages will be at opposite extremes whilst adjacent carriages will be in the mid point of their travel. This means that while the carriages at their extremes and imposing an axial rather than rotary force on the rotor, the adjacent carriage pairs will be exerting a rotary force on the rotor.

It appears to me that this device should start running as soon as it is assembled and require no energy input to start or continue it's motion.

Am I wrong? The laws of thermodynamics would suggest so, however such a general rule does not explain what is happening in this device. Can anyone comment on why, given the geometry of this device and the arrangement of magnets and interposed low-reluctance paths, this device would not behave as I suggest?

There is more info about the device on my website: tomboy-pink[ dot ]co[ dot ]uk/sfmm
There is an simulation of the device running at: youtu[ dot ]be/mjZMPHsw5po
The complete CAD model is available at: github[ dot ]com/prajna-pranab/sfmm-Mk1