# Controlling a circular magnetic field with microcontroller

I have this idea for a project and I'm looking for some direction. There is a "clock" in a recent tv show that I want to recreate. See this image , or This imageIf you're familiar with Westworld you'll know it.

I started looking at magnetic sand and then at ferrofluid. Ferrofluid seems to give the effect that I'm looking for but I have no idea where/what to even begin looking at.

To me I see a circular electromagnet, the field could be altered to give the desired affect with the ferrofluid.

So at stasis there would be a stable field and it would look like the first image. It could dynamically shift to look similar to the second image.

My question is where do I start here? Googling for "control circular magnetic field with arduino" didn't net me much. Most were create a electromagnet with a relay etc.

Would I need to control one large field, multiple smaller ones?

I don't mean for this to be vague, as I said, I'm not sure where to even start here. Maybe this isn't possible.

• So do you want something similar to a compass but with magnetic sand? Apr 24, 2020 at 18:20
• Sort of. More like a sunspot. Normally it would just be a ring but then I could control where on that ring I wanted activity. See this video from .25 to .35. That affect. Sunspot Apr 24, 2020 at 18:28
• Motor + permanent magnet? Apr 24, 2020 at 18:31
• @SpehroPefhany would that give the resolution he wants? maybe it would resemble a bit the first picture, but it wouldn't help at all with the second one where you have many "tendrils" of different sizes that are individually controlled.
– jDAQ
Apr 24, 2020 at 18:37
• Resolution was one of the things I was curious about. Can I get any sort of detail with a single field. Maybe not detail , but detail and control? Apr 24, 2020 at 18:53

To get the ring shape, you will need to use a magnetic trap, the proof of concept of this would be to have 2 coils in the shape you want (the circle), spaced apart by about 1.4x how wide you want the circle to be.

To get the spikes, you will need magnetic traps aswell, though this time it can just be a single coil in the shape of the spikes, this likely means you will have to settle for radius out shapes for hands on the clock, you would turn on these coils in sequence to move the hands.

The amount of current you will need to run through the wires will also be fairly high, you can reduce it by having more turns, and likely will only work well while flat, in a vertical situation against gravity the control scheme would get quite difficult to make it a somewhat even thickness,

To best explain the image, the ferrofluid will gather at the pole of a magnet, 2 coils with opposing current flow will make a consistent pole between them that is attracting it into that shape, you need 2 coils here as you want the entire ring shape,

This would be the point in the 2b diagram where all of the field lines are bunched up tightly,

For the hands as you just need the fluid trapped inside the profile of the coil, so a single coil can be used.

• I was just going to ask what sort of amperage are we talking about here ? Apr 24, 2020 at 23:03
• I'm not particularly familiar with how easily it is to move ferrofluid, so start with thin wire coils, about 100 turns with half an amp, then trim from there? Apr 24, 2020 at 23:07
• Ok perfect, that gives me a starting point. Apr 24, 2020 at 23:09