Thought I would share a new idea that I was working on. The idea came about by trying to figure out how a magnet and coil would interact in such a way that they would aid the motion causing the EMF instead of resisting it. The drawings should explain the setup pretty well. But the key idea here is how the flux crosses the cores making the core on the other side have a field that is in the same direction as the magnet's. This little hack could lead to an interesting interaction between the magnet, core and coil. Sadly FEMM cannot simulate this setup as it's not possible to model it in 2d if someone has a 3d FEM simulator I would be very interested to see the results.

1. Shows the overall setup
2. Shows the flux path of the setup
3. Shows the natural state of the system if the coil is open i.e. the magnet wants to move away from the core
4. Shows what happens when the magnet is pushed towards the core with the coil shorted
5. Shows what happens when the magnets is pushed away from the core with the coil shorted

The hypothesis is that when the magnet is moving towards the shorted coil+core it will experience a resisting force that is smaller that if the coil was open and doing nothing. And when it's moved away from them it will experience a larger force pushing it away than if the coil was open. So with each cycle there is a kinetic energy gain opposed to no energy gain if the coil was open.

The closer the magnet gets to the the coil/core the smaller the flux path distance becomes and thus more flux through the coil/core. When it moves away the opposite happens.


Again this is just a hypothesis and must be confirmed. If anyone out there has Ansys Maxwell, would be great to see if this assumption is true.

True, but that difference in an unsaturated ferromagnetic path length compared to the effective gap lengths represents, IMO, negligible mmf difference therefore, essentially, no appreciable change in flux for the magnetic circuit. Also, does not the coil and its core have to displace along with the magnet?

This can be controlled by air gaps, I also hinted at this in image #2 where there was another path behind the magnet.




Meanwhile I have been entertaining a different design variant which removed the need of the "diode" magnets or air gaps. And a 3d simulation might come soon too due to a little helper.

Got the first 3d simulation result. Currently not showing much just the field. Currently the field is equally divided as the magnet is perfectly in the center.

It can be modeled in FEMM, see image.  The force on the moving part is not in the direction you stated, it is pulled inwards.  I have put the moving part outside the ends of the top and bottom rails where it becomes obvious that is the direction.  There is a 10mm grid in the image and the depth is 10mm for those interested.  The pull-in force by the FEMM stress tensor method is 1.8 Newtons and the flux in the coil is 2.56E-4 Webers.  Inward movement does not change the coil flux much as Bistander predicted.  It increases the coil flux slightly.  And if that slight increase drives current in the shorted coil, its effect is not to enhance the movement, but just the opposite as in normal motors.  Sorry about that.

Smudge

Hey Smudge, that's actually a clever model you have there, I didn't think of that. I might use it to speed up simulation times.


Meanwhile I have the first 3d simulation results in and they also seem to indicate the same result as Smudge got, that there is indeed an attracting force not repelling. I used multiple refining passes to ensure the force would converge as much as possible but it's clearly attracting.


Before giving up on this idea I would like to try a few variations. The result also seems to contradict a very crude experiment I did in real life where a repulsive force seemed to be present i.e. a coil+core repels a magnet if their fields are parallel and in the same direction, but this may have been a poorly setup experiment.


Edit: @Smudge, I spoke a bit too soon about your 2d model, one key point is to have the part which has the field in the same direction as the magnet closest to the magnet, in your 2d design case it's fartest from the magnet.