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### Topic: Magnetic Levitation (Read 11108 times)previous topic - next topic

#### liuzengqiang

#15
##### May 12, 2011, 11:35 pm

Well as there will then be a greater mass in one place due to the mirror shard, won't that end just want to face downwards all the time so then it won't spin as freely?

You know I have my theory hat on, right?

#16
Use mylar?

#### raron

#17
##### May 13, 2011, 03:41 am
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I have no idea how to accomplish it, but it would be great if some kind of motor effect could be induced to impart a small spin force to the spheres, without having to set them spinning by hand.

They do spin for quite a while, when set going, but eventually slow down.

Ideas anyone?

I think you pretty much answered yourself there. One possibility could be to glue two (or more, just keep it balanced) small lightweight magnets to the side (or inside) of it, and have two corresponding electromagnets next to them mounted on the suspension assembly (preferably some distance away so as to not disturb the magnetic suspension too much). Keep the magnet and electromagnets N-S direction tangential to the suspension axis, and then you can make it spin. Hmm, not sure if that came out right, but I hope its understandable. The Arduino could control them as well. I'd suggest keeping the rotational speed low.

#### simon.monk

#18
##### May 13, 2011, 08:27 am
Quote
Well as there will then be a greater mass in one place due to the mirror shard, won't that end just want to face downwards all the time so then it won't spin as freely?

Not in the case of this one - it has a neodinium magnet in the top - gives a much more impressive gap

Over the weekend, I'll do some experiments and see how long it keeps spinning. Its hard to get just the right amount of spin without it falling off, but from memory, from the fastest you can spin it without knocking it off, it will spin for a few minutes.

I think thin skewed longitude lines and a gentle draft from above (or below) might give the desired effect. Assuming the whole thing is fitted to the ceiling.
--
I write books about Arduino and Electronics: http://simonmonk.org

#### focalist

#19
##### May 13, 2011, 08:41 am
Since it's in a pretty significant magnetic field, I'm wondering if a coil, of very thin wire, placed off center would work.  The magentic field (which is changing pretty often, switching to maintain the suspension) passing through the coil would induce a current and that current flow produces it's own field.  That offcenter, small field should impart a force, which being unequal (off center) would cause the ball to spin.

I'm just shooting in the dark for this one.. but is there a reason it won't work?  Seems easy enough to try if you are experimenting anyway..

The only problem I can think of is that the force may be either to small to have any real effect, or too large, and cause it to spin much too fast.

Kind of an air-bearinged induction motor?

#### simon.monk

#20
##### May 13, 2011, 10:04 am
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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?)
--
I write books about Arduino and Electronics: http://simonmonk.org

#### mowcius

#21
##### May 13, 2011, 01:56 pm
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.

#### simon.monk

#22
##### May 13, 2011, 02:08 pm
Quote
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.
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I write books about Arduino and Electronics: http://simonmonk.org

#### mowcius

#23
##### May 13, 2011, 02:14 pm

Quote
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.

#### simon.monk

#24
##### May 13, 2011, 02:22 pm
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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.

--
I write books about Arduino and Electronics: http://simonmonk.org

#### focalist

#25
##### May 14, 2011, 05:51 pm
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.

#### simon.monk

#26
##### May 15, 2011, 09:05 pm
Quote
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 write books about Arduino and Electronics: http://simonmonk.org

#### simon.monk

#27
##### Jun 04, 2011, 11:41 pm
I finally got around to making a better video of this.
--
I write books about Arduino and Electronics: http://simonmonk.org

#28
##### Jun 11, 2011, 04:11 am

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