STEORN DEMO LIVE & STREAM in Dublin, December 15th, 10 AM

[mondrasek]

IMHO the subject of proper material selection from an engineering point of view has not been fully addressed by the replicators.

1st there is the issue of toroid core material.  Some of the important material properties that need to be considered are geometry and permeability (there are many others).  If the toroid dimensions are not considered wrt the rotor PM dimensions you will not be able to fully tap the attractive rotor PM potential and maximizing rotor torque.  For example, a PM will have less attractive force to a ferrous material that is too thin.  This goes the same for permeability.  I think of permeability as being similar to “magnetic domain density” of a material.  So if permeability is too low, then there are not enough magnetic domains for the rotor PMs to align to achieve maximum attraction/rotor torque.  If permeability is too high, you will require extra electrical input power to saturate the cores OR suffer decreased rotor torque (both bad).  That is further address below. 

Since it takes ever increasing amounts of energy to saturate a material the closer you get to 100% (not really achievable), we should target a value where the maximum torque per input energy is maximized.  If we assume this to be ~95% saturation (just for example purposes) then we need to select a toroid core shape and material that will saturate to 95% and thus attract the rotor PMs to ~95% of their maximum and no more.  The “gap” between the rotor PMs and the toroid core needs to be taken into account in this, since the windings will necessitate some gap.  But adjusting your setup for more gap than necessary may likely be another design flaw.

2nd, we need to wrap the toroid core with the proper number of wraps (amp-turns) and wire diameter (resistance value per length) to minimize the power requirement to saturate to (again) an optimum value, in this example again ~95%.  Any more power used is just pointless.  Any less means the rotor PMs are not optimally released from attraction to the toroid core after passing TDC and are therefore dragging on the system, thus reducing rotor torque.  So, for example, if you are only saturating your core to 5%, then 95% of the rotor PM attraction is working as negative torque after passing TDC.  And while it is obviously possible to make motors spin in this mode it is hardly optimal from an electrical input energy vs. rotor torque stand point.  This also explains why the replications to date appear to run faster with more electrical input.  If adding more electrical power increases RPM/torque, then you are not electrically saturating the toroid core material, not fully releasing the rotor PMs, and can never fully achieve the maximum rotor torque potential of the rotor PMs you are using.

So choosing any toroid material may get you a running motor, but nothing near what I believe Steorn is demonstrating (or think they have).  Selecting a core with a relative permeability of ~120 because JLN did that is also not correct.  The balance between all of the above described material properties (and more) needs to be considered (or engineered) for the purpose of maximizing usable torque output energy and minimizing required electrical input energy.

FWIW.

M.

[futuristic]

More from Naudin: http://www.youtube.com/watch?v=Trgve4eUN2A

[k4zep]

IMHO the subject of proper material selection from an engineering point of view has not been fully addressed by the replicators.

1st there is the issue of toroid core material.  Some of the important material properties that need to be considered are geometry and permeability (there are many others).  If the toroid dimensions are not considered wrt the rotor PM dimensions you will not be able to fully tap the attractive rotor PM potential and maximizing rotor torque.  For example, a PM will have less attractive force to a ferrous material that is too thin.  This goes the same for permeability.  I think of permeability as being similar to “magnetic domain density” of a material.  So if permeability is too low, then there are not enough magnetic domains for the rotor PMs to align to achieve maximum attraction/rotor torque.  If permeability is too high, you will require extra electrical input power to saturate the cores OR suffer decreased rotor torque (both bad).  That is further address below. 

Since it takes ever increasing amounts of energy to saturate a material the closer you get to 100% (not really achievable), we should target a value where the maximum torque per input energy is maximized.  If we assume this to be ~95% saturation (just for example purposes) then we need to select a toroid core shape and material that will saturate to 95% and thus attract the rotor PMs to ~95% of their maximum and no more.  The “gap” between the rotor PMs and the toroid core needs to be taken into account in this, since the windings will necessitate some gap.  But adjusting your setup for more gap than necessary may likely be another design flaw.

2nd, we need to wrap the toroid core with the proper number of wraps (amp-turns) and wire diameter (resistance value per length) to minimize the power requirement to saturate to (again) an optimum value, in this example again ~95%.  Any more power used is just pointless.  Any less means the rotor PMs are not optimally released from attraction to the toroid core after passing TDC and are therefore dragging on the system, thus reducing rotor torque.  So, for example, if you are only saturating your core to 5%, then 95% of the rotor PM attraction is working as negative torque after passing TDC.  And while it is obviously possible to make motors spin in this mode it is hardly optimal from an electrical input energy vs. rotor torque stand point.  This also explains why the replications to date appear to run faster with more electrical input.  If adding more electrical power increases RPM/torque, then you are not electrically saturating the toroid core material, not fully releasing the rotor PMs, and can never fully achieve the maximum rotor torque potential of the rotor PMs you are using.

So choosing any toroid material may get you a running motor, but nothing near what I believe Steorn is demonstrating (or think they have).  Selecting a core with a relative permeability of ~120 because JLN did that is also not correct.  The balance between all of the above described material properties (and more) needs to be considered (or engineered) for the purpose of maximizing usable torque output energy and minimizing required electrical input energy.

FWIW.

M.

Very well put.  Looks like we need a good materials specialist here for core selection!!

Ben

[mondrasek]

Very well put.  Looks like we need a good materials specialist here for core selection!!

Not to slight anyone...  I am sure there are many experts in the field here already.  But it has been recommended to me that we listen to Overconfident.  I think he is 0c on this board.  I've seen some promising posts by him so far on other boards.

The relationship of a ferrite material's relative permeability to saturation due to a PM field is what I thought was needed for the first step.  And I've yet to find it.  Anyone have reference info for this?

[danmarius7]

For anyone interested in material-core selection, almost everything you need is here: http://ecee.colorado.edu/~ecen5797/course_material/Ch13slides.pdf . At page 41 especially one will find core loss in ferrite core, but ferrite core is for high frequencies. So unless you're spinning that device at 500000 rpm I would not use ferrite for the core.