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I'm just getting into electronics, and I would like to build an electromagnetic mixer. See here. Most of the tutorials I have found have magnets stuck to a motor spinning under a non magnetic material causing a piece of ferrous material attracted to the magnet to spin in a glass or plastic container.

I'm thinking of one with NO moving parts to wear out: instead of a motor spinning, have a series of electromagnets in a circular pattern. I'm thinking 8 equally spaced from each other (octagon with them at the corners). It would work by energizing two of the electromagnets at a time across from each other in the circle with opposite poles, one North the other South. Then quickly turn off those two and energize the next two opposing electromagnets in the series in a clockwise direction.This turning on and off would cause the ferrous material to spin. By controlling how fast the magnets swap you would control the spin.

Now the Help I need:

  1. Is this feasible?
  2. How do I control the turning on and off, using simple components.
  3. I would like to use a 10k ohm potentiometer to control the rate of spin (magnet swap). Mainly because I have one laying around.
  4. Since each magnet will be energized in ether direction at some point in the sequence, how do I swap it.
  5. Would I require a cooling system?

(Key Point of Design: NO moving Parts)

Thanks in advance for any help given. I'm a student mechanical engineer, whose got a love of electronics and control systems I really want to get seriously into electronics.

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  • \$\begingroup\$ Thanks for the quick responses.when I wrote simple components I meant stuff like caps and resistors.I haven't used an arduino before and sourcing one where live is close to impossible.so a pure analog system is what I was thinking. \$\endgroup\$ – user20725 Mar 26 '13 at 1:39
  • \$\begingroup\$ Just for future reference extra comments should be either an edit to the original question or added as a comment underneath, not posted as an answer. \$\endgroup\$ – PeterJ Mar 26 '13 at 1:41
  • \$\begingroup\$ This sound a lot like the drive electronics for a brushless motor. In your case, the rotor would be the permanent magnet stirrer. Search BLDC on the Internet for ideas. \$\endgroup\$ – Pablo Maurin Mar 28 '13 at 0:58
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The minimum coil requirement to produce a perfectly good rotating magnetic field is three and this is used all over the world in 3-phase induction and synchronous motors. What you have is a bar magnet so it's a synchronous motor. I'd consider building it this way and using 3 small audio amps each fed with sine-waves that are 120º apart (see below).

If you were using a stepper motor you'd need something "intelligent" to control the coil signals and ditto for this idea but it could be simpler than investing time trying to program an arduino by using conventional logic gates. A CD4017 can be used to generate an approximate sinewave using resistors on its output.

In fact one 4017 can produce all three sinwaves - each sinewave output would choose different outputs of the 4017 for selection via resistors. This means you get three sinewaves frequency-controllable from the clock input of the 4017. Here's a quick circuit that uses a 4015 shift register to show how it can be done: -

digital synthesis of sinewave

This idea is just to avoid using an arduino or PIC mcu, either of which could do the same as the logic. Here's a method: http://interface.khm.de/index.php/lab/experiments/arduino-dds-sinewave-generator/

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Firstly, may I suggest building the simple version (using a magnet and motor) first, then building this idea when you're more confident with electronics? This is some advice I have found useful in my experience--start small, then work to make it larger.

Now, do address your questions:

  1. As far as I can see, it should be feasible. The concept is similar (in some ways) to the way a stepper motor works.
  2. Please define "simple components," and from what perspective they are simple. An Arduino would be a very simple way to control the magnets (from a programming perspective), but it isn't a simple component electronically.
  3. The usage of your 10 kOhm pot is feasible, but exactly how depends on the answer to (2).
  4. Again, dependent on (2).
  5. It depends on the length of time you're running this... I doubt it, though.

You'll be able to get better answers when you have more specific questions...

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If you can find and dismantle an old 5.25" floppy disk drive, you will find (in most of them) a motor assembly with a large number of poles - 12 or 18 - each with a coil on it. These are driven in threes, i.e. every third one is connected together. Energising these three windings in turn provides a relatively slow rotation, ideal for your application. This will pull round one magnet, or an assembly with 4 or 6 alternating N and S poles for more pull.

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