a coil, of very thin wire, placed off center would work.
Its got to be worth a try. All these vague memories of Flemming's left hand law. Time to get my school physics books out I think. I'm guessing that the secondary rotation inducing coil on the side of the object should be orthogonal to the suspension coil and have its terminals connected together?
The coils control is PWM'd so it probably makes quite a lot of electromagnetic flux (do I here the sound of proper Physicists cringing?)
Well the problem I see is that it's a spherical metal ball. There are no poles on it and nothing irregular that can be pulled upon by a second magnet.
Pulling on it with a second magnet would simply make it move more towards that magnet (unless you could somehow pull on some part of it at an angle whilst shielding the rest of the ball from the magnetic attraction.
Well the problem I see is that it's a spherical metal ball
.. actually, no they are plastic with a fixed magnet in the top.
Si:
Well the problem I see is that it's a spherical metal ball
.. actually, no they are plastic with a fixed magnet in the top.
Ahh I see where I made the mistake. It's probably becuase the last version of this I saw for myself was suspending a metal ball.
Hmm, there are a few possiblities there then 
Another advantage of using a hall effect sensor (or even a distance sensor) in the middle of the electromagnet end to measure the distance to the object would be that you could make the object oscillate and still know where it is. With one sensor horizontally, you only know if the object's in the right place or not.
With one sensor horizontally, you only know if the object's in the right place or not.
Nearly 
In my setup the photosensor setup gives a position on the basis of how much of the narrow beam of the sensor is in the shadow of the object. Just plain 'its there or not' is not stable enough, you need a position and velocity. But yes, a Hall effect device would give this.
Yeah, it's all that flux that I'm betting you can take advantage of. Even a small coil (I would think just as you mentioned, orthogonically mounted, offcenter to rotation radius, and with coil ends connected) should make a field, and all it has to do is overcome air drag. I doubt a ferrite would even be needed, so the weight might be negligable in terms of throwing the ball off center of balance enough to fall out of the suspension field.
a coil, of very thin wire, placed off center would work.
I did give it a go over the weekend, without any immediate success - I think I might need a bigger coil.
I'll give it another try some time. But it was definitely worth a quick try.
I finally got around to making a better video of this.
Neat project!
You might be able to spin the sphere if you make your rig like a 3 phase motor but, you will have the rotor/armature spinning on it's magnetic axis. You will need 2 armature poles "I think" and you will need 3 coils to make a stator. The stator needs to fire in a rotating manner like a 3 phase motor stator does. If you google the operation of a 3 phase motor you might be able to see what you need.
Mark
Thanks, I'll look into it.
