I have a coil. I have a current => I have a magnetic field ! Wait, do I ?

A naive first approach

We received the coils denominated SDE1006A-681K. These are 680 µH inductance coils.

We roughly soldered two wires on each pole of the coil as you can see on the image below for very basic testing.

Next we needed to connect it to the IoT node. As a very basic montage for testing, we configured user button with polling on the IoT node to drive one of the GPIO pin we have on high when pressed.

We used a resistance to limit the current output. As we wanted a current of the ordre of the mA we used a resistance around 1 kΩ. We brought the magnetic marble near the coil, far enough to not be attracted by the coil with no current flowing through but close enough to be affected by the generated magnetic field.

We pressed the button and … SURPRISE ! Nothing happened.

More, more, more ! More power !

In need for more power, we headed to the e-lab. We connected the coils as follow :

On the left is the DC voltage source. On the bottom right we can see the marble, and the coil with its wires hold by a vice.

The DC voltage source has two parameters : the voltage we want it to output, and the current limitation. If the current flowing through the montage should go higher than the limitation, the voltage source will drop so it stays within the current limitation.

As such, with the very low resistance of our coil and because the generated magnetic field depends only on the current flowing through the coil, we were able to use the DC voltage source as a DC current.

One needs to keep in mind that this is a gross montage, and a risky one as with high currents flowing through the coil the latter will heat up a lot. With this in mind, we kept constant monitoring on the montage and never let the generator on for more than few seconds.

At first we were desperate as we weren’t noticing any effect on the marbles. With perseverance and faith in the physical laws of this world, we were first able to notice a slight movement of the marble. Wheeew ! Finally !
Little by little we were able to make a marble move, then a torus as you can see in the videos below.

Marble flip
Torus flip. We weren’t able to use the hole we drilled as the friction was too important.

By the end of the day, these tests have raised serious power issues as we experienced that the bare minimum current we need is roughly 500 mA. We need to keep in mind however that these test were for the lowest inductance coil we ordered.

With these power issues into account, we will also have to find a way to flip one marble without flipping the neighboring others. Also as the magnetic field of the marbles is unexpectedly more powerful than we thought, we’ll also have problems with the marbles alone, without accounting the magnetic field we generate.

What now ?

Basically, we’ll have to find a solution such that we can flip a sole marble by hand without flipping inadvertently the neighboring ones WHILE being able to manipulate these same marbles with the coil.

We’re actually testing a lot of different configuration of magnets, magnet size, spacing between the magnets, size of the openings in the wood (which directly impact the friction with the marbles and thus the liberty of the marbles), support material…

We’ll need to discuss this with Alexis and do some more testing with the other coils once we receive them.

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