>There is a construction article in the September 2003 issue of "Nuts &
>Volts" magazine (page 58) describing how to do exactly what you
>want to do. From the article: "The design problem has to do with
>overcoming Earnshaw's Theorem ..."

Actually, the page I originally linked has construction instructions for
the inverse of that system  It's a cradle for a bar magnet, which is a
little closer to what I'm going for.  In any case, finding construction
instructions isn't what I'm worried about.  I want to know whether using
permanent magnets to assist the electromagnets is a feasible option, and
some help compensating for the inherent lag from the coil.

The reason I'm concerned about power consumption is that I want this to be
somewhat portable.  Ideally able to run for a couple of hours on
batteries.  I expect that would be difficult to do, but I thought using
permanent magnets as well as the solenoids would not only decrease the
power consumption, but might decrease the instability in the system (a
small movement can, apparently, cause the system to oscillate until it
falls off the cradle under some circumstance).  With the right control
system (I.E. prediction using time differential comparison of the field at
each solenoid) I bet Icould compensate for the instability.

And if anyone has any useful suggestions concerning the particular
orientation in which to mount the coils and magnets, I'd appreciate those
too.  So far, the best idea I have for making a system that won't tip over
is putting a hexagon of coils on the base, with a smaller triangle of
magnets on the model.

--Brendan

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